Metallized Film Selection for Capacitor Manufacturing
This technical reference document provides detailed information about tongfeng product specifications, characteristics, and performance parameters. Use this information to support your design and analysis activities.
Electrical characteristics are specified over the operating temperature range unless otherwise noted. Parameters are guaranteed by design, testing, or statistical analysis. Typical values is the most likely parametric norm at 25Ā°C.
Thermal characteristics require careful attention during system design. The junction-to-ambient thermal resistance depends on the mounting configuration, PCB copper area, and airflow conditions. Use thermal simulation tools to predict operating temperatures under actual conditions.
Reliability data is based on accelerated life testing and field failure analysis. Mean time between failures (MTBF) calculations follow industry-standard methodologies. Contact BeiLuo for detailed reliability reports and qualification data.
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š Customer Cases
Major Appliance Manufacturer
Consumer Electronics
Challenge
Needed to improve capacitor reliability in high-volume production of residential air conditioners
Solution
Applied the guidelines from this article for capacitor selection and derating
Customer Feedback
"The technical guidance helped us reduce field failures by 60% and improve overall product quality."
Frequently Asked Questions
1. What is the difference between BOPP and PET metallized films?
BOPP (biaxially oriented polypropylene) and PET (polyethylene terephthalate) have different properties: BOPP: Dielectric constant: 2.2, Dissipation factor: 0.02%, Max temperature: 105C, Dielectric strength: ~400V/um, Self-healing: Excellent, Cost: Lower. PET: Dielectric constant: 3.3, Dissipation factor: 0.5%, Max temperature: 125C, Dielectric strength: ~300V/um, Self-healing: Good, Cost: Higher. BOPP is preferred for: AC applications, High-frequency filtering, Cost-sensitive designs, General-purpose capacitors. PET is preferred for: High-temperature applications, DC-link capacitors, Space-constrained designs (higher capacitance density).
2. How do I select film thickness for my capacitor design?
Film thickness selection depends on voltage rating and application: Thinner films (4-6um): Higher capacitance density, Lower voltage rating, Lower cost per capacitance. Thicker films (8-12um): Higher voltage rating, Lower capacitance density, Higher mechanical strength. General guidelines: <250V: 4-5um film, 250-450V: 6-8um film, >450V: 10-12um film or series connection. Voltage stress design: Typically 30-50V/um for reliable long life. Example: 450V capacitor using 6um film: Stress = 450V / 6um = 75V/um (too high). Better: Use 8um film: 450V / 8um = 56V/um (acceptable). Or use two 6um layers in series: 450V / 12um = 37.5V/um (excellent).
3. What is heavy edge metallization and when should I use it?
Heavy edge metallization has thicker aluminum at the film edges: Standard metallization: 8-15nm thickness throughout. Heavy edge: 20-40nm at edges, standard in middle. Benefits of heavy edge: Lower contact resistance at end spray. Better current handling. Reduced heating at contact point. Improved reliability in high-current applications. Use heavy edge for: Motor run capacitors, DC-link capacitors, Any application with significant ripple current. Standard metallization is acceptable for: Signal coupling capacitors, Low-current applications, Cost-sensitive consumer products. Tongfeng offers various heavy edge thicknesses to match current requirements.
4. What quality controls are important for metallized films?
Important quality controls for metallized films include: Film thickness uniformity - affects capacitance tolerance. Metallization thickness consistency - affects ESR and current capability. Margin accuracy - affects voltage withstand. Dielectric strength testing - ensures voltage rating. Metallization adhesion - prevents peeling during winding. Visual inspection - detects defects and contamination. Roll geometry - affects winding performance. Tongfeng's quality system includes: Statistical process control. 100% inspection of critical parameters. Certificate of analysis with each batch. Traceability to raw materials. We can provide detailed quality data and test reports upon request.
5. How should metallized films be stored and handled?
Proper storage and handling of metallized films: Storage conditions: Temperature: 5-35C (ideal 20-25C), Humidity: 40-60% RH, Avoid direct sunlight and UV exposure, Store in original packaging. Shelf life: Typically 12-24 months under proper conditions. Handling precautions: Avoid touching metallized surface (oils from skin). Use clean gloves when handling. Prevent creasing or folding. Use proper tension during unwinding. Control static electricity. Quality checks before use: Visual inspection for defects. Metallization resistance check. Film thickness verification. First article inspection for winding. Following these practices ensures consistent capacitor quality and performance.
6. Can I get custom film specifications from Tongfeng?
Yes, Tongfeng offers custom film specifications: Custom widths: 20mm to 400mm. Custom thicknesses: 4um to 12um. Special metallization patterns: Segmented, Tapered, Custom designs. Custom margins: Various margin widths available. Special packaging: Custom roll lengths, Core sizes. Custom specifications require: Minimum order quantities (typically 1000-5000kg). Lead times of 4-8 weeks. Possible tooling charges for new patterns. Our FAE team can work with you to define custom requirements and coordinate with Tongfeng for quotation and production.
7. What causes capacitance drift in film capacitors?
Capacitance drift in film capacitors can be caused by: Temperature effects: Capacitance increases with temperature (~0.2%/C for BOPP). Voltage effects: Capacitance decreases slightly with voltage (non-linear dielectric). Aging: Very gradual decrease over time (typically <1% over 10 years). Mechanical stress: Winding tension changes can affect capacitance. Humidity: Can affect capacitance in unsealed capacitors. Manufacturing variations: Film thickness variations, Winding tension variations, Metallization variations. Typical capacitance tolerance is Ā±5% or Ā±10%. For tighter tolerance, select higher grade or adjust winding process. Temperature coefficient must be considered for precision applications.
8. How do I calculate the capacitance for a wound film capacitor?
Capacitance of a wound film capacitor is calculated by: C = Īµā Ć Īµr Ć A / d, where: Īµā = 8.854 Ć 10^-12 F/m (permittivity of free space), Īµr = dielectric constant (2.2 for BOPP, 3.3 for PET), A = effective plate area (mĀ²), d = dielectric thickness (m). For a wound capacitor: A = 2 Ć W Ć L, where W = film width, L = film length (both plates). Example calculation: 6um BOPP film, 100mm width, 100m length: A = 2 Ć 0.1m Ć 100m = 20mĀ², d = 6 Ć 10^-6m, C = 8.854e-12 Ć 2.2 Ć 20 / 6e-6 = 64.9uF. Practical capacitance may differ due to: Margin area not contributing, Winding imperfections, Film thickness variations.