Whiskers – a growing problem?

Writing about whiskers in November tends to associate peoples’ thoughts with “Movember” — the month for men (or women) to grow facial hair in aid of testicular cancer research.

However, zinc whiskers are entirely different, an unusual phenomenon that can cause trouble in computing environments at any time of the year.

If you’ve not heard of this before, and you are responsible for running a sensitive site and/or critical applications, then it would be worthwhile to listen to the experience of Wander ter Kuile of Waterloo Air Products.

According to Wander, zinc whiskers have been a nuisance since they were first discovered and documented in the early twentieth century when they were responsible for short circuits in electronic devices using pure tin solder.
 
“Zinc whiskers are very small crystalline structures which can grow on bare metal surfaces,” he explains. “They pose a serious threat to buildings where they can be found on a variety of metal components, in electrical conduits, in suspended ceilings and access floor panels. But they are a far more serious threat to data centre environments, particularly when they become airborne. The phenomenal growth in data centres, has thrown the problem into the spotlight as IT managers grapple with the problem and prevent system failures which could prove costly.”

The whiskers are described as being approximately two microns in diameter but over many years have been recorded several millimetres longer. They can usually be found on bare metal surfaces of access flooring systems and affected components can include some wood-core and concrete-core computer room flooring panels. The whiskers grow on the plenum side of the floor panels or the exposed surfaces of the structural components. They can also be found in the fabric of buildings, notably suspended ceilings and electrical conduits, as well as equipment racks and actual computing systems.

Ferrous metals such as steel are normally plated to prevent corrosion. Zinc is a common plating material, but a normal bi-product of the plating process is high molecular level stresses. The crystalline structure within the metal will attempt to relieve the stress by growing crystals, which are literally forced through the surface of the metal, giving the appearance of whiskers.

“To date there is no evidence to suggest that temperatures or humidity exacerbates their growth,” comments Wander. “It therefore appears that if components are destined to grow whiskers, they will grow regardless of the environmental conditions.

“Problems only arise when they break free and circulate in the air, as they can then get blown into equipment. An unexplained hardware or software failure could be the first sign that there is a problem.”
So why is this a problem now?

“The frequency of companies migrating to new systems increases the number of incidences and secondly, there are a substantial number of ‘legacy’ data centres that have been in use for many years, long enough to grow whiskers, he says.

“It is simply a matter of time before they present a problem. Thirdly, technology has resulted in dramatic shrinkages of componentry and circuits making them more vulnerable to a whisker attack.

Prevention

Only components made from ferrous metals are said to be at risk. Removing floor panels and ensuring a rigorous cleaning programme is carried out is one solution, but this would need to be carried out regularly and is likely to incur extra maintenance costs.

“Alternatively, ensure that any plating applied to metal surfaces is done using hot dipped galvanisation (HDG),” advises Wander, adding “whiskers do not grow on HDG plating.

“Some companies may suggest painting over the zinc coating, but this is a short term fix as whiskers will continue to grow through the paint. Using a manufacturer who understands the problems is essential.

In addition, to prevent the risk of zinc whiskers entering your equipment, HEPA filtration is recommended and often deployed by businesses running critical applications.

Preventative steps

  • Ensure painted or coated products destined for your data centres are wrapped as soon as possible after the process.
  • If supplied by a subcontractor the items should be air blown prior to packing
  • Galvanised components should, prior to wrapping, be air blown to remove any manufacturing residues
  • Products requiring sub-assembly should not be left uncovered.
  • Finished products should be air blown and wrapped immediately

“Zinc whiskers have been around for a long time but rarely are they talked about by customers or equipment vendors. A serious approach to Zinc whiskers will ensure that, wherever possible, the risks are reduced,” says Wander.
Zinc Whisker photo copyright to Peter Bush.

 

For more information please contact;

Wander ter Kuile
Technical Manager
Tel: 01622 711511. Fax: 01622 717861