Mini LED, also known as “sub-millimeter light-emitting diode,” is a type of LED chip with a much smaller size. Typically, the chip size of a Mini LED ranges from 50 to 200 μm. This means that within the same area, Mini LEDs can accommodate a greater number of light beads, allowing for more precise local dimming control.

Mini LED technology was initially widely used in the television industry. However, in recent years, as backlight technology has continued to advance and the size of LED chips has been reduced to 50 μm, the application of Mini LED backlighting has gradually expanded from TVs—suitable for long-distance viewing—to monitors, which are better suited for close-up use.

Compared to traditional monitors, Mini LED displays offer more refined image quality, higher brightness, and a thinner form factor. They fully retain the RGB primary colors, resulting in better color integrity and a wider color gamut, with brightness levels approaching those of OLED displays. Since Mini LEDs are smaller than conventional LEDs, they enable more precise control of the LCD panel’s backlight. When combined with advanced local dimming technology, this results in significantly higher contrast. As a result, Mini LED displays are notably thinner. All these advantages make Mini LED an ideal choice for professional display applications where color accuracy, resolution, and overall performance are critical.

Essentially, Mini LED still falls under the category of LCD screens, consisting of a backlight module, liquid crystal layer, color filter, and other components. The backlight module serves as the primary light source and is made up of many LED beads arranged in sequence. The most noticeable difference between Mini LED and traditional LCDs lies in the size of the LED beads—Mini LED panels can accommodate significantly more LEDs within the same panel size, resulting in a substantial boost in display brightness.

Mini LED has already become the best current option and is considered a transitional technology from small-pitch LED to Micro LED in the long term. Compared to small-pitch LEDs, Mini LED displays offer smaller LED chip sizes, denser LED arrangements, and higher resolution (PPI), making them particularly suitable for large-size 4K/8K LED TVs.

•  Advantages of Mini LED

 

• Requirements of Display Products

• Trends of Display Products

• Technology Route: Smaller LED Chips

• Different Substrates Comparison for Mini LED

• Glass Substrate Structure for Passive Mini LED

• High Reliability Tests for Mini LED to Enable the Technology Used in Automotive

  

• Examples of Mini LED used in Automotive Applications

If you have any questions, please contact our Orient Display engineers.

Phantom Glass is a brand of high-end tempered glass screen protectors designed for electronic devices like smartphones, tablets, and laptops.

It is the one of the toughest, strongest glass screen protection available in the market.

Key features include:

• High-strength protection: It can withstand heavy impacts, scratches, and daily wear and tear.
• Ultra-clear transparency: It’s almost invisible, maintaining the original clarity and color of your device’s screen.
• Fingerprint and smudge resistance: It has a special coating that makes it easier to clean and keeps the screen looking fresh.
• Easy installation: Typically designed for bubble-free application.
• Perfect fit: Custom-made for different brands and models of devices.

Best-in-Class Impact Resistance
9H Surface Hardness

Phantom Glass is manufactured with ion-exchange strengthened glass, offering superior durability against impacts, scratches, and surface wear.
In rigorous testing, Phantom Glass successfully passed 10 consecutive drops from a height of 1 meter directly onto the screen, meeting stringent standards required for aerospace-grade products.

Engineered for extreme resilience, Phantom Glass ensures maximum protection and structural integrity under the most demanding conditions.

In short, Phantom Glass is designed to protect your device screen as much as possible without affecting how it looks or feels.

 

Constructions and data:

 

IEC 61000-4-2 is an electromagnetic compatibility (EMC) standard developed by the International Electrotechnical Commission (IEC), specifically aimed at testing the immunity to electrostatic discharge (ESD). This standard is designed to evaluate and verify the ability of electronic equipment and systems to withstand electrostatic discharge. It defines the procedures for electrostatic discharge testing and various testing levels.

1. IEC 61000-4-2 Testing Levels

The IEC 61000-4-2 standard defines two main types of discharges:

1) Contact Discharge: Electrostatic discharge is directly applied to the device through a test electrode in contact with it.

