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.