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Zinc Whiskers
What are zinc whiskers?
- Zinc whiskers ‘grow’ (rather like crystals) from metal surfaces that have been coated with zinc to help protect them from corrosion. Whisker growth appears to be limited to electroplated surfaces (for example: the Zintek process) rather than those that have been hot-dipped or sprayed, and is caused by internal stresses incurred during the plating process. Fine zinc filaments, normally only a few microns in width, but of several hundred microns to millimetres in length, develop from the plated surface.
- Although zinc whiskers have been found on a wide range of surfaces, access floor tiles are of particular concern, as they have large surface areas, and are often moved during day-to-day maintenance. The zinc whiskers are fragile and can easily be broken off the tile - some whiskers may then get into the supply airflow and be carried to the hardware via the ducting beneath the flooring, as in the above case.
Why are zinc whiskers a problem?
- Conductive zinc whiskers have been known about for many years but older electronic designs with larger gaps between components and pins were less likely to be compromised. As circuitry has evolved it has become more closely packed and operating voltages are lower. The whiskers can become long enough to bridge many gaps between pins of components in newer installations and the ever denser geometry of the new technologies means that this problem could increase.
- Financial companies, in particular, have become increasingly aware of failures in their electrical installations, in particular data processing equipment, caused by small metallic particles of zinc being deposited on PCBs causing intertrack conduction.
- The source of the zinc has been traced to the zinc coating on the underside of raised access floor tiles. Examination showed that zinc whiskers were present and were being carried in the air flow from pressurised under-floor plenums into the intake vents of electronic equipment.
Guidance
- In the UK, The Association of Raised Access Floor Manufacturers has informed its member companies about this problem and most of them now use hot dip galvanised steel sheet rather than zinc electroplating.
- When specifying raised access floors, ensure that you specify hot-dip galvanizing, or zinc-spraying, and do not specify electroplating.
- A considerable amount of more detailed information is available elsewhere on the internet. Use this Google link.
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Page last reviewed: 09/10/2006
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Comment: 27/03/2007
There is some debate as to whether this problem is equally applicable to the pedestals of raised access floor systems. Some experts consider it is an equal problem whilst others think it is a lesser problem as (a) pedestals are moved less than panels and there is thus less chance of the whiskers being disturbed and "breaking-free", and (b) because the incidence of reported problems has been far less. Some recommend that specifying hot-dip galvanizing, or even powder coating, may be desirable in areas containining highly-sensitive electronic equipment.