ASSEMBLY METHOD

  1. AUTOMOTIVE LAMP Q&A
  2. ASSEMBLY METHOD

Product Structure Design Specifications - Electromagnetic Compatibility (EMC)

Product Structure Design Specifications - Electromagnetic Compatibility (EMC)

Electromagnetic compatibility refers to the capability of a device to function without malfunction in its intended electromagnetic environment. The rapid development of science and technology has led to an increase in modern electronic and electrical devices and household appliances, with more advanced performance and higher usage density. This has resulted in increased mutual interference within electrical and electronic systems. To ensure proper functioning under complex electromagnetic environments, serious EMC design is essential during the structural design phase.

1. Introduction of Electromagnetic Compatibility

1.1 Electromagnetic Compatibility of Electronic Devices

Electromagnetic Disturbance (EMD) and Electromagnetic Interference (EMI):

  • Electromagnetic Disturbance: Any electromagnetic phenomenon that could degrade the performance of a device, equipment, or system. This includes electromagnetic noise, unwanted signals, or changes in the propagation medium.
  • Electromagnetic Interference: Points to the consequences of electromagnetic disturbances. Often used interchangeably with EMD.

Immunity and Electromagnetic Susceptibility (EMS):

  • Immunity: The ability of a device, equipment, or system to perform its functions without degradation in the presence of electromagnetic disturbances.
  • Susceptibility: A measure of the magnitude of unwanted responses to the electromagnetic environment. Lower susceptibility means poorer immunity. This characteristic is referred to as EMS.

Electromagnetic Compatibility (EMC):

  • EMC is the potential of a device, equipment, or system to function without unacceptable generation or response to electromagnetic disturbances in its environment. EMC encapsulates both EMI and EMS. To ensure compatibility, it is necessary to control electromagnetic emission and enhance immunity.

International Special Committee on Radio Interference (CISPR):

  • Established in 1934 by the International Electrotechnical Commission to study radio interference and develop standards to protect broadcast reception.
  • In 1989, the European Community issued directive 89/336/EEC, mandating EMC certification for products sold in the EC market starting January 1, 1996. This directive had global implications and made EMC a vital international trade indicator. CISPR's scope has expanded to protect all radio reception.

International Electrotechnical Commission (IEC):

  • IEC has two technical committees related to EMC standardization: CISPR and the Electromagnetic Compatibility Committee TC77, established in 1981.
  • TC77 initially focused on low-voltage grid systems below 9 kHz but now covers the entire frequency range and EMC-related products.
  • CISPR has developed 14 standards, including CISPR 22 for radio disturbance measurement, and TC77 has developed 25 IEC standards, with the IEC 61000-4 series being the most comprehensive.

EMC Testing and Standardization in China:

  • Efforts toward EMC testing began in the 1960s. In 1986, China formed the National Radio Interference Standardization Committee to develop EMC standards systematically according to CISPR/IEC.
  • China has over sixty national EMC standards, including GB4365 (1995) for terminology and GB/T 6113 (1995) for measuring apparatuses.

Electromagnetic Interference: The Three Essential Elements:

  • Source of Interference
  • Interference Propagation Path
  • Sensitive Device

2. Common Electromagnetic Interference Modes in Electronic Device Structure Design

  • Conducted Interference: Typically caused by crosstalk through power supply, cables, wiring systems, and grounding systems.
  • Radiated Interference: High frequencies of electromagnetic energy are more likely to produce radiation. Radiation is more pronounced at frequencies higher than MHz, with increased power for conductor lengths of a quarter wavelength or more.
  • Inductive and Coupling Interference

3. Main Methods for Electromagnetic Compatibility Design

Shielding:

  • Electrostatic Shielding: Suppresses parasitic capacitive coupling by shielding and grounding electromagnetic energy.
  • Magnetic Shielding: Targets low-impedance sources with materials of high magnetic permeability (e.g., iron-nickel alloys or pure iron).
  • Electromagnetic Shielding: Avoids high-frequency electromagnetic radiation using metal materials (ferromagnetic or non-ferromagnetic) to reflect and absorb fields.

Filtering:

  • Active or Passive Filters: Designed as band-pass, high-pass, or low-pass filters to filter out interference signals from power lines, signal lines, and control lines.

Grounding:

  • Combination Unit Circuit Grounding
  • Single-Point Grounding: Simple but less effective for high-frequency circuits.
  • Multi-Point Grounding: Suitable for frequencies above 10 MHz; requires careful design.
  • Overall System Grounding: Separates analog, digital, and chassis grounds, combining them into a single earth ground to reduce electromagnetic noise and interference.

4. Bonding Technology

Overview:

  • Mechanical bonding interconnects metal shells or frames to prevent potential differences that could cause electromagnetic interference. This bonding applies to device metal enclosures, enclosures to ground planes, signal return lines to ground lines, and grounding planes to earth ground.

Types and Methods of Bonding:

  • Direct Bonding: Joins two metal members directly, secured by bolts, riveting, welding, or brazing.
  • Indirect Bonding: Connects two metal members through a transitional conductor (bonding strips or sheets), less effective than direct bonding.

Forms and Materials of Bonding Strip (Sheet):

  • Conductive flat sheets should preferably be made of copper or aluminum.

General Principles of Bonding Technology:

  • Ensure tight contact between metal surfaces.
  • Bonding strips should be vibration-resistant and flexible.
  • Strips should withstand maximum currents without overload and damage.
  • Prevent electrochemical corrosion between bonding strips and metals.
  • Use short, wide, and straight bonding strips to meet low resistance and inductance requirements.

5. Design Details of Prevention of Interference

1. System Design Scheme:

  • Determine interference prevention standards based on equipment or system requirements.
  • Design interface circuits with balanced interfaces and isolation transformers where necessary.
  • Avoid high-speed pulse signals and use gradual rise/fall times.
  • Use large-scale integrated circuits to reduce loop areas and enhance immunity.
  • Implement special isolation measures for key circuits: local shielding, filtering.
  • Apply grounding schemes based on the system's working principles.

2. Structural Design:

  • Define materials for shielding enclosures based on performance requirements.
  • Define low-impedance bonding points on shielding enclosures.
  • Use welding for permanent bonding; electromagnetic sealing gaskets for non-permanent bonding.

3. Circuit and PCB Design:

  • Determine the number of PCB layers based on cost and EMC requirements.
  • Position high-speed and sensitive signals close to ground layers.
  • Use different ground and power lines for different circuit types.

4. Cable Design:

  • Use ground lines next to signal lines in flat cables.
  • Employ twisted pairs and coaxial cables with proper grounding. Avoid running cables through gaps or openings in shielding bodies.
Back