Anisotropic copper etching with monoethanolamine-complexed cupric ion solutions

Monoethanolamine (MEA)-complexed cupric ion solution was used as a non-ammoniacal solution for copper etching on printed circuit boards (PCB). The copper dissolution behaviour of this MEA-complexed cupric solution containing 1 M CuCl₂ and 3.3 to 10 M MEA was studied by the potentiodynamic method at various temperatures (25–55 °C) and pH values (10–6.5). The effects of these factors on dissolution rate and etching factor of the copper patterns of PCBs were discussed. It was found that the highest corrosion current density (i_corr) was obtained with MEA concentration at about 5 M. Activation energies (E_a) of MEA-complexed cupric solutions were measured and the heat of adsorption (H_ads), which accounts for the chemisorption of the MEA ligands on the copper surface was calculated. H_ads was found to increase with solution containing excess MEA ([MEA] > 5 M), indicating the inhibition behaviour of MEA. Hence with lower pH, i_corr increased because the concentration of MEA ligands decreased due to acid reaction. The etching factor of copper patterns of PCBs with 75 m/75 m, line/space (L/S), were also tested by spray etching method. A high etching factor can be achieved for etchants containing high MEA concentration, which means MEA affects the etching factor since the inhibitive property of MEA reduces the undercut. Although the etching rate of MEA-complexed cupric etchant is still much lower than the ammoniacal etchant, the etching factor of the forward etchant (>3) is better than the latter (<2).