US 20060157838 A1
A semiconductor card is made using a method which, in one molding step, forms a plastic body on a substrate attached to a surrounding frame by narrow connecting segments spanning a peripheral opening. The connecting segments are motivated downward by pins outside of the card periphery, holding the substrate against a lower level of the mold cavity during molding. Molded wings extending laterally from the card periphery are also formed. Following molding and curing, the casting is removed and the card singulated by excising the wings from the card. The resulting card has smooth edge surfaces and precise dimensions. Separate glob top encapsulation is avoided.
1. A packaging method comprising:
supplying a substrate in strip form comprising an internal substrate and an external frame connected thereto by at least one connecting segment formed by a peripheral opening, the internal substrate having at least one semiconductor component located on the circuit side thereof connected to external contacts of the internal substrate;
locating at least a portion of the strip in a molding assembly having a molding cavity having internal surfaces in first and second mold plates for moving the internal substrate to a level differing from the level of the external frame;
molding a plastic body on the circuit side of the internal substrate, the body including edge portions formed outwardly from the internal substrate for forming the card, and a plurality of wings extending outwardly from the edge portions; and
removing the molded casting from the molding assembly for separating the internal substrate from the wings.
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10. A semiconductor card comprising:
a printed circuit substrate having a circuit side, a back side and a peripheral substrate edge having front and back edge corners, the printed circuit substrate including a plurality of conductors on the circuit side and a plurality of external contacts on the back side connected to the plurality of conductors;
at least one semiconductor component on the circuit side connected to the plurality of conductors;
a plastic body molded to the circuit side of the substrate extending laterally from the peripheral substrate edge to form a card having a front face and a back face with a smooth card edge connecting the front and back faces for encapsulating the at least one semiconductor component and the plurality of conductors while leaving the plurality of external contacts exposed; and
a plurality of narrow ends of connecting segments of the printed circuit substrate intersecting with a peripheral edge and exposed therein.
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20. A module formed using a semiconductor card having a card outline, the module comprising:
a strip of planar insulating material having a circuit side and a back side;
a peripheral opening defining the outer edge of a substrate and the inner edge of a frame, the opening having an inner edge inside of the card outline and an outside edge outside of the card outline; and
a plurality of connecting segments of the strip connecting the substrate to the frame, the connecting segments configured for forced movement to a level different from the frame, wherein the substrate, frame, opening and segments comprise the module.
This application is a continuation of application Ser. No. 09/878,302, filed Jun. 11, 2001, pending.
1. Field of the Invention
This invention relates generally to semiconductor manufacture. More particularly, the invention pertains to an improved semiconductor card, and to improved methods and systems for fabricating the card.
2. State of the Art
One type of electronic assembly containing semiconductor components is generally referred to as a “card.” Examples of such “cards” include multimedia cards such as used in digital cameras and the like, memory cards, smart cards, and personal computer memory card international association (PCMCIA) cards. The instant patent application refers to these types of cards as “semiconductor cards.” These cards are sometimes referred to as “daughter boards.”
Typically, a semiconductor card comprises a substrate which may be a thin printed circuit board (PCB) upon which electronic components are mounted. Such components may include, for example, at least one semiconductor die and/or die package as well as resistors, capacitors, inductors and the like to form a desired circuitry. The substrate includes conductors for providing power supply and interconnection of the various components. Typically, the components are mounted on one side, i.e., “circuit” side of the substrate, and are electrically interconnected to external contacts on the opposing side by interlevel conductors. The external contacts are arranged for electrical contact with a next level package, i.e., mother board. In use in an exemplary electronic apparatus, such as a digital camera, the card may be inserted into a slot or other receiver for interconnection with a motherboard, and provide for example, flash memory for digitally recording images.
Semiconductor cards are typically intended for repeated handling by the public, necessitating protection of the components from mechanical forces, moisture, radiation and stray electrical currents. In the industry, the semiconductor components and interconnecting conductors on the circuit side of a card substrate have typically been encapsulated by first applying “glob top” encapsulant. Then, a separately formed protective cover produced by injection molding is adhesively attached over the circuit side of the substrate to form the semiconductor card. However, use of a separately formed cover not only adds undesirable thickness to the card, it requires additional process steps, and is subject to deleterious detachment of the cover from the substrate. In addition, any variation in mounted component height and overlying glob top material will result in card thickness variation.
For most applications, it is desirable to make the card as thin as possible. The use of thin cards saves space within the equipment in which the card is used, as well as storage space, and a saving in encapsulation material is also realized.
