WO2008054670A1 - Integrated heat spreaders for leds and related assemblies - Google Patents

Integrated heat spreaders for leds and related assemblies Download PDF

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Publication number
WO2008054670A1
WO2008054670A1 PCT/US2007/022576 US2007022576W WO2008054670A1 WO 2008054670 A1 WO2008054670 A1 WO 2008054670A1 US 2007022576 W US2007022576 W US 2007022576W WO 2008054670 A1 WO2008054670 A1 WO 2008054670A1
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WIPO (PCT)
Prior art keywords
thermally conductive
light emitting
conductive layer
emitting device
assembly according
Prior art date
Application number
PCT/US2007/022576
Other languages
French (fr)
Other versions
WO2008054670A9 (en
Inventor
Nicholas W. Medendorp
Peter Andrews
Original Assignee
Cree, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
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First worldwide family litigation filed litigation Critical https://patents.darts-ip.com/?family=39060231&utm_source=google_patent&utm_medium=platform_link&utm_campaign=public_patent_search&patent=WO2008054670(A1) "Global patent litigation dataset” by Darts-ip is licensed under a Creative Commons Attribution 4.0 International License.
Application filed by Cree, Inc. filed Critical Cree, Inc.
Priority to EP07852925.2A priority Critical patent/EP2078311B1/en
Priority to JP2009534641A priority patent/JP2010508655A/en
Priority to CN2007800467074A priority patent/CN101606247B/en
Publication of WO2008054670A1 publication Critical patent/WO2008054670A1/en
Publication of WO2008054670A9 publication Critical patent/WO2008054670A9/en

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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/0201—Thermal arrangements, e.g. for cooling, heating or preventing overheating
    • H05K1/0203—Cooling of mounted components
    • H05K1/0204—Cooling of mounted components using means for thermal conduction connection in the thickness direction of the substrate
    • H05K1/0206—Cooling of mounted components using means for thermal conduction connection in the thickness direction of the substrate by printed thermal vias
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/64—Heat extraction or cooling elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/26—Layer connectors, e.g. plate connectors, solder or adhesive layers; Manufacturing methods related thereto
    • H01L2224/31—Structure, shape, material or disposition of the layer connectors after the connecting process
    • H01L2224/32—Structure, shape, material or disposition of the layer connectors after the connecting process of an individual layer connector
    • H01L2224/321—Disposition
    • H01L2224/32151—Disposition the layer connector connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive
    • H01L2224/32221—Disposition the layer connector connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked
    • H01L2224/32225—Disposition the layer connector connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being non-metallic, e.g. insulating substrate with or without metallisation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H01L2224/4805—Shape
    • H01L2224/4809—Loop shape
    • H01L2224/48091—Arched
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    • H01—ELECTRIC ELEMENTS
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    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H01L2224/481—Disposition
    • H01L2224/48151—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive
    • H01L2224/48221—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked
    • H01L2224/48225—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being non-metallic, e.g. insulating substrate with or without metallisation
    • H01L2224/48227—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being non-metallic, e.g. insulating substrate with or without metallisation connecting the wire to a bond pad of the item
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/73—Means for bonding being of different types provided for in two or more of groups H01L2224/10, H01L2224/18, H01L2224/26, H01L2224/34, H01L2224/42, H01L2224/50, H01L2224/63, H01L2224/71
    • H01L2224/732—Location after the connecting process
    • H01L2224/73251—Location after the connecting process on different surfaces
    • H01L2224/73265—Layer and wire connectors
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    • H01—ELECTRIC ELEMENTS
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    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/01—Chemical elements
    • H01L2924/01019—Potassium [K]
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    • H01—ELECTRIC ELEMENTS
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    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/01—Chemical elements
    • H01L2924/01025—Manganese [Mn]
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    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/01—Chemical elements
    • H01L2924/01057—Lanthanum [La]
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    • H01L2924/01078—Platinum [Pt]
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    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/01—Chemical elements
    • H01L2924/01079—Gold [Au]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/01—Chemical elements
    • H01L2924/01087—Francium [Fr]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/15—Details of package parts other than the semiconductor or other solid state devices to be connected
    • H01L2924/181—Encapsulation
    • H01L2924/1815—Shape
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/19—Details of hybrid assemblies other than the semiconductor or other solid state devices to be connected
    • H01L2924/191—Disposition
    • H01L2924/19101—Disposition of discrete passive components
    • H01L2924/19107—Disposition of discrete passive components off-chip wires
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/30—Technical effects
    • H01L2924/301—Electrical effects
    • H01L2924/3011—Impedance
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/62—Arrangements for conducting electric current to or from the semiconductor body, e.g. lead-frames, wire-bonds or solder balls
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/64—Heat extraction or cooling elements
    • H01L33/647—Heat extraction or cooling elements the elements conducting electric current to or from the semiconductor body
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/09—Shape and layout
    • H05K2201/09209—Shape and layout details of conductors
    • H05K2201/09654—Shape and layout details of conductors covering at least two types of conductors provided for in H05K2201/09218 - H05K2201/095
    • H05K2201/09781—Dummy conductors, i.e. not used for normal transport of current; Dummy electrodes of components
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/10—Details of components or other objects attached to or integrated in a printed circuit board
    • H05K2201/10007—Types of components
    • H05K2201/10106—Light emitting diode [LED]
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
    • H05K2203/04—Soldering or other types of metallurgic bonding
    • H05K2203/049—Wire bonding

Definitions

  • This invention relates to semiconductor devices, and more particularly to semiconductor light emitting devices and related methods and packages.
  • Light emitting diodes and laser diodes are well known solid state electronic light emitting devices capable of generating light upon application of a sufficient voltage.
  • Light emitting diodes and laser diodes may be generally referred to as light emitting devices ("LEDs").
  • LEDs light emitting devices
  • Light emitting devices generally include a p-n junction formed in an epitaxial layer grown on a substrate such as sapphire, silicon, silicon carbide, gallium arsenide and the like. The wavelength distribution of the light generated by the LED generally depends on the material from which the p-n junction is fabricated and the structure of the thin epitaxial layers that make up the active region of the device.
  • an LED chip typically includes a substrate, an n-type epitaxial region formed on the substrate and a p-type epitaxial region formed on the n-type epitaxial region (or vice-versa).
  • an anode ohmic contact is formed on a p-type region of the device (typically, an exposed p-type epitaxial layer) and a cathode ohmic contact is formed on an n-type region of the device (such as the substrate or an exposed n-type epitaxial layer).
  • an LED chip To use an LED chip in a circuit, it is known to enclose an LED chip in a package to provide environmental and/or mechanical protection, color selection, focusing and the like.
  • An LED package also includes electrical leads, contacts or traces for electrically connecting the LED package to an external circuit.
  • an LED chip In a typical LED package, an LED chip is mounted on a reflective cup by means of a solder bond or conductive epoxy. One or more wirebonds connect the ohmic contacts of the LED chip to leads which may be attached to or integral with the reflective cup.
  • the reflective cup may be filled with an encapsulant material containing a wavelength conversion material such as a phosphor.
  • LED packages Light emitted by the LED at a first wavelength may be absorbed by the phosphor, which may responsively emit light at a second wavelength.
  • the entire assembly is then encapsulated in a clear protective resin, which may be molded in the shape of a lens to collimate the light emitted from the LED chip.
  • a clear protective resin which may be molded in the shape of a lens to collimate the light emitted from the LED chip.
  • Some LED packages have one or more LED chips mounted onto a carrier such as a printed circuit board (PCB) carrier.
  • PCB printed circuit board
  • Encapsulant materials such as silicone gels
  • silicone gels typically have high coefficients of thermal expansion.
  • the encapsulant material may expand.
  • the lens As the lens is mounted within a channel defined by the sidewalls of the reflector cup, the lens may travel up and down within the sidewalls as the encapsulant material expands and contracts. Expansion of the encapsulant material may extrude the encapsulant into spaces or out of the cavity such that, when cooled, it may not move back into the cavity. This could cause delamination, voids, higher triaxial stresses and/or the like, which may result in less robust light emitting devices. Accordingly, there continues to exist a need in the art for more effective methods for heat spreading and lowering thermal resistances of LED systems.
  • a light emitting device (LED) assembly may include an electrically insulating substrate and a thermally conductive layer on a surface of the insulating substrate.
  • a light emitting device may be on the thermally conductive layer so that the thermally conductive layer is between the light emitting device and the electrically insulating substrate.
  • the thermally conductive layer may extend beyond an edge of the light emitting device in at least one direction a distance greater than half of a width of the light emitting device.
  • a plurality of thermally conductive vias may be thermally coupled to the thermally conductive layer, and portions of the substrate adjacent the light emitting device may be free of the thermally conductive vias.
  • the thermally conductive vias may extend from the thermally conductive layer through the electrically insulating substrate.
  • the thermally conductive layer may include a metal layer such as a copper layer.
  • the thermally conductive layer may be electrically conductive, and the light emitting device assembly may also include a first electrical coupling between a first terminal of the light emitting device and the thermally conductive layer.
  • An electrode may be on the electrically insulating substrate with the electrode and the thermally conductive layer being electrically isolated, and a second electrical coupling may be provided between a second terminal of the light emitting device and the electrode.
  • the thermally conductive layer may be electrically conductive
  • the light emitting device assembly may further include first and second electrodes, each of which is electrically isolated from the thermally conductive layer.
  • a first electrical coupling may be provided between a first terminal of the light emitting device and the first electrode, and a second electrical coupling may be provided between a second terminal of the light emitting device and the second electrode.
  • the thermally conductive layer may be electrically conductive, and the thermally conductive layer may be a substantially circular thermally conductive layer. Moreover, a first portion of the substantially circular thermally conductive layer may be electrically isolated from a second portion of the substantially circular thermally conductive layer.
  • the substantially circular thermally conductive layer may include a plurality of notches around a perimeter thereof. Moreover, each of the notches may extend radially from the perimeter of the thermally conductive layer toward the light emitting device.
  • a conductive trace on the electrically insulating substrate may extend from the substantially circular thermally conductive layer.
  • a light emitting device assembly may include an electrically insulating substrate having opposing first and second surfaces.
  • a first thermally conductive layer may be provided on the first surface of the electrically insulating substrate, and a second thermally conductive layer may be provided on the second surface of the electrically insulating substrate.
  • a light emitting device may be provided on the first thermally conductive layer so that the first thermally conductive layer is between the light emitting device and the electrically insulating substrate.
  • a plurality of thermally conductive vias may be thermally coupled between the first and second thermally conductive layers, and portions of the substrate between the light emitting device and the second thermally conductive layer may be free of the thermally conductive vias.
  • the thermally conductive vias may extend from the first thermally conductive layer through the electrically insulating substrate to the second thermally conductive layer.
  • the first thermally conductive layer may extend beyond edges of the light emitting device a distance greater than half of a width of the light emitting device.
  • Each of the first and second thermally conductive layer may include respective first and second metal layers, such as respective copper layers, and the first thermally conductive layer may be electrically isolated from first and second terminals of the LED.
  • the first and second thermally conductive layers may be electrically conductive, and the light emitting device assembly may further include a first electrical coupling between a first terminal of the light emitting device and the first thermally conductive layer.
  • An electrode may be provided on the electrically insulating substrate with the terminal and the first and second thermally conductive layers being electrically isolated.
  • a second electrical coupling may be provided between a second terminal of the light emitting device and the electrode.
  • the first and second thermally conductive layers may be electrically conductive, and the light emitting device assembly may further include first and second electrodes, each of which is electrically isolated from the first and second thermally conductive layers.
  • a first electrical coupling may be provided between a first terminal of the light emitting device and the first electrode, and a second electrical coupling may be provided between a second terminal of the light emitting device and the second electrode.
  • the first thermally conductive layer may be electrically conductive, and the first thermally conductive layer may be a substantially circular thermally conductive layer. A first portion of the substantially circular thermally conductive layer may be electrically isolated from a second portion of the substantially circular thermally conductive layer. Moreover, the substantially circular thermally conductive layer may include a plurality of notches around a perimeter thereof. In addition, a conductive trace on the electrically insulating substrate may extend from the substantially circular thermally conductive layer.
  • a light emitting device (LED) assembly may include an electrically insulating substrate and a substantially circular thermally conductive layer on a surface of the insulating substrate.
  • a light emitting device may be provided on the substantially circular thermally conductive layer so that the substantially circular thermally conductive layer is between the light emitting device and the electrically insulating substrate.
  • a first portion of the substantially circular thermally conductive layer may be electrically isolated from a second portion of the substantially circular thermally conductive layer.
  • the substantially circular thermally conductive layer may include a plurality of notches around a perimeter thereof. Moreover, each of the notches may extend radially from the perimeter of the substantially circular thermally conductive layer toward the light emitting device.
  • a conductive trace on the electrically insulating substrate may extend from the substantially circular thermally conductive layer.
  • the substantially circular thermally conductive layer may extend beyond edges of the light emitting device a distance greater than half of a width of the light emitting device.
  • the substantially circular thermally conductive layer may include a metal layer.
  • the light emitting device assembly may further include a second thermally conductive layer on a second surface of the electrically insulating substrate so that the electrically insulating substrate is between the substantially circular thermally conductive layer and the second thermally conductive layer.
  • a plurality of thermally conductive vias may be thermally coupled between the substantially circular thermally conductive layer and the second thermally conductive layer, and portions of the substrate between the light emitting device and the second thermally conductive layer may be free of the thermally conductive vias.
  • first and second terminals of the light emitting device may be electrically isolated from the substantially circular thermally conductive layer.
  • Figures IA-E are cross-sectional views illustrating light emitting device packages with a thermally conductive layer according to some embodiments of the present invention.
  • Figures 2-3 are cross sectional views of light emitting device packages including lenses according to additional embodiments of the present invention.
