Abstract:
A plurality of semiconductor die is packaged into one component. The inventive design comprises devices which have been singularized, packaged and thoroughly tested for functionality and adherence to required specifications. A plurality of packaged devices is then received by a housing. The conductive leads of the packaged devices are electrically coupled with pads manufactured into the housing. These pads are connected to traces within the housing, which terminate externally to the housing. Input/output leads are then electrically coupled with the traces, or are coupled with the traces as the housing is manufactured. The input/output leads provide means for connecting the housing with the electronic device or system into which it is installed. A lid received by the housing hermetically seals the packaged die in the housing, and prevents moisture or other contaminants which may impede the proper functionality of the die from entering the housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of application Ser. No. 08/650,894, filed May 17, 1996 now U.S. Pat. No. 6,555,399, which is a continuation of application Ser. No. 08/402,753, filed Mar. 10, 1995, abandoned, which is a continuation of application Ser. No. 08/152,072, filed Nov. 15, 1993, abandoned, which is a continuation of application Ser. No. 07/916,811 filed Jul. 20, 1992, abandoned, which is a division of application Ser. No. 07/675,208 filed Mar. 26, 1991, now U.S. Pat. No. 5,155,067, issued Oct. 13, 1992. 

   BACKGROUND OF THE INVENTION 
   Field of the Invention 
   This invention relates to the field of semiconductors and, more specifically to a method for manufacturing a type of multi-chip module. 
   Many types of semiconductor devices are made using similar manufacturing procedures. A starting substrate, usually a thin wafer of silicon, is doped, masked, and etched through several process steps, the steps depending on the type of devices being manufactured. This process yields a number of die on each wafer produced. Each die on the wafer is given a brief test for functionality, and the nonfunctional die are mechanically marked or mapped in software. This brief test is only a gross measure of functionality, and does not ensure that a die is completely functional or has specifications that would warrant its assembly in a package. 
   If the wafer has a yield of grossly functional die which indicates that a good quantity of die from the wafer are likely to be fully operative, the die are separated with a die saw, and the nonfunctional die are scrapped while the rest are individually encapsulated in plastic packages or mounted in ceramic packages with one die in each package. After the die are packaged they are rigorously tested. Components which are shown to be nonfunctional or which operate at questionable specifications are scrapped or devoted to special uses. 
   Packaging unusable die only to scrap them after testing is costly. Given the relatively low profit margins of commodity semiconductor components such as dynamic random access memories (DRAMs) and static random access memories (SRAMs), this practice would seem especially wasteful. However, no thorough and cost effective method of testing an unpackaged die is available which would prevent this unnecessary packaging of nonfunctional and marginally functional die. 
   The practice of packaging die only to find the component must be scrapped can especially affect yields on multi-chip modules (MCMs). With MCMs, several unpackaged die are assembled into a single component, then the component is tested as a single functional unit. If a single die is nonfunctional or operates outside of acceptable specifications, the entire component fails and all die in the package are scrapped or an attempt is made to “re-work” the MCM. There is presently no cost-effective way to reclaim the functioning die. Statistically, the yields of MCMs decrease in proportion to the increasing number of die in each module. The highest density modules have the lowest yields due to their increased total silicon surface area. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention, in an embodiment, provides an MCM which has a higher probability of receiving only good die as compared with present MCMs of equal density. This produces a higher yield. 
   The present invention, in an embodiment, also provides an MCM which is less expensive to produce than present MCMs due to its higher yield. 
   The present invention, in an embodiment, further provides a high density MCM. 
   The present invention, in an embodiment, still further provides a module having very short trace lengths to enable data transfer very quickly between the multiple die contained in the MCM and the system into which the MCM is installed. 
   The present invention, in an embodiment, yet further provides a rugged, hermetically sealed MCM which typifies devices produced to satisfy high reliability and military usage requirements. 