A further requirement for semiconductor cards is that the peripheral outlines and card dimensions be as uniform as possible, so that proper effective insertion into a card receiver is assured. Specifications on the peripheral outline and dimensions of semiconductor cards have been set by various industry standard setting bodies, e.g., PCMCIA.
In present methods of manufacture, components for several semiconductor cards are fabricated and wire bonded on a strip of e.g., circuit board. The strip may be viewed as equivalent to the lead frame in die manufacture. The individual cards are then separated from the strip using a singulation process such as sawing. Often the singulation step produces slivers, and forms substrate edges which are rough or sharp. These defects can adversely affect the peripheral outline, dimensions, appearance and use of the card.
The need exists for a method to encapsulate a semiconductor card whereby the card has reduced thickness as well as less variation thereof. In addition, the desired method will produce a card with improved precision in peripheral outline, dimensions and appearance, and at lower cost.
In accordance with the present invention, an improved semiconductor card is provided. In addition, a method and a system for fabricating the improved card are disclosed.
The semiconductor card includes a substrate such as a printed circuit board (PCB). The substrate comprises an electrically insulative material such as an organic polymer resin reinforced with glass fibers, and may include more than one layer. The substrate has a circuit side with a pattern of conductors thereon, and an opposing back side with a pattern of external contacts thereon. Electronic components, such as semiconductor dice, resistors, capacitors, and the like, are formed or mounted on the circuit side of the substrate. The semiconductor dice may comprise bare dice wire bonded to the conductors, bumped dice flip chip mounted to the conductors, or semiconductor packages bonded to the conductors. A single molding step serves to encapsulate the circuit side of the substrate and simultaneously form card surfaces and edges with smooth rounded or oblique corners.
A substrate may be initially formed as a segment of a substrate strip containing more than one module having a substrate separated therefrom by a peripheral opening. The strip is similar in function to a semiconductor lead frame, and permits various fabrication processes to be performed on one or more substrates at the same time. The substrate is connected to the strip with connecting segments similar to tie bars on a semiconductor lead frame.
A molding assembly is adapted to form a plastic body larger than the substrate, and simultaneously encapsulates circuit components, such as dice, resistors, capacitors, bond wires, etc., on the substrate as the card body is formed. Plastic wings are also formed by molding, extending outwardly from a central portion of the card edges along major sides of the card periphery.
Prior to introducing molding compound, a plurality of down-set pins are inserted downward through the upper plate, outside of the card periphery, to depress the connecting segments and attached substrate downward into a cavity. The resulting substrate will be lower than the frame portion of the module, and provide the back side of the semiconductor card.
Following molding, the casting is removed and desingulated by cutting off the wings.
The method is much simpler and quicker than the prior method in which the circuit side of a card is glob topped and then covered by a separately molded cap which is cemented thereto.
The invention is described and illustrated herein below in terms of a semiconductor card 10 which is exemplified by a “multimedia card.”
As shown in
The front face 20 and back face 22 of the semiconductor card 10 are joined by a peripheral edge 36 having rounded corners 38. In accordance with the invention, the longitudinal edge 40 about the front face 20, and the longitudinal edge 42 about the back face 22 are shown as rounded to a radius 21 of e.g., about 0.20 mm for ease of use. See
As depicted in
As shown in
The substrate 12 includes a circuit side 62 (
The external contacts 18 are configured for mating electrical engagement with corresponding contacts (not shown) on a mother board circuit or other electrical assembly (not shown). As illustrated, the external contacts 18 may be planar pads formed of a non-oxidizing conductive material such as gold. However, other configurations for the external contacts 18 may be used, including bumps, pins, or pillars, for example, where the particular application permits.
In other processes for making semiconductor cards 10, semiconductor element 16 and electrical component 74 together with other apparatus on the circuit side 62 are encapsulated with a glob-top material which is cured prior to forming the outer card surfaces. No such encapsulation is utilized in the present invention. As described herein, a method of the invention provides for a single encapsulation step by precise molding that simultaneously encapsulates active semiconductor element 16 and electrical component 74 on the circuit side 62 of the substrate 12 and forms smooth outer surfaces of the semiconductor card 10, including rounded or drafted (angular) peripheral edges 36.
