Heat dissipating component using high conducting inserts

Details Heat dissipating component using high conducting inserts Heat dissipating component using high conducting inserts

2001-12-13

2004-07-06

McKinnon, Terrell (Department: 3743)

Heat exchange

Heat transmitter

C165S080300, C165S905000, C361S704000, C361S697000, C257S720000

Reexamination Certificate

active

06758263

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a heat dissipating component capable of managing the heat from a heat source such as an electronic device. More particularly, the present invention relates to a heat dissipating component effective for dissipating the heat generated by an electronic device, wherein the heat dissipating component is constructed by assembling together an anisotropic graphite planar element with a high thermal conductivity core element.
BACKGROUND OF THE INVENTION
With the development of more and more sophisticated electronic devices, 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 the negative effects of excessive heat.
With the increased need for heat dissipation from microelectronic devices, thermal management becomes an increasingly important element of the design of electronic products. 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.
Several types of heat dissipating components are utilized to facilitate heat dissipation from electronic devices. The present invention is directly applicable to several of these heat dissipating components, including those generally referred to as heat spreaders, those generally referred to as cold plates, and those generally referred to as heat sinks, among others.
These heat dissipating components facilitate heat dissipation from the surface of a heat source, such as a heat-generating electronic device, to a cooler environment, usually air. In many typical situations, heat transfer between the solid surface of the electronic device and the air is the least efficient within the system, and the solid-air interface thus represents the greatest barrier for heat dissipation. The heat dissipating components seek to increase the heat transfer efficiency between the electronic device and the ambient air primarily by increasing the surface area that is in direct contact with the air or other heat transfer media. This allows more heat to be dissipated and thus lowers the electronic device operating temperature. The primary purpose of a heat dissipating component is to help maintain the device temperature below the maximum allowable temperature specified by its designer/manufacturer.
Typically, the heat dissipating components are formed of a metal, especially copper or aluminum, due to the ability of metals like copper to readily absorb heat and transfer it about its entire structure. In the case of heat sinks, copper heat sinks are often formed with fins or other structures to increase the surface area of the heat sink, with air being forced across or through the 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 metallic heat dissipating components. One limitation relates to the relative isotropy of a metal that is, the tendency of a metallic structure to distribute heat relatively evenly about the structure. The isotropy of a metal means that heat transmitted to a metallic heat dissipating component becomes distributed about the structure rather than being preferentially directed to a desired location.
In addition, the use of copper or aluminum heat dissipating elements can present a problem because of the weight of the metal, particularly when the heat transmitting area of the heat dissipating component is significantly larger than that of the electronic device. For instance, pure copper weighs 8.96 grams per cubic centimeter (g/cm
3
) and pure aluminum weighs 2.70 g/cm
3
(compare with graphite articles, which typically weigh less than about 1.8 g/cm
3
).
For example, 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 metallic heat sinks are employed, the sheer weight of the metal 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 the case of larger heat dissipating components such as for example that class of components known as heat spreaders, the weight of a pure copper heat spreader requires special mechanical features and designs to hold the heat spreader.
What is desired, therefore, is a heat dissipating component effective for dissipating heat from a heat source such as an electronic device. The heat dissipating component should advantageously be relatively anisotropic, as compared to a metal like copper or aluminum and exhibit a relatively high ratio of thermal conductivity to weight. One group of materials suitable for use in heat sinks are those materials generally known as graphites, but in particular anisotropic graphites such as those based on natural graphites and flexible graphite as described below.
Graphites are made up of layer planes of hexagonal arrays or networks of carbon atoms. These layer planes of hexagonally arranged carbon atoms are substantially flat and are oriented or ordered so as to be substantially parallel and equidistant to one another. The substantially flat, parallel equidistant sheets or layers of carbon atoms, usually referred to as graphene layers or basal planes, are linked or bonded together and groups thereof are arranged in crystallites. Highly ordered graphites consist of crystallites of considerable size: the crystallites being highly aligned or oriented with respect to each other and having well ordered carbon layers. In other words, highly ordered graphites have a high degree of preferred crystallite orientation. It should be noted that graphites possess anisotropic structures and thus exhibit or possess many properties that are highly directional e.g. thermal and electrical conductivity and fluid diffusion.
Briefly, graphites may be characterized as laminated structures of carbon, that is, structures consisting of superposed layers or laminae of carbon atoms joined together by weak van der Waals forces. In considering the graphite structure, two axes or directions are usually noted, to wit, the “c” axis or direction and the “a” axes or directions. For simplicity, the “c” axis or direction may be considered as the direction perpendicular to the carbon layers. The “a” axes or directions may be considered as the directions parallel to the carbon layers or the directions perpendicular to the “c” direction. The graphites suitable for manufacturing flexible graphite sheets possess a very high degree of orientation.
As noted above, the bonding forces holding the parallel layers of carbon atoms together are only weak van der Waals forces. Natural graphites can be treated so that the spacing between the superposed carbon layers or laminae can be appreciably opened up so as to provide a marked expansion in

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