Interfacial reactions between Cu and SnAgCu solder doped with minor Ni

•Effects of minor Ni addition on SnAgCu/Cu interfacial reactions are investigated.•Minor Ni addition shows strong effects.•Minor Ni addition significantly reduces the Cu6Sn5 grain size.•Minor Ni addition enhances the Cu6Sn5 growth but inhibits Cu3Sn. The interfacial reactions between Cu and SnAgCu-based solders were investigated. Two types of SnAgCu-based solders were used, one was Sn–1.0Ag–0.5Cu (SAC105) and the other was Sn–1.2Ag–0.5Cu–0.05Ni (LF35), where the composition was in wt.%. The addition of Ni in the SnAgCu-based solder was found to have significant effects on the morphological evolution and growth of the Cu6Sn5 and Cu3Sn phases formed at the solder/Cu interfaces. At the Ni-added LF35/Cu interface after liquid/solid reaction at 260°C, the Cu6Sn5 phase presented a microstructure with a much smaller grain size. During subsequent solid/solid reaction at 150 and 200°C, the growth of the Cu6Sn5 phase was significantly enhanced at the LF35/Cu interface but that of the Cu3Sn phase was inhibited. A potential mechanism was proposed to explain the effects of Ni addition on the solder/Cu interfacial reactions.