Experiments on the thermal resistance of deformable thermal interface materials under mechanical loading

Abstract

Experiments have been performed to characterize the thermal resistance of thermal interface materials that deform under mechanical loading. TIMs in this category include elastomeric silicon rubber based TIM gap pads and pourable paste-like composite materials that set when cured. This paper reports on extensive experiments performed to characterize the overall thermal resistance of TIM pads composed of a silicon rubber base material enhanced with metallic filler particles. It is found that TIM pad thermal resistance decreases with applied load, reaching an asymptotic minimum thermal resistance which is dependent on initial thickness and material formulation. The critical pressure required to achieve minimum resistance is identified for all tested samples and is strongly dependent on material formulation. It is shown that the minimum thermal TIM resistance is not dependent on the size of the TIM sample under test when it is represented as the unit thermal resistance. Careful examination of the data shows that the apparent density of these TIM materials increases with load. Surprisingly the effective thermal conductivity initially increases with load but then maximizes and decreases as the load and the material strain surpass some critical value.