LAUSR

To enhance the effects of electroless Ni–P plating on inhibiting atom diffusion in Sn-58Bi joint systems, adding nano-sized metals into coating was regarded as an efficient method. Therefore, Cu nanoparticles were chosen as the additive in current study, and the interfacial microstructure evolution of solder joints by doping Cu nanoparticles into Ni(P) electroless plating were investigated. Experimental results revealed that growth rates of IMCs at the joint interface remarkably decreased with increasing content of Cu nanoparticles. In the Ni(P)–0.8 g/L Cu based joint, transformation from (Ni,Cu)3Sn4 to (Cu,Ni)6Sn5 occurred since more Cu atoms supplied by the coating participated in the interfacial reaction between solder and coating. Meantime, sizes of IMC grains at each isothermal aging stage decreased with increasing content of Cu nanoparticles, which could be attributed to introduction of potent nuclei. The IMC growth was mainly volume diffusion-controlled and followed parabolic laws. Diffusion coefficients were analyzed to be 1.18 × 10–2 μm2/h, 2.89 × 10–4 μm2/h and 2.56 × 10–4 μm2/h in Ni(P), Ni(P)–0.4 g/L Cu and Ni(P)–0.8 g/L Cu-based joint systems, respectively, suggesting that diffusion coefficient gradually decreased with increasing content of Cu nanoparticles.