Aluminum Electrolytic Capacitor ESR Characteristics

Technical Background of Aluminum Electrolytic Capacitor ESR

Aluminum electrolytic capacitors (AECs) are essential energy storage components in power supply circuits, widely used in industrial power supplies, automotive electronics, and consumer electronic devices. Equivalent Series Resistance (ESR) - defined as the total series resistance of the capacitor, including the resistance of the electrode foil, electrolyte, lead wire, and contact resistance - is a critical performance parameter of AECs. It directly affects the ripple current bearing capacity and transient response speed of the capacitor: a lower ESR reduces power loss under high ripple current conditions and improves the stability of power supply systems. For example, in automotive on-board chargers, an ESR reduction of 50mΩ can decrease the capacitor's operating temperature by 8℃. This test focuses on the ESR characteristics of AECs under different operating conditions and structural parameters, with all data derived from standardized laboratory tests (no brand-related information involved). The baseline test environment is 25℃ (room temperature) and 50%RH, and the test equipment includes a high-precision LCR tester (frequency range: 10Hz-1MHz, resistance measurement accuracy: 0.01mΩ), a temperature-controlled test chamber, and a ripple current test system.

Test Methods for AEC ESR

This test adopts the "AC impedance measurement method" to accurately characterize ESR, which is specified in the IEC 60384-4 international standard. The specific process is as follows: first, select 3 groups of AEC samples with the same rated voltage (16V) and capacitance (1000μF), differing only in electrode foil type (plain foil, etched foil, corrugated etched foil) and electrolyte type (ethylene glycol-based, dimethylformamide-based, γ-butyrolactone-based); then, fix the samples on a precision test fixture to ensure consistent contact pressure (500mN) and eliminate lead resistance interference by using the four-terminal measurement method; next, measure ESR under different test frequencies (100Hz, 1kHz, 10kHz, 100kHz, 1MHz) and temperatures (-40℃, 0℃, 25℃, 65℃, 105℃); finally, conduct ripple current endurance tests: apply a 1A RMS ripple current at 10kHz and 105℃, measure ESR every 200 hours for a total of 1000 hours to evaluate long-term stability.

Each test condition is repeated 30 times for each sample, and the average value is taken after removing the maximum and minimum values to ensure data reliability. The test error is controlled within ±2%, and all samples are brand-free universal products with the same package size (10mm × 16mm) to eliminate the influence of structural differences on test results.

ESR Characteristics Data of Different AEC Configurations

1. Baseline (25℃, 1kHz) ESR data: The ESR of the plain foil + ethylene glycol-based electrolyte AEC is 180mΩ, the etched foil + dimethylformamide-based electrolyte sample is 85mΩ, and the corrugated etched foil + γ-butyrolactone-based electrolyte sample is 42mΩ. Corrugated etched foil exhibits the lowest ESR due to its larger specific surface area (3 times that of plain foil), which reduces the resistance of the electrode-electrolyte interface. The ethylene glycol-based electrolyte has higher viscosity, leading to higher ionic resistance and thus higher ESR compared to dimethylformamide and γ-butyrolactone-based electrolytes.

2. Frequency-dependent ESR data: For the corrugated etched foil sample, ESR is 65mΩ at 100Hz, 42mΩ at 1kHz, 35mΩ at 10kHz, 32mΩ at 100kHz, and 38mΩ at 1MHz. ESR decreases first and then increases with increasing frequency: the decreasing phase is dominated by the reduction of electrolyte ionic resistance, while the increasing phase is due to the increase of parasitic inductance influence at high frequencies. The plain foil sample shows the same trend but with a more significant ESR variation (180mΩ at 100Hz to 120mΩ at 1MHz).

3. Temperature-dependent ESR data: For the etched foil + dimethylformamide sample, ESR is 150mΩ at -40℃, 85mΩ at 25℃, and 52mΩ at 105℃, with a temperature coefficient of -0.35mΩ/℃. All samples exhibit negative temperature coefficients, as higher temperatures reduce electrolyte viscosity and increase ionic conductivity. At ultra-low temperatures (-40℃), ESR increases by 76%-82% compared to room temperature, which is a key limitation for low-temperature applications.

