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Corrosion of stainless steel 316 as anode in electrically tin plating over copper panels

2003

We are manufacturing printed circuit boards. One of the process utilize SS316 as anodes in a tin sulphate 18 gm per liter of tin metal /10%sulfuric acid solution, ST301 brightener( grain refiner) for plating tin over copper surface as etch resist. There are 2 lines, installed a year 6 months ago. Lately one of the anodes were corroding and gassing both at anodes and cathodes ( copper panels ) and the other tanks is fine. The bath solution turn greenish on the gassing anode tank while the other stay clear and yellowish ( normal ). When analyzed iron on the problem tank, the result was 900 ppm of iron, while the other has only 9 ppm, an indication of anode corrosion as we had found that when the anode is pulled out and examined. The SS316 is corroded to point of breaking off. So can anyone advice a solution to this problem? Is there a simple way of checking SS316?

Thanks,

Wai Ng
- Toronto, Ontario, Canada

A fix is to use pure tin anodes. Another fix is to replace the 316 anode on a periodic schedule. The problem is that the 316 will do reasonably well, but when the iron builds to a given level the ferric/ferrous sulphate ferrous sulphate [affil links] will start to pit the SS. The higher the content, the faster the attack. Once the anode is pitted, it will be attacked even faster.Your green color is from the dissolved nickel in the tank.

James Watts
- Navarre, Florida
2003