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Brown staining on electroless nickel plating

We are experiencing a problem with brown staining/ tarnishing appearing a few hours later on radio components that we are electroless nickel plating . The components are machined from solid aluminium billets and are electroless coated for one hour using a high phosphorous solution. After plating they are rinsed in de - ionised water and then blown with compressed air to clear any blind holes , corners, etc.Does anyone have any advise for us ? We cannot use any de - watering or oil based coatings as some components are then powder coated afterwards .

MARK WRIGHT
electroplating shop - DURBAN, KZN, SOUTH AFRICA
2006

The problem described comes from the bath constituents, contaminants and maintenance schedule, perhaps combined with transfer times, rinse pH and temperature. When plating Al, zinc is a common source of contamination which dissolves from the zincate layer. If you are using a proprietary chemistry ask your vendor. With home brew baths it's all guess and try.

Guillermo Marrufo
Monterrey, NL, Mexico
2006

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2006

Your staining is most likely due to contaminates and rinse water. The addition of another rinse after plating containing approx. 5% chromic acid at about 40C will probably help eliminate staining and should not effect subsequent organic coatings.

Ron Duncan [deceased]
- LaVergne, Tennessee
It is our sad duty to note Ron's passing on Dec. 15, 2006. A brief obituary opens Episode 13 of our Podcast.