Dissolution and interfacial reactions of Fe in molten Sn-Cu and Sn-Pb solders

Solder pots used in wave soldering are usually made using different kinds of steel. Dissolution and interfacial reactions of the Fe substrate in molten Sn-Pb and Sn-Cu solders are investigated in this study. FeSn₂ phase is formed in the Sn-0.7wt%Cu/Fe couples reacted at 250, 400, and 500 °C, as well as in the Sn-37wt%Pb/Fe couples reacted at 250 and 400 °C. The activation energies of formation are 123 and 121 kJ/mol in the Sn-Cu/Fe and Sn-Pb/Fe couples, respectively. FeSn phase is the reaction product in the Sn-37wt%Pb/Fe couples reacted 500 °C. The dissolution rates of Fe in the Sn-0.7wt%Cu melt are much higher than those in-the Sn-37wt%Pb melt. The FeSn₂ phase layer in the Sn-Cu/Fe couple is not as dense as that in the Sn-Pb/Fe couple and accounts for the very different dissolution rates. Detachment of the reaction FeSn₂ phase into the solder matrix is observed in the Sn-Cu/Fe couples, and is a potential contaminant source in wave soldering.