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

During a barrel bath electroplating process, it is difficult to determine the current density relevant to metal deposition alone and in this connection, to provide 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 current density expended on metal deposit. The value of the current efficiency in this case may be determined experimentally in the bath, and we can provide the required metal deposit weight (or average thickness) with high accuracy. Between the plating pulses, when the bath current is zero, one can measure the value of the overpotential near the cathode and store it. During the next plating pulse, one can provide an overpotential equal to the reference. 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 error of the metal deposit weight required was less than one third of the error of a system with an up-dated ampere-minute meter.