Fatigue and Shear Properties of Novel Lead-free Solder Joints with Low Melting Temperatures

The reliability of Sn–Ag–Cu (SAC)-based solder alloys has been extensively researched since the ban on lead in the electronics industry. Recently, solder alloys with the ability to reflow at lower temperatures have been gaining growing attention due to the reduced defects in complex assemblies. In this study, individual solder joints were tested using the Instron micromechanical testing system to investigate the shear and fatigue properties. Two new solder alloys (Sn–58Bi–0.5Sb–0.15Ni and Sn–42Bi–0.5Sb) with low melting temperatures were studied and compared to Sn–3.5Ag and Sn–3.0Ag–0.8Cu–3.0Bi. Electroless nickel immersion silver (ENIG) was the board surface finish for all solder alloys. Sn–3.5Ag solder alloy with an organic surface protection (OSP) surface finish was also tested for comparison. Three strain rates were selected for the shear tests. The shear strength of each solder alloy was measured. A constant strain rate was utilized for the cyclic fatigue tests. The fatigue life of each alloy at different stress amplitudes was measured. The results showed that Sn–3.0Ag–0.8Cu–3.0Bi demonstrated superior shear and fatigue properties but was more susceptible to brittle failure. For the Sn–3.5Ag solder alloy, the OSP surface provided better interfacial toughness than the ENIG surface finish.