Zinc Whisker Management, Testing and Consultancy
Why Zinc Whiskers Remediation is so Important
Zinc whiskers are a serious threat that can grow in Data Center’s and WILL cause hardware failures. Critical Facilities Solutions Zinc Whisker Testing & Consultancy services assure its clients a Data Center that is either free of zinc whiskers, or one that is professionally managed thereby eliminating many potential data corruption and server performance problems in the process. While there is no permanent ‘cure’ for Zinc Whiskers besides a full blown replacement of all effected parts, CFS will extract the majority of the longer dangerous zinc whiskers that threaten your systems with a report and management plan on completion or a full certification, if none are found, from CFS.
Formation and Characteristics
Zinc whiskers are a phenomenon that can occur on bare metal surfaces. Metal surfaces are coated with zinc in a galvanisation process to help protect them from corrosion. While several techniques are used, such as hot-dip or spraying, whisker growth appears to be limited to electroplated samples. The whiskers are zinc crystals formed by the degradation (corrosion) of the galvanised metal surface. Several industry studies have shown that whisker growth is dependent on internal stresses during the plating process. The crystalline structure within the metal will attempt to relieve the internal stress by enlarging the structure through the growth of crystals. The growth path is outward and the material is literally pushed out of the surface of the metal.
These crystalline growths (whiskers) are typically 2 microns in diameter and over time (many years) can grow to be several millimetres in length, up to 10mm although typically <1mm. Under proper lighting, they can be visible to the naked eye on surfaces. The whisker formation process consists of an unpredictable incubation period, typically lasting months or even years without any growth at all, followed by a period of growth at rates as high as 1mm per year. Some zinc coated surfaces may never grow whiskers. Unfortunately, accelerated techniques do not currently exist to predict if, when, and to what extent a zinc-coated surface will produce whiskers.
Effects of Zinc Whiskers: System Failures
While whiskers remain attached to their source ie floor panel, pedestal etc they are basically benign, however when the whiskers are disturbed and dislodged they become airborne and circulate freely throughout the environment. Disturbance is likely to be caused by routine maintenance activities in a Data Center, including lifting, sliding and reinstalling of access floor tiles and the pulling of electrical cable in the subfloor space. For efficient cooling the forced air-system typically pressurises the subfloor space with chilled air. Perforated floor tiles and air vents provide channels through which the cool air, including the zinc whiskers, can pass into the above floor space. Ultimately many whiskers can pass into the electronic hardware through vents and fans on the equipment. Once inside the equipment zinc whiskers, which are electrically conductive structures, can cause various electrical failures, ranging from intermittent to permanent short circuits. Whisker debris can also become a physical impediment to moving parts or obscure optical surfaces and sensors within some equipment (such as disk or tape drives) The first identification of zinc whiskers, and its associated system failures, occurred in the 1940’s. Renewed interest has arisen triggered by the apparent increase in reported failures. Several factors appear to contribute to the apparent increase:
- Continuous miniaturisation of electronic components technological advances have led to more densely packed circuitry and tighter spacing between conductors, therefore smaller conductive particles can now cause shorts.
- Reduction in circuit voltages and currents newer systems operate at lower levels and therefore energy from these components may not be sufficient to melt a zinc whisker, resulting in increased risk for permanent shorts.
- Age of existing floor structures many facilities now have flooring that has been in place for in excess of 10 years thus whiskers are of a length capable of bridging exposed conductor spacing’s.
- Increased maintenance and up-grade activity in raised-floor facilities any activity that involves moving flooring can dislodge whiskers, in today’s high-tech environments it is more commonplace for computing facilities to undergo regular maintenance activity, ie adding, removing hardware, repositioning and reconfiguring equipment etc.
During a one-month period, a NASA Data Center experienced at least 18 catastrophic power supply failures in newly installed mass memory storage devices. The ensuing failure investigation determined that the causes of failure were electrical short circuits’ These had been caused by small metallic filaments growing on the underside of raised floor tiles and support structures that had been dislodged during maintenance and distributed throughout the Data Center by forced air cooling systems.