Study on the metallurgical reaction law and mechanism of the Ni-xCu alloys/pure Sn solid-liquid interface

In this study, Ni-xCu alloy substrates/pure Sn soldering joints were prepared, and the metallurgical reaction law and mechanism of the Ni-xCu/Sn solid-liquid interface were studied based on electron probe microanalyzer (EPMA) and electron backscatter diffraction (EBSD). Results showed that with the increase of Cu content in the Ni-xCu alloys, the reactants at the Ni-xCu/Sn interface changed from (Ni,Cu)3Sn4 single phase (x ≤ 40 wt%) to (Ni,Cu)3Sn4 and (Cu,Ni)6Sn5 two phases (50 wt% ≤ x ≤ 60 wt%), and then transformed into (Cu,Ni)6Sn5 single phase (70 wt% ≤ x). Correspondingly, the thickness of the intermetallic compound (IMC) layer presented four stages: decreased slowly, increased slightly, increased significantly and decreased sharply. The evolution mechanism of the phase structure was clarified according to the critical Cu concentration theory for (Cu,Ni)6Sn5 phase growth. In addition, the evolution mechanism of the IMC layer thickness was explained based on the studies of (Ni,Cu)3Sn4 growth thermodynamics and (Cu,Ni)6Sn5 lattice antiphase boundary array.