  • Figures 4A-C are plan views illustrating thermally conductive layers of light emitting devices according to some embodiments of the invention.
  • Figures 5 is a perspective view illustrating multi-chip light emitting device packages according to still other embodiments of the present invention.
  • first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.
  • Embodiments of the invention are described herein with reference to cross-sectional, perspective, and/or plan view illustrations that are schematic illustrations of idealized embodiments of the invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, a region illustrated or described as a rectangle will, typically, have rounded or curved features due to normal manufacturing tolerances. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region of a device and are not intended to limit the scope of the invention.
  • the term semiconductor light emitting device may include a light emitting diode, laser diode and/or other semiconductor device which includes one or more semiconductor layers, which may include silicon, silicon carbide, gallium nitride and/or other semiconductor materials.
  • a light emitting device may or may not include a substrate such as a sapphire, silicon, silicon carbide and/or another microelectronic substrates.
  • a light emitting device may include one or more contact layers which may include metal and/or other conductive layers.
  • ultraviolet, blue and/or green light emitting diodes may be provided. Red and/or amber LEDs may also be provided.
  • the design and fabrication of semiconductor light emitting devices are well known to those having skill in the art and need not be described in detail herein.
  • LEDs semiconductor light emitting devices
  • semiconductor light emitting devices may be gallium nitride-based LEDs or lasers fabricated on a silicon carbide substrate such as those devices manufactured and sold by Cree, Inc. of Durham, North Carolina.
  • the present invention may be suitable for use with LEDs and/or lasers as described in United States Patent Nos.
  • LEDs and/or lasers may be configured to operate such that light emission occurs through the substrate.
  • the substrate may be patterned so as to enhance light output of the devices as is described, for example, in the above-cited U.S. Patent Publication No. US 2002/0123164 Al.
  • each of substrates 100a-k may have respective upper surfaces 105a-k and lower surfaces 103a-k as shown.
  • Each of the substrates 100a-k may include a printed circuit board (PCB) substrate, an aluminum block substrate, an alumina substrate, an aluminum nitride substrate, a sapphire substrate, and/or a silicon substrate, and/or any other suitable substrate material, such as a T-Clad thermal clad insulated substrate material, available from The Bergquist Company of Chanhassen, MN.
  • a PCB substrate may include standard FR-4 PCB, a metal-core PCB, flex tape, and/or any other type of printed circuit board.
  • a patterned metal feature(s) may be formed on upper surfaces 105a-k of the respective substrates 100a- k.
  • the patterned metal feature(s) may include a thermally conductive layer(s) 112a-k, meniscus control feature(s) 303 and/or 304 (as shown in Figure3), a wirebond pad(s) 305 (as shown in Figure 3), and/or electrodes 110a-k and/or 11 la-k.
  • the conductive features on top surfaces 105a-k of substrate 100a-k may be formed, for example, using a plating process. A plating process may be used to plate a thin or thick metallic film on a substrate.
  • a titanium adhesion layer and a copper seed layer may be sequentially sputtered onto the substrate. Then, approximately 75 microns of copper may be plated onto the copper seed layer.
  • the adhesion layer and seed layer may be sputtered using, for example, a metal mask to form a desired pattern.
  • a plating process may also be used to form conductive metal vias through a substrate.
  • a deposited metal film may be patterned using standard lithographic processes to provide metal features on the substrate having desired patterns.
  • first and second meniscus control features 303 and 304 may be formed of a material different from the thermally conductive layer 112g and/or the wirebond pads 305.
  • the meniscus control features 303 and 304 may comprise a polymer such as a solder mask material including, for example, polyimide.
  • a polymer such as polyimide may provide a suitable material for use as a meniscus control feature because polyimide may provide a relatively a low surface energy, which may provide improved meniscus control properties.
  • Lateral dimensions (parallel to the substrate) and thicknesses of the thermally conductive layers 112a-k may vary based on the heat spreading properties of the materials used. Heat spreading may be increased when a diameter or width (parallel to the surface of the substrate) of the thermally conductive layer 112a-k extends from an edge or edges of the LED source 114a-k a distance that is at least half of the width of the LED source 114a-k, and according to some embodiments of the present invention, a distance that is at least the width of the LED source 114a-k. Moreover, the thermally conductive layer 112a-k may extend beyond edges of the LED 114a-k a distance greater than twice a thickness of the thermally conductive layer.
  • the thermally conductive layer 112a-k may include a layer of a metal (such as copper, aluminum, gold, tin, tin-silver, and/or copper-tin), a layer of a ceramic (such as aluminum- nitride), and/or a layer of a semiconductor material (such as silicon carbide).
  • a metal such as copper, aluminum, gold, tin, tin-silver, and/or copper-tin
  • a layer of a ceramic such as aluminum- nitride
  • a layer of a semiconductor material such as silicon carbide
  • the copper thermally conductive layer(s) may be configured so that a ratio of a diameter or width (parallel to the surface of the substrate) of the copper thermally conductive layer(s) 112a-k with respect to a thickness (perpendicular to the surface of the substrate) may be in the range of at least about 25 to about 140.
  • the aluminum thermally conductive layer(s) may be configured so that a ratio of a diameter or width (parallel to the surface of the substrate) of the aluminum thermally conductive layer(s) 112a-k with respect to a thickness (perpendicular to the surface of the substrate) may be in the range of at least about 7 to about 50.
  • One or more of the electrodes 110a-k and/or 11 la-k may be formed on an upper surface 105a-k of the respective substrate 100a-k.
  • one or more lower electrodes 1 lOc'-g' and/or 11 lc'-g' may be formed on a lower surface 103c-g of the respective substrate lOOc-g as shown in FIGS. IC-E, 2, and 3.
  • One or more conductive vias 122c-g may connect one or more of the lower electrodes 1 lOc'-g' and/or 11 lc'-g 1 to various features on an upper surface 105c-g of the respective substrate 100c-g.
  • one of the conductive vias 122c-g and/or 122c'-g' may electrically connect electrodes 1 lOc-g and/or 11 lc-g with respective lower electrodes 1 lOc'-g 1 and/or 11 IcVg'.
  • respective conductive features formed on upper surfaces 105c-g of substrates 100c-g may be formed of a same material.
  • the conductive features may include copper deposited using a plating process.
  • some conductive features may include additional metals.
  • the thermally conductive layer(s) 112a-k may be plated and/or coated with additional metals and/or other materials to make the thermally conductive layer(s) 112a-k more suitable for mounting a respective LED chip 114a-k thereon.
  • the thermally conductive layer(s) 112a-k may be plated with additional layers such as, for example, additional adhesive, bonding, reflector, die attach pad and/or barrier layers (not shown). These layers can be in addition to the thermally conductive layer, and these additional layers may also be thermally conductive.
  • a direct die attach may be performed using flux instead of Au/Sn solder paste to reduce a thermal resistance between an LED 114a-k and the respective thermally conductive layer 112a-k and/or to reduce voiding.
  • Direct die attach may enable use of a discrete zener device for ESD protection in another area of the LED system.
  • the LED(s) 114a-k and respective thermally conductive layer(s) 112a-k may be configured to provide coupling with vertical, planar, and/or flip-chip LEDs.
  • a thermally conductive layer 112a-e may be formed on an upper (primary) surface 105a-e of respective substrate 100a-e.
  • a second thermally conductive layer 113c-e may also be formed on a lower (secondary) surface 103c-e of the respective substrate 103C-E.
  • thermally conductive vias 201d-e may be thermally coupled between first thermally conductive layer(s) 112d-e and second thermally conductive layer(s) 113d-e.
  • the thermally conductive vias 201d-e may extend through the substrate 100d-e to improve thermal coupling between the first thermally conductive layer(s) 112d-e and the second thermally conductive layer(s) 113d-e.
  • a profile of each via through the substrate (as viewed from above or below the substrate) may take any shape such as a circle, a square, a polygon, etc.
  • Each thermally conductive via 201d-e may extend from any portion of the respective thermally conductive layer 112.
  • the thermally conductive vias 201d-e may be provided between the LED 114d-e and the second thermally conductive layer 113d-e to increase thermal conduction.
  • the thermally conductive vias 201d-e may be spaced apart from (or laterally offset from) the respective LED 114d-e to improve a mechanical coupling between the LED 114d-e and the thermally conductive layer 112d-e.
  • a portion of the thermally conductive layer 112d-e that is free of thermally conductive vias 201d-e may provide a more planar surface to improve mechanical coupling with the LED 114d-e.
  • first and second thermally conductive layers 112a-e and/or 113c-e may be electrically isolated from the electrodes 110a-e and/or 11 la-e as illustrated in FIGS. IA, 1C, and/or ID.
  • This electrical isolation may be provided, for example, so that a material(s) for the thermally conductive layer(s) and for the electrodes may be different.
  • wirebonds 128a-e may be used to provide electrical coupling between the LEDs 114a-e and the respective electrodes 11 la-e.
  • wirebonds 128a' and 128c'-d' may provide electrical coupling between LED's 114a and 114c-d and respective electrodes 110a and 1 lOc-d.
  • the thermally conductive layer 112b and the electrode 110b may be provided as a continuous/patterned layer of an electrically and thermally conductive material.
  • a patterned layer layer of a thermally conductive material may provide the thermally conductive layer 112b, the electrode 110b, and a conductive trace therebetween.
  • thermally conductive layer(s) 112h-i may be electrically coupled to respective electrode(s) 11 lh-i through conductive trace(s) 402h-i.
  • Second thermally conductive layer 113e may be electrically coupled to an electrode 11Oe 1 as shown in Figure IE.
  • the first thermally conductive layer 112e may be electrically coupled to an electrode HOe 1 on the lower surface 103e of the substrate lOOe through electrically and thermally conductive vias 20 Ie as shown in Figure IE.
  • structures of Figures IA-E may be used together with lenses and/or reflection devices as illustrated, for example, in Figures 2 and 3.
  • the structure of Figure 2 may be used with the lens of Figure 3 and/or the structure of Figure 3 may be used with the lens of Figure 2.
  • structures including thermally conductive layers, thermally/electrically conductive vias, LEDs, electrodes, and/or substrates according to embodiments of the present invention may be used with additional elements of LED packaging as discussed, for example, in U.S. Patent Application Serial Nos. 11/044,126 and 11/336,369, the disclosures of which are incorporated herein by reference as if set forth fully herein.
  • the LED package of Figure 1 A may include a thermally conductive layer 112a between the LED 114a and the substrate 100a, and the thermally conductive layer 112a may extend beyond edges of the LED 114a a distance greater than half a width of the LED 114a, and according to some embodiments of the present invention, a distance that is greater than a width of the LED 114a.
  • the LED may be a horizontal LED such that both electrodes (i.e., the cathode and anode) thereof are on the surface of the LED 114a opposite the substrate 100a. Wirebonds 128a and 128a 1 may provide electrical coupling between the LED 114a and the electrodes I l ia and 110a.
  • the lower surface 103a of the substrate 100a opposite the LED 114a may thus be free of electrical connection.
  • heat from the LED may be spread through the thermally conductive layer 112a and into the substrate 100a.
  • the thermally conductive layer 112a may include an electrically and thermally conductive material such as copper.
  • the backside 103a of the substrate 100a may be thermally coupled to a heat sink and/or to a thermally conductive portion of another substrate (such as a printed circuit board) so that heat is conducted away from the substrate 100a.
  • the LED package of Figure 1 B may include a thermally conductive layer 112b between the LED 114b and the substrate 100b, and the thermally conductive layer 112b may extend beyond edges of the LED 114b a distance greater than half a width of the LED 114b, and according to some embodiments of the present invention, a distance that is greater than a width of the LED 114b.
  • the LED may be a vertical LED such that the electrodes (i.e., the cathode and anode) thereof are on opposite surfaces of the LED 114b.
  • Wirebond 128b may provide electrical coupling between a first electrode of the LED 114b and the electrodes 11 1b.
  • a second electrode of the LED 114b may be coupled directly to the thermally conductive layer 112b.
  • the thermally conductive layer 112b and the electrode 110b and a trace therebetween may be formed from a same layer of an electrically and thermally conductive material so that a second wirebond is not required.
  • the lower surface 103b of the substrate 100b opposite the LED 114b may thus be free of electrical connection.
  • heat from the LED 1 14b may be spread through the thermally conductive layer 112b and into the substrate 100b.
  • the thermally conductive layer 112a may include an electrically and thermally conductive material such as copper.
  • the backside 103b of the substrate 100b may be thermally coupled to a heat sink and/or to a thermally conductive portion of another substrate (such as a printed circuit board) so that heat is conducted away from the substrate 100b.
  • a second wirebond may be provided between the second electrode on a surface of the LED 114b opposite the thermally conductive layer 112b and the thermally conductive layer 112b.
  • the LED package of Figure 1 C may include a thermally conductive layer 112c between the LED 114c and the substrate 100c, and the thermally conductive layer 112c may extend beyond edges of the LED 114a a distance greater than half a width of the LED 114c, and according to some embodiments of the present invention, a distance that is greater than a width of the LED 114c.
  • the LED may be a vertical LED such that the electrodes (i.e., the cathode and anode) thereof are on opposite surfaces of the LED 114c.
  • Wirebond 128c may provide electrical coupling between a first electrode of the LED 114c and the electrode 111c.
  • the layer 112c may also be electrically conductive, and a second electrode of the LED 114c may be coupled directly to the thermally and electrically conductive layer 112c, and wirebond 128c 1 may provide electrical coupling between the thermally conductive layer 112c and the electrode 110c.
  • a conductive trace may be provided between the thermally conductive layer 112c and the electrode 110c as discussed above with respect to Figure IB so that a second wirebond is not required.
  • a second thermally conductive layer 113c may be provided on a backside 103c of the substrate 100c to enhance coupling of heat from the substrate 100c to a heat sink and/or to a thermally conductive portion of another circuit board (such as a printed circuit board).
