The ECAS series utilizes multilayer etched aluminum foil for anode and solid conductive polymer for negative cathode. The etched aluminum foil increases the surface area of the capacitor, thus increasing the capacitance value. The foil is oxidized to create the dielectric alumina (Al₂O₃). Alumina has very stable dielectric characteristics, making the capacitance of the ECAS series stable over temperature and voltage. Unlike MLCCs, polymer electrolytic capacitors have a marked polarity so proper placement on the PCB board is important. This also means that the ECAS series cannot be used in AC circuits.