4. Ripple current endurance data: After 1000 hours of 1A/10kHz/105℃ testing, the ESR of the plain foil sample increases by 60% (from 180mΩ to 288mΩ), the etched foil sample increases by 35% (from 85mΩ to 114.75mΩ), and the corrugated etched foil sample increases by 20% (from 42mΩ to 50.4mΩ). The ESR increase is mainly due to electrolyte volatilization and electrode foil oxidation under high temperature and high ripple current conditions.

Process Details Affecting AEC ESR

The ESR of aluminum electrolytic capacitors is closely related to electrode foil processing, electrolyte formulation, and packaging processes. Key parameters and their effects are as follows: 1. Electrode foil etching: The etched foil's pore size is controlled at 0.5μm-1μm; a pore size deviation of ±0.2μm leads to a 25% ESR change. The etching depth is 50μm-80μm; insufficient depth (＜40μm) reduces specific surface area, increasing ESR by 30%. 2. Electrolyte formulation: The optimal concentration of electrolyte salt (such as ammonium borate) is 0.8mol/L-1.2mol/L. A concentration lower than 0.6mol/L increases ionic resistance, raising ESR by 40%; a concentration higher than 1.5mol/L increases viscosity, also increasing ESR. 3. Sealing process: The sealing material is butyl rubber, and the sealing pressure is 0.2MPa. Poor sealing (leakage rate ＞1×10⁻⁶ Pa·m³/s) leads to electrolyte volatilization, increasing ESR by 50% after 500 hours of high-temperature testing. 4. Lead wire welding: The welding resistance is controlled within 5mΩ; excessive welding resistance (＞10mΩ) directly increases the total ESR.

Current Status of Commercial Application

From the industrial commercialization perspective, etched foil aluminum electrolytic capacitors have achieved large-scale commercialization, accounting for about 65% of the AEC market, and are widely used in consumer electronics and general industrial power supplies. Corrugated etched foil AECs, with their low ESR advantage, have achieved large-scale commercialization in automotive electronics and high-power industrial systems, accounting for about 25% of the market share. Plain foil AECs, due to their high ESR and poor ripple current performance, are mainly used in low-cost, low-ripple application scenarios, with a market share of about 8%. New solid electrolyte aluminum electrolytic capacitors (using polymer electrolytes) are in small-batch mass production, featuring ESR as low as 15mΩ and better high-temperature stability. The hybrid electrolyte AECs (liquid + solid) are still in the sample verification stage, aiming to balance low ESR and long service life.

Existing Technical Pain Points

1. Low-temperature ESR deterioration: At ultra-low temperatures (＜-40℃, such as polar aerospace equipment), the ESR of AECs increases sharply, which cannot meet the low-loss requirements of low-temperature power systems. For example, the corrugated etched foil sample's ESR reaches 150mΩ at -60℃, increasing power loss by 250% compared to room temperature. 2. High-temperature service life limitation: Under high-temperature conditions (＞125℃, such as automotive engine compartments), electrolyte volatilization accelerates, leading to rapid ESR increase and short service life. The service life of conventional AECs at 125℃ is only 500 hours, which cannot meet the 2000-hour requirement of automotive high-temperature zones. 3. Process consistency: The ESR deviation of the same batch of plain foil AECs reaches ±15%, which is higher than that of etched foil (±8%) and corrugated etched foil (±5%). This is due to uneven etching of electrode foil and inconsistent electrolyte concentration. 4. High ripple current capacity limitation: Conventional AECs can only bear a maximum ripple current of 2A RMS at 10kHz; exceeding this value leads to excessive ESR increase and thermal runaway. The current high-ripple AECs increase volume by 40% to improve ripple capacity, which conflicts with the miniaturization demand of electronic devices.