How damage is caused
How contamination damages ICT equipment.
Contaminants can affect ICT equipment in different ways, according to its composition and properties. PM can comprise organic, inorganic, synthetic or metallic materials, alone or combined. It can be abrasive, corrosive, electrically or thermally conductive, insulating, or hygroscopic. Its effect on ICT equipment falls into three categories:
- Electrical: Some PM particularly zinc whiskers is conductive, and can cause impedance changes or bridge tracks in electronics circuit boards.
- Chemical: Corrosion of surfaces, dendrite growth and material property changes such as embrittlement or clouding of optical surfaces.
- Mechanical: Obstruction of cooling air flow, interference with moving parts, abrasion, optical interference, interconnect interference, deformation of magnetic media and other surfaces, and other similar effects.
These effects can be caused by one form of PM, several forms combined, or by combinations of particulate and gaseous contamination. Elevated humidity can also accelerate contaminant damage, particularly corrosion. The damage arises as the contaminants accumulate. The rate of accumulation is related to contaminant concentration and the volume of air passing through the susceptible equipment. Therefore, forced-air cooled equipment may be more susceptible to accumulated PM than liquid or free convection cooled equipment. Examples of susceptibilities include:
Fans, heat sinks and cooling mechanisms – Current CPU heatsink designs typically feature thin, closely spaced metal cooling fins. These are susceptible to blockage, especially if the contaminant has significant fibre content. The cooling efficiency of the heatsink, and of any attached fan, is compromised. This can cause intermittent or permanent equipment failure, as well as increased energy demand as the fans work harder to overcome the airflow restrictions.
Magnetic media and optical drive mechanisms Particulate contaminants can cause abrasion or block moving parts within media drive positioning and auto-loading functions. Particles can cause deformation of media surfaces, or interfere with head contact or spacing. In extreme cases contaminants may abrade read/write heads and may also interfere with the optical signal used to read or write data on the media. Magnetic media can also generate contamination in the form of oxide flake-off.
Electronics circuit boards and connectors. Contaminants, especially zinc whiskers, can be electrically conductive. If these settle within ICT equipment so as to bridge between signal tracks on an electronics circuit board, they can cause a short circuit resulting in either intermittent or permanent equipment failure. Short circuits can also be caused by less obvious mechanisms such as leakage paths created by moisture-laden hygroscopic particulate accumulation. Water-soluble ionic salts can also produce electrically conductive contaminants if they absorb sufficient moisture from the ambient air. Whereas particle accumulation may take place over a number of years, the change in conductivity can occur suddenly. Sudden spikes in humidity can trigger equipment failure.
Gaseous contamination susceptibility. Sulphur bearing gases such as sulphur dioxide (SO?) and Hydrogen Sulphide (H?S), are the most common gases in data centres causing corrosion. SO? is a product of fossil fuel combustion, organic waste incineration, and is also found in paper, fabrics, food preservatives, fumigants and refining. It reacts with water to form sulphuric acid, which is highly corrosive. Sulphur bearing gases can also react with silver inside electronic components to form silver sulphide (Ag?S) flowers. Such formations have been known to create enough mechanical stress to cause component failure.
