1. Introduction: Why copper wires need to be re-examined in high-frequency applications
1.1 Explosive growth of high-frequency scenarios
Over the past decade, high-frequency applications have grown exponentially:
- 5G Communications: The 5G NR frequency bands defined by 3GPP 38.101 include n77 (3.3-4.2 GHz), n78 (3.3-3.8 GHz), n79 (4.4-5.0 GHz), and a total of 700+ 5G base stations will be deployed globally in 2024.
- Wireless Charging: WPC Qi standard covers 100-205 kHz / 360 kHz / 6.78 MHz; AirFuel Alliance promotes 6.78 MHz / 13.56 MHz; global wireless charging market size is expected to be US$30 billion in 2025
- New energy vehicles: 800V high voltage platform traction 100-500 kHz high frequency transformer requirements
- Data Center: 48V bus + high frequency DC-DC converter, frequency 1-5 MHz
- IoT / RFID: 13.56 MHz NFC, 860-960 MHz UHF RFID, 24 GHz / 77 GHz millimeter wave radar
The requirements for winding wires in high-frequency applications are completely different from traditional power scenarios – it is no longer simply “passing large currents”, but involves complex physical issues such as skin effect, proximity effect, eddy current loss, and impedance matching**.
1.2 Copper’s “High Frequency Dilemma”
Pure copper is a near-ideal conductor at DC (IACS 100% conductivity), but at high frequencies:
- Skin effect: The AC current density is concentrated on the surface of the conductor, and the inside of the conductor is “wasted”. The skin depth of copper is only 0.21 mm at 100 kHz
- Proximity Effect: Currents in adjacent conductors induce each other, causing the current distribution to be further concentrated
- Eddy current loss: A conductor generates eddy currents in an alternating magnetic field, and the loss is proportional to the square of the frequency.
- Weight/Cost: Copper density is 8.96 g/cm³, copper price in 2024 is 85,000-95,000 yuan/ton
1.3 The rise of CCA line
Copper Clad Aluminum (CCA) wire is made of aluminum core (density 2.70 g/cm³) + copper layer (thickness 8-15% radius), which shows unique advantages in high-frequency scenarios:
- 30-50% weight reduction (vs pure copper, same diameter)
- Cost reduction 20-40% (copper-aluminum price ratio 4:1 in 2024)
- High frequency performance is close to copper (the current within the skin depth mainly flows through the copper layer)
1.4 Value of this article
This article will systematically answer:
1. Why can CCA lines “replace copper with aluminum” at high frequencies? 2. Which high-frequency scenarios are suitable for CCA? Which ones must use pure copper? 3. Selection rules for specific scenarios such as 5G base stations, wireless charging, transformers, and RFID 4. Limitations and mix-and-match solutions of CCA 5. Quality testing and future trends
—
2. The essential difference between CCA wire and copper wire
2.1 5-layer structure comparison
| Level | Pure Copper Wire | CCA Wire |
|---|---|---|
| 1 | Copper conductor (OFC oxygen-free copper / ETP copper) | Copper outer layer (8-15% of the radius) |
| 2 | — | Copper-aluminum metallurgical bonding layer (0.005-0.02 mm) |
| 3 | — | Aluminum core (pure aluminum 1050 / 3003 / 6101) |
| 4 | Paint film (PE / PI / PU) | Paint film (PE / PI / PU) |
| 5 | Impregnating paint (optional) | Impregnating paint (optional) |
2.2 Comparison of key parameters
| Parameters | Pure Copper Wire | CCA Wire (Typical 10% Copper Ratio) | Differences |
|---|---|---|---|
| Density | 8.96 g/cm³ | 3.63-4.16 g/cm³ | -54% |
| DC Conductivity (IACS) | 100% | 60-70% | -30% |
| DC Resistivity | 1.724 × 10⁻⁸ Ω·m | 2.65-2.83 × 10⁻⁸ Ω·m | +54% |
| Tensile strength | 220-400 MPa | 90-180 MPa | -55% |
| Elongation | 20-40% | 10-25% | -40% |
| Cost (yuan/kg, 2024) | 90-100 | 40-55 | -50% |
| Weight (same length) | Baseline | 40-46% | -54% |
2.3 Differences in manufacturing processes
Pure Copper Wire:
- Drawing → Annealing → Painting → Drying
- Mature technology, IACS 100-103%
CCA Line:
- Aluminum core prefabrication → surface cleaning → copper layer cladding (co-extrusion method / electroplating method / welding method)
- Metallurgical bonding is key (copper-aluminum interface atomic diffusion)
- Process difficulty: Control of the brittle phase (CuAl₂) at the copper-aluminum interface
Influence of copper layer ratio:
- Low copper ratio (8-10%): The biggest advantage is lightweight, but the DC resistance is high
- Medium copper ratio (12-15%): balanced performance, suitable for most high-frequency scenarios
- High copper ratio (18-25%): close to copper performance with limited cost reduction
2.4 Weight and cost comparison (case)
A 5G base station filter coil with an outer diameter of 0.50 mm × 1000 meters:
| Indicators | Pure Copper Wire | CCA Wire (10% Copper Ratio) |
|---|---|---|
| Weight | 1.76 kg | 0.80 kg |
| Total cost | 158 yuan | 40 yuan |
| DC resistance | 87.0 Ω/km | 137.0 Ω/km |
| 100 kHz impedance | 87.0 + j0.5 Ω/km | 137.0 + j0.4 Ω/km |
| Weight Difference | Baseline | -54% |
| Cost Variance | Baseline | -75% |
Key Findings: The reactance of the CCA wire (j0.4) at 100 kHz is almost the same as that of the copper wire (j0.5), the impedance difference is mainly in the resistance (real part). However, the Q value of the filter is mainly determined by the inductance. The inductance value formed by the copper layer + paint film is close to that of the copper wire.
—
3. Core physics of high-frequency scenes: skin effect
3.1 The physical nature of skin effect
When an AC current passes through a conductor, eddy currents are induced inside the conductor. According to Lenz’s law, the magnetic field generated by eddy currents will offset the effect of the original magnetic field inside the conductor, causing the current density to concentrate on the surface of the conductor.
This phenomenon is called Skin Effect.
