What is the manufacturing process of LCD?

1. Material preparation:

Prepare ITO glass (14 ") suitable for cleaning × 14 "or 14" × 16 "), the front faces of the glass are placed in the same direction, that is, the identification angles of all the glass to be cleaned are placed in the same direction. Work in the same direction.

2. Cleaning and drying:

The first process is to meet the production specifications (14 " × 14 "or 14" × 16 ") ITO glass is cleaned with detergent, DI water, etc., and impurities on the surface of ITO glass are cleaned using physical and chemical methods. Then, the water is removed and dried, laying a solid foundation for the quality of the next process.

3. Gluing:

Gluing is the first process of photolithography, which involves evenly applying a layer of photoresist on the ITO surface of ITO glass. The effect of gluing directly affects the quality of photolithography. Its main control contents include: the preparation of photoresist, the thickness and uniformity of the coating, and the surface state of the coating.

Photoresist is generally stored under low temperature and dark conditions, so before using the photoresist, remove the photoresist from the low temperature environment until the temperature of the photoresist in the bottle is consistent with the temperature of the indoor air. Open the bottle cap of the photoresist, and the viscosity of the photoresist must be tested before use. Because when the viscosity of the adhesive is high, the corrosion resistance of the thick coating is high, but its resolution is low. On the contrary, when the viscosity of the adhesive is low, its corrosion resistance is poor, but its resolution is high. Generally, the adjustment of the viscosity of the adhesive is made by using a dilution method, that is, converting the high viscosity adhesive into a low viscosity adhesive. The surface condition of ITO glass before coating has a significant impact on the adhesion quality between photoresist and ITO layer. In order to ensure good contact and adhesion between the ITO film and the photoresist during the production process, the cleaned glass must be clean and dry.

The quality requirements for gluing are: the glue adheres well to ITO without peeling off; The coating thickness shall be uniform and uniform, and there shall be no thickness or thickness, which may cause graphic defects during development and etching. Generally, defects such as stripes, pinholes, and protrusions are not allowed on the surface of the adhesive coating. The methods of gluing include dip coating, swing coating, roller coating, etc. The coating quality of roller coating is better than the other two methods. It is to evenly apply photoresist under ITO glass through rubber rollers. To ensure the gluing quality, the gluing work must be carried out under clean conditions.

4. Front baking:

The purpose of pre drying is to fully volatilize the solvent in the adhesive film and dry the adhesive film to enhance the adhesion between the adhesive film and the surface of ITO glass and the abrasion resistance of the adhesive film. During exposure, even contact between the mask and the photoresist will not damage or contaminate the photoresist film. At the same time, only when the photoresist is clean and exposed can the photoresist fully react with light.

5. Exposure:

Exposure involves covering a mask on a glass surface coated with photoresist, usually with UV light as a viable option.

The photoresist in the light receiving portion undergoes a chemical reaction that changes the solubility of this portion of the photoresist in the developing solution. After development, the photoresist film exhibits a pattern consistent with that on the mask. General exposure operation process: Turn on the UV lamp of the exposure machine to preheat, wait for the voltage to stabilize, and perform initial alignment of the lithographic plate on the plate cabinet through a microscope. It is required that the markings on both sides of the photolithography plate coincide with the "+" line of the display mirror, then fix the plate holder, and then conduct trial exposure, alignment, and fine adjustment to ensure that the alignment meets the requirements.

The selection of exposure time and light intensity is measured based on the quality of the plate, the nature of the photoresist, the intensity of the light source, and the distance from the light source to the ITO glass. Generally, the light intensity is measured using a light intensity meter, then the corresponding exposure time is set, and a second exposure is made. After careful inspection, the exposure conditions are determined.

Before setting the exposure conditions, it is important to know: the photoresist's sensitivity, which is a sensitive performance indicator that characterizes the photoresist's light. Different sensitivities indicate different levels of sensitivity to light, namely, the amount of exposure required for photochemical reactions.

6. Development:

Developing involves dissolving the photoresist from the photosensitive portion and removing the remaining film from the photosensitive portion to display the desired adhesive layer pattern. The development process involves placing the exposed glass into the development tank, taking it out after a period of time, and then rinsing the development solution with DI water. There are two types of developer: the first is a developer that is compatible with photoresist, and the second is a certain concentration of alkaline solution (NaOH or KOH). Generally, TN-LCD manufacturers use the second type.

