Effect of Cr additions on interfacial reaction between the Sn–Zn–Bi solder and Cu/electroplated Ni substrates

Intermetallic compounds (IMCs) growth on the Sn–8Zn–3Bi (–Cr) solder joints with Cu and electroplated Ni substrates was investigated after aging at 150 °C. It was found that the IMCs were the Cu5Zn8 and Ni5Zn21 at the solder/Cu and solder/Ni interface, respectively. The IMCs growth rate at the Sn–8Zn–3Bi–Cr/Cu and Ni interface was slower than that at Sn–8Zn–3Bi/Cu interface (about 1/2 times) and Sn–8Zn–3Bi/Ni interface (about 1/4 times) during aging. The reason may be that Cr reacts with Zn and forms the Sn–Zn–Cr phase which block the diffusion of Zn atom to the interface and slow down the IMCs growth rate.