A New Accelerated Method to Characterize Degradation of Thermal Interface Materials

Abstract

Abstract. Due to advances in 3D integration and miniaturization of chips, the power density and number of hotspots within electronic packages have increased rapidly. A major bottleneck in the chip-to-coolant thermal resistance pathway is the interfacial resistance at solid–solid contacts, and, therefore, thermal interface materials (TIMs) are employed to minimize interfacial thermal resistance. However, thermal greases (paste-like materials) often degrade over time via pumpout (material moves out of the interface) and dryout (phase separation of the composite material) phenomena due to repeated heating and cooling. Traditional reliability testing methods, such as thermal cycling, have long testing periods. In this study, to accelerate the observation of the degradation of thermal greases, we propose adding mechanical cycling while maintaining a constant heat flowrate. We investigate the reliability of three thermal greases at different oscillation amplitudes and squeezing pressures using a novel custom-designed and machined experimental rig. We leverage high-resolution infrared imaging of thermal grease to capture steady-state 2D temperature maps, from which we calculate mechanical and thermal reliability metrics such as void fraction and comparison of area-normalized thermal resistance at the beginning and end-of-life. Our results uncover that the mechanical reliability of thermal greases depends on the ratio of elastic modulus to viscosity, with higher ratios being more desirable. Meanwhile, the thermal reliability depends upon the synergy of material properties with a higher elastic modulus and higher thermal conductivity, resulting in a lesser increase in thermal resistance over the lifetime of thermal greases.