3.2 Skin depth formula
The skin depth δ is defined as the depth at which the current density decays to 1/e (approximately 36.8%) of the surface value:
“` δ = √(ρ / (π × f × μ)) “`
Among them:
- ρ = resistivity (Ω·m)
- f = frequency (Hz)
- μ = magnetic permeability (H/m)
3.3 Skin depth at different frequencies (copper)
| Frequency | Skin depth (mm) | Applicable scenarios |
|---|---|---|
| 50 Hz | 9.33 | Power transformers / industrial motors |
| 1 kHz | 2.08 | Audio / Universal Power |
| 10 kHz | 0.66 | Switching power supply primary |
| 100 kHz | 0.21 | Wireless Charging / 5G Filter |
| 1 MHz | 0.066 | High frequency transformer / RFID |
| 10 MHz | 0.021 | High frequency induction heating |
| 100 MHz | 0.0066 | RF Antenna |
| 1 GHz | 0.0021 | Microwave devices |
3.4 100 kHz Case: 5G Filter Coil
A 5G AAU filter coil with a conductor diameter of 0.50 mm:
- Skin depth δ = 0.21 mm
- Conductor radius = 0.25 mm
- Theoretical delta to radius ratio = 0.21/0.25 = 0.84
- Actual current density distribution: surface 100%, center 32% (can still carry some current)
Key Insights:
- 0.50 mm diameter copper wire at 100 kHz, 60% of current flows through outer layer 0.21 mm
- If using CCA wire (copper layer 0.05 mm thick), the outer layer mainly uses copper layer → the equivalent copper loss is close to that of pure copper wire
- The central aluminum core still contributes little at 100 kHz due to eddy current losses
Conclusion: In the 100 kHz + 0.50 mm diameter scenario, the high-frequency performance of a CCA line with a copper layer accounting for 10% can reach 80-90% of that of pure copper.
3.5 Frequency inflection point of skin effect
| Frequency range | Loss dominance | Optimization strategy |
|---|---|---|
| < 10 kHz | DC resistance | Lower resistance (copper); CCA slightly worse |
| 10-100 kHz | The skin effect begins | The advantages of CCA appear |
| 100 kHz-1 MHz | Skin effect + eddy current | CCA has the greatest advantage |
| 1-10 MHz | Skin + proximity | Stranded Litz wire; CCA advantage reduced |
| > 10 MHz | Plated copper/silver/Litz wire | CCA not applicable |
—
4. Proximity effect and multi-stranded Litz lines
4.1 Physics of Proximity Effect
Proximity Effect means that currents in adjacent conductors will induce each other, causing the current distribution to skew to one side. In high-frequency transformers and motor windings, the proximity effect is often more serious than the skin effect.
Proximity Effect Loss Vs Skin Effect Loss:
- Skin effect: self-loss in a single conductor
- Proximity effect: mutual losses between multiple/multilayer conductors
- In compact windings, proximity effect losses can be 5-10 times the skin effect
4.2 Introduction of Litz Wire
In order to solve the proximity effect, the industry invented Litz wire – braided from multiple strands of independently insulated thin wires (enameled wire):
- Diameter of each strand < 1/3 of skin depth
- Braiding makes each strand evenly positioned in the magnetic field
- Each thin wire carries current independently and the current is evenly distributed
Typical Litz wire specifications: At 100 kHz, 5× 0.05 mm (5 strands of 0.05 mm enameled wire) is equivalent to 1× 0.21 mm solid copper wire.
4.3 Comparison of enameled wire braiding parameters
| Frequency | Skin depth | Recommended single wire diameter | Number of litz wire strands |
|---|---|---|---|
| 100 kHz | 0.21 mm | 0.07 mm | 5 |
| 200 kHz | 0.15 mm | 0.05 mm | 7 |
| 500 kHz | 0.094 mm | 0.04 mm | 10 |
| 1 MHz | 0.066 mm | 0.03 mm | 16 |
| 2 MHz | 0.047 mm | 0.02 mm | 25 |
4.4 CCA wire vs Litz wire vs solid copper
| Solution | 100 kHz loss | 1 MHz loss | Cost | Applicable frequencies |
|---|---|---|---|---|
| Solid Copper 0.50 mm | Baseline (1.0×) | Baseline (1.0×) | High | DC-50 kHz |
| Solid Copper 0.21 mm | 0.85× | 0.95× | Medium | DC-200 kHz |
| CCA 0.50 mm (10% copper) | 0.95× | 1.40× | Low | DC-500 kHz |
| CCA 0.50 mm (15% copper) | 0.88× | 1.20× | Mid-Low | DC-500 kHz |
| Leeds 5× 0.07 mm | 0.55× | 0.85× | High | 100 kHz-1 MHz |
| Leeds 16× 0.05 mm | 0.30× | 0.65× | Extremely high | 500 kHz-10 MHz |
Key Findings:
- Below 100 kHz: CCA is close to pure copper
- 100-500 kHz: CCA has the greatest advantages (50-70% lower cost, 10-20% higher loss)
-> 500 kHz: Litz line is preferred, CCA advantage decreases
4.5 The critical role of the Rac/Rdc ratio
Rac/Rdc = AC resistance / DC resistance, the gold standard for measuring high frequency losses.
| Frequency | Solid copper 0.50 mm | CCA 0.50 mm (10%) | Leeds 5×0.07 mm |
|---|---|---|---|
| 1 kHz | 1.001 | 1.001 | 1.001 |
| 10 kHz | 1.012 | 1.010 | 1.005 |
| 100 kHz | 1.450 | 1.480 | 1.150 |
| 500 kHz | 3.200 | 3.700 | 1.820 |
| 1 MHz | 4.800 | 6.500 | 2.500 |
Insight:
- Below 100 kHz: solid copper, Rac/Rdc = 1.0-1.5
- 100 kHz knee: CCA is better than Litz wire (cost perspective)
- 1 MHz: Litz line has obvious advantages
—
5. Comparison of 5 key electrical properties
5.1 DC resistance
| Indicators | Solid Copper | CCA (10%) | CCA (15%) | Leeds 5×0.07 |
|---|---|---|---|---|
| Diameter 0.50 mm | 87.0 Ω/km | 137.0 Ω/km | 118.0 Ω/km | 81.0 Ω/km |
| Diameter 1.00 mm | 21.7 Ω/km | 34.0 Ω/km | 29.5 Ω/km | 20.3 Ω/km |
| Diameter 2.00 mm | 5.42 Ω/km | 8.55 Ω/km | 7.36 Ω/km | 5.05 Ω/km |
Insight: The DC resistance of CCA is 30-60% higher than that of pure copper, but the Rac gap shrinks significantly at high frequencies.
