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Tin-Zinc Whiskers - Less Likely Than Pure Tin or Pure Zinc?

We are a manufacturer of switching products that go into medical equipment, so recently reading the 1994 article from Metal Finishing hit close to home. We used to use cadmium plating on the outer housing of our assembly (which I now read could whisker as well) and switched to a Tin-Zinc plating. The topic was touched on in couple of postings but never really answered. Are there any publications that compare pure tin, pure zinc, and zinc alloys (specifically tin-zinc) for their risk of whiskering?

Michael Wood
Designer - Carpentersville, Illinois, USA
November 4, 2009

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Hi, Michael. I do not have the hard data that you seek, but I think you are on the right track. My understanding is that the whiskers are a crystal growth that are powered by the stresses in the plated deposit, and that alloys are far less susceptible because the growth is much harder to build with the dislocations that would be inherent in a multi-metal crystal. My understanding is also that the main reason a small amount of lead was included in tin-lead plating for so many years was not for solderability but to deter whisker growth.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 5, 2009