Wetting behavior and mechanical properties of Sn-10Sb solder/Ni-plated Cu system with different surface structures

The Sn-10Sb alloy is a high-temperature lead-free solder for soldering with Cu substrates. It often causes brittle solder joints and poor reliability due to the generation of an over-thick interfacial layer. Adding Ni plating to Cu substrates can suppress the generation of an excessively thick interfacial layer. This paper investigated the wettability and bonding strength of two different surface structures of Ni-plated Cu substrates with Sn-10Sb solder. Sn-10Sb solder exhibited a contact angle of 69 degrees on the rough Ni-plated Cu substrate and 80 degrees on the smooth one. TEM and XPS analyses demonstrated that the interfacial reaction product between the Ni-plated Cu substrate and the solder was (Cu, Ni)6Sn5. The finer grains on the smooth Ni-plated surface inhibit the diffusion of Cu atoms into the solder and the slower the interfacial reaction rate, which is more conducive to the generation of stable (Cu, Ni)6Sn5 phase. Therefore, the bonding strength ratio between the Ni-plated Cu substrate with a smooth surface and the solder is better.