Air Discharge: Electrostatic discharge is applied by bringing the test electrode close to the device (without direct contact).

Each type of discharge has different voltage test levels to simulate the intensity of electrostatic discharge that might be encountered in various environments. The standard test levels defined in IEC 61000-4-2 are as follows:

Contact Discharge Levels:

• Level 1: 2 kV
• Level 2: 4 kV
• Level 3: 6 kV
• Level 4: 8 kV
• Special Level: > 8 kV (Higher voltage levels can be defined by the user based on actual needs)

Air Discharge Levels:

• Level 1: 2 kV
• Level 2: 4 kV
• Level 3: 8 kV
• Level 4: 15 kV
• Special Level: > 15 kV (Similarly, higher voltage levels can be defined by the user based on actual needs)

For LCD Display only, the maximum testing is Level 4.

 

2. Test Procedure

During the actual testing process, the equipment must undergo a series of prescribed electrostatic discharge operations to ensure it can withstand the expected electrostatic discharge environment. The specific testing procedure includes:

1) Selecting the Test Level: Choose the appropriate test level (Level 1 to Level 4, or a higher special level) based on the expected usage environment of the equipment.

2) Setting Up the Test Equipment: Use an electrostatic discharge gun and other necessary testing equipment as specified by the IEC 61000-4-2 standard.

3) Discharge Methods:

• Contact Discharge: Directly contact the tip of the discharge gun with the metal parts of the equipment.
• Air Discharge: Bring the tip of the discharge gun close to the non-metallic parts of the equipment, gradually approaching until a discharge occurs.

4) Repeating the Discharge: Typically, multiple discharges (usually 10 or more) are required at each test point to verify the equipment’s electrostatic discharge immunity across all test points.

5) Observation and Recording: After each discharge, observe the equipment’s response (such as reboot, data loss, function failure, etc.) and record the test results.

 

3. Main Phenomena of LCD Screen ESD Test Failures

When an LCD screen fails an ESD (Electrostatic Discharge) test, the following phenomena are commonly observed:

1) Screen Flickering or Blinking: The display may flicker or blink intermittently due to instability caused by electrostatic discharge.

2) Permanent Display Artifacts: Permanent lines, spots, or distortions may appear on the screen, indicating damage to the LCD panel or circuitry.

3) Screen Freezing: The display may freeze or become unresponsive, requiring a reboot or power cycle to recover.

4) Color Distortion: Colors on the screen may become distorted or incorrect, which could be due to damage to the display driver or other electronic components.

5) Loss of Display Functionality: The screen may go completely blank or fail to display any image, suggesting a more severe failure of the screen’s internal components.

6) Touch Function Malfunction (if applicable): In touch-enabled LCD screens, the touch function may become unresponsive or erratic after an ESD event.

7) Unexpected Reboots: The device might reboot unexpectedly due to the ESD affecting the device’s power management or control circuits.

8) Data Loss or Corruption: There may be a loss or corruption of data, particularly if the ESD affects the memory or storage components.
These phenomena indicate that the LCD screen or its associated electronics have been compromised by electrostatic discharge, requiring further investigation and potentially additional shielding or circuit protection.

 

4. Electrostatic Discharge (ESD) Improvement Measures

1) Preventive Measures During the Design Phase

a. Board-Level Design

• Ground Plane Design: Ensure that the PCB has a complete ground plane to enhance its resistance to interference. A solid ground plane helps in providing a low-impedance path for current flow, effectively reducing noise and improving the overall electromagnetic compatibility (EMC) of the board.
• ESD Protection Devices: Add ESD protection devices on critical signal lines, such as TVS (Transient Voltage Suppression) diodes and ESD protection capacitors. These components help to clamp voltage spikes and safely dissipate ESD energy, protecting sensitive circuits from damage.
• Signal Return Path Optimization: Optimize the signal return paths to minimize the ESD current passing through critical circuits. Properly designed return paths ensure that the ESD currents are directed away from sensitive areas, reducing the potential for circuit damage and improving overall ESD resilience.

