Electrolytic capacitors are one of the commonly used components in electronic circuits, and their performance stability directly affects the reliability of the entire electronic equipment. However, due to their special structure and working principle, electrolytic capacitors also have a relatively high failure rate in electronic equipment. This article systematically analyzes the common failure modes, root causes, and corresponding preventive measures for electrolytic capacitors.

1. Main Failure Modes of Electrolytic Capacitors

1.1 Leakage

Leakage is one of the most common failure forms of electrolytic capacitors. The working electrolyte of aluminum electrolytic capacitors is acidic. Once it leaks out, it can seriously contaminate and corrode the components and printed circuit boards around the capacitor. Simultaneously, leakage inside the electrolytic capacitor causes the working electrolyte to gradually dry up, losing its ability to repair the anode oxide film dielectric, leading to capacitor breakdown or deterioration of electrical parameters and failure. The main reasons for leakage include poor sealing structure, aging and cracking of rubber plugs, defects in mechanical sealing processes, and improper installation methods.

1.2 Bulging and Bursting

When the internal pressure of an electrolytic capacitor increases abnormally, bulging or even bursting can occur. This is usually caused by gas generation inside the capacitor: when the AC component in the working voltage is too large, the oxide film dielectric has many defects, or harmful anions such as chloride ions are present, the leakage current can be significant, accelerating the electrolysis process and gas generation. Most electrolytic capacitors now use an explosion-proof shell structure, adding a fold seam on the upper part of the metal shell that opens when the pressure is high to reduce internal pressure. However, if overvoltage, rapid charging/discharging, or reverse voltage are applied, bursting can still occur.

1.3 Deterioration of Electrical Parameters

Capacity decay is a typical failure manifestation of electrolytic capacitors. In the early stages of operation, the electrolyte of an aluminum electrolytic capacitor continuously repairs and thickens the anode oxide film, causing a slow decrease in capacity. In the later stages of use, as the electrolyte is significantly depleted, the solution becomes viscous, the resistivity increases, and the thickened electrolyte cannot fully contact the oxide film layer on the aluminum foil surface, reducing the effective area of the electrode plates and causing a sharp decline in capacitance.

Increase in ESR is another common issue. ESR gradually increases as the electrolyte dries up and the electrode material oxidizes, leading to increased power consumption and heat generation in AC circuits, which accelerates capacitor aging.

Increase in leakage current is also a common form of electrolytic capacitor failure. Factors such as low process levels, damage and contamination of the oxide film, poor working electrolyte formulation, and low purity of raw materials can all cause leakage current to exceed standards.

1.4 Short Circuit and Open Circuit

Short-circuit failure occurs when the anode aluminum oxide dielectric film ruptures, allowing the electrolyte to directly contact the anode. The aluminum oxide film may be locally damaged due to material defects, process issues, or environmental conditions. If the electrolyte cannot effectively repair these damaged areas, micro-pores or penetrating holes form, leading to capacitor breakdown.

Open-circuit failure usually manifests as the anode foil tab suffering from electrochemical corrosion and breaking, especially in high-temperature or humid environments. This failure mode is more common in high-voltage, high-capacity capacitors. Additionally, poor riveting between the anode foil tab and the anode foil can lead to poor contact, causing intermittent open circuits in the capacitor.

2. Root Causes of Electrolytic Capacitor Failure

2.1 Electrical Stress Factors

Overvoltage is an important factor leading to electrolytic capacitor failure. When the voltage applied to an electrolytic capacitor exceeds its rated voltage, the electric field strength inside the capacitor increases, which may cause dielectric breakdown. Especially when voltage fluctuations or surges exist in the circuit, the capacitor is more susceptible to damage due to overvoltage.

Excessive ripple current also seriously affects capacitor life. When ripple current passes through an electrolytic capacitor, it generates heat inside. If the ripple current is too large, excessive heat is generated, accelerating the drying and aging of the internal electrolyte. When designing circuits, it is essential to ensure that the ripple current is within the capacitor's rated range.

Application of reverse voltage is fatal to polarized electrolytic capacitors. When the positive and negative poles are connected reversely, the insulation resistance of the capacitor decreases, and the leakage current increases sharply, which can damage the capacitor in a short time.

2.2 Thermal Stress Factors

Excessively high ambient temperature accelerates the chemical reactions inside the electrolytic capacitor, causing the electrolyte to volatilize and dry up, significantly reducing the capacitor's service life. Typically, the life of an electrolytic capacitor decreases exponentially with temperature increase; for every 10°C rise in operating temperature, the life is approximately halved.

Poor heat dissipation is another key factor. If the capacitor is installed in a location with poor heat dissipation conditions or is near other heating components, the capacitor's own temperature will rise, accelerating its aging process. Especially in power supply circuits, capacitors close to heat sinks and high-power components are more likely to be damaged due to overheating.

2.3 Manufacturing Process and Material Factors

Electrode material quality issues directly affect capacitor performance. If the purity, structure, etc., of the electrode material do not meet requirements, it may cause abnormal chemical reactions between the electrode and the electrolyte, affecting the capacitor's life.

