Aluminum electrolytic capacitor failure modes
Aluminum electrolytic capacitors are widely used in electronic circuits for energy storage and filtering. Despite their reliability, these capacitors can fail due to various mechanisms. Understanding these failure mechanisms and modes can help prevent circuit issues and improve design longevity. In mission critical applications, engineers often prevent electrolytic capacitor failure by derating voltage and temperature, using capacitors with higher reliability ratings, and performing regular maintenance checks.This article will focus on common failure modes of aluminum electrolytic capacitors, their causes, and visual signs of failure.
Useful life of an aluminum electrolytic capacitor
The useful life of an aluminum electrolytic capacitor refers to the expected operational lifespan before its performance significantly degrades. Capacitor degradation is usually marked by increased equivalent series resistance (ESR) and reduced capacitance. A capacitor’s useful life is usually specified by the manufacturer in hours, based on rated temperature, voltage, and ripple current conditions. However, actual lifespan can vary depending on operating conditions. Exceeding rated temperature, voltage, or ripple current can shorten the useful life of an aluminum electrolytic capacitor.

Capacitor degradation can be caused by various operating conditions, including excessive temperature, voltage, and ripple current. As capacitors degrade, their performance deviates from the specified characteristics. This can lead to a reduction in capacitance, increased leakage current, and a shorter useful lifespan. These effects can compromise circuit reliability and performance.
Symptoms of electrolytic capacitor failure
Common signs of aluminum electrolytic capacitor failure include bulging or swelling of the case. This often happens due to internal pressure buildup from electrolyte degradation. Leakage of electrolyte and ruptured vents are also common visual signs.
Electrically, failure can show as increased equivalent series resistance, reduced capacitance, and an increase in dissipation factor (tangent of loss angle). These changes can lead to poor filtering performance and signal instability. Higher leakage current and unstable circuit behavior may also indicate failure. Figure 2 shows the capacitance of an aluminum electrolytic capacitor decreasing over time due to degradation.

Common aluminum electrolytic capacitor failure modes
The most common failure mode in aluminum electrolytic capacitors is electrolyte leakage. This occurs when the liquid electrolyte escapes, causing degraded performance. While electrolyte leakage is the primary issue, there are other failure modes. These include open circuits, short circuits, a drop in capacitance (increase in dissipation factor), and increased leakage current.
1. Electrolyte leakage in aluminum electrolytic capacitors
Operating electrolytic capacitors at high temperatures can accelerate leakage or vaporization of the electrolyte. This loss of electrolyte often leads to an increase in ESR and a decrease in capacitance. The rise in ESR further accelerates self-heating in the component. Excessive self-heating, in turn, speeds up wear-out and aging, leading to degradation and, ultimately, failure of the electrolytic capacitor. In some cases, self-heating can trigger a buildup of gases inside an electrolytic capacitor, leading to the explosion of the component and failure of the circuit.
2. Open circuit
The open circuit failure mode occurs when the capacitor loses electrical continuity, preventing current flow. It is often caused by internal disconnection due to corrosion, mechanical stress, or excessive heat damaging the internal connections. Open circuits can also result from the complete evaporation of the electrolyte, especially in aged capacitors. This failure mode leads to a loss of capacitance, disrupting circuit functionality, particularly in filtering and energy storage applications.
3. Short circuit
The short circuit failure mode in aluminum electrolytic capacitors occurs when the dielectric layer breaks down, allowing current to flow directly between the capacitor’s plates. This failure is often caused by excessive voltage stress, thermal degradation, or manufacturing defects. A short circuit can result in high current flow, potential overheating, and damage to surrounding components. Proper voltage derating and quality control can help reduce the risk of this failure mode.
4. Drop in capacitance
This electrolytic capacitor failure mode is directly related to the primary failure mode: electrolyte leakage. As the integrity of a capacitor’s seal deteriorates, it leads to a gradual loss of electrolyte through vaporization. This loss of electrolyte results in an increase in the dissipation factor (tangent of the loss angle) and a drop in capacitance. Figure 3 shows the dissipation factor of an electrolytic capacitor increasing over time due to degradation.

5. Increase in leakage current
An increase in leakage current in aluminum electrolytic capacitors occurs when the dielectric layer degrades or becomes damaged, reducing its insulating properties. This can result from excessive voltage stress, high temperatures, or electrolyte contamination. Elevated leakage current leads to higher power dissipation, increased self-heating, and accelerated capacitor aging. In severe cases, it can cause thermal runaway or complete failure of the capacitor.
How to prevent electrolytic capacitor failure
To prevent capacitor failure, it is essential to avoid exposing components to mechanical stress during assembly. Ensure that capacitors are operated within the environmental conditions specified in the datasheet, including temperature and humidity limits. Additionally, proper mounting and effective thermal management are crucial to prevent damage from vibration and excessive heat.
Regular monitoring of key parameters, such as ESR, leakage current, and capacitance, helps detect early signs of aluminum electrolytic capacitor failure. Tracking these metrics during routine maintenance can reveal gradual degradation, such as rising ESR or increasing leakage current, which may indicate electrolyte loss or dielectric weakening. Early detection allows for timely component replacement, reducing the risk of unexpected circuit failure.