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Tin plating reel to reel aluminum

I am running reel to reel aluminum material that requires a light tin plate (10-20u). We have developed the necessary zincating process to combat the aluminum oxide. In sampling however, we found that we were unable to lay down tin plate that would not rub off. We found inconsistent adhesion. In the past we have been able to do this. I have a feeling that the reason is relative to the current of the tin, with it being low due to the light spec. Does anybody have a ballpark range for current density in ASF for this application? I have heard about immersion tin, and am also interested in that as a posssible alternative. Thank you in advance for any comments.

Alex Sanchez
Plating Shop Employee - Addison, Illinois, USA
February 15, 2008

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Alex, it all depends on what type of bath you are using. Acid tin is normally electroplated at between 10-25ASF, whilst fluoroborate tin is 25-125ASF. Tin from potassium stannate is plated at 30-100ASF and sodium stannate at 15-20ASF. An immersion tin can be deposited from a very hot but not boiling solution of sodium and tin cyanides, but I would not be too keen to operate this process!
I have never heard of tin plating on to a zincated aluminium, but presumably it can be done. The most common metals are copper and nickel onto aluminium, so it may be worth trying plating one of these before topcoating with tin. By the way, why are you reel-to-reel plating aluminium with tin?

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
February 17, 2008