Accelerating effect of ammonia on electroless copper deposition in alkaline formaldehyde-containing solutions

The influence of ammonia on autocatalytic reduction of Cu(II) by formaldehyde (electroless copper plating) in solution containing Cu(II)–EDTA complex and additives (Na diethyldithiocarbamate and K4Fe(CN)6), was studied. Small additions of ammonia (1–3 mM) accelerated effectively the copper deposition at 20–30 °C by a factor of 2–4. In presence of ammonia copper layers of a higher real surface area (roughness factor Rf reached 22) and high electrocatalytic activity in anodic formaldehyde oxidation reaction were formed. The accelerating action of ammonia is explained by assuming that the copper surface of high catalytic activity forms at cathodic reduction of a mixed Cu(II) complex with EDTA and ammonia, and the liberated ammonia molecules participate again in the mixed complex formation at the copper surface.