Influence of minute amount of elements Bi, Ag and In on surface tension and soldering process performance of tin–lead based solders

Abstract

A new method of measuring surface tension of liquid alloy solders, based on the interference principle between laser wave and liquid surface tension stationary wave, was employed to characterize the surface-active effect of some elements which can remarkably reduce the surface tension of liquid solders. The focus was placed on investigating the influence of minute amounts of elemental bismuth (Bi), silver (Ag) and indium (In) on surface tension and soldering process performance of tin–lead (Sn–Pb) based solders. The dependences of the surface tension of Sn–Pb solders vs. weight percentage of elements Bi, Ag and In in the solders were investigated. The experimental results showed that elements Bi and In have a strong effect on reduction of the surface tension of solders with the minute addition amount of 0.8–1.0 wt %, and the effect of element Ag is relatively weak. However, Ag has the strongest effectiveness on improving the wettability of the solders due to the comprehensive excellent function of reducing both the surface tension of liquid solders and the interface tension between liquid solder and solid base metal.