Bo Song, Michael H. Azarian and Michael G. Pecht
Center for Advanced Life Cycle Engineering (CALCE), University of Maryland, College Park, MD 20740, USA
One of the critical failure modes caused by dust contamination in electronics is surface insulation resistance degradation, or impedance degradation. Impedance degradation can lead to intermittent or permanent failure of PCB assemblies. In this study, two outdoor natural dust samples were collected from the field. We experimentally demonstrated that natural dust can cause impedance degradation under controlled temperature (20°C to 60°C) and relative humidity (50% to 95%) conditions. Critical transition ranges of relative humidity for the two dust samples were determined. Below the starting point of the transition range, the impedance was constant. Above the starting point of the range, the impedance degraded by orders of magnitude. The value of the critical transition range decreased with an increase in dust deposition density. Significant impedance degradation was observed as the temperature was raised from 20°C to 50°C. For each 10°C increase of temperature, the impedance dropped by approximately one order of magnitude. The failure mechanisms behind the impedance degradation processes associated with dust are discussed. Critical relative humidity of mixed salts, percentage of deliquescent substance, deposition density, and moisture sorption capacity were found to be key factors of dust that determine the effect of dust on impedance degradation.
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