Shear strength and fracture surface analysis of BiAgNiCuGe/Cujoint

The microstructure, joint shear strength and fracture surface of high-temperature lead-free solder Bi-xAg-0.4Ni-0.2Cu-0.1Ge(x=2, 5, 8, 11, 14) were analyzed with scanning electron microscopy, energy dispersive X-ray spectrometry and electronic tensile testing machine.The results show that interface microstructure mainly consists of primary Ag, primary crystal Bi, eutectic phase and little NiBi₃ phase.With the increasing of Ag in solder, primary Ag increases gradually and shear strength heightens obviously.No intermetallic compound forms between solder and Cu substrate, which join mainly through the diffusion of liquid solder atoms to Cu crystal boundaries.The diffusion of Bi to Cu crystal boundary is more than that of Ag.The interface between solder and Cu substrate is the weak region of joint and is shear fracture starting point.