A Study on Wetting by Solders by Surface Tension Methods (Report 1)

Equilibrium Wetting

Abstract

Important factors in testing methods of quantitatively evaluating the wettability of a soldering system are discussed. It is shown that adhesion tension obtained directly by the surface tension method is a basic important factor governing wetting phenomena, and that the wetting behaviour may be interpreted from various points of view such as spreading or penetration characteristics of the soldering system. Experimental results obtained by surface tension methods on the equilibrium wetting of copper by tin-lead solders with rosin flux are described. These give an explanation of the discrepancies between the results of area-of-spread and capillary-penetration tests and give an insight into the slight difference between the results of area-of-spread tests and the practical assessments of soldering performance. It is found that adhesion tension exerts dominant influences on practical soldering, and the surface tension method can be expected to be useful for the quantitative evaluation of actual solderability.