Perfect Electroless Nickel Rack?June 17, 2008
Circuit boards will abrade any coating. Therefore I want to construct a rack that is intrinsically non-plating in electroless nickel. Furthermore, it must not plate in immersion gold further down the line as the electroless nickel will plate on top of the gold on subsequent cycles.
I'm thinking of a cadmium or lead containing alloy to shut down the EN reaction. Why hasn't this been tried?
Less preferable, would be a coating of Cadmium-gold if there even is such a thing?
Things I have considered:
1. Titanium readily plates up with immersion gold. I expect the gold to plate over with EN on subsequent cycles so I don't think this is a promising approach.
2. The pre-clean line contains acids that will corrode nickel-containing steels and especially copper.
3. A rack constructed from 1/2" PVC square rod is too brittle.
4. Halar or KF coating does not stand up to the abrasion.
Engineer - Rochester, NY, U.S.A.
June 20, 2008
The answer to the first question is easy as both of those metals will dissolve slightly in the EN and both are extreme brighteners at trace levels, so their use will poison your EN tank and will affect the properties of the EN before you can not use it any longer.
Look into Ultra high molecular weight PE (UHMW PE). It is great stuff, but I do not know if it will take the high temp of the EN. It is extremely abrasion resistant, but can not be welded by normal hot air means.
What have the professional rack making companies said about your problem?
- Navarre, Florida
June 21, 2008
The "professional rack making companies" are quite happy to re-coat the racks every 3 months thank you very much. Furthermore, if they had the ingenuity to solve this challenge they wouldn't be making racks!
I should add that the preferred style of rack is to have a series of opposing channels approximately 0.200" wide to slip the circuit boards into. UMHWPE channels are simply not available unless machined which is expensive. Even if they were, I don't see how you would join them to the rack structure without screws.
printed circuits - Rochester, NY, U.S.A.
June 23, 2008
Hi, Peter. A milling machine can cut a groove like that very quickly; I don't think it should be expensive. The screws could be countersunk to stay out of the way and could also be made of UHMWPE although that would probably be fairly costly. Or the screws could come into tapped holes in the UHMWPE from the other side (the heads of the screws on the other side of the frame and plastisol coated).
Ted Mooney, P.E. RET
Pine Beach, New Jersey
June 25, 2008
UNMWPE would work for the channels, although I see nothing wrong with CPVC which is easier to work with. The big challenge is the rack frame.
I am trying to get away from plastisol, or any, coatings. Aluminum (especially 6063) works well in all the baths in the line except for the cleaner tank which contains HCL. I would expect the tenacious oxide layer of Zirconium to protect in the same way and hold up to the cleaner too, although Zr sells for about $100/pound!
- Rochester, NY, U.S.A.