The Solderability of Some Tin, Tin Alloy and Other Metallic Coatings

SYNOPSIS

The solderability of various coatings of tin, of alloys of tin with lead, zinc, cadmium, and of cadmium and silver has been compared. A spread-of-drop type test was employed which was thought to give the best assessment of solderability of surfaces. For most types of coating, the influence of coating thickness, basis metal, undercoat layers, and after-treatment was studied, and some specimens were stored for periods up to two years to examine the effect of storage on solderability. Mot-dipped tin or electroplated tin coatings of 0·0003 in. thickness or more were found to be superior and least influenced by basis metal, undercoat or storage. There seemed to be no advantage in using tin alloy coatings if solderability is the only criterion. Coatings on steel or over a nickel undercoat were not appreciably affected by storage whereas coatings on copper or over a copper underlayer slowly decreased in solderability especially at 50°C resulting from formation of inter-metallic compound and consequent loss of free tin. This deterioration was only serious with coatings of less than 0·0003 in. thickness. Soldering difficulties with tin coated brass, said to be encountered in practice, were not found in the present tests. General recommendations are made from the results of the investigation for achieving high initial solderability and retainment of solderability during storage.