5.2 AC resistance Rac
0.50 mm solid copper vs CCA at 1 MHz:
| Frequency | Solid Copper Rac | CCA (10%) Rac | CCA (15%) Rac |
|---|---|---|---|
| 100 kHz | 126.2 Ω/km | 202.8 Ω/km | 174.6 Ω/km |
| 500 kHz | 278.4 Ω/km | 506.0 Ω/km | 436.4 Ω/km |
| 1 MHz | 417.6 Ω/km | 890.5 Ω/km | 708.9 Ω/km |
Insight: At 1 MHz, CCA AC resistance is nearly 2 times that of pure copper due to the sharp increase in eddy current losses in the aluminum core.
5.3 Q value comparison
Q value (quality factor) = ωL/R, is crucial for resonant circuits.
50 μH coil (0.50 mm diameter) at 100 kHz:
| Indicators | Solid Copper | CCA (10%) | Leeds 5×0.07 |
|---|---|---|---|
| DC resistance | 0.87 Ω | 1.37 Ω | 0.81 Ω |
| 100 kHz impedance | 0.92 Ω | 1.46 Ω | 0.95 Ω |
| Q-value | 34.2 | 21.5 | 33.0 |
| 1 MHz Impedance | 4.18 Ω | 8.91 Ω | 2.69 Ω |
| 1 MHz Q value | 7.5 | 3.5 | 11.7 |
Insight:
- 100 kHz: Copper Q 34, CCA Q 22, 35% difference
- 1 MHz: Litz wire has a Q value of 12, which is better than solid copper (Q=7.5)
5.4 Loss and temperature rise
| Indicators | Solid Copper | CCA (10%) | Leeds 5×0.07 |
|---|---|---|---|
| 100 kHz losses (same current) | Baseline +0% | +57% | +5% |
| 100 kHz temperature rise (same losses) | Baseline | +30% | +3% |
| 1 MHz loss | Baseline +0% | +210% | -55% |
| 1 MHz Temperature Rise | Baseline | +150% | -40% |
Insight:
- 100 kHz: CCA temperature rise controllable (+30%)
- 1 MHz: CCA not available
- Litz line has significant advantages at 1 MHz+
5.5 EMI performance
Copper: Magnetic permeability 1 (paramagnetic), no additional electromagnetic interference
CCA: Copper layer + aluminum core structure, there are tiny eddy currents at the interface, and EMI is slightly worse than pure copper (5-10%)
Litz wire: Braided structure + multiple independent paint films, EMI is better than solid copper (-10-20%)
—
6. 100 kHz case: 100 W wireless charging transmitter coil
6.1 Scene description
WPC Qi standard wireless charging transmitting coil, operating frequency 110-205 kHz, power 100 W, coil outer diameter 80 mm.
6.2 Comparison of three options
| Indicators | Solid Copper 0.50 mm | CCA 0.50 mm (10%) | Leeds 5×0.07 mm |
|---|---|---|---|
| Weight | 25.0 g | 11.3 g | 7.5 g |
| Cost | 22.5 yuan | 6.8 yuan | 25.0 yuan |
| DC resistance | 8.7 Ω | 13.7 Ω | 8.1 Ω |
| 100 kHz impedance | 9.2 Ω | 14.6 Ω | 9.5 Ω |
| Loss | 2.8 W | 4.2 W | 2.9 W |
| Efficiency | 97.2% | 95.8% | 97.1% |
| Temperature rise | 35 K | 50 K | 36 K |
| Charging Speed | Baseline | -1.5% | Baseline |
| BOM Cost | Baseline | -70% | +11% |
6.3 Key Decisions
Select CCA:
- Reasons: cost sensitive, temperature rise of 50 K within 100°C limit, efficiency loss of 1.5% acceptable
- Solution: 100 W wireless charging transmitter coil
Choose Leeds Line:
- Reasons: efficiency priority, strict temperature rise, life requirement 5 years+
- Solution: High-end mobile phone wireless charging, medical equipment
Choose solid copper:
- Reason: Mature technology, high reliability, life span 10 years+
- Solutions: Industrial wireless charging, rail transit
6.4 Lifespan and Reliability
| Indicators | Solid Copper | CCA | Litz Wire |
|---|---|---|---|
| Thermal cycle life | 25 years | 15 years | 20 years |
| Vibration tolerance | +30% | Baseline | -10% |
| Copper-aluminum diffusion | Not applicable | Risk items | Not applicable |
| Welding Reliability | High | Medium | High |
CCA Lifetime Risk:
- The Kirkendall Effect will occur at the copper-aluminum interface at 150°C+ for a long time, forming voids
- Lifespan decays exponentially with temperature: 15 years at 120°C → 8 years at 150°C → 4 years at 180°C
- 178°C soldering process requires strict control of heating time
—
7. 5G base station filter scenario
7.1 5G filter requirements for winding wires
The filters (bandpass/cavity/medium) in the 5G base station AAU (Active Antenna Unit) require:
- Operating frequency: 3.3-4.2 GHz (n77 band)
- Quality factor Q: > 2,000 (dielectric filter)
- Temperature Stable: ±2 ppm/°C
- Power Capacity: 100 W+ (single channel)
- Lifetime: 15 years
7.2 Winding wire selection for 5G filter
| Frequency | Winding line scheme | Target |
|---|---|---|
| < 1 GHz | Solid Copper / Silver Plated Copper | General Purpose |
| 1-3 GHz | Silver plated copper / Litz wire | High Q |
| 3-5 GHz | Silver plated copper + dielectric ceramic | High Q + low loss |
| 5-10 GHz | Silver plated copper + planar microstrip | High frequency GHz |
| > 10 GHz | Silver plated copper + PCB integration | mmWave |
7.3 Limitations of CCA in 5G
Skin depth at 3.3 GHz:
“` δ = √(ρ / (π × f × μ)) δ = √(1.724×10⁻⁸ / (π × 3.3×10⁹ × 4π×10⁻⁷)) δ = √(1.39×10⁻¹²) δ ≈ 1.18 μm “`
Key Findings:
- 3.3 GHz skin depth only 1.18 μm
- CCA copper layer thickness typically 30-100 μm (10-15% radius, 0.50 mm diameter)
- The current is concentrated in the outer layer 1.18 μm
- If the copper layer is < 1.18 μm, the aluminum core may be exposed to high frequency currents → Aluminum resistivity is 60% higher and losses surge
Conclusion:
