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Thermal interface material with controlling graphite to line vertically and some thermal management materials
Keywords: Thermal interface material, high thermal conductivity, flexibility
To enhance heat dissipation in electronic devices, TIM (Thermal Interface Material) with high thermal conductivity is becoming very important. Grease is typical TIM, which is used as thinly as possible at assembly due to thermal conductivity of that is low to get small thermal resistance. But Grease is pumped out during heat shock test because of its relatively low viscosity. From the view point of thermal resistance, metal alloy is the best however Indium that is often used to be as metal alloy is known as rare material. In addition, melting temperature of Indium is around 150 degree Celsius, so packages with Indium could not pass through reflow process. To solve above problems the sheet composed of graphite fillers and soft rubber was developed. Graphite fillers are oriented vertically so there are many heat paths from heat source and heat sink. Also soft rubber within the sheet makes the sheet flexibility to attach to the heat sink and heat source ever when shape of them has warpage. The thermal resistance of the developed sheet was lower than that of conventional sheet which has fillers oriented horizontally. Thermal resistance did not change after three times reflow process during some reliability tests that are humidity, heat shock and heat storage. There was no pumping out during heat shock test. Consequently it shows that the developed sheet will be applied to TIM in CPU and power device using hybrid cars instead of conventional TIMs. In addition, we are going to explain other thermal management material we are developing.
Rei Yamamoto,
Hitachi Chemical Co.,Ltd.
Tsukuba, Ibaraki
JAPAN


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