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Post-plating Cleanliness Test for Electroless Nickel



October 6, 2010

Hello All,

We have the opportunity to gain some business from a competitor. Parts that they have EN plated corrode over time. The EN is applied over ferrous material. We believe this is because of poor rinsing leaving possibly acidic residue on the parts. Is there a good post-plating cleaning test one can use to verify the quality of the rinsing step?

Thanks,

Michael Costello
Engineer - Grand Junction, Colorado



First of two simultaneous responses -- October 7, 2010

Sounds like a hypothetical question, not based on fact. Your idea of improper rinsing may be correct but there are many other more probable causes, like too thin a plate, bath chemistry out of balance, improper pre-cleaning, exposure to harsh environments, etc.
G. Marrufo

Guillermo Marrufo
Monterrey, NL, Mexico



Second of two simultaneous responses -- October 8, 2010

Michael,

Don't try to second guess why your competitor is having problems with corrosion, optimise your system to provide the best corrosion resistance.

I would recommend a high phos nickel with a minimum thickness of 0.001", but if your costs allow try going for 0.002".

Is the ferrous alloy a low alloy steel? If so then the pre-cleaning prior to plating needs to be robust to ensure there is no contamination on the surface of the steel. A low alloy steel will not need a strike prior to plating.

You shouldn't need any special finishing after plating with a high phos system, just rinse well in cold running water, possibly finish off with a demin rinse if towns water is of low quality, this will prevent unsightly stains on the surface of your nickel. If you do feel you need a rinse at the end then firstly talk to your nickel chemistry supplier and see if they have anything, otherwise I have used a dilute chromic acid rinse before (Note chromic acid is not RoHS compliant so use it with caution if you choose this route).

Brian Terry
Aerospace - Yeovil, Somerset, UK



October 13, 2010

Thank you both for your input. I should have been clearer in my original post (and on many other occasions not germane to the current discussion). The corrosion is not observed on the plating. It is seen on a NiCr wire that is welded to the plated parts. The corroding wire is in a sealed chamber, and the corrosion is observed only in parts produced by one supplier. The customer is requiring a cleanliness spec, and we are to come up with a meaningful test to measure the cleanliness of the plated parts after plating. We could use the ROSE test from the circuit board industry, but we were wondering if there was a cleanliness test specific to the plating world.

Michael Costello
- Grand Junction, Colorado


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