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topic 7627

Chromate conversion coatings and passivation treatments for Copper


Q. I am making a heat sink from Copper material. Is Iridite (Mil-C-5541) an effective treatment for corrosion protection or is Iridite just for Aluminum alloys?

Bob Diamond
- Hauppauge, New York


A. Iridite is a [Macdermid] trade name for a variety of conversion coatings. The conversion coatings used on copper are different than those for zinc. They do provide some corrosion protection but are primarily used as a passivation to prevent oxidation.

Gene Packman
process supplier - Great Neck, New York


Q. We use copper emitter plates which are powder coated to provide insulation. Various areas on the plates are left bare to provide a contact with various electrical components and power terminals. We are having a problem with tarnishing of the copper prior to assembly. One suggestion has been to clear passivate the plates. Does anybody know if this would have a detrimental effect on the electrical conduction between the plate and the components to be fitted? Can anybody suggest an alternative means to prevent the tarnishing?

John Austin
- Gateshead, Tyne & Wear, UK


A. Hi John. Whatever you do to limit the oxidation will improve, not hinder, the electrical conduction. Chromate conversion coating is one approach, but I'd also consider treatment with benzotriazole. Good luck.

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


RFQ: I need to find a shop in the Boston area that can apply a chromate conversion coating for copper to printed circuits to prevent oxidation. We would like the same basic treatment that copper foil manufacturers (Gould, Mitsubishi, etc.) use in their processing. Eventually, we would want to be able to set up our own panel processing -- please recommend suppliers of treatment chemicals as well.

Thanks for your help.

Jim F [last name deleted for privacy by Editor]
- Boston, Massachusetts

Ed. note: Readers, please see our "I Need a Finishing Service" page to view current RFQs or to post your own RFQ.


Q. We are currently having the exterior of some copper coils finished with Luster-On Cobra C conversion coating to prevent cosmetic discoloration during humidity exposure. Does anyone know of any military/commercial/industrial specifications - along the lines of ASTM B921 [link by ed. to spec at TechStreet] or Mil-C-5541 [link by ed. to spec at TechStreet] - that could be called out on our part drawings to specify this finish?

Thanks !

Rich I [last name deleted for privacy by Editor]
aerospace - Moorestown, New Jersey

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