  • heat from the LED 114c may be spread through the thermally conductive layer 112c and into the substrate 100c and the second thermally conductive layer 113c.
  • the thermally conductive layers 112c and 113c may each include a thermally conductive material such as copper.
  • the backside 103c of the substrate 100c may be thermally coupled to a heat sink and/or to a thermally conductive portion of another substrate (such as a printed circuit board) so that heat is conducted away from the substrate 100c.
  • the LED 114c is a horizontal LED
  • the second wirebond 128c' may be provided between the second electrode on a surface of the LED 114c opposite the thermally conductive layer 112c and the electrode 110c.
  • secondary electrodes 111c' and 110c' may be provided on the backside 103 c of the substrate 100c, and the secondary electrodes 111c' and 110c 1 may be electrically coupled to the electrodes 111c and 110c on the frontside 105c of the substrate 100c through electrically conductive vias 122c and 122c'.
  • the substrate 100c can thus be mounted on a printed circuit board with the secondary electrodes 111c' and 110c' providing electrical coupling to the printed circuit board.
  • conductive vias 122c and 122c 1 and secondary electrodes 111c' and 110c' may be omitted if electrical coupling to another substrate is provided directly to the electrodes 111c and 110c.
  • electrically conductive vias and secondary electrodes as discussed above with respect to Figure 1C may be applied to the structures of Figures IA and/or IB according to some embodiments of the present invention.
  • secondary electrodes on the backside 103 a of substrate 100a of Figure IA may be electrically coupled to electrodes I l ia and 11 Oa using respective conductive vias through the substrate 100a.
  • secondary electrodes on the backside 103b of substrate 100b of Figure IB may be electrically coupled to electrodes 111b and 110b using respective conductive vias through the substrate 100b.
  • the LED package of Figure ID may include a thermally conductive layer 112d between the LED 114d and the substrate 10Od, and the thermally conductive layer 112d may extend beyond edges of the LED 114d a distance greater than half a width of the LED 114d, and according to some embodiments of the present invention, a distance that is greater than a width of the LED 114d.
  • the LED may be a horizontal LED such that the electrodes (i.e., the cathode and anode) thereof are on a surface of the LED 114d opposite the substrate 10Od. Wirebonds 128d and 128d' may provide electrical coupling between electrodes of the LED 114d and the electrodes 11 Id and HOd.
  • a second thermally conductive layer 113d may be provided on a backside 103 d of the substrate lOOd to enhance coupling of heat from the substrate 10Od to a heat sink and/or to a thermally conductive portion of another circuit board (such as a printed circuit board).
  • thermally conductive vias 20 Id may improve thermal coupling between the first thermally conductive layer 112d and the second thermally conductive layer 1 13d.
  • heat from the LED 114d may be spread through the thermally conductive layer 112d and through the thermally conductive vias 20 Id to the second thermally conductive layer 113d.
  • the thermally conductive layers 112d and 113d and the thermally conductive vias 20 Id may each include a thermally conductive material such as copper.
  • the backside 103d of the substrate 10Od may be thermally coupled to a heat sink and/or to a thermally conductive portion of another substrate (such as a printed circuit board) so that heat is conducted away from the substrate 10Od.
  • a second electrode of the LED 1 14d may be coupled directly to the thermally conductive layer 112d, and wirebond 128d' may provide electrically coupling between the thermally conductive layer 1 12d and the electrode 11Od.
  • wirebond 128d' may provide electrically coupling between the thermally conductive layer 1 12d and the electrode 11Od.
  • a conductive trace may be provided between the thermally conductive layer 112d and the electrode 1 1Od as discussed above with respect to Figure 1 B so that a second wirebond is not required.
  • secondary electrodes 11 Id' and 11Od' may be provided on the backside 103d of the substrate 10Od, and the secondary electrodes 11 Id' and HOd' may be electrically coupled to the electrodes 11 Id and 11Od on the frontside 105d of the substrate lOOd through electrically conductive vias 122d and 122d'.
  • the substrate 10Od can thus be mounted on a printed circuit board with the secondary electrodes 11 Id' and HOd' providing electrical coupling to the printed circuit board.
  • conductive vias 122d and 122d' and secondary electrodes 11 Id' and 11Od' may be omitted if electrical coupling to another substrate is provided directly to the electrodes 11 Id and 11Od.
  • the LED package of Figure IE may include a thermally conductive layer 112e between the LED 114e and the substrate 10Oe, and the thermally conductive layer 112e may extend beyond edges of the LED 114e a distance greater than half a width of the LED 114e, and according to some embodiments of the present invention, a distance that is greater than a width of the LED 114e.
  • the LED may be a vertical LED such that the electrodes (i.e., the cathode and anode) thereof are on opposite surfaces of the LED 114e.
  • Wirebond 128e may provide electrical coupling between a first electrode of the LED 114e and the electrodes 1 1 Ie.
  • a second electrode of the LED 114e may be electrically and mechanically coupled to the thermally conductive layer 112e.
  • a second thermally conductive layer 113e may be provided on a backside 103e of the substrate lOOed to enhance coupling of heat from the substrate lOOe to a heat sink and/or to a thermally conductive portion of another circuit board (such as a printed circuit board).
  • thermally conductive vias 20 Ie may improve thermal coupling between the first thermally conductive layer 112e and the second thermally conductive layer 1 13e.
  • heat from the LED 114e may be spread through the thermally conductive layer 112e and through the thermally conductive vias 20 Ie to the second thermally conductive layer 113e.
  • the thermally conductive layers 112e and 1 13e and the thermally conductive vias 20 Ie may each include a thermally conductive material such as copper.
  • the backside 103e of the substrate lOOe may be thermally coupled to a heat sink and/or to a thermally conductive portion of another substrate (such as a printed circuit board) so that heat is conducted away from the substrate 10Oe. If the LED 114e is a horizontal LED, a second electrode of the LED 114e may be coupled to the thermally conductive layer 112e using a second wirebond.
  • secondary electrodes 11 Ie' and HOe' may be provided on the backside 103e of the substrate 10Oe.
  • the secondary electrode 11 Ie' may be electrically coupled to the electrode 11 Ie on the frontside 105e of the substrate lOOe through electrically conductive via 122e.
  • the secondary electrode HOe' may be electrically coupled to the second thermally conductive layer 113e through a trace on the backside 103e of the substrate 10Oe. Accordingly, electrical coupling between the LED 114e and the electrode 11Oe' may be provided through the first thermally conductive layer 112e, through the thermally conductive traces 20 Ie, and through the second thermally conductive layer 113e.
  • the secondary electrode 11Oe' and the second thermally conductive layer 113e may be provided as portions of a same layer of an electrically and thermally conductive layer and/or electrical coupling to another substrate may be provided directly to the second thermally conductive layer 113e.
  • the substrate 10Oe can thus be mounted on a printed circuit board with the secondary electrodes H ie' and 11 Oe' providing electrical coupling to the printed circuit board.
  • a metal and/or reflective cup (or ring) 212 may be provided around the LED 114f , and a pre-formed lens 210 may be secured within the reflective cup or ring 212 using an adhesive material 211.
  • An electrically insulating material 213 may be provided between the ring 212 and the substrate 10Of and/or other layers (such as electrodes 11Of and/or 11 If) on the substrate 10Of.
  • the first and second thermally conductive layers 112f and 113f may be thermally coupled using thermally conductive vias 20 If that extend through the substrate lOOf to the second thermally conductive layer 113f.
  • the integrated heat spreading system including the thermally conductive layers 112f and 113f and the thermally conductive vias 20 If may be electrically isolated from electrodes of the LED 114f and/ or from electrodes 1 1Of, 11Of , 11 If, and/or 11 If . Electrodes of the LED 114f may be electrically coupled to the electrodes 11OA and/or 11 IA by wirebonds 128f and 128f . Lenses and reflective cups may be fabricated as discussed, for example, in U.S. Patent Application No. 11/044,126 entitled "Methods For Packaging A Light Emitting Device And Packaged Light Emitting Devices" and filed January 27, 2005, the disclosure of which is hereby incorporated herein in its entirety by reference.
  • a light emitting device assembly may include one or more encapsulated regions according to some embodiments of the present invention. More particularly, a first meniscus control feature 303 on the substrate lOOg may encircle the thermally conductive layer 112g to define a region confining an encapsulant material 301 on upper surface 105g of the substrate lOOg within the periphery of the first meniscus control feature 303.
  • a second meniscus control feature 304 may surround the region 301 and, together with the first meniscus control feature 303, may define an annular (or ring-shaped) region confining a lens material 302 on the upper surface 105g of the substrate lOOg surrounding the first encapsulant region 301.
  • the encapsulant material 301 may be dispensed as a liquid confined by the first meniscus control feature 303 and then cured.
  • the lens material 302 may then be dispensed as a liquid confined by the second meniscus control feature 304 and then cured.
  • the encapsulant material 301 and/or the lens material 302 may be an epoxy material(s).
  • the lens material 302 may enclose and encompass the encapsulant material 301. While the lens material 302 may be annular as discussed above, the lens material 302 may be provided according to other shapes depending on shapes of the first meniscus control feature 303 and the second meniscus control feature 304 and depending on volumes of the encapsulant and/or lens materials dispensed. For example, the lens material may have an oval periphery. It will be understood that for a feature to "encircle” or “surround” a region, the feature need not be continuously formed around the region. Although the figures illustrate continuous meniscus control features, it may be possible for a meniscus control feature to include gaps or voids therein which do not affect the meniscus control function of the feature. Moreover, the feature need not form a circle, but could be provided in other two dimensional shapes such as ellipses, polygons, etc.
  • the wirebond pads 305 and 305' may be formed on the upper surface 105g of substrate lOOg within the lens region surrounded by the second meniscus control feature 304.
  • One of the conductive vias 122g may electrically couple a wire bond pad 305 and/or 305' with a respective lower electrode 11 Ig' and/or HOg'.
  • Another of the electrically conductive vias 122g may electrically couple a lower electrode 11 Ig' and/or HOg' with a respective electrode 11 Ig and/or 11Og on an upper surface 105g of the substrate 10Og.
  • an electrically and thermally conductive via 20 Ig may electrically couple the thermally conductive layer 112g with a lower electrode 11 Ig' and/or HOg 1 so that a lower surface of a vertical LED may be electrically coupled to one of the lower electrodes 11 Ig 1 and/or HOg 1 thereby eliminating one of the wirebonds 128g and/or 128g'.
  • the structure including LED 114g; vias 122g, 122g', and 20 Ig; thermally conductive layers 112g and 113g; wirebond pads 305 and 305'; and electrodes H Ig, 11 Ig', HOg, and 11Og' may be provided without encapsulant material 301 and lens material 302 so that the LED 114g is exposed as shown in Figures IA-E.
  • the structure of Figure 3 may be provided with the reflector and lens structure of Figure 2 instead of the encapsulant material and lens material.
  • Lenses may be fabricated as discussed, for example, in U.S. Patent Application No. 11/197,096 entitled “Packages for Semiconductor Light Emitting Devices Utilizing Dispensed Encapsulants And Methods Of Packaging The Same” and filed August 4, 2005, and in U.S. Patent Application No. 11/336,369 entitled “Packages For Semiconductor Light Emitting Devices Utilizing Dispensed Reflectors And Methods Of Forming Same” and filed January 20, 2006. The disclosures of both of the above referenced applications are hereby incorporated herein in their entirety by reference.
  • the thermally conductive layer(s) 112a-g may be circular in a plan view or may have other shapes such as an oval, a polygon, etc.
  • the thermally conductive layer(s) 112a-g may be substantially circular as shown in Figures 4A-C.
  • a substantially circular shape for example, may efficiently spread heat while reducing unnecessary expansion (due to heating) that may result from an increased distance from an LED source 114a-g to corners of a square or rectangular thermally conductive layer.
  • an LED 114h may be provided on a substantially circular thermally conductive layer 112h. More particularly, the thermally conductive layer 112h may have a gap 40 Ih therein electrically isolating a portion 112h' of the thermally conductive layer 112h.
  • a trace 402h may provide electrical coupling between the thermally conductive layer 112h and electrode 11 Ih, and a trace 403h may provide electrical coupling between the portion 112h' and electrode 11Oh.
  • a first wirebond may provide electrical coupling between the main portion of the thermally conductive layer 112h and the LED 114h, and a second wirebond may provide electrical coupling between the portion 112h' and the LED 114h.
  • the portion 112h' may provide a relatively large area for a wirebond connection without significantly reducing a heat spreading capacity of the thermally conductive layer 112h.
  • a first surface of the LED 114h may be electrically and mechanically bonded (for example, using solder) to the main portion of the thermally conductive layer 112h, and a wirebond may provide electrical coupling of a second surface (opposite the thermally conductive layer) to the portion 112h' of the thermally conductive layer.
  • the thermally conductive layer 112h may be electrically isolated from the electrodes 11 Ih and HOh (so that one or both of traces 402h and/or 403h may be eliminated). Without traces 402h and/or 403h, wirebonds may provide electrical coupling between the LED 114h and electrodes 11 Ih and/or HOh.
  • a second thermally conductive layer may be provided on a surface of the substrate lOOh opposite the thermally conducive layer 112h as shown, for example, in Figures 1C, ID, and IE, and/or thermally conductive vias through the substrate 11Oh may provide thermal coupling between the thermally conductive layers on opposite sides of the substrate lOOh as shown, for example, in Figures ID and IE.
  • notches 404i may be provided in the substantially circular thermally conductive layer 112i to reduce stress/strain due to thermal expansion. Heat generated by the LED 114i may thus be dissipated across the relatively large thermally conductive layer 112i while reducing thermal stress/strain across the thermally conductive layer. As shown in Figure 4B, the notches 404i may be spaced around peripheral portions of the thermally conductive layer 112i. Moreover, the notches 112i may extend radially toward the LED 112i to reduce impedance of heat flow from the LED 114i toward edges of the thermally conductive layer 112i.
