Ask the Experts
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?
Expert Panel Responses
Gold should not form oxides from sitting around orheating. Gold is a noble metal because it doesn't form many harmfulcompounds. One thing that can occur with gold is it has a strong affinityfor sulfur. If there is a source of sulfur, such as rubber, or evenpolluted air, you can form compounds that will start the discolorationprocess.
In some cases depending on the solder paste flux being used Ihave seen where during the reflow process of SiP devices the flux outgassingacross a gold pad will show some discoloration (easily described as oxidation).Even after successful flux removal the stain is still evident on the pad. Wewere able to remedy this condition and "brighten" the gold pads againwith an appropriate aqueous wash solution.
Also J.T. in your case what you could be seeing is the copperlayer underneath the very thin layer of gold changing color. It may haveleached or bled through microscopic copper particles during the platingprocess. Now only the copper is oxidized and when the visual light refractsacross the gold it will look oxidized.
If you contact me and start by sending me a photograph of theboards in question it is highly possible we can find a remedy for thissituation and recover this inventory.
Technical Expert Sales Support
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 removeoxidation from the pad areas, however this will require a cleaning agent andmost likely an automated cleaning system including heat and agitation. Depending on the quantity of boards involved.
It is worth testing a cleaningprocess to determine if the boards can be salvaged. If you do not have acleaning system, you can send your boards to a third party outsourcing thecleaning process.
Application Technology Manager
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".
Whatdoes it look like? Why do you think that the boards are oxidized? Describe theproblem. Do you have any photos?
I'veattached a Process Solutions Consulting brochure that describes my services,but I also work with Hesse & Knipps. I can answer some basic questions andwill dialog with you to help.
- There are no known oxides of gold. The gold has not oxidized.
- 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.
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.