Suppressing the growth of Cu–Sn intermetallic compounds in Ni/Sn–Ag–Cu/Cu–Zn solder joints during thermal aging

This study aims to investigate the interfacial reactions and cross-interaction of Ni/Sn–3.0Ag–0.5Cu/Cu–xZn (Ni/SAC/Cu–xZn; x = 0, 15, and 30 wt.%) solder joints. In comparison with the Ni/SAC/Cu solder joint, Ni/SAC/Cu–15Zn and Ni/SAC/Cu–30Zn solder joints revealed thinner Cu6Sn5-based intermetallic compounds (IMCs) at both Ni/SAC and SAC/Cu–Zn interfaces after aging at 150 °C for 40 days. (Cu,Ni)6(Sn,Zn)5/(Cu,Ni)6Sn5 dual-phase formed at the Ni side, while (Cu,Ni)6(Sn,Zn)5 single-phase at the Cu–Zn side. Interestingly, the interfacial IMCs grew very slowly, and no void formed in these Zn-contained solder joints during the heating process. Also, the dissolved Zn in the solder alloy reduced the elemental cross-interaction between Ni and Cu–Zn substrates. The noticeable thermal stability of Ni/SAC/Cu–Zn solder joints is attributed to the Zn redistribution retarding the reaction of Ni, Cu and Sn. Phase formation and IMCs suppression mechanisms in Ni/SAC/Cu–Zn solder joints were probed and discussed.