Effect of TiO2 additions on Sn-0.7Cu-0.05Ni lead-free composite solder

The effect of TiO2 addition on the microstructure, melting behavior, microhardness and interfacial reaction between Sn-0.7Cu-0.05Ni and a Cu-substrate were explored. Samples with various TiO2 percentages (0, 0.25, 0.5, 0.75 and 1.0 wt.%) were prepared using a microwave-assisted sintering powder metallurgy method. Microstructural analysis reveals that TiO2 was uniformly distributed along the grain boundary of the bulk solder. Differential scanning calorimetry (DSC) results showed a decrease in the undercooling while melting temperature of the solder slightly increase. The thickness of the interfacial intermetallic compounds of the solder joint was reduced with the addition of TiO2 particles. This thickness reduction indicates that the presence of a small amount of TiO2 particles is effective in suppressing the growth of the intermetallic compound layer. Small dimples on the fracture surface have revealed that the Sn-Cu-Ni composite solder exhibits typical ductile failure. Overall, the addition of TiO2 to Sn-0.7Cu-0.05Ni solder dramatically increases its shear strength and hardness and improves its wetting properties and fracture surface.