Regardless of the particular application to which the card circuit is directed, semiconductor card 10 of the invention includes a plastic body 14 which is molded directly to the circuit side 62 of substrate 12, covering semiconductor element(s) 16, electrical component(s) 74 and exposed conductors, bond pads, etc., which are mounted thereon. As shown in
Furthermore, the molding apparatus 80 is modified to form wings 148 (see
Turning now to
The mold cavity 100 includes a central depressed region 134 defined by arcuate or drafted walls 136. In addition, outward cavity extensions or “wing cavities” 150 are shown on four sides of the central depressed region 134. Each wing cavity 150 has an outer sloped or rounded wall 152 for ease of mold release. Thus, the central depressed region 134 is at a level 154 below the level 158 of lower side 144. A step 146 upward from central depressed region 134 attains an intermediate level 156 forming the base of each wing cavity 150.
As shown in
Another feature of the upper plate 86 comprises a plurality of down-set pin holes 106, each located above a connecting segment 56. See
The down-set holes 106 and down-set pins 102 are positioned entirely within the wing cavities 150, outside of the peripheral edge 36 of the semiconductor card 10. The down-set pin 102 is shown as being generally cylindrical with an outer end 166 and an inner end 164 (see
The substrate 12 is shown with a circuit side 62 on which are mounted exemplary semiconductor elements 16 with connecting bond wires 17. The substrate 12 is held downward to depressed portion 112 (not shown) by the connecting segments 56, generally preventing passage of pressurized fluid polymer 15 (not shown) onto the substrate's opposing back side 64. For reference purposes, the peripheral opening 54 over the majority of the substrate 12 generally has a width 55 extending from the inner end 170 to the opening's outer edge 174 (see also
Following molding and solidification of the casting in the molding apparatus 80, the unsingulated semiconductor card 10 may be ejected from the mold by further insertion of down-set pins 102, or use of other pins, not shown. Ease of ejection is enabled by the use of sloped lateral surfaces and rounded or oblique corners on the molded casting 180.
In the manufacture of the semiconductor card 10 of the invention, the steps involved may be summarized as including:
a. A strip 44 of a dielectric material is provided in sheet form;
b. A peripheral opening 54 is formed in at least one portion of the strip 44 designated as a module 48, in which the peripheral opening 54 defines the boundaries of a substrate 12. Opposing sides of the substrate 12 are connected to a frame 46 of the module 48 by connecting segments 56 of the module 48. Other openings 82 for indexing and handling are also provided.
c. A circuit is formed on the “circuit” side 62 of the substrate 12, including at least one semiconductor element 16, as well as electrical component(s) 74 and interconnecting conductors.
d. External contacts 18 are formed on the opposing back side 64 of the substrate 12 and connected to the circuit.
e. A set of plates 84, 86 are configured for molding a plastic body 14 peripherally about the circuitized substrate 12 and over portions of the circuit side 62 thereof. Down-set pin holes 106 are provided outside of the card's peripheral outline 70 in an upper mold plate 86 for insertion of down-set pins 102 to motivate the connecting segments 56 (and attached substrate 12) downward to a lower level against a lower surface of the internal mold cavity 100 in the lower plate 84.
f. The lower plate 84 and upper plate 86 are assembled with module 48 therebetween. The molding apparatus 80 is connected to a supply of molding compound and clamped shut. Down-set pins 102 are positioned in the down-set pin holes 106 to force the substrate 12 downward to a seated position.
g. Pressurized fluid polymer 15 is introduced into the molding apparatus 80 under conditions which rapidly fill the mold cavity 100, encapsulating the circuit and forming a plastic body 14.
h. After curing and cooling of the pressurized fluid polymer 15, the mold is opened and the molded module 48 removed therefrom. Pins may be inserted in down-set pin holes 106 and used as ejection tools for releasing the module.
i. The semiconductor card 10 is singulated from its module 48 by cutting along the card's peripheral outline 70.
j. If desired, exposed ends 56A of the connecting segments 56 within the semiconductor card 10 may be cut back. If necessary, flash residue may be removed.
In another embodiment of the invention, the molding apparatus 80 may be configured to cover portions of both faces 20, 22 of a substrate 12. The mold cavity 100 of lower plate 84 is varied by providing one or more additional cavities and associated runners for introducing pressurized fluid polymer 15.
As described herein, the invention provides a semiconductor card by a method that eliminates a separate glob top encapsulation step, and ensures smooth card edges which are rounded or oblique. Desired card dimensions are readily maintained, and flash material requiring removal is minimized. If desired, the molding assembly may be configured to form several cards simultaneously.
It is apparent to those skilled in the art that various changes and modifications may be made in the manufacturing methods and apparatus of the invention as disclosed herein without departing from the spirit and scope of the invention as defined in the following claims.