The current efficiency is an important matter in plating shops; that is, the relation between the amount of deposited metal and plating time or consumption of electric power, etc. at cathode and the relation between the amount of dissolved metal and maintenance of bath composition at anode. However, there have been few reports on current efficiency at cathode or anode of copper cyanide plating baths. The author determined the current efficiency at anode or cathode in the baths by changing the plating conditions such as concentrations of primary chemicals, electrolytic conditions, and additives.
The results were summarized as follows.
(1) Increase of copper concentration and decrease of free cyanide concentration improved the cathode efficiency, but concentrations of alkali metal carbonate and hydroxide had little effects.
(2) The cathode efficiency was remarkably improved at high temperature and with air agitation, but it decreased at high cathode current density; and little effects were given by employing PR current.
(3) Most additives had little effects on the cathode efficiency. However, the addition of compounds containing sulfur and having good effects on brightness, such as thiosulfate, thiocyanide, etc. improved the cathode efficiency.
(4) Contrary to the cathode, at anode, increase of concentration of both copper and free cyanide improved anode efficiency and also good effects were given at high temperature, with air agitation, and by employing PR current.
(5) As to additives; addition of compounds containing sulfur also had good effects on the anode efficiency as the same as at the cathode.
(6) As to anode materials; electrolytic copper showed better results for improving the anode efficiency as compared with rolled copper and phosphor copper.
(7) As the results mentioned above, it may be suggested that the cathode efficiency is mainly controlled by concentration of cuprons ion near the cathode surface, and the anode efficiency is mainly controlled by passive film produced on the anode surface.