Stressed metals can sprout circuit-shorting “whiskers”
In humans, acute stress has been linked to hair loss. In metals like tin and zinc, the opposite is true, as stressed bits of metal can sprout wispy, hair-like structures commonly known as metal whiskers. Before any stressed, balding folks feel jealous of these growths, they’re actually worse than any hair loss you’ve experienced, because these whiskers can cause everything from equipment failures to fires, often in delicate electronics or equipment.
Unlike your hairs which are discrete structures assembled by special cells in your skin, metal whiskers are simply outgrowths of the same metal the larger object is made of. They’re basically a function of the metal’s crystal structure being bent and warped in new ways, with single rods of metal being extruded from the surface of the object. These whiskers don’t branch, and generally start growing at a perpendicular angle to the objects surface, although once they get going they can start clumping and bunching into a tangled rat’s nest that would be a challenge for any hair brush.
Hazardous hairiness
Many metals seem to be capable of growing metal whiskers. copper, cadmium, silver, gold, zinc and even alloys have been found to grow whiskers, although the biggest problem is tin. Tin seems to be relatively whisker-prone, which is a problem because tin is often used in soldering electronic circuits. The whiskers can end up making new connections in electronic devices that can cause short circuits, a phenomenon that has crippled computer networks, pacemakers, a nuclear reactor and even satellites. Even more dramatically, thin whiskers conducting a current can heat up enough to combust, leading to fires in computer banks. In some cases, particularly tiny bits of metal were found to have become airborne, drifting through the air until settling between other components, causing short circuits where whiskers weren’t even growing in the first place.
Engineers have yet to isolate a single reason for a piece of metal to fuzz itself up. Various stresses on the metal, from mechanical stress to stresses induced by diffusion of different metals have been linked to whisker growth, and so effective preventative measures aren’t always obvious. Lead used to help block the formation of metal whiskers, but it’s now banned from use in consumer electronics out of concern for human health. One of the more popular options now is conformal coatings, which basically coat your object in a protective sheath that is strong enough to stop whiskers from growing out of the metal before they get started.
Source: Metal whiskers – It’s like hair, on metals. And it’s a huge problem. by Umair Hussaini, Technobyte
