Capacitor plague
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The capacitor plague was a problem related to a higher-than-expected failure rate of non-solid aluminium electrolytic capacitors between 1999 and 2007, especially those from some Taiwanese manufacturers, due to faulty electrolyte composition that caused corrosion accompanied by gas generation; this often resulted in rupturing of the case of the capacitor from the build-up of pressure.
Failed aluminium electrolytic capacitors with open vents in the top of the can, and visible dried electrolyte residue (reddish-brown color)
Results of fire on a printed circuit board, caused by leaked electrolyte which short-circuited conductors carrying power
Closeup of a broken electrolytic capacitor vent and dried electrolyte residue
Failed Chhsi capacitor with crusty electrolyte buildup on the top
Aluminum electrolytic capacitor
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Aluminum electrolytic capacitors are (usually) 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 aluminum 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 (cathode) (-) 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 with non-solid electrolyte have a wide range of styles, sizes and series
Basic principle of anodic oxidation, in which, by applying a voltage with a current source, an oxide layer is formed on a metallic anode
Opened winding of a capacitor with multiple connected foils
Construction of a typical single-ended aluminum electrolytic capacitor with non-solid electrolyte