Packaging for a Semiconductor Die

This invention relates to the field of semiconductors. More specifically, it describes 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 insure 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 turn out 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 a waste of time and materials, and is therefore 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 adversely 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.

An object of this invention is to provide a MCM which has a higher probability of receiving only good die as compared with present MCMs of equal density. This produces a higher yield.

Another object of this invention is to provide an MCM which is less expensive to produce than present MCMs due to its higher yield.

It is a further object of this invention to provide a high density MCM.

A fourth object of this invention is to provide a module having very short trace lengths thereby being able to transfer data very quickly between the multiple die contained in the MCM and the system into which the MCM is installed.

It is another object of this invention to provide a rugged hermetically sealed MCM which typifies devices produced to satisfy high reliability and military usage requirements.

These objects of the present invention are accomplished by 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.

The inventive module has the advantage of using only fully tested and burned in die. Present designs of MCMs package several untested or poorly tested die together, and then fully test the module after it 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 re-work the MCM by replacing all "bad" die. The inventive design, however, allows for the assembly of only functional die, therefore increasing the yield of the completed assembly.

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. 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.

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 in the detailed description.

In addition to supplying memory, the invention would make a convenient way to package different types of components in the same housing, for instance 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.

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.

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 consists of 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 a 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 36 to the side 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 a 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 CAS0, CAS1, CAS2, and CAS3. In the bottom device, CAS0 will be connected to CAS on the die within, and CAS1-CAS3 will be no connects. On the second device, CAS1 is connected to CAS on the die within, and CAS0, CAS2, and CAS3 are no connects. The third device has only CAS2 active, and the top device has only CAS3 active. If stacked packages as described are used, it is invalid for more 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 housing 70, each SRAM package is fabricated with a number of chip enable (CE) pins, the number of pins corresponding 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, CE0 and 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 CE0 and CE1 (0,0). On the second package, only CE1 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 to 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 CE0 and CE1. 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.

What have 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 x1, x4, x16, or x32 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.