Tin whiskering risk factors

Whiskers are elongated single crystals of pure tin that have been reported to grow to more than 10 mm (250 mils) in length (though they are more typically 1 mm or less) and from 0.3 to 10 μm. in diameter typical 1-3 μm). Whiskers grow spontaneously without an applied electric field or moisture (unlike dendrites) and independent of atmospheric pressure (they grow in vacuum). Whiskers may be straight, kinked, hooked, or forked and some are reported to be hollow. Their outer surfaces are usually striated. Whiskers can grow in nonfilament types which are sometimes called lumps or flowers. Whisker growth may begin soon after plating. However, initiation of growth may also take years. The unpredictable nature of whisker incubation and subsequent growth is of particular concern to systems requiring long term, reliable operation.