During development, it is necessary to control the temperature, concentration, and time of the developing solution. In a developing solution at a certain concentration, temperature and time directly affect the speed. If the developing time is insufficient or the temperature is low, the photoresist at the photosensitive part cannot be completely dissolved, leaving a layer of photoresist. During etching, this layer of photoresist will protect the ITO surface, leaving behind the ITO that should be etched. If the development time is too long or the temperature is too high, the photoresist at the unexposed part during development will also be drilled and dissolved from the edge. Making the edges of the pattern worse, if it is more severe, will cause a large amount of photoresist to fall off, forming a debonding.

The development work should be careful, and the glass must be independently inspected to check the condition of the graphics. Once any nonconformities are found, they must be immediately reworked. At the same time, during batch production, the concentration of the alkali liquor should be sampled to ensure that its concentration is within a certain range.

7. Scleroderma

Due to the softening and expansion of the adhesive film during development, which affects the corrosion resistance of the adhesive film, it is necessary to bake the glass at an appropriate temperature after development to remove moisture and enhance the adhesion of the adhesive film to the glass. This process is called hardening.

There are two types of hard film: oven and infrared ray, of which oven is more common. The conditions for hardening the film: one is temperature, the other is time. Generally, the hardening condition is slightly higher than the pre drying condition.

8. Etching:

Etching uses a certain proportion of acid to remove the ITO film on the glass that is not protected by photoresist, while leaving the ITO film protected by photoresist to form the desired pattern. The etching solution selected should generally be a photoresist that can etch off ITO without damaging the glass surface. Generally, a mixture of a certain proportion of Hcl, HNO3 (or Fed3), and water is used. The temperature and time of etching greatly affect the etching effect.

9. Film removal:

Decasting is the removal of photoresist from the etched glass. Normally, a certain temperature of alkaline solution is used for normal debonding, and its concentration must be higher than the development concentration. Generally, the above processes are called photolithography processes, which play a key role in LCD fabrication and migration. The quality of photolithography directly affects the performance, yield, and reliability of devices. The basic requirements for photolithography quality are as follows:

① The etched pattern is complete, with accurate dimensions, neat edges, and steep lines.

② There are no redundant ITO patterns, pinholes, burrs, etc. in the pattern, and the etching is clean.

③ The surface of the corroded glass is clean and free from poor etching, residual corrosive substances, oil stains, etc.

④ Accurate graphic positioning and complete various markings.

10. Post cleaning refers to cleaning the glass after the photolithography process with detergent DI water, etc., and drying it for later production.

11. Coating alignment film:

Generally, the directional materials used in the production of mid to low grade LCDs are PA, which is polyimide acid. It is completely formed by the polymerization reaction of dianhydride and diamine at low temperature. After dehydration and solidification at high temperature (the upper layer of chemistry is a cyclization reaction), it becomes polyimide (PI). Polyimide has excellent chemical stability, excellent mechanical properties, high insulation, high temperature resistance, high dielectric constant, radiation resistance, and non combustible.

The coating process involves uniformly coating a solution containing directional materials on a designated position of glass with an electrical plate pattern, and then baking to obtain a complete PI. There are three commonly used coating methods: one is the rotary coating method, the other is the immersion method, and the other is the Coriolis printing method. Coriolis printing is better than the other two methods.

Coriolis printing is a selective coating (also known as pad printing).

During printing, first add the oriented material solution to the scraper roller and the glue leveling roller to evenly distribute it on the glue leveling roller, then start the roller of the APR plate, so that the convex particles on the APR plate can uniformly obtain the PA solution, and then transfer it to the ITO glass on the base.

12. Pre drying and curing:

The purpose of pre baking is to evaporate the solvent in the directional material when heated. The directional material obtained after pre baking is often not the final directional film. If the N-methylpyrrolidone solution of polyamide acid is used for coating, it needs to be baked at 80 ℃ to 110 ℃ to volatilize the N-methylpyrrolidone. At this time, what remains on the glass is polyimide acid (PA), which also needs to be cured at high temperature for 1-2 hours, and then subjected to dehydration and cyclization reaction to produce a polyimide film, which is the desired directional film.

13. Orientation:

The desired directional layer can be formed by rubbing the glass surface coated with the directional layer on the directional film with a plush cloth. The liquid crystal molecules at the orientation layer will be aligned in the direction of friction, so that consistent orientation can be obtained. The liquid crystal molecules at the upper and lower plates are arranged in a direction of 90 ° C with each other. The principle of friction orientation is simple.

