Design Considerations for Electrodeposition onto a High Resistance Electroless Flash in a Continuous Plater

Abstract

The buildup of copper by electrodeposition onto a high resistance electroless flash has been studied in a roll‐to‐roll continuous plater employing copper fluoborate at ambient temperature. Input to the plater was circuit‐patterned polyimide tape having an initial deposit which ranged from 2.4 μin. electroless copper through 146 μin. electroless plus electroplated copper. Buildup of copper through one (or more) plating loops was traced by atomic absorption analysis of millimeter‐sized pattern sections cut from the tape; this analysis followed an abrupt interruption in steady‐state plating and a rapid ejection of the tape from the plater. By this technique, copper distributions along and across the tape were determined. Thickness buildups to 400 μin. at tape speeds of 2.3 and 3.1 ft/min are reported. The copper distributions have been used to compute maximum and average cathodic current densities, and , respectively, for selected plater configurations and input copper thicknesses. Significant asymmetries in local plating rate due to the high input tape resistance were observed and the ratio was as high as in some cases. Since excessive cathodic current densities can degrade performance of the plated product, the regulation of within definable limits is a critical aspect of plater design. A correlation of to input thickness of the electroless flash and to applied plating currents is presented and its implications with respect to plater design examined.