Mechanism of Electroless Copper Plating from EDTA-Complex Bath

Polarization characteristics were investigated for electroless copper plating baths consisting of copper sulfate, EDTA, formaldehyde, glycine, potassium hexacyanoferrate (II) and triethanolamine. The effects of bath composition and convection on the electrode processes-oxidation of formaldehyde, deposition of copper and anodic dissolution of copper-were evaluated using a rotating copper disk as the working electrode. It was inferred that the rate of oxidation of formaldehyde was proportional to the amount of formaldehyde adsorbed in accord with the Langmuir isotherm. It was further suggested that hexacyanoferrate (II) was adsorbed in accord with the Langmuir isotherm for dissociation adsorption (n=2), retarding the above electrode processes. The effect of electrode rotation was significant only at high current densities where the diffusion of copper complex from/to the electrode was rate-determinating, while no substantial effect was found on local processes near the rest potential.