Electrolytic capacitors are among the most critical components in electronic systems, especially in power supplies, converters, and control circuits.

The aging processes and failure characteristics of these components have a significant impact on the overall reliability of the system.

They age over time as their electrolyte evaporates, causing increases in ESR (equivalent series resistance) and reductions in capacitance.

Because they degrade predictably with temperature, voltage, and ripple current, they often determine mean time to failure (MTTF) for many systems, particularly power electronics.

Impact on System Reliability

Electrolytic capacitors often are:

• The first component to fail in SMPS and inverters.
• Critical for filtering so that failure may cause ripple increase, output instability, or system shutdown.
• Primary drivers of maintenance intervals in industrial electronics.

Failure Mechanisms

The evaporation of the electrolyte leads to drying and capacitance loss, resulting in increased temperature and ripple current. 

Oxide layer degradation increases leakage current and ESR, leading to overvoltage and surge issues.

The deterioration of seals can lead to electrolyte leakage, corrosion, increased humidity, and thermal cycling. Mechanical stress can lead to failures in solder joints, as well as issues caused by vibration and shock.

Mitigation Strategies

To mitigate failures in power systems, use high-temperature (105–125 °C) or long-life types to extend service life.

Derating voltage (≤80%) and ripple (≤70%) reduce internal heating.

Adding thermal management (cooling airflow) lowers core temperature.

Use polymer or film capacitors instead of electrolytic ones, as they do not have the risk of drying out.

Perform accelerated aging tests to validate long-term degradation.

Reliability Prediction

The evaluation of electrolytic capacitor failures in reliability estimation involves using the MIL-HDBK-217 part stress analysis tables or Telcordia SR-332 model, along with FMEA and FMECA methods. Common failures for these capacitors include increased equivalent series resistance (ESR) and open circuits. In reliability block diagrams (RBD) modeling, the electrolytic capacitor is the primary failure in the power chain.

Additionally, their mean time between failures (MTBF) is a significant factor in the overall system failure rate, often ranking among the top three contributors to failures as follows:

1. Electrolytic capacitor with 35% failures
2. MOSFET with 23% failures
3. Diodes with 17% failures

Summary

Unlike most solid-state parts, electrolytic capacitors are reliability bottlenecks because they deteriorate over time and with increasing temperature. 

In reliability estimation, it is crucial to explicitly model their behavior, instead of lumping it into generic part-count models.