PLATING OF COPPER IN TUBULAR HOLES WITH ROTATING SCREW ELECTRODES

Electrodeposition of copper into tubular electrodes using co-axial rotating screw counterelectrodes (RSEs) was investigated, and the results are compared with the periodic oscillatory technique commonly used in plating through-holes. Two length-to-diameter aspect ratios (ARs) of 4: 1 and 8: 1 and acid copper sulfate solutions with and without brightener were studied. The horizontal oscillatory mode (HOM) produced non-uniform deposits for both ARs, the addition of brightener being ineffective in minimizing high end-to-center deposit thickness ratios. The RSE mode provides enhanced mass transfer and reduced ohmic resistance in the hole, resulting in excellent thickness uniformity, especially with solutions containing brightener. With 4:1 AR holes, uniform deposits were obtained with a current density of 40 mA cm-2. However, a reduced current density of 10 mA cm-2 was required to produce the same uniformity in 8:1 AR holes with averaged end-to-center thickness ratios of 0.93:1.