b. Enclosure Design

• Conductive Coating: Apply a conductive coating on the inside of plastic enclosures to provide a shielding effect. This coating helps to block and dissipate electrostatic discharge (ESD), protecting the internal components.
• Grounding of Metal Enclosure: Ensure that the metal enclosure is properly grounded to provide an effective path for ESD discharge. Good grounding helps in safely dissipating static electricity away from sensitive electronics.
• Increase Grounding Area Between TFT LCD Metal Frame and Product PCB: Expand the grounding area between the metal frame of the TFT LCD and the product’s PCB. This helps to create a more effective ESD path and improves overall device immunity to electrostatic discharges.
• Increase Floating Gap Between Enclosure and TFT Touch Screen: Increase the floating gap between the enclosure and the TFT touch screen. A larger gap can help to minimize the direct impact of ESD on the touch screen by providing more space for potential discharge to dissipate without affecting the sensitive components.

2) Wiring and Layout Optimization

• Protection of Critical Components: Place sensitive components away from areas that are likely to come into contact with ESD, such as buttons, connectors, and interfaces. This reduces the risk of ESD reaching these components and causing damage.
• Short Grounding Wires: Minimize the length of grounding wires to reduce ground resistance and inductance. Shorter grounding paths provide a more efficient route for ESD currents to dissipate, improving overall protection.
• Isolation Zones: Create dedicated ESD protection zones on the PCB to isolate sensitive circuits from areas that might come into contact with ESD. This can involve adding barriers, grounding planes, or guard traces to shield critical components from potential discharge paths.

3) Filtering and Buffering

• Filtering Capacitors: Add filtering capacitors to critical signal lines to absorb ESD pulses.
• Series Resistors: Place small resistors in series with signal lines to limit ESD current.

4) Filtering and Buffering

• Filtering Capacitors: Add filtering capacitors on critical signal lines to absorb ESD pulses.
• Series Resistors: Place small resistors in series with signal lines to limit ESD current.

5) Shielding and Grounding

• Shielding Covers: Install metal or ITO (Indium Tin Oxide) shielding covers on LCD monitors to reduce the direct impact of ESD.
• Grounding Path Optimization: Ensure that shielding covers, conductive coatings, and metal enclosures have good grounding connections to form a low-impedance ESD discharge path.

6) Interface and Button Protection

• Interface Protection: Add ESD protection devices, such as TVS diodes, at the input and output interfaces of the display.
• Button Protection: Design proper shielding and grounding for buttons to reduce ESD interference conducted through them.

7) Power and Ground Line Handling

• Isolation Transformers: Use isolation transformers to separate the power section from the signal section, reducing the possibility of ESD conduction through the power supply.
• Ground Line Handling: Add common mode chokes and filtering capacitors at the power input to reduce the possibility of ESD conduction through power lines.

8) Product Testing and Validation

• ESD Gun Testing: Use an ESD gun for simulated testing to identify weak points and implement corrective measures.
• Repeated Validation: Conduct repeated ESD tests in different environments to ensure that corrective measures are effective.

9) Material Selection

• Antistatic Materials: Choose materials with antistatic properties for the monitor enclosure, such as antistatic plastics.
• Conductive Rubber: Use conductive rubber at buttons and interfaces to enhance antistatic capability.

 

5. Specific Improvement Examples

1) SD Protection for Monitor Interfaces

To protect the HDMI, VGA, USB, and other interfaces on a monitor from ESD (Electrostatic Discharge), consider the following protection strategies:

• Parallel TVS Diodes: Install Transient Voltage Suppression (TVS) diodes in parallel on the signal lines of HDMI, VGA, USB, and other interfaces. TVS diodes help clamp voltage spikes caused by ESD, protecting sensitive circuitry from high-voltage surges.
• Adding Small Capacitors: Place small capacitors near the interfaces to form low-pass filters. These capacitors help to absorb and filter out high-frequency ESD pulses, further protecting the internal components of the monitor.

