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Chromate conversion coatings and other passivation treatments for Copper

Q. I am making a heat sink from Copper material. Is Iridite (MIL-C-5541 [affil link]) 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 [adv: item on eBay or Amazon] . Good luck.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - 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 note: Sorry, this RFQ is outdated so private contact is no longer available, but public technical replies are still welcome! No public brand/source suggestions please ( huh? why?)

Ed. note: Readers, please see our "Hotline Public Forum" 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 [affil link] or MIL-C-5541 [affil link] - 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

Q. I am looking for a way to coat keypad contacts to improve reliability. The contacts have been cleaned with 00 steel wool [on eBay or Amazon affil link] so any protective coating they might have had is gone. Is there some kind of protective/conductive coating that I can apply at home?

Yossi David
- Binyamina, Israel
December 11, 2017

Electroless Liquid Silver Plating Solution

on eBay or


(affil links)

December 2017

A. Hi Yossi. I think sodium benzotriazole will be your best bet, although silver plating is another choice if you can find one of those proprietary re-silvering solutions in Israel. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

Specification for Chromate Conversion Coating of Copper

Q. I spec MIL-DTL-5541 [affil link or DLA] F to protect most aluminum parts I design.
I am not too familiar with copper and wanted to know if there is there an equivalent spec for copper?

My google search leads me to a bunch of websites that mention conversion coating copper but no mention of specs that for this process.

Fernando Ortiz
Mechanical Engineer - Plano, Texas, US
September 25, 2019

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