Effect of Ag content on microstructure and mechanical properties of Sn−xAg−0.5Cu solder joints under rapid thermal shock

The effects of Ag content on the microstructure and shear strength of Sn−xAg−0.5Cu solder joints under rapid thermal shock were investigated using high-frequency induction heating equipment. The results show that the increased Ag content can make the surface of the solder joint denser and smoother and reduce the generation of long strips of Cu6Sn5 intermetallic compound (IMC) inside the solder joint, thus enhancing the oxidation resistance of the solder joint. Ag accelerates the growth rate of the IMC layer at the solder joint interface, the growth rate of the Cu6Sn5 layer is determined by both bulk diffusion and grain boundary diffusion, and the growth rate of the Cu3Sn layer is determined by both bulk diffusion and interfacial reaction. In the rapid thermal shock environment, the fracture mode of the solder joint converts from ductile fracture to brittle fracture. At the same time, the high Ag content shortens the fracture mode transition time of the solder joint and reduces the thermal fatigue resistance of the solder joint.