The production process of aluminum electrolytic capacitors involves multiple precise procedures such as material preparation, core package assembly, and housing encapsulation. The detailed flow and key points are as follows:
High-purity aluminum foil selection: Use aluminum foil with a purity of over 99.95%, typically 10-100μm thick.
Electrochemical corrosion:
Immerse the aluminum foil in electrolytes like hydrochloric acid or sulfuric acid, and apply an alternating voltage for corrosion to form a honeycomb-like microporous structure, increasing the surface area (specific surface area can reach 100-300 times the original area) to enhance capacitance.
Corrosion parameters (voltage, temperature, time) must be precisely controlled to avoid excessive pore size or breakdown.
Oxide film formation:
Apply a direct current voltage to the corroded aluminum foil to generate an extremely thin aluminum oxide (Al₂O₃) insulating layer on the surface, serving as the dielectric layer of the capacitor (thickness about 0.1-1μm, determining the withstand voltage).
Select aluminum foil with a purity slightly lower than that of the anode foil, which is also corroded to increase the surface area but does not require an oxide film. It conducts electricity through an electrolyte or conductive polymer later.
Traditional liquid electrolyte: Prepared from solvents like ethylene glycol and propylene glycol, mixed with solutes such as boric acid and ammonium salts (e.g., ammonium tetraborate), requiring control of viscosity, conductivity, and temperature stability.
Solid electrolyte (conductive polymer): Uses materials like polypyrrole and polyaniline to improve temperature resistance and lifespan (commonly used in solid electrolytic capacitors).
Use polypropylene (PP) or polyethylene (PE) films, which are required to have uniform thickness and good insulation to isolate the anode and cathode foils and prevent short circuits.
Stack the anode foil, separator, and cathode foil in the order of "anode foil-separator-cathode foil-separator," or wind them into a cylindrical core package (winding type), or stack them into a square shape (lamination type).
In the winding process, uniform tension must be controlled to avoid foil wrinkles or misalignment, which affects electrical performance.
Anode lead-out: Weld an aluminum strip or nickel strip on the anode foil as the positive lead, with firm welding points to avoid excessive contact resistance.
Cathode lead-out: The cathode foil is connected to the housing (negative electrode) through an electrolyte or conductive polymer, or a cathode lead is welded (for some models).
The wound core package needs to be pressed into shape to ensure a compact structure, reduce internal voids, and prevent electrolyte leakage.
Housing: Commonly used aluminum shells, surface-treated with electroplating for rust prevention, and the bottom is stamped with explosion-proof patterns (cross-shaped or K-shaped) to prevent overpressure explosion.
Cover: Mostly made of insulating materials (such as PP), integrated with pin holes and sealing rubber rings. In some models, the cover also serves as the negative lead-out terminal.
After placing the core package into the aluminum shell, inject the prepared electrolyte. The injection volume must be controlled (excess is prone to leakage, insufficient affects lifespan), and vacuum exhaust is performed to remove internal air.
Crimping sealing: Press the cover and aluminum shell tightly through mechanical crimping, combined with a sealing rubber ring to prevent electrolyte leakage.
Solid capacitor encapsulation: If a conductive polymer is used, polymer filling is performed first, and then the housing is encapsulated without the need for injection.
Connect the capacitor to a DC power supply (close to the rated voltage) for aging, with the temperature controlled at 85-130°C for several to tens of hours.
Function: Repair oxide film defects, stabilize electrolyte performance, and improve capacitor reliability.
Capacitance (C): Measured with an LCR bridge, requiring a tolerance within ±10% or ±20% of the rated value.
Dissipation Factor (tanδ): Tests the loss of the electrolyte equivalent series resistance (ESR), and low tanδ is required for high-frequency applications.
Leakage Current (IR): Apply the rated voltage and measure the leakage current, which must meet the standard (e.g., ≤0.01μA/μF).
Withstand Voltage Test: Apply 1.1-1.3 times the rated voltage to check for breakdown.
