Wetting Properties of Sn-Pb, Sn-Zn and Sn-Zn-Bi Lead-free Solders

Abstract. Three studies on Sn-40Pb, Sn-9Zn and Sn-8Zn-3Bi Pb-free solders were conducted. Spreading of the solders was investigated on 0.13 µm roughness Cu substrate at 250°C. Sn-40Pb has a contact angle of 6°, which is seven times better than Sn-9Zn and Sn-8Zn-3Bi solders. Wetting balance was used to study the wetting time, wetting force and surface tension at different temperatures using two different fluxes. For Sn-8Zn-3Bi solder, MHS (commercial name) flux gives higher wetting force and wetting time compared to HCI flux for increasing temperatures. The surface tension of Sn-40Pb solder decreases with increasing temperature whereas the surface tension of Sn-9Zn and Sn-8Zn-3Bi solders is not influenced by the temperature. However, the addition of 3% Bi reduces the surface tension of the Sn-Zn-Bi system. A study on the spreading of Sn-9Zn solder alloy on Cu with surface roughness between 0.33 and 1.53 µm was also conducted. Surface roughness below 0.62 µm does not contribute to the improvement of wetting but above 0.62 µm, there was an improvement in the contact angle and spreading area.