TIN PLATING PROBLEMS
A discussion started in 2002 but continuing through 20192002
Q. I'm from a company in South Africa. Tin plating is one of the new ventures that our company started and needless to say we have a few problems and I wonder if someone could shed some light on some of my questions. We are plating onto copper and brass respectively (with tin). Please try and answer the questions as laboriously as possible.
1. How do other companies get their current onto their strip of metal?
2. The top and bottom of the strip will have a different thickness of tin. Why? We use Titanium baskets, and the strip runs horizontally.
3. Our passifier discolours the strip. Are there other types that we can use?
4. We used copper cyanide in one of the baths, it was suggested to leave it out of the process. Now the plated metal discolours (goes black). Do you suggest putting the copper cyanide back into the equation?
5. Is temperature control very important? Why?
6. The 'whiskers'-issue. How, why, how to get it away?
7. What is the voltage required on what thickness of strip?
8. After plating and a few hours has past the plated metal starts to turn black. Why and how do I prevent this?
I know these questions must be elementary to you, but it will help us a lot if you could answer some of them, without getting too frustrated!
Thank you,Aletta Renee van der Vyver
- Johannesburg, Gauteng, South Africa
Sounds like you having a lot of difficulties. Let me try to help you with your questions one by one.
1. Pending the type work you have your choices are to rack plate with rack to connect the work on to, barrel plate using steel media for electrical contact, or get electroless or immersion plating bath. However, electroless/immersion tin baths require very specific conditions to operate and are not widely used and may not get the plating thickness that you want.
2.Your different in plating thickness is caused by top part of your strip is a high current density area compare to the bottom. This means the top part wants to plate faster. Try increasing the distance between the anode basket and your work. This will reduce your thickness difference. A thick copper under plate and lowering your plating current may help in this area also.
3. Can't help here.
4. If you are using copper as a strike to help your adhesion, leave this step in the process.
5. Temperature control is important pending on the bath. A high operating temperature will improve your plating rate with baths that are alkaline based. However, acid tin baths do not like too high operating temperature and prefer to be operated at room temperature.
6. There is a lot information published on tin whiskers. A good book on the subject is "Soldering in Electronics" by R.J. Klein Wassink =>
Tin whiskers growth occurs only with pure tin under certain conditions such as long term storage with high humidity. Tin-lead alloys, bright tin, and I think reflowed tin is not prone to whisker growth.
7. The best method to set-up your plating parameters is current and time. Set your current per the surface area of your work. For example, 2.5 to 4.0 amps/dm2. A few trials you can determine a plating rate vs current and time. Note there are other variables that will affect your plating rate such as solution metal concentration, temperature, acid or caustic concentration, bath contamination, and so on. Also note the fast plating rate is not always the best. I seen too many people who use the maximum plus current to get the work out. In the end, they generate poor quality work, rework, and scrap.
8. What you may have is tarnishing of your work. Be sure you have good rinsing and drying after plating. The more rinsing the better.You could try an alcohol dip before drying to remove water on or in the plating surface.
I hope this helps and good luck.Karl Weyermann
- Lebanon, Kentucky
November 19, 2014
Top and bottom will have different thicknesses. Lowering the Current can improve the variance. Or using shields might help. Cathode part nearer to anode basket tends to get higher thickness. Shielding some part of cathode with non-conductive material will reduce thickness.
Voltage can be calculated using Faraday's Law.
Rinsing your product using deionised water before drying using hot air will reduce discoloration.
- OSAKA, JAPAN
October 18, 2018
Q. Hi, I'm currently looking for solution to resolve dull or black plating in barrel for tin plating. Can anyone brief or explain the aspect or reason which can contribute to this dull plating or any recommendation to solve this problemNavaletchumy d/o Vijaya kumaran
- Seremban, Malaysia
A. Hi Navaletchumy. Please give us a starting point :-)
Are you doing alkaline tin plating or bright acid tin? Could the dullness/blackness be fretting corrosion from prolonged tumbling? Have you done any Hull Cell testing? Do you have any photos to show us what you mean by 'dull or black'. Is this a problem which just occurred for the first time, or does it come and go, or is this a new plating line which has not generated proper parts yet.
Most plating texts will introduce you to troubleshooting the process. "The Canning Handbook" [link is to info about book at Amazon] says dull deposit (in Bright Acid Tin) bath may be due to excess chloride, lack of brightener, temperature too high, sulphuric acid concentration too low, anodes passive, current density too low, metal concentration too high, or suspended solids. Good luck.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"
Cracks in tin plated surfaceMay 21, 2019
Q. We have a problem with our tin plated surface. We have cracks in the plating.
We are doing a nickel strike and nickel layer before tin plating (to avoid tin whiskers).
Meanwhile we changed already our cleaning bath, HCl bath, nickel strike and nickel bath. And now we can only change the tin bath anymore to hopefully solve our problem.
Is there a possibility to analyse our liquid to avoid this problem in the future? Tin bath is methanesulfonate bath.
HTMS - Mechelen Noord, Belgium
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