Abstract
Conductive anodic filament (CAF) formation, a failure mode in printed wiring boards (PWBs) exposed to high humidity and high voltage gradient, has caused catastrophic field failures. This study quantified the effect of flux chemistry, applied voltage (V), spacing (L), and temperature on the failure rate. Test vehicles, which had hole-to-hole spacing of 0.5 mm or 0.75 mm, were processed with one of three water-soluble fluxes (WSFs), and a heated control was also evaluated. The samples were placed in a temperature humidity chamber at 85%RH, at one of three temperatures: 75°C, 85°C, or 95°C. A voltage of 150 V or 200 V was applied to the test vehicle and periodically removed so that a measurement could be taken. A specially designed linear circuit was used to determine when the insulation resistance dropped significantly, indicating a failure. Activation energies were determined. The mean time to failure was a function of L 4 /V 2 .
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