Measurement and prediction of contact angles of Pb-free Sn-Ag solder alloys on Cu substrate

The contact angle (Theta) of molten Sn and Sn-Ag alloys (0.5, 1.5, 3.5, 6 wt.% Ag) on Cu substrates have been studied by using sessile drop method at various temperatures (230, 250, 275 and 300 degrees C). Experimental results showed that additions of Ag to Sn resulted in a continuous decrease in the Theta up to 3.5 wt.% above which the Theta value was increased. Increasing alloy temperature also decreased the Theta proportionally. Experimental results revealed that a correlation between the Theta, alloy composition and the alloy temperature exists which yielded an empirical model to predict the Theta at a given Ag content and temperature for a given Sn-Ag alloy. The empirical model predicts the Theta reasonably well with the present work and the other published works.