Abstract: Spent ferric chloride etching compositions are regenerated by electrolysis which includes introducing spent ferric chloride etching composition containing total iron content substantially equal to the original total iron content of fresh etching composition into the anode compartment of an electrolysis cell that contains an anode compartment, a cathode compartment, and an anion-exchange membrane separating the compartments, and applying voltage of +0.6 to +1.5 volts versus a saturated calomel electrode to the anode.

Abstract: Substantially nonconductive or semiconductive surfaces of through holes can be electroplated directly, without an intervening non-electrolytic metallization, by a stepwise process which includes the application to the through holes of a polyelectrolyte surfactant in solution in combination with the application of a conductive metal containing material.

Abstract: A rotating disk electrode system operates at constant speed in a solution whose metal ion concentration is held constant at multiple concentrations within a range of concentration. The current at the working electrode is recorded, while the potential at the working electrode is swept at a predetermined rate for each of the concentration values. The diffusion limiting current is determined for each of the concentration values. Then the rotating disk electrode system is operated continuously in a metal plating bath whose metal ion concentration can vary. A voltage applied to the working electrode produces a current at the electrode whose magnitude is compared to the values of the previous calibration to determine the current metal ion concentration. Alternatively, a rotating disk electrode system is operated over a range of speeds in a solution whose ion concentration is held constant over a range of concentration.