Wetting kinetics of eutectic lead and lead-free solders: Spreading over Cu surface

Wetting kinetics of Sn, eutectic, Sn-Ag, euteotic Sn-Cu, and eutectic, Pb-Sn was studied using a real time in situ monitoring of the triple line movement, facilitated by a hot-stage microscopy system under a controlled atmosphere. A significantly different kinetics of lead vs. lead-free solders is documented. In case of the eutectic lead solder, four characteristic spreading stages were identified. Spreading of lead-free solders features two stages with a sharp change of the spreading rate at the early stages of rather insignificant spreading. SEM and EDX analysis of the re-solidified solder surface within a halo region is discussed.