Copper Foil for NEV Motors: Technical Principles and Industry Applications
Introduction
The rapid development of the new energy vehicle (NEV) industry has placed higher technical demands on drive motor systems. As a core component of NEVs, the drive motor’s operating efficiency, power density, and reliability directly affect the vehicle’s range and safety performance. Copper foil, as an important functional material, plays a crucial role in electromagnetic shielding, thermal management, and structural support in NEV drive motor systems.
This article systematically elaborates on the technical principles, application forms, and selection points of copper foil in the field of NEV drive motors.
I. Technical Characteristics of NEV Drive Motors
1.1 Basic Principles and Structure of Drive Motors
NEV drive motors mainly adopt two types: permanent magnet synchronous motors (PMSM) and asynchronous induction motors (IM). Permanent magnet synchronous motors dominate the passenger vehicle sector due to their high efficiency and high power density.
The core structure of a drive motor includes: a stator assembly (stator core and stator windings) responsible for generating a rotating magnetic field; a rotor assembly (permanent magnet or squirrel-cage structure) realizing electromagnetic torque output; a housing and end covers providing mechanical support and heat dissipation channels; and a motor controller responsible for real-time control of the operating status.
1.2 EMI Characteristics of a Drive Motor
The drive motor system generates complex electromagnetic interference during operation. The main sources of interference include:
Controller Switching Actions: IGBT or MOSFET power devices switch at a PWM carrier frequency of 10-20kHz, generating high-order harmonics that can extend to several MHz, radiating outwards through the DC bus cable and motor phase lines.
High-Frequency Harmonics from the Motor Body: The PWM modulation waveform contains abundant high-order harmonics, interfering with vehicle communication systems and sensor signals.
Bearing Current: Shaft voltage problems caused by asymmetrical magnetic fields may lead to bearing electrical corrosion during high-speed operation.
According to the EMC standards for new energy vehicles, the electromagnetic radiation of the drive system must meet CISPR 25 Class 3 or higher standards.
1.3 Thermal Management Requirements for Drive Motors
The power density of drive motors in new energy vehicles typically reaches 3-5 kW/kg, far exceeding that of traditional industrial motors. Typical thermal management solutions include: water-cooling channel design for the housing, heat-conducting impregnation treatment of the winding ends, and interference fit between the stator core and the housing. Copper foil material has a thermal conductivity of 401 W/(m·K) and can be used as a key component for heat dissipation channels.
II. Technical Characteristics of Copper Foil Materials
2.1 Basic Physical Parameters of Copper Foil
| Parameter | Value |
|---|---|
| Material | Pure Copper (Cu≥99.9%) |
| Density | 8.96g/cm³ |
| Conductivity | 5.96×10⁷S/m (100%IACS) |
| Thermal Conductivity | 401W/(m·K) |
| Melting Point | 1083°C |
2.2 EMI Shielding Effectiveness of Copper Foil
The electromagnetic shielding effectiveness of copper foil mainly stems from reflection loss and absorption loss. Copper’s conductivity is approximately 1.6 times that of aluminum. A 0.05mm thick copper foil can provide 60-70dB of shielding effectiveness in the 1MHz to 100MHz frequency band, and a 0.1mm thick foil can achieve 75-85dB.
2.3 Performance Comparison of Copper Foil and Aluminum Foil
| Performance Indicators | Copper Foil | Aluminum Foil |
|---|---|---|
| Conductivity | 5.96×10⁷S/m | 3.77×10⁷S/m |
| Thermal Conductivity | 401W/(m·K) | 237W/(m·K) |
| Shielding Effectiveness (Equal Thickness) | Benchmark | Approximately 60% of Copper |
| Corrosion Resistance | Excellent | Moderate (Easily Oxidized) |
Copper foil has significant advantages in electrical conductivity, thermal conductivity, and long-term stability, making it more suitable for the high reliability requirements of new energy vehicles drive motor.
III. Typical Applications of Copper Foil in NEV Drive Motor
3.1 Motor Controller Housing Shielding
The motor controller (Inverter) is the largest source of EMI radiation in the drive system.
