Designing a Cleanroom for LCD Display Screen Manufacturing Needs

1. Why does the production of LCD display screens need to be clean and dust-free?
1) The core processes of LCD display screens production mainly include the following aspects:
♦ Film formation: Deposit metals, oxides, nitrides and other materials on the glass substrate to form a homogeneous and stable thin film layer.
♦ Photolithography: Including three steps of coating, exposure and development, so as to leave a pattern corresponding to the mask on the thin film layer.
♦ Etching: Use wet or dry methods to clean the photoresist used as a protective mask.
♦ Color film (CF) process: Form a color filter on the glass substrate so that the LCD display screens can display color images.
♦ Cell process: The prepared TFT glass and CF glass are assembled, including the dripping of liquid crystal, the coating of frame glue, vacuum bonding, frame glue curing, etc. 
♦ Module process: Assemble the LCD unit with the backlight source, circuit board, etc. to form an LCD module. 
♦ Inspection and distribution: Perform various performance tests on the completed LCD module, and package and distribute the qualified display screens.

2) Adverse effects of particle contaminants on various links of LCD screen production
♦ Impact on photolithography accuracy: During the photolithography process, particle contaminants may fall on the photoresist or mask, which will make the local thickness of the photoresist uneven, resulting in different light transmittance during exposure, affecting the accuracy of the photolithography pattern, causing deviation, deformation or inaccurate size of the circuit pattern formed by photolithography, and ultimately affecting the performance and function of components such as TFT (thin film transistor). If the particles are on the mask, they will block the light, causing defects in the pattern transferred to the photoresist, and reducing the resolution and repeatability of the photolithography.
♦ Abnormal etching: During etching, particulate contaminants may adhere to the surface of the substrate, blocking the contact between the etchant and the film, making the etching process uneven, causing insufficient or excessive etching, destroying the integrity of the circuit pattern, and causing defects in the electrodes, channels and other structures of the TFT, affecting the electrical properties of the TFT, such as threshold voltage drift, reduced carrier mobility, etc., which in turn affects the display effect of the LCD screen, resulting in uneven display, dark spots and other problems.
♦ Color deviation: In the color film process, particulate contaminants may fall on the production area of the color filter. If it falls on the red, green and blue filter layers, it will affect the filter's light transmission and absorption characteristics, resulting in an imbalance in the color mixing ratio, causing color deviation and uneven color on the display, and reducing the color accuracy and vividness of the displayed image.
♦ Effects on transmittance: Particulate contaminants may also make the surface of the color film uneven, increase light scattering, reduce the transmittance of the color film, reduce the brightness of the display, deteriorate the contrast, blur the image display effect, and affect the visual experience.
♦ Destroy of the orientation of liquid crystal: During the cell forming process, particulate contaminants may enter the liquid crystal layer. If the particles are large, they will directly destroy the orientation of the liquid crystal molecules, so that the liquid crystal molecules cannot be arranged in the predetermined direction, resulting in uneven distribution of the electric field in the liquid crystal cell, affecting the modulation of the liquid crystal on light, and causing display defects such as dark spots and bright lines on the display screen.
♦ Uneven cell thickness: Particulate contaminants will make the gap between the two substrates uneven, resulting in inconsistent cell thickness. Changes in cell thickness will affect the optical properties and response time of the liquid crystal molecules, causing differences in the display effects of the display screen in different areas, such as poor uniformity of color and brightness when the viewing angle changes, and even unstable display.
♦ Generation of bright or dark spots: During the polarizer lamination process, particulate contaminants are sandwiched between the polarizer and the liquid crystal cell, which will cause problems in the optical matching between the polarizer and the liquid crystal cell, resulting in abnormal refraction or scattering of light at specific locations, resulting in bright or dark spots. During the installation of the driver IC and other components, particulate contaminants may affect the electrical connection between components, resulting in unstable signal transmission and display abnormalities.
♦ Reduction of the uniformity of the backlight source: When the backlight source is assembled, particulate pollutants may adhere to the surface or inside of the backlight source, blocking the propagation of light, making the light emitted by the backlight source uneven, and then causing uneven brightness of the display screen as a whole, affecting the display quality.
In summary, the influence of particulate pollutants runs through all links of LCD screen production. Therefore,LCD screen have very high requirements for the cleanliness of the production environment. Clean rooms are important facilities in the production process of LCD screens in the LCD display industry. They can control particulate pollutants, temperature, humidity, air pressure, etc. in the production environment to ensure production quality, reduce production losses, and improve production efficiency.

