Thermo-mechanical properties of high performance thermal interface gap filler pads

A thermal interface material (TIM) with the highest thermal conductivity does not automatically deliver the best thermal management performance. It is just as important to achieve the best surface contact between TIM and various substrates. Softer interface materials like silicone gap fillers tend to lower contact resistance and thermal impedance. More importantly, the low modulus of silicone gap fillers also decreases the stress due to the large mismatch of the coefficient of thermal expansion (CTE) in microelectronic packages with die chips, heat sinks, heat spreaders, and substrates. However, decreasing the modulus of the gap fillers is often associated with increased creep behavior under compression as well as poor recovery upon removal of the stress. The desired thermal gap fillers must remain elastic at low temperatures and keep thermal stability at high temperatures while still maintaining good thermal conductivity. For the investigation described herein, DMA (Dynamic Mechanical Analysis) was used to characterize the viscoelastic creep and stress relaxation properties of silicone gap fillers at various conditions. New thermal gap fillers using silicone chemistry were developed for this study to provide low modulus and high elasticity and were investigated along with commercially available silicone gap fillers. Thermal impedance properties at different operating conditions such as during long term exposure for elevated temperatures and humidity were also monitored with corresponding thermo-mechanical properties in DMA.