An investigation was conducted into the chemical reaction in an interface layer consisting of three phases, which were metal, electrolyte, and air generated during zinc electroplating. The plating bath was a zinc sulfate solution of pH 4.0 and a SUS 304 metal rod that had had its surface oxidized in a 10 vol. % nitric acid solution was used as an electrode. The electrode, hung perpendicularly using an electronic balance, was partially immersed in the plating bath. The wetting behavior of the solution before electrolysis and the spreading wetting that occurred during zinc electroplating were evaluated in-situ as the variation of the loads using the electronic balance. The wetting of the SUS 304 electrode by the solution decreased significantly as a result of the oxidation of its surface by the nitric acid solution. On the other hand, the as-deposited zinc enhanced the wetting of the electrode surface and resulted in spreading wetting by the solution. The developing solution proceeded up along the sidewall of the SUS 304 electrode, reaching a height of about 1mm above the plating bath during zinc electroplating. Hydroxide ions were formed by the reduction of oxygen that occurred in the upper region of the wetting film, and zinc electroplating occurred preferentially in the lower region of the SUS 304 electrode close to the counter electrode. A white precipitation was formed spontaneously in the intermediate region of the thin film. This precipitate was zinc hydroxide produced by the reaction caused between hydroxide ions moving down from the upper side and zinc ions supplied up through the thin film from the plating bath.
Cracks are often formed in nickel-alloy plating by high tensile stress. Therefore, an accurate crack detection method is required. The method for detecting cracks in Ni-W plating film with electrochemical impedance spectroscopy (EIS) was studied in the present paper. The impedance of Ni-W plating film without cracks in 1M sulfuric acid solution shows two capacitive loops. The impedance of Ni-W plating film with cracks in 1M sulfuric acid solution shows also two capacitive loops. The capacitive loops of impedance of Ni-W plating film without crack were smaller than those of Ni-W plating film with cracks. Curve-fitting was performed for the impedance spectra by assuming equivalent circuits, and the calculated impedance spectra were in agreement with the experimental results. In those results, the charge transfer resistance and double-layer capacitance varied with the area of cracks in Ni-W plating film. It can be concluded that impedance analysis can detect cracks in Ni-W plating film.
A printed circuit board with a fine Cu pattern was fabricated by electroless plating and laser irradiation. A glass fiber-reinforced epoxy resin plate was immersed in a Pd2+ solution and a Cu layer was then deposited on the epoxy resin by Cu electroless plating. After Cu plating, the Cu deposited specimen was irradiated with a pulsed Nd-YAG laser through an iris diaphragm and a convex lens to remove the Cu layer locally in air or doubly distilled water. The width of the Cu removed area increased with increasing the laser power and with decreasing the scanning rate of the laser beam. When laser irradiation was performed in doubly distilled water, the Cu layer around the laser-irradiated area rolled up, resulting in the formation of less precise patterns. Fine Cu-pattern coils with 60 μm width and 20 μm intervals were fabricated on the epoxy resin by laser irradiation in air.