2. How can clean rooms effectively improve the product yield of LCD display manufacturing?
Clean rooms can effectively improve the product yield of LCD display manufacturing by controlling environmental parameters, personnel management, equipment and material management, etc., as follows:
1) Strict control of environmental parameters
♦ Temperature and humidity control: In LCD display production, processes such as lithography and film formation are extremely sensitive to temperature and humidity. Temperature fluctuations can cause thermal expansion and contraction of lithography equipment, affecting lithography accuracy; humidity changes may cause the substrate to absorb moisture, affecting the deposition quality of the film. The clean room needs to be equipped with a high-precision air conditioning system to control the temperature at 22±1℃ and the humidity at 45%±5% RH to ensure the stability of the process and the consistency of the product.
♦ Air purification: The use of high-efficiency air filtration systems, such as HEPA (high-efficiency particulate air filter) and ULPA (ultra-high-efficiency particulate air filter), can filter out particle pollutants of 0.3 microns and above, with a filtration efficiency of more than 99.97%, which can effectively prevent particle pollutants from falling on substrates, photoresists and other materials, and reduce display defects caused by particle pollution.
♦ Micro-vibration control: The process equipment such as lithography and exposure in LCD display production is very sensitive to vibration. Small vibrations can cause deviations and misalignment of the lithography pattern. Clean rooms should adopt measures such as vibration isolation floors and vibration isolation brackets to control the vibration amplitude at the micro-nano level to ensure the stable operation of process equipment.
♦ Static electricity control: Static electricity can absorb dust particles and may also cause problems such as abnormal orientation of liquid crystal molecules and damage to circuit components. The floor, walls and equipment of the clean room should be made of anti-static materials. The staff should wear anti-static clothing, shoe covers and gloves, etc. At the same time, static elimination equipment such as ion fans should be installed to control the static voltage below 100V to effectively prevent static hazards.

2) Strengthen personnel management
♦ Strict training and assessment: Strict clean room operation standard training is carried out for staff entering the clean room, including how to wear clean clothes correctly, how to operate equipment to avoid particles, etc. After training, assessment is carried out. Only those who pass the assessment can enter the clean room to work, ensuring that the staff understands and abides by the various regulations of the clean room and reduces pollution caused by human factors.
♦ Restrict personnel flow: Reduce unnecessary personnel movement and activities in the clean room, formulate reasonable personnel walking routes, avoid frequent cross-flow of personnel, so as to reduce air flow disturbance and particle emission caused by personnel activities and reduce pollution risks.

3) Strengthen equipment and material management
♦ Equipment cleaning and maintenance: Regularly carry out deep cleaning and maintenance of production equipment, use special cleaning tools and cleaning agents to remove dust, oil and other pollutants on the surface and inside of the equipment. During equipment maintenance, ensure that maintenance personnel comply with clean room specifications, prevent the introduction of new contaminants during the maintenance process, ensure that the equipment is in optimal operating condition, and reduce product defects caused by equipment contamination.
♦ Material cleaning and transfer: All materials entering the clean room, such as glass substrates, photoresists, liquid crystal materials, etc., must be strictly cleaned and purified at the entrance to remove dust and impurities on the surface. Use dedicated material transfer equipment to keep the materials clean during the transfer process and prevent the introduction of contaminants during the material transfer process.

4) Real-time monitoring and data management
♦ Environmental monitoring system: Install an air quality monitoring system in the clean room to monitor parameters such as particle concentration, temperature and humidity, and pressure difference in the air in real time. Once the parameters exceed the set range, the system immediately issues an alarm, and the staff can take timely measures to adjust to ensure that the clean room environment always meets production requirements.
♦ Data analysis and improvement: Comprehensively analyze the environmental data, production process data, and product quality data of the clean room to find out the relationship between environmental factors and product yield, discover potential problems and improvement points through data analysis, formulate targeted measures, and continuously optimize the operation management of the clean room to improve product yield.

