Bending Strength and Color of Electroless Copper from Baths Containing Dipyridyl

For the purpose of optimizing autocatalytic electroless plating conditions for improved bend strength and appearance of copper coatings, experiments on 10 mu m copper foils at various 2,2'-dipyridyl amounts and bath temperatures were performed. It was found that at < =40 deg C dipyridyl additions do not improve the coating bend strength and the color turns blue. At > =70 deg C, the optimum range for commercial purposes, a dramatic improvement in bend strength is observed and the coating acquires copper color and glossy surface. The transition range is 50 deg C to 60 deg C. This behavior is associated with dipyridyl adsorption on the substrate. The baseline plating bath included, in mol/L, 0.03 CuSO sub 4 mult5H sub 2 O, 0.036 EDTA, 0.08 HCHO, and had a pH of 12.0; the amount of dipyridyl was varied from 25 to 500 mg/L.