RPP Plating (PRP, Reverse Pulse Plating)
Electrodeposition using a DC rectifier supplying current for a predetermined amount of time, and then reversing that current for a shorter time period, to lay down a finer grain structure, and reduce the porosity of the deposit.

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March 29, 2004

Description: pH is normally within the range 3.8 to 4.2, 4.0 being optimal for most stamperforming applications. In a normally functioning bath, the pH rises gradually and the galvanics technician/operator adds small amounts of sulfamic acid to compensate.

If, during the course of a plating cycle, the pH starts to go down (assuming no sulfamic acid has been just added), then this is the inducation of a problem with the chemistry of the bath.

Causes Anodes have become passive High pH for long periods (24 hours or more) Low boric acid level (<30g/l) Low flow

Solution Remove and clean anodes. First rinse thoroughly with DI water, and then soak in 25-30 g/l sulfamic acid solution for a minimum of 4 hours. Then rinse thoroughly with DI water and replace in cell. Dummy plate in the cell at 2.0 volts for 3-4 hours. This should activate the anodes Check pH frequently (daily or several times per day). Maintain the pH within the specified range by using sulfamic acid when the pH rises to 4.1-4.2. Make sure pH meters/probes are calibrate. Never reuse calibration buffer for more than 8 hours. Keep a spare pH probe on hand. Make additions of boric acid using the "boric bag" or "boric sock". Check filters and verify good flow in the cells by observing the turbulence and overflow in the cell.

Effects: Compressive stress which will lead to problems in the molding process. Continued operation at low pH can cause permanent damage to the electroforming bath.