3. Design requirements for clean rooms in LCD display manufacturing
The design requirements for clean rooms in LCD display manufacturing involve many aspects, including site selection and layout, air purification, building decoration, etc. The following are the specific contents:
1) Site selection and layout
♦ Site selection requirements: Clean rooms should be located in areas with low atmospheric dust concentration and good natural environment, away from pollution sources such as chemical and metallurgical industries, to reduce the impact of external pollutants on clean rooms. At the same time, convenient transportation should be considered to facilitate the transportation of raw materials and products.
♦ Plane layout: According to the process of LCD display production technology, the various functional areas of the clean room, such as photolithography area, film forming area, packaging area, etc., should be reasonably planned to minimize the flow routes of materials and personnel and avoid cross contamination. Areas of different cleanliness levels should be effectively isolated, and the entry and exit of personnel and materials between different areas should be controlled by setting up buffer rooms, airlocks, etc.
♦ Design of personnel and material flow: Set up independent personnel channels and material channels. Personnel need to go through the dressing room, air shower room, etc. for purification before entering the clean room; materials need to enter through the transfer window, cargo shower room, etc., and the material transfer route should avoid crossing the personnel flow route to prevent the contaminants carried by personnel and materials from spreading to each other.

2) Air purification system
♦ Cleanliness level: According to the requirements of LCD display production process, the cleanliness level of the clean room usually needs to reach ISO 5 (10,000) or even higher. In key process areas such as lithography and packaging, ISO 4 (1,000) or ISO 3 (100) may be required to meet the needs of high-precision production. .
♦ Airflow organization: Use unidirectional flow or mixed flow airflow organization. Unidirectional flow is used in key process areas to make the air flow at a uniform speed and direction to quickly take away pollutants; mixed flow can be used in auxiliary areas to reduce costs. Reasonably design the position and number of air supply and return air outlets to ensure uniform airflow in the room, avoid dead corners of airflow, and reduce the accumulation of pollutants.
♦ Air filtration: A multi-stage air filtration system is configured, generally including primary, medium and high efficiency filters. Primary filters can filter out large dust particles, medium efficiency filters further remove smaller particles, and high efficiency filters (HEPA) or ultra-high efficiency filters (ULPA) can filter out particles of 0.1 microns or even smaller, ensuring that the air entering the clean room is highly clean.

3) Building decoration
♦ Walls and floors: The walls should be made of smooth, flat, dust-resistant and corrosion-resistant materials, such as color steel plates, stainless steel plates, etc. The corners of the walls should be made into arc corners for easy cleaning; the floor is generally made of anti-static, wear-resistant and easy-to-clean epoxy self-leveling floor or PVC roll floor, and the floor and wall should be skirted to prevent dust accumulation.
♦ Door and window design: Doors and windows should have good sealing performance, and use broken bridge aluminum or stainless steel door and window frames, with double-layer hollow glass, which can not only ensure good thermal insulation performance, but also prevent the entry of outside air and dust. The door should be opened in the direction of high cleanliness, and automatic induction doors or door closers should be used to reduce the impact of personnel operations on the clean room environment.
♦ Electrical system: The electrical equipment and lines in the clean room should meet the requirements of fire prevention, explosion prevention, anti-static, etc., and use wires and cables with protective coatings to prevent dust and moisture from entering the interior of the electrical equipment. Set up a backup power supply system to ensure that key equipment such as air purification systems and process equipment can continue to operate when the city power is cut off, avoiding production interruptions and product scrapping caused by sudden power outages.
♦ Lighting system: Lighting should use non-glare and non-stroboscopic lamps, such as LED lamps. The lamps should be embedded in the ceiling, with a flat and smooth surface for easy cleaning, and have good sealing performance to prevent dust from entering the interior of the lamps. The lighting should be reasonably designed according to the working requirements of different areas. The lighting in the general production area is 300-500lux, and the lighting in the inspection area should not be less than 750lux.

