Role of titanium on the reactive spreading of lead-free solders on alumina

The wetting of Sn3Ag-based alloys on Al2O3 has been studied using the sessile-drop configuration. Small additions of Ti decrease the contact angle of Sn3Ag alloys on alumina from 115 degrees to 23 degrees. Adsorption of Ti-species at the solid-liquid interface prior to reaction is the driving force for the observed decrease in contact angle, and the spreading kinetics is controlled by the kinetics of Ti dissolution into the molten alloy. The addition of Ti increases the transport rates at the solid-liquid interface, resulting in the formation of triple-line ridges that pin the liquid front and promote a wide variability in the final contact angles.