  • the electrodes 11 Ii and 11Oi, the traces 402i and 403i, the conductive vias 122i, and the substrate lOOi may be provided and/or function as discussed above with respect to corresponding elements of Figure 4A.
  • the electrically isolating gap 401h-i of Figures 4A-B may be formed using a solder mask when plating the thermally conductive layer, or the gap may be formed by subsequently patterning the thermally conductive layer (for example, using photolithographic mask and etch operations).
  • This gap 40 Ih or 40 Ii may electrically isolate cathode and anode portions of the substantially circular thermally conductive layer while providing significant heat spreading.
  • Electrically conductive traces 402h-i and/or 403h-i may electrically couple the portions 112h-i and/or 112h'-i' of the thermally conductive layer to the electrodes 110h-i and/or 110h-i.
  • a substantially circular thermally conductive layer 1 12k may be electrically isolated from one or both of the electrodes 111k and/or 110k as shown in Figure 4C.
  • the gap of Figures 4A and 4B may be omitted from the thermally conductive layer 112k, and notches 404k may be substantially evenly spaced around peripheral portions of the thermally conductive layer 112k.
  • the notches 404k may be spaced by approximately 120 degrees around the substantially circular thermally conductive layer 112k.
  • the notches may be spaced by approximately 90 degrees around the substantially circular thermally conductive layer.
  • the notches 112k may extend radially toward the LED 112k to reduce impedance of heat flow from the LED 114k toward edges of the thermally conductive layer 112k.
  • the electrodes 1 11k and 110k, the trace 402k, the conductive vias 122k, and the substrate 100k may be provided and/or function as discussed above with respect to corresponding elements of Figures 4A-B.
  • the LED may be a vertical LED with a first surface electrically and mechanically bonded (for example, soldered) to the thermally conductive layer, and a wirebond may provide electrical coupling between a second surface of the LED 114K and the electrode 110k.
  • the LED 114k may be a horizontal LED with a first wirebond providing electrical coupling between a first portion of the LED 114k and the thermally conductive layer 1 12k and with a second wirebond providing electrical coupling between a second portion of the LED and the electrode 11 Ok.
  • any of the thermally conductive layers 112h, 112i, and/or 112k of Figures 4A-C may be electrically coupled to a second thermally conductive layer on an opposite side of the substrate 10Oh, 10Oi, and/or 100k, for example, using thermally conductive vias.
  • any such thermally conductive vias may be offset relative to the LED 114h, 114i, and/or 1 14k to provide a more planar surface to which the LED may be bonded.
  • the one or more thermally conductive vias may be provided directly between the LED and the second thermally conductive layer on the opposite side of the substrate.
  • any of the patterns of thermally conductive layers 112h, 112i, and/or 112k discussed above with respect to Figures 4A-C may be used for the thermally conductive layers discussed herein with respect to Figures IA-E, 2, 3, and/or 5.
  • each of the substantially circular thermally conductive layers 112h, 112i, and/or 112k may extend beyond edges of the respective LED 114h, 114i, and/or 114k a distance that is greater than half of a width of the LED, and according to some embodiments of the present invention, a distance that is greater than a width of the LED.
  • FIG. 5 Further embodiments of the present invention may include a plurality of LEDs on a same substrate, such as a three-chip-in series layout illustrated in Figure 5.
  • three LEDs 114j, 114j', and 114j" may be electrically coupled in series.
  • each LED 114j, 114j', 114j" may be provided in a configuration similar to that discussed above with respect to Figure IA.
  • Electrodes 11 Ij and/or HOj may be electrically coupled to respective conductive traces 50 Ij, and additional conductive traces may be provided between LEDs 114j, 114j', and/or 114j".
  • each LED 114j, 114j', and/or 114j" may be electrically coupled to traces using respective wirebond pairs 128j, 128j', and/or 128j".
  • the thermally conductive layers 1 12j, 112j', and/or 112j" may be electrically isolated from the electrodes HOj and/or 11 Ij and/or from traces 50 Ij.
  • wirebond connections directly between LEDs and/or directly to the electrodes 11 Ij and/or 11Oj.
  • horizontal LEDs may be used with both electrical couplings to each LED on a surface of the LED opposite the substrate 10Oj.
  • first electrical couplings may be from LEDs 114j, 114j', and/or 114j" to the respective thermally conductive layer H2j, 112j', and/or 112j", and second electrical couplings may be provided using wirebonds to surfaces of the LEDs 114j, 114j', and/or 114j" opposite the substrate 10Oj.
  • Second thermally conductive layers may be provided on a backside of the substrate 10Oj opposite the thermally conductive layers 112j, 112j', and/or 1 12j" as discussed above with respect to Figures IC-E, 2, and 3.
  • a separate second thermally conductive layer may be provided for each of the first thermally conductive layers 112j, 112j', and/or 112j". If no electrical connections are provided to a backside of the substrate 10Oj, a continuous second thermally conductive layer 505 may be provided across the backside 103j of the substrate 10Oj.
  • thermally conductive vias may be provided through the substrate 10Oj between one or more of the thermally conductive layers 112j, 112j', and/or 112j" and any such second thermally conductive layer on the backside 103j of the substrate 10Oj.
  • the series of LED chips 114j, 114j ! , 114j " may also be coupled to an ESD (electrostatic discharge) protection chip 502 (such as a zener diode).
  • ESD electrostatic discharge
  • Integrated heat spreading may provide conditions more favorable for the use of thin film and direct bond technologies, allowing multiple LED chips on a single small form factor LED package. According to some embodiments of the present invention, heat generated by such a multi-chip assembly may be transferred away from the LEDs more effectively.
  • Each of the thermally conductive layers 112j, 112j', and/or 112j" may be substantially circular and/or may include notches therein as discussed above with respect to Figures 4A-C.
  • a reflective cup, a preformed lens, meniscus control features, and/or liquid dispensed/cured lenses may be provided for the LED's 114j, 114j', and/or 114j" as discussed above with respect to Figures 2 and/or 3.
  • a thermally conductive layer (e.g., thermally conductive layers 112a-k discussed above) according to some embodiments of the present invention may thus provide a heat spreader that is integral with respect to the substrate (e.g., substrates 100a-k discussed above) on which it is formed. Thermal transport of heat from an LED (e.g., LEDs 114a-k) into the substrate and/or a heat sink can be improved, so that the LED can be operated at higher power, for example, up to 5 Watts.
  • Thermally conductive layers according to some embodiments of the present invention may be formed using thin film processing of highly conductive metals and photolighographic patterning. Thermally conductive layers according to some embodiments of the present invention may enable direct flux die attach and/or attachment of a discrete zener diode for ESD protection.
  • the thermally conductive layers 112a-k discussed above with respect to Figures IA-E, 2, 3, 4A-C, and 5 may be formed, for example, by plating, sputtering, and/or evaporating one or more layers of a metal(s) such as nickel, copper, gold, and/or silver.
  • Thermally conductive vias e.g., conductive vias 201d-g
  • the thermally conductive layers 112a-k may enable a direct die attach of the LED 114a-k, for example, using flux instead of a gold/tin solder paste. A thickness of a bond between the LED and the thermally conductive layer may thus be reduced to improve a thermal interface and to reduce voiding.
  • multiple LED chips may be provided on a same substrate as shown, for example, in Figure 5.
  • multiple LEDs of a same color such as red, blue, green, or white
  • a combination of red, blue, and green LEDs may be provided on a same substrate.
  • direct die attachment may enable provision of an LED and a discrete zener diode (for ESD protection) on a same substrate as shown in Figure 5.
  • Use of thin film technology may also enable provision of a thermally conductive layer and/or thermally conductive vias that are electrically isolated as shown, for example, in Figures IA, ID, 2, and 3. Stated in other words, the thermal path may be electrically isolated.
  • a thermally conductive layer (e.g., layers 112a-k) may be formed by sputtering a seed layer (such as a layer of titanium) through a stencil to provide a desired pattern of the thermally conductive layer on the substrate (e.g., substrates 100a-k).
  • a copper may then be plated on the seed layer.
  • the seed layer may have a thickness, for example, in the range of about 20 micrometers to about 150 micrometers, and the copper layer may have a thickness of about 75 micrometers.
  • a thermally conductive layer (e.g., layers 112a-k) may be formed by printing a paste (including a thermally conductive metal) through a stencil and baking to remove organics. The resulting metal layer may be subjected to an anneal and/or a stamping operation to reduce porosity, increase thermal conductivity, increase planarity, etc. - According to still other embodiments of the present invention, a thermally conductive layer (e.g., layers 1 12a-k) may be provided as a metal perform that is pressed into place, and the perform may then be further subjected to an anneal to improve adhesion to the substrate.
  • a thermally conductive layer formed according to any of the techniques discussed above may be further subjected to a rolling and/or stamping operation to further improve characteristics thereof.
  • the LED 114a-k may be centered relative to the respective thermally conductive layer 112a-k according to some embodiments of the present invention.
  • the LED 114a-k is not required to be centered relative to the respective thermally conductive layer 112a-k according to all embodiments of the present invention.
  • the LED 114a- k for example, may be offset relative to a center of the respective thermally conductive layer 112a-k according to some embodiments of the present invention.
  • the LED 114a-k may be provided adjacent to an edge of the respective thermally conductive layer 112a-k so that the thermally conductive layer does not extend significantly beyond at least one edge of the LED 114a-k.

Abstract

A. light emitting device (LED) assembly may include an electrically insulating substrate (100a-k) and a thermally conductive layer (112a-k) on a surface (105a-k) of the insulating substrate (100a-k). A light emitting device (114a-k) may be on the thermally conductive layer (112a-k) so that the thermally conductive layer (112a-k) is between the light emitting device (114a-k) and the electrically insulating substrate (100a-k). Moreover, the thermally conductive layer may extend beyond an edge of the light emitting device (114a-k) in at least one direction a distance greater than half of a width of the light emitting device (114a-k).

Description

INTEGRATED HEAT SPREADERS FOR LEDS AND RELATED ASSEMBLIES
FIELD OF THE INVENTION
[0001] This invention relates to semiconductor devices, and more particularly to semiconductor light emitting devices and related methods and packages.
BACKGROUND
[0002] Light emitting diodes and laser diodes are well known solid state electronic light emitting devices capable of generating light upon application of a sufficient voltage. Light emitting diodes and laser diodes may be generally referred to as light emitting devices ("LEDs"). Light emitting devices generally include a p-n junction formed in an epitaxial layer grown on a substrate such as sapphire, silicon, silicon carbide, gallium arsenide and the like. The wavelength distribution of the light generated by the LED generally depends on the material from which the p-n junction is fabricated and the structure of the thin epitaxial layers that make up the active region of the device.
[0003] Typically, an LED chip includes a substrate, an n-type epitaxial region formed on the substrate and a p-type epitaxial region formed on the n-type epitaxial region (or vice-versa). To facilitate application of a voltage to the device, an anode ohmic contact is formed on a p-type region of the device (typically, an exposed p-type epitaxial layer) and a cathode ohmic contact is formed on an n-type region of the device (such as the substrate or an exposed n-type epitaxial layer).
[0004] To use an LED chip in a circuit, it is known to enclose an LED chip in a package to provide environmental and/or mechanical protection, color selection, focusing and the like. An LED package also includes electrical leads, contacts or traces for electrically connecting the LED package to an external circuit. In a typical LED package, an LED chip is mounted on a reflective cup by means of a solder bond or conductive epoxy. One or more wirebonds connect the ohmic contacts of the LED chip to leads which may be attached to or integral with the reflective cup. The reflective cup may be filled with an encapsulant material containing a wavelength conversion material such as a phosphor. Light emitted by the LED at a first wavelength may be absorbed by the phosphor, which may responsively emit light at a second wavelength. The entire assembly is then encapsulated in a clear protective resin, which may be molded in the shape of a lens to collimate the light emitted from the LED chip. Some LED packages have one or more LED chips mounted onto a carrier such as a printed circuit board (PCB) carrier.
[0005] During operation of the LED or LEDs, large amounts of heat may be generated. Much of the heat may be dissipated by the substrate and the reflector cup, each of which may act as a heatsink for the package. However, the temperature of the package may still increase significantly during operation. Substrates typically have low thermal conductivity. Additionally, while the reflective cup directs light upward, some light may be absorbed by the reflector cup or there may be reasons not to use a separate metal piece as a metal reflector.
[0006] Encapsulant materials, such as silicone gels, typically have high coefficients of thermal expansion. As a result, when the package heats up, the encapsulant material may expand. As the lens is mounted within a channel defined by the sidewalls of the reflector cup, the lens may travel up and down within the sidewalls as the encapsulant material expands and contracts. Expansion of the encapsulant material may extrude the encapsulant into spaces or out of the cavity such that, when cooled, it may not move back into the cavity. This could cause delamination, voids, higher triaxial stresses and/or the like, which may result in less robust light emitting devices. Accordingly, there continues to exist a need in the art for more effective methods for heat spreading and lowering thermal resistances of LED systems.
SUMMARY
[0007] According to some embodiments of the present invention, a light emitting device (LED) assembly may include an electrically insulating substrate and a thermally conductive layer on a surface of the insulating substrate. A light emitting device may be on the thermally conductive layer so that the thermally conductive layer is between the light emitting device and the electrically insulating substrate. Moreover, the thermally conductive layer may extend beyond an edge of the light emitting device in at least one direction a distance greater than half of a width of the light emitting device. [0008] In addition, a plurality of thermally conductive vias may be thermally coupled to the thermally conductive layer, and portions of the substrate adjacent the light emitting device may be free of the thermally conductive vias. Moreover, the thermally conductive vias may extend from the thermally conductive layer through the electrically insulating substrate. The thermally conductive layer may include a metal layer such as a copper layer.
