Conductive anodic filament enhancement in the presence of a polyglycol-containing flux [PWBs]

Under certain environmental conditions, printed wiring boards (PWB) respond to applied voltages by developing subsurface deposits of copper salts extending from anode to cathode along separated fiber/epoxy interfaces. These deposits are termed conductive anodic filaments (CAF). In this work, the dimensions and growth patterns of a CAF has been determined by serial sectioning. The CAF growth pathway is characterized and the spatial distribution of the copper salts is quantified with scanning electron microscopy (SEM). The chemical composition of the CAF is determined using energy dispersive X-ray analysis (EDX). The failure phenomena known as CAF poses serious long term reliability risks in electronic applications where the PWB is exposed to adverse and hostile environments or those with closely spaced conductors. Recent ion chromatography results indicate a correlation between the polyglycol and halide content of the soldering flux, and a substrate's susceptibility to CAF formation.