4. Energy-saving optimization plan for clean rooms in the LCD display industry
The energy-saving optimization plan for clean rooms in the LCD display industry mainly includes the following aspects:
1) Optimize the building envelope
♦ Check and repair the leaks in the envelope: Regularly check the walls, ceilings, doors and windows of the clean room, and repair the leaks in time if they are not sealed tightly or damaged to prevent the infiltration of cold and hot air.
♦ Add insulation materials: Add high-efficiency insulation materials such as polystyrene foam boards and polyurethane foam boards to the envelope to reduce heat transfer and reduce air conditioning load.

2) Optimize the air handling system
The air conditioning system is one of the most energy-consuming equipment in the photoelectric purification workshop, and its optimized management is crucial for energy saving and consumption reduction.
♦ Reasonably set the fresh air ratio: Use the enthalpy control method to monitor the enthalpy of indoor and outdoor air in real time. When the enthalpy of outdoor air is lower than that of indoor air, appropriately increase the amount of fresh air introduced, use the outdoor low-temperature fresh air to bear part of the indoor cold load or heat load, and reduce the operating time and energy consumption of the air conditioning system's refrigeration and heating equipment.
♦ Optimize airflow organization: Use Computational Fluid Dynamics (CFD) software to simulate and analyze the airflow in the clean room, and optimize the location, quantity and form of the air supply and return air outlets based on the simulation results. For example, one-way flow is used in key process areas to ensure high cleanliness, and mixed flow is used in auxiliary areas. On the premise of meeting the cleanliness requirements, the total air supply volume of the system is reduced, thereby reducing the fan energy consumption.
♦ Intelligent group control technology: For clean rooms with multiple air-conditioning units, an intelligent group control system is used. According to factors such as indoor and outdoor environmental parameters and clean room load changes, the operation combination of air-conditioning units is automatically optimized so that each unit operates under efficient conditions. For example, when the load is low, some units are automatically shut down, and only a few units are kept running to avoid inefficient idling of equipment.

3) Energy saving of lighting system
♦ Lighting zoning and timing control: Lighting zoning control is performed according to the functional areas of the clean room, such as production areas, corridors, equipment maintenance areas, etc. During non-working hours, automatically turn off or dim the lighting in non-production areas; set timer switches for production areas, open and close in advance according to production shifts, and prevent lights from being left on all the time.
♦ Use energy-saving lighting fixtures: Replace all of them with LED lighting fixtures, which have high luminous efficiency, low energy consumption, and long life. Compared with traditional fluorescent lamps, LED lamps can save about 30% - 50% of electricity, and can provide more stable lighting effects that are closer to natural light, which is conducive to improving production quality.

4) Energy saving of process equipment
♦ Optimization of equipment sleep and standby modes: Transform LCD display production equipment to have smarter sleep and standby modes. When the equipment has no production tasks for a short period of time, it automatically enters a low-power standby state; when it is idle for a long time, it enters a deep sleep mode and shuts down unnecessary subsystems, such as display screens, some drive circuits, etc., to reduce equipment energy consumption.
♦ Optimize equipment operating parameters: Through experiments and data analysis, determine the  best operating parameters of production equipment in different process stages. For example, in the cleaning process of the LCD panel, the temperature, flow rate and spraying time of the cleaning liquid are reasonably adjusted to reduce the energy consumption of the heating and pumping equipment while ensuring the cleaning effect.

5. Higher requirements for clean rooms in OLED and Micro-LED manufacturing
Compared with traditional LCD manufacturing, OLED (organic light-emitting diode) and Micro-LED (micro light-emitting diode) manufacturing have higher requirements for clean rooms in terms of cleanliness level, temperature and humidity control, anti-static requirements, vibration control, etc., as follows:

1) Cleanliness level
♦ OLED manufacturing: OLED materials and devices are extremely sensitive to particulate pollutants. Tiny particles may cause pixel short circuits, uneven light emission and other problems, affecting display effects and product yields. Therefore, OLED manufacturing usually requires clean rooms to reach ISO level 4 or higher, that is, the number of particles greater than or equal to 0.1 microns per cubic meter of air does not exceed 1,000.
♦ Micro-LED manufacturing: The chip size of Micro-LED is extremely small, and the processes such as lithography and transfer in the process have extremely high requirements for environmental cleanliness. Generally, it needs to be carried out in an ISO Class 3 or even higher clean room. The number of particles greater than or equal to 0.1 microns per cubic meter of air must be controlled within 100 particles to prevent particulate contaminants from damaging tiny chips and ensure the performance and reliability of the chips.