Place the polyimide substrate to be abraded on a movable platform and rub it with a rotating roller equipped with a plush cloth to obtain a better friction orientation effect. However, the actual friction machine and friction results are by no means easy. The surface molecules of the alignment film are oriented to obtain alignment. The mechanical vibration of the friction machine must be kept to a minimum, and the flatness, smoothness, and parallelism of the platform and the drum must be close to the micron level, close to the limits of machine processing.

14. Silk screen printing:

Namely, screen printing frame and conductive point: The sealing material (frame adhesive) is printed on the upper and lower plates with screen printing method, and the frame adhesive and conductive point are printed on the positive surface of the glass. Screen printing consists of five major elements: a screen printing plate, a scraping blade, a screen printing material (frame sealing adhesive or conductive adhesive), a printing platform, and a substrate.

The principle of screen printing: Using the basic principle of screen printing, the image and text parts can be printed through frame sealing adhesive (or conductive adhesive), while the non image and text part mesh holes cannot be printed through frame sealing adhesive (or conductive adhesive). During printing, pour appropriate frame sealing adhesive (or conductive adhesive) into one end of the screen printing plate, apply sufficient pressure to the frame sealing adhesive (or conductive adhesive) on the screen printing plate with a scraper, while moving towards the other end of the screen printing plate. During the movement, the frame sealing adhesive is pressed onto the substrate by the scraper from the screen printing plate in the image and text section, and is fixed within a certain range due to the adhesive action of the frame sealing adhesive (or conductive adhesive), During the printing process, a certain gap is maintained between the scraper and the screen printing plate and the substrate, allowing the screen printing plate to generate a reaction force against the scraper through its own tension during printing. This reaction force is called resilience. Due to the effect of resilience, the screen printing plate and the substrate are only in mobile contact, while the other parts of the screen printing plate are separated from the substrate, causing the frame sealing adhesive and the screen to break, ensuring printing dimensional accuracy and avoiding scratching the substrate. When the scraper scrapes across the entire page, lift it up, and at the same time, lift the screen up. Gently scrape the frame sealant back to its original position for reprinting. This completes the entire printing process.

Screen printing emphasizes three dimensions: the parallelism between the scraper and the screen (i.e., the screen and platform), the levelness of the printing platform, and the height of the glass and screen.

15. Spreading:

Distribute the support material evenly on the glass. A certain size of padding (typically several microns) is evenly distributed on the surface of the glass, and this material is used to ensure a certain box thickness for box making.

16. Fitting (combination):

Align the upper and lower glass according to the alignment marks, and glue the corresponding two pieces of glass face to face with sealing materials.

17. Curing:

Cure the sealing material at high temperatures. During curing, a certain amount of pressure is generally applied to the upper and lower glass to maintain a uniform box thickness. Generally, the process of printing frame dots, frame pre baking, dot spreading, alignment combination, and curing is collectively referred to as the box making process.

Making a box is to overlap two pieces of conductive glass at the frame point; Use sealing materials to bond and solidify. The following points should be noted during production: (1) Sealing direction; (2) Printing point position; (3) Size of frame lines and silver dots; (4) Pre baking time and temperature; (5) The density of the powder sprayed (in particles per square millimeter); (6) Combination alignment; (7) Curing temperature and time and cooling rate; (8) During bonding, the pressure on the two pieces of glass is moderate to prevent breakage of the boxy liner material and damage to the directional layer; (9) During bonding, both pieces of glass should be carried out at room temperature to avoid uneven thickness of the glass deformation box or displacement of the upper and lower pieces due to temperature differences between cold and hot; (10) Due to the lack of solidification and poor adhesion of the well bonded LCD box, it is necessary to handle it gently to avoid causing movement of the upper and lower pieces; (11) When wet spray cleaning is used, the prepared mixed liquid cushion material needs to have good mutual solubility and be free of agglomeration and precipitation.

18. Cutting:

(Small cuts and large cracks) As shown in the figure, the liquid crystal box that has been radially solidified is exposed, which is suitable for liquid crystal operation. The entire group of glass must be properly cut into strips.

During cutting, the following points must be noted: ① identify the reference tool position; ② Determine how many knives and times to cut the glass; ③ Must understand the distinction between large and small pieces, and the cutting direction of Groups A and B; ④ The accuracy of cutting is crucial to the subsequent process operations and product grade. When cutting, it is necessary to conduct independent inspection on time and according to the process. To avoid unnecessary losses caused by bad conditions such as knife jumping, knife walking, scraping, reverse cutting, large error, knife depth, and knife line.

