Lift off reliability model for aluminum and copper wire bonds

Abstract

Future generation of switches for power electronic will additionally base on the new wide band gap semiconductor GaN or SiC (WBG). These materials support high switching frequency possibility and higher switching current densities. Wide band gap materials enable high application temperatures up to 250°C. Unfortunately, high temperature capability needs also a high number of thermal cycles. These paper shows on the example of a frame module concept the comparison of different die attach joining techniques with the focus on the reliability issue on wire and ribbon bonds. Depending on the application and mission profile a high thermal cycling capability is necessary. For this reason, new high temperature joining techniques for die attach, e.g. Silver sintering or diffusion soldering, were developed in the recent past. All of this new joining techniques are focusing on higher electrical, thermal and thermo-mechanical performance of power modules. By using an optimized metallization system for the WBG, the numbers of thermal cycles can be increased and the maximum operating temperature advances up to 300°C. The present work shows an active power cycling capability of different wire and ribbon bonds and the failure mechanism will be discussed. A calculation model describes the reliability for the different wire diameter and the impact of bonding materials. This reliability calculation basing on materials and geometry data explains the thermo-mechanical effects. Through these physical background an understanding about the large number of more than 1.000.000 thermal cycles with a 150 K temperature swing from +30°C to +180°C is now possible. These analyses provide the basic knowledge for a reliable design basing on current, mission profile and reliability including the optimization for future high end applications with wire or ribbon bonding technique.