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Particulate and gaseous contamination: effect on computer reliability and monitoring.

Article Excerpt
INTRODUCTION

It is known that particulate and gaseous contamination in data centers can degrade computer reliability. Dust settled on printed circuit boards can lead to electrical shorting of closely spaced features with a voltage drop across them and it can corrode the circuit board metal traces and components. The electrical shorting occurs when ionic bridges created by the ionic components in the dust absorb moisture from the environment. Corrosion requires the presence of ionic components in the dust as well as moisture in the air. It can occur on non-electrically energized hardware. Corrosion can also be caused by gases in the air in the presence of moisture. Besides corrosion and ion migration, dust can degrade computer reliability by entering electrical connectors. Dust in power connectors can cause overheating due to i2R losses. Dust in signal connectors can cause electrically noisy contacts.

Harmful dust in data centers is generally high in sulfur-and chlorine-bearing salts. The source of this harmful dust is mainly outdoor dust, dust from industrial operations and from data center humidifiers. The harmful gases in data centers are generally sulfur-bearing gases such as sulfur dioxide and hydrogen sulfide from volcanic activity, the burning of low-grade coal for home heating, large-scale power generation and automobile exhaust. Sulfur-bearing gases have also been known to originate from furnishings, such as carpets, in data centers.

As already mentioned, moisture in the air is a necessary ingredient for corrosion or ion migration. The relative humidity threshold above which corrosion or ion migration can occur depends on the type of metal being corroded and the specific particulate or gaseous contamination (Rice et. al., 1981). Typically, as shown in Figure 1, corrosion becomes negligible below about 50% relative humidity.

[FIGURE 1 OMITTED]

This paper is based mostly on IBM research done in the 1980s and on the authors' experiences over the past 30 years.

DUST CONTAMINATION

The most important parameter controlling corrosion is the relative humidity in the data center. Each salt contaminant has a deliquescent relative humidity above which the salt will absorb moisture and become wet. Wet salt can corrode metal. For example, as shown in Figure 2, magnesium chloride dust on steel will corrode steel under relative humidity conditions above its deliquescent relative humidity of 32%. Since most data centers relative humidity is in the range 40-60%, well above 32%, magnesium chloride is very corrosive to metallic hardware (see Figure 3). Magnesium chloride dust,...