Abstract:
A semiconductor package for a semiconductor chip, e.g., a memory chip, is disclosed. The semiconductor package includes a substrate having a generally rectangular perimeter with four sidewalls and a chamfer between adjacent first and second ones of the sidewalls. The memory chip is electrically coupled contacts provided on an opposite surface of the substrate. The contacts are in a row along only the one sidewall of the substrate. A body of a plastic encapsulant covers the first surface of the substrate, the memory chip, and at least two of the sidewalls of the package. The entire perimeter of the substrate, including all four sidewalls and the chamfer, are covered by the plastic encapsulant. Alternatively, only two or three of the sidewalls are covered by the plastic encapsulant, with the other sidewall(s) being exposed and vertically coplanar with a respective sidewall of the plastic encapsulant.

Description:
RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 09/656,253, entitled “Semiconductor Memory Cards And Method Of Making Same” filed Sep. 6, 2000. 
    
    
     BACKGROUND 
     A. Technical Field: 
     This invention relates to packaging memory cards, such as flash or ROM memory cards. 
     B. Related Art 
     A recent global spate of portable electronic devices such as computers, electronic toys, PDAs, cameras, smart phones, digital recorders, pagers, and such has spawned a concomitant need for compact, removable data storage components. One response to this demand has been development of so-called “memory cards.” Typically, a memory card contains at least one or more semiconductor memory chips within a standardized enclosure that has connectors thereon for electrical connection to external circuitry. Examples of these include so-called “PC Cards” and “MultiMediaCards” made in accordance with standards promulgated by such trade associations as Personal Computer Memory Card International Association (“PCMCIA”) and MultiMediaCard Association (“MMCA”), respectively. 
     An exemplary embodiment of such a memory card, namely, a MultimediaCard  10 , is illustrated in top plan, cross-sectional side elevation, and bottom plan views of  FIGS. 1-3 , respectively. Card  10  illustrated has standardized dimensions of 32 mm long×24 mm wide×1.4 mm thick, and typically includes a memory capacity of 2 to 32 megabits (“MB”) of memory, which is accessed through seven contacts  22  located on a bottom surface of card  10  using, e.g., a standard serial port interface (“SPI”) interface. A simple chamfer  30  on one corner of card  10  prevents incorrect insertion of card  10  into a connector in a host device. 
     Memory card  10  comprises a rectangular substrate  12 , such as a printed circuit board (“PCB”), and one or more semiconductor memory dies or “chips” 14 mounted on and electrically connected thereto using, e.g., a layer  16  of adhesive and conventional wire bonds  18 , respectively. Surface mounting passive components  20 , e.g., resistors, may also be mounted on and connected to substrate  12 . Contacts  22  are connected through substrate  12  to memory circuits defined by foregoing components and serve as input-output terminals of card  10 . 
     When components  14 ,  20  have been mounted on and connected to substrate  12 , chip  14  is protectively encapsulated by a “glob-topping” process. A glob  24  of a viscous encapsulant is dispensed onto a top surface of chip  14 , allowed to flow over its sides to said surface of substrate  12 , and cured to form a protective envelope over chip  14 . An external cover or housing  26  (shown by dotted outline in  FIG. 1 ) of thin sheet metal or plastic is installed over substrate  12  assembly by embedding said top surface of assembly in a bed  28  of an adhesive contained in housing  26 . 
     While said foregoing method provides a useable memory product, it is always desirable in a rapidly evolving market such as this to develop new fabrication methods that simplify a product, reduce its costs, and enhance its functionality. 
     SUMMARY 
     This invention provides methods for making a memory card, e.g., a MultiMediaCard, that eliminate a need for an external housing and a separate encapsulation step, and that enables more memory to be packaged in a same size of card. 
     In one of said methods, a substrate having opposite first and second surfaces is provided. A memory die, or chip, is mounted on and electrically connected to said first surface of said substrate, e.g., by wire bonding. Said second surface of said substrate is attached to a first surface of a flat carrier sheet, e.g., an adhesive tape. In one embodiment, a mold is placed on said first surface of said carrier sheet such that said chip and said first surface of said substrate are enclosed in a cavity defined by said mold and said carrier sheet. Said chip and said first surface of said substrate are encapsulated in a monolithic body of hardened plastic, e.g., by injecting a fluid plastic, such as a filled liquid epoxy resin, into said cavity and curing said resin to harden same. Completed cards are then detached from said carrier sheet for use. 
