Influence of Chloride Ion in Acid Tin Methanesulphonate Electrolytes

SUMMARY

The effects of trace amounts (<500 mg l⁻¹) of chloride ions in acid tin methanesulphonate plating solutions are presented. Thermodynamic calculations show the main species in the stannous methanesulphonate electrolytes is stannous ion and soluble complexes of Sn(II)-Cl are present. Solubility calculations show no formation of an insoluble Sn(II)-Cl complex. Electrochemical studies reveal the role of chloride ion is significant in inhibiting stannous reduction in low current density areas and only at very high Cl⁻ concentrations where the current is kinetically controlled. At typical plating current densities of about 20 mA cm⁻² to 40 mA cm⁻², the current is under diffusion control and commercial plating lines should not expect any difficulties from trace amounts of chloride in the electrolyte during tin plating.

Keywords:

• tin
• methanesulphonic acid
• chloride
• plating