Preliminary Studies of Tin and Tin Rich Coatings as Electrical Contact Materials

The soaring price of gold has led the gold-using industries to search for alternative materials. Gold plating on electrical connectors and circuit boards has been commonplace, and in some cases, the only viable material. However in other cases its use is an unnecessary expense. Tin and tin alloy coatings have been used extensively in the electronics industry, particularly to confer solderability to the substrate, and many people have seen them as possible alternatives to gold plating in a number of connector applications. First the literature on the properties of tin and tin alloys pertaining to their use as contact materials is reviewed, including some information regarding contact resistance and the effects of atmospheric pollutants. Second, some of the basic theory regarding contact resistance are reviewed; and last, an experimental procedure devised to provide basic contact resistance and data on different tin-based coatings for different loads using conical, hemispherical, and chisel shaped indenters are described. The results of these measurements are reported and compared with gold-plated finishes.