| Popis: |
The industrial electroless copper plating solutions containing formaldehyde as reducing agent are known from the middle of the last century and are widespread in the practice up to now. They are widely used in electronics for deposition of metallic copper layers on semiconductors or dielectrics (silicon wafers, resins etc.). Since such kind solutions are alkaline (formaldehyde is strong enough reducing agent for Cu(II) only in alkaline solutions), ligands are needed for preventimg of formation of Cu(OH)2 precipitate and binding Cu(II) into complexes Ethylenediaminetetraacetic acid (EDTA) is one of the most widely used ligand in alkaline electroless copper plating baths due to its perfect chelating properties. The possible solution equilibria in alkaline Cu(II)-EDTA-formaldehyde solutions are discussed in details. The data on use of EDTA in electroless copper plating as a Cu(II) ligand are enough wide-ranging, but, it is worth noting that practically all data are obtained at room or higher temperature. Therefore in this work copper coatings were deposited from alkaline formaldehyde-containing solutions, using EDTA as Cu(II) ligand at temperatures, mainly lower than room temperature. The experiments were carried out in electroless plating solutions at pH 12.0 - 13.0 and 5 - 30 °C temperature during 0.5 and 1h (Fig. 1). The thickness of the compact copper coatings obtained under optimal operating conditions in 1 h can reach ca. 4 μm, depending on the pH and temperature. The maximum values of plating rate are reaching at pH 12.5 at all investigated temperatures. The real surface areas (R f) of deposited copper coatings vary widely, i. e. from ca. 3.1 up to 39.3. The maximum R f values were obtained at pH 12.0 for investigated temperatures. The anodic formaldehyde oxidation measurements were carried out in formaldehyde solution at pH 12.5. It was found, that the rate of formaldehyde anodic oxidation depends on conditions of the formation of copper coatings – the highest rate of HCHO oxidation was determined on the surface’s electrolessly obtained at 5 °C and pH 13.0. Acknowledgment This research was funded by a Grant (No. LAT-12/2016) from the Research Council of Lithuania. |
