Solderable electrogalvanized steels have been developed as alternatives to Sn and Pb-Sn steels. This paper reports the effects of plating solution additives on solderabilitiy-specifically solder spreadability, solder wettability measured by Meniscograph and solder peeling strength.
Various additives, including buffer agents, alloying additives, surfactants, brighteners and impurities that might be expected to enter during the plating process, were studied.
Additives that were codeposited with or contained in the Zn layers influenced not only their appearance and crystalline structure, but also their solderability. The addition of Mo and Cr codeposited as oxides, and of brighteners such as gelatine and acrylamide, decreased solderability greatly. It was found that solder wettability was the most sensitive property to the presence of additives, and codeposition of Fe, Ni and Co tended to decrease wettability.
It is inferred that the decrease in solderability due to the additives is caused not by change in the crystalline structure of the Zn layers, but rather by the additive elements and oxides codeposited or included therein.