US 20050093672 A1
The present invention relates to the methods of construction for inductive components of, preferably, ferromagnetic materials such as inductors, chokes, and transformers when used as an integral part of the fabrication of PCB's or FLEX's. In one preferred embodiment, holes are formed through a ferromagnetic substrate and plated with conductive material. The arrangement of these holes, and the subsequent design that ensues, will form the inductive components within the plane of the media in which the device is formed; using the substrate for a magnetic core. By using this approach, the inductive components can be miniaturized to physical sizes compatible with the requirements of modem surface mount technology (SMT) for integrated circuitry (IC). This process also allows these components to be fabricated using mass production techniques, thereby avoiding the need to handle discrete devices during the manufacturing process. In another preferred embodiment, a series of thin, concentric high permeability rings are etched on a substrate to provide high permeability transformers and inductors having minimal eddy current effects.
2. A miniature inductor/transformer having minimal eddy current effects comprising:
a stack of a plurality of substantially identical thin concentric ferromagnetic rings respectively separated by their dielectric layers;
a first printed circuit and a second printed circuit on opposite sides of said stack of the concentric ferromagnetic rings; and
conductive via holes through said stack in electrical contact with said printed circuits, the axis of said via holes being substantially parallel to the center axis of said concentric rings.
3. A miniature inductor/transformer comprising:
a thin layer of ferromagnetic ferrite material on a substrate; and
a plurality of plated vias through said ferrite material, said vias providing electrical windings of said inductor/transformer.
4. A method for making a miniature inductor/transformer comprising:
forming a thin layer of ferromagnetic on a thin sheet of insulating material;
laminating said sheet having said layer of ferromagnetic material between first and second thin sheets;
forming through holes through said laminated sheets;
plating electrically conductive material within said through holes, forming a printed electrical circuit on said first and second thin sheets in electrical contact with said conductive through holes, said printed circuitry providing a portion of an electrical winding of the inductor/transformer.
5. The method of
6. The method of
7. The method of making a plurality of miniature inductor/transformers comprising:
laminating a plurality of spaced ferromagnetic cores with top and bottom layers of circuitry.
8. The method of
9. The method of
10. The method of
11. The method of
12. The method of
13. A method for making a miniature inductor/transformer comprising:
forming a first thin sheet having a printed electrical circuit thereon,;
forming a second thin sheet having a printed circuit thereon;
laminating said sheet having said layer of ferromagnetic material between said first and second thin sheets;
forming through holes through said laminated sheets; and
plating electrically conductive material within said through holes in electrical contact with said printed circuitry on said first and second thin sheets, said conductive through holes providing a portion of an electrical winding of the inductor/transformer.
14. The method of
15. The method of
26. A method for making devices for use in printed circuit board design comprising;
printing a circuit pattern onto said circuit board;
forming holes which go through said circuit board;
filling said holes with a conductive material; and
using the connections and said pattern such that a device is created which uses said circuit board as a magnetic core.
27. The method of
28. An inductor or transformer comprising:
a slab of magnetic material having a series of spaced holes therethrough;
an electrically conductor material within said holes, and
electrical printed circuits located on the top and bottom surfaces of said slab respectively in electrical contact with said conductive material.
29. A method for making a miniature inductor/transformer having minimal eddy current effects comprising:
etching a thin sheet of ferromagnetic metal to form a plural array of ten or more concentric narrow continuous rings of said ferromagnetic metal;
stacking four or more of said arrays separated by a dielectric material to form a plurality of cores, said cores so constructed having a very small cross-sectional area defined by the thickness of the sheet of ferromagnetic material and the width of said concentric narrow rings so as to minimize the eddy current effect;
laminating said stack of arrays between copper sheets;
forming said copper sheets into printed circuits;
forming vias through said printed circuits proximate said laminated ferromagnetic arrays; and
plating said vias in electrical contact with said printed circuitry to form electrical windings.
