Interfacial reaction of Ni/Sn-9Zn/Ni solder joint undergoing liquid-solid thermomigration

This study investigated the interfacial reaction of Ni/Sn-9Zn/Ni solder joints undergoing liquid-solid thermomigration by reflowing the solder joints on a hot plate. The simulated working temperature and temperature gradient across the liquid solder layer were about 240 °C and 976 °C/cm, respectively. Zn and Ni atoms were forced to migrate towards the cold end by temperature gradient, which resulted in the thickness of the interfacial IMCs at the cold end was larger than those at the hot end. After reflow for 60 min, the initial Ni₅Zn₂₁ IMC at the hot end was totally transformed into τ phase. However, in addition to the initial Ni₅Zn₂₁ IMC, a layer of τ phase formed at both Ni₅Zn₂₁/Ni and Ni₅Zn₂₁/solder interfaces at the cold end. The growth of the interfacial IMCs was reaction-controlled at the cold end and volume diffusion-controlled at the hot end.