Effects of In and Ni Addition on Microstructure of Sn-58Bi
Solder Joint
In this study, the effect of adding 0.5 wt.% and 1 wt.% In and Ni to Sn-58Bi solder on intermetallic compound (IMC) layers at the interface and the microstructure of the solder alloys were investigated during reflow and thermal aging by scanning electron microscopy and electron probe micro-analysis. The results showed that the addition of minor elements was not effective in suppressing the IMC growth during the reflow; however, the addition of 0.5 wt.% In and Ni was effective in suppressing the IMC layer growth during thermal aging. The thickening kinetics of the total IMC layer was analyzed by plotting the mean thickness versus the aging time on log–log coordinates, and the results showed the transition point from grain boundary diffusion control to a volume diffusion control mechanism. The results also showed that the minor addition of In can significantly suppress the coarsening of the Bi phase.