Electronic power modules, such as IGBT or MOSFET based inverters are gaining more importance today as hybrid and electric cars require lighter and more and more reliable traction systems. Following the new demands the size of the power packages and the size of the chips inside get smaller, however the powering requirements remain the same or even increase. This leads to increasing power densities within the chips, which may lead to overheating or ultimately to failure of the component. For reliable operation, the junction temperature of power components must be kept below a certain limit, and in order to achieve this, the selection of proper interface materials is a must.
This presentation describes a methodology to measure the bulk thermal conductivity of TIM materials used in power electronics applications. This new methodology follows the principles of the industrial standard ASTM D5470 test standard, however focuses on eliminating the issues associated to the standard test approach. This way the measured TIM conductivity data becomes more accurate even at higher conductivity domains (in the range of 20 W/mK and beyond), with small scatter and very good reproducibility among test sites. We will also introduce a structure function based test method to assess the reliability of selected TIM materials. The use of these tools can improve product design by enabling simple and accurate material comparison, selection and ultimately lifetime estimation of a material or even the final product.