1997 Volume 15 Issue 4 Pages 681-687
A method to measure the surface tension of liquid solder alloys has been developed by the use of wetting balance. In principle, non-wetting Al2O3 rod was immersed into the molten solder bath under the fixed speed. The force acts on Al2O3 rod was measured and then the surface tension was calculated by analyzing the measured force. The theoretical model was based on the hypothesis that the meniscus configuration of molten solder gradually varies depending on the depth of rod and its radius, and also the configuration shows stable form when the depth exceeded the critical value. After exceeding the critical depth, the force increased in proportion to the depth of rod, therefore, the surface tension could be measured by analyzing the obtained force-time curve. As a result, the surface tension of 63Sn-37Pb solder (504 K, in air atmosphere) was 0.53 N/m ; the value is reduced by the use of soldering flux. The surface tension of Sn-Ag-Bi system lead-free solders have been also measured. Increasing of Bi content decreased the surface tension. The effect of flux on the reduction of surface tension is similar to that in 63Sn-37Pb solder.