- 5G filters (3-6 GHz) are not suitable for CCA
- Pure copper/silver plated copper is still recommended
7.4 5G indirect association
Where CCA really comes into play in 5G systems:
- 5G base station power supply: 48V → 12V DC-DC converter (100-500 kHz)
- 5G AAU cooling fan motor: 50/60 Hz power frequency
- 5G base station air conditioner: motor winding
- 5G Device Interconnect: Coaxial Cable/Braided Wire
CCA penetration rate (5G indirect scenario): 20-30%
—
8. Wireless charging (Qi/WPT) CCA advantages
8.1 Wireless charging standard
- WPC Qi: 100-205 kHz (mainstream mobile phones)
- AirFuel Resonant: 6.78 MHz
- AirFuel Inductive: 110-205 kHz
- WPT Industrial 100W+: 85-110 kHz
- EV Wireless Charging: 85 kHz (SAE J2954)
8.2 CCA market in wireless charging
| Scenario | Power | Frequency | CCA Penetration |
|---|---|---|---|
| Mobile phone wireless charging | 5-15 W | 110-205 kHz | 60-70% |
| Desktop wireless charging | 15-30 W | 110-205 kHz | 50-60% |
| Industrial wireless charging | 100-500 W | 85-205 kHz | 30-40% |
| Electric vehicle wireless charging | 3-22 kW | 85 kHz | 5-15% |
| Medical wireless charging | 5-50 W | 100-205 kHz | 40-50% |
8.3 100 W wireless charging case (cost analysis)
| Indicators | Solid Copper | CCA (10%) | CCA (15%) | Litz Wire |
|---|---|---|---|---|
| Weight | 25 g | 11 g | 14 g | 7.5 g |
| Cost | 22.5 yuan | 6.8 yuan | 9.0 yuan | 25.0 yuan |
| 100 kHz efficiency | 97.2% | 95.8% | 96.7% | 97.1% |
| Temperature rise | 35 K | 50 K | 42 K | 36 K |
| BOM cost ratio | Baseline | -70% | -60% | +11% |
Key Insights:
- CCA (10%) cost reduction of 70%, efficiency loss of 1.5% – best value for money
- CCA is the first choice for high-volume consumer electronics
- Litz wire is the first choice for industrial/medical applications
8.4 Advantages of CCA braided wire in wireless charging
Wireless charging coils often use Braided Wire:
- Braided wire diameter 0.50-2.00 mm
- Braided from multiple strands of 0.05-0.10 mm enameled wire
- 30-50% larger surface area than solid wire
- Better heat dissipation
- Better flexibility
CCA Braided Wire:
- Aluminum core + copper layer + braid
- Cost reduction 40-60%
- Performance close to pure copper braided wire (100-200 kHz)
—
9. High frequency transformer scenario
9.1 High frequency transformer frequency range
| Scene | Frequency | Power | Winding wire |
|---|---|---|---|
| Switching Power Supplies Primary | 50-100 kHz | 50-500 W | Solid Copper / CCA |
| DC-DC Converters | 100-500 kHz | 10-500 W | CCA / Litz Wire |
| Planar Transformers | 500 kHz-2 MHz | 5-100 W | Copper Foil / Litz Wire |
| Resonant Converter | 1-10 MHz | 1-50 W | Litz Wire |
| EV Traction DC-DC | 100-200 kHz | 1-5 kW | Copper Foil / Litz Wire |
| Data Center VRM | 1-5 MHz | 100-500 W | Litz Wire / PCB |
9.2 100 kHz switching power supply case
A 100 W flyback switching power supply, frequency 100 kHz:
| Solution | Weight | Cost | Efficiency |
|---|---|---|---|
| Copper enameled wire 0.40 mm | 12.5 g | 5.6 yuan | 92% |
| CCA 0.40 mm (10%) | 5.7 g | 1.8 yuan | 90% |
| CCA 0.40 mm (15%) | 6.8 g | 2.3 yuan | 91% |
| Leeds 5×0.10 mm | 3.5 g | 4.5 yuan | 92% |
Key Insights:
- CCA (15%) close to copper performance, 60% lower cost
- Litz wire has the smallest weight but high cost
- CCA is the first choice for 100 W switching power supply
9.3 Planar Transformer PCB Integration
PCB Planar Transformer:
- Copper foil (35-105 μm) sinks into the inner layer of PCB
- Frequency 500 kHz-2 MHz
- Good heat dissipation (PCB copper layer direct heat dissipation)
- Mature manufacturing process
CCA in PCB planar transformer:
- Difficulty electroplating CCA copper layer (poor adhesion between aluminum core and PCB resin)
- Usually pure copper foil is still used
- Advantage scenarios: high power + high current
9.4 EV 800V high voltage DC-DC case
An 800V platform EV, 2 kW DC-DC converter (400V → 12V), frequency 200 kHz:
| Solution | Weight | Cost | Efficiency |
|---|---|---|---|
| Copper foil 0.20 mm (4 layers) | 86 g | 53 yuan | 96.5% |
| CCA 0.20 mm (16% copper) | 38 g | 22 yuan | 95.0% |
| Leeds 100×0.05 mm | 22 g | 85 yuan | 97.0% |
Key Findings:
- CCA efficiency decreases by 1.5% at 200 kHz
- 56% weight reduction
- Cost reduction 58%
- Lifetime 15 years (150°C limit)
—
10. RFID/NFC antenna scenario
10.1 RFID frequency and scenarios
| Frequency band | Frequency | Typical applications | Reading distance |
|---|---|---|---|
| LF | 125-134 kHz | Animal identification, access control | < 0.5 m |
| HF | 13.56 MHz | NFC, library, ticketing | 0.1-1 m |
| UHF | 860-960 MHz | Logistics, retail | 1-10 m |
| Microwave | 2.45 GHz | Industrial, medical | 1-5 m |
10.2 HF RFID 13.56 MHz
13.56 MHz Skin depth (copper): ~17 μm
Common winding wires:
- Enameled copper wire 0.10-0.30 mm
- Copper foil (PCB integration)
- Printed antenna (copper paste or conductive silver paste)
CCA in HF RFID:
- At 13.56 MHz, CCA copper layer needs to be > 17 μm
- CCA copper layer 10% → 0.30 mm diameter CCA copper layer 30 μm ✅
- Applicable scenarios: HF RFID tags, smart cards, ticketing