Electrolyte quality is equally critical. Unreasonable electrolyte formulation, insufficient purity, or impurities can make the capacitor's electrical performance unstable, leading to problems such as increased leakage current and capacity decay.

Manufacturing process defects, such as improper winding process or incomplete sealing, may cause internal short circuits, open circuits, or allow external moisture, oxygen, etc., to enter the capacitor interior, causing corrosion and performance degradation.

2.4 Environmental and Usage Factors

Mechanical stress such as vibration and impact may cause deformation or disconnection of the internal structure of the capacitor, leading to failure. Especially for ceramic capacitors, mechanical stress can generate cracks, causing short circuits or capacity decay.

Chemical corrosion is also a factor that cannot be ignored. The use of cleaning agents, adhesives, or coating agents containing halogens (such as chloride ions) may intrude into the capacitor and cause corrosion, leading to performance degradation or failure.

Natural aging is an inevitable process for electrolytic capacitors. As usage time increases, the electrolyte inside the electrolytic capacitor gradually dries up, and the electrode material undergoes chemical reactions such as oxidation, causing the capacitor's performance to gradually decline and eventually fail.

3. Detection and Diagnosis Methods for Electrolytic Capacitor Failure

3.1 Visual Inspection

Observe the appearance of the electrolytic capacitor for abnormalities such as bulging, leakage, or discoloration. Bulging indicates increased internal pressure, usually due to overheating or overvoltage causing internal gas generation; leakage may mean poor sealing or excessive internal pressure. The appearance of oil stains on the circuit board below the capacitor is also a clear sign of leakage.

3.2 Electrical Performance Testing

Capacitance measurement uses a capacitance meter or the capacitance range of a multimeter to measure the capacitance of the electrolytic capacitor and compare it with the nominal value to determine if there is capacity decay. Usually, if the capacity drops below 70% of the nominal value, the capacitor can be considered failed.

ESR measurement uses a dedicated ESR tester to measure the equivalent series resistance of the capacitor. An increase in ESR often reflects the degradation of the capacitor earlier than capacity reduction and is an important indicator for predicting capacitor life.

Leakage current test measures the leakage current of the electrolytic capacitor under a specified DC voltage. Leakage current exceeding the specified value indicates defects or aging in the capacitor's internal dielectric.

3.3 Temperature Monitoring

Use an infrared thermal imager or thermocouple to measure the surface temperature of the capacitor during operation. Capacitors with severe leakage often heat up abnormally, and touching them with a finger may even feel hot, which can help quickly locate faulty capacitors.

4. Measures to Prevent Electrolytic Capacitor Failure

4.1 Reasonable Selection and Design

In the circuit design stage, appropriate capacitor models should be selected based on actual working conditions, ensuring that parameters such as the capacitor's rated voltage and ripple current withstand capability have sufficient margin. For high-frequency and high-ripple current applications, low-ESR type electrolytic capacitors should be selected.

In filter circuit design, voltage fluctuations and surge protection should be considered to avoid overvoltage impact on the capacitor. For applications with reverse voltage risks, non-polar electrolytic capacitors or protective measures should be considered.

4.2 Optimizing Working Conditions

Controlling the operating temperature is key to extending capacitor life. Ensure that capacitors are away from heat sources, provide good ventilation and heat dissipation conditions, and use forced cooling measures if necessary. In high-temperature environments, high-temperature resistant models of electrolytic capacitors (such as 105°C or 125°C series) should be selected.

Avoiding over-stress use includes preventing overvoltage, overcurrent, and reverse voltage. Especially in power supply circuits, overvoltage protection circuits and soft-start circuits should be added to reduce current impact at the moment of power-on.

4.3 Improving Installation and Maintenance Quality

When installing electrolytic capacitors, ensure the polarity is correct and avoid applying mechanical stress to the leads. The clamps used for fixation should securely fix the capacitor without damaging the outer insulation jacket of the capacitor.

For electrolytic capacitors that have been stored for more than one year, the leakage current should be measured before installing them on the circuit to ensure it does not exceed the standard range. If necessary, DC aging treatment can be performed, gradually increasing the voltage and detecting the leakage current value to ensure stable performance.

Regular maintenance inspections are also an important measure to prevent capacitor failure. Especially for electronic equipment used in high-temperature, high-humidity, or vibrating environments, key capacitors' ESR and capacity should be regularly detected, and degraded capacitors should be replaced promptly.

Conclusion

The failure modes of electrolytic capacitors are diverse, with complex causes involving multiple factors such as electrical stress, thermal stress, manufacturing processes, and usage environment. By understanding the failure mechanisms of electrolytic capacitors and adopting reasonable selection, design, and maintenance measures, the service life and reliability of electrolytic capacitors can be significantly improved, thereby ensuring the stable operation of the entire electronic equipment. In practical applications, combining various methods such as visual inspection, electrical parameter measurement, and temperature monitoring can detect potential faults early, avoiding equipment failures caused by capacitor failures.