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topic 9994

Conductive chromates for aluminum


2001

Q. We plate aluminum pads for electronics. As part of the process flow, the aluminum is chromated with a solution consisting of a Cr (III) compound, a fluoride and a tin (4) compound. The chromate is conductive. We find occasional corrosion that we suspect may be due to high levels of fluoride and chloride in the chromate solution. Is anyone aware of any commercial or non-commercial chromate formulations that provide both corrosion protection (without the use of significant amounts of fluorides or chlorides) and a conductive surface?

Charles Rosenstein
- Jerusalem, ISRAEL


2001

"Electrolytic and Chemical Conversion Coatings"
by Biestek & Weber

from Abe Books
or
info on Amazon

"Surface Properties of Conversion Coated Aluminum"
by Raj & Ali

from Abe Books
or
info on Amazon

A. I'm not really sure if this will work as base for plating on aluminum but if you're looking for chrome-based corrosion protection, you might try Alodine or Iridite process.

Dado Macapagal
- Toronto, Ontario, Canada


A. Hi Charles. Dado has mentioned two tradenames for proprietary chromate conversion coating chemistry. Mil-C-5541 [link is to free spec at Defense Logistics Agency, dla.mil] covers the topic of corrosion resistant chromate conversion coating, and specifically addresses conductivity as well. It's actually a pretty well established technology.

If you wish to plate the aluminum, though, the conventional approach is not to chromate it, but to zincate it first and then electroplate it; alternately if the plating will be tin plating, there are processes like Atotech's Alstan, which start with a stannate immersion rather than the zincate immersion. Good luck!

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



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