Application Scheme: A 0.05-0.1mm thick copper foil is attached to the inside of the controller’s aluminum alloy housing. The copper foil and housing are connected with low impedance using conductive tape. The copper foil coverage area should reach more than 80% of the inner wall area of the housing, and the overlap width at the joint should be more than 20mm.
Technical Effect: Effectively attenuates radiated emissions by 20-30dB, ensuring compliance with CISPR 25 Class 3 limits.
3.2 Motor Cable Shielding
The high-speed cable between the drive motor and the controller is an important channel for EMI conduction and radiation.
Application Scheme: Use a 0.1mm thick copper foil-wrapped cable with a wrapping angle of 45 degrees and an overlap rate of not less than 15%. The shielding layers at both ends of the cable are connected to the equipment interface with low impedance through a 360-degree ring crimping method.
Technical Requirements: The overlap resistance should be less than 10mΩ, and the insulation resistance of the shielding layer to ground should be greater than 100MΩ.
3.3 Drive Motor End Shielding
The ends of the motor windings are the main radiation area of high-frequency leakage magnetic fields.
Application Solution: Install a copper foil shielding cover inside the motor end cover. The copper foil thickness is typically 0.035-0.05mm, and the shape is customized according to the end profile.
3.4 DC/DC Converter and OBC Shielding
DC/DC converters and on-board chargers (OBCs) also generate significant EMI interference during operation.
Application Solution: Attach copper foil to the inner wall of the DC/DC converter housing, in conjunction with input and output filter capacitors. A copper foil shielding layer is placed between the internal PCB and the housing of the OBC, and a copper frame shielding cover is used for critical power device areas.
IV. Copper Foil Selection Technical Guide
4.1 Thickness Specifications
| Application | Recommended Thickness | Shielding Effectiveness |
|---|---|---|
| PCB Grade Shielding | 0.035mm | 40-50dB |
| End Shielding | 0.05mm | 60-70dB |
| Controller Housing Shielding | 0.05-0.1mm | 65-80dB |
| Cable Shielding | 0.1mm | 70-80dB |
| High Power Converter Shielding | 0.1-0.2mm | Above 80dB |
4.2 Material and Surface Treatment Selection
Electrolytic Copper Foil Produced through electrolytic deposition, with copper purity ≥99.8%, lower cost, suitable for general industrial applications.
Rolled Copper Foil Produced through mechanical rolling, with copper purity ≥99.9%, excellent ductility, suitable for complex curved surface forming.
| Surface Treatment | Characteristics | Applicable Scenarios |
|---|---|---|
| Bare Copper | Excellent solderability, prone to oxidation | Internal Shielding |
| Tin Plating | Anti-oxidation, good solderability | Cable Shielding |
| Nickel Plating | Corrosion resistant, high temperature resistance | Harsh Environments |
4.3 Adhesive Performance Requirements
Temperature resistance requirements for adhesives in automotive applications:
| Thermal Class | Temperature Range | Applicable Scenarios |
|---|---|---|
| Basic Grade | -40°C to +85°C | Passenger Cabin |
| Advanced Grade | -40°C to +125°C | Engine Compartment |
| Extreme Grade | -40°C to +150°C | Near Drive Motor |
Adhesive performance should meet LV312 or equivalent enterprise standard requirements.
V. Installation Process Specifications
5.1 Surface Treatment Requirements
Before applying copper foil, the surface to be applied must be cleaned: remove oil, release agents, and other contaminants; the surface roughness Ra value of the metal should be within the range of 1.6-3.2μm.
5.2 Application Process Control
- Ambient temperature: 15°C to 35°C
- Relative humidity: 40%-70%
- Application pressure: uniformly compacted to ensure no air bubbles remain
- Curing time: 24 hours at room temperature, or 30 minutes at 60°C
5.3 Grounding Design Specifications
- Shortest grounding path principle
- Combination of multi-point grounding and single-point grounding
- Grounding conductor cross-sectional area not less than 4mm²
- Contact resistance at overlap should be less than 5mΩ
VI. Industry Application Cases
Case 1: Pure Electric Passenger Vehicle Drive Motor Controller
Application Background: 800V high-voltage platform vehicle model, motor controller power density reaches 25kW/L. EMC testing revealed excessive radiation in the 30MHz-100MHz frequency band.
