Effect of Ag₃Sn on Fracture Behaviors of Sn-3.5Ag Lead-Free Solder during In Situ Tensile Test at Low Temperature

In situ tensile tests on Sn-3.5Ag lead-free solder were performed with different rates of 10 μm/s and 300 μm/s at − 198 °C liquid nitrogen temperature. Microstructure evolution and deformation behavior of Sn-3.5Ag solder were observed by optical metallographic microscopy. The morphological influence of the second-phase particles Ag₃Sn on fracture behaviors was investigated by scanning electron microscopy. The results showed that plastic deformation occurred at the low tensile rate, while no fracture toughness was observed at the high tensile rate. Several fracture modes were observed, including intergranular fracture and transgranular fracture. The morphology and distribution of the second-phase particles had a significant impact on the fracture behavior of solder. The long rod-shaped second-phase particles perpendicular to the tensile direction were difficult to fracture, while the parallel second-phase particles were broken into segments. The smaller second-phase particles barely deformed, and the voids nearby provided a favorable pathway for fracture.