[0009] The thermally conductive layer may be electrically conductive, and the light emitting device assembly may also include a first electrical coupling between a first terminal of the light emitting device and the thermally conductive layer. An electrode may be on the electrically insulating substrate with the electrode and the thermally conductive layer being electrically isolated, and a second electrical coupling may be provided between a second terminal of the light emitting device and the electrode.
[0010] The thermally conductive layer may be electrically conductive, and the light emitting device assembly may further include first and second electrodes, each of which is electrically isolated from the thermally conductive layer. A first electrical coupling may be provided between a first terminal of the light emitting device and the first electrode, and a second electrical coupling may be provided between a second terminal of the light emitting device and the second electrode.
[0011] The thermally conductive layer may be electrically conductive, and the thermally conductive layer may be a substantially circular thermally conductive layer. Moreover, a first portion of the substantially circular thermally conductive layer may be electrically isolated from a second portion of the substantially circular thermally conductive layer. In addition or in an alternative, the substantially circular thermally conductive layer may include a plurality of notches around a perimeter thereof. Moreover, each of the notches may extend radially from the perimeter of the thermally conductive layer toward the light emitting device. In addition, a conductive trace on the electrically insulating substrate may extend from the substantially circular thermally conductive layer.
[0012] According to additional embodiments of the present invention, a light emitting device assembly may include an electrically insulating substrate having opposing first and second surfaces. A first thermally conductive layer may be provided on the first surface of the electrically insulating substrate, and a second thermally conductive layer may be provided on the second surface of the electrically insulating substrate. In addition, a light emitting device may be provided on the first thermally conductive layer so that the first thermally conductive layer is between the light emitting device and the electrically insulating substrate. Moreover, a plurality of thermally conductive vias may be thermally coupled between the first and second thermally conductive layers, and portions of the substrate between the light emitting device and the second thermally conductive layer may be free of the thermally conductive vias.
[0013] The thermally conductive vias may extend from the first thermally conductive layer through the electrically insulating substrate to the second thermally conductive layer. In addition, the first thermally conductive layer may extend beyond edges of the light emitting device a distance greater than half of a width of the light emitting device. Each of the first and second thermally conductive layer may include respective first and second metal layers, such as respective copper layers, and the first thermally conductive layer may be electrically isolated from first and second terminals of the LED.
[0014] The first and second thermally conductive layers may be electrically conductive, and the light emitting device assembly may further include a first electrical coupling between a first terminal of the light emitting device and the first thermally conductive layer. An electrode may be provided on the electrically insulating substrate with the terminal and the first and second thermally conductive layers being electrically isolated. A second electrical coupling may be provided between a second terminal of the light emitting device and the electrode.
[0015] The first and second thermally conductive layers may be electrically conductive, and the light emitting device assembly may further include first and second electrodes, each of which is electrically isolated from the first and second thermally conductive layers. A first electrical coupling may be provided between a first terminal of the light emitting device and the first electrode, and a second electrical coupling may be provided between a second terminal of the light emitting device and the second electrode.
[0016] The first thermally conductive layer may be electrically conductive, and the first thermally conductive layer may be a substantially circular thermally conductive layer. A first portion of the substantially circular thermally conductive layer may be electrically isolated from a second portion of the substantially circular thermally conductive layer. Moreover, the substantially circular thermally conductive layer may include a plurality of notches around a perimeter thereof. In addition, a conductive trace on the electrically insulating substrate may extend from the substantially circular thermally conductive layer.
[0017] According to still other embodiments of the present invention, a light emitting device (LED) assembly may include an electrically insulating substrate and a substantially circular thermally conductive layer on a surface of the insulating substrate. A light emitting device may be provided on the substantially circular thermally conductive layer so that the substantially circular thermally conductive layer is between the light emitting device and the electrically insulating substrate.
[0018] A first portion of the substantially circular thermally conductive layer may be electrically isolated from a second portion of the substantially circular thermally conductive layer. The substantially circular thermally conductive layer may include a plurality of notches around a perimeter thereof. Moreover, each of the notches may extend radially from the perimeter of the substantially circular thermally conductive layer toward the light emitting device.
[0019] In addition, a conductive trace on the electrically insulating substrate may extend from the substantially circular thermally conductive layer. The substantially circular thermally conductive layer may extend beyond edges of the light emitting device a distance greater than half of a width of the light emitting device. The substantially circular thermally conductive layer may include a metal layer.
[0020] The light emitting device assembly may further include a second thermally conductive layer on a second surface of the electrically insulating substrate so that the electrically insulating substrate is between the substantially circular thermally conductive layer and the second thermally conductive layer. A plurality of thermally conductive vias may be thermally coupled between the substantially circular thermally conductive layer and the second thermally conductive layer, and portions of the substrate between the light emitting device and the second thermally conductive layer may be free of the thermally conductive vias. Moreover, first and second terminals of the light emitting device may be electrically isolated from the substantially circular thermally conductive layer. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figures IA-E are cross-sectional views illustrating light emitting device packages with a thermally conductive layer according to some embodiments of the present invention.
[0022] Figures 2-3 are cross sectional views of light emitting device packages including lenses according to additional embodiments of the present invention.
[0023] Figures 4A-C are plan views illustrating thermally conductive layers of light emitting devices according to some embodiments of the invention.
[0024] Figures 5 is a perspective view illustrating multi-chip light emitting device packages according to still other embodiments of the present invention.
DETAILED DESCRIPTION
[0025] The present invention will now be described more fully with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Like numbers refer to like elements throughout.
[0026] It will be understood that when an element such as a layer, region or substrate is referred to as being "on" another element, it can be directly on the other element or intervening elements may also be present. It will be understood that if part of an element, such as a surface, is referred to as "inner," it is farther from the outside of the device than other parts of the element. Furthermore, relative terms such as "beneath" or "overlies" may be used herein to describe a relationship of one layer or region to another layer or region relative to a substrate or base layer as illustrated in the figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. Finally, the term "directly" means that there are no intervening elements. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
[0027] It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.
[0028] Embodiments of the invention are described herein with reference to cross-sectional, perspective, and/or plan view illustrations that are schematic illustrations of idealized embodiments of the invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, a region illustrated or described as a rectangle will, typically, have rounded or curved features due to normal manufacturing tolerances. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region of a device and are not intended to limit the scope of the invention.
[0029] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and this specification and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0030] Various embodiments of the present invention used to package a semiconductor light emitting device will be described herein. As used herein, the term semiconductor light emitting device (LED) may include a light emitting diode, laser diode and/or other semiconductor device which includes one or more semiconductor layers, which may include silicon, silicon carbide, gallium nitride and/or other semiconductor materials. A light emitting device may or may not include a substrate such as a sapphire, silicon, silicon carbide and/or another microelectronic substrates. A light emitting device may include one or more contact layers which may include metal and/or other conductive layers. In some embodiments, ultraviolet, blue and/or green light emitting diodes may be provided. Red and/or amber LEDs may also be provided. The design and fabrication of semiconductor light emitting devices are well known to those having skill in the art and need not be described in detail herein.
[0031] For example, semiconductor light emitting devices (LEDs) discussed herein may be gallium nitride-based LEDs or lasers fabricated on a silicon carbide substrate such as those devices manufactured and sold by Cree, Inc. of Durham, North Carolina. The present invention may be suitable for use with LEDs and/or lasers as described in United States Patent Nos. 6,201,262; 6,187,606; 6,120,600; 5,912,477; 5,739,554; 5,631,190; 5,604,135; 5,523,589; 5,416,342; 5,393,993; 5,338,944; 5,210,051; 5,027,168; 5,027,168; 4,966,862 and/or 4,918,497, the disclosures of which are incorporated herein by reference as if set forth fully herein. Other suitable LEDs and/or lasers are described in published U.S. Patent Publication No. US 2003/0006418 Al entitled Group III Nitride Based Light Emitting Diode Structures With a Quantum Well and Superlattice, Group III Nitride Based Quantum Well Structures and Group III Nitride Based Superlattice Structures, published January 9, 2003, as well as published U.S. Patent Publication No. US 2002/0123164 Al entitled Light Emitting Diodes Including Modifications for Light Extraction and Manufacturing Methods Therefor, the disclosures of which are hereby incorporated herein in their entirety by reference. Furthermore, phosphor coated LEDs, such as those described in U.S. Patent Publication No. 2004/0056260 Al, entitled Phosphor- Coated Light Emitting Diodes Including Tapered Sidewalls and Fabrication Methods Therefor, the disclosure of which is incorporated by reference herein as if set forth fully, may also be suitable for use in embodiments of the present invention. The LEDs and/or lasers may be configured to operate such that light emission occurs through the substrate. In such embodiments, the substrate may be patterned so as to enhance light output of the devices as is described, for example, in the above-cited U.S. Patent Publication No. US 2002/0123164 Al.
[0032] Referring to the embodiments of FIGS. IA-E, 2, 3, 4A-C, and 5, each of substrates 100a-k (also referred to as submounts) may have respective upper surfaces 105a-k and lower surfaces 103a-k as shown. Each of the substrates 100a-k may include a printed circuit board (PCB) substrate, an aluminum block substrate, an alumina substrate, an aluminum nitride substrate, a sapphire substrate, and/or a silicon substrate, and/or any other suitable substrate material, such as a T-Clad thermal clad insulated substrate material, available from The Bergquist Company of Chanhassen, MN. A PCB substrate may include standard FR-4 PCB, a metal-core PCB, flex tape, and/or any other type of printed circuit board.
[0033] As illustrated in FIGS. IA-E, 2, 3, 4A-C, and 5, a patterned metal feature(s) may be formed on upper surfaces 105a-k of the respective substrates 100a- k. The patterned metal feature(s) may include a thermally conductive layer(s) 112a-k, meniscus control feature(s) 303 and/or 304 (as shown in Figure3), a wirebond pad(s) 305 (as shown in Figure 3), and/or electrodes 110a-k and/or 11 la-k. The conductive features on top surfaces 105a-k of substrate 100a-k may be formed, for example, using a plating process. A plating process may be used to plate a thin or thick metallic film on a substrate. In a typical plating process, a titanium adhesion layer and a copper seed layer may be sequentially sputtered onto the substrate. Then, approximately 75 microns of copper may be plated onto the copper seed layer. Alternatively, the adhesion layer and seed layer may be sputtered using, for example, a metal mask to form a desired pattern. A plating process may also be used to form conductive metal vias through a substrate. In an alternative, a deposited metal film may be patterned using standard lithographic processes to provide metal features on the substrate having desired patterns.
[0034] In some embodiments of the invention illustrated in Figure 3, first and second meniscus control features 303 and 304 may be formed of a material different from the thermally conductive layer 112g and/or the wirebond pads 305. For example, the meniscus control features 303 and 304 may comprise a polymer such as a solder mask material including, for example, polyimide. A polymer such as polyimide, for example, may provide a suitable material for use as a meniscus control feature because polyimide may provide a relatively a low surface energy, which may provide improved meniscus control properties.
[0035] Lateral dimensions (parallel to the substrate) and thicknesses of the thermally conductive layers 112a-k may vary based on the heat spreading properties of the materials used. Heat spreading may be increased when a diameter or width (parallel to the surface of the substrate) of the thermally conductive layer 112a-k extends from an edge or edges of the LED source 114a-k a distance that is at least half of the width of the LED source 114a-k, and according to some embodiments of the present invention, a distance that is at least the width of the LED source 114a-k. Moreover, the thermally conductive layer 112a-k may extend beyond edges of the LED 114a-k a distance greater than twice a thickness of the thermally conductive layer. According to some embodiments of the present invention, the thermally conductive layer 112a-k may include a layer of a metal (such as copper, aluminum, gold, tin, tin-silver, and/or copper-tin), a layer of a ceramic (such as aluminum- nitride), and/or a layer of a semiconductor material (such as silicon carbide). With a layer of copper provided as a thermally conductive layer 112a-k, the copper thermally conductive layer(s) may be configured so that a ratio of a diameter or width (parallel to the surface of the substrate) of the copper thermally conductive layer(s) 112a-k with respect to a thickness (perpendicular to the surface of the substrate) may be in the range of at least about 25 to about 140. With a layer of aluminum provided as a thermally conductive layer 112a-k, the aluminum thermally conductive layer(s) may be configured so that a ratio of a diameter or width (parallel to the surface of the substrate) of the aluminum thermally conductive layer(s) 112a-k with respect to a thickness (perpendicular to the surface of the substrate) may be in the range of at least about 7 to about 50.
[0036] One or more of the electrodes 110a-k and/or 11 la-k may be formed on an upper surface 105a-k of the respective substrate 100a-k. In addition, one or more lower electrodes 1 lOc'-g' and/or 11 lc'-g' may be formed on a lower surface 103c-g of the respective substrate lOOc-g as shown in FIGS. IC-E, 2, and 3. One or more conductive vias 122c-g may connect one or more of the lower electrodes 1 lOc'-g' and/or 11 lc'-g1 to various features on an upper surface 105c-g of the respective substrate 100c-g. For example, one of the conductive vias 122c-g and/or 122c'-g' may electrically connect electrodes 1 lOc-g and/or 11 lc-g with respective lower electrodes 1 lOc'-g1 and/or 11 IcVg'. Accordingly, respective conductive features formed on upper surfaces 105c-g of substrates 100c-g may be formed of a same material. For example, the conductive features may include copper deposited using a plating process.
