2025-10-25
During ESD static discharge testing of TFT-LCD display modules, various functional defects frequently occur in the LCD display modules. These defects are irreversible and constitute “hard damage.”
This article focuses on three key aspects: the challenges posed by ESD static electricity to the LCD display industry, the definition and generation principles of ESD static electricity, and common models of ESD static discharge.
01 The Trouble of ESD to the LCD Display Industry
Have you ever encountered this problem: “Whenever we use our phones, especially in dry winter environments, they often freeze, shut down unexpectedly, display black screens, or show abnormal visuals.” In reality, the vast majority of these issues are closely related to ESD interference and damage caused by electrostatic discharge. However, ESD is something we “can neither see nor touch.” Consequently, ESD is considered the “greatest potential killer” affecting product quality in the TFT-LCD optoelectronic display industry. ESD protection has thus become a critically important aspect of quality control for LCD display modules.
ESD damage to LCD display modules can generally be categorized into two types: sudden damage and latent damage.
① Sudden damage: Refers to severe damage to relevant electronic components and materials within the LCD display module, resulting in functional loss. Such damage is typically detectable during quality inspection in the manufacturing process. Consequently, it primarily incurs rework and repair costs for the factory, while customers face direct damage to the LCD display module.
② Latent Damage: This refers to partial damage to electronic components or materials within the LCD display module where normal functionality remains intact. Such damage cannot be effectively detected through verification methods during manufacturing. However, during subsequent use, it causes product instability, intermittent performance issues, and reduced lifespan. Consequently, it poses a greater threat to product quality and incurs immeasurable after-sales costs for manufacturers.
Among these two types of LCD module damage caused by ESD, latent damage accounts for nearly 90%, while sudden damage constitutes only about 10%. This means that 90% of ESD-induced LCD module damage cannot be effectively detected or intercepted at the factory level, only becoming apparent once the product reaches the end user. This is the primary challenge ESD poses to the LCD display industry. To mitigate these issues, the industry adheres to the principles of “prevention over cure” and “design first, remediation second.” Consequently, rigorously monitoring and ensuring the ESD resistance of products throughout the LCD display module design, selection, manufacturing, and reliability testing processes remains the sole effective approach currently available to the industry.
Common ways ESD static electricity is generated include: contact, friction, or sliding between two objects; separation of two objects; and proximity between two charged objects. ESD static electricity typically exhibits the following key characteristics.
02 ESD Static Electricity Definition and Causes
① ESD：Electronic Static Discharge
That is: Electrostatic Discharge. It refers to the phenomenon where two objects carrying different electrostatic charges experience a sudden, rapid transfer of charge in an extremely short time due to direct contact or electrostatic field induction, thereby generating a high-current pulse. Simply put: it is the process where, once static electricity accumulates to a certain level, it suddenly finds a “pathway” to rapidly transfer the charge.
Common methods for generating ESD static electricity include:
a. Contact, friction, or sliding between two objects;
b. Separation of two objects;
c. Approaching of two charged objects.
ESD static electricity typically exhibits the following key characteristics:
a. High voltage. Static voltage can reach thousands or even tens of thousands of volts. During dry winters, the voltage causing the “electric shock” sensation when putting on clothes often approaches several thousand volts. Despite the high voltage, the total charge quantity is generally small.
b. Short duration. The entire ESD discharge process typically completes within nanoseconds to microseconds.
c. Instantaneous high current. During ESD discharge, charge transfer occurs in an extremely short timeframe, resulting in very large peak currents.
② Principles of ESD Electrostatic Generation
The generation of ESD static electricity primarily involves two stages: static electricity generation (charge separation) and static electricity discharge (charge transfer). We will elaborate on these two main stages in detail:
a. Generation of Electrostatic Charge (Charge Separation):
The generation of electrostatic charge is fundamentally a process of “electron gain and loss.” This concept of electron gain and loss involves the atoms that compose all matter. Atoms consist of a positively charged nucleus at their center and negatively charged electrons orbiting around it. Under normal circumstances, the positive and negative charges within an atom are balanced, resulting in the object maintaining a neutral charge state.
When two different materials come into contact and separate rapidly, the atoms of one material possess a stronger binding force for electrons than those of the other material. At the instant of contact, electrons transfer from the material with weaker binding force to the material with stronger binding force. The material that loses electrons becomes positively charged overall because its atomic nuclei retain their positive charge while the number of electrons decreases. Conversely, the material that gains electrons becomes negatively charged overall because its atomic nuclei retain their positive charge while the number of electrons increases. This process of contact and rapid separation between two different materials generates ESD static electricity.
b. Electrostatic Discharge (Charge Transfer):
When a charged object approaches a lower-potential object, the electric field strength between them increases sharply. When this field strength exceeds the dielectric breakdown threshold of the surrounding medium, the air “breaks down,” instantly becoming conductive and forming a discharge channel. This process facilitates charge transfer. In summary, the generation of ESD static electricity can be summarized as follows: During the contact and rapid separation of two different materials, the gain and loss of electrons lead to the generation of charge, which accumulates on the materials. When a charged object approaches a low-potential object, the air undergoes “breakdown,” forming a discharge channel that allows the stored charge on the materials to transfer.
Therefore, having grasped the principles behind ESD static electricity generation, it should now be clear that the key material requirements in LCD display modules—specifically controlling the appropriate impedance range and triboelectric voltage—are fundamentally aimed at reducing the risk of charge generation, preventing charge accumulation, and enabling rapid charge dissipation.
03 Common Modes of ESD Electrostatic Discharge
Based on the preceding explanation of ESD static electricity generation principles, it is evident that ESD encompasses both mechanical phenomena (such as mutual friction and stripping) and electrical properties. Therefore, simulating ESD is essential to evaluate the ESD resistance of LCD display modules, electronic components, and critical materials.
Currently, there are four primary models for simulating ESD discharge: Human Body Model (HBM), Machine Model (MM), Component Discharge Model (CDM), and Field Induced Model (FIM). Since the Field Induced Model (FIM) is less commonly used, it will not be elaborated upon here.
① Human Body Model (HBM)
Human Body Model (HBM): This model simulates the process of a static-charged human body touching a grounded product in a factory environment. Its purpose is to assess whether products can withstand ESD damage during production, assembly, and transportation, not for everyday usage scenarios. In the LCD display industry, where human contact with LCD display modules is most frequent, the HBM mode is predominantly used for ESD testing to classify products’ static discharge levels (contact discharge).
② Machine Model (MM) Discharge Mode
Machine Model (MM) discharge mode: The full English name is Machine Model, referring to situations where the machine itself (such as a robotic arm) accumulates static electricity. When the robotic arm picks up a product, the static discharges through the product’s connection pins. The MM mode primarily simulates electrostatic discharge generated by machinery during automated production or processing.
Note: For permitted machinery on production lines, ionizing fans can generally eliminate static electricity by neutralizing it through absorption of oppositely charged ions.
③ Component Discharge Mode (CDM)
Component Discharge Mode (CDM): The full English name is Charged-Device Model. This primarily refers to a scenario where static electricity accumulates inside a product due to friction or other factors, yet the product remains undamaged during this accumulation process. When the connection pin of this electrically charged product contacts a grounded object, the static electricity inside the product discharges through the connection pin, causing a discharge phenomenon.CDM discharges occur within a much shorter timeframe—typically just a few microseconds—and are more challenging to accurately simulate.
To learn more about ESD static electricity and comprehensive static control throughout the entire LCD display module manufacturing process, join the NOSEDISPLAY Technical Forum. （www.nosedisplay.com）