Corrosion-Resistant Outdoor Electronics

Abstract

The operating telephone companies are committed to assuring reliable and continuous quality telephone service. Environmental durability must be designed into the components of the electronic coin telephone that is often located in uncontrolled environments and in areas of continuous exposure to corrosive pollutants. To observe and quantify the effect of the environmental pollutants on coin telephone equipment, functional but unhoused electronic printed circuit board assemblies, a fully assembled, unhoused electronic chassis and coin acceptor, and a fully housed electronic chassis and coin acceptor were placed in a chamber and exposed to a pollutant-containing environment along with copper, nickel, and electroplated gold control coupons. The test pollutant atmosphere was a Battelle Laboratories Class III atmosphere consisting of air at 30°C and 70% relative humidity with H2S, Cl2, and NO2 at 100, 20, and 200 ppb, respectively. We report the results of Auger electron spectroscopy with Ar+ ion depth profiling that was done on various electronic components from housed and unhoused circuit packs and the control coupons. In general, corrosion film thicknesses on circuit components were less than coupon film thicknesses. This is attributed to the circuit pack geometry and component shrouding. A theoretical model supports the experimental results. Repeated functional testing at 95% relative humidity of both the housed coin telephone and unhoused assemblies was performed after exposure in the polluted atmosphere. After exposure, all circuits performed according to specification with respect to laboratory central office equipment and a fully active coin operation telephone line.