Soft-Metal Whiskers

Soft-metal whiskers, tiny metallic protrusions that grow like hair from soft metals, are a problem that can cause electronic short circuits leading, in some cases, to the failure of heart pacemakers, avionic relays, and satellites. What to do with the unwanted whiskers---and, in the first place, understanding how they form---is a problem that's been around for fifty years. Now, researchers at Drexel University have arrived at what they think is an explanation for the cause of whiskers and a potential method for alleviating them. Basically, the whiskers form because of reactions between oxygen and the soft metal such as tin or indium. The reaction results in a volume increase that pushes the whiskers out. The whiskers that form do not have to break off in order to be troublesome; sometimes they cause mischief merely by bridging two neighboring electronic pathways that are supposed to be insulated from each other. The Drexel scientists believe that an oxygen-barrier coating on pertinent surfaces should prevent whiskers from developing. (Barsoum et al. Physical Review Letters, 12 November 2004; contact Elizabeth Hoffman, enh22@drexel.edu