Yu-chih Huang

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. FeSn 2 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 FeSn 2 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 FeSn 2 phase into the solder matrix is observed in the Sn-Cu/Fe couples, and is a potential contaminant source in wave soldering.

Size and substrate effects upon undercooling of Pb-free solders

The primary solidification phase is the principal factor for the degrees of undercooling. Easier nucleation results in smaller degrees of undercooling, and the tendency of nucleation is Ni 3 Sn 4 ≫Ag 3 Sn≫Cu 6 Sn 5 ≫β 3 B 2 ;-Sn. The substrate is also an important factor for undercooling. The tendency of nulceation is Ni 3 Sn 4 on Ni 3 Sn 4 ≫Ag 3 Sn on Ni 3 Sn 4 ≫Ag 3 Sn on Ag 3 Sn≈Cu 6 Sn 5 on Cu 6 Sn 5 ≫Ag 3 Sn on Cu 6 Sn 5 ≈Cu 6 Sn 5 on Ag 3 Sn. When the primary solidification phase and the substrates are the same, the degrees of undercooling could be different if the compositions of the melts are different. However, this compositional effect is not as significant when compared with the primary solidification phase and substrate factors. The relative orders of undercooling of solders remain the same for samples of different sizes, but the degrees of undercooling and their variations are more significant for smaller solders.