What is EMI?

Electromagnetic interference (EMI) is a signal or radiation that is radiated into the air or transmitted through power or signal lines in such a way that it may endanger the proper functioning of radio navigation or other safety services, or may seriously affect, hinder or repeatedly interrupt licensed radio communication services. Radio communication services include, but are not limited to, AM/FM commercial broadcasting, television, cellular radio communications, radar, air traffic control, pagers and Personal Communications Services (PCS). These licensed or unlicensed radio services, such as wireless LAN or Bluetooth, as well as unintentional radiators, such as digital devices, including computer systems, can cause EMI.

How is EMI generated?

During the production process, the machines used, the temperature and humidity of the production workshop, the materials in the environment and other factors will become factors that cause the display to generate EMI. Electromagnetic interference is caused by electromagnetic fields generated by man-made electrical or electronic devices, natural sources and events. Whenever electronic signals meet at the same frequency, they interfere with each other, causing EMI.

Improvement plan for radiation protection and EMI reduction during TFT display production

1. Use filters and anti-interference capacitors

• Filter application: Add filters (such as LC filters) to the power supply and key signal lines to effectively suppress high-frequency noise conduction and reduce electromagnetic interference.

• Anti-interference capacitor design: Add bypass capacitors or decoupling capacitors to the power input end of the drive circuit to block high-frequency interference and ensure signal integrity.

• EMI filter inductor: Add inductor components to the power supply line of the TFT display module to weaken electromagnetic waves, especially in high-frequency environments.

2. Improve the backlight module design

• Backlight drive circuit optimization: Improve the frequency of the backlight drive circuit and its control circuit, and select a more stable driver IC to reduce electromagnetic wave radiation.

• Backlight module housing shielding: Use a metal backplate or add conductive materials around the backlight module to effectively reduce the radiation of the backlight module. In addition, a shielding coil can be installed at the power input end.

• Frequency modulation: By adjusting the PWM (pulse width modulation) frequency of the backlight drive, avoid specific radiation-sensitive frequency bands to reduce interference.

3. Choose low-radiation components

• Low-radiation driver chip: Choose a low-radiation driver chip that meets EMI/EMC (electromagnetic compatibility) standards to reduce the electromagnetic interference of the chip itself and reduce interference with other circuit components.

• Anti-electromagnetic interference materials: For example, use flexible printed circuit board (FPC) materials with anti-interference capabilities, and use high-performance capacitors, inductors and other components in key locations.

4. Application of shielding materials

• Metal shielding layer: Add a thin metal shielding layer (such as aluminum foil or copper foil) around the TFT module to effectively block the leakage of high-frequency electromagnetic waves. The thickness of the metal material and the shielding effect must be taken into account. Too thick will affect the thinness of the module.

• Conductive coating: Use conductive coating materials such as nanosilver, conductive ink, etc. on the surface of the module to form a conductive film to absorb and guide electromagnetic waves.

• Shielding film layer design: Set a conductive shielding film near the backlight source and driver IC of the display module to reduce the radiation generated by the core components.

5. Grounding and electrostatic protection measures

• Grounding: All metal shielding layers and conductive coatings must be well grounded to form a closed loop to effectively absorb electromagnetic waves. And ensure good grounding conductivity to avoid the formation of current loops that cause more radiation.

• Electrostatic discharge protection: Anti-static components (such as ESD diodes) are installed at the input and output interfaces of the module to avoid electromagnetic interference caused by static electricity accumulation and discharge, and protect the circuit stability of the module.

6. Design optimization and test verification

• Simulation testing: Use EMI simulation tools (such as CST, HFSS) for testing and optimization during the product design phase to ensure that potential electromagnetic interference problems are discovered and resolved during the simulation phase.

• Strict testing and certification: Conduct electromagnetic compatibility (EMC) testing, including conduction and radiation testing, and improve the module based on the test results to ensure compliance with relevant electromagnetic compatibility standards (such as CISPR, FCC, CE, etc.).

7. Optimize module wiring design

• Reasonable wiring layout: When designing the wiring of the TFT module, try to avoid parallel layout of high-frequency signal lines and sensitive components, and shorten the length of the signal line to reduce radiation.

• Increase the ground layer: Use a multi-layer PCB design, increase the ground layer, and form multi-point grounding, thereby forming a stable signal return path and reducing radiation. The spacing of the ground layer should be properly designed to reduce interference

• Signal and power layering: Arrange high-speed signals and power circuits in layers to avoid direct contact with each other and reduce the possibility of mutual interference.