 

2) ESD Protection for Buttons

To protect buttons from electrostatic discharge (ESD), the following measures can be implemented:

• Conductive Rubber Pads: Place conductive rubber pads between the buttons and the circuit board to ensure effective grounding when the buttons are pressed. The conductive rubber provides a path for ESD to dissipate safely to the ground, reducing the risk of damage to the circuit.
• Series Resistors: Insert small resistors in series with the button lines. These resistors help limit the ESD current that might flow into the circuit, providing additional protection for sensitive components by reducing the impact of ESD pulses.

3) ESD Protection for Power Lines

To protect against electrostatic discharge (ESD) through the power lines, the following measures can be used:

• Common Mode Chokes: Install common mode chokes at the power input. These chokes help suppress common-mode noise and reduce the amount of ESD energy that can be conducted through the power lines.
• X/Y Capacitors: Use X and Y capacitors at the power input to filter out ESD pulses conducted through the power lines. X capacitors are placed across the line and neutral, while Y capacitors are connected between the line/neutral and ground. Together, they form an effective filtering network to absorb and mitigate high-frequency ESD pulses.

4) Reset Pin with RC Circui

To protect the reset pin from ESD and ensure stable operation, an RC (Resistor-Capacitor) circuit can be added. The suggested values for the components are:

• R1 = 1 kΩ (1 kilo-ohm): This resistor helps to limit the current flowing to the reset pin, providing a buffer against sudden voltage spikes due to ESD.
• C1 = 0.1 µF (microfarad): This capacitor acts as a filter, smoothing out any rapid voltage changes and providing stability to the reset signal.
• C2 = 0.047 µF (microfarad): An additional capacitor can be placed in parallel to further refine the filtering, ensuring the reset pin is less susceptible to high-frequency noise and ESD pulses.

This RC circuit helps to debounce the reset pin and provides added protection against electrostatic discharge and transient voltage fluctuations.

5) Adding an ESD Ring

It is recommended to add TVS ESD protection devices at electrostatic contact points to take advantage of their antistatic properties, forming an ESD discharge path and enhancing protection. Additionally, include an electrostatic discharge ring (ESD ring) on the panel. This ring provides a path to ground for electrostatic discharge, thereby protecting the VCOM and Gate lines from potential damage.

 

6) Add a TVS at Each VCOM Point

It is recommended to add a TVS (Transient Voltage Suppression) diode at each VCOM point for enhanced ESD protection. Specifically, use the ULC0511CDN in a DFN1006 package from LeiMao Electronics. This component has been successfully applied and has shown satisfactory results among many display customers.

7) Exposed Traces on the Panel

Apply insulating glue or tape over any exposed traces on the panel. This helps to prevent accidental short circuits and protects the traces from ESD damage.

8) Unused Pins

Unused pins should not be left floating; instead, they should be connected to MVDDL (minimum voltage differential digital logic). This prevents floating pins from picking up noise or causing unintended behavior in the circuit.

9) Software Reset

Implement a software reset function. This allows the system to recover from unexpected conditions or malfunctions due to ESD events or other issues by resetting the software to a known good state.

10) Example: Automotive LCD Display Screen

Problem Description: During electrostatic discharge (ESD) testing, the screen passed at ±6 kV contact discharge but failed at ±8 kV air discharge.

Analysis: The LCD screen is connected to the main controller via wires, and the interface type used is LVDS (Low-Voltage Differential Signaling). Currently, large screens primarily use LVDS and VBO (Video Bus Output) differential interfaces, which are effective at suppressing common-mode interference. The screen flickering observed during testing may be caused by interference affecting the LVDS cables. Contact discharge of 500V-1000V was applied to each signal line of the LVDS cables, and it was found that screen flickering occurred at 500V-1000V on both pairs of differential clock lines. This confirmed that the differential clock signals are particularly susceptible to ESD interference.

