page_title: Aluminum electrolytic capacitor
section_title: Failure modes
hierarchical_section_title: Aluminum electrolytic capacitor / Reliability, lifetime and failure modes / Failure modes
caption_attribution_description: Deutsch: Aluminium-Elektrolytkondensator mit geöffneten Sollbruchstellen im Becher, sog. "bad caps". English: Aluminum electrolytic capacitor (green cylinders) with opened breaks at tops, as defective capacitors, or "bad caps".
context_page_description: Aluminium electrolytic capacitors are polarized electrolytic capacitors whose anode electrode is made of a pure aluminum foil with an etched surface. The aluminum forms a very thin insulating layer of aluminium oxide by anodization that acts as the dielectric of the capacitor. A non-solid electrolyte covers the rough surface of the oxide layer, serving in principle as the second electrode of the capacitor. A second aluminum foil called “cathode foil” contacts the electrolyte and serves as the electrical connection to the negative terminal of the capacitor.
  Aluminum electrolytic capacitors are divided into three subfamilies by the type of electrolyte:
  non-solid aluminum electrolytic capacitors,
  solid manganese dioxide aluminum electrolytic capacitors, and
  solid polymer aluminium electrolytic capacitors.
  Aluminum electrolytic capacitors with non-solid electrolyte are the most inexpensive type and also those with widest range of sizes, capacitance and voltage values. They are made with capacitance values from 0.1 µF up to 2,700,000 µF, and rated voltages values from 4 V up to 630 V. The liquid electrolyte provides oxygen for re-forming or self-healing of the dielectric oxide layer.
context_section_description: Aluminum electrolytic capacitors with non-solid electrolytes have, in terms of quality, a relatively negative public image. This is contrary to industrial experience, where electrolytic capacitors are considered to be reliable components if used within their specified specifications during the calculated lifetime. The negative public image might be, among other reasons, because failed electrolytic capacitors in devices are easily and immediately visible. This is exceptional and not the case with other electronic components.
  As with any industrial product, specific causes of failure modes are known for aluminum electrolytic capacitors with non-solid electrolytes. They can be differentiated in failures causes by capacitor development and production, by device production, by capacitor application or by external influences during use.
  The capacitor manufacturing industries can only influence the first failure mode. Most manufacturers have had well-structured quality control departments for decades, supervising all development and manufacturing steps. Failure mode flow charts demonstrate this. However, a typical physically or chemically caused major failure mode during application, like "field crystallization" for tantalum capacitors, is not known for non-solid aluminum electrolytic capacitors.
caption: Failed aluminum electrolytic capacitors with open vent caused by using a wrong electrolyte
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