     Said methods eliminate a need for an external housing on said card and a separate chip encapsulation step. These enable a reduction in card height, or incorporation of more memory chips in a card with a standardized height using die-stacking techniques. Said methods are well adapted to volume production techniques. 
     A better understanding of above and other features and advantages of this invention may be had from a consideration of a detailed description below of some exemplary embodiments thereof, particularly if such consideration is made in conjunction with appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is top plan view of a prior art memory card, with separate external housing shown in dotted outline to reveal card details; 
         FIG. 2  is a cross-sectional side elevation view into said conventional card shown in  FIG. 1 , as revealed by a cross-section taken therein along lines II-II; 
         FIG. 3  is a bottom plan view of said prior art card shown in  FIGS. 1 and 2 ; 
         FIG. 4  is a top plan view of an exemplary embodiment of a memory card made in accordance with a method of this invention; 
         FIG. 5  is a cross-sectional side elevation view into said card shown in  FIG. 4 , as revealed by a cross-section taken therein along lines V-V; 
         FIG. 6  is a bottom plan view of said card shown in  FIGS. 4 and 5 ; 
         FIG. 7  is a top plan view of a plurality of memory card subassemblies connected together in a strip form during fabrication and before being encapsulated in accordance with a method of this invention; 
         FIG. 8  is a top plan view of said plurality of memory card subassemblies shown in  FIG. 7  attached to an elongated carrier sheet after being separated and during encapsulation in accordance with a method of this invention; 
         FIG. 9  is a top plan view of said plurality of memory cards subassemblies shown in  FIG. 8  after being encapsulated; 
         FIG. 10  is a top plan view of a plurality of memory card subassemblies connected together in a strip form during fabrication and before being encapsulated in accordance with another method of this invention; 
         FIG. 11  is a top plan view of said plurality of memory card subassemblies shown in  FIG. 10  attached to an elongated carrier sheet after being separated and during encapsulation in accordance with a method of this invention; 
         FIG. 12  is a top plan view of said plurality of memory cards subassemblies shown in  FIG. 11  after being encapsulated and singulated; 
         FIG. 13  is a cross-sectional side elevation view into a memory card having two stacked chips in accordance with one embodiment of this invention; 
         FIG. 14  is an enlarged partial cross-sectional elevation view into said memory card shown in  FIG. 4 , as revealed by a cross-section taken therein along lines XIV-XIV; and, 
         FIG. 15  is an enlarged partial cross-sectional elevation view into one of said memory cards shown in  FIG. 12 , as revealed by a cross-section taken therein along lines XV-XV. 
     
    
    
     DETAILED DESCRIPTION 
     A memory card  110  made in accordance with one exemplary embodiment of methods of this invention is illustrated in top plan, cross-sectional side elevation, and bottom plan views of  FIGS. 4-6 , respectively. In  FIG. 1 , a “mold cap,” or hardened plastic body  132  encapsulating electronic components  114  and  120  and top surface of substrate  112  is shown in dotted outline to reveal underlying detail. Cross-sectional elevation view into card  110  of  FIG. 5  is produced by taking a section in  FIG. 4  along lines V-V. Top plan views of two alternative embodiments of memory card  110  at various stages in its production are shown in  FIGS. 7-9 , and  10 - 12 , respectively. 
     As may be seen by reference to  FIGS. 4-6 , memory card  110  is identical in size and contains elements similar to those of prior art memory card  10  illustrated in  FIGS. 1-3 . Similar elements in card  110  are referenced by similar reference numbers, plus 100. Novel card  110  comprises a rectangular substrate  112 , e.g., a PCB, having respective first and second surfaces  111  and  113  and a semiconductor memory chip  114  mounted on and electrically connected on first surface  111 . Chip  114  is mounted on first surface  111  of substrate  112  with a layer  116  of adhesive and electrically connected to said first surface with conventional wire bonds  118 . Particular contents of memory card  110  and configuration of external contacts  122  may vary depending on particular application. For example, a plurality of memory chips and passive components may be used, or passive components may be omitted, or memory management chips may be included, among other possibilities. Again, certain industry standards apply in certain cases. 
