Study on the reliability of novel Au-30Ga solder for high-temperature packaging

Abstract As a novel high-temperature solder with suitable eutectic temperature and excellent solderability, Au-30Ga eutectic alloy shows high application potential as a packaging material for high-power devices. In this work, the evolution of microstructure, shear strength and fracture mechanism of Au-30Ga/Ni solder joint during soldering and aging was studied. It was found that with the increase of soldering time, Ga was seriously consumed to form Ga-Ni interfacial intermetallic compounds (IMCs), resulting in the formation of Ga-poor region near the interface layer. Au7Ga3 phase would be first formed at the valley area of Ga3Ni2 IMC layer. The dominant IMCs growth mechanism eventually transformed from grain-boundary diffusion to volume diffusion after soldering for 0.49 min. The diffusion coefficients are 1.64×10-14 and 3.77×10-19 m2/s at 500 °C (soldering) and 300 °C (solid-state aging), respectively. With the coarsening of IMC layers, the fracture mechanism of joint changed from solder control mode to solder/IMC mixed control mode. When the thickness is 4.36 μm, the joint strength reaches the maximum value of 77.7 MPa. Furthermore, a reliability evaluation equation of Au-30Ga/Ni solder joint was established to optimize soldering process and solder composition.