30. A method for making a miniature inductor/transformer comprising:
forming a thin layer of a ferromagnetic on a thin sheet of insulating material;
etching said thin layer to form ten or more thin discrete continuous ferromagnetic members;
forming a first thin sheet having a printed electrical circuit thereon
forming a second thin sheet having a printed circuit thereon;
stacking four or more of said sheets having said etched ferromagnetic material members between said first and second thin sheets;
forming through holes through said laminated sheets; and plating electrically conductive material within said through holes in electrical contact with said printed circuitry on said first and second thin sheets, said conductive through holes providing a portion of an electrical winding of the inductor/transformer.
This application claims the benefit of U.S. Provisional Application No. 60/234,636 filed Sept. 22, 2000 entitled “Electronic Transformer/Inductor Devices And Methods For Making Same” and U.S. Provisional Application No. 60/237,356 filed Sept. 27, 2000 entitled “Electronic Transformer/Inductor Devices And Methods For Making Same.”
The present invention relates to inductive components and methods for manufacturing these components.
Inductive components are commonly fabricated using ferromagnetic cores and windings of insulated electrical wire. The ferromagnetic cores are typically toroidal cores, rod cores, or assemblies made of a lower E shaped ferromagnetic part and a ferromagnetic cap connecting the three legs of the E such as shown in
The toroid and rod cores are manually or automatically wound with the insulated copper wire to form a number of multiple turn windings for a transformer or a single winding for an inductor. The assembly is then typically encapsulated to protect the wires. The circuit connection is made by the solder termination of the wires as required by the application. This approach has high labor costs because of individual part handling. It has large variability in electronic parameters such as leakage inductance, distributed and inter-winding capacitance, and common mode imbalance between windings because of the difficulty in exact placement of the copper wires.
The E shaped and encompassing cap assembly of
Power transformers constructed as shown in
The preferred embodiments of the present invention provide inductors and transformers and methods of manufacturing these devices which offer very significant advantages over the state-of-the-art. These inductors and transformers connected in accordance with this invention have a number of applications in the electronics, telecommunication and computer fields. In one preferred embodiment described below, a rectangular slab of ferromagnetic material is encapsulated between printed circuitry. A plurality of through holes (vias) are drilled through or formed during manufacture of the slab from the top face of the slab to the bottom face of the slab, the number of holes corresponding to the number of desired turns of the windings. This embodiment utilizes Ampere's Law in a very novel manner to form a transformer, inductor, or the like within the circuit board rather than the use or assembly of discrete inductive devices to the circuit board. Thus, the windings are not insulated electric wires. Rather, the holes through the slab are made electrically conductive by through hole plating or the like and electrically connect with the printed circuits encapsulating the slab. This pattern of plated through holes and the printed circuitry form the inductor and transformer windings with the core of the inductors and transformers being the drilled or formed slab of ferromagnetic material. This embodiment provides substantial improvements, particularly in fabricating high frequency inductors and transformers.
In another preferred embodiment described below, the core of the inductors or transformers comprises cores formed by a multi-layer series of thin concentric ferromagnetic metal rings supported on a suitable substrate such as a flex circuit (FLEX) or printed circuit board (PCB). Through holes proximate these concentric ring cores provide electrical connection with printed circuitry to provide the inductor and transformer windings. This embodiment enables construction of high permeability inductors and transformers having minimal eddy current effects. Inductors and transformers so constructed have particular application for miniature low frequency power supplies.
In addition to the advantages described above, the preferred embodiments have a number of additional significant advantages. These include: superior heat removal, outside connections that are more accessible to simplify electrical connection, shorter flux paths to increase magnetic performance, simpler fabrication, interconnections that are more integrated, smaller inductive devices, superior performance, and excellent manufacturing repeatability.
