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Too much phosphorous in electroless nickel

1996

I have some problems with the amount of phosphorus in an electroless nickel coating on aluminum parts. Our spec requires that the phosphorus be a "high phosphorus" coating of 10 to 13 percent. One of our suppliers uses a bath that states the phosphorus content is 10.5 to 13 percent. The problem is that checks of the plated parts show that the phosphorus content of the nickel coating on the parts can be as low as 9.2 percent phosphorus.

Question: What is the accepted/spec'd definition of a "high phosphorus" electroless nickel coating? 10 to 13... 9 to 14...?

Question: Do aluminum parts plate out differently than steel parts? i.e., does the phosphorus content vary more on aluminum parts as opposed to steel parts?

Jason Ingram

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1996

Jason,
I have done a fair amount of electroless plating, but am not a technical expert. It is my belief, from several sources, that P is controlled by the bath make up and operational use. IE: the exact pH, temperature, and nickel/hypo concentrations affect the amount of P. Also, as many baths age (tank turnovers) they change the P content and the internal stress. In day to day operation of an average job shop, the P content will be on the low end of advertised. 9.2%P does not surprise me, but I am a pessimist.

Definition of a "high P" EN is totally with your customer. Conventional is 10 -13% but that is subject to great amount of disagreement. Running High P EN baths are a pain trying to maintain 11.0-11.5%P in comparison to the numerous 4-7% baths that are sold. Anyone that says otherwise is extraordinarily sharp, or lucky or unaware of what he is producing. After the first molecule layer of nickel, it should not make any difference what the substrate is because it is plating on EN.

James Watts
- Navarre, Florida