10.3 UHF RFID 900 MHz
900 MHz skin depth (copper): ~2.2 μm
Key Findings:
- CCA copper layer 30 μm (0.30 mm diameter) is much larger than 2.2 μm
- But UHF RFID usually uses PCB printed antenna (copper etched)
- CCA wire is not common in UHF RFID
10.4 NFC smart card case
NFC smart card antenna operating frequency 13.56 MHz:
| Plan | Weight | Cost | Reading distance |
|---|---|---|---|
| Painted copper wire 0.10 mm | 0.15 g | 0.6 yuan | 8 cm |
| CCA 0.15 mm (10%) | 0.07 g | 0.20 yuan | 7 cm |
| Copper foil + PCB | 0.20 g | 0.40 yuan | 8 cm |
| Aluminum etching + coating | 0.06 g | $0.10 | 4 cm |
Key Findings:
- CCA cost reduced by 67%, read distance reduced by only 12%
- CCA is the first choice for large quantities of NFC cards (bus/access control)
10.5 IoT sensor antenna
Many IoT sensors use the 13.56 MHz / 433 MHz / 900 MHz / 2.4 GHz frequency bands:
- 13.56 MHz: CCA applicable, cost sensitive
- 433 MHz / 900 MHz: usually PCB planar antenna
- 2.4 GHz WiFi/BLE: PCB planar antenna is the main component
- 24 GHz / 77 GHz Radar: PCB Microstrip + Silver Plated
—
11. 6 key selection decision matrix
11.1 Decision matrix
The following table is a comparison of CCA vs copper vs litz wire in 6 key selection dimensions:
| Dimensions | Pure Copper | CCA (10%) | Litz Wire |
|---|---|---|---|
| DC Resistance | Baseline (+0%) | +57% | +5% |
| 100 kHz loss | Baseline | +57% | +5% |
| 1 MHz loss | Baseline | +210% | -55% |
| Weight | Baseline | -54% | -30% |
| Cost | Baseline | -50% | +10% |
| Lifespan (150°C) | 25 years | 8-10 years | 20 years |
| Welding | Easy | Medium | Easy |
| Vibration tolerance | +30% | Baseline | -10% |
| Corrosion Resistance | +20% | Baseline | +5% |
11.2 Frequency vs Program Decision
| Frequency | Diameter < 0.30 mm | Diameter 0.30-1.00 mm | Diameter > 1.00 mm |
|---|---|---|---|
| DC-50 kHz | Copper | Copper / CCA | Copper |
| 50-200 kHz | Copper / CCA | CCA / Litz | Copper / Litz |
| 200-500 kHz | CCA / Litz Line | Litz Line | Litz Line |
| 500 kHz-2 MHz | Litz wire | Litz wire | Litz wire / copper foil |
| > 2 MHz | Litz wire / copper foil | copper foil | copper foil |
11.3 Power vs Solution Decision
| Power | Frequency < 200 kHz | Frequency 200 kHz-1 MHz | Frequency > 1 MHz |
|---|---|---|---|
| < 10 W | Copper/CCA | Copper/CCA | Litz wire |
| 10-100 W | Copper / CCA | CCA / Litz Wire | Litz Wire |
| 100 W-1 kW | Copper / CCA | Litz Wire / Copper Foil | Litz Wire / Copper Foil |
| > 1 kW | Copper / copper foil | Litz wire / copper foil | Litz wire |
11.4 Temperature vs Program Decision
| Temperature | Copper | CCA (10%) | Litz Wire |
|---|---|---|---|
| < 105°C | 25 years | 15-20 years | 20-25 years |
| 105-130°C | 20 years | 10-15 years | 15-20 years |
| 130-155°C | 15 years | 5-8 years | 10-15 years |
| 155-180°C | 10 years | 3-5 years | 8-10 years |
| > 180°C | 5 years | Not recommended | Not recommended |
11.5 Cost Sensitivity Decisions
| Cost sensitivity | Recommended solutions |
|---|---|
| Very Low (Consumer Electronics) | CCA (10% Copper) |
| Low (Industrial) | CCA (15% Copper) |
| Medium (Professional Equipment) | Copper / Litz Wire |
| High (Aerospace / Medical) | Copper / Litz Wire |
11.6 Weight Sensitivity Decisions
| Weight sensitivity | Recommended solutions |
|---|---|
| Not Sensitive | Copper |
| Medium | CCA |
| High (Aviation / Drone) | Leeds Line / CCA |
| Extremely High (Satellite) | Litz Line |
11.7 Lifetime Requirement Decision
| Lifetime requirements | Recommended solutions |
|---|---|
| < 5 years | CCA Free |
| 5-10 years | CCA + temperature derating |
| 10-20 years | Copper / Litz wire |
| > 20 years | Copper |
—
12. Limitations of CCA line
12.1 5 unavailable scenarios
1. High temperature scene (>200°C)
- The CuAl₂ brittle phase forms at the copper-aluminum interface above 200°C
- Long-term operating temperatures 150°C+ CCA should be avoided
- Alternatives: Pure Copper/Nichrome/Silver
2. High current scenario (>10 A)
- Below 5 A: CCA close to copper
- 5-10 A: CCA slightly worse
-> 10 A: CCA not available
- Reason: current density, temperature rise of connection point
3. High power and high frequency power (>1 kW)
- Below 100 W: CCA Advantages
- 100 W-1 kW: CCA aggravated
-> 1 kW: CCA not available
- Reason: Eddy current loss + heat dissipation
4. Outdoor exposure scenes
- Rain + salt spray: The copper layer is corroded and the aluminum core is exposed → rapid oxidation
- Outdoor life: reduced from 15 years to 5-8 years
- Alternative: CCA + outer sheath / pure copper
12.5 Welding process restrictions
- CuAl₂ is easily formed at the copper-aluminum interface during the soldering process at 178°C
- Welding time must be < 3 seconds
- CCA is disabled for some soldering processes (>250°C)
12.2 5 partially available scenarios
1. IF 200-500 kHz
- 10-20% increase in losses
- Suitable for cost-sensitive industrial scenarios
2. Short-term transient overload
- 50% increase in short-term current density acceptable
- Long-term overloading will not work
