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Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Discoloration of bright acid tin plating
A. Just to add my personal experience, we noticed that our material would slowly turn blue after a day or two, and it's been slowly getting worse. Our rinses after our Stannous Tin plate had a failure of a pump and it just slowly got the drag in from the Stannous Tin. This caused residue to form and slowly turn blue. The pH of the Rinse was all the way down to 1.9
Fixing the pump and cleaning the rinse fixed the issue for us.
- Pottstown, Pennsylvania
July 12, 2022
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⇩ Related postings, oldest first ⇩
Q. Hello Sir,
Why does tinning done on copper turn black?
What is the reason why Tin turns black after some period of time.
Please help.
Engineer - Mumbai, Maharashtra, India
February 14, 2012
Hi, Abhiraj.
You posted this in a Q&A thread about immersion tin plating. Are you doing immersion tin? ... or are you doing alkaline tin plating, or bright acid tin plating please? Have you been plating successfully for years and this problem has cropped up, or are you starting a new plating line and having plated successfully yet? :-)
Sorry, but it is tough to reply in a meaningful way to your question. As an example, one case of 'black' tin plating on this forum was ultimately found to be fretting corrosion due to a vibratory feeder left on all night -- it's very difficult to suggest the answer with no details. Thanks!
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
February 15, 2012
Q. We are doing bright acid tinning for past 30 years and more on copper; this is the first time the problem has occurred.
We are doing Stannous tin plating.
There has been discolouration to blue.
Please help
Engineer - Mumbai, Maharashtra, India
February 15, 2012
A. Hi Abhiraj. Thanks for the details.
I hate to be a bearer of bad news, but this sounds to me like gross contamination of the tank with another metal. I would suggest trying some Hull Cell panels to see if they shed any light about where in the current density range the problem is minimized or maximized, and carefully checking your additions history to see if there is any chance of a bad add, including the possibility of incorrect anode material. But I suspect someone added the wrong chemical.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
February 16, 2012
Q. Hi,
I have come to this site as I was browsing information regarding discoloration on the leads and heatsinks on Power device packages (tab mounted devices).
We are encountering discoloration on packages after 6-10 months.
We are having tin plating process (electroplating) with Nickel as base metal (Sn over Ni). And the plating solution compose of MSA, Tin con, And Additives. Our rinsing after plating only comprises of Tap Water, followed by DI water and with final rinse of Hot DI water.
Can you help me find ways in solving this? Though I have some ideas like lacking of TSP neutralizer may contribute to this problem.
July 3, 2013
A. Hi Aiza,
Tin discoloration could due to incomplete removal of tin plating solution residues (e.g. MSA) or tin oxidation upon storage. TSP neutralizer can improve thorough rinse off tin plating residues while you may insert additional post dip before final rinse which is so called "solder guard" by form a hydrophobic film on tin surface to repel oxygen/moisture during storage to minimize chance of tin oxidation.
Regards,
David
David Shiu
- Singapore
A. I agree with David, and suspect that oxidation is the main culprit. To avoid rapid staining, we blew the parts dry after it came out of the hot water. After it was dry, we would give it a dip in stearic acid ⇦ this on eBay or Amazon [affil links] (beef fat extract) in a Xylene ⇦ this on eBay or Amazon [affil links] solution. It worked very well. We got the dip formula out of some specification where it was a note.
James Watts- Navarre, Florida
Your responses are of great help. With the aide of evaluation we are on the process of qualifying neutralizer for the plating process.
- Taguig City, Metro Manila, Philippines
Q. We plated tin on copper parts and we noticed that the tin finish was not conforming.
Please, is it possible to replate those non conforming parts without stripping them before ?
- Lyon, France
August 27, 2013
A. Hi Gino,
Without knowing the specifics of non-conformance I would suggest that if it is anything other than thickness you will need to strip and re-plate. If you are low on thickness it may be possible to reactivate the plating and continue to obtain the required thickness, but I must admit that if any length of time has passed then you will be very lucky to get good adhesion.
Aerospace - Yeovil, Somerset, UK
August 29, 2013
Q. Hi David Shiu,
Can you suggest possible "solder guard" (hydrophobic chemicals) as post rinse for tin plating? This is just an alternative post rinse in case TSP neutralizer fails the qualification. Thank you.
- Taguig City, Metro Manila, Philippines
September 27, 2014
A. Hi Adeliza,
As I'm not allowed to mention any particular commercial product name here, you may contact well known proprietary chemical suppliers which most of them do supply "Solder Guard" post treatment chemicals for tin plating process.
To verify if the chemical works, you may observe water droplet contact angle on tin deposit after post treatment. Without treatment, contact angle is small (~45°). After treatment, contact angle shall increase to 90° or above.
Regards,
David
David Shiu
- Singapore
October 7, 2014
Q. Hi all. I have a problem with my plating products. My company plated copper in MSA tin solution. And after plating we soaked in TSP (trisodium phosphate ⇦ this on eBay or Amazon [affil links] ). But the finishing was poor. Yellow stains were appearing, and since [then] we have some black stains and black marks on the finished products. Since I'm new to plating industry I think your opinion and suggestion are very useful. With all respect.
Muhammad SyafiqPlating - Shah Alam, Selangor, Malaysia
June 13, 2016
Q. Hi, I tested some tin parts in a hot water (130 °F) and after 5 minutes the parts have some stains. What could cause this?
Marco Devora- Chihuahua,Chihuahua, Mexico
June 15, 2016
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