BRIEF DESCRIPTION OF THE DRAWINGS
Having thus summarized the general nature of the invention and its essential features and advantages, certain preferred embodiments and modifications thereof will become apparent to those skilled in the art from the detailed description herein having reference to the figures that follow, of which:
Preferred embodiments of the present invention have a very different core and winding arrangement. In one of these preferred embodiments shown generally in
The windings 32, 34 as shown in
Ampere's law constrains the flux path independent of the shape of the core; therefore, as discussed in detail below, it is not necessary to actually fabricate the donut shape of the toroid to create devices that behave similarly.
Fabrication as Part of a FLEX
One method of fabrication is to embed a multiplicity of ferromagnetic slabs (cores 90) within the top and bottom layers of FLEX 92 circuits such as shown in
Fabrication as Part of a PCB
Another method of fabrication shown in
Fabrication without a FLEX or PCB
Another method of fabrication is shown in Figure 11 in which a multiplicity of cores 210 are retained on a carrier 212. Each core 210 is molded with appropriate holes 214. Standard industry conductive ink screening processes are then used to form the circuits on the top 215 and bottom 216 of the cores 210 while simultaneously filling the holes 214 to make the required connection between the top 215 and bottom 216 sides.
Novel Employment of Ampere's Law
The embodiments of the invention described above, with conductive vias through the magnetic slab, employ Ampere's Law in a very novel manner. The vias are formed in such fashion as to allow a flux path to exist between two windings formed on the substrate. Thus, as shown in
It will be apparent that the proper selection of via holes enables many different shapes of virtual cores and arrangements of cores on substrates. Thus, many independent magnetic circuits can be constructed on the same substrate. Because of this, it is possible to construct more complex circuits than simple inductors and transformers by the appropriate placement of vias and circuit conductors on the top and bottom surfaces 52, 54 of the ferromagnetic slab 50 shown in
Inductors and transformers useful for high frequency circuits such as are used for radio frequencies, typical ranges being 100 KHz to 100 MHz, can be constructed in accordance with the foregoing embodiments. The ferromagnetic slab 50 is advantageously formed of a thin layer of ferrite material having typical permeabilities in the range of 100 to 10,000 and resistivity in the range of 1,000 ohm/cm to 109 ohm/cm. Typical ferrite compositions include ferric oxide and alnico. Such ferrite materials have a sufficiently high resistivity such that the plated vias through the slab are insulated one of the other. The transformers and inductors so constructed are adapted for miniaturization. They eliminate the need for complicated pins or lead-frames. Thus, a slab 1.5 inches long, 1 inch wide and 0.05 inches thick with 0.03 inch diameter vias can provide the core for two or more transformers. The ferromagnetic slabs may be very small. Surface pads on the top and bottom surfaces form the connections, and can be surface mounted directly to PCB's, thus reducing the footprint of the device and making more room for other components. The plotted windings are substantially in two parallel planes. Therefore the windings of a ten (10) layer planar transformer device, a typical application, can be reduced in overall height by a factor of five (5). The ferromagnetic slab may be very thin, e.g., 0.05 inches, so that the inductors and transformers of the invention may be constructed substantially in one very thin plane instead of a three-dimensional E core construction further reducing the overall height by a large factor.
