Characteristic morphologies that cause failure of Au80Sn20/AlN substrate solder joint under combined temperature cycle and current switch cycle tests

With the requirement of lead-free soldering technology in electronic industry for manufacturing lead-free electronic devices, Au80Sn20 solder has been developed and applied in high-power devices due to its excellent physical and chemical properties. However, the application of new type of chip in high-power devices leads to the exposure of the Au80Sn20 solder joints to the complex environment of temperature cycle and current switch cycle, which seriously affects the reliability of solder joints in practical applications. In this study, the solder joint structure and simulation platform were designed independently. The failure mechanism of Au80Sn20/AlN substrate solder joint under temperature cycle and current switch cycle was studied by analyzing the changes in morphological characteristics of solder joint and composition in different working times. It was found that the failure process of solder joint involved the generation of steps along the grain boundary and phase boundary, and the failure was caused by the gradual expansion of steps. Owing to the uneven distribution of Cu and Ni in Au5Sn and AuSn phases, the volume difference among different phases was generated, which promoted the formation of phase boundary steps. The grain boundary steps were formed due to the formation of Au3Cu phase at the grain boundary, resulting in the volume difference between grain boundary and grain. Based on the research results, the idea of improving solder joint reliability by adjusting microstructure of Au80Sn20 solder is put forward, which plays a theoretical guiding role in the optimization of targeted performance of Au80Sn20 solder.