Display screens are ubiquitous in today's world. Do you still recall the TVs or computer monitors from 20 years ago? They were square, bulky, and hefty. Now, take a glance at the flat, thin, and lightweight screen in front of you—have you ever wondered why there's such a significant difference?
In reality, the monitors from two decades ago were CRT (Cathode Ray Tube) displays, which required ample space to accommodate the inner components. The screen before you now, however, is an LCD (Liquid Crystal Display) screen.
As mentioned earlier, LCD stands for Liquid Crystal Display. It is a modern display technology that capitalizes on the optical-electrical characteristics of liquid crystal.
Liquid crystal is a substance with properties of both a liquid and a solid crystal. It does not emit light itself, but it can perfectly allow light to pass in a specific direction. Simultaneously, under the influence of an electric field, the liquid crystal molecules rotate, causing the light passing through it to also rotate. In essence, liquid crystal serves as a switch for light, playing a pivotal role in display technology.
The development of LCD technology spans decades, resulting in various types, with three primary categories: TN LCD, STN LCD, and TFT LCD.
TN LCD is an older and simpler technology capable of displaying only black and white. It finds application in small devices like calculators.
STN LCD features liquid crystals that rotate at greater angles compared to TN LCD, offering different electrical characteristics that enable the display of more information. Improved versions include DSTN LCD (double layer) and CSTN LCD (color). This type of LCD was commonly used in early phones, computers, and outdoor devices.
TFT LCD, the latest generation of LCD technology, is employed in various display scenarios, including electronic devices, motor cars, and industrial machines. The term 'transistor' indicates the presence of integrated circuits in TFT LCD, giving it the advantage of high resolution and full-color display.
Given that TFT LCD has the broadest application market, let's delve further into the manufacturing process of TFT LCD.
The manufacturing process of TFT LCD can be simplistically divided into three parts, progressing from bottom to top: the light system, circuit system, and the light and color control system. In the manufacturing process, we initiate with the inner light and color control system, then extend to the entire module.
The TFT LCD manufacturing process conventionally consists of three primary stages: array, cell, and module. The initial two steps focus on producing the light and color control system, encompassing TFT, CF (color filter), and LC (liquid crystal), collectively referred to as a cell. The final step involves the assembly of the cell, circuit, and light system.
To enhance efficiency, this step involves a series of procedures performed on a large glass, which will be subsequently cut into smaller pieces.
Introducing a crucial material known as ITO (Indium tin oxide), it possesses the dual characteristics of electrical conductivity and optical transparency. Additionally, it can be easily deposited as a thin film, making it widely utilized for circuit creation on glass.
Now, let's delve into the production of TFT (Thin Film Transistor) and CF (Color Filter). A commonly employed method is the PR (photoresist) method, which will be exemplified in the TFT production process.
Deposit semiconductor material and ITO in designed order on glass substrate.
Photoresist coating.
Partial exposure, then clean the exposed photoresist.
Tear off the semiconductor and ITO without the cover of photoresist to form part of the circuit.
Clean the remain photoresist.
To build the whole circuit, we often need to repeat the steps for 5 times.
Create a black matrix on the glass substrate as the boundary using PR method.
Coat red, green and blue material within black matrix separately using PR method.
Coat a overcover on RGB (red, green and blue) layer.
Deposit ITO circuit.
During this phase, we combine the TFT and CF glass while simultaneously filling in the LC.
1. Coat a polyimide film on the ITO side of both TFT and CF glass. This film serves to constrain the initial direction of LC molecules.
2. Use glue to create a boundary for LC on both pieces of glass. Additionally, on the CF glass, apply an extra layer of conductive adhesive to facilitate the connection of LC molecules to the control circuit.
3. Fill the LC within the established boundary.
4. Fuse the two glass pieces together, then cut the large glass into smaller pieces according to predefined standards.
5. Attach polarizer film on both sides of the cut glass.
Begin by connecting the cell to the circuit system:
1. Link the cell to the driver IC.
2. Connect the driver IC to the FPC (flexible printed circuit).
3. Establish a connection from the FPC to the outer PCBA (printed circuit board assembly).
1. Attach the light source, typically LED or CCFL, onto the light guide plate, beneath which a reflector film is placed.
2. Layer the diffuser film and prism film on the light source. Along with the reflector film, these two films transform the point light from the source into area light, enhancing light intensity.
3. Connect the light source to the light control circuit, often another type of PCBA.
In the final step, assemble all these components along with the screen frame and conduct an aging test.
This concludes the post. If you find it helpful or wish to learn more about TFT LCD, feel free to leave your comments below or contact us.
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