Ni addition to Cu alloy affects the diffusion of Cu and Sn atoms, which in turn affects the growth of the Cu₃Sn.

A Ni-rich interfacial reaction layer ((Ni,Cu)₃Sn) about 600 nm in thickness was formed at the Cu-0.2%Ni/Cu₃Sn interface.

Thermodynamic analysis revealed that a diffusion path was from the Cu₃Sn to the Cu-0.2%Ni, by way of (Ni,Cu)₃Sn.

Calculation results are interpreted as the (Ni,Cu)₃Sn mitigates the effect of Ni on the diffusion driving force.