Stock material or miscellaneous articles – Self-sustaining carbon mass or layer with impregnant or...
Reexamination Certificate
2002-11-15
2003-12-16
Jones, Deborah (Department: 2835)
Stock material or miscellaneous articles
Self-sustaining carbon mass or layer with impregnant or...
C428S209000, C428S402000, C428S403000, C428S407000, C428S446000, C428S447000, C361S709000, C423S448000
Reexamination Certificate
active
06663964
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heat dissipating structure, and in particular to a heat dissipating structure used as a thermal interface provided between a heat generating electronic component and a heat dissipating component such as a heat sink or a circuit board for the purposes of cooling the heat generating electronic component.
2. Description of the Prior Art
In the circuit design of recent electronic equipment such as televisions, radios, computers, medical instruments, office equipment and communication devices, advances in miniaturization of these devices has led to great increases in complexity in the circuit design. For example, electronic equipment incorporating hundreds of thousands of transistors, and integrated circuits for other electronic equipment are now being produced. The complexity of the circuit designs continues to increase, and the demands continue for incorporating even smaller electronic components into even smaller areas, and increasing the numbers of electronic components even further.
As a result, a more effective method of diffusing the heat generated by these electronic components, which is a common cause of malfunction or failure of such components, is now required. In other words, as the degree of integration of LSI devices such as CPUs, driver ICs and memory used in electronic equipment such as personal computers, digital video disc players and mobile telephones has increased, large numbers of heat diffusion methods, as well as heat diffusion members and materials used in such methods, have been proposed.
In conventional electronic equipment and the like, a heat sink utilizing a metal sheet with a high thermal conductivity such as brass is used to suppress increases in the temperature of any particular electronic component during use of the equipment. This heat sink conducts the heat generated by the electronic component, and uses the temperature difference with the outside air to radiate the heat away from the component surface.
In order to ensure that heat generated from the electronic component is conducted efficiently into the heat sink, the heat sink must be in close contact with the electronic component. However, due to differences in the height between individual electronic components, and the tolerances allowed during the assembly process, a variety of methods are used to improve the thermal conductivity from the electronic component to the heat sink, including using heat conducting sheets with good flexibility, and inserting heat conducting grease between the electronic component and the heat sink in order to lower the thermal contact resistance therebetween.
Examples of the above type of heat conducting sheet include a graphite sheet with a heat conducting silicone rubber coating provided on either one surface or both surfaces thereof, as disclosed in Japanese Post-examination Patent Publication (kokoku) No. 3-51302 (JP3-51302B), and a heat dissipating structure comprising a silicone rubber layer filled with an electromagnetic wave shielding material laminated onto a graphite film, as disclosed in Japanese Laid-open publication (kokai) No. 11-340673 (JP11-340673A).
However, although the graphite sheet used in the heat dissipating structure disclosed in the aforementioned Japanese Laid-open publication (kokai) No. 3-51302 (JP3-51302A) is an anisotropic high thermal conductivity material with a thermal conductivity of 5 W/m·K in the direction through the lamination, and 500 W/m·K in directions along the material surface, the sheet itself displays considerable hardness, and when covered with a heat conducting silicone rubber, the observed reduction in thermal contact resistance is not always entirely satisfactory. Consequently, a heat dissipating structure capable of further reducing the thermal contact resistance has been keenly sought.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a heat dissipating structure capable of reducing the thermal contact resistance between a heat generating electronic component and a heat dissipating component, and markedly improving the heat radiation.
As a result of intensive investigations aimed at resolving the above problems, the inventors of the present invention developed a heat dissipating structure comprising an uncured composition which is a solid sheet at room temperature and is capable of conforming to any shape required of the surface layer and contacting the surface with good thermal conductivity, and is consequently easily positioned or removed from between an electronic component and a heat dissipating component such as a heat sink, and yet is capable of offering excellent heat dissipating performance by softening under the influence of heat generated during operation of the electronic component, and markedly reducing the thermal contact resistance.
In other words, as a device for resolving the aforementioned problems, the present invention provides a heat dissipating structure for positioning between an electronic component and a heat dissipating component, comprising a graphite sheet and a heat conducting composition layer provided on at least one surface of the graphite sheet, wherein the heat conducting composition has no fluidity at room temperature when the electronic component is not operating, but undergoes a reduction in viscosity, softens or melts, under the influence of heat generated during operation of the electronic component.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As follows is a description of specifics of the present invention using a series of embodiments.
Graphite Sheet
Provided a sheet of the present invention is formed from graphite, there are no particular restrictions on the production method or the like. The thickness of the sheet should preferably be from 0.01 to 1.5 mm, and even more preferably from 0.1 to 1.0 mm. If the sheet is too thin, the mechanical strength deteriorates and the sheet becomes brittle, whereas if the sheet is too thick, the flexibility becomes inadequate. This type of graphite sheet can be obtained easily as a commercially available product.
Heat Conducting Material
A heat conducting material used in the present invention has no fluidity at room temperature when the electronic component is not operating, but displays a reduction in viscosity, softens or melts, under the influence of heat generated during operation of the electronic component. Specifically, any materials which undergo a reduction in viscosity, soften or melt within a temperature range from 40 to 100° C. can be used.
Specific examples of suitable heat conducting materials include heat conducting compositions comprising an organic resin which forms a matrix phase, and a heat conducting filler.
[Resin Component]
Organic resins which can be used in such heat conducting compositions must have good heat resistance at the operating temperatures of the electronic component, must display no fluidity at room temperature when the electronic component is not operating, but display softening, a reduction in viscosity, or undergo melting at the operating temperature of the electronic component. Provided the organic resin has these characteristics, then almost any resin can be used without any particular restrictions. Examples of suitable resins include silicone resins, &agr;-olefin based resins, and paraffin based resins, although of these, silicone resins are preferred.
More specific examples of silicone resins ideally suited to the present invention are described below.
Any silicone resin may be used provided the heat conducting composition is essentially solid (non-fluid) at room temperature, but softens, reduces in viscosity or melts, so that at least the surface thereof becomes fluid, at temperatures within a range between 40° C. and the maximum temperature reached due to the heat generated by the heat generating electronic component, namely 40 to 100° C., and preferably 40 to 90° C. This requirement is an important factor in causing softening of the matrix phase.
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Mita Kunihiko
Suzuki Akio
Yoneyama Tsutomu
Bahta Abraham
Shin-Etsu Chemical Co. , Ltd.
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