2) Temperature and humidity control
♦ OLED manufacturing: The physical and chemical properties of OLED materials are sensitive to changes in temperature and humidity. Temperature fluctuations may cause changes in the evaporation rate of OLED materials, affecting the thickness and uniformity of the organic layer; humidity changes may cause OLED devices to become damp, causing problems such as electrode corrosion and reduced luminous efficiency. Therefore, the temperature of the OLED clean room is usually controlled at 23±1℃ and the humidity is controlled at 40%±5% RH.
♦ Micro-LED manufacturing: In the process of epitaxial growth, chip manufacturing and packaging of Micro-LED, precise control of temperature and humidity is crucial. Temperature deviation will affect the growth quality of the epitaxial layer and the performance consistency of the chip. Humidity changes may cause water vapor to be adsorbed on the chip surface, affecting the accuracy of processes such as photolithography. The temperature of the clean room is generally required to be controlled at 22±0.5℃, and the humidity is controlled at 30%±3% RH.

3) Anti-static requirements
♦ OLED manufacturing: OLED materials and devices usually have high resistance and are prone to accumulate static electricity. Static discharge may break down OLED devices, causing permanent damage and reducing product yield. Therefore, OLED clean rooms need to take strict anti-static measures, such as using anti-static floors, walls and workbenches, staff wearing anti-static clothing, shoes and gloves, equipped with ion fans, etc., to control the static potential below 100V.
♦ Micro-LED manufacturing: Micro-LED chips are more sensitive to static electricity due to their small size and high integration. Static electricity may cause damage to the internal circuit of the chip, reduced luminous performance and other problems. The anti-static requirements of Micro-LED clean rooms are more stringent. In addition to conventional anti-static measures, special anti-static treatment is required for production equipment and tools to control the static potential below 50V.

4) Vibration control
♦ OLED manufacturing: In the OLED evaporation, photolithography and other processes, tiny vibrations may cause the equipment to lose precision, affect the deposition uniformity of organic materials and the accuracy of patterns, and further affect the performance and display quality of OLED devices. Therefore, OLED clean rooms need to take effective vibration isolation measures to control the vibration amplitude below the micron level.
♦ Micro-LED manufacturing: Micro-LED processes such as photolithography and chip transfer have extremely high precision requirements. Vibration may cause problems such as photolithography pattern offset and inaccurate chip transfer position, reducing product consistency and yield. Micro-LED clean rooms usually need to adopt more advanced vibration isolation technology and equipment, such as air spring vibration isolation systems, active vibration isolation platforms, etc., to control the vibration amplitude at the submicron level or even smaller.

5) Gas purity
♦ OLED manufacturing: In the OLED evaporation process, high-purity carrier gas and reaction gas are required to ensure that the evaporation and deposition process of organic materials is not interfered by impurity gases. For example, the purity of nitrogen used to transport organic materials is usually required to reach more than 99.999% to prevent impurity gases from reacting with organic materials and affecting the luminous performance and life of OLEDs.
♦ Micro-LED manufacturing: In the epitaxial growth process of Micro-LEDs, higher gas purity requirements are required. For example, the purity of gases such as ammonia (NH₃) and hydrogen (Hâ‚‚) used to grow materials such as gallium nitride (GaN) must reach more than 99.9999%, otherwise impurity gases may introduce defects and affect the quality of the epitaxial layer and the luminous efficiency of Micro-LEDs.

6. Application of modular clean rooms in the LCD Display Screen industry
The application of modular clean rooms in the LCD Display Screen industry is mainly reflected in the following aspects:
1) Plant structure construction
♦ Rapid construction: In the construction of LCD Display Screen production plants, modular clean rooms can be assembled quickly. Unlike traditional on-site construction methods, the components of modular clean rooms are prefabricated in the factory and then transported directly to the construction site for splicing, which greatly shortens the construction period and enables LCD production lines to be put into use faster and seize market opportunities.
♦ Flexible layout: LCD production processes are complex, and different production links have different requirements for space layout and environment. Modular clean rooms can flexibly adjust the size, shape and combination of rooms according to production processes and process requirements, and facilitate the construction of different functional areas, such as array process areas, color filter process areas, module assembly areas, etc., to improve the space utilization rate of the factory.
♦ Scalability: With the technological development and market demand changes in the LCD industry, manufacturers may need to expand production capacity or upgrade processes. Modular clean rooms are easy to expand and transform. By simply adding or replacing the corresponding modules, new production needs can be met, avoiding the cost and time waste caused by large-scale demolition and reconstruction.