[0037] In some other embodiments of the present invention, some conductive features may include additional metals. For example, the thermally conductive layer(s) 112a-k may be plated and/or coated with additional metals and/or other materials to make the thermally conductive layer(s) 112a-k more suitable for mounting a respective LED chip 114a-k thereon. For example, the thermally conductive layer(s) 112a-k may be plated with additional layers such as, for example, additional adhesive, bonding, reflector, die attach pad and/or barrier layers (not shown). These layers can be in addition to the thermally conductive layer, and these additional layers may also be thermally conductive. In an alternative, a direct die attach may be performed using flux instead of Au/Sn solder paste to reduce a thermal resistance between an LED 114a-k and the respective thermally conductive layer 112a-k and/or to reduce voiding. Direct die attach may enable use of a discrete zener device for ESD protection in another area of the LED system. The LED(s) 114a-k and respective thermally conductive layer(s) 112a-k may be configured to provide coupling with vertical, planar, and/or flip-chip LEDs.
[0038] As illustrated in FIGS. IA-E, a thermally conductive layer 112a-e may be formed on an upper (primary) surface 105a-e of respective substrate 100a-e. As shown in Figures 1C- IE, a second thermally conductive layer 113c-e may also be formed on a lower (secondary) surface 103c-e of the respective substrate 103C-E. As shown in Figures ID-E, thermally conductive vias 201d-e may be thermally coupled between first thermally conductive layer(s) 112d-e and second thermally conductive layer(s) 113d-e. The thermally conductive vias 201d-e may extend through the substrate 100d-e to improve thermal coupling between the first thermally conductive layer(s) 112d-e and the second thermally conductive layer(s) 113d-e. A profile of each via through the substrate (as viewed from above or below the substrate) may take any shape such as a circle, a square, a polygon, etc. Each thermally conductive via 201d-e may extend from any portion of the respective thermally conductive layer 112. According to some embodiments of the present invention, the thermally conductive vias 201d-e may be provided between the LED 114d-e and the second thermally conductive layer 113d-e to increase thermal conduction. According to some other embodiments of the present invention, the thermally conductive vias 201d-e may be spaced apart from (or laterally offset from) the respective LED 114d-e to improve a mechanical coupling between the LED 114d-e and the thermally conductive layer 112d-e. For example, a portion of the thermally conductive layer 112d-e that is free of thermally conductive vias 201d-e may provide a more planar surface to improve mechanical coupling with the LED 114d-e.
[0039] Because the thermally conductive layers 112a-e and/or 113c-e may be formed using thin film technologies according to some embodiments of the present invention, first and second thermally conductive layers 112a-e and/or 113c-e may be electrically isolated from the electrodes 110a-e and/or 11 la-e as illustrated in FIGS. IA, 1C, and/or ID. This electrical isolation may be provided, for example, so that a material(s) for the thermally conductive layer(s) and for the electrodes may be different. As shown in Figures IA-E, wirebonds 128a-e may be used to provide electrical coupling between the LEDs 114a-e and the respective electrodes 11 la-e. As shown in Figures IA and IC-D, wirebonds 128a' and 128c'-d' may provide electrical coupling between LED's 114a and 114c-d and respective electrodes 110a and 1 lOc-d. As shown in Figure IB, the thermally conductive layer 112b and the electrode 110b may be provided as a continuous/patterned layer of an electrically and thermally conductive material. For example, a patterned layer layer of a thermally conductive material may provide the thermally conductive layer 112b, the electrode 110b, and a conductive trace therebetween. As shown in Figures 4A-B, thermally conductive layer(s) 112h-i may be electrically coupled to respective electrode(s) 11 lh-i through conductive trace(s) 402h-i. Second thermally conductive layer 113e may be electrically coupled to an electrode 11Oe1 as shown in Figure IE. The first thermally conductive layer 112e may be electrically coupled to an electrode HOe1 on the lower surface 103e of the substrate lOOe through electrically and thermally conductive vias 20 Ie as shown in Figure IE.
[0040] While not shown in Figures IA-E, structures of Figures IA-E may be used together with lenses and/or reflection devices as illustrated, for example, in Figures 2 and 3. Moreover, the structure of Figure 2 may be used with the lens of Figure 3 and/or the structure of Figure 3 may be used with the lens of Figure 2. Moreover, structures including thermally conductive layers, thermally/electrically conductive vias, LEDs, electrodes, and/or substrates according to embodiments of the present invention (as discussed, for example, with respect to Figures IA-E, 2, 3, 4A- B, and 5) may be used with additional elements of LED packaging as discussed, for example, in U.S. Patent Application Serial Nos. 11/044,126 and 11/336,369, the disclosures of which are incorporated herein by reference as if set forth fully herein.
[0041] More particularly, the LED package of Figure 1 A may include a thermally conductive layer 112a between the LED 114a and the substrate 100a, and the thermally conductive layer 112a may extend beyond edges of the LED 114a a distance greater than half a width of the LED 114a, and according to some embodiments of the present invention, a distance that is greater than a width of the LED 114a. Moreover, the LED may be a horizontal LED such that both electrodes (i.e., the cathode and anode) thereof are on the surface of the LED 114a opposite the substrate 100a. Wirebonds 128a and 128a1 may provide electrical coupling between the LED 114a and the electrodes I l ia and 110a. The lower surface 103a of the substrate 100a opposite the LED 114a may thus be free of electrical connection. During operation, heat from the LED may be spread through the thermally conductive layer 112a and into the substrate 100a. The thermally conductive layer 112a may include an electrically and thermally conductive material such as copper. Moreover, the backside 103a of the substrate 100a may be thermally coupled to a heat sink and/or to a thermally conductive portion of another substrate (such as a printed circuit board) so that heat is conducted away from the substrate 100a.
[0042] The LED package of Figure 1 B may include a thermally conductive layer 112b between the LED 114b and the substrate 100b, and the thermally conductive layer 112b may extend beyond edges of the LED 114b a distance greater than half a width of the LED 114b, and according to some embodiments of the present invention, a distance that is greater than a width of the LED 114b. Moreover, the LED may be a vertical LED such that the electrodes (i.e., the cathode and anode) thereof are on opposite surfaces of the LED 114b. Wirebond 128b may provide electrical coupling between a first electrode of the LED 114b and the electrodes 11 1b. A second electrode of the LED 114b may be coupled directly to the thermally conductive layer 112b. As further shown in Figure IB, the thermally conductive layer 112b and the electrode 110b and a trace therebetween may be formed from a same layer of an electrically and thermally conductive material so that a second wirebond is not required. As with the structure of Figure IA, the lower surface 103b of the substrate 100b opposite the LED 114b may thus be free of electrical connection. During operation, heat from the LED 1 14b may be spread through the thermally conductive layer 112b and into the substrate 100b. The thermally conductive layer 112a may include an electrically and thermally conductive material such as copper. Moreover, the backside 103b of the substrate 100b may be thermally coupled to a heat sink and/or to a thermally conductive portion of another substrate (such as a printed circuit board) so that heat is conducted away from the substrate 100b. If the LED 114b is a horizontal LED, a second wirebond may be provided between the second electrode on a surface of the LED 114b opposite the thermally conductive layer 112b and the thermally conductive layer 112b.
[0043] The LED package of Figure 1 C may include a thermally conductive layer 112c between the LED 114c and the substrate 100c, and the thermally conductive layer 112c may extend beyond edges of the LED 114a a distance greater than half a width of the LED 114c, and according to some embodiments of the present invention, a distance that is greater than a width of the LED 114c. Moreover, the LED may be a vertical LED such that the electrodes (i.e., the cathode and anode) thereof are on opposite surfaces of the LED 114c. Wirebond 128c may provide electrical coupling between a first electrode of the LED 114c and the electrode 111c. The layer 112c may also be electrically conductive, and a second electrode of the LED 114c may be coupled directly to the thermally and electrically conductive layer 112c, and wirebond 128c1 may provide electrical coupling between the thermally conductive layer 112c and the electrode 110c. In an alternative, a conductive trace may be provided between the thermally conductive layer 112c and the electrode 110c as discussed above with respect to Figure IB so that a second wirebond is not required.
[0044] In Figure 1C, a second thermally conductive layer 113c may be provided on a backside 103c of the substrate 100c to enhance coupling of heat from the substrate 100c to a heat sink and/or to a thermally conductive portion of another circuit board (such as a printed circuit board). During operation, heat from the LED 114c may be spread through the thermally conductive layer 112c and into the substrate 100c and the second thermally conductive layer 113c. The thermally conductive layers 112c and 113c may each include a thermally conductive material such as copper. Moreover, the backside 103c of the substrate 100c may be thermally coupled to a heat sink and/or to a thermally conductive portion of another substrate (such as a printed circuit board) so that heat is conducted away from the substrate 100c. If the LED 114c is a horizontal LED, the second wirebond 128c' may be provided between the second electrode on a surface of the LED 114c opposite the thermally conductive layer 112c and the electrode 110c.
[0045] As further shown in Figure 1C, secondary electrodes 111c' and 110c' may be provided on the backside 103 c of the substrate 100c, and the secondary electrodes 111c' and 110c1 may be electrically coupled to the electrodes 111c and 110c on the frontside 105c of the substrate 100c through electrically conductive vias 122c and 122c'. The substrate 100c can thus be mounted on a printed circuit board with the secondary electrodes 111c' and 110c' providing electrical coupling to the printed circuit board. In an alternative, conductive vias 122c and 122c1 and secondary electrodes 111c' and 110c' may be omitted if electrical coupling to another substrate is provided directly to the electrodes 111c and 110c. [0046] Moreover, electrically conductive vias and secondary electrodes as discussed above with respect to Figure 1C may be applied to the structures of Figures IA and/or IB according to some embodiments of the present invention. For example, secondary electrodes on the backside 103 a of substrate 100a of Figure IA may be electrically coupled to electrodes I l ia and 11 Oa using respective conductive vias through the substrate 100a. Similarly, secondary electrodes on the backside 103b of substrate 100b of Figure IB may be electrically coupled to electrodes 111b and 110b using respective conductive vias through the substrate 100b.
[0047] The LED package of Figure ID may include a thermally conductive layer 112d between the LED 114d and the substrate 10Od, and the thermally conductive layer 112d may extend beyond edges of the LED 114d a distance greater than half a width of the LED 114d, and according to some embodiments of the present invention, a distance that is greater than a width of the LED 114d. Moreover, the LED may be a horizontal LED such that the electrodes (i.e., the cathode and anode) thereof are on a surface of the LED 114d opposite the substrate 10Od. Wirebonds 128d and 128d' may provide electrical coupling between electrodes of the LED 114d and the electrodes 11 Id and HOd.
[0048] In Figure ID, a second thermally conductive layer 113d may be provided on a backside 103 d of the substrate lOOd to enhance coupling of heat from the substrate 10Od to a heat sink and/or to a thermally conductive portion of another circuit board (such as a printed circuit board). In addition, thermally conductive vias 20 Id may improve thermal coupling between the first thermally conductive layer 112d and the second thermally conductive layer 1 13d. During operation, heat from the LED 114d may be spread through the thermally conductive layer 112d and through the thermally conductive vias 20 Id to the second thermally conductive layer 113d. The thermally conductive layers 112d and 113d and the thermally conductive vias 20 Id may each include a thermally conductive material such as copper. Moreover, the backside 103d of the substrate 10Od may be thermally coupled to a heat sink and/or to a thermally conductive portion of another substrate (such as a printed circuit board) so that heat is conducted away from the substrate 10Od.
[0049] If the LED 114d is a vertical LED, a second electrode of the LED 1 14d may be coupled directly to the thermally conductive layer 112d, and wirebond 128d' may provide electrically coupling between the thermally conductive layer 1 12d and the electrode 11Od. In an alternative, a conductive trace may be provided between the thermally conductive layer 112d and the electrode 1 1Od as discussed above with respect to Figure 1 B so that a second wirebond is not required.
[0050] As further shown in Figure ID, secondary electrodes 11 Id' and 11Od' may be provided on the backside 103d of the substrate 10Od, and the secondary electrodes 11 Id' and HOd' may be electrically coupled to the electrodes 11 Id and 11Od on the frontside 105d of the substrate lOOd through electrically conductive vias 122d and 122d'. The substrate 10Od can thus be mounted on a printed circuit board with the secondary electrodes 11 Id' and HOd' providing electrical coupling to the printed circuit board. In an alternative, conductive vias 122d and 122d' and secondary electrodes 11 Id' and 11Od' may be omitted if electrical coupling to another substrate is provided directly to the electrodes 11 Id and 11Od.
[0051] The LED package of Figure IE may include a thermally conductive layer 112e between the LED 114e and the substrate 10Oe, and the thermally conductive layer 112e may extend beyond edges of the LED 114e a distance greater than half a width of the LED 114e, and according to some embodiments of the present invention, a distance that is greater than a width of the LED 114e. Moreover, the LED may be a vertical LED such that the electrodes (i.e., the cathode and anode) thereof are on opposite surfaces of the LED 114e. Wirebond 128e may provide electrical coupling between a first electrode of the LED 114e and the electrodes 1 1 Ie. A second electrode of the LED 114e may be electrically and mechanically coupled to the thermally conductive layer 112e.
[0052] In Figure IE, a second thermally conductive layer 113e may be provided on a backside 103e of the substrate lOOed to enhance coupling of heat from the substrate lOOe to a heat sink and/or to a thermally conductive portion of another circuit board (such as a printed circuit board). In addition, thermally conductive vias 20 Ie may improve thermal coupling between the first thermally conductive layer 112e and the second thermally conductive layer 1 13e. During operation, heat from the LED 114e may be spread through the thermally conductive layer 112e and through the thermally conductive vias 20 Ie to the second thermally conductive layer 113e. The thermally conductive layers 112e and 1 13e and the thermally conductive vias 20 Ie may each include a thermally conductive material such as copper. Moreover, the backside 103e of the substrate lOOe may be thermally coupled to a heat sink and/or to a thermally conductive portion of another substrate (such as a printed circuit board) so that heat is conducted away from the substrate 10Oe. If the LED 114e is a horizontal LED, a second electrode of the LED 114e may be coupled to the thermally conductive layer 112e using a second wirebond.
