Tin Plating Stains

Question:

We are having problems with a yellow stain on some of our tin plated parts. The plating process consists of an initial copper deposit followed by a tin deposit and alkaline rinse. Do you have any suggestions on how to eliminate or at least minimize this problem? S.T.

Answer:

Here are a few things that can cause the staining you are observing.

• Copper is present in your stannous tin plating bath. Look at the rinsing process between the copper and tin plating baths.
• The alkaline rinse is no longer able to neutralize the dragout from the stannous tin solution. Check the alkalinity of the rinse.
• The final rinse is contaminated with dragged-in material from the alkaline rinse. Look at the rinsing steps after the alkaline rinse.

If you need more help with the troubleshooting of this problem get yourself a copy of the book, Trouble in Your Tank, 3rd Edition, by Lawrence J. Durney, which is published by Products Finishing's owner Gardner Publications, 888-527-8803.