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

摘要

The dissolution process of nickel in liquid Pb-free 87.5 percent Sn-7.5 percent Bi-3 percent In-1 percent Zn-1 percent Sb and 80 percent Sn-15 percent Bi-3 percent In-1 percent Zn-1 percent Sb soldering alloys has been investigated by the rotating disc technique at 250-450 deg C. The temperature dependence of the nickel solubility in soldering alloys obeys a relation of the Arrhenius type c_s = 4.94 x 10~2 exp(-39500/RT) percent for the former alloy and c_s = 4.19 x 10~2 exp(-40200/RT) percent 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) x 10~(-5) ms~(-1) at disc rotational speeds of 6.45-82.4 rad s~(-1). Appropriate diffusion coefficients vary from 0.16 x 10~(-9) to 2.02 x 10~(-9) m~2 s~(-1). With both alloys, the Ni_3Sn_4 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 Ni_3Sn_4 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 percent.