Reduce the risk of Zinc Whiskers with the correct choice of cable containment finishes

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What are Zinc Whiskers? Known to exist since the 1940’s, Zinc Whiskers are believed to have caused failure in many computer environments each year. They are believed, primarily, to be caused by forming on the exposed underside of galvanised floor tiles. Zinc Whiskers can also grow on any electroplated metal which in turn may be found in equipment racks and cabinets, inner door skins, mounting rails and cable containment. In the process of electroplating, a continuous layer of zinc atoms, are added to the surface under ‘compressive stress’. The atoms are squeezed together and force Zinc Whiskers to extend from the surface as illustrated in this photograph.

The whiskers grow at a rate of about 250 microns per annum and have a diameter of 2 microns. The whiskers will reach up to 1cm in length and can become a problem to electronics when they reach a length of 500 microns and can break off and become airborne.

What Happens? Zinc is a metal and therefore a conductor of electricity. If a Zinc Whisker comes to rest on an exposed circuit card inside equipment, it will very likely cause a short, possibly an intermittent, short which is difficult, and expensive, to detect and fix. Symptoms of Zinc Whisker related failures

range from minor data corruption or anomalies to catastrophic hardware failures. A commonly reported problem is a high incidence of power supply failures.

What to do? As Zinc Whiskers occur on a surface finish that has been electroplated it would, therefore be prudent to remove, as far as possible, all instances, where this form of coating is offered, from all data centre and computer room environments. Support Comms would point specifiers and clients towards the European cabling specification BSEN 50174-1 standard where recommendations are made to the use of factory made fittings which will minimise or prevent the need to reduce the amount of bending and cutting of cable basket thus alleviating the implied stress on the containment this activity causes.

The solution is to use a stable material which will be free of the occurrence of Zinc Whiskers. Hot-dipped galvanising is such a material. However, care must be taken as there are 2 distinct types of hot-dip galvanised finish available for cable containment products commonly known as pre-galv and post-galv. The pre-galv surface is clean and smooth whereas the post-galv is uneven and has a tendency to deposit flakes of zinc that could be equally damaging as zinc whiskers as well as damaging to delicate data cables. Therefore it is recommended, that In order to eliminate the risk of Zinc Whiskers, the solution is to use a material, flake free, hot-dipped, pre-galvanised finish, to BS EN 10346 (is the Standard for PG material) or equivalent should be specified.

Conclusion Where possible use materials and/or finish where zinc whiskers will not be formed. Steel fabricated containment should be of the hot dipped, pre-galvanised finish. Also to minimise or prevent on site cutting and fabrication by using factory made fittings and accessories.

Pre-Galv Type Hot-Dip Galvanising Process (BS EN 10346)

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