Abstract

Thermal Interface Materials (TIMs) are utilized as contact material between an electronic component (e.g. power electronics of e-cars) and the heat sink. The considerably increased power requirements and the continuing trend towards miniaturization in electronic devices lead to an increased performance and desire a suitable characterization to understand the behavior of Thermal Interface Materials. As a key component in the thermal management of electronic components, TIMs should have high electrical insulation properties (dielectric strength of about 5 kV) and high thermal conductivity to prevent an overheating in electronic components. With so many TIMs available on the market, it is getting more and more difficult to make the right decision when selecting a best matched TIM for the specific application. Parameters such as thermal resistance, thermal conductivity, electrical insulation, contact pressure dependency and price play an important role in TIMs selection. Data sheet specifications for thermal resistance are mostly determined by the ASTM D5470 method. In this case, TIMs characterization is performed under highly favorable conditions (polished surfaces, excessive pressure conditions). However, these values differ when TIMs are used for electronic applications. This can lead to incorrect thermal management design and thus damage the electronic component. In this study, a fast method for characterization of the thermal resistance of TIMs under realistic operating conditions was developed. A 3 D printed test rig was built up to measure the thermal resistance of TIM samples (pads and foils) at different contact pressures, volume and heat flow rates. The heat source was uniform distributed as well as only locally applied which is typical for practical applications. For the study four commercially available TIMs were selected and characterized: Elastomer, silicone, phase change material (PCM) and graphite foil with support layers. The measured temperatures were used to calculate the thermal resistance of the respective TIMs. The results show a strong dependence of the thermal resistance on the sample thickness and the contact pressure for all samples. The PCM sample showed the lowest thermal resistance and elastomer sample showed the highest. Applying a non-uniform heat source, the graphite foil could not demonstrate its benefit in terms of in-plane heat distribution, like a heat spreader. A comparison of the measured values with the manufacturer's data showed a deviation between ASTM method and typical operation conditions as investigated here. Using this method TIM materials and systems can be fast characterized and allows a rapid indication of the applicability of the desired TIM under relevant operation conditions.