Effects of Sb addition on grain ripening growth at interface of Sn-Ag-Cu-xSb/Cu in wetting reactions

Four different solder alloys of Sn-3.5Ag-0.7Cu-xSb (x=0, 0.5, 1.0, and 2.0) were used to investigate the microstructure evolution, grain size distribution of intermetallic compound (IMC), and the relationship between copper atomic diffusion and channel width under different reflow time (t = 48, 240, 3600, and 7200s). Flux-driven ripening (FDR) theoretical model is adopted to analyze the grain ripening growth mechanism. Results show that the morphology of scallop-like Cu₆Sn₅ grains is affected by composition of the solder alloys and reflow time. The average size of the scallop-like Cu₆Sn₅ grains in Sb-free solder joints is 14.2μm for the reflow time of 7200s, while it decreases to 11.9μm in 1.0 wt.% Sb-containing solder joints. The scallop-like Cu₆Sn₅ morphology becomes more faceted when the amount of Sb increases to about 2.0 wt.%. The size distribution of scallop-like Cu₆Sn₅ grains is in good agreement with FDR theoretical model and the average radius of Cu₆Sn₅ grains is proportional to the cubic root of reflow time. The relationship between the diffusivity of copper element passing through channel and the channel width has been analyzed by FDR theoretical model. Results show that the diffusivity of copper atomic is lowest when the amount of Sb is about 1.0 wt. %.