Solution: Add ferrite beads (magnetic rings) to the LVDS lines. After adding the magnetic rings, the ESD tests were conducted again, and the tests passed successfully. The chosen ferrite bead has the following frequency impedance characteristic curve:
[Include the frequency impedance characteristic curve of the ferrite bead here if available in a visual format.]
By implementing these ferrite beads, the susceptibility to ESD interference was significantly reduced, stabilizing the differential clock signals and preventing screen flickering.

11) Antistatic Methods for Different Enclosures

TFT LCD displays are easily affected by electromagnetic interference (EMI) and electrostatic discharge (ESD), especially when they have built-in touchscreens. Regarding ESD, TFT LCD displays are mounted flush on the exterior of the device. Discharges can reach the edges of the LCD frame and are not completely dissipated by the product enclosure.

Looking at it in more detail, the frame of an LCD screen is usually connected to the signal ground (GND) of the product’s PCB. Therefore, any discharged current can flow into the device’s board. The solution depends on whether the final product’s enclosure is conductive or non-conductive.

• Conductive (Metal) Enclosure: Ensure tight electrical bonding on all surfaces between the LCD frame and the edges of the bezel step. Use a transparent conductive coating, such as ITO (Indium Tin Oxide), with surface resistivity extending to the edges of the bezel step.
• Non-Conductive Enclosure: Provide the TFT LCD display as an entry point for ESD. Use shielded flat cables to connect the LCD frame to the PCB ground; increase the insulation gap (floating) between the product enclosure and the LCD display module.

12) Example: White Screen/Blue Screen Issue

A “white screen” or “blue screen” refers to the module’s screen displaying only the backlight, as it does when initially powered on, without any response even when adjusting the contrast.
This issue occurs because interference is applied to the module’s power supply lines (VDD or VSS) or to the RESET signal line during operation, causing the module to reset. The reset results in the initialization of the module’s internal registers and turns off the display.

Solution:

• If the interference is on the power supply lines, it is recommended to add a decoupling capacitor (10 µF) and a filtering capacitor (0.1 µF/0.01 µF) between the VDD and VSS power lines as close to the module as possible.
• If the interference is on the RESET signal line, it is advisable to add a filtering capacitor (with a capacitance of 0.1 µF or 0.01 µF) between the RESET signal line and VSS as close to the module as possible.
  The choice of capacitor values should be determined based on the actual test results.

13) Display Shows Incorrect Characters or Random Pixels (Data Errors) That Can Only Be Resolved by Power Cycling

This issue occurs because interference is applied to the control signals, causing the register parameters to be modified. Typically, when displaying data, there is no repeated writing to the main working register parameters, leading to the described issue.

Solution:
If interference is present on the transmission lines:

• Use ferrite beads, or shield the lines with materials like tin foil or thin copper sheets.
• Change the routing of the transmission lines to avoid areas with interference.
• Shorten the length of the transmission lines or add line drivers to increase drive strength and improve noise immunity.

14) What to Do If Interference Points Cannot Be Found or Circuit Precautions Are Insufficient to Eliminate Interference?

If interference cannot be identified or circuit precautions fail to prevent its impact, consider the following solutions:
Periodic Register Initialization: Instead of using the RESET signal, perform operations directly on the registers for initialization. If a crash occurs and cannot be recovered, use the RESET signal for initialization. However, this may cause screen flickering during normal display. To ensure normal display is not affected by initialization:
a. Use Register Read Data for Initialization: Use data read from registers, such as reading display status words or specific SRAM unit data, as the basis for determining whether initialization is needed.
b. Use Negative Display Module with Backlight Control: For modules with a negative display, turn off the backlight when not in use, making it difficult to see the display content. When the display content needs to be observed, turn on the backlight, using this moment as the point to reinitialize the module, which is less noticeable.

