Abstract
Steels electroplated with Pb-Sn alloys are generally used as a solderable outer package materials for electrical machinery. Solderable electrogalvanized steels have been developed as a replacement of such steels.
This paper reports various post-treatments for electrogalvanized steel that resulted in both good solderability and good corrosion resistance, and the soldering mechanism is discussed. A large number of post-treatment solutions containing surfactants, waxes and corrosion inhibitors were prepared and coated on the steel. The addition of a styrene-maleic acid copolymer and a wax to a post-treatment solution that contained a phosphoric acid ester and CrO3 increased corrosion resistance without decreasing solderability.
In terms of the soldering mechanism, it is assumed that the Zn layer elutes into the soldering bath so that while small amount of zinc remains in the layer, the major portion is concentrated on the solder surface.
