Conductive contamination
Semiconductors and sensitive electronics used in current Information Technology equipment have allowed for the manufacture of very high density electronic circuitry. While new technology allows for significant increases or capacity in a smaller physical space, it is susceptible to contamination, especially contamination particles that will conduct electricity. Since the early 1990s, it has been determined that data center environments may contain sources of conductive contamination. Contaminants include; carbon fibers, metallic debris such as aluminum, copper and steel filings from construction, and zinc whiskers from zinc-electroplated materials used in raised floor structures.
Although very small, and at times not easily seen without the visual aide of magnifying lenses, this type of contamination can have disastrous impacts on equipment availability and reliability. Errors, component damage and equipment outages caused by conductive contamination can be difficult to diagnose. Failures may be at first attributed to other more common factors such as lightning events or electrical power quality or even just presumed to be defective parts.
The most common conductive contamination in raised-floor data centers is what is known as zinc whiskers. It is the most common because it is frequently found on the underside of certain types of access floor tiles. Typically, the wood core style floor tile has a flat steel bottom. The steel may be coated with zinc either by a hot dip galvanize process or by zinc electroplate. The zinc electroplate steel exhibits a phenomena which appears as whisker-like growths on the surface. These small particles of approximately 1-2 mm (.04-.08 in.) in length, can break away from the surface and get pulled into the cooling air stream. Eventually they my be ingested by the equipment air, settle on a circuit board and create a problem. If you suspect that you may have this type of problem, contact your service representative.
Airborne particulates (including metal flakes or particles) and reactive gases acting alone or in combination with other environmental factors such as humidity or temperature might pose a risk to the 9176 that is described in this document. Risks that are posed by the presence of excessive particulate levels or concentrations of harmful gases include damage that might cause the 9176 to malfunction or cease functioning altogether. This specification sets forth limits for particulates and gases that are intended to avoid such damage. The limits must not be viewed or used as definitive limits because numerous other factors, such as temperature or moisture content of the air, can influence the impact of particulates or environmental corrosives and gaseous contaminant transfer. In the absence of specific limits that are set forth in this document, you must implement practices that maintain particulate or gas levels that are consistent with the protection of human health and safety. If it is determined that the levels of particulates or gases in your environment have caused damage to the 9176, there may be a provision of repair or replacement of 9176 or parts on implementation of appropriate remedial measures to mitigate such environmental contamination. Implementation of such remedial measures is a customer responsibility.
| Contaminant | Description |
|---|---|
| Gaseous contamination | Severity level G1 as per ANSI/ISA 71.04-19851 which states that the reactivity rate of copper coupons shall be less than 300 Angstroms per month (Å/month, ~ 0.0039 μg/cm2-hour weight gain).2 In addition, the reactivity rate of silver coupons shall be less than 200 Å/month (~ 0.0035 μg/cm2-hour weight gain).3 As a best practice, the reactive monitoring of gaseous corrosivity should be conducted approximately 2 inches (5 cm) in front of the frame on the air inlet side at one-quarter and three-quarter frame height off the floor or where the air velocity is much higher. |
| Particulate contamination | Datacenters must meet the cleanliness level of ISO 14644-1 class 8. For data
centers without airside economizer, the ISO 14644-1 class 8 cleanliness may be met simply by the
choice of the following filtration:
The deliquescent relative humidity of the particulate contamination should be greater than 70% RH.4 Datacenters must be free of zinc whiskers.5 |
- ANSI/ISA-71.04.1985.
Environmental conditions for process measurement and control systems: Airborne contaminants.
Instrument Society of America, Research Triangle Park, NC, 1985. - The derivation of the equivalence between the rate of copper corrosion product thickness growth in Å/month and the rate of weight gain assumes that Cu2S and Cu2O grow in equal proportions.
- The derivation of the equivalence between the rate of silver corrosion product thickness growth in Å/month and the rate of weight gain assumes that Ag2S is the only corrosion product.
- The deliquescent relative humidity of particulate contamination is the relative humidity at which the dust absorbs enough water to become wet and promote corrosion and/or ion migration.
- As a best practice, one method that can be used to assess the presence of zinc whiskers is as follows. Surface debris is randomly collected from 10 areas of the data center on a 1.5-cm diameter disk of sticky electrically conductive tape on a metal stub. If examination of the sticky tape in a scanning electron microscope reveals no zinc whiskers, the data center is considered free of zinc whiskers.
- If there is any question about potential corrosive gases or level of particulates, contact your representative for assistance in monitoring the environment.
Beyond the specific information provided in this document, it is recommended that the customer's facility meet the general guidelines published in the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) Handbook.