Influence of Temperature on Electroless Copper Deposition from Formaldehyde-Containing Solutions Using 2-Hydroxy-1,2,3-Propanetricarboxylic Acid As Cu(II) Ligand
The substrate was a smooth Pt sheet (1´1 cm) electroplated with Cu for 20 min from acid copper solution (1.0 mol l-1 CuSO4 + 0.5 mol l-1 H2SO4) at 1.5 A dm-2. Before the electroless plating the electroplated substrate was activated for 30 s in acid PdCl2 solution (1 g l-1). The main electroless copper plating experiments were carried out for 30 or 60 min. in 50 ml of the solution containing (mol l-1): CuSO4×5H2O – 0.05; citrate – 0.3; formaldehyde – 0.15.
Our studies were carried out in electroless plating solutions at pH 12.0 – 13.0 and 10 – 30 °C temperature. It was found that the autocatalytic reduction of Cu(II) by formaldehyde from Cu(II)-citrate solutions containing begins at pH above 12 and accelerates with a further increase in pH and temperature. The thickness of the compact copper coatings obtained under optimal operating conditions in 1 h can reach ca. 3 μm. From Cu(II)-citrate solutions deposited copper coatings real surface areas (Rf) vary widely, i. e. from ca. 2.5 up to 15.0. The maximum Rf values were obtained at pH 12.5 solution at 20 °C temperature. Results were compared with those for systems operating with other copper (II) ligands.