“Lumpy” Stannate Tin

Ask an Expert From: Products Finishing, ,

Posted on: 5/16/2013

I am having problems plating stannate tin on parts that have a copper flash. Parts are “lumpy” and dewetted.

Q. I am having problems plating stannate tin on parts that have a copper flash. Parts are “lumpy” and dewetted. What do you think is the problem? A.G.

A. I would start by looking at your stannate tin plating steps. A tin strike at 40–60 ASF for approximately 1 minute and then plating at 30 ASF for the required time is pretty much the standard process. Assuming this is the general procedure you are using, here are some possible causes for your “lumpy” deposit:

ProblemPossible Cause
Rough deposit
Stannite ions present in the bath.
  1. Are anodes uniformly filmed?
  2. Is current density correct?
  3. Add 20% by volume hydrogen peroxide at approximately 1.5 mL per L of bath. This addition oxidizes stannite ions to stannate.
Spongy deposit

Stannite ions present in the bath.

  1. See Rough deposit above.
  2. Excessive sodium hydroxide in bath. Lower by adding 100 mL of acetic acid per L of plating solution.

 


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