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-----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]1999
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, P.E.
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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
Mabank, Texas USA
1999
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