The capacitors may fail to open circuit, short circuit or change in their parameters/specifications. Here in this article, we will discuss the different failure modes of various capacitor types.

Failure Modes of Aluminum and Tantalum Electrolytic Capacitors

  • If electrolytic capacitors are not hermetically sealed, the electrolyte in these capacitor eventually evaporates causing increased ESR which causes increased heating, which causes the safety seal on the capacitor to pop, because if it does not pop, the capacitor explodes.
  • Electrolytic capacitors may fail for surges in voltage applied. If voltage surges above the voltage safety margin, the capacitor may not fail instantly, but over time, the capacitors reform to the voltage they are being used at, and any voltage surge may destroy them.
  • The typical failure mode of an electrolytic capacitor is that the ESR becomes quite high and therefore it cannot be considered to be a Low ESR capacitor anymore. High ESR is basically the same as putting a resistor in series with a capacitor. The circuit will not perform properly and will have increased noise.
  • Another failure mode of electrolytic capacitors is that the capacitor maintains acceptable ESR but that its capacitance is much lower than it should be. This might be due to leakage of electrolytic capacitors. This can be considered as degradation failure (wear-out).
  • An electrolytic capacitor can fail open so that it is disturbing the flow of electricity in the circuit and then the circuit is no longer working at all. This might be due to corrosion of leads, mechanical damage to lead connections, or evaporation of electrolyte due to operation of the vent. It is possible for a capacitor to fail open without any visible signs.
  • An electrolytic capacitor can fail shorted which is probably the worst thing that could happen. A shorted capacitor would probably damage the entire circuit to an extent that it would be impossible to easily repair. It is possible for a capacitor to fail shorted also with no visible signs.
  • Soldering can also be critical to electrolytic capacitors, as they are on the topside of the board and are exposed to heat during the soldering process. This heat, which will probably be the highest temperature the capacitor will be exposed to during its lifetime, can induce failures. This is especially challenging in RoHS-compliant (Pb-free) solder processes, as the reflow soldering temperatures are higher and the standard electrolytic capacitors may not withstand them. Some manufacturers have electrolytic SMT capacitors that suit the higher solder temperatures required by Pb-free processes.
  • Incorrect mounting or handling of capacitors may also damage them. Large capacitors can be improperly used as handles for the board, which can cause internal damage.
  • Also, board flexure can cause mechanical stress, resulting in cracks. Heat produced in the washing/dryer or mounting processes can cause the electrolyte in aluminum capacitors to reach its boiling point, which might destroy the part. In radial aluminum electrolytics, the sleeve may also shrink when heated, causing at least a visual defect.
  • Improper voltage derating can damage tantalum capacitors; most tantalum manufacturers recommend derating the voltage down to 50% to 66% of rated voltage.

Design Guidelines for Aluminum and Tantalum Electrolytic Capacitors

  • Commercial grade aluminum capacitors normally lasts within 2 to 3 years. It might fail early when overstressed. Military grade capacitors can be used for the high reliability applications. Military grade capacitors are made with very high quality electrolyte, which may last about 20 years.
  • Incorrect mounting or handling of capacitors may also damage them. Special care must be taken with respect to the correct mounting of polarized capacitors, such as tantalum and aluminum electrolytics. For example, aluminum capacitors are dc only, and if ac voltage is applied to them it can result in catastrophic failures, including open or short circuits, leakage of electrolyte, or venting of the capacitor. For most aluminum capacitors, component manufacturers can provide terminations, such as J-leads or three-terminal snap-ins, to help prevent incorrect mounting.
  • Drifting parameters vary by technology and by conditions in the application. It is important for designers to know how capacitors react during wear-out, as it may be a factor, depending on how long their application is designed to last.
  • There is no wear-out mechanism for solid aluminum or tantalum capacitors, which is a major advantage over wet aluminum capacitors.