Improvement Solution: A 0.1mm electrolytic copper foil was attached to the inside of the controller housing, with conductive tape used to overlap the copper foil and the housing. An EMI filter was added at the cable entry point.
Application Effect: Radiated emissions were reduced by 25dB, achieving CISPR 25 Class 3 certification.
Case Two: Plug-in Hybrid Vehicle OBC
Application Background: The car radio experienced interference under 6.6kW charging conditions.
Improvement Solution: A 0.05mm copper foil shield was installed in the power module area inside the OBC, and copper foil wrapping was added to the input cables.
Application Effect: Radio noise was eliminated, and the vehicle’s EMC verification was passed.
Case Three: New Energy Commercial Vehicle Drive Motor
Application Background: The commercial vehicle drive motor has a power of 150kW and an operating temperature range of -40°C to +150°C. The original aluminum foil shielding experienced performance degradation after high-temperature aging.
Improved Solution: A 0.1mm tin-plated copper foil shielding cover is used at the motor end, with resistance welding used for the copper foil overlaps.
Application Results: After 1000 hours of high-temperature aging test, the shielding effectiveness retention rate is greater than 95%.
VII. Product Technical Specifications
| Technical Parameters | Specifications |
|---|---|
| Thickness | 0.035 / 0.05 / 0.1 / 0.2 mm |
| Width Range | 10-500mm (Customizable) |
| Copper Material | Pure Copper (Cu≥99.9%) |
| Surface Treatment | Bare Copper / Tin Plating / Nickel Plating / Silver Plating |
| Adhesive Type | Acrylic Adhesive (Temperature Resistance -40°C to +150°C) |
| Standards | IEC 60250, ASTM B152, QC/T 1037 |
| Product Certifications | IATF16949, ISO9001, UL, REACH, RoHS |
VIII. Common Technical Questions
Q1: Why does the drive motor of a new energy vehicle require copper foil shielding?
The electromagnetic environment of the drive motor system in a new energy vehicle is complex. High-frequency interference generated by the controller’s PWM switching action and high-order harmonic radiation from the motor windings may interfere with vehicle CAN communication, radar sensors, and wireless systems. Copper foil shielding is a key technical measure to ensure the electromagnetic compatibility of the entire vehicle.
Q2: How to choose between copper foil and aluminum foil?
Copper foil has a conductivity 1.6 times that of aluminum, providing better shielding, and is also corrosion-resistant and has a longer lifespan. Although it is more expensive, its overall cost-effectiveness is better. Copper foil is recommended for high-reliability applications.
Q3: Can copper foil replace traditional metal casings?
Copper foil is mainly used as an inner shielding layer for existing metal casings, with a thickness of only 0.035-0.2mm, which cannot independently meet mechanical strength requirements.
Q4: How to estimate the amount of copper foil needed?
Taking a Class A passenger car as an example: the motor controller requires approximately 0.5-1.0㎡, the drive cable requires approximately 20-30㎡, and the DC/DC and OBC require approximately 0.3-0.5㎡. The total amount used per vehicle is approximately 25-35㎡.
Conclusion
The electromagnetic compatibility (EMC) design of new energy vehicle drive motor systems directly impacts the overall vehicle safety and user experience. Copper foil, with its excellent electrical and thermal conductivity and reliable long-term stability, demonstrates irreplaceable technological advantages in areas such as drive controller shielding, cable shielding, and thermal management.
With the widespread adoption of 800V high-voltage platforms and silicon carbide power devices, the EMC challenges of new energy vehicle drive systems will further escalate. As a key functional material, copper foil will play an increasingly important role in the future development of the new energy vehicle industry.
Our company has 30 years of experience in the functional materials industry and can provide new energy vehicle customers with comprehensive technical services, including copper foil selection consultation, application solution design, and PPAP document support.
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This article was compiled by Zhengzhou LP Industry Co., Ltd., specializing in the research and manufacturing of electrical wire and functional materials for thirty years.