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

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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) 3 Sn 4 single phase (x ≤ 40 wt%) to (Ni,Cu) 3 Sn 4 and (Cu,Ni) 6 Sn 5 two phases (50 wt% ≤ x ≤ 60 wt%), and then transformed into (Cu,Ni) 6 Sn 5 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) 6 Sn 5 phase growth. In addition, the evolution mechanism of the IMC layer thickness was explained based on the studies of (Ni,Cu) 3 Sn 4 growth thermodynamics and (Cu,Ni) 6 Sn 5 lattice antiphase boundary array.