Investigation of pressure dependence of interface thermal resistance in thermal greases by transient thermoreflectance

Abstract

The laser-based, non-destructive, front heating/front detection type transient thermo-reflectance (TTR) method was adapted to measure soft materials, and it was subsequently deployed to measure the thermal properties of a couple of popular Thermal Interface Materials (TIM) used in the microelectronics industry. Both the thermal conductivity of the TIM layer and the interface thermal resistance between the TIM and the solid substrate can be measured. A special fixture was built that enables precise control of the applied pressure on the TIM, in the range 0 to 4000 kPa and above. As a result, the TTR measurement system can be used to extract the variation of the above mentioned TIM thermal properties with the applied pressure. Our results show that the interface thermal resistance decreases with the applied pressure until about 800 kPa after which it stays constant. The values are relatively small, suggesting very good thermal interface resistance. Overall it was found that compared to other systems, such as the those described by standard ASTM D5470, the laser based method used here possesses unique characteristics that makes it is better suited for measuring the interface thermal resistance in TIM films.