Evolution of shear strength and microstructure of die bonding technologies for high temperature applications during thermal aging

Wide bandgap materials have become very attractive for power electronics due to their physical properties that allow junction temperatures up to a theoretical limit of 600°C. In contrast, the maximum operation temperature of conventional silicon semiconductors is limited to approximately 200°C. The high-temperature operation of wide bandgap switches allows an increasing power density of power converters due to the reduced complexity of thermal management systems, leading to highly miniaturized power converters for example for automotive and aircraft applications. However, the reliability of wide bandgap devices at high temperatures is limited by the maximum operation temperature of conventional interconnection materials. The aim of this study is to investigate die attach technologies that are suitable to fulfill high temperature and high power requirements. Therefore, this work focuses on solder joints made of gold-germanium (AuGe12), zinc-aluminum (ZnA15), and lead tin (PbSn5) alloys, as well as die bonding by low temperature sintering of silver nano particles. For this reason, the evolution of the interfacial microstructure of test devices, assembled with different high temperature die attachment technologies, were monitored using cross sectioning techniques and scanning electron microscope (SEM) images. The evolution of the shear strength with time during high temperature storage was investigated. A comparison between shear test results and the evolution of the microstructure is given. The results show that sintered test devices feature a much higher shear force after high temperature storage due to the proceeding sintering of the particles, while the mechanical stability of all solders decreases with storage time.