Grain morphology evolution and mechanical strength change of intermetallic joints formed in Ni/Sn/Cu system with variety of transient liquid phase soldering temperatures

The grain morphology evolution and mechanical strength change of the intermetallic joints formed in a Ni/Sn/Cu system by the transient liquid phase (TLP) soldering at 260 °C, 300 °C and 340 °C were investigated. The grain morphology evolution of the (Cu, Ni)6Sn5 intermetallic compounds (IMCs) was highly correlated with the Ni concentration gradient across the joints and strongly affected by the soldering temperatures, which was analyzed in detail from the aspect of thermodynamics. The shear strengths of the three types of intermetallic joints were 49.8 MPa, 50.3 MPa and 42.7 MPa, respectively. The correlation between the grain morphology evolution and the mechanical strength change of the intermetallic joints was revealed.