Thin Film Capacitors
1. Thin Film Capacitors Overview
Film capacitors are capacitors made of plastic film (such as polypropylene, polyester, etc.) as dielectrics and metal foil or metalized film as electrodes. Its internal structure usually adopts a winding or stacking process, and the electrodes and dielectric layers are arranged alternately. The external structure is formed into a cylindrical or rectangular structure by epoxy resin or plastic encapsulation.
2. What are the Main Types of Thin Film Capacitors?
Depending on the dielectric material, film capacitors can be divided into the following types:
Polyester (PET) Capacitors: also known as polyethylene capacitors, low cost and good temperature resistance.
Polypropylene (PP) Capacitors: excellent high-frequency characteristics, low loss, suitable for high-precision circuits.
Polystyrene (PS) Capacitors: high stability, often used in precision instruments.
Metalized Film Capacitors: electrodes using a metallization process, with self-healing characteristics and higher reliability.
3. What are the Core Characteristics of Thin Film Capacitors?
Non-polarity: no need to distinguish between positive and negative poles, suitable for AC and DC circuits.
High-frequency Response: wide frequency response range, suitable for high-frequency signal processing.
Low Loss: extremely low dielectric loss, which can reduce energy loss.
High Insulation Impedance: small leakage current and good long-term stability.
4. What are Thin Film Capacitors Used for?
Signal Processing: signal coupling, filtering, and bypassing in analog circuits.
Power Supply System: power supply noise suppression, filtering, and energy storage, such as UPS and switching power supplies.
Industrial Electronics: motor control, inverter, new energy equipment (such as solar drive).
Consumer Electronics: used to improve sound quality in high-end audio equipment.
5. What are the Structural Characteristics of Thin Film Capacitors?
Electrode Material: metal foil or metalized film (such as aluminum and zinc), the latter can reduce volume and improve self-healing ability.
Packaging Form: common epoxy encapsulation, plastic shell, or metal shell packaging to meet different environmental requirements.
Process Optimization: metallized polypropylene film capacitors (such as MKP type) achieve thinner dielectric layers and improve capacity density through evaporation process.
6. Notes for Thin Film Capacitors
Installation Requirements: Strictly follow the polarity (if any), voltage, and temperature parameters to avoid damage caused by overload.
Quality Assurance: High-quality film capacitors must pass to withstand voltage, temperature rise, and life tests to ensure long-term reliability.
7. Typical Brands for Thin Film Capacitors
Panasonic
Nichicon
TDK-EPCOS
Murata
Vishay
Cooke Kolb
And so on…
8. Thin Film Capacitors FAQs
1) What factors affect the life of film capacitors?
Voltage Stress: Long-term overvoltage will accelerate dielectric aging.
Temperature Environment: High temperature causes insulation performance to deteriorate, and the operating temperature needs to be controlled.
Mechanical Stress: Avoid bending the pins or applying external pressure during installation.
2) What is the “self-healing mechanism” of film capacitors?
Film capacitors achieve self-healing through metallized evaporation electrode design: When the local dielectric breaks down, the metal layer around the breakdown point will evaporate quickly, isolating the defective area and avoiding short-circuit failure. This feature significantly improves the reliability of the device, especially for high-demand scenarios such as automotive electronics.
3) What are the key applications of film capacitors in new energy vehicles?
Inverter System: Used for DC bus support and filtering of motor drive circuits, it needs to withstand high-frequency and high-voltage pulses.
On-board Charger (OBC): Realize power conversion and power factor correction, requiring low loss and long life.
Battery Management System (BMS): used for voltage sampling and balancing circuits, requiring high precision and low-temperature drift characteristics.
4) Why has metalized film become the mainstream process?
Metalized film forms a nano-scale metal layer on the surface of the medium through a vacuum evaporation process. Compared with the traditional foil structure:
Smaller Volume: The volume is reduced by more than 30% at the same capacitance.
Better self-healing Property: The evaporation response speed of the metal layer is faster, reducing the risk of failure.
Lower Cost: Reduce the amount of metal materials and is suitable for large-scale production.
5) Why are film capacitors preferred in high-frequency scenarios?
Stable Frequency Characteristics: The dielectric loss (tanδ) of polypropylene (PP) film is still less than 0.1% at frequencies above 1MHz, which is better than the frequency sensitivity characteristics of ceramic capacitors.
Low ESR/ESL: The optimized winding structure can reduce the equivalent series resistance (<10mΩ) and inductance (<10nH), which is suitable for RF filtering and resonant circuits.
6) Do film capacitors meet environmental protection requirements?
Film capacitors from mainstream brands (such as Panasonic and TDK) already comply with RoHS and REACH standards:
No Harmful Substances: The dielectric material and encapsulation resin do not contain heavy metals such as lead and cadmium.
Recyclable Design: The shell adopts a detachable structure, and the metal and plastic components can be recycled by classification.