Thermal cycle reliability and creep behavior of nano-IMC mixed solder joints

Herein, the microstructure evolution, crack initiation and propagation, and β-Sn recrystallization behavior of nano-intermetallic compound (nano-IMC)-mixed solder joints were investigated during thermal cycles. Further, the influence of the nano-IMC on the creep characteristics of solder joints is discussed. Results showed that the IMC layer and Ag₃Sn coarsened with increasing thermal cycles. Under cyclic stress, crack initiation at the solder joint corner of the chip side propagated along the IMC layer with increasing thermal cycles. β-Sn grains recrystallized near the crack on the solder joints, and this phenomenon can be inhibited by introducing an appropriate amount of nano-IMC. However, when excessive IMC was added (SAC305 + 20 wt% Sn–10Cu), Cu₆Sn₅ particles accumulated and grew in the solder joint with increasing thermal cycles. Thus, the dislocation pinning effect was weakened, and β-Sn grains recrystallized under cyclic stress. Nanoindentation experiments demonstrate that the addition of nano-IMC reduces the stress sensitivity index as well as increase the stress index and creep resistance of the solder joints.