Removing red discoloration from gold IC pins - Page 1
Forum section: electronics / repair

author: hotdiode
author_rank: Newbie
timestamp: January 24, 2024, 02:01:32 am
content: I got a tray of PGA chips that are ceramic with gold pins. They are all tested functional and most look fine, but maybe 10% of them have a red discoloration on some of the exposed gold, such as the pins, the pad where the pin is bonded to the ceramic package, and the gold around the lid on the top of the chip. Photo is attached showing the worst of it.From what I've read this is due to sulphur in the air reacting with the gold over time. These chips came from somebody's garage after a few decades and had no moisture or temperature control which was likely a factor.IPA does not remove the red discoloration. Mechanical abrasion using a pencil eraser easily removes it but I can only clean around the lids that way, not the individual pins. Plus these are 132-pin parts and I'd rather not hand-clean each pin on each chip somehow.Is there any better way to clean the pins without damaging the chip? Something I could spray on and wash off perhaps?

author: jpanhalt
author_rank: Super Contributor
timestamp: January 24, 2024, 05:27:17 am
content: The usual homeowner's solution on the Internet is white vinegar. Citric acid might be more effective. Lemon juice has both citric acid and ascorbic acid (a good reducing agent). It works on silver and copper tarnish.Here's a home brew electrolytic method to clean tarnished silver. I haven't tried it:https://www.compoundchem.com/2013/12/16/removing-tarnish-silver/#:~:text=Line%20bowl%20with%20the%20foil,sulphide%20tarnish%20will%20swiftly%20disappear.

author: MarkT
author_rank: Frequent Contributor
timestamp: January 24, 2024, 01:00:01 pm
content: QuoteOld soft toothbrush perhaps?

author: RoGeorge
author_rank: Super Contributor
timestamp: January 24, 2024, 02:26:42 pm
content: Starting from the toothbrush idea, toothpaste is also softly abrasive, might worth trying toothbrush + toothpaste + water.

author: coromonadalix
author_rank: Super Contributor
timestamp: January 24, 2024, 05:32:20 pm
content: deoxit ? i would avoid any abrasives, if some residues persist and you socket the chip ...

author: hotdiode
author_rank: Newbie
timestamp: January 24, 2024, 08:16:39 pm
content: Since I have more of these chips than I'll need I figured I could sacrifice one for science. Using a toothbrush to get between the pins was a great idea!Using a soft bristle toothbrush to agitate the surface I tried:1. Dry brush: no effect2. IPA: no effect3. Distilled water: no effect4. Generic PCB flux remover spray: no effect5. Toothpaste: no effect6. Rust-Off spray: no effect7. Distilled white vinegar: No effect8. Bartender's Friend powder: Works! But takes a lot of mechanical effort; I think a electric rotating toothbrush would help significantly if used cautiously.9. Ascorbic acid: Mostly works, I got the best result applying powder directly to the chip and scrubbing it in with a wet toothbrush. Removes the red but doesn't quite restore the gold luster.10. Deoxit: no effect, which was surprising.No idea what the long term outcome of using these substances will be so keep that in mind.EDIT: Updated with some other suggestions, thanks for those.

author: pickle9000
author_rank: Super Contributor
timestamp: January 24, 2024, 08:32:50 pm
content: Try glass cooktop cleaner and ipa when done.Its a very fine abrasive. Weiman Cook Top Heavy Duty Cleaner

author: jpanhalt
author_rank: Super Contributor
timestamp: January 24, 2024, 08:54:48 pm
content: Try lemon juice or anything else with ascorbic acid. Not all acids are the same. For example, acetic acid (vinegar) doesn't form complexes with metals like citric acid does. It has virtually no reducing power. If the gold plating is involved (i.e., oxidized/"tarnished" by sulfur), reducing it will reverse the process. Same goes for the more complicated aluminum foil and sodium bicarbonate method. The aluminum foil is oxidized (loses one or more electrons) and the silver/gold is reduced back to metal.If you have an ultrasonic cleaner, I would use that with the various liquids, not just dipping in them. Of course, abrasives will remove both the tarnish and gold plating, which is probably very thin.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 25, 2024, 07:35:09 am
content: Since pencil eraser did work, I would also try making plenty of pencil eraser debris first (with the help of something else than the PGAs), then try to clean the pins with that eraser debris and a dry toothbrush.

author: macboy
author_rank: Super Contributor
timestamp: January 25, 2024, 02:17:39 pm
content: Since the eraser and bartender's powder work, then I would think toothpaste would work for you, but not all are equal. Some have much more aggressive abrasives, like special extra scrubby ones like "pearl drops" which heavy smokers or wine drinkers might use (note the "triple power whitening" tag line). An oscillating electric toothbrush would probably help too. If you don't already own one, you can probably get a disposable one with a comic/cartoon character on it for a few dollars. Hopefully you don't mind Dora or Spongebob doing your dirty work.I do however agree that you should explore non-mechanical means first.

author: jpanhalt
author_rank: Super Contributor
timestamp: January 25, 2024, 02:27:44 pm
content: Underlying all the suggestions is an assumption that discoloration needs to be removed. Is that true? If it is just cosmetic, leave it be. Even if you planned to solder to them, the flux might fix the problem.