2) Production process control
The key processes in LCD production have extremely high requirements for environmental cleanliness, temperature, humidity and vibration, as follows:
♦ Photolithography process: The modular clean room can provide an independent, highly clean and stable environment for the photolithography area. Through the precise air filtration system and environmental control system, it can ensure that there is no particle pollution and temperature and humidity fluctuations during the photolithography process, thereby improving the photolithography accuracy and ensuring the pattern quality and resolution of the LCD panel.
♦ In the LCD coating process, various functional films need to be deposited on the glass substrate under a vacuum environment. The modular clean room can integrate vacuum coating equipment and be equipped with corresponding vacuum systems, gas supply systems and exhaust gas treatment systems to form a complete coating module. This integrated design is not only convenient for process control and equipment maintenance, but also can effectively prevent external impurities from entering the coating environment, improving the uniformity and quality of the coating.
♦ Liquid crystal perfusion: Liquid crystal perfusion is the process of filling liquid crystal materials into the liquid crystal box. Modular cleanrooms can provide strict cleanliness and temperature control to prevent liquid crystals from being contaminated and oxidized, while ensuring stable pressure and flow during the infusion process, ensuring the accuracy and consistency of liquid crystal infusion, thereby improving the display performance and reliability of LCD panels.

3) Environmental pollution control
♦ Partition isolation: In the LCD display screen production process, different process links produce different types and degrees of pollutants. Modular cleanrooms can separate areas with higher pollution risks from key process areas by setting up clean areas of different levels and adopting effective isolation measures, such as airlocks and transfer windows, to prevent the spread of pollutants and protect product quality.
♦ Local purification: For some specific process points or equipment with extremely high cleanliness requirements, such as high-precision detection equipment, liquid crystal dropping devices, etc., local purification modules can be set up in modular cleanrooms, and efficient air purification equipment and airflow organization methods can be used to form a higher level of clean environment in local areas to meet process requirements.
♦ Waste gas treatment: Various pollutants such as organic waste gas and acid-base waste gas will be generated during the LCD production process. Modular clean rooms can integrate special exhaust gas treatment modules. According to the composition and properties of the exhaust gas, corresponding treatment technologies such as activated carbon adsorption, acid-base neutralization, catalytic combustion, etc. are used to purify the exhaust gas so that it meets the emission standards and reduces pollution to the environment.

4) Material storage and processing
The materials used in the LCD display screen manufacturing process, such as glass substrates, color filters, polarizers, etc., need to be stored and processed in a dust-free and dry environment. The clean drying box provides a low-humidity and dust-free environment to ensure the quality of these sensitive materials.

5) Personnel and logistics management
The modular clean room uses facilities such as air showers, cargo showers, and transfer windows to clean personnel and items to prevent contamination. At the same time, the micro-positive pressure design is maintained to ensure that polluted air does not enter the high-cleanliness workshop.

6) Inspection and maintenance
♦ Convenient maintenance: The modules of the modular clean room are relatively independent, and the layout of equipment and systems is clearer and more reasonable, which is convenient for maintenance personnel to inspect and maintain. When a module fails, it only needs to be isolated from other modules for separate repair or replacement, which will not affect the operation of the entire production system, reducing maintenance costs and downtime.
♦ Online monitoring: Modular clean rooms are usually equipped with advanced environmental monitoring systems and equipment operation monitoring systems, which can monitor the temperature, humidity, cleanliness, pressure difference and other environmental parameters in the clean room and the operating status of the equipment in real time. Through data analysis and fault diagnosis technology, potential problems can be discovered in time, and measures can be taken in advance to deal with them, ensuring the stable operation of the clean room and product quality.