Question posed by theModerator to Carol Handwerker:
As you point out, stress is typically considered a necessary but not sufficient condition for tin whiskers. Although care is taken to ensure that stress is minimized in the final product, it will never be totally reduced. From your perspective, what are the most important processing precautions that can be taken to truly minimize the impact of tin whiskers on product reliability?

Dr. Handwerker responded: As you point out, stress is typically considered a necessary but not sufficient condition for tin whiskers. Although care is taken to ensure that stress is minimized in the final product, it will never be totally reduced. From your perspective, what are the most important processing precautions that can be taken to truly minimize the impact of tin whiskers on product reliability

I think the most important thing to do from what we know right now is to make sure there is no copper in the electrodeposited film either intentionally or unintentionally. A lot of the electrolytes that are used are acidic, and you can actually get a fair amount of copper deposited if it’s first dissolved and then immediately deposited on the substrates as the components are being electroplated. So if we can make sure that the electrolytes are robust with respect to copper being incorporated into the cells, I think that certainly will help.

The other processing precautions are to really try to operate within the conditions that the electrolyte manufacturers have come up with and actually to make sure there is not a lot of organic that’s being kept in the baths because the baths are being held for too long.

And then the other thing that I mentioned before is I think Alloy 42 because of the CTE mismatch between tin and copper: I think it’s just a very bad combination when you’re trying to minimize the formation of whiskers. I think if we could do those things plus using the nickel underlayer I think is really important.