Shrinking computer hardware calls for sharper contamination management

October 5, 2010

Data centre operators face continued pressure to deliver faster computing power and more capacity from less space. And shrinking component technology is allowing them to do this. But data centres typically also house objects that are galvanized for corrosion resistance; some emit zinc whiskers which can increasingly compromise computer reliability.

Raised access floor structures which have been electroplated are a particularly significant zinc whisker source, as they have a large surface area and are often disturbed during maintenance activities. Once released, whiskers can be transported by the centre’s forced air cooling and then by equipment fans onto the computers’ electronics. Here, they can cause intermittent or permanent short circuits, impede moving parts, or obscure optical surfaces and sensors on magnetic storage drives.

The apparent rise in such failures can be attributed to several possible factors. With continuous component miniaturization, more densely packed circuitry and tighter conductor spacing, smaller conductive particles can now cause shorts. Furthermore, permanent shorts are more likely, as reduced voltage operation means insufficient energy to melt problematic whiskers. As floor structures age to 10 years or more, longer whiskers with more bridging potential become more prevalent, while increased maintenance and upgrade activity dislodges even more whiskers.

Airborne whiskers are a potential health hazard as well. The nature and extent of this is not well understood, but exposure to inhalation of whiskers must certainly be prevented.

Sampling should be conducted by competent personnel who understand the need to contain, rather than spread, contamination during the sampling process. Scanning Electron Microscopy (SEM) is the most common method for confirming zinc whisker contamination. Using a laboratory for SEM analysis is not the cheapest way of identifying suspect sources, but it is the most conclusive.

Both short and long term remediation options are available if contamination is identified. In the short term, protectively coated electronics can replace affected components, and floor tile handling activity can be minimized. Longer term solutions include: carefully planned removal of affected or suspect tiles and other items, a thorough cleaning of the data centre using H-type vacuums, and installation of replacement floor structures, not prone to whisker formation. Simply washing infested materials is ineffective, as whiskers can grow back and need to be professionally extracted from the environment. Conformal coating is a possible solution, but it requires long-term testing for validation as whiskers can potentially grow through some coatings. The best approach for any situation depends on the extent of contamination, the condition of the tiles and structure, the size and location of the affected area, cost, time and management commitment to minimize the problem.

ISO 14644 provides a standard for air cleanliness, with nine classifications defined by the number of microscopic particles per cubic meter of air. Most data centres need to meet Class 8 (3.52 million 0.5?m particles/m-³) or Class 9 (35.2 million 0.5?m particles/m-³) standards.