Network Communications News (NCN) September 2016 - Page 30

S P E C I A L F E AT U R E cable management & labelling Metal whiskers are a crystalline metallurgical phenomenon whereby metal grows fine, filiform hairs. The weakest zinc There is a lack of clear guidance when it comes to the issue of zinc whiskers in data centre environments. Tim Brown of Unitrunk examines the phenomenon and the risks it poses, and looks at what can be done to combat those risks during specification. T here is considerable confusion in the data centre sector over the phenomenon known as zinc whiskers. Despite the risk that zinc whiskers pose, specifications are rarely stringent enough to eliminate the problem altogether, with the cable management industry seemingly bearing the brunt of the attention and focus when other parts of the building specification, such as computer floor tiles and supports, should be equally considered. So what are zinc whiskers and why are they a problem? Put simply, metal whiskers are a crystalline metallurgical phenomenon whereby metal grows fine, filiform hairs. Although this phenomenon tends to occur primarily on elemental metal surfaces, it has also been reported on alloy systems. It is accepted that the presence of whiskers can cause short circuits and arcing in electrical and electronic equipment. Not the cat’s whiskers Looking at zinc whiskers specifically, it is generally accepted that their presence has been responsible for increased system failure rates in computer machine rooms. Zinc whiskers grow from galvanised (electroplated) metal surfaces at a rate of up to 1mm per year with a diameter of a few micrometres. Whisker growth in both zinc and tin is generally believed to occur as a relief mechanism (similar to a pressure valve) that will reduce compressive stresses existing within pure metal plating. In general, growth is most likely induced by a range of stresses such as those resulting from: Residual stress within the plating – caused by the plating chemistry, plating p \܈YX[X[ܚ[˜Y\][˂ LHXHX[Y[Y[8$[][˚[  ̌ M MN