Effects of High-Density Current on the Reliability of Ni-Sn Solid-Liquid Interdiffusion Joints with Al Interlayer

Electric vehicles are becoming increasingly popular as environmentally friendly alternatives to conventional fossil fuel-based vehicles. The need to improve their performance demands design of materials that can withstand high current density without adversely affecting their durability. In this study, the influence of high-density current on the structure of a Ni-Sn solid-liquid interdiffusion joint with an Al interlayer was examined. The temperature at the joint region increased to 240 degrees C without external heating under energization of 20 kA/cm(2). After 100 h of energization, several structural evolutions from the initial state were observed in the joint region, including precipitation of Al3Ni at the cathode-side Al/Ni interface and enrichment of Ni concentration on both sides of the Ni-Sn intermetallic compound (IMC) layer. Electromigration influenced the precipitation position of the Al3Ni grains. However, there was only a trace of electromigration in the Ni enrichment behavior of the Ni-Sn IMC layer, because thermal and stress migration were very active there. The degree of Ni enrichment in the energized Ni-Sn IMC layer was much higher than that in the Ni-Sn IMC layer annealed at 300 degrees C for 100 h. This result implies that a high-density current activates the thermal migration and stress migration. The influence on the reliability of the joint is a concern because the high degree of Ni enrichment in the energized Ni-Sn IMC layer generates many Kirkendall voids.