15) Electrostatic Interference Testing on Product Enclosure (Especially Product Panel) Causes White Screen or Display Errors on the Module

This type of interference is mostly caused by the module’s metal frame or glass interfering with the module’s circuitry. To improve this situation, consider the following methods:

1. Connect the module’s metal frame to ground.
2. Connect the module’s metal frame to VSS (ground of the circuit).
3. Leave the module’s metal frame floating (not connected to anything).
4. Add an insulating pad between the module’s metal frame and the metal enclosure; the thicker the insulating pad, the greater the reduction of static electricity.

These four methods should be tested in the actual product to determine which one is most effective.

16) White Screen or Display Errors Occur Even Without External Interference Source
This situation also falls under interference, but it is due to internal system interference, mainly caused by software conflicts. The first step is to identify the pattern of when the interference occurs. Such issues are more likely to happen during the module’s write process, leading to the module freezing or displaying errors.
Common causes include:

• Interrupt routines interfering during module operations (I/O addressing mode), leading to incorrect operations such as modified control signals or data, which can cause the module to freeze or display incorrectly.
  Solution: Disable interrupt responses while operating the module to prevent interference during critical processes.

17) Example: When using a TFT display and a product chassis made of metal, an 8000V electrostatic discharge (ESD) test was conducted, which caused the display to show a garbled screen. Resetting and reinitializing the module had no effect, and the device had to be powered off and restarted to return to normal operation. Industry regulations do not allow grounding of the chassis.
As a solution, the metal chassis was replaced with an acrylic (organic glass) enclosure, and a timed loop refresh (initialization) program was added to the main software routine. During the ESD test, when the LCD module is reset due to static discharge, the refresh (initialization) program corrects the issue, causing only a brief flicker before returning to normal operation, thus passing the test.

18) Example: Using a TFT display, an 8kV electrostatic discharge (ESD) test was conducted on the product chassis, resulting in the module showing no display
To improve this, a 330μF capacitor and a surge protection diode (P6K1) were added to the power pin of the module, and a 330μF capacitor was added to the output (VOUT) of the driver power supply. These measures significantly improved the situation. Additionally, the module’s metal frame was insulated from the chassis, maintaining a 2mm gap, which helped pass the ESD test.
However, despite these improvements, there were still occasional instances of no display. To fully resolve this, a periodic initialization routine was added to the program to reset the module and recover from interference. This completely solved the display interference issue.

19) Example: When using a TFT display, during a test where a 4kV, 150Hz positive pulse group interference signal was applied to the system’s main power line, the display showed garbled characters
To address this issue, a surge absorber was added to the power line at the LCD module interface, and the length of redundant transmission lines was reduced. These measures allowed the system to pass the test.

20) When using a TFT display on a switchgear cabinet, the module showed no display under high-voltage electromagnetic interference
To resolve this issue, the system power supply was replaced with an isolated power supply. A 0.01μF capacitor was connected to the /RESET pin of the module, the jumper connecting the module’s metal frame to VSS was disconnected, and an insulating pad was added to isolate the module’s metal frame from the switchgear cabinet.

21) The connection cable between the TFT display and the system motherboard is over 700mm long. When repeatedly writing graphic data, the right side of the graphic progressively duplicates the rightmost byte of graphic data

Measurements of the input signal waveform at the module interface were good, with /WR = 0 width of 2μs. Adding capacitors and pull-up resistors to the interface signals showed no significant improvement. Shortening the cable and adding ferrite beads provided noticeable improvement, but did not completely solve the issue.
Inserting a Schmitt trigger circuit (74HC14) into the /WR signal line completely resolved the problem. Additionally, inserting a 680Ω resistor into the /WR signal line also achieved a complete fix.

