Interfacial reactions between Sn–8Zn–3Bi– xNi lead-free solders and Cu substrate during isothermal aging

Abstract

In this work, interfacial reactions of Sn–8Zn–3Bi– xNi ( x = 0, 1) lead-free solders with Cu substrate and the growth of intermetallic compounds (IMCs) during isothermal aging were investigated. After soldering at 250 °C for 90 s, the Cu 5Zn 8 and CuZn 5 phases formed at the Sn–8Zn–3Bi/Cu interface and only the Cu 5Zn 8 phase was found at the interface of the solder with addition of Ni. During aging treatment at 150 °C for 100, 400 and 900 h, the CuZn 5 IMC at the Sn–8Zn–3Bi/Cu interface transformed to the Cu 5Zn 8 due to Cu atoms diffusing from Cu substrate. The Cu 5Zn 8 IMC layer at solder/Cu interfaces grew thicker with increasing the aging time and the growth was diffusion controlled. Moreover, the thickness of the IMC layer at the Sn–8Zn–3Bi/Cu interface was thicker than that at the Sn–8Zn–3Bi–1Ni/Cu interface. The reduction effect of Ni addition to the solder on the interfacial reaction might be attributed to the formation of the Ni 5Zn 21 IMC in the solder bulk, which effectively suppressed the diffusion of Zn atoms to the interface to react with Cu.