   The present invention, in one exemplary embodiment, comprises packaging each die individually, for example in a thin small outline package (TSOP), testing the components including use of burn-in to eliminate “infant mortality” failing, then assembling a number of functional packaged components together in a single multi-chip module. A resulting multi-chip module is also encompassed by the present invention. 
   The present invention, in a further exemplary embodiment, comprises packaging multiple memory die in the form of an MCM. 
   The present invention, in yet another exemplary embodiment, comprises packaging different types of components in the same housing, for instance a microprocessor (MPU) together with a primary or secondary cache memory. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The preferred embodiments of the invention are illustrated in the accompanying drawings, in which: 
       FIG. 1  is a top view of an embodiment employing four Type I TSOP packages; 
       FIG. 2  is a side cutaway view of the  FIG. 1  embodiment; 
       FIG. 3  is a top view of an embodiment employing two Type II TSOP packages; 
       FIG. 4  is a side cutaway view of the  FIG. 3  embodiment; 
       FIG. 5  is a top view of an embodiment employing four Type II TSOP packages in a stacked arrangement; 
       FIG. 6  is a side cutaway view of the  FIG. 5  embodiment; and 
       FIG. 7  is a side cutaway view of an embodiment employing packages stacked four high. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1  (top view) and  2  (side view) show an embodiment of the invention incorporating four individually packaged die (not shown), with each TSOP package  10  having gull-wing style leads  12 . The MCM housing  14  is shown with SOJ style I/O leads  16 . The invention comprises a number of die which could have been packaged according to normal production procedures for sale as regular commodity devices, or could be manufactured especially for use in an MCM. The packages shown  10  are Type I TSOP packages, but Type II TSOP, SIP, DIP, ZIP, or various other package types could be used with the invention. TSOPs, however, have the advantage of being very small and thin, in fact not much larger than unpackaged die, and therefore provide for a very small assembled MCM, which is one reason for the development of MCMs. 
   The housing  14  can be manufactured from ceramic, plastic, composite (graphite/ceramic, etc.), or other workable material. The housing  14  has conductive pads  18  for electrical attachment of the leads  12  of the packages  10 . The pads  18  are coupled with traces (not shown) manufactured into the housing  14  which provide an electrical pathway from the leads  12  on the packages  10  to the outside of the housing  14 . The actual pinouts of the traces manufactured into the housing  14  depend on the design and intended use of the module. Traces of this type have been used with ceramic semiconductor packages. The conductive traces (not shown) within the housing  14  are attached to the conductive leads  16  of the housing  14  by means such as side brazing. Alternately, surface mount type leads  16 , such as the small outline “J” (SOJ) leads shown, can be attached to the traces and manufactured into the housing  14 , thereby being firmly attached to the housing  14 . The manufacture of SOJ lead types, as well as other lead types, are well known in the art. 
   To assemble the MCM, the packages  10  are inserted into the housing  14 , and the leads  12  of the packages  10  are electrically coupled to the pads  18  of the housing  14  by coupling means  22  such as solder, conductive epoxy, conductive polymer, wire bonding, tape automated bonding, or other workable means. 
   After the leads  12  of the packages  10  are coupled with the pads  18  of the housing  14 , a lid  20  is attached to the housing  14  to seal the packages  10  in the housing  14 . The lid  20  can be plastic, ceramic, metallic, or composite, depending on the type of material from which the housing  14  is made. With some materials, such as ceramic and glass, the lid  20  will provide a hermetic seal. A hermetic seal will resist the entrance of moisture or other substances, which might cause the package  10  to malfunction, into the housing  14 . The lid  20  can be attached directly to the flat surface of the housing  14 , or a recess  24  can be manufactured into the top surface of the housing  14  to receive the lid  20 . The attachment means  26  varies with the type of material used to make the lid  20 . With a plastic or composite lid and housing, either an epoxy or a polyamide material, both of which are known in the art, can be used with equal success to enjoin the lid  20  to the housing  14 . In ceramic embodiments, some sealing means are more costly but more reliable, and could be used in high-stress situations. Other lower cost adhesives will work for normal usages. Glass is one high reliability attachment means which can be used to attach a ceramic or metal lid to a ceramic housing. Another high reliability adhesive is solder. Polyamide and epoxy are two medium reliability attachment means. 
