Effect of Cu-Ni cross-solder interaction on liquid-solid interfacial reaction in Cu/Sn/Ni solder joint

The effect of Cu-Ni cross-solder interaction on liquid-solid interfacial reaction in Cu/Sn/Ni solder joint at 250°C was investigated. The results show that the Cu-Ni cross-solder interaction occurs after liquid-solid reaction for 10 min, the initial Cu6Sn5 and Ni3Sn4 form during immersing soldering at the Sn/Cu and Sn/Ni interfaces, and both transform into (Cu, Ni)6Sn5, their morphologies change from scallop shape to rod shape. With increasing reaction time, the interfacial IMCs remain as (Cu, Ni)6Sn5, while their morphologies become more uneven. The IMCs at the Sn/Cu and Sn/Ni interfaces grow thicker with increasing reaction time, and their growth indexes are 0.32 and 0.61, respectively. At the beginning of the liquid-solid reaction, the Sn/Cu interfacial IMC is thicker than the Sn/Ni interfacial IMC. However, after liquid-solid reaction for 2 h, the result reverses due to the Cu-Ni cross-solder interaction, and the thicknesses reach 15.78 and 23.44 μm after reaction for 6 h, respectively.