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December 5, 2011

Immersion Gold PCB's with Oxidation

I have immersion gold PCBs that have developed oxidation.

Is there a specific material/process to recover these boards?



J. T.

Experts Comments

Gold should not form oxides from sitting around or heating.  Gold is a noble metal because it doesn't form many harmful compounds. One thing that can occur with gold is it has a strong affinity for sulfur. If there is a source of sulfur, such as rubber, or even polluted air, you can form compounds that will start the discoloration process.

In some cases depending on the solder paste flux being used I have seen where during the reflow process of SiP devices the flux outgassing across a gold pad will show some discoloration (easily described as oxidation). Even after successful flux removal the stain is still evident on the pad. We were able to remedy this condition and "brighten" the gold pads again with an appropriate aqueous wash solution.

Also J.T. in your case what you could be seeing is the copper layer underneath the very thin layer of gold changing color. It may have leached or bled through microscopic copper particles during the plating process. Now only the copper is oxidized and when the visual light refracts across the gold it will look oxidized.

If you contact me and start by sending me a photograph of the boards in question it is highly possible we can find a remedy for this situation and recover this inventory.

 
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Charlie Pitarys
Technical Expert Sales Support
Kyzen Corporation
Charlie Pitarys has over thirty years of industry experience and has been with KYZEN for twenty-one years. Charlie is a former Marine and a retired Sargent First Class in the Army Reserves. His previous employers include Hollis and Electrovert. Charlie continues to use his expertise on cleaning processes and machine mechanics to help KYZEN customers and partners improve their cleaning operations.

It is possible to remove oxidation from the pad areas, however this will require a cleaning agent and most likely an automated cleaning system including heat and agitation.  Depending on the quantity of boards involved.

It is worth testing a cleaning process to determine if the boards can be salvaged. If you do not have a cleaning system, you can send your boards to a third party outsourcing the cleaning process.

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Umut Tosun
Application Technology Manager
Zestron America
Mr. Tosun has published numerous technical articles. As an active member of the SMTA and IPC organizations, Mr. Tosun has presented a variety of papers and studies on topics such as "Lead-Free Cleaning" and "Climatic Reliability".
  1. There are no known oxides of gold. The gold has not oxidized.
  2. If there is a contaminant on the boards it may have oxidized, but I can't tell what that might be without doing some chemical analysis.

What does it look like? Why do you think that the boards are oxidized? Describe the problem. Do you have any photos?

I've attached a Process Solutions Consulting brochure that describes my services, but I also work with Hesse & Knipps. I can answer some basic questions and will dialog with you to help.

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Lee Levine
President, Consultant
Process Solutions Consulting Inc.
Lee Levine has been a Process Engineer and Metallurgist in the semiconductor industry for 30 years. He now operates his own company Process Solutions Consulting Inc where he consults on process issues and provides SEM/EDS and metallography services.
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