Grain Orientation and Prediction of Thermal Shock Fatigue of Sn-3Ag-0.5Cu Solder Joints for Fan-Out Wafer Level Packaging

In this study, the grain orientation, microstructure evolution and fatigue life prediction of Sn-3Ag-0.5Cu (SAC305) solder joints in fan-out wafer level packaging are studied in terms of thermal shock tests. The heterogenous evolution of microstructures in SAC305 solder joints was investigated using thermal shock and electron backscattered diffraction (EBSD) analysis. When the number of thermal shocks reached 600, the local deformation caused by the thermal expansion mismatch caused the heterolattices in the joint to rotate toward the corners. During deformation, the formation of sub-grains is accompanied by increasing misorientation, accumulation of plastic slip in the strained local area, and activation of the slip system. After that, the stress-strain distribution of SAC305 solder joints during thermal shock was studied using the multi-physics coupling model, and the Coffin-Manson life model was used to simulate the number of failure cycles of solder joints after thermal shock. It is found that for a single solder joint, the number of failure cycles of the solder joints with the upper and lower parts in contact with other materials is basically 600–700 times. The work in this paper provides new insights into the further study of the early stages of grain orientation, microstructural deformation and the accumulation of stored energy associated with these deformations, providing support for a more in-depth study of recrystallization and crack propagation phenomena during thermal shock.