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Chromate conversion alternative for aluminum heat sinks?

I am looking for an alternative to chromate conversion for some heat sinks that we use. We are trying to eliminate the use of hexavalent Chromium for RoHS compliance reasons. The heat sinks are currently made from 1100 aluminum sheet that is punched and formed. Since we pass a current through the heat sink we don't want to use a finish that significantly increases electrical resistance. What would you suggest?

Steven Lamusga
electronics manufacturing - Libertyville, Illinois, USA
2006

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First of two simultaneous responses --

There are several Non-Hex alternatives for Chemical Conversion Films on aluminum. The problem is that only one has thusfar shown itself capable of passing the requirements set forth in Mil-DTL-81706. That chemical is a Trivalent Chromium Pretreatment developed by the US Navy and licensed to Sur-Tec International, Luster-On, Henkel Surface Technologies and Metalast. These licensed versions are currently in the final phase of testing for inclusion in Mil-QPL-81706. Of all the chemistries tested, this is the only on that will pass a "bare salt spray". MIL-C-5541 is in final stages of rewrite to provide for non-hexavalent based conversion films.

Justin Crisp
- Indianapolis, Indiana, USA
2006

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Second of two simultaneous responses --

There are a number of trivalent chromium based hex chrome alternatives on the market. We use one which is based on a US Navy patented process. Also, a chemical supplier in greater Chicago by the name of Sanchem has a 100% chrome-free, permanganate process which is reported to work well. Search the web for the name BIBBER and permanganate and all roads will lead you to SANCHEM.

Milt Stevenson, Jr.
Syracuse, New York
2006

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2006

Hello to all,
I work for a company manufacturing electronic devices for European and US customers, which need to comply to environmental exposure such as salt fog and humidity exposure.
We are now searching for environmentally safe surface treatments, and for an electrically conductive coating for Aluminum we have come across ALBAR-L3 and CE-283 which is apparently based on trivalent chrome, not hexavalent.
Do any of you have experience with these coatings? specifically with salt fog exposure of coated Aluminum? both the corrosion resistance and electrical conductivity are important to us.
Thanks...

Baruch Barazani
electronics manufacturer (OEM) - Rehovot, Israel

Ed. note: We don't compare proprietary products on these pages, Baruch, but we have appended your inquiry to an earlier discussion, and you can see that this issue of trivalent chromating of aluminum is a hot topic around the world.

Our company has been using a licensed version of the Trivalent Chromium Pretreatment developed by the US Navy for a year now and we have seen no problems with corrosion or electrical properties.

Justin Crisp
- Indianapolis, Indiana, USA
2006

Has anyone seen published information stating that chem film per MIL-C-5541 meets the RoHS requirement because it constitutes less than 0.01% of the component being supplied and therefore meets the threshold? I received a call from a customer who states there are some suppliers making that statement.

Michael Marion
- Lititz, Pennsylvania ,USA
2006

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Best alternative to Hexavalent chromium is the TCP process which meet fully the requirements of Mil-c-5541 . I am running several lines with the process successfully without any problem . The application is easy and the result is fully approved .

Yehuda Blau
YB Plating Engineering and Quality - Haifa Israel
2006