Limitations and accuracy of steady state technique for thermal characterization of solid and composite materials

The steady state method is a commonly used and in principle simple way to measure thermal resistance and conductivity of thermal interface materials (TIMs). A heat flow through the TIM has to be generated and the temperature gradient across the TIM has to be measured. This is also defined by the ASTM standard ASTM D5470 [4]. To generate the heat flow the TIM must be positioned between a hot and a cold plate. However, for the new generation of highly conductive and thin TIMs the resolution of the common steady state technique often reaches its limit. To increase the resolution of the steady state equipment beyond the state-of-the- art the test systems must be analyzed and parasitic effects be studied. Accuracy and resolution depend not only on the precision of the setup, but decisively on the selection and execution of the measuring method conformed to the specific measurement task. In this paper we will present a test stand for thermal characterization of TIMs, die attachs and substrates based on the mentioned steady state method. It has been developed as a platform which allows the integration of various modules for characterization of different materials under different conditions, e.g. mated surface, finish, operation temperature, pressure, aging etc.