Capacitor failure is a critical issue in electronic systems. It often leads to degraded circuit performance or complete malfunction. Common failure modes include open circuits, short circuits, loss of capacitance, increased leakage current, and dielectric breakdown. These failures can arise from various mechanisms, such as electrical overstress, thermal degradation, mechanical stress, and environmental factors like humidity or contamination. In this article, we explore various capacitor failure modes and the mechanisms behind them.
Factors that affect capacitor lifetime
Capacitor lifetime refers to the period during which a capacitor can function effectively within its specified performance parameters. This period varies depending on the type of capacitor, its design, and its operating conditions. Manufacturers provide estimated lifetime ratings in datasheets, offering guidance for selecting capacitors suited to specific applications.
Several factors influence the lifetime of a capacitor, including operating temperature, applied voltage, ripple current, and environmental conditions. Capacitors subjected to excessive heat, high voltage, or continuous high ripple currents tend to degrade more quickly. Other factors like mechanical stress, humidity, and contamination can also reduce their lifespan. Proper selection, derating, and thermal management can help mitigate these effects and extend the capacitor’s useful life.
Indicators of capacitor failure: symptoms and visual Signs
Capacitor failure often manifests through both electrical and physical symptoms. Electrically, a failing capacitor may cause circuit instability, irregular voltage levels, or complete circuit failure. You might observe performance issues such as increased noise, reduced capacitance, or a higher equivalent series resistance (ESR). In some cases, the affected system may exhibit intermittent operation or fail to power on altogether, indicating a potential issue with the capacitor. Figure 1 shows the capacitance of an aluminum electrolytic capacitor dropping over time due to degradation.

Visual signs of capacitor failure are often noticeable upon inspection. Common indicators include a swollen or bulging casing, which suggests internal pressure build-up. Leaking electrolyte, visible as a dark or crusty residue around the capacitor’s base, is another clear warning sign. In severe cases, the capacitor may exhibit burns, cracks, or physical ruptures. These visual cues are critical for identifying failed capacitors during routine maintenance or troubleshooting.
What are the common capacitor failure modes?
Capacitor failure modes can be broadly classified into two categories: catastrophic and degradation failures. Catastrophic failures, such as open circuits and short circuits, result in the immediate and complete loss of functionality. Degradation failures, on the other hand, occur gradually and include issues like reduced insulation resistance, increased leakage current, and loss of capacitance. These failures can significantly impact circuit performance over time.
Some of the most common capacitor failure modes include open circuits, short circuits, loss of capacitance, increased leakage current, and dielectric breakdown. Other less frequent failure modes include excessive equivalent series resistance (ESR), mechanical cracking, and seal failure.
1. Open circuits
An open circuit is a common capacitor failure mode where the capacitor loses electrical continuity, effectively breaking the circuit. This can result from internal disconnections, such as broken leads or degraded electrode connections, often caused by mechanical stress, thermal cycling, or manufacturing defects. Open circuit failures render the capacitor non-functional, leading to disruptions in circuit performance.
2. Short circuits
A short circuit is a common failure mode in capacitors, occurring when the dielectric material breaks down, allowing current to flow directly between the electrodes. This failure often results from electrical overstress, such as voltage surges exceeding the capacitor’s rated voltage, or physical damage to the dielectric layer. Short circuits can lead to overheating, circuit malfunction, or even catastrophic damage, depending on the application. Effective design, proper voltage derating, and quality control during manufacturing can help minimize this risk.
3. Loss in capacitance
Capacitance loss occurs when a capacitor’s ability to store and release energy diminishes, often due to internal degradation. In electrolytic capacitors, this may result from electrolyte evaporation or leakage. Ceramic capacitors can lose capacitance due to cracks or deterioration in the dielectric material. Film capacitors may face similar issues, often linked to dielectric breakdown or physical damage. This failure mode can significantly impair circuit functionality by reducing energy storage efficiency.
4. Increase in leakage current
An increase in leakage current is a common capacitor failure mode, often indicating degraded dielectric integrity. It occurs when the insulating properties of the dielectric weaken due to factors like excessive voltage, high temperature, or aging. This leads to higher current flow through the capacitor, reducing efficiency and potentially causing overheating or circuit malfunction. Regular monitoring and ensuring operation within specified limits can help mitigate this issue. Figure 2 shows how the lifetime of a capacitor varies with temperature.

5. Dielectric breakdown
Dielectric breakdown occurs when the dielectric material fails to withstand the applied voltage. This results in a sudden short circuit, rendering the capacitor non-functional. The breakdown can be caused by excessive voltage stress, contamination, or defects in the dielectric material. Over time, factors like thermal aging and repeated voltage surges increase the likelihood of dielectric failure, compromising the capacitor’s performance and reliability.
Dominant failure modes in different capacitor types
Dominant failure modes vary from one capacitor type to another, depending on their construction and materials. For electrolytic capacitors, the most common failure modes include electrolyte leakage, which results in a loss of capacitance, increased leakage current due to degraded dielectric materials, and high equivalent series resistance (ESR), which causes inefficient operation and potential overheating. These failures often stem from prolonged exposure to high voltage, excessive temperature, or mechanical stress.
For ceramic capacitors, failure modes often include cracking of the ceramic body due to mechanical stress or thermal shock, increased leakage current due to breakdown of the dielectric, and loss of capacitance often caused by voltage overstress or environmental factors. In film capacitors, common failure modes include open circuits, where internal connections fail, short circuits due to dielectric breakdown, and capacitance loss resulting from aging or environmental stress. These failure modes can significantly impact the reliability and performance of circuits.
Capacitor failure mechanisms
Capacitor failure mechanisms describe the physical or chemical processes that lead to failure modes in capacitors. These mechanisms often arise from material degradation, manufacturing defects, or external stresses. For example, dielectric breakdown occurs when excessive voltage causes the insulating material to fail, leading to catastrophic failure such as a short circuit.
Thermal and electrical stresses are significant contributors to capacitor failure mechanisms. High temperatures accelerate the breakdown of dielectric materials and increase the risk of electrolyte evaporation in electrolytic capacitors. Electrical overstress, such as voltage surges, can degrade insulation or cause arcing, resulting in reduced performance or complete failure.
Environmental factors also play a key role in failure mechanisms. Humidity and contaminants can penetrate a capacitor’s protective coating, leading to surface leakage or corrosion. Additionally, mechanical stresses, such as vibrations or improper mounting, can create microcracks in the dielectric material, making the capacitor prone to electrical and thermal failures over time.
Best practices for preventing capacitor failure
Mitigating capacitor failure requires a combination of careful component selection, proper design practices, and regular maintenance. Choosing high-quality capacitors rated for the specific voltage, temperature, and frequency requirements of the application is essential. Derating the voltage and operating the capacitor below its maximum rated limits can also improve reliability. Additionally, designers should consider the operating environment and select capacitors with suitable temperature and humidity tolerances.
Implementing regular maintenance and monitoring practices can further reduce the risk of failure. Inspecting capacitors for visual signs of wear, such as bulging or leakage, allows for early detection and replacement before critical failure occurs. Employing predictive maintenance tools, like ESR meters and thermal imaging, can help identify aging capacitors without disrupting operations. By combining these proactive measures, electronic systems can achieve greater longevity and reliability.