Creep and thermomechanical fatigue properties of in situ Cu6Sn5 reinforced lead-free composite solder

In this research, a composite solder, which consisted of the Sn–3.5Ag eutectic solder matrix and Cu6Sn5 intermetallic compounds (IMCs) as reinforcements, was prepared by in situ method. Cu and Sn metallic particles were added into the molten Sn–3.5Ag eutectic solder to form Cu6Sn5 reinforcements in solder matrix. After rolling, the Cu6Sn5 IMCs are crushed into fine particles and distributed uniformly in the composite solder. The creep and thermomechanical fatigue (TMF) properties of the Sn–3.5Ag eutectic solder and its in situ Cu6Sn5 reinforced composite solder joints were successively investigated. The experimental results showed that the in situ Cu6Sn5 reinforced composite solder joint exhibited better steady-state creep strain rate, lesser TMF damages and higher residual shear strengths after different number of TMF cycles as compared to the Sn–3.5Ag eutectic solder joint. These indicated that the in situ Cu6Sn5 reinforced composite solder possessed excellent creep resistance and TMF properties. Besides, the fracture mode of the in situ Cu6Sn5 reinforced composite solder joint and the role of the in situ Cu6Sn5 reinforcing particles were analyzed.