     In another possible embodiment (not illustrated) chip  114  may be mounted on and electrically connected to first surface  111  of substrate  112  using well known “flip chip,” or “C4” method of die-to-substrate attachment. In such mounting, it may be desirable to underfill a narrow space between chip  114  and first surface  111  of substrate  112  with a solid insulative material, e.g., a hardened epoxy resin, in a known manner. Surface mounting passive components  120 , e.g., resistors, may also be mounted on and electrically connected to first surface  111  of substrate  112 . As in prior art memory card  10 , input-output contacts  122  are located at an edge of bottom surface  113  of card  110 , and a chamfer  130  is provided on one corner thereof for one-way-only insertion of card into a host device connector. 
     However, comparing novel card  110  shown in  FIGS. 4-6  with prior art card  10  shown in  FIGS. 1-3  also reveals some important differences. For example, thin metal or plastic external housing  26 , bed  28  of adhesive, and glob-top encapsulation  24  over chip  14  of prior art card  10  are replaced in novel card  110  by a single hardened plastic body  132  which more effectively encapsulates electronic components  114  and  120 , and respective first surface  111  and side walls  158  of substrate  112 . Moreover, replacement of such former elements and manufacturing processes related thereto by said single latter element and encapsulation process frees up additional space H (see  FIG. 5 ) in card  110  above chip  114 , namely, about 0.3 mm. This space can be used e.g., to mount additional components. For example, as shown in  FIG. 13 , a second memory chip  114  can be mounted on top of first-mounted memory chip  114  above and electrically connected to first surface  111  of substrate  112  using die-stacking techniques disclosed in, e.g., U.S. application Ser. No. 09/536,574, filed Mar. 28, 2000, and assigned to an assignee hereof. This increases memory capacity of card  110  while retaining said same, standard form factor. 
     Said methods for making memory card  110  shown in  FIGS. 4-6 , as described below in connection with  FIGS. 7-9 , and  10 - 12 , respectively, are readily adapted to simultaneous production of a number of cards in an elongated strip form. However, such methods are easily extended to manufacture of a single memory card  110 , or alternatively, to simultaneous production of a rectangular array thereof (not illustrated), e.g., a 4×4 array of memory cards  110 . 
     Thus, one method includes providing a continuous substrate strip  134  having opposite first and second surfaces  136 ,  138  and a plurality of individual chip-mounting sites  140  on said first surface thereof (see  FIG. 7 ). A memory chip  114  and additional passive components  120 , if any, are mounted on and electrically connected to first surface  136  of strip substrate  134  in corresponding ones of mounting sites  140 , as described above. Alternatively, a plurality of memory chips and passive devices, or one or more memory devices and no passive devices, may be mounted on first surface  136  of strip substrate  134 . Numbers and types of memory chips and passive components are application specific, and not limiting of this invention. 
     As illustrated in  FIG. 7 , after electronic components  114  and  120  are mounted on and electrically connected to corresponding ones of mounting sites  140  on first surface  136  of strip substrate  134 , substrate  134  is cut along dotted lines  142  to divide assembled strip  134  into a plurality of individual substrate assemblies  144 , each having a corresponding individual substrate  112 . Respective second surfaces  138  of each individual substrate assembly  144  are temporarily attached to a first surface  146  of a flat carrier sheet  148  (see  FIG. 8 ) such that individual assemblies  144  are attached to carrier sheet  148  in a spaced-apart relationship, as shown in  FIG. 8 . Carrier sheet  148  may be a plastic film with an adhesive thereon, or a polyimide film with an adhesive thereon. 
     Substrate assemblies  144  can be temporarily attached to carrier sheet  148  with a “tacky,” i.e., partially cured, adhesive. It is desirable that said adhesive form a seal between opposing second surfaces  138  of individual substrate assemblies  144  and first surface  146  of carrier sheet  148  to prevent encapsulant from entering between said opposing surfaces during an encapsulation procedure. Said adhesive may be of a known type that is initially tacky but which loses adhesion when exposed to ultraviolet (“U.V.”) light. In such an embodiment, subsequent detachment of parts from carrier sheet  148  comprises exposing said adhesive to ultraviolet light and lifting said parts away from sheet  148 . 
