Evaluation of Joining Properties between Potential-Controlled Ni–Cu Alloy Plating Film and Pb-Free Solder

To improve the reliability of solder joint, Ni–Cu alloy plating films with three-dimensional structures were fabricated on Cu substrates via electroplating. By varying the plating potential, the morphology of the Ni–Cu alloy plating films was controlled, and their effect on solder joint microstructure and mechanical properties was investigated. Sn–5Sb lead-free solder was used to join the plated Cu substrates, followed by aging at 200°C for up to 100 h. Surface observations revealed that more negative plating potentials promoted the formation of larger and more numerous three-dimensional structures. Cross-sectional analysis showed that Cu–Ni–Sn and Cu–Sn reaction layers formed at the solder interface and thickened with aging. Shear test showed that the joint strength decreased after 25 h of aging and remained nearly constant thereafter. In addition, joints with Ni–Cu alloy plating exhibited lower shear strength than those without plating. Fractographic analysis showed that fracture initially occurred within the solder and Cu–Ni–Sn reaction layers, whereas prolonged aging induced fracture propagation through the solder, Cu–Ni–Sn, and Cu–Sn reaction layers.