Properties of silver-tin alloys obtained from pyrophosphate-cyanide electrolytes containing EDTA salts

Abstract

Silver-tin alloy coatings are electrodeposited from a newly developed EDTA containing cyanide-pyrophosphate electrolyte and some properties of the obtained coatings, such as microhardness, internal stress, abrasion resistance, plug-in forces and electrical contact resistance depending upon the applied current density or the tin content of the alloy, respectively, are investigated. The co-deposition of tin leads to the change of the tensile stress of pure silver coatings to compressive stress in the formed solid solution of the alloy and to almost stress free coatings at high current densities. The microhardness runs over a maximum at current densities, where the silver lattice is saturated with tin and the deposition of phase heterogeneous coatings starts. The abrasion resistance diminishes at increased tin content, and the changes of the electrical contact resistance are in the opposite direction. The measured plug-in forces show the lubricating properties of the alloy coatings.