Effect of Cryogenic Temperature on Mechanical Fracture mechanism of Cu/Sn3.0Ag0.5Cu-Solder/Cu Joint

The mechanical degradation mechanism of Cu/Sn3.0Ag0.5Cu-Solder/Cu joints in different low temperature environments were investigated in this paper. The results showed that the fracture mode transformed from ductile to brittle, and the fracture location was transferred from solder layers to intermetallic compound layers with the decrease of temperature. The cryogenic temperature factor severely inhibited the movement of dislocations, and the brittle fractures were prone to occur at the layers with high-density dislocations. When the temperature dropped drastically, the IMC easily cracked at the interface due to mutual extrusion, further evolved into microvoids causing fracture behavior at the IMC layer in the end. The changing of crystal structure played a crucial role on the changing of fracture mode. The isotropic $\alpha$-Sn relieved the stress generated by the ultrasonic wave to a certain extent.