     When substrate assemblies  144  are attached to carrier sheet  148 , each of chips  114 , corresponding wire bonds  118 , and corresponding chip-mounting sites  140  are encapsulated in a monolithic body  132  of hardened plastic (see  FIGS. 4-6 ). This can be effected in a number of different ways. As shown in  FIG. 8 , a mold  150  (shown by dashed outline) having a plurality of cavities  152  therein is placed on first surface  146  of carrier sheet  148  such that each individual substrate assembly  144  is enclosed in a separate corresponding cavity  152  between mold  150  and carrier sheet  148 . Carrier sheet  148  may be provided with a plurality of tooling holes  154  for appropriate relative alignment of substrate assemblies  144  with mold cavities  152 . Cavities  152  are each filled with a fluid plastic, e.g., an epoxy resin, and said resin is cured to harden same. When encapsulation is complete, mold  150  is removed from carrier sheet  148  to leave a plurality of completed memory cards  110  attached thereto, as shown in  FIG. 9 . Completed memory cards  110  are then detached from carrier sheet  148  for, e.g., post-encapsulation testing and packaging. 
     It may be noted in  FIGS. 4-6  that side walls  156  of plastic body  132  are spaced outside of corresponding side walls  158  of respective individual substrates  112  (see enlarged section of  FIG. 14 ), which results from interior side walls  160  of mold cavities  152  being positioned outside of side walls  158  of respective individual substrates  112  during encapsulation (see  FIG. 8 ). However, in other possible embodiments, one or more of corresponding respective side walls  156  and  158  of plastic body  132  and respective individual substrates  112  may be coplanar, as shown in  FIG. 15  and described in more detail below. 
     In an alternative embodiment illustrated in  FIGS. 10-12 , a memory chip  114  and additional passive components  120 , if any, are mounted on and electrically connected to first surface  136  of strip substrate  134  in corresponding ones of chip-mounting sites  140 , as described above, to form a single strip assembly  162  ( FIG. 10 ). However, strip substrate  134  is not divided into individual assemblies, as above. Instead, second surface  138  of undivided strip assembly  162  is then attached to first surface  146  of carrier sheet  148 , and memory chips  114 , passive components  120 , and at least first surface  136  of strip assembly  162  are encapsulated in a single monolithic body  132  of hardened plastic, as follows. 
     As shown in  FIG. 11 , a mold  164  having a single cavity therein is placed on first surface  146  of carrier sheet  148  such that at least first surface  136  of substrate strip assembly  162 , including chips  114  and passive components  120 , are enclosed in cavity  166  between mold  164  and carrier sheet  148 . Cavity  166  is then filled with a fluid plastic, and said plastic is hardened into a single-piece plastic body  132  (see  FIG. 11 ). 
     When plastic body  132  is hardened, mold  164  is removed from carrier sheet  148 , and plastic body  132  and underlying strip substrate  134  are cut through with, e.g., a saw  168  along cutting lines  142 , i.e., perpendicular to a long side of strip substrate assembly  162 , to define a plurality of individual memory cards  110  attached to carrier sheet  148  and separated from each other by a width W of said cut (see  FIG. 12 ). 
     In yet another possible embodiment (not illustrated), strip substrate assembly  162  can be encapsulated in a single-piece body of encapsulant and then cut into individual memory cards  110  using apparatus and methods described in U.S. Pat. No. 5,981,314 to T. P. Glenn, et al., which is incorporated herein in its entirety by this reference. 
     It may be noted that in embodiments requiring cutting, plastic body  132  and/or strip substrate  134  can be precisely sawed through downwards from a top surface of plastic body  132  to, but not through, carrier sheet  148 , with currently available semiconductor wafer sawing equipment, and that such cutting procedure simultaneously forms coplanar side walls  156  and  158  on both severed plastic body  132  and severed substrate  112  of each memory card  110  where such sawing has taken place, as shown enlarged in  FIG. 15 . It may be further noted that, if a one-way keying chamfer  130  is not molded into each memory card  110  during encapsulation, as illustrated in  FIG. 9 , chamfer  130  can be precisely sawed into an appropriate corner of each card  110  after cards  110  are separated from carrier sheet  148 . 
     As will be apparent by now to those of skill in this art, many modifications, variations, and substitutions are possible in this invention&#39;s methods and materials without departing from its spirit and scope. Accordingly, this invention&#39;s scope should not be limited by any particular embodiments illustrated and described herein, as these are merely exemplary in nature. Rather, this invention&#39;s should commensurate with that of claims appended hereafter and their substantial equivalents.