Effects of multiple reflows on intermetallic morphology and shear strength of SnAgCu–xNi composite solder joints on electrolytic Ni/Au metallized substrate

The present work prepared composite lead free solders by adding 0.5, 1 and 2 wt.% of dendrite Ni micro-particles to Sn3.8Ag0.7Cu solder paste. Melting behaviors of composite solders were determined by differential scanning calorimeter (DSC). The wetting ability was evaluated with the spread area on Ni/Au finished Cu pad. The interface microstructure, morphology and shear strength were examined for composite solder joints on the electrolytic Ni/Au metallized Cu substrate with one, two, four, and six reflows, respectively. It was found that the intermetallic compound (IMC) shifted from the needle-like (CuNi)6Sn5 on the non-composite joint to dual layers of facet-like (CuNi)6Sn5 and boomerang shape (NiCu)3Sn4 with 0.5 wt.% Ni addition, and only boomerang shape (NiCu)3Sn4 was formed at the interface between the composite solder and Ni layer when Ni addition exceeded 1 wt.%. The thickness of IMC increased with the increasing number of reflows. Regardless of the number of reflows, the shear strength of composite solder joints showed increased trend as Ni content increased. The fracture of all joints happened in the solder bulk, which revealed that the failure was ductile.