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What are the reactions in acid tin fluoborate plating?

Please I want to know the desired and undesired reations in an acid tin fluoborate bath. Lets say a copper plate is plated! If it is possible, I looking for detailed reactions. Please I have been looking everywhere and I can not find anything!

DUMISANI MKHWANAZI
DURBAN INSTITUTE OF TECHNOLOGY - DURBAN, SOUTH AFRICA
2005

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Tin fluoborate solutions are usually use because other metals such as lead also have soluble fluoborates. This makes tin-lead alloy plating quite easy. The anode is usually tin, so the anodic reaction is Sn(0) oxidising to Sn(2+), whilst the cathodic reaction is the reduction of Sn(2+) to Sn(0). The fluoboric acid just cats as the anion of the tin cations. However, the process needs free fluoboric acid and the greater it is, the greater the bath stability; there is a down side inasmuch as the free fluoboric acid limits the maximum current density. I also recall reading somewhere that one side reaction of electrolysing free fluoboric acid is the generation of hydrofluoric acid. This is not a good idea! However, I cannot vouch for the reliability of this side reaction. From my experience with fluoborates, I have never had any real problems with the chemistry, except if you have an air leak into the filtration system, you will run the risk of throwing out tin and lead as their oxidised metal oxides.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2005