Interfacial interaction of solid nickel with liquid Pb-free Sn–Bi–In–Zn–Sb soldering alloys

The dissolution process of nickel in liquid Pb-free 87.5% Sn–7.5% Bi–3% In–1% Zn–1% Sb and 80% Sn–15% Bi–3% In–1% Zn–1% Sb soldering alloys has been investigated by the rotating disc technique at 250–450 °C. The temperature dependence of the nickel solubility in soldering alloys obeys a relation of the Arrhenius type cs = 4.94 × 102 exp(−39500/RT)% for the former alloy and cs = 4.19 × 102 exp(−40200/RT)% for the latter, where R is in J mol−1 K−1 (8.314 J mol−1 K−1) and T is in K. Whereas the solubility values differ considerably, the dissolution rate constants are rather close for these alloys and fall in the range (1–9) × 10−5 m s−1 at disc rotational speeds of 6.45–82.4 rad s−1. Appropriate diffusion coefficients vary from 0.16 × 10−9 to 2.02 × 10−9 m2 s−1. With both alloys, the Ni3Sn4 intermetallic layer is formed at the interface of nickel and the saturated or undersaturated melt at dipping times of 300–2400 s. The other Ni–Sn intermetallic compounds are found to be missing. A simple mathematical equation is proposed to evaluate the Ni3Sn4 layer thickness in the case of undersaturated melts. The tensile strength of the nickel-to-alloy joints is 94–102 MPa, with the relative elongation being 2.0–2.5%.