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Plating occurring under the masking

2004

Hi

We have a rhodium and copper plating workshop. We do Rho.and copper plating on gold plated bangles (base metal brass) by using stop-off lacquer. My problem is that sometimes even if we take great care, plating reaches under the masking. I want to know what care should we take to prevent it and secondly I want to know reasons behind it.

Thank you for reading my question.

HITESH SONI
plating shop - Mumbai, Maharashtra, India

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For electroplating to occur, the electrolyte must get between the mask and the working electrode. This can only occur if the mask debonds from the working electrode surface. I suspect that you are using a mask that is incompatible with the plating solutions and it is starting to be stripped along the interface between the mask and the substrate.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2004

I have non technical opinions. Some maskants are made with a poor adhesion to the substrate to allow better removal after plating. Peelable is the prime example, but I found different capabilities of the couple dozen maskants that I have tried over the years. Next problem is most are at least somewhat vinyl based (or similar) which has a coefficient of thermal expansion that is about 10 times that of the substrate which will cause delamination tendencies on OD's. Quite possibly the largest cause is the trimming of the mask which is done by humans. Dull blades, bad angles, rushing and just sloppy work will have tiny amounts of the edge with lifting and or puckering. Gas formation further pushes the mask away which allows it to become worse- IE: a snowball curve in the bad direction.

James Watts
- Navarre, Florida
2004

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2004

Try using beewax to fill into trimmed edges.

Good luck

Khair Shishani
aircraft maintenance - Al Ain, UAE

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