Effect of certain impurity elements on the Wetting properties of 600% tin-40% lead solders

Abstract

There is a lack of data and agreement on the effects of impurities on the wetting properties of tin-lead solders. There is some evidence that certain impurity elements may impair the wetting properties of these solders and this is of particular importance in the electronics industry where high-speed, mass-soldering processes are employed. The discrepancies that exist between various national specifications for solders illustrate the uncertainty on the levels of impurities that can be tolerated in solders. This paper describes an extensive programme of research into the effects of certain trace impurities and percentage additions of various elements on the wetting properties of 60Sn-40Pb solder on copper, brass, and mild steel. The effects of aluminium, antimony, arsenic, bismuth, cadmium, copper, phosphorus, sulphur, and zinc were studied. Well established solderability testing techniques, namely, area-of-spread and rotary-dip tests, were used to study the effects of these impurities. In addition, a certain number of tests were carried out on a ‘surface-tension balance’ solderability tester. From the results obtained, some tentative impurity limits are suggested which may be of particular importance for modern mass-soldering techniques.