High-temperature storage (stored at 105°C for thousands of hours), high-low temperature cycling (-40°C to +85°C), moisture resistance testing, etc., to verify lifespan and stability.
Printing Identification: Screen-print rated voltage, capacitance, temperature resistance grade, polarity, and other information on the housing surface.
Grading and Screening: Classify according to electrical performance parameters and eliminate defective products.
Packaging and Warehousing: Use anti-static packaging, store by specifications, and avoid high-temperature and humid environments.
Key Process Difficulties
Corrosion and Oxide Film Control: The uniformity of pore size and the thickness of the oxide film directly affect capacitance and withstand voltage.
Sealing Technology: The leak-proof process of liquid capacitors determines their lifespan, and the polymer filling of solid capacitors needs to be uniform.
Low ESR Design: Reduce the equivalent series resistance by optimizing the foil structure, electrolyte formula, or using solid-state processes.
Through the above processes, aluminum electrolytic capacitors achieve the characteristics of high capacitance and high withstand voltage, and are widely used in power supplies, consumer electronics, and other fields.
Consumer Electronics
Mobile Phones: Used in the power filter circuit of mobile phone chargers to smooth the output DC voltage, reduce voltage fluctuations and noise, and provide a stable power supply for mobile phone charging. In the peripheral circuits of the power management chip inside the mobile phone, it also plays the role of decoupling and filtering to ensure the stable operation of the chip.
Laptops: In the computer power adapter, it rectifies and filters the input AC power to output stable DC power for the computer. The aluminum electrolytic capacitors on the computer motherboard are used in the power supply circuits of various chips, such as CPU and GPU, to provide them with stable voltage, filter out high-frequency noise in the power supply, and prevent interference with other circuits.
Household Appliances
Air Conditioners: In the inverter circuit of air conditioners, it is used to smooth the DC bus voltage and provide a stable power supply for the inverter module, so that the air conditioner compressor can operate stably to achieve energy saving and precise temperature control. It can also be used in the control circuits of the indoor and outdoor units of air conditioners to stabilize the voltage of the control signal.
Microwave Ovens: In the power circuit of microwave ovens, it filters the high voltage output by the high-voltage transformer and provides a stable DC high voltage for the magnetron to ensure the normal operation of the magnetron and generate microwaves to heat food.
Industrial Equipment
Frequency Converters: Used in the DC link of frequency converters to store energy and smooth the DC voltage, provide a stable DC power supply for the inverter, and at the same time withstand the large ripple current generated during the operation of the frequency converter to ensure the stable operation and efficient conversion of the frequency converter.
Industrial Robots: In the joint drivers of industrial robots, they can withstand high vibration and a wide temperature range, smooth power fluctuations, reduce electromagnetic interference, provide a stable power supply for the drivers, and ensure the precise control and stable movement of the robot joints.
New Energy
New Energy Vehicles: In the on-board charger (OBC), it needs to have high withstand voltage, strong ripple current bearing capacity, and good low-temperature performance to adapt to high-power charging and a wide voltage range. In the power system of the vehicle, it is used in the power management module to stabilize the voltage output by the battery and provide a stable power supply for equipment such as the motor controller and DC/DC converter.
Photovoltaic Inverters: In photovoltaic power stations, the internal temperature of the photovoltaic inverter is high and it needs to withstand a large number of charge-discharge cycles. Aluminum electrolytic capacitors use special electrolytes and structural designs to maintain a long lifespan at high temperatures, and are used to store electric energy and balance the grid load to improve power generation efficiency and system stability.
Communication Equipment
5G Base Stations: The power module of 5G base stations needs to maintain low ESR in the high-frequency band. The high-frequency and low-loss characteristics of aluminum electrolytic capacitors can effectively filter out high-frequency noise and ripple in the power supply, reduce switching losses, improve the efficiency and stability of the base station power supply, and ensure the normal operation of the base station.
Routers: In the power circuit of routers, it filters and stabilizes the input power supply and provides a stable DC power supply for each chip and circuit of the router to ensure that the router will not fail due to power fluctuations during long-term operation.
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