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.

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.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1(top view) and2(side view) show an embodiment of the invention incorporating four individually packaged die (not shown), with each TSOP package10having gull-wing style leads12. The MCM housing14is shown with SOJ style I/O leads16. 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 shown10are 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 housing14can be manufactured from ceramic, plastic, composite (graphite/ceramic, etc.), or other workable material. The housing14has conductive pads18for electrical attachment of the leads12of the packages10. The pads18are coupled with traces (not shown) manufactured into the housing14which provide an electrical pathway from the leads12on the packages10to the outside of the housing14. The actual pinouts of the traces manufactured into the housing14depend 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 housing14are attached to the conductive leads16of the housing14by means such as side brazing. Alternately, surface mount type leads16, such as the small outline “J” (SOJ) leads shown, can be attached to the traces and manufactured into the housing14, thereby being firmly attached to the housing14. The manufacture of SOJ lead types, as well as other lead types, are well known in the art.

To assemble the MCM, the packages10are inserted into the housing14, and the leads12of the packages10are electrically coupled to the pads18of the housing14by coupling means22such as solder, conductive epoxy, conductive polymer, wire bonding, tape automated bonding, or other workable means.

After the leads12of the packages10are coupled with the pads18of the housing14, a lid20is attached to the housing14to seal the packages10in the housing14. The lid20can be plastic, ceramic, metallic, or composite, depending on the type of material from which the housing14is made. With some materials, such as ceramic and glass, the lid20will provide a hermetic seal. A hermetic seal will resist the entrance of moisture or other substances, which might cause the package10to malfunction, into the housing14. The lid20can be attached directly to the flat surface of the housing14, or a recess24can be manufactured into the top surface of the housing14to receive the lid20. The attachment means26varies with the type of material used to make the lid20. 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 lid20to the housing14. 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 4show an embodiment of the invention incorporating die (not shown) packaged in Type II TSOP packages30. Many of the elements of this embodiment are similar to the elements of the previously described embodiment.

In the present embodiment, through-hole DIP leads34are brazed to the side36of the housing32thereby coupling with traces (not shown) manufactured into the housing32. This embodiment incorporates packages30with leads38specially formed for use with the invention. The leads38extend directly out from the body of the package30and rest on a shelf40manufactured as an element of the housing32. Upon the shelf40are conductive pads18which connect with traces (not shown) manufactured into the housing32which run to the outside of the housing32.

FIGS. 5 and 6show an MCM having two semiconductor packages50,52, one50stacked on top of the other52, 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 housing54is manufactured with two shelves56,58of different levels, with each level having pads18for coupling the leads38,38′ of the packages50,52. Traces (not shown) manufactured into the housing54couple with the pads18, and terminate externally to the housing54. Packages52are placed in the housing54and the leads38′ are electrically coupled with pads (not shown) on the lower shelf58. The upper level of semiconductor packages50are placed in the housing54and the leads38are electrically coupled with pads18on the upper shelf56. The embodiment ofFIGS. 5 and 6may require that leads38,38′ on the packages50,52be formed especially for use with the inventive module. The package leads38for use on the upper shelf56have a greater distance to span than the package leads38′ for use on the lower shelf58. 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. 7describes an MCM having a plurality of stacked semiconductor packages60,62,64,66. In this stacked embodiment, TSOP packages are used which have been produced especially for use in the inventive module. In the embodiment ofFIG. 7, four TSOP devices are stacked or “piggybacked” one on top of another. The leads68are electrically coupled with the same output leads of the device below it, with the leads68of the bottom device66being coupled with pads (not shown) on the housing70.

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 CAS0, CAS1, CAS2, and CAS3. In the bottom device, CAS0will be connected to CAS on the die within, and CAS1-CAS3will be no connects. On the second device, CAS1is connected to CAS on the die within, and CAS0, CAS2, and CAS3are no connects. The third device has only CAS2active, and the top device has only CAS3active. 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 CAS0-CAS3. This design allows piggybacked devices and therefore a very small, highly dense module.

If SRAMs are used in the housing70, 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, CE0and CE1. 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 CE0and CE1(0, 0). On the second package, only CE1will 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 CE0and CE1. This design allows four piggybacked SRAM TSOP devices and therefore a very small, highly dense module.

In a piggybacked embodiment, only the leads68of the bottom device66are physically coupled to the housing, its leads being connected by solder reflow, conductive epoxy, or other workable means. To provide added support to the devices60,62,64,66to prevent excess stress on the leads68, the packages themselves can be connected with a material72such as nonconductive epoxy, organic resin, polyamide, nonconductive polymer, or with other workable means. The embodiment again shows the use of DIP style leads34on the housing70, 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 ofFIGS. 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.