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Gold Plating on Slightly Oxidized Copper Surface





Through 500X OM, I found there is some oxidized spots on copper surface. Since our products is very sensitive on resistance, could the oxidized spots influence resistance of surface conductivity?
Ps. the oxidized spots can not be observed on 100X OM.

Tong Wang
Buyer - Taiwan R.O.C.
June 14, 2009



August 20, 2009

Dear Mr. Tong Wang,
Definitely oxidation will affect to the conductivity of copper.
You can use conc. or 50% HCl acid followed by water rinse for removing oxidized spot from the copper surface.

Regards,

Gurudatta Thakur
- India



I have to disagree with Mr. Thakur's suggestion. "Conc" HCl or even 50% HCl should not be used here. If the oxidation is minor 10% v/v sulfuric acid dip is sufficient followed by a drag out, water rinse then a DI rinse. This is assuming that the parts are copper plated.
With that aside, we know that Mr Wang is a buyer. We don't really know if he has any plating related tanks in his plant. It is not unusual for copper to oxidize slightly. Why not measure the contact resistance in ohms at the point of oxidation to see if it's acceptable for your application?

Mark Baker
Fellow plater - Syracuse, NY, USA
August 21, 2009



I agree with Mark. However, I would also like to suggest the copper is either chemically or electropolished so that it has an oxidising-resistant coating that will have a more consistent resistance to it. Product consistency is the key to good process control.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
September 10, 2009



September 23, 2009

The title of the question was - "Gold Plating on slightly oxidised copper" - although it was not mentioned again in the letter or in any of the responses so far.

It is not impossible to gold plate over slightly oxidised copper. Resistance is not a problem as the gold will carry the current. The big problem is that the gold will probably blister or fall off!

As the letter is short on detail, I shall make a wild guess.
Are we talking about a connector or a printed circuit with gold contacts and some exposed copper with spots of oxide?

In that case, there is no evidence that the gold has not been properly applied and contact resistance is not compromised. Oxide spots on copper are usually due to poor protection in storage. Unless there is a copper/copper contact, resistance is irrelevent. If the parts are soldered, good fluxing will probably remove any small amount of oxide on the surface

geoff smith
Geoff Smith
Hampshire, England



October 7, 2009

If the slightly oxidized copper is on a printing board or similar you can easily remove the oxidation spots by using a cotton bud dipped in a Potassium cyanide solution. 5% KCN in DI water should be quite enough. Just be careful to put away the Hydrochloric acid during that operation (!). The surface has to be rinsed and washed well to eliminate traces of cyanide.
If you use Hydrochloric acid this can affect your working piece or board and even cause more oxidation spots!
And by the way I just wondered what a 50% HCl is? The conc. HCl is 36%. At 37% we call it fuming Hydrochloric acid - it's the strongest available on the market, you cannot dissolve more HCl gas in water at standard pressure -and temperature.
Best regards and good luck!

Lionel Zollinger
- Bangkok, Thailand



Do I need to point out that advising someone with unknown technical knowledge or available precautions to wash components in cyanide is highly irresponsible.
I hope that Tong will have the good sense to ignore this.
I am very surprised that it was accepted for publication.

geoff smith
Geoff Smith
Hampshire, England
October 9, 2009



October 12, 2009

Hi, Geoff. We'd prefer if you used a term like "risky" or "imprudent" or "dangerous". Starting down the "highly irresponsible" may evolve into name calling very quickly :-)

You are certainly right to advise extreme caution with cyanide! But in truth we rarely know the degrees, certifications, haz-mat training, and continuing education of any writer, and never of the readers, who outnumber the writers by at least 100:1.

As for "accepted for publication", please realize that this is just a public forum that receives hundreds of submissions a day. Within available time restraints and technical knowledge, we do try to purge spam and blatant advertisements, correct obvious misspellings, and re-word awkward constructions generated by machine translation; and I try to keep my eyes open to contribute where I can -- sorry I missed this one. But public responses are the only form of "peer review" in the process.

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey



Dear Mr. Smith,
I take the opportunity to write a few words concerning this 'copper oxide removal with Potassium cyanide solution'.
First, it is really not my aim to suggest a dangerous and toxic process. If possible I always would propose an easy non-toxic way. Maybe I wrote this one too quickly. Sorry for that. The response was purely scientific, as KCN is an excellent spot-remover for copper and silver. But as Mr. Tong is a buyer and not the chemical or plating expert you are completely right and he should forget about this Cyanide cleaning. Instead the use of a soft brush and an alkaline industrial degreasing agent or a buffing remover could do the job as well, these products contain also non-toxic mild deoxidizing agents. So I would like to suggest this easy and non dangerous way.
It was not my intention to do harm at all, I hope you understand what I mean. I am highly concerned for security matters in the plating field, don't misunderstand me.
And finally in a plating department there are the experts knowing exactly what they do and have the knowledge about dangerous and toxic chemical products.
With my best regards

Lionel Zollinger
- Bangkok, Thailand
October 16, 2009



October 19, 2009

Lionel

Nice to hear from you. Ted worries that my response was a criticism of you personally. That was certainly not my intention and I apologise if I gave offense.
My challenge was ad verbum not ad hominem and I plead not guilty to any charge of mens rea.
Perhaps we should also remember that qui tacet consentare.

geoff smith
Geoff Smith
Hampshire, England




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