[0053] As further shown in Figure IE, secondary electrodes 11 Ie' and HOe' may be provided on the backside 103e of the substrate 10Oe. The secondary electrode 11 Ie' may be electrically coupled to the electrode 11 Ie on the frontside 105e of the substrate lOOe through electrically conductive via 122e. The secondary electrode HOe' may be electrically coupled to the second thermally conductive layer 113e through a trace on the backside 103e of the substrate 10Oe. Accordingly, electrical coupling between the LED 114e and the electrode 11Oe' may be provided through the first thermally conductive layer 112e, through the thermally conductive traces 20 Ie, and through the second thermally conductive layer 113e. According to some embodiments of the present invention, the secondary electrode 11Oe' and the second thermally conductive layer 113e may be provided as portions of a same layer of an electrically and thermally conductive layer and/or electrical coupling to another substrate may be provided directly to the second thermally conductive layer 113e. The substrate 10Oe can thus be mounted on a printed circuit board with the secondary electrodes H ie' and 11 Oe' providing electrical coupling to the printed circuit board.
[0054] Referring to Figure 2, according to some embodiments of the present invention, a metal and/or reflective cup (or ring) 212 may be provided around the LED 114f , and a pre-formed lens 210 may be secured within the reflective cup or ring 212 using an adhesive material 211. An electrically insulating material 213 may be provided between the ring 212 and the substrate 10Of and/or other layers (such as electrodes 11Of and/or 11 If) on the substrate 10Of. The first and second thermally conductive layers 112f and 113f may be thermally coupled using thermally conductive vias 20 If that extend through the substrate lOOf to the second thermally conductive layer 113f. As further illustrated in Figure 2, the integrated heat spreading system including the thermally conductive layers 112f and 113f and the thermally conductive vias 20 If may be electrically isolated from electrodes of the LED 114f and/ or from electrodes 1 1Of, 11Of , 11 If, and/or 11 If . Electrodes of the LED 114f may be electrically coupled to the electrodes 11OA and/or 11 IA by wirebonds 128f and 128f . Lenses and reflective cups may be fabricated as discussed, for example, in U.S. Patent Application No. 11/044,126 entitled "Methods For Packaging A Light Emitting Device And Packaged Light Emitting Devices" and filed January 27, 2005, the disclosure of which is hereby incorporated herein in its entirety by reference. [0055] As shown in Figure 3, a light emitting device assembly may include one or more encapsulated regions according to some embodiments of the present invention. More particularly, a first meniscus control feature 303 on the substrate lOOg may encircle the thermally conductive layer 112g to define a region confining an encapsulant material 301 on upper surface 105g of the substrate lOOg within the periphery of the first meniscus control feature 303. A second meniscus control feature 304 may surround the region 301 and, together with the first meniscus control feature 303, may define an annular (or ring-shaped) region confining a lens material 302 on the upper surface 105g of the substrate lOOg surrounding the first encapsulant region 301. The encapsulant material 301 may be dispensed as a liquid confined by the first meniscus control feature 303 and then cured. The lens material 302 may then be dispensed as a liquid confined by the second meniscus control feature 304 and then cured. The encapsulant material 301 and/or the lens material 302 may be an epoxy material(s).
[0056] As illustrated in Figure 3, the lens material 302 may enclose and encompass the encapsulant material 301. While the lens material 302 may be annular as discussed above, the lens material 302 may be provided according to other shapes depending on shapes of the first meniscus control feature 303 and the second meniscus control feature 304 and depending on volumes of the encapsulant and/or lens materials dispensed. For example, the lens material may have an oval periphery. It will be understood that for a feature to "encircle" or "surround" a region, the feature need not be continuously formed around the region. Although the figures illustrate continuous meniscus control features, it may be possible for a meniscus control feature to include gaps or voids therein which do not affect the meniscus control function of the feature. Moreover, the feature need not form a circle, but could be provided in other two dimensional shapes such as ellipses, polygons, etc.
[0057] As further shown in Figure 3, the wirebond pads 305 and 305' may be formed on the upper surface 105g of substrate lOOg within the lens region surrounded by the second meniscus control feature 304. One of the conductive vias 122g may electrically couple a wire bond pad 305 and/or 305' with a respective lower electrode 11 Ig' and/or HOg'. Another of the electrically conductive vias 122g may electrically couple a lower electrode 11 Ig' and/or HOg' with a respective electrode 11 Ig and/or 11Og on an upper surface 105g of the substrate 10Og. In another alternative (not shown), an electrically and thermally conductive via 20 Ig may electrically couple the thermally conductive layer 112g with a lower electrode 11 Ig' and/or HOg1 so that a lower surface of a vertical LED may be electrically coupled to one of the lower electrodes 11 Ig1 and/or HOg1 thereby eliminating one of the wirebonds 128g and/or 128g'. Moreover, the structure including LED 114g; vias 122g, 122g', and 20 Ig; thermally conductive layers 112g and 113g; wirebond pads 305 and 305'; and electrodes H Ig, 11 Ig', HOg, and 11Og' may be provided without encapsulant material 301 and lens material 302 so that the LED 114g is exposed as shown in Figures IA-E. In an alternative, the structure of Figure 3 may be provided with the reflector and lens structure of Figure 2 instead of the encapsulant material and lens material.
[0058] Lenses may be fabricated as discussed, for example, in U.S. Patent Application No. 11/197,096 entitled "Packages for Semiconductor Light Emitting Devices Utilizing Dispensed Encapsulants And Methods Of Packaging The Same" and filed August 4, 2005, and in U.S. Patent Application No. 11/336,369 entitled "Packages For Semiconductor Light Emitting Devices Utilizing Dispensed Reflectors And Methods Of Forming Same" and filed January 20, 2006. The disclosures of both of the above referenced applications are hereby incorporated herein in their entirety by reference.
[0059] According to some embodiments of the present invention, the thermally conductive layer(s) 112a-g may be circular in a plan view or may have other shapes such as an oval, a polygon, etc. By way of example, the thermally conductive layer(s) 112a-g may be substantially circular as shown in Figures 4A-C. A substantially circular shape, for example, may efficiently spread heat while reducing unnecessary expansion (due to heating) that may result from an increased distance from an LED source 114a-g to corners of a square or rectangular thermally conductive layer.
[0060] As shown in the plan view Figure 4A, an LED 114h may be provided on a substantially circular thermally conductive layer 112h. More particularly, the thermally conductive layer 112h may have a gap 40 Ih therein electrically isolating a portion 112h' of the thermally conductive layer 112h. A trace 402h may provide electrical coupling between the thermally conductive layer 112h and electrode 11 Ih, and a trace 403h may provide electrical coupling between the portion 112h' and electrode 11Oh. With a horizontal LED 114h (having both electrodes on an upper surface thereof), a first wirebond may provide electrical coupling between the main portion of the thermally conductive layer 112h and the LED 114h, and a second wirebond may provide electrical coupling between the portion 112h' and the LED 114h. The portion 112h' may provide a relatively large area for a wirebond connection without significantly reducing a heat spreading capacity of the thermally conductive layer 112h. With a vertical LED 114H (having electrodes on opposite surfaces thereof), a first surface of the LED 114h may be electrically and mechanically bonded (for example, using solder) to the main portion of the thermally conductive layer 112h, and a wirebond may provide electrical coupling of a second surface (opposite the thermally conductive layer) to the portion 112h' of the thermally conductive layer.
[0061] According to still other embodiments of the present invention, the thermally conductive layer 112h may be electrically isolated from the electrodes 11 Ih and HOh (so that one or both of traces 402h and/or 403h may be eliminated). Without traces 402h and/or 403h, wirebonds may provide electrical coupling between the LED 114h and electrodes 11 Ih and/or HOh. Moreover, a second thermally conductive layer (not shown) may be provided on a surface of the substrate lOOh opposite the thermally conducive layer 112h as shown, for example, in Figures 1C, ID, and IE, and/or thermally conductive vias through the substrate 11Oh may provide thermal coupling between the thermally conductive layers on opposite sides of the substrate lOOh as shown, for example, in Figures ID and IE.
[0062] As shown in Figure 4B, notches 404i may be provided in the substantially circular thermally conductive layer 112i to reduce stress/strain due to thermal expansion. Heat generated by the LED 114i may thus be dissipated across the relatively large thermally conductive layer 112i while reducing thermal stress/strain across the thermally conductive layer. As shown in Figure 4B, the notches 404i may be spaced around peripheral portions of the thermally conductive layer 112i. Moreover, the notches 112i may extend radially toward the LED 112i to reduce impedance of heat flow from the LED 114i toward edges of the thermally conductive layer 112i. The electrodes 11 Ii and 11Oi, the traces 402i and 403i, the conductive vias 122i, and the substrate lOOi may be provided and/or function as discussed above with respect to corresponding elements of Figure 4A.
[0063] As further shown in FIGS. 4 A and 4B, the electrically isolating gap 401h-i of Figures 4A-B may be formed using a solder mask when plating the thermally conductive layer, or the gap may be formed by subsequently patterning the thermally conductive layer (for example, using photolithographic mask and etch operations). This gap 40 Ih or 40 Ii may electrically isolate cathode and anode portions of the substantially circular thermally conductive layer while providing significant heat spreading. Electrically conductive traces 402h-i and/or 403h-i may electrically couple the portions 112h-i and/or 112h'-i' of the thermally conductive layer to the electrodes 110h-i and/or 110h-i.
[0064] According to further embodiments of the present invention, a substantially circular thermally conductive layer 1 12k may be electrically isolated from one or both of the electrodes 111k and/or 110k as shown in Figure 4C. Moreover, the gap of Figures 4A and 4B may be omitted from the thermally conductive layer 112k, and notches 404k may be substantially evenly spaced around peripheral portions of the thermally conductive layer 112k. With three notches as shown in Figure 4C, for example, the notches 404k may be spaced by approximately 120 degrees around the substantially circular thermally conductive layer 112k. With four notches, the notches may be spaced by approximately 90 degrees around the substantially circular thermally conductive layer.
[0065] Moreover, the notches 112k may extend radially toward the LED 112k to reduce impedance of heat flow from the LED 114k toward edges of the thermally conductive layer 112k. The electrodes 1 11k and 110k, the trace 402k, the conductive vias 122k, and the substrate 100k may be provided and/or function as discussed above with respect to corresponding elements of Figures 4A-B. By way of example, the LED may be a vertical LED with a first surface electrically and mechanically bonded (for example, soldered) to the thermally conductive layer, and a wirebond may provide electrical coupling between a second surface of the LED 114K and the electrode 110k. In an alternative, the the LED 114k may be a horizontal LED with a first wirebond providing electrical coupling between a first portion of the LED 114k and the thermally conductive layer 1 12k and with a second wirebond providing electrical coupling between a second portion of the LED and the electrode 11 Ok.
[0066] Any of the thermally conductive layers 112h, 112i, and/or 112k of Figures 4A-C may be electrically coupled to a second thermally conductive layer on an opposite side of the substrate 10Oh, 10Oi, and/or 100k, for example, using thermally conductive vias. According to some embodiments of the present invention, any such thermally conductive vias may be offset relative to the LED 114h, 114i, and/or 1 14k to provide a more planar surface to which the LED may be bonded. According to other embodiments of the present invention, the one or more thermally conductive vias may be provided directly between the LED and the second thermally conductive layer on the opposite side of the substrate. Moreover, any of the patterns of thermally conductive layers 112h, 112i, and/or 112k discussed above with respect to Figures 4A-C may be used for the thermally conductive layers discussed herein with respect to Figures IA-E, 2, 3, and/or 5. Moreover, each of the substantially circular thermally conductive layers 112h, 112i, and/or 112k may extend beyond edges of the respective LED 114h, 114i, and/or 114k a distance that is greater than half of a width of the LED, and according to some embodiments of the present invention, a distance that is greater than a width of the LED.
[0067] Further embodiments of the present invention may include a plurality of LEDs on a same substrate, such as a three-chip-in series layout illustrated in Figure 5. In Figure 5, three LEDs 114j, 114j', and 114j" may be electrically coupled in series. For purposes of illustration, each LED 114j, 114j', 114j" may be provided in a configuration similar to that discussed above with respect to Figure IA. Electrodes 11 Ij and/or HOj may be electrically coupled to respective conductive traces 50 Ij, and additional conductive traces may be provided between LEDs 114j, 114j', and/or 114j". As shown in Figure 5, each LED 114j, 114j', and/or 114j" may be electrically coupled to traces using respective wirebond pairs 128j, 128j', and/or 128j". As shown in Figure 5, the thermally conductive layers 1 12j, 112j', and/or 112j" may be electrically isolated from the electrodes HOj and/or 11 Ij and/or from traces 50 Ij.
[0068] While a pair of wirebonds is provided for each LED in Figure 5, a number of wirebonds and/or traces may be reduced by providing wirebond connections directly between LEDs and/or directly to the electrodes 11 Ij and/or 11Oj. As further shown in Figure 5, horizontal LEDs may be used with both electrical couplings to each LED on a surface of the LED opposite the substrate 10Oj. With vertical LEDs, first electrical couplings may be from LEDs 114j, 114j', and/or 114j" to the respective thermally conductive layer H2j, 112j', and/or 112j", and second electrical couplings may be provided using wirebonds to surfaces of the LEDs 114j, 114j', and/or 114j" opposite the substrate 10Oj.
[0069] Second thermally conductive layers may be provided on a backside of the substrate 10Oj opposite the thermally conductive layers 112j, 112j', and/or 1 12j" as discussed above with respect to Figures IC-E, 2, and 3. For example, a separate second thermally conductive layer may be provided for each of the first thermally conductive layers 112j, 112j', and/or 112j". If no electrical connections are provided to a backside of the substrate 10Oj, a continuous second thermally conductive layer 505 may be provided across the backside 103j of the substrate 10Oj. Moreover, thermally conductive vias may be provided through the substrate 10Oj between one or more of the thermally conductive layers 112j, 112j', and/or 112j" and any such second thermally conductive layer on the backside 103j of the substrate 10Oj.
