Influence of Ultrasound vs Stirring on Electrolytic Silver Coating Distribution in Patterned Cavities

Improvement of electrolytic coating thickness distribution is a major economic issue, especially in complex shapes such as grooves or holes. An attractive possibility for influencing this distribution resides in the use of plating bath stirring by mechanical methods or by ultrasound. The latter leads to an increase in overall stirring of the medium by the combined action of convection flows and cavitation bubbles. This paper deals with the influence of agitation conditions, especially in forced convection conditions (mechanical or ultrasonic), on the thickness dispersion of a silver electrolytic coating inside a groove. It is interesting to note that an electrolytic movement allows improvement of thickness distribution by replenishing the interface in electroactive species. By placing at the same agitation level, i.e., at the same mass transfer conditions to allow comparison, it has been shown that use of low frequency ultrasound ensures the best homogeneity. Dispersion values at 20 kHz, evaluated on the basis of homogeneity criteria calculated with a dedicated software, are less than 5%, whereas they are close to 10% with high frequency ultrasound or with mechanical agitation. Comparable results have been obtained by operating a scale change in a larger volume tank.