Comprehensive physical analysis of bond wire interfaces in power modules

Power modules based on insulated gate bipolar transistors have become very widely used units in energy technology. Handling large currents and high voltages at high switching frequencies leads to degradation of materials in the devices, especially at interfaces and interconnections, eventually causing failures. In this paper we present a review on the set of our experimental and theoretical studies allowing comprehensive physical analysis of changes in materials under active power cycling with focus on bond wire interfaces and thin metallisation layers. The developed electro-thermal and thermo-mechanical models that can be applied to mimic the device under particular operation conditions and to evaluate stress factors related to heat dissipation are briefly presented. The results of modelling, which predict materials degradation, are compared with a few exemplary cases obtained using the micro-sectioning combined with optical microscopy and scanning electron microscopy assisted by focused ion beam milling. These experimental results show very good agreement with wear out effects predicted by simulations. Additionally, measurements of resistance using four-point probe method are demonstrated to be a very powerful tool to map the degradation of individual components and interfaces.