Deposition of Airborne Sulfate, Nitrate, and Chloride Salts as It Relates to Corrosion of Electronics

Abstract

Corrosion of electronic equipment and devices is caused by a combination of corrosive gas and corrosive particle deposition to surfaces. Chemical and electrochemical interactions of these gases and particles with the surfaces contributes to the degradation and eventual wear out of the equipment or, in extreme cases, to premature failure. While the reactions of corrosive gases with materials used in electronics have been investigated in some detail, degradation caused by particles has received little attention. In earlier studies, we reported on single point measurements of airborne concentrations and multiple point measurements of surface accumulation rates of corrosive ionic substances at electronic equipment installations. From that data it could not be determined if the large variations (more than a factor of two) in surface accumulation rates of the major ionic substances were a result of variations in airborne concentrations of the corrosive ions or in the deposition process. In this study compact personal air sampling pumps have been used to collect corrosive species contained in total suspended particulates at many sites within an equipment room at locations in Newark, New Jersey, and Neenah, Wisconsin. The airborne concentrations of the major corrosive ionic substances measured across the equipment rooms exhibit variations of < ± 15%. This work shows that: (i) airborne indoor concentrations of these corrosive species are sufficiently constant (σ is 8 and 2% of the mean for fine particle sulfate at Newark and Neenah, respectively) across the equipment room that results from a single sampler are representative of the concentrations across the entire room; and (ii) the variation in surface accumulation rates of corrosive ionic substances (σ is 46 and 36% of the mean for fine particle sulfate at Newark and Neenah, respectively) is not attributable to the airborne concentrations and thus should be attributed to other factors probably related to air currents. This work further demonstrates that designing equipment and air distribution networks to minimize turbulence at surfaces is likely to reduce corrosion and degradation by at least a factor of 2–5.