Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1997-06-04
2001-11-13
Thompson, Gregory (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C174S015200, C165S104330
Reexamination Certificate
active
06317321
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the thermal management of packaged semiconductor chips, and, in particular, is directed to thermal management accomplished by incorporating phase change materials within and/or around semiconductor chip electronic packages.
BACKGROUND OF THE INVENTION
Packaging is one of the final steps in the process of manufacturing semiconductor chips. In packaging, a fabricated semiconductor chip is mounted within a protective housing. At the present moment, the art of semiconductor chip technology has evolved far more rapidly than the integrally related technology of packaging the semiconductor chips. The packaging requirements of the newer, smaller, more powerful semiconductor chips are quickly progressing beyond the capabilities of traditional packaging technology and the conventional materials and designs presently utilized are fast becoming obsolete. The packaging demands of new semiconductors require configurations to accommodate increasing numbers of electrical interconnections, space constraints due to decreasing system size, reduction in costs, improved reliability, and increasing heat transfer capabilities.
The need to adequately transfer heat out of increasingly smaller semiconductor packages and more compact housing arrangements has spawned significant interest in the development of new packaging materials and more thermally efficient configurations. Currently, semiconductor packaging commonly utilizes the art of attaching an external heatsink to improve the heat transfer characteristics of many chip packages which, by themselves, do not adequately transfer heat away from the semiconductor chip. However, with decreasing size, increasing heat concentration and high density packaging of new semiconductor chips the standard addition of an external heatsink often is no longer practical, sufficiently thermally efficient or effective.
A significant limitation on the operation and reliability of semiconductor chip packages is the efficient and effective extraction of heat. It is desirable to provide the chip packages with heat transfer mechanism to maintain them within a predetermined safe operating temperature range.
SUMMARY OF THE INVENTION
According to the present invention, an improved electronic package has been developed in which phase change material is incorporated inside and/or around the package. By including an effective amount of a phase change material with a package, an electronic device is enabled to operate at a nearly constant temperature. Accordingly, for devices which operate for a predictable length of time, an effective amount of phase change material to be incorporated can be calculated, such that use of an external heatsink attachment may be eliminated, or relegated to back-up utility.
Phase change materials are materials which, when heated, undergo isothermal changes in physical state, e.g., from a solid into a liquid, from a liquid to a gas, or from one solid phase to another solid phase. Subsequent removal of heat from the liquid or gas phase returns the material back to its solid or liquid phase. In application within an electronic package, as heat is generated by an operating device within the package, the incorporated phase change material, in effect, absorbs the generated heat, using the heat to isothermally convert from one phase to another. The phase change material is maintained at a constant temperature, and, in turn, the electronic device is able to “dump” its heat to effect the phase change and also maintain itself at a constant temperature. No additional heatsink or heat dissipation attachment is required as long as sufficient phase change material is present to absorb the heat generated during a finite, predictable electronic device operational period. Once all of the phase change material has been converted to its next phase through absorption of heat, a continued flow of heat energy from the electronic device would then cause the temperature of the phase change material to rise, and the effectiveness as an isothermal heat absorber becomes exhausted.
When the electronic device is not in operation, heat, in turn, no longer is generated, and, the device, the package, and the incorporated phase change material are allowed to cool. As they cool, the phase change material gives off heat to the surrounding environment and returns to its original state as a solid or liquid. The material then is ready to once again serve to absorb heat from the electronic device during the next operational period. In practice, heating and cooling may actually occur simultaneously, with the lower phase solid or liquid always being present as the case may be.
The desired operating temperature of a semiconductor chip generally ranges from about 50 to about 80° C. Accordingly, it is preferred to select and utilize a phase change material whose phase changing temperature is in that same temperature range. Some liquid phase change materials, such as certain alcohols, change to vapor phase at or about 70° C.; but, the volume of the material expands extremely when the phase changes from liquid to vapor, and, this volume increase presents considerable containment issues. Accordingly, solid to liquid phase change materials are preferred, since their expansions are significantly smaller. Several such materials have been suggested in the prior art, including waxes, metals (such as gallium, cesium, rubidium, and the like), and alloys (such as Bi/Pb/Sn/In, and the like).
Preferably, according to the present invention, phase change material is encapsulated, such that it readily can be incorporated into semiconductor chip electronic package assemblies. Encapsulation accommodates introduction of the phase change material into close proximity of the electronics within and/or around the package and/or enclosed semiconductor chip by integrating it within the package design itself, without concern regarding contamination, containment, or degradation.
In a preferred embodiment, phase change material is encapsulated, using conventional, commercially available microencapulation techniques, to produce pellets or microspheres of encapsulated phase change materials. Typically, the material may be encapulated with impermeable, structually sound material, such as shellac or gelation, to produce micropheres ranging in diameter from about five to about five thousand microns, having shells about one micron thick.
The encapsulated phase change material readily can be incorporated into or added to conventional electronic package assemblies. For example, injection molding plastic compositions could be modified by adding microspheres containing phase change material to the standard blend. Encapsulated phase change material also could be applied to selected surfaces by loading paints with phase change microspheres. The phase change materials mixed with epoxies, pyralene, silicones, and the like further could be strategically applied or added to an electronic package.
The use of phase change materials as disclosed could prove to be very useful to control the operating temperature of electronics at a constant or low value. This is particularly advantageous for low voltage electronics designs, currently emerging in the electronics industry, which are very sensitive to temperature variations. Phase change materials further may be very appropriate in the area of portable electronics, where weight, size, cost, or complexity of a heatsink or fan may be considered onerous. Phase change materials accommodate long, cool operation of an integrated chip, without the need for a heatsink element.
REFERENCES:
patent: 4047198 (1977-09-01), Sekhon et al.
patent: 4727455 (1988-02-01), Neidis et al.
patent: 4912548 (1990-03-01), Shanker et al.
patent: 5007478 (1991-04-01), Sengupta
patent: 5046365 (1991-09-01), Kumley et al.
patent: 5224356 (1993-07-01), Colvin et al.
patent: 5349237 (1994-09-01), Saytra et al.
patent: 5455458 (1995-10-01), Quon et al.
patent: 5341874 (1993-12-01), None
patent: 4083395 (1992-03-01), None
IBM Tech Disclosure Bulletin, “Substrate Mounte
Fitch John Stuart
Hamburgen William Riis
Compaq Computer Corporation
Hamilton Brook Smith & Reynolds P.C.
Thompson Gregory
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