Effect of cooling condition and Ag on the growth of intermetallic compounds in Sn-based solder joints

The intermetallic compound growth in Sn/Cu and Sn–3.5Ag/Cu solder joints undergoing cooling has been in-situ observed using synchrotron radiation X-ray imaging technique. The overall thickness of intermetallic compound attained during cooling condition is dependent on the rates of Cu precipitation or deposition from the bulk solder and Cu diffusion from grain boundary at interface. Although the net increase in IMC thickness contributed predominantly by deposition kinetics is greater for air cooling than in furnace cooling from the start temperature of 300∘C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$300\,^\circ \hbox {C}$$\end{document} for the first 20 min, the former solidifies before 30 min and the latter stays in liquid state for 1 h due to slower cooling rate and attains a bigger IMC of size about 14.5 μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu $$\end{document}m. In context of Sn–3.5Ag solders subjected to air cooling from 275 ∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^\circ $$\end{document}C, the presence of Ag contributes to the increment in overall IMC thickness during the cooling period. For the improvement in solder joints reliability, faster cooling rate and limiting the Ag content can be employed as the materials design and processing parameters.