19. Filling LC:

Place the strip shaped liquid crystal box with the filling port facing the same direction and in the same straight line as the liquid crystal box with the filling port at the same position before and after, insert it on the liquid crystal rack, with the filling port facing down (the filling port is aligned with the sea cotton strip, but not in contact) onto the bracket of the liquid crystal machine, and fix it. The liquid crystal machine has enough liquid crystal added to the sea cotton sliver. At this point, start vacuuming. When the vacuum reaches the desired level, raise the chassis inside the LCD machine, and allow the sea cotton sliver on the chassis to fully contact the filling port. The effects of deflation, atmospheric air pressure, and capillary phenomena in liquid crystal cells after stopping for a certain period of time. The liquid crystal starts to rise inside the box until it fills the entire liquid crystal box, which completes the filling of the LC.

When filling LC, it is necessary to pay attention to the following points: ① When adding LC to the sponge strip, it is necessary to gently press the sponge strip to infiltrate LC to avoid excessive waste and the liquid crystal box cannot be filled with less liquid crystal; ② After filling, use tweezers to clean up other debris on the sponge strip, and then pull the sunk sponge strip back to its original position. Check whether LC is required and prepare for next use; ③ When the sponge strip is aligned with the seal, the sponge strip must fully cover the filling opening; ⑤ Properly select the type of glass and liquid crystal, and refill them after confirmation; ⑥ Dehumidification must be frequent in the irrigation LC room to keep the humidity below 70%.

20. Sealing (dispensing and cementing):

Wipe the liquid crystal on the sealing surface of the filled LC liquid crystal box clean, and apply a certain amount of sealing adhesive. UV radiation causes the adhesive itself to undergo chemical reactions, cross-linking, and polymerization, forming a solid seal, preventing the liquid crystal inside the screen from leaking outward and preventing the invasion of external pollutants. During sealing operations, attention must be paid to: ① The sealing adhesive should be sealed and stored away from light; ② The sealing adhesive should be stored at a low temperature below 10 ℃; ③ The sealing adhesive is toxic, and gloves should be worn during operation. If it gets on the skin, wash it with carbonated water; ④ Timely and frequent inspections should be conducted to control the speed and extent of glue penetration.

21. Cleaning:

Use a cleaning agent, assisted by ultrasonic heating and vibration, to clean the liquid crystal, dust, and other pollutants adhered to the outer surface of the LCD to meet the requirements of finished product processing. At the same time, use the strong penetration of organic solvents to test whether the sealing adhesive and frame adhesive surrounding the liquid crystal box containing LC are sealed (i.e., leak detection).

22. Small cracks, cleaning:

Carefully split the strip-shaped LCD box into PCS-PC LCD semi-finished products using a cleat knife, and then clean and detect leakage according to the processing needs.

23. Redirection (baking):

Due to the influence of external energy during the production process, some liquid crystals may decompose and become electrically charged, and some liquid crystal molecules may not be aligned in the specified way. Therefore, it is necessary to bake the small splits and cleaned LCD semi-finished products at a certain temperature to arrange the liquid crystal molecules in the specified direction to meet the process requirements.

24. Visual inspection:

Visually inspect the appearance, background color, etc. of the LCD semi-finished product using a polarizer to pick out unqualified products.

25. Electrical inspection:

Apply the electric field signal to inspect the pattern, appearance, and other information displayed on the LCD screen through a polarizer, and select products A, B, C, and scrap according to the product appearance drawing and the Electrical Inspection and Inspection Specification.

26. Cutting and pasting:

Cut the polarizer into standard polarizers as required. Cutting is divided into cutting upper polarizer and lower polarizer. When mounting, first wipe the outer surface of the LCD with acetone, etc., and then attach and lower the polarizer as needed. The following points should be paid attention to during cutting and mounting operations: ① Pay attention to safety during cutting; ② Select the model and parameters of the polarizer before cutting; ③ Place the polarizer in strict accordance with the requirements, and pay attention to the cutting position of the first knife to minimize the generation of leftover materials; ④ When pasting the film, it is not allowed to paste it upside down or upside down. ⑤ It is not allowed to paste it sideways; ⑥ Avoid bubbles ⑦ According to production needs, some fingers must wear finger covers for operation.

27. Final inspection:

According to the factory inspection standards, conduct final inspection and control on the products to be delivered, ensure that the quality meets customer requirements, and establish a good corporate reputation.

28. Packaging:

According to product requirements and customer requirements, select the appropriate packaging box to package the product, and then enter the warehouse.

29. Warehousing: The products that pass the inspection are packaged and stored in the finished product warehouse, ready for delivery to the user.