     FIGS. 3 and 4  show an embodiment of the invention incorporating die (not shown) packaged in Type II TSOP packages  30 . Many of the elements of this embodiment are similar to the elements of the previously described embodiment. 
   In the present embodiment, through-hole DIP leads  34  are brazed to the side  36  of the housing  32  thereby coupling with traces (not shown) manufactured into the housing  32 . This embodiment incorporates packages  30  with leads  38  specially formed for use with the invention. The leads  38  extend directly out from the body of the package  30  and rest on a shelf  40  manufactured as an element of the housing  32 . Upon the shelf  40  are conductive pads  18  which connect with traces (not shown) manufactured into the housing  32  which run to the outside of the housing  32 . 
     FIGS. 5 and 6  show an MCM having two semiconductor packages  50 ,  52 , one  50  stacked on top of the other  52 , which provides a higher density module. The MCM can have several stacks of devices, depending on the MCM density specification. In the present embodiment, the housing  54  is manufactured with two shelves  56 ,  58  of different levels, with each level having pads  18  for coupling the leads  38 ,  38 ′ of the packages  50 ,  52 . Traces (not shown) manufactured into the housing  54  couple with the pads  18 , and terminate externally to the housing  54 . Packages  52  are placed in the housing  54  and the leads  38 ′ are electrically coupled with pads (not shown) on the lower shelf  58 . The upper level of semiconductor packages  50  are placed in the housing  54  and the leads  38  are electrically coupled with pads  18  on the upper shelf  56 . The embodiment of  FIGS. 5 and 6  may require that leads  38 ,  38 ′ on the packages  50 ,  52  be formed especially for use with the inventive module. The package leads  38  for use on the upper shelf  56  have a greater distance to span than the package leads  38 ′ for use on the lower shelf  58 . Rather than forming different lengths of leads, it is possible to use a package with one type of lead on the lower shelf such as a straight lead, and a package with a different type of lead on the upper shelf such as a gull wing or J lead. 
     FIG. 7  describes an MCM having a plurality of stacked semiconductor packages  60 ,  62 ,  64 ,  66 . In this stacked embodiment, TSOP packages are used which have been produced especially for use in the inventive module. In the embodiment of  FIG. 7 , four TSOP devices are stacked or “piggybacked” one on top of another. The leads  68  are electrically coupled with the same output leads of the device below it, with the leads  68  of the bottom device  66  being coupled with pads (not shown) on the housing  70 . 
   To access the data from an MCM having multiple DRAM devices, the DRAMs housed in the MCM must be fabricated with more than one CAS pin. The number of CAS pins on each DRAM must equal (or exceed) the number of packages in the housing. Each device will have only one CAS pin active, the others being “no connects.” In an embodiment with four DRAM packages, each package will have one active CAS and three CAS no connects, the CAS pins on each device being numbered CAS 0 , CAS 1 , CAS 2 , and CAS 3 . In the bottom device, CAS 0  will be connected to CAS on the die within, and CAS 1 -CAS 3  will be no connects. On the second device, CAS 1  is connected to CAS on the die within, and CAS 0 , CAS 2 , and CAS 3  are no connects. The third device has only CAS 2  active, and the top device has only CAS 3  active. If stacked packages as described are used, it is invalid for than one package to have RAS and CAS both active simultaneously. The MCM of this embodiment would contain four different designs of DRAM devices, and the housing would also require four CAS pins designated CAS 0 -CAS 3 . This design allows piggybacked devices and therefore a very small, highly dense module. 