3. Quasi-static (< 1 kHz)
- Loss increased by 50%+
- Suitable for scenarios where insulation requirements are higher than conductivity requirements
4. High frequency connecting wire (without winding)
- Coaxial cable, braided wire
- Suitable for non-main coils
5. Shield/ground layer
- The shielding efficiency is close to that of pure copper
- Weight / cost advantage
12.3 5 absolutely unusable scenarios
1. Nuclear Magnetic Resonance (MRI): NMR compatibility requires extremely high magnetic field stability 2. Superconducting circuit: CCA resistance is not zero 3. Precision instrument: Temperature coefficient 4×10⁻³/°C (aluminum) vs 4×10⁻³/°C (copper), but the actual difference is significant 4. Long-term charging equipment: After charging for ten years, the CCA life is insufficient 5. High humidity + condensation environment: The aluminum core will completely fail after the copper layer is damaged
—
13. Mix and match scheme: Copper + Litz wire + CCA composite
13.1 Three types of mix-and-match solutions
Option A: Copper for main coil + CCA for shielding
- Main coil Litz wire (high frequency)
- Shielded CCA braided wire (low cost)
- Usage scenarios: wireless charging high-end products
Plan B: Litz wire for high frequency + CCA for low frequency
- Litz wire in high frequency region (>200 kHz)
- Low frequency region (< 200 kHz) CCA
-Usage scenario: DC-DC converter
Scheme C: DC + high frequency branch line
- CCA for DC component (large current)
- Litz wire for high frequency components (eddy current suppression)
- Usage scenario: EV traction (DC + PWM high frequency)
13.2 Project example: 5G base station 200 W DC-DC
A 5G base station 200 W DC-DC converter (48V → 5V), frequency 250 kHz:
| Solution | Weight | Cost | Efficiency |
|---|---|---|---|
| All copper enameled wire | 180 g | 95 yuan | 94.5% |
| All CCA | 81 g | 33 yuan | 91.5% |
| All litz wire | 60 g | 125 yuan | 96.0% |
| **Mix and Match (Main Coil Leeds + Shielded CCA)** | 78 g | $65 | 95.6% |
Best solution: Mix and match – main coil Litz wire (high efficiency) + shielded CCA braided wire (low cost).
13.3 Litz wire + CCA composite wire
New generation composite line:
- Center: CCA (aluminum core + copper layer)
- Outer layer: Litz braid of painted copper wire
- Combination: low high frequency loss of Litz wire + lightweight of CCA
Advantages:
- Frequency 100-500 kHz performance close to Litz wire
- Weight lower than Litz wire
- Lower cost than Litz wire
Limitations:
- Complex manufacturing process
- Industry standards have not yet been established
—
14. 5 key quality inspections
14.1 Key quality inspection items
| Testing items | Standards | Qualification standards | Testing significance |
|---|---|---|---|
| Copper layer thickness | Metallographic section | 8-15% radius | Determines high frequency performance |
| DC resistance | IEC 60851 | ≤ 105% of nominal value | Conductive properties |
| Skin depth integration | Eddy current test | 100 kHz ≤ 1.5× DC resistance | High frequency performance |
| Coating adhesion | Bend test | Folded 3 times without falling off | Coating is reliable |
| Aging test | 200°C × 168 h | Resistance increase < 5% | Lifetime |
14.2 Standardization of copper layer thickness
Definition of copper layer ratio:
- 8% copper: economical type (high frequency and low consumption scenario)
- 10% copper: universal type (mainstream for wireless charging)
- 12% Copper: Enhanced (Industrial Control)
- 15% copper: high-end type (close to copper performance)
- 18-25% copper: quasi-copper type (cost balance)
Measurement method:
- Metallographic microscope: accuracy ±0.5 μm
- XRF spectrum: accuracy ±1 μm
- Eddy current thickness gauge: accuracy ±2 μm
14.3 High frequency resistance measurement
LCR meter measurement:
- 1 kHz-1 MHz impedance analysis
- Calculate Rac/Rdc ratio
- Determine whether specifications are met
Impedance Analyzer Measurement:
- 1 MHz-3 GHz S-parameters
- Extract equivalent circuit
- Simulation optimization
14.4 Aging test
Accelerated Aging:
- 200°C × 168 h (1 week)
- 200°C × 1000 h (6 weeks)
- Measure resistance change ΔR/R₀
Life extrapolation:
- 150°C life: 1000°C life × 2^((200-150)/10) ≈ 32× ≈ 8-15 years
- 130°C life: 150°C life × 2^((150-130)/10) ≈ 4× ≈ 15-20 years
14.5 Welding Compatibility Test
Solder Wetness Test:
- 250°C solder dip for 3 seconds
- Check wetted area ≥ 95%
- Solder joint pull-off force ≥ 5 N
Kirkendall Effect Test:
- Long-term high temperature (150°C × 1000 h)
- Metallographic section examination of copper-aluminum interface
- Void < 5% area
—
15. 8 FAQ + Summary + Future Trends
15.1 FAQ (8 high-frequency questions)
Q1: Can CCA wire be used in 50 Hz industrial motors?
A: It can be used, but the advantages are limited. The 50 Hz skin depth is 9.33 mm, which is much larger than the CCA copper layer (30-100 μm), so the CCA DC resistance is basically the upper limit of performance. CCA losses are 30-60% higher than pure copper at 50 Hz. Unless cost/weight is extremely sensitive, pure copper is superior.
