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Problem with acid tin bath brightener

(-----) 2003

Q. I have acid tin brightener bath after three month the color of bath turn yellow what reason and how can treat.

Hoba Ahmed
- Egypt


A. Enthone, for one company, sells a material to treat their tin solution. Our cost analysis showed that it was cheaper to generate a new tank solution than treat the old one. Less down time and less pain also.

James Watts
- Navarre, Florida

Tin and Solder Plating
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A. Hoba-

Just because the bath changed color does not mean you have a problem. Acid tin baths do discolor as you use them. Is the tin deposit still giving you good results? What is being told to you is a clarification chemical. A bath three months old should never require this treatment. Do you filter the bath constantly? Should have a chiller to maintain temperature no more than 65-70 degrees F.

You should also be using sulfuric acid at 10 % for your acid after cleaning. Chlorides kill acid tin. If you are using muriatic acid, not good.

William F. Hemp
- Grand Rapids, Michigan


A. I disagree in part with Mr. Hemp. The color change your bath experiences is normal due to the oxidation of the tin in solution from stannous to stannic. Generally, if you wish to use color as a guide to when a bath should be discarded, cut or "clarified" (flocc'ed) the color to look for is a dark "coffee with cream". At this point you will find that you are having difficulty maintaining brightness despite additions of additives. This would be different from chloride contamination which regardless of color will result in a dull or etched finish despite treatments or addition agents.

As to temperature, some brightener systems enable operation at temperatures up to 95 °F. Ideally, the trade off between conductivity, chilling cost and brightener cost is about 80 to 85 °F with modern brightener systems.

Gene Packman
process supplier - Great Neck, New York


A. Dear Sir,

The problem of your bath becoming yellow is in fact an oxidation to metastanic salts - It should not be a problem to plate from an electrolyte in that stage providing you are depositing from Sn+2. The presence of such by product in large amounts causes premature yellow deposits and sometimes problems with solderability.

You may reduce the presence of the metastanic salts in your bath by filtering from time to time with "granular" activated carbon "not powder", the same type you use in water softening equipments or deionizers. It depends of what kind of brightener system you are using, the bath will be able to work at around 40C !

The use of Clarifiers or polyelectrolytes designed specifically for that purpose by vendors of processes,is also an alternative, however you should bear in mind that the amount of sludge produced by this treatment is tremendous and carries along a major portion of good brightener as well as some Sn+2 from your bath.

Domingos J C Spinelli
SurTec do Brasil Ltda - S B Campo SP, Brazil

October 7, 2008

Q. I must say I am very new to Electrolytic Tin plating. I have been using a commercial solution of Tin(II)in Sulfuric Acid for the past three months. I have noticed that the solution is now turning yellow. Any ideas what could be happening.

Thanks for your help.

Maurice Mason
Plating Engineer - Danbury , Connecticut, USA

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