Through these improvement measures, the radiation and electromagnetic interference of the TFT module can be effectively reduced, thereby improving the electromagnetic compatibility and anti-interference performance of the product, and providing a more stable and reliable display solution for electronic equipment.

Specific recommendations for the design of electromagnetic interference (EMI) and electrostatic discharge (ESD) protection for the entire enclosure:

1. Grounding and closed loop design

• Shielded grounding design: Ensure that the housing is in good contact with the ground wire of the internal circuit to form a closed loop and avoid signal leakage. All conductive materials and shielding structures need to be firmly grounded and the grounding point resistance should be reduced.

• Multi-point grounding: If the housing is designed with a large size, grounding can be arranged at multiple key points to evenly disperse the current and reduce the static accumulation effect.

• Isolation belt design: Set an isolation belt in the connection area between the housing and the circuit board to avoid static conduction and interference caused by direct contact.

2. Shell structure design

• Optimization of shield connection structure: Gaps and connection parts of the shell are prone to become electromagnetic leakage paths. Elastic conductive materials (such as conductive rubber pads) can be added at these locations to achieve effective shield connection.

• Sealing design: Metal sealing rings or electromagnetic shielding gaskets are designed at the interfaces and gaps of the shell to prevent external electromagnetic waves from entering the device and avoid internal signal leakage.

• Thread and seam design: The thread and seam positions need to be designed as a conductive connection method with good electrical contact to ensure that static electricity and electromagnetic interference can be conducted and directed to the ground wire.

3. Selection of housing material

• Antistatic plastic: For plastic shells, antistatic agents or antistatic plastics (such as ABS+PC composite materials) can be used to reduce static electricity accumulation. Antistatic materials can effectively reduce the impact of high-voltage static electricity release.

• Conductive plastic: Conductive plastics with added carbon fiber or carbon nanotubes are selected to improve the conductivity and shielding properties of the material while ensuring mechanical properties.

• Flexible shielding materials: For seams and interfaces, flexible materials such as conductive foam and conductive rubber can be used to avoid electromagnetic wave leakage while reducing the risk of gap discharge.

4. Electrostatic discharge protection design

• ESD protection components: Install anti-static components (such as ESD diodes and TVS tubes) at key interfaces of the shell (such as USB, HDMI, headphone jack, etc.) to quickly discharge high-voltage static electricity through the components to ensure that the circuit is not affected by 15kV discharge.

• Anti-static wiring: When laying out the PCB, place the key grounding points close to the shell interface to form an effective current discharge path, reduce the electrostatic discharge path, and improve anti-interference performance.

• Electrostatic dissipation layer: Add an electrostatic dissipation layer on the inside of the entire shell to prevent static electricity from accumulating on the surface and quickly dissipating it through grounding. This can be achieved by adding conductive filling materials at key locations.

5. Shell shielding design

• Conductive coating: Conductive materials (such as conductive ink or nanosilver) are applied inside the whole housing to form a uniform conductive film to provide effective electromagnetic shielding. The thickness of the coating needs to be adjusted according to the electromagnetic shielding performance to ensure 15kV protection.

• Metallized housing: If the weight allows, a metal housing (such as aluminum alloy, stainless steel) can be used directly. The metal material itself has a good shielding effect. The metal housing needs to maintain sufficient grounding to ensure that electromagnetic interference can be quickly guided to the ground.

• Metal plating: For plastic housings, you can consider adding a metal plating layer (such as copper plating, nickel plating) on the surface to enhance EMI shielding capabilities while maintaining housing strength and lightness.

（Metal case）

6. Testing and Verification

• ESD discharge test: Use standard electrostatic discharge test equipment to perform 15kV contact discharge and air discharge tests to confirm the anti-static and anti-electromagnetic interference effects of the shell. It is recommended to use the IEC 61000-4-2 standard for verification.

• EMI radiation test: After the equipment is installed, perform a full range of EMI tests to ensure that the shielding effect of the shell meets the design requirements and complies with relevant EMC standards.

• Durability test: Perform durability tests on the anti-static and shielding layers to ensure that they can maintain good effects under long-term use, frequent plugging and unplugging, or environmental changes.

  
  

Through the comprehensive application of the above designs and materials, the EMI shielding and electrostatic protection capabilities of the entire machine casing can be effectively improved to meet the 15kV protection standard and ensure the safety and reliability of the equipment in a high electromagnetic environment.

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