The purpose of this research is to examine the effect of plating current density as well as bath pH on the morphology and solderability of Pb-free pure Sn, plated from alkaline baths on copper substrates. Pure Sn coatings were prepared from a plating electrolyte composed of sodium stannate, sodium hydroxide, and sorbitol as an additive. The bath pH was changed from 9 to 14 and the plating current density was varied from 5-25 mA cm-2. The solderability of the Sn platings was estimated by spread ratio measurement according to JIS-Z-3197 standard. The obtained coatings were polycrystalline having a tetragonal β-Sn structure. The deposits were spongy and porous at pH ≈ 9-10. As the bath pH was increased from 11-13, the film growth improved, the best crystallinity of film was obtained at pH 13 and a current density of 15-20 mA cm-2. The coatings possess optimum microhardness and spreadability at a current density of 15 mA cm-2 and bath pH ∼12-13. It is shown that the optimization of current density and bath pH is necessary for the better strength and solderability of Sn coatings when alkaline baths are employed.
