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Electroless nickel and tin-nickel plating, could it be possible?

We plate aluminum shield with electroless nickel prior to a tin-nickel plating. After electroless nickel, the plating looks appealing however as we proceed to tin-nickel plating we observed some black substances on recessed areas. What do you think is the cause of the black powder substances?

Zenaida R. Adorable
plating services company - Quezon City, Philippines
2005

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Ed. note: You may want to hear "The Lost Art of Tin-Nickel Plating".

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How recessed are the recessed areas? There is insufficient information to give a judged answer. It could be that the areas are suffering from a lower current density than other areas, so you are getting a different alloy composition. Alternatively, it could be due to solution entrapment from upstream tanks or the effects of solution depletion from the alloy plating tank.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2006

I have had similar problems in low current density areas. Some tin-nickel solutions have a starter solution component that plays a huge role in throwing power and bath stability. At first I thought a starter component only had to be added when you make up the bath new, but I was wrong. If it is ammonia ⇦this on eBay or Amazon [affil links] based, volatility is a major factor so the starter solution has to be replenished per so many ampere hours. We also had to change the filter often, dummy plate, and watch the PH and temperature of the bath closely. This was not my favorite bath to troubleshoot! You should refer to the tech data sheet from your supplier to make sure everything is in range. I can't give you specific range parameters because I don't know who your supplier is, or what type of tin-nickel you have. Hope this will be helpful!

Mark Baker
process engineer - Malone, New York
2006