Q2: Can CCA wire be used in a long-term working environment of 100°C?
A: Yes. CCA life 15-20 years at 100°C (copper-aluminum diffusion controlled). But at 130°C+ the lifespan drops sharply to 5-8 years.
Q3: Are CCA wire and copper-plated aluminum wire (CCA reversed) the same thing?
A: No. CCA (Cuprel) = copper clad aluminum, aluminum core + copper layer. CCA reversed = aluminum clad copper, copper core + aluminum layer. The latter is used less and costs slightly more.
Q4: Can CCA wire be welded directly?
A: Yes, but there are restrictions. Recommended soldering temperature ≤ 250°C, soldering time ≤ 3 seconds. The CuAl₂ brittle phase may form in the copper layer during the soldering process at 178°C+.
Q5: How to choose between CCA wire and tinned copper wire?
A: Tinned copper wire: pure copper core + solder coating, used for PCB soldering. CCA wire: aluminum core + copper layer for high frequency winding. The two are different: Tinned copper wire costs similar, but CCA weighs 50% less.
Q6: Are CCA lines useful in 5G base stations?
A: 5G direct scenario (3-6 GHz filter) is not applicable (skin depth is too shallow). Applicable to 5G indirect scenarios (power supply/fan/motor).
Q7: What about CCA wire and aluminum enameled wire?
A: Aluminum enameled wire is 30-50% cheaper than CCA, but its high-frequency performance, welding performance, and lifespan are inferior. CCA is a high-end alternative.
Q8: Can CCA wire pass IEC certification?
A: Yes. IEC 60851 and IEC 60317 cover all tests of enameled wires. CCA is certified after passing the same test.
15.2 Summary of core points
CCA Advantages: 1. Weight reduction 30-50% (vs. pure copper) 2. Cost reduction by 30-50% (copper-aluminum price ratio in 2024: 4:1) 3. 100-500 kHz high frequency performance is close to copper (loss increased by 10-30%) 4. The welding performance is close to that of copper (temperature/time needs to be controlled)
CCA Limitations: 1. DC resistance is 30-60% higher than copper 2. Lifespan drops sharply at high temperatures (>150°C) 3. > 1 MHz Eddy current losses are significant 4. Lifespan is significantly reduced in outdoor/condensation environments 5. High current (>10 A) applications are limited
Core Decision:
- Below 100 kHz + 100 W: CCA has the greatest advantages
- Below 1 MHz + 100 W: Litz wire is better
- 5G filter (3-6 GHz): CCA not applicable
- High temperature/outdoor/high power: CCA not available
Engineering significance:
- Wireless charging 100 W: 70% cost reduction, 1.5% efficiency loss
- 5G base station DC-DC: cost reduced by 60%, weight reduced by 56%
- NFC smart cards: 67% lower cost, only 12% lower read range
15.3 Five major trends in the future
Trend 1: 5G/6G promotes high-frequency CCA standardization
- 5G penetration rate is expected to be 60% in 2025
- 6G 100 GHz + communications promote high-frequency CCA standardization
- IEC 60851 + IPC-4562 adds CCA medium and high frequency provisions
Trend 2: Wireless charging drives mass production of mid-frequency CCA
- Wireless charging market size will reach US$30 billion in 2025
- CCA IF 100-205 kHz standard is mature
- The industry predicts that CCA wireless charging penetration rate will be 70%+ in 2027
Trend 3: Composite Wire (Copper + Leeds + CCA) Popularity
- Different solutions for main coil + shield + high frequency unit
- Intelligent product design
- Performance / cost balance
Trend 4: 100% Recycled Copper CCA Top Layer
- EU mandates recycled materials to account for 30% in 2030
- Recycled copper CCA has started small batches
- Carbon Footprint Certification (CFP) becomes a competitive point
Trend 5: Automated CCA manufacturing costs reduction
- Current CCA manufacturing: semi-automatic
- 2027-2030: fully automated
- Expected cost reduction of 20-30%
15.4 CCA learning path
Entry Level (1-3 months):
- Understand the essential difference between CCA vs copper
- Master skin effect and proximity effect physics
- Learn basic selection rules
Advanced level (3-12 months):
- Familiar with 100 kHz-1 MHz frequency band differences
- Master Rac/Rdc measurement methods
- Learn to mix Litz wire + copper
Expert Level (12 months+):
- Lead the design of high-frequency projects
- Optimize Rac/Rdc parameters
- Solve welding/aging/vibration problems
—
Appendix A: 25 Key Parameters Cheat Sheet
| Category | Parameters | Units | Copper Typical | CCA Typical | Standard |
|---|---|---|---|---|---|
| Conductor | Diameter | mm | 0.10-5.00 | 0.20-5.00 | IEC 60317 |
| Conductor | Density | g/cm³ | 8.96 | 3.63-4.16 | — |
| Conductor | Resistivity | Ω·m | 1.724×10⁻⁸ | 2.65-2.83×10⁻⁸ | IEC 60028 |
| Conductor | Temperature coefficient | 1/°C | 0.00393 | 0.00393 | IEC 60028 |
| Conductor | Magnetic permeability | H/m | 4π×10⁻⁷ | 4π×10⁻⁷ | — |
| Copper Layer | Thickness | % Radius | 100% | 8-25% | — |
| Paint film | Thickness | mm | 0.06-0.11 | 0.06-0.11 | IEC 60317 |
| Breakdown | Voltage | kV | 2.5-10 | 2.5-5 | IEC 60851 |
| High frequency | Skin depth 100 kHz | mm | 0.21 | 0.21 | — |
| High frequency | Skin depth 1 MHz | mm | 0.066 | 0.066 | — |
| High frequency | Skin depth 1 GHz | μm | 2.10 | 2.10 | — |
| DC | IACS | % | 100% | 60-70% | IEC 60028 |
| DC | Resistance 0.50 mm | Ω/km | 87.0 | 137.0 | — |
| Loss | 100 kHz Rac/Rdc | Times | 1.45 | 1.48 | — |
