Wettability of Sn-Zn, Sn-Ag-Cu and Sn-Bi-Cu alloys on copper substrates

Abstract

The wettability of Sn9mass% Zn and Sn3mass% Ag0.5mass% Cu eutectic alloys and the new lead-free alloys Sn-17mass% Bi-0.5mass% Cu and Sn-30mass% Bi-0.5mass% Cu on a Cu substrate has been investigated by the sessile drop method in Ar atmosphere as a function of time and temperature. The wetting time for Sn-Bi-Cu alloys is much longer than that for Sn-3mass% Ag-0.5mass% Cu eutectic alloy at their liquidus or eutectic temperature. However, the Sn-9mass% Zn alloy has poor wettability on a Cu substrate since Zn may be oxidized to ZnO, resulting in ZnO covering the surface of the droplet. The contact angles of the ternary alloys on a Cu substrate do not decrease monotonically with increasing temperature but do change with time. The wettability on a Cu substrate increases in the order Sn-9mass% Zn, Sn-3mass% Ag-0.5mass% Cu, Sn-17mass% Bi-0.5mass% Cu, Sn-30mass% Bi-0.5mass% Cu, as indicated by their contact angles of 115.8, 49.6, 37.6 and 27.1°, respectively, at 523 K. The addition of Bi clearly greatly improves the wettability of the alloys. © 2012 The Japan Institute of Metals.