A novel method of controlling metal deposition during a pulse plating process

During a barrel bath electroplating process, it is difficult to determine t he current density relevant to metal deposition alone and in this connectio n, to pro,ide the required metal deposit weight (or average thickness) with a high degree of accuracy. Our investigations have shown that the constant value of the overpotential near the cathode yields the constant value of c urrent density expended on metal deposit. The value of the current efficien cy in this case may be determined experimentally in the bath, and we can pr ovide the required metal deposit weight (or average thickness) with high ac curacy. Between the plating pulses, when the bath current is zero, one can measure the value of the overpotential near the cathode and store it. Durin g the next plating pulse, one can provide an overpotential equal to the ref erence. A control system for metal deposit weight based on this method was designed and tested in a gold pulse plating process. The root-mean square e rror of the metal deposit weight required was less than one third of the er ror of a system with an up-dated ampere-minute meter.