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topic 3762

Tin Whisker problem


I am a hardware engineer. I have a problem of shorting two pins of a terminal block of a module on the field. This 5 mm spacing terminal block pins are tin plated. I think the cause of this shorting is whiskers (Based on articles of NASA about whisker). I wonder if there is way to recreate the short, in other words how to generate the whisker growth to have a short between two pins and how to prevent the short. Thanks.

[name removed at writer's request]

Whiskers are believed to be a stress-relief process that purer metals tend to undergo spontaneously. Consequently the way to produce them is with highly stressed pure tin deposits. The way to discourage them is via a stress relieving process and/or by including alloying metals in the deposit.

Historically, lead was used and is useful in even fairly low concentration. But with environmental pressures against lead, whiskering has become a bigger problem even though it was thoroughly researched decades ago. You might do a lit search about tin-bismuth as I understand that a small amount of bismuth in the deposit is effective in minimizing whiskering.

Our FAQs will link you to several other letters here about tin whiskers.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


It sounds like a small amount of Lead in the Tin deposit would eliminate the whiskering (2%-10%). Hot Oil Flowing will also help if you don't want to use Lead. I've been looking in to the Tin/Bismuth deposits and their use in extreme cold environments. I know that they help control Tin Pest problems (flaking) at temperatures below -42C. The Aerospace Industry is especially interested in this. I've been trying to find a supplier for this but they are still in development.

jim conner
Jim Conner
Anoplex - Dallas, Texas USA

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