22) Example: Blue Screen on LCD Display

During ESD (Electrostatic Discharge) testing, an industrial display experienced blue screens every time the system was tested at ±6kV on the network port, USB, and serial port, causing the system to crash. It would recover automatically after power cycling, but the test was not passed. The board had previously undergone multiple design revisions focusing on grounding, filtering, and isolation, but these did not resolve the issue. Therefore, this time, a strategy was adopted to diagnose and rectify the root cause to identify and address the system’s weaknesses.
Analysis and Solution:
Based on the observed phenomenon, it was suspected that the CPU functional unit was being affected by interference. The core sub-board (CPU module circuit) pins were analyzed, and signals were identified as being particularly sensitive and prone to ESD interference based on practical experience and signal functionality.
To identify ESD-sensitive signals, an ESD gun was used to apply contact discharge at voltages of 100V, 300V, 600V, and 1000V to various signal pins on the core sub-board. During these tests, the problem did not reoccur, ruling out those signals as the source of the issue.
Further analysis of sensitive circuits on the core sub-board revealed that when a 100V contact discharge was applied to the sensitive DDR_CLK signal, the problem consistently reoccurred. Each time the discharge was applied, the issue was replicated. The DDR_CLK trace was 4 mils wide, and the design did not include test pads, limiting available mitigation options.
To determine if the static electromagnetic field was affecting the DDR_CLK clock signal, a grounded metal wire was placed directly above the DDR_CLK trace, and the ESD gun was used to discharge at the ground wire’s copper lug at 6kV. The issue was reproduced within five discharges, confirming that the electromagnetic radiation from the ESD was impacting the DDR_CLK signal and DDR components.
Resolution:
After confirming that the electromagnetic radiation was affecting the DDR module on the core board and causing the ESD issue to recur, a copper foil was used to shield and ground the core board area, protecting the sensitive DDR signals and module. After shielding the core board module, contact discharges were applied to the IO interfaces at ±6kV, 8kV, and 10kV, with each test involving 40 consecutive discharges. The system continued to operate normally, indicating that the issue was resolved.
Cause Analysis:
Further verification determined that the ESD affecting the entire system was due to radiative coupling or capacitive coupling. Analysis showed that the electrostatic discharge path was as follows: IO interface → single board PGND → metal backing plate → metal chassis → chassis cover → ground wire.
This path explains how the ESD was able to impact the sensitive components, confirming the need for additional shielding and grounding to protect against interference.

When the chassis cover is not screwed onto the metal chassis or when the cover is not in place, it was observed that there were no issues with electrostatic discharge (ESD). This ruled out the problem of radiative coupling. In this case, the ESD discharge path is as follows: IO interface → single board PGND → metal backing plate → metal chassis. This suggests that there is electrostatic capacitive coupling between the sensitive DDR area on the core board and the chassis cover (as they are very close to each other), as shown in the diagram below.

In summary, a simplified model of the electrostatic coupling on the core sub-board of the entire system is shown in the diagram below:

When diagnosing the issue, after adding a shielding cover to the core sub-board, the electrostatic coupling model at this point is shown in the diagram below.
From the diagram, it can be seen that after adding a shielding cover to the core sub-board, the electrostatic energy from the chassis back cover is directly coupled to the metal shield. This energy is then discharged to the ground through the shielding cover’s grounding pins, thereby preventing ESD from directly coupling into the DDR-sensitive module and resolving the issue.
Based on the above analysis, the ESD problem was caused by capacitive coupling of electrostatic interference from the chassis back cover to the DDR module circuit.
Since the core sub-board is a platform product of the client company and the DDR circuitry on the module is highly sensitive, it is recommended to use a shielding cover to protect the sensitive core sub-board module for both testing and mass production. This solution is simple, effective, and reliable.

 

23) EMI Protection for LCD Displays

The main approach is to shield components that are easily affected by EMI.
a. For sensitive components such as the Touch controller and LCD driver IC, use EMI shielding fabric to provide single-sided or double-sided protection.
b. Since some LCD screens emit high-frequency signals, shielding can be applied using a metal frame on the bottom and an ITO (Indium Tin Oxide) layer on the top.