Effect of Trace Elements on Etching of Aluminum Electrolytic Capacitor Foil

An investigation was made as to the effect of trace impurities, particularly bismuth and boron, on etching morphology and capacitance of aluminum electrolytic capacitor foil. It was found that as little as 2 wt‐ppm bismuth in foil strongly accelerated surface etching, inhibited tunneling, and consequently lowered capacitance. 3 wt‐ppm boron also enhanced surface etching, but lowered capacitance less than bismuth. The reason for these results was considered