| Loss | 1 MHz Rac/Rdc | Times | 4.80 | 6.50 | — |
| Weight | 1000 meters | kg | 1.76 | 0.80 | — |
| Cost | 2024 Yuan/kg | Yuan | 90-100 | 40-55 | — |
| Strength | Tensile | MPa | 220-400 | 90-180 | ASTM D3039 |
| Strength | Elongation | % | 20-40 | 10-25 | ASTM D3039 |
| Lifetime | 130°C | Years | 20 | 15-20 | Arrhenius |
| Lifetime | 150°C | Years | 15 | 8-10 | Arrhenius |
| Lifetime | 180°C | Years | 10 | 3-5 | Arrhenius |
| Lifetime | 200°C | Years | 5 | Not recommended | Arrhenius |
| Soldering | Temperature | °C | 250-380 | 230-260 | IPC J-STD |
| Welding | Time | s | < 5 | < 3 | IPC J-STD |
—
Appendix B: 8 high-frequency scenario project suggestions
Project 1: 100 W wireless charging transmitter coil
- Current status: pure copper enameled wire 0.50 mm
- Retrofit: CCA 0.50 mm (10% copper)
- Effect: 70% cost reduction, 1.5% efficiency loss
- Payback period: Instant
Project 2: 5G Base Station 200 W DC-DC
- Current status: pure copper enameled wire 0.40 mm
- Retrofit: Mix and match (main coil Litz + shielded CCA)
- Effect: cost reduced by 32%, efficiency increased by 1.1%
- Payback period: 3-6 months
Project 3: 100 kHz switching power supply
- Current status: pure copper enameled wire 0.40 mm, efficiency 92%
- Retrofit: CCA 0.40 mm (15% copper)
- Effect: cost reduced by 60%, efficiency reduced by 1%
- Payback period: < 1 month
Project 4: NFC Smart Card Antenna
- Current status: pure copper enameled wire 0.10 mm
- Retrofit: CCA 0.15 mm (10% copper)
- Effect: Cost reduced by 67%, reading range reduced by 12%
- Payback period: Instant
Project 5: 13.56 MHz RFID tag
- Current status: pure copper enameled wire 0.10 mm
- Retrofit: CCA 0.15 mm (10% copper)
- Effect: Cost reduced by 60%, reading range reduced by 8%
- Payback period: Instant
Project 6: EV 800V DC-DC Converter
- Current status: Pure copper foil 0.20 mm × 4 layers
- Retrofit: CCA 0.20 mm (16% copper) × 4 layers
- Effect: Cost reduced by 58%, weight reduced by 56%
- Payback period: 6-12 months
Project 7: Industrial Wireless Charging 500 W
- Current status: pure copper enameled wire 1.00 mm
- Modification: Litz wire 50×0.10 mm
- Effect: Efficiency maintained, weight reduced by 30%
- Payback period: 12-18 months
Project 8: IoT Sensor 13.56 MHz Antenna
- Current status: pure copper enameled wire 0.10 mm
- Retrofit: CCA 0.10 mm (8% copper)
- Effect: Cost reduced by 50%, performance maintained
- Payback period: Instant
—
Appendix C: 5 common selection mistakes
Mistake 1: Rejecting CCA based on IACS conductivity alone
Symptoms: CCA 60-70% IACS is considered to perform far worse than Copper 100% IACS and is not available
The truth:
- Rac/Rdc ratio determines actual losses at high frequencies
- 100 kHz Rac/Rdc: Copper 1.45, CCA 1.48 (2% difference)
- 1 MHz Rac/Rdc: Copper 4.80, CCA 6.50 (35% difference)
- Negligible CCA performance loss in 100 kHz + 0.50 mm scenario
Correct approach:
- Calculate Rac/Rdc at target frequency
- Compare actual losses (not just DC resistance)
- Use CCA boldly below 100 kHz
Mistake 2: Wrong selection of CCA in 5G high frequency (>3 GHz)
Symptoms: Think that CCA must be used for high frequencies because copper is too expensive
The truth:
- > 3 GHz skin depth < 1.2 μm
- The CCA copper layer basically carries the current from the aluminum core
-Surge in eddy current losses in aluminum cores
- 5G filter (3-6 GHz) CCA not available
Correct approach:
- 5G filter (3+ GHz): pure copper / silver plated copper
- 5G indirect scenario (power supply/motor): CCA applicable
Mistake 3: CCA is used in high temperature/outdoor scenes
Symptoms: Ambient temperature and humidity are not taken into account
The truth:
- 130°C+ CCA life decreases sharply (8-10 years → 3-5 years)
- The copper-aluminum interface will form CuAl₂ voids after long-term operation at 150°C+
- Rapid oxidation of aluminum core after corrosion of outdoor copper layer
Correct approach:
- Below 100°C: CCA life 15-20 years
- 130°C+: CCA use with caution
- Outdoor: CCA + outer sheath / pure copper
Error 4: CCA poor soldering/broken solder joint
Symptoms: Insufficient pull-off force of solder joints after welding
The truth:
- 178°C+ soldering process may form CuAl₂ brittle phase
- Too long welding time (>5 seconds) can easily damage the interface
- Improper selection of flux
Correct approach:
- Solder temperature ≤ 250°C, time ≤ 3 seconds
- Use active flux
- Cool immediately after welding
Mistake 5: Blind pursuit of “lowest power consumption”
Symptoms: All high-frequency scenarios use Litz wires
The truth:
- Litz wire costs 200-300% higher
- Litz wire has limited advantages below 100 kHz
- Excessive selection results in 50-200% cost waste
Correct approach:
- Below 100 kHz: CCA preferred
- 100-500 kHz: CCA/Litz line trade-off
-> 500 kHz: Litz line required
—
Contact LP Winding Wire (LNPU)
Email: office@lpwindingwire.com WhatsApp: 0086-19337889070 Factory: 60 acres, ISO9001/14001/45001 three certifications Product: Round wire 0.016-7.0mm + Flat wire Thickness 0.8-10mm Width 2-25mm Standards: IEC 60317 + NEMA MW + GB/T 6109 + JIS C 3202 Experience: 30 years export experience, 50+ countries Small batch: 50 kg minimum order Features: R&D capabilities + process standardization + long-term export stability