   If SRAMs are used in the housing  70 , each SRAM package is fabricated with a number of chip enable (CE) pins, the number of pins corresponding to the number of bits required for chip select. In an embodiment with four SRAM packages two bits are necessary to select only one of the four devices in the stack. This requires two bits, so each SRAM package will have two CE pins, CE 0  and CE 1 . A laser blown fuse, a current blown fuse, or another type of workable fuse on each CE pin selects the binary code which will activate a particular SRAM device. On the bottom package, for example, both fuses will be blown causing the bottom chip to respond to a 0 on both CE 0  and CE 1  (0, 0). On the second package, only CE 1  will be blown, causing the second SRAM package to respond to a 0, 1. The third package will respond to 1, 0 while the top device corresponds to 1, 1. The MCM of this embodiment, therefore, would contain four different types of devices and the housing would require two CE pins designated CE 0  and CE 1 . This design allows four piggybacked SRAM TSOP devices and therefore a very small, highly dense module. 
   In a piggybacked embodiment, only the leads  68  of the bottom device  66  are physically coupled to the housing, its leads being connected by solder reflow, conductive epoxy, or other workable means. To provide added support to the devices  60 ,  62 ,  64 ,  66  to prevent excess stress on the leads  68 , the packages themselves can be connected with a material  72  such as nonconductive epoxy, organic resin, polyamide, nonconductive polymer, or with other workable means. The embodiment again shows the use of DIP style leads  34  on the housing  70 , but other lead designs as previously described are also workable and may be preferable for some applications. 
   Using the method described a module can be produced which has short trace lengths and transfers data quickly between the multiple die contained in the MCM and the system into which the MCM is installed. The inventive module has the advantage of using only fully tested and burned in die. Present designs of MCMs comprise several untested or poorly tested die packaged together. The package is fully tested only after the module is assembled. With present designs, if a single die is not functional the entire assembly is scrapped, including any functional die packaged in the module, or attempts are made to rework the MCM by replacing all malfunctioning die. The inventive design allows for the assembly of only functional die and yields are increased. 
   The individual die packages can be regular production die packaged in a TSOP package, or may be die packaged as TSOP packages but with leads formed especially for use in the MCM. As noted above, die in other types of packages can also be used, such as small outline “J” leaded (SOJ) packages, dual inline packages (DIP), or zigzag inline packages (ZIP), but with TSOPs a very small final module can be produced, much smaller than if SOJ, DIP or ZIP style components are used. A highly dense module is one of the advantages of MCMs. 
   As previously described, the housing into which the packaged die are assembled can be manufactured from ceramic, plastic, composite, or any other workable material. The interior of the housing contains pads for attaching the leads of the individual die packages. The pads on the interior of the housing are coupled with conductive traces which run through the material of the MCM housing to the exterior of the housing. The conductive traces may be attached to conductive leads on the exterior of the housing by means such as side brazing. Alternately, surface mount type leads or small outline “J” (SOJ) leads can be attached to the traces and manufactured into the housing. The manufacture of these lead types, as well as others, are well known in the IC packaging art. The conductive leads on the exterior of the MCM provide a means of providing power, control, and data input/output (I/O) between the multiple die on the interior of the housing and the system into which the assembled MCM is installed. 
   The multiple die on the interior of the housing can be arranged in a number of different positions, as described above. 
   In addition to supplying memory, the invention provides a convenient method to package different types of components in the same housing, for example a microprocessor (MPU) together with a primary or secondary cache memory. MPUs and cache memory are increasingly used together in computers, and a module which supplies both would be an effective and desirable computer component. 
   What has been described are specific configurations of the invention, as applied to particular embodiments. Clearly, variations can be made to the original designs described in this document for adapting the invention to other embodiments. For example, the housing can be manufactured with different lead types, or semiconductor packages with different lead types can be packaged in the housing. The MCM can also be manufactured with ×1, ×4, ×16, or ×32 data widths, or with other data widths not specifically mentioned. The number of devices in a particular described embodiment is not the important element. For example, in the embodiment of  FIGS. 5 and 6 , a plurality of devices other than four can be stacked, and fewer or more than four stacks can be designed. Therefore, the invention should be read as limited only by the appended claims.