| Abstract [eng] |
Electroless metal coating technique is one of the elegant ways of metal coating by controlling the temperature and pH of the plating bath in which there is no usage of electric current. The industrial electroless copper plating solution containing formaldehyde as reducing agent are known from the middle of the last century and are widespread in the practice up to now. However many chemical compounds used in such kind technological processes are hazardous for total environment, therefore the efforts are made to displace those substances with less hazardous or purely harmless compounds. Generally two classes of chemical compounds were proposed as EDTA alternative, namely alditols (polyhydroxylic alcohols) and hydroxypolycarboxylic acids. The aim of the work was to investigate peculiarities of formaldehyde containing alkaline electroless copper deposition systems using environment friendly hydroxycarboxylic acids as Cu(II) ligands. Two new Cu(II) ligands, namely citric acid and D-isomer of tartaric acid, were applied for the systems of electroless copper deposition. The results of the investigations show that the ligands mentioned can be successful applied in the processes of electroless copper deposition using formaldehyde as reducing agent. Citric acid (2-hydroxypropane-1,2,3-tricarboxylic acid) and different isomers of tartaric acid (2,3-dihydroxybutanedioic acid), namely L- and D-tartrate, and their racemic mixture DL-tartrate, forming sufficiently stable complexes with copper(II) ions in alkaline solutions, was found to be a suitable ligand for copper(II) chelating in alkaline (pH > 12) electroless copper deposition solutions. The thickness of the compact copper coatings obtained under optimal operating conditions in 1 h reaches ca. 3 mm. The plating solutions were stable and no signs of Cu(II) reduction in the bulk solution were observed. The anodic oxidation of HCHO on electrochemically and electrolessly deposited copper electrodes was investigated by means of cyclic voltammometry. The measurements of the mixed potential of copper electrode were performed in the course of electroless copper deposition. The results obtained were compared with the data obtained in the systems with other ligands. The possible equilibria in the solutions under investigation were discussed and specified. |