Further Preferred Embodiments of Transformer/Inductor Devices Having High Flex Densities and Minimal Eddy Current
Many inductive devices such as low frequency power transformers require cores having relatively high relative permeabilities typically in the range of 10,000 to 100,000. However, the improvements afforded by the preferred embodiments are applicable to lower and higher values, e.g., a range of 1,000 to 1,000,000. Certain metals and metal alloys provide these high flex densities including steel, iron, silica iron, 78 permalloy, Mumetal, purified iron, and supermalloy. Although these high flex densities can offer distinct advantages in constructing transformers and inductors, the low resistivity of the metals allow induced eddy currents to flow which counteract the benefits of the higher flux densities. The induced eddy currents 300 caused by the magnetic flux flowing in a metal core are illustrated in
The fabrication of one embodiment of this invention enabling use of ferromagnetic metal for the core material is illustrated in
A plurality of core laminations are formed by first laminating the sheets of ferromagnetic metal to a PCB or FLEX 290 and then etching away portions of the ferromagnetic sheet to form a pattern of a plurality of closely spaced, narrow continuous core segments. Thus,
An enlarged view of a single core array 315 is illustrated in
The next fabrication step is to stack a plurality of the PCB and FLEX layers 310 with the arrays 315 substantially in alignment. As shown in
As part of the stacking process, a thin layer of dielectric material 340 is placed adjacent to the top surface of each etched concentric ring array 315. Typically, an epoxy material is used. This dielectric sheet and the dielectric sheet supporting the etched ferromagnetic rings may be of different materials. Representative materials include epoxies and acrylics manufactured by Dupont and Rogers Corp. for manufacturing of PCB boards and FLEX. Epoxies and prepregs (and epoxies with glass) are generally used to construct PCB boards and acrylics are generally used to manufacture FLEX. During the laminating process, the voids 325, voids 330 and voids 335 shown in
As described above, the electrical windings of the preferred embodiments of this invention are advantageously provided by conductive through hole vias in contact with printed circuitry on both sides of the core structures. The fabrication steps for windings of the embodiments of
The completed structure is illustrated in
The embodiment shown in
Individual transformers and inductor devices are extracted from the laminated array of
The Advantages of the Preferred Embodiments
One Piece Core:
In E core construction, as shown in
If an intentional gap is desired in the embodiments of
Reduction of Eddy Currents:
Inductors and transformers constructed in the manner of
Windings formed in accordance with the preferred embodiments can be formed into surface mount leads without the need for separate lead-frame constructions, complicated pinning or end plating.
Because the etched transformers/inductors are manufactured employing identical processes used to manufacture PCB's or FPC's, the transformers can advantageously be an integral part of the power supply or circuit assembly thereby reducing the physical size, reducing the connections, and, in general, making the assembly more compact and smaller. Circuit components can be placed directly above or below the etched transformer, using the transformer area as the carrier for the balance of the circuitry so that the area of the entire circuit would be as small as the area of the transformer.
Cores constructed in accordance with the preferred embodiments offer a more efficient flux path with fewer losses than traditional transformers. These characteristics more closely resemble a toroid in design and function. The magnetic flux path is shorter than comparable transformers using traditional cores such as E-Cores and PQ Cores.
The preferred embodiments can be made smaller because they do not require complicated pins or lead-frames. Surface pads on the top and bottom surfaces form the connection themselves and they can be surface mounted directly to PCB's thus reducing the footprint of the device and making more room for other components. Windings are in 2 planes therefore the windings of a ten- (10) layer planar transformer device, a typical application, can be reduced in overall height by a factor of five (5). The “core” is in one plane instead of a three-dimensional E core construction further reducing the overall height by a large factor.
The preferred embodiments can be made from flex circuits and much less expensive to manufacture than multi-layer planar windings. Also eliminating and the need for lead-frame's, potting, and cap gluing thus making the device easier to manufacture.
A significant feature of inductors and transformers constructed in accordance with the preferred embodiments of the invention is that the heat generating windings of are not buried within an assembly or wound on top of each other as in traditional transformers nor are they stacked together as in planar transformers. Instead, the plated windings substantially reside on the top and bottom planes of the transformer or inductor device. This layout offers superior heat dissipation with no trapped heat buried within windings. The PCB can be advantageously attached to a heat sink, separated only by a thin solder mask typically only 0.005 inches thick, placing half of the windings in thermal contact with the heat sink, thereby offering a superior surface area to heat ratio.
While the invention has been described herein with reference to certain preferred embodiments, these embodiments have been presented by way of example only, and not to limit the scope of the invention. Accordingly, the scope of the invention should be defined only in accordance with the claims that follow.