25v Electrolytic Capacitors

Gideon Analytical Laboratories received five 25 volts (v) 120 microfarad (μF) electrolytic capacitors that were failing in the field. A capacitor stores electrical energy. They have two terminals separated by some type of insulating material, known as a dielectric. Usually, these dialectics are metal plates and the dielectric is made of materials like ceramics, mylar, or glass. Electrolytic capacitors are a type of capacitor that uses an electrolyte as one of its plates to achieve a larger capacitance per unit volume. The storage potential of a capacitor is known as capacitance and is measured in farads, and since most capacitors are generally small, microfarads are the most often used measurement of capacitance. The goal was to evaluate these five 25v 120μF electrolytic capacitors.

Failure analysis ensued. First, the leakage currents were tested on each capacitor. The capacitors were decapsulated. Visual examination of each capacitor revealed the Kraft papers were completely saturated with electrolyte; there were no foreign materials embedded within the anode foil. The aluminum oxide layers were brittle and had cracks running parallel to their thickness. The oxide and anode foil was etched to observe any defects more easily. There was aluminum oxide dislodged. SEM-EDS micrographs revealed a close up look at the deep etching. The aluminum metal was sandwiched between the aluminum oxide layers. The oxide should not be loose or have cracks in it, but it did. These holes and cracks caused abnormal levels of leakage current.

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