Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Inorganic compound
Reexamination Certificate
1999-10-01
2001-01-16
Johnson, Jerry D. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Inorganic compound
C508S155000, C508S161000, C508S208000, C257S713000
Reexamination Certificate
active
06174841
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a heat-reducing silicone grease composition and, more particularly, to a thermally conductive grease composition well suited for heat reduction of electronic parts. Further, the invention relates to a semiconductor device that is provided with a heat-reducing silicone grease composition to enable efficient removal of the heat generated from electronic parts and prevent the semiconductor performance from deteriorating or being damaged by a temperature rise due to heat generation.
BACKGROUND OF THE INVENTION
Packaged IC units as electronic parts packaged on a printed wiring substrate, including a central processing unit (CPU), generate heat during the operation to raise the temperature, and thereby their performance is lowered or ruined at times. Therefore, it is necessary for the packaged IC units to be equipped with a heat dissipating means. Hitherto, the method of providing a heat dissipater on the surface of a packaged IC unit by pressure welding to utilize convection for improving the heat-dissipating efficiency has been proposed, and put to practical use.
However, such a method cannot avoid leaving gaps in the heat dissipater-packaged IC unit interface, so that the packaged IC unit and the heat dissipater have a reduced contact area in their pressure-welded plane. Accordingly, the heat dissipation efficiency cannot be achieved as it was designed. In order to close up those gaps, it has been carried out to lay a heat-reducing sheet, heat-reducing grease or the like between the packaged IC unit and the heat dissipater (as disclosed, e.g., in Japanese Tokkai Sho 56-28264 (U.S. Pat. No. 4,265,775) and Japanese Tokkai Sho 61-157587, wherein the term “Tokkai” means a “unexamined published patent application). In the case of a heat-reducing sheet, the material for heat reduction is molded in advance into a sheet having a thickness adequate for securing strength. Because of its thickness, the sheet increases in thermal resistance to fail in achieving sufficient heat reduction efficiency.
On the other hand, the heat-reducing grease has the advantage of making it possible to close up the gaps between the packaged IC unit and the heat dissipater by applying pressure thereto even when they have rough surfaces. Hitherto, the heat-reducing grease containing zinc oxide powder, boron nitride (having a hexagonal crystal structure: h-BN) powder or the like as a main component has been proposed. However, such a mineral itself has low thermal conductivity. For instance, the thermal conductivity of zinc oxide is about 20 W/mk and that of boron nitride (h-BN) is about 60 W/mk. Therefore, the, foregoing grease is unsatisfactory in heat-reducing properties.
In addition, the grease containing aluminum nitride having high thermal conductivity of about 320 W/mk as a main component has so far been proposed (e.g., in Japanese Tokkai Sho 52-125506). While the aluminum nitride can ensure satisfactory heat-reducing properties in the grease, it has also the disadvantage of hardness. More specifically, when the grease is applied to a packaged IC unit, such as CPU, having a bare surface, cases are often met with that the aluminum nitride in the grease damages the silicon surface of the packaged IC unit because of its high Mohs's hardness of 7-9 to mar the characteristics of the packaged IC unit.
SUMMARY OF THE INVENTION
As a result of our intensive study to develop highly efficient heat-reducing grease which involves no risk of damaging the silicon surface but has high thermal conductivity, it has been found that very good results can be obtained when the aluminum nitride powder used in grease has its average particle size in a particular range and contains no particles 100 &mgr;m or greater in size.
Therefore, a first object of the invention is to provide a high-efficiency silicone grease composition for heat reduction, which has high thermal conductivity and does not damage the silicon surface of a packaged IC unit, such as CPU.
A second object of the invention is to provide a semiconductor device wherein the heat-reducing silicone grease according to the present invention is laid between a packaged IC unit and a heat dissipater.
One of the aforementioned objects is attained with a heat-reducing silicone grease composition comprising a mixture of (A) 50-95 weight % of aluminum nitride powder having an average particle size of 0.5-10 &mgr;m and containing no particles 100 &mgr;m or greater in size, (B) 5-50 weight % of liquid silicone having a viscosity of 50-500,000 cs at 25° C. and (C) 0-30 weight % of at least one powder selected from the group consisting of zinc oxide, alumina, boron nitride and silicon carbide powders.
The other object is achieved with a semiconductor device to which the foregoing silicone grease composition is applied.
As the present heat-reducing silicone grease composition is free of aluminum nitride particles the sizes of which are not smaller than 100 &mgr;m, there is no fear of damaging the packaged IC unit surface. Further, the present grease composition has excellent extensibility and high thermal conductivity, so that the present semiconductor device can acquire very good heat-dissipating properties. Therefore, the reliability of electronic parts as a whole can be improved by incorporating semiconductor devices according to the invention in the electronic parts.
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patent: 6015777 (2000-01-01), Lostritto, Jr. et al.
Isobe Kenichi
Takahashi Takayuki
Yamada Kunihiro
Johnson Jerry D.
Millen White Zelano & Branigan
Shin-Etsu Chemical Co. , Ltd.
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