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Pale parts after Ni/Sn electro plating

June 21, 2012

Q. We have found pale parts after Ni/Sn electroplating on racks. The paleness occurs mostly on one side of the parts closest to the Ni anode.

All parts are pale on all the racks with moderate variation.
Big and small parts are the same. The difference between anode side and rack side is also fairly consistent across the racks.

We are normally supposed to add Fluoride, as this would usually drop over time. The addition is to compensate for the drop. This has not taken place because the fluoride sample testing that takes place weekly proves that the fluoride has stayed stable and not dropped over time as normally expected.

Volume load on the line has stayed the same.

Thickness of the plating is stable.

All other bath parameters are btw. spec limits.

The parts looks a little like the bathroom mirror or maybe a little more 'whiteish'

If someone could direct me to the most probable causes for paleness I would very pleased.

Klaus Bertelsen
Manufacturing - Nyraad, Denmark

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July 2, 2012

A. Alloy plating is not easy and needs careful control. It sounds to me like you are getting a difference in alloy composition and this is causing your difference in colour. The side nearest the anode will experience the highest cathodic current density and since the ratio of Ni:Sn will be current density dependent, you will see a variation in composition. If possible, use two sets of anodes and position the workpiece midway between the two anodes, so each side gets the same level of exposure; alternatively, try slowly rotating the workpiece about the vertical axis. Also do a Hull cell test to see what current density gives you the required colour and reflectivity. You also may want to check your anodes are functioning correctly and not passivating.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

July 3, 2012

A. Fluoride testing. My guess is that you are testing for total fluoride and not available fluoride. There can be a massive difference in a well used tank. You need to know the "available".

James Watts
- Navarre, Florida

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