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What is the manufacturing process of TFT lcd display?


Displays are everywhere these days. Do you remember TVs or computer monitors from 20 years ago? They are square, big and heavy. Now let’s take a look at the flat, thin and light screen in front of you. Have you ever wondered why there is such a big difference?

In fact, monitors from 20 years ago were CRT (cathode ray tube) monitors that required a lot of space to run the internal components. The screen in front of you now is an LCD (LCD) screen.



What is an LCD display?
As mentioned earlier, LCD is the abbreviation of Liquid Crystal Display. It is a new display technology that utilizes the photoelectric properties of liquid crystals.

A liquid crystal is a state of matter that has the properties of liquid and solid crystals. It doesn’t emit light by itself, but it allows light to pass perfectly in a specific direction. At the same time, the liquid crystal molecules will rotate under the action of the electric field, and the light passing through it will also rotate. In other words, liquid crystals can be used as optical switches, which is the key to display technology.

Types of LCD Displays
LCDs have been around for decades. Basically there are TN LCD, STN LCD and TFT LCD.

TN LCD: TN stands for Twisted Nematic. It’s an old and simple technology that can only display white and black and is used for calculators and other small things.

STN LCD: STN stands for Super Twisted Nematic. STN Compared with TNN, the liquid crystal in the LCD has a larger rotation angle than the liquid crystal in the LCD, and has different electrical characteristics, so that the STN LCD can display more information. There are many improved versions of STN LCD, such as DSTN LCD (dual layer) and CSTN LCD (color). This type of LCD was used in many early telephones, computers, and outdoor equipment.

TFT LCD: TFT is used for thin film transistors. It is the latest generation of liquid crystal display technology, which has been applied to all display scenarios such as electronic equipment, automobiles, and industrial machinery. When you see the word “transistor,” you probably realize that TFT integrated circuits exist in LCDs. That’s right, and it’s also the secret of LCD that TFT has the advantages of high resolution and full color display.
Now that TFT LCD has the largest application market, let’s take a closer look at what is the manufacturing process of TFT LCD?



TFT LCD manufacturing process
Simply put, we can use TFT LCD to be divided into three parts: optical system, circuit system and light control system. During the manufacturing process, we start with the internal light control system and then extend to the entire module.

Traditionally, the TFT LCD manufacturing process is divided into three main parts: array, unit and module. The first two steps are to make the light color control system, including TFT, CF (color filter) and LC (liquid crystal) called cell. The final step is to assemble the battery, circuitry and light system.

1. Array

To increase productivity, in this step we will perform a series of operations on a large piece of glass, which will then be cut into smaller pieces in the next step.

First, I would like to introduce an important ITO material. ITO, the abbreviation of Indium tin oxide, has electrical conductivity and light transmission, and is easy to deposit into a thin film. Therefore, it is widely used to make circuits on glass.

Thin film transistor:

Semiconductor material and ITO are deposited on the glass substrate in a designed order.
Photoresist coating.
Spot exposure, followed by cleaning of the exposed photoresist.
Tear off the semiconductor and ITO, without photoresist coverage, to form part of the circuit.
Clean up residual photoresist.
Usually more than 5 steps need to be repeated to build the whole circuit.

2. Cells

In this step, we will assemble the TFT and CF while filling the glass LC.

A polyimide film was coated on the ITO surface of TFT and CF glass to confine the initial orientation of LC molecules.
Use glue on the two pieces of glass to create the border for the liquid crystal. And apply a layer of conductive glue on the CF glass. This allows the LC to link the molecule to the control circuit.
Fill the LC within the boundary.
Two pieces of glass are glued together, and the large piece of glass is cut into smaller pieces that meet the standard.
Polarizing film is attached to both sides of the cut glass.


3. Module

First connect the battery to the electrical system.

Connect the battery to the driver IC.
Connect the driver IC to the FPC (Flexible Printed Circuit).
Connect the FPC to the external PCBA (Printed Circuit Board Assembly).
Next, prepare the lighting system

Paste the light source, usually LED or CCFL, on the light guide plate, and stick the reflective film under the light guide plate
Place the diffuser film and the prism film on the light source in sequence. These two films are used together with the reflective film to convert the point light of the light source into surface light and enhance the light intensity.
Connecting the light source to the light control circuit is always another PCBA.
In the last step we need to assemble all this with the screen frame and do a burn-in test.
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