Copper foil for high-frequency inductors is a key conductive material in the manufacture of high-frequency inductor windings. High-frequency inductors operate typically from hundreds of kHz to tens of MHz, widely used in switching power supplies, inverters, wireless charging, RFID, medical equipment, and communication equipment.
I. Working Characteristics and Principles
1.1 Working Principle
Inductors work on electromagnetic induction. At high frequencies, the following effects must be considered:
- Skin Effect: δ=66.1/√f (mm), high-frequency current flows on conductor surface
- Proximity Effect: Adjacent conductors influence each other, increasing AC resistance
- Parasitic Capacitance: Affects self-resonant frequency (SRF)
- Eddy Current Loss: High-frequency magnetic fields induce eddy currents
1.2 Operating Characteristics
- Wide frequency range: 50kHz to 30MHz+
- High heat dissipation requirements: Increased AC resistance generates more heat
- High Q-value requirements: Higher Q = lower losses
1.3 Core Application Areas
- Switching power supplies (100kHz-1MHz)
- Wireless charging (100-200kHz)
- RFID (13.56MHz+)
- Medical equipment (several MHz to tens of MHz)
- Communication equipment (several MHz to several GHz)
II. Core Requirements for Copper Foil
2.1 Low DC and AC Resistance
- Copper content ≥99.90%, conductivity IACS ≥98%
- Low impurity content (strict control of Fe, S)
- Uniform microstructure
2.2 Thickness Selection for Skin Effect
| Frequency | Skin Depth | Recommended Thickness |
|---|---|---|
| 100kHz | 0.21mm | 0.05-0.15mm |
| 500kHz | 0.094mm | 0.03-0.08mm |
| 1MHz | 0.066mm | 0.02-0.06mm |
| 5MHz | 0.030mm | 0.01-0.025mm |
| 10MHz | 0.021mm | 0.01-0.018mm |
| 20MHz | 0.015mm | 0.008-0.012mm |
| 50MHz | 0.009mm | 0.005-0.008mm |
2.3 High-Frequency Magnetic Properties
- Low eddy current loss: thin foil reduces eddy currents
- Good thermal stability
2.4 Mechanical Properties
- Tensile strength: 200-320MPa
- Elongation: ≥5-35%
- Good flexibility
III. Specifications
3.1 Copper Foil Substrate
- Material: C11000 pure copper, copper content ≥99.90%
- Conductivity: IACS ≥98%
- Thickness: 0.005-0.5mm
- Width: 5-300mm
3.2 Mechanical Properties
| State | Tensile Strength | Elongation | Applications |
|---|---|---|---|
| O State | 200-260MPa | ≥35% | Bending and forming |
| H04 State | 260-320MPa | ≥20% | Shape retention |
| H06 State | ≥320MPa | ≥5% | High strength |
3.3 High-Frequency Performance
| Frequency Range | Thickness | State | Applications |
|---|---|---|---|
| 50-500kHz | 0.03-0.15mm | O/H04 state | Wireless charging, SMPS |
| 500kHz-5MHz | 0.01-0.08mm | O state | DC-DC, resonant circuits |
| 5-30MHz | 0.005-0.03mm | O state | RF circuits, RFID |
| >30MHz | Multi-strand | O state | Microwave circuits |
IV. Selection Guide
4.1 By Frequency
- Low frequency (50-500kHz): 0.03-0.15mm
- Medium frequency (500kHz-5MHz): 0.01-0.08mm
- High frequency (5-30MHz): 0.005-0.03mm
- Ultra-high frequency (>30MHz): Multi-strand ultra-thin foil
4.2 By Power Level
- Small power (<10W): 0.02-0.05mm
- Medium power (10-100W): 0.03-0.1mm
- High power (>100W): 0.05-0.2mm
4.3 By Core Type
- Ferrite core: Select thickness based on frequency
- Amorphous alloy: For high-power applications
- Air-core: Consider mechanical strength and heat dissipation
V. Dimensional Tolerance
Thickness tolerance: ±0.005mm (high precision) to ±0.001mm (ultra-high precision)
Width tolerance: ±0.1mm (high precision) to ±0.05mm (ultra-high precision)
Thickness uniformity: ≤±3% (standard) to ≤±1% (precision)
VI. Production Process
Raw material (C11000 electrolytic copper) → Smelting → Hot rolling → Cold rolling → Annealing → Slitting
Key controls: Copper content ≥99.90%, thickness uniformity ±0.001mm, smooth surface, clean edges
VII. Quality Inspection
- Dimensional: Thickness gauge (0.001mm accuracy)
- Appearance: Surface/edge defect inspection
- Performance: Conductivity (eddy current meter, IACS ≥98%), mechanical properties
VIII. Supplier Selection
Key points: Material quality, high-frequency foil supply capability, thickness control precision, thickness uniformity, testing capability
Testing process: Dimensional inspection → Performance test → High-frequency evaluation → Winding suitability test
IX. Common Specifications
| Power Level | Thickness | State |
|---|---|---|
| Small (<10W) | 0.02-0.05mm | O state |
| Medium (10-100W) | 0.03-0.1mm | O/H04 state |
| High (>100W) | 0.05-0.2mm | H04/H06 state |
X. Conclusion
30 years of experience exporting electrical wire and metal foil. C11000 pure copper, copper content ≥99.90%, IACS ≥98%, thickness 0.005-0.5mm, frequency range 50kHz to 30MHz+, thickness tolerance ±0.001mm, test reports provided, customization available.
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