Stock material or miscellaneous articles – Self-sustaining carbon mass or layer with impregnant or...
Reexamination Certificate
2000-02-25
2002-11-19
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Self-sustaining carbon mass or layer with impregnant or...
C428S131000, C361S709000, C165S905000, C165S907000, C257S712000, C257S722000, C423S414000, C423S44500R, C423S448000
Reexamination Certificate
active
06482520
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a system for managing the heat from a heat source like an electronic component. More particularly, the present invention relates to a system effective for dissipating the heat generated by an electronic component.
BACKGROUND OF THE ART
With the development of more and more sophisticated electronic components, including those capable of increasing processing speeds and higher frequencies, having smaller size and more complicated power requirements, and exhibiting other technological advances, such as microprocessors and integrated circuits in electronic and electrical components and systems as well as in other devices such as high power optical devices, relatively extreme temperatures can be generated. However, microprocessors, integrated circuits and other sophisticated electronic components typically operate efficiently only under a certain range of threshold temperatures. The excessive heat generated during operation of these components can not only harm their own performance, but can also degrade the performance and reliability of the overall system and can even cause system failure. The increasingly wide range of environmental conditions, including temperature extremes, in which electronic systems are expected to operate, exacerbates these negative effects.
With the increased need for heat dissipation from microelectronic devices caused by these conditions, thermal management becomes an increasingly important element of the design of electronic products. As noted, both performance reliability and life expectancy of electronic equipment are inversely related to the component temperature of the equipment.
For instance, a reduction in the operating temperature of a device such as a typical silicon semiconductor can correspond to an exponential increase in the reliability and life expectancy of the device. Therefore, to maximize the life-span and reliability of a component, controlling the device operating temperature within the limits set by the designers is of paramount importance.
Heat sinks are components that facilitate heat dissipation from the surface of a heat source, such as a heat-generating electronic component, to a cooler environment, usually air. In many typical situations, heat transfer between the solid surface of the component and the air is the least efficient within the system, and the solid-air interface thus represents the greatest barrier for heat dissipation. A heat sink seeks to increase the heat transfer efficiency between the components and the ambient air primarily by increasing the surface area that is in direct contact with the air. This allows more heat to be dissipated and thus lowers the device operating temperature. The primary purpose of a heat sink is to help maintain the device temperature below the maximum allowable temperature specified by its designer/manufacturer.
Typically, heat sinks are formed of a metal, especially copper or aluminum, due to the ability of copper to readily absorb heat and transfer it about its entire structure. In many applications, copper heat sinks are formed with fins or other structures to increase the surface area of the heat sink, with air being forced across or through the copper fins (such as by a fan) to effect heat dissipation from the electronic component, through the copper heat sink and then to the air.
Limitations exist, however, with the use of copper heat sinks. One limitation relates to copper's relative isotropy—that is, the tendency of a copper structure to distribute heat relatively evenly about the structure. The isotropy of copper means that heat transmitted to a copper heat sink become distributed about the structure rather than being directed to the fins where most efficient transfer to the air occurs. This can reduce the efficiency of heat dissipation using a copper heat sink. In addition, the use of copper or aluminum heat sinks can present a problem because of the weight of the metal, particularly when the heating area is significantly smaller than that of the heat sink. For instance, pure copper weighs 8.96 grams per cubic centimeter (g/cc) and pure aluminum weighs 2.70 g/cc (compare with pure graphite, which weighs between about 1.4 and 1.8 g/cc). In many applications, several heat sinks need to be arrayed on, e.g., a circuit board to dissipate heat from a variety of components on the board. If copper heat sinks are employed, the sheer weight of copper on the board can increase the chances of the board cracking or of other equally undesirable effects, and increases the weight of the component itself. In addition, since copper is a metal and thus has surface irregularities and deformations common to metals, and it is likely that the surface of the electronic component to which a copper heat sink is being joined is also metal or another relatively rigid material such as aluminum oxide or a ceramic material, making a complete connection between a copper heat sink and the component, so as to maximize heat transfer from the component to the copper heat sink, can be difficult without a relatively high pressure mount, which is undesirable since damage to the electronic component could result.
What is desired, therefore, is a thermal management system effective for dissipating heat from a heat source such as an electronic component. The thermal management system should advantageously be relatively anisotropic as compared to copper, exhibit a relatively high ratio of thermal conductivity to weight, and be capable of conformable mating with the surface of the heat source.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a thermal management system for a heat source, the thermal management system being effective to increase the useful area of the surface of the heat source from which heat is to be dissipated.
Another object of the present invention is to provide a thermal management system exhibiting a relatively high degree of anisotropy.
Still another object of the present invention is to provide a thermal management system capable of forming a desirably complete thermal connection with the surface of the heat source without the need for a high pressure mount.
Yet another object of the present invention is to provide a thermal management system having a relatively high ratio of thermal conductivity to weight.
Still another object of the present invention is to provide a thermal management system that can be fabricated so as to locate the heat dissipation surfaces thereof so as to maximize the dissipation of heat from the heat source.
These objects and others that will become apparent to the artisan upon review of the following description can be accomplished by providing a heat source, such as an electronic component, the heat source having an external surface. A thermal interface mounted to the external surface of the heat source is also provided, where the thermal interface comprises an anisotropic flexible graphite sheet having a planar area greater than the area of the external surface of the heat source. In another embodiment of the invention, the thermal management system includes a heat sink which comprises a graphite article shaped so as to provide a heat collection surface and at least one heat dissipation surface, wherein arranging the heat collection surface of the graphite article in operative connection with a heat source causes dissipation of heat from the heat source through the at least one heat dissipation surface of the graphite article. The graphite article useful as the heat sink of this embodiment of the invention comprises compressed particles of exfoliated graphite, such as anisotropic flexible sheets of compressed particles of exfoliated graphite laminated into a unitary article or particles of exfoliated graphite compressed into a desired shape. In addition, the graphite article can be formed of high density graphite fabricated from finely divided carbonaceous particles.
Graphites are made up of layer planes of hexagonal arrays or networks of carbon atoms. These layer planes of hexagonally
Boss Wendy
Cartiglia James R.
Jones Deborah
Waddey & Patterson , P.C.
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