ELECTRODEPOSITION OF BRIGHT TIN FROM NEUTRAL GLUCONATE BATHS

The mechanism of the action of additives on electrodeposition of bright tin from neutral gluconate baths was studied by means of a-c impedance measurements on the electrode surface. The double layer capacitance and the charge transfer resistance were obtained f rom impedance diagrams for additive-free, PEG-containing and PEG-formaldehyde-containing baths. By addition of formaldehyde to the PEG-containing bath, the polarization curve shifted to a noble potential, increased the double layer capacitance, and decreased the charge transfer resistance. In the bright tin plating from gluconate baths, formaldehyde was found to have a great effect on the surface morphology of tin deposits in the presence of PEG.