[0070] In addition, the series of LED chips 114j, 114j!, 114j " may also be coupled to an ESD (electrostatic discharge) protection chip 502 (such as a zener diode). Integrated heat spreading, according to embodiments of the present invention, may provide conditions more favorable for the use of thin film and direct bond technologies, allowing multiple LED chips on a single small form factor LED package. According to some embodiments of the present invention, heat generated by such a multi-chip assembly may be transferred away from the LEDs more effectively.
[0071] Each of the thermally conductive layers 112j, 112j', and/or 112j" may be substantially circular and/or may include notches therein as discussed above with respect to Figures 4A-C. Moreover, a reflective cup, a preformed lens, meniscus control features, and/or liquid dispensed/cured lenses may be provided for the LED's 114j, 114j', and/or 114j" as discussed above with respect to Figures 2 and/or 3.
[0072] A thermally conductive layer (e.g., thermally conductive layers 112a-k discussed above) according to some embodiments of the present invention may thus provide a heat spreader that is integral with respect to the substrate (e.g., substrates 100a-k discussed above) on which it is formed. Thermal transport of heat from an LED (e.g., LEDs 114a-k) into the substrate and/or a heat sink can be improved, so that the LED can be operated at higher power, for example, up to 5 Watts. Thermally conductive layers according to some embodiments of the present invention may be formed using thin film processing of highly conductive metals and photolighographic patterning. Thermally conductive layers according to some embodiments of the present invention may enable direct flux die attach and/or attachment of a discrete zener diode for ESD protection.
[0073] More particularly, the thermally conductive layers 112a-k discussed above with respect to Figures IA-E, 2, 3, 4A-C, and 5 may be formed, for example, by plating, sputtering, and/or evaporating one or more layers of a metal(s) such as nickel, copper, gold, and/or silver. Thermally conductive vias (e.g., conductive vias 201d-g) may be provided using a highly thermally conductive material such as copper in a hole through the substrate to aid thermal transport of heat through the substrate. Moreover, the thermally conductive layers 112a-k may enable a direct die attach of the LED 114a-k, for example, using flux instead of a gold/tin solder paste. A thickness of a bond between the LED and the thermally conductive layer may thus be reduced to improve a thermal interface and to reduce voiding.
[0074] By providing relatively precise patterning of the thermally conductive layer (for example, using photolithographic patterning) multiple LED chips may be provided on a same substrate as shown, for example, in Figure 5. For example, multiple LEDs of a same color (such as red, blue, green, or white) may be provided on a same substrate. In an alternative, a combination of red, blue, and green LEDs may be provided on a same substrate. In addition, direct die attachment may enable provision of an LED and a discrete zener diode (for ESD protection) on a same substrate as shown in Figure 5. Use of thin film technology may also enable provision of a thermally conductive layer and/or thermally conductive vias that are electrically isolated as shown, for example, in Figures IA, ID, 2, and 3. Stated in other words, the thermal path may be electrically isolated.
[0075] According to some embodiments of the present invention, a thermally conductive layer (e.g., layers 112a-k) may be formed by sputtering a seed layer (such as a layer of titanium) through a stencil to provide a desired pattern of the thermally conductive layer on the substrate (e.g., substrates 100a-k). A copper may then be plated on the seed layer. The seed layer may have a thickness, for example, in the range of about 20 micrometers to about 150 micrometers, and the copper layer may have a thickness of about 75 micrometers.
[0076] According to some other embodiments of the present invention, a thermally conductive layer (e.g., layers 112a-k) may be formed by printing a paste (including a thermally conductive metal) through a stencil and baking to remove organics. The resulting metal layer may be subjected to an anneal and/or a stamping operation to reduce porosity, increase thermal conductivity, increase planarity, etc. - According to still other embodiments of the present invention, a thermally conductive layer (e.g., layers 1 12a-k) may be provided as a metal perform that is pressed into place, and the perform may then be further subjected to an anneal to improve adhesion to the substrate. Moreover, a thermally conductive layer formed according to any of the techniques discussed above may be further subjected to a rolling and/or stamping operation to further improve characteristics thereof. [0077] As discussed above with respect to Figures IA-K, 2-3, 4A-C, and 5, the LED 114a-k may be centered relative to the respective thermally conductive layer 112a-k according to some embodiments of the present invention. The LED 114a-k, however, is not required to be centered relative to the respective thermally conductive layer 112a-k according to all embodiments of the present invention. The LED 114a- k, for example, may be offset relative to a center of the respective thermally conductive layer 112a-k according to some embodiments of the present invention. Moreover, the LED 114a-k may be provided adjacent to an edge of the respective thermally conductive layer 112a-k so that the thermally conductive layer does not extend significantly beyond at least one edge of the LED 114a-k.
[0078] In the drawings and specification, there have been disclosed typical embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.

Claims

That Which Is Claimed Is:
1. A light emitting device (LED) assembly comprising: an electrically insulating substrate; a thermally conductive layer on a surface of the insulating substrate; and a light emitting device on the thermally conductive layer so that the thermally conductive layer is between the light emitting device and the electrically insulating substrate; wherein the thermally conductive layer extends beyond an edge of the light emitting device in at least one direction a distance greater than half of a width of the light emitting device.
2. A light emitting device assembly according to Claim 1, further comprising: a plurality of thermally conductive vias, wherein the thermally conductive vias are thermally coupled to the thermally conductive layer and wherein portions of the substrate adjacent the light emitting device are free of the thermally conductive vias.
3. A light emitting device assembly according to Claim 3, wherein the thermally conductive vias extend from the thermally conductive layer through the electrically insulating substrate.
4. A light emitting device assembly according to Claim 1, wherein the thermally conductive layer comprises at least one of a metal layer, a ceramic layer, and/or a semiconductor layer.
5. A light emitting device assembly according to Claim 4, wherein the thermally conductive layer comprises a copper layer.
6. A light emitting device assembly according to Claim 1, wherein the thermally conductive layer is electrically conductive, the light emitting device assembly further comprising: a first electrical coupling between a first terminal of the light emitting device and the thermally conductive layer; an electrode on the electrically insulating substrate wherein the electrode and the thermally conductive layer are electrically isolated; and a second electrical coupling between a second terminal of the light emitting device and the electrode.
7. A light emitting device assembly according to Claim 1 , wherein the thermally conductive layer is electrically conductive, the light emitting device assembly further comprising: first and second electrodes, each of which is electrically isolated from the thermally conductive layer; a first electrical coupling between a first terminal of the light emitting device and the first electrode; and a second electrical coupling between a second terminal of the light emitting device and the second electrode.
8. A light emitting device assembly according to Claim 1, wherein the thermally conductive layer is electrically conductive and wherein the thermally conductive layer comprises a substantially circular thermally conductive layer.
9. A light emitting device assembly according to Claim 8, wherein a first portion of the substantially circular thermally conductive layer is electrically isolated from a second portion of the substantially circular thermally conductive layer.
10. A light emitting device assembly according to Claim 8, wherein the substantially circular thermally conductive layer comprises a plurality of notches around a perimeter thereof.
11. A light emitting device assembly according to Claim 10, wherein each of the notches extends radially from the perimeter of the thermally conductive layer toward the light emitting device.
12. A light emitting device assembly according to Claim 8, further comprising: a conductive trace on the electrically insulating substrate, wherein the conductive trace extends from the substantially circular thermally conductive layer.
13. A light emitting device according to Claim 1 wherein the thermally conductive layer extends beyond opposing edges of the light emitting device a distance greater than half of a width of the light emitting device.
14. A light emitting device according to Claim 1 wherein the thermally conductive layer extends beyond an edge of the light emitting device in at least one direction a distance that is greater than a width of the light emitting device.
15. A light emitting device assembly comprising: an electrically insulating substrate having opposing first and second surfaces; a first thermally conductive layer on the first surface of the electrically insulating substrate; a second thermally conductive layer on the second surface of the electrically insulating substrate; a light emitting device on the first thermally conductive layer so that the first thermally conductive layer is between the light emitting device and the electrically insulating substrate; and a plurality of thermally conductive vias, wherein the thermally conductive vias are thermally coupled between the first and second thermally conductive layers and wherein portions of the substrate between the light emitting device and the second thermally conductive layer are free of the thermally conductive vias.
16. A light emitting device assembly according to Claim 15, wherein the thermally conductive vias extend from the first thermally conductive layer through the electrically insulating substrate to the second thermally conductive layer.
17. A light emitting device assembly according to Claim 15, wherein the first thermally conductive layer extends beyond an edge of the light emitting device in at least one direction a distance greater than half of a width of the light emitting device.
18. A light emitting device assembly according to Claim 15 wherein the first thermally conductive layer extends beyond any edge of the light emitting device in at least one direction a distance greater than a width of the light emitting device.
19. A light emitting device assembly according to Claim 15 wherein the first thermally conductive layer extends beyond opposing edges of the light emitting device a distance greater than half of a width of the light emitting device.
20. A light emitting device assembly according to Claim 15, wherein each of the first and second thermally conductive layers comprises at least one of a metal layer, a ceramic layer, and/or a semiconductor layer.
21. A light emitting device assembly according to Claim 20, wherein the first thermally conductive layer and/or second thermally conductive layer comprises a copper layer.
22. A light emitting device assembly according to Claim 20 wherein the first thermally conductive layer is electrically isolated from first and second terminals of the LED.
23. A light emitting device assembly according to Claim 15, wherein the first and second thermally conductive layers are electrically conductive, the light emitting device assembly further comprising: a first electrical coupling between a first terminal of the light emitting device and the first thermally conductive layer; an electrode on the electrically insulating substrate wherein the terminal and the first and second thermally conductive layers are electrically isolated; and a second electrical coupling between a second terminal of the light emitting device and the electrode.
24. A light emitting device assembly according to Claim 15, wherein the first and second thermally conductive layers are electrically conductive, the light emitting device assembly further comprising: first and second electrodes, each of which is electrically isolated from the first and second thermally conductive layers; a first electrical coupling between a first terminal of the light emitting device and the first electrode; and a second electrical coupling between a second terminal of the light emitting device and the second electrode.
25. A light emitting device assembly according to Claim 15, wherein the first thermally conductive layer is electrically conductive and wherein the first thermally conductive layer comprises a substantially circular thermally conductive layer.
26. A light emitting device assembly according to Claim 25, wherein a first portion of the substantially circular thermally conductive layer is electrically isolated from a second portion of the substantially circular thermally conductive layer.
27. A light emitting device assembly according to Claim 25 wherein the substantially circular thermally conductive layer comprises a plurality of notches around a perimeter thereof.
28. A light emitting device assembly according to Claim 25, further comprising: a conductive trace on the electrically insulating substrate, wherein the conductive trace extends from the substantially circular thermally conductive layer.
29. A light emitting device (LED) assembly comprising: an electrically insulating substrate; a substantially circular thermally conductive layer on a surface of the insulating substrate; and a light emitting device on the substantially circular thermally conductive layer so that the substantially circular thermally conductive layer is between the light emitting device and the electrically insulating substrate, wherein an edge of the substantially circular thermally conductive layer extends laterally beyond an edge of the light emitting device.
30. A light emitting device assembly according to Claim 29, wherein a first portion of the substantially circular thermally conductive layer is electrically isolated from a second portion of the substantially circular thermally conductive layer.
31. A light emitting device assembly according to Claim 29, wherein the substantially circular thermally conductive layer includes a plurality of notches around a perimeter thereof.
32. A light emitting device assembly according to Claim 31 , wherein each of the notches extends radially from the perimeter of the substantially circular thermally conductive layer toward the light emitting device.
33. A light emitting device assembly according to Claim 29, further comprising: a conductive trace on the electrically insulating substrate, wherein the conductive trace extends from the substantially circular thermally conductive layer.
34. A light emitting device assembly according to Claim 29 wherein the substantially circular thermally conductive layer extends beyond an edge of the light emitting device a distance greater than half of a width of the light emitting device.
35. A light emitting device assembly according to Claim 29 wherein the substantially circular thermally conductive layer extends beyond an edge of the light emitting device a distance greater than a width of the light emitting device.
36. A light emitting device assembly according to Claim 29 wherein the substantially circular thermally conductive layer extends beyond opposing edges of the light emitting device a distance greater than half of a width of the light emitting - device.
37. A light emitting device assembly according to Claim 29, wherein the substantially circular thermally conductive layer comprises at least one of a metal layer, a ceramic layer, and/or a semiconductor layer.
38. A light emitting device assembly according to Claim 29, further comprising: a second thermally conductive layer on a second surface of the electrically insulating substrate so that the electrically insulating substrate is between the substantially circular thermally conductive layer and the second thermally conductive layer; and a plurality of thermally conductive vias, wherein the thermally conductive vias are thermally coupled between the substantially circular thermally conductive layer and the second thermally conductive layer and wherein portions of the substrate between the light emitting device and the second thermally conductive layer are free of the thermally conductive vias.
39. A light emitting device according to Claim 38 wherein first and second terminals of the light emitting device are electrically isolated from the substantially circular thermally conductive layer.
40. A light emitting device assembly according to Claim 29, further comprising: a second thermally conductive layer on a second surface of the electrically insulating substrate so that the electrically insulating substrate is between the substantially circular thermally conductive layer and the second thermally conductive layer; and a plurality of thermally conductive vias, wherein the thermally conductive vias are thermally coupled between the substantially circular thermally conductive layer and the second thermally conductive layer and wherein the thermally conductive vias extend through portions of the electrically insulating substrate outside a region of the electrically insulating substrate defined by a periphery of the light emitting device.
PCT/US2007/022576 2006-10-31 2007-10-25 Integrated heat spreaders for leds and related assemblies WO2008054670A1 (en)

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