Basic Manufacturing Knowledge and Product Concepts of LCD

As product managers or enthusiasts of intelligent devices, the following basic knowledge and concepts about the LCD you should know to make the right decision.

Many intelligent terminals use the TFT LCD module as the human-machine interface (HMI) given its high performance in display quality, cost efficiency, and custom flexibility, for instance, a typical computer monitor, television screen, and mobile.

As product managers of the terminals, or only enthusiasts who are interested in intelligent products, you should know the basic manufacturing knowledge and product concepts of LCD for making the right decision.

It also can help you to communicate with your suppliers, give ideas of what can be tailored in the interface, and make the selection.

I. TFT LCD manufacturing processes

From a product perspective, we can divide the TFT LCD module into three layers, from bottom to top: backlight unit, electrical system, and light-and-color control system.

Learn more about TFT-LCD: “What are active matrix LCD and TFT-LCD?"

From the manufacturing process perspective, it starts from the light-and-color control system and then assembles all three parts.

Therefore, there are three main processes, the TFT array process, the cell layer process, and LCD module assembly.

The first two processes are about the production of the light-and-color control system, including TFT substrate, CF substrate, and LC (liquid crystal), collectively referred to as LCD panel.

The last step is the integration and assembly of the LCD panel, electrical system, and backlight unit.

▶ TFT array process

This process is to produce usable thin-film transistors (TFT) substrate and color filter(CF) substrate.

The TFT array process is similar to making the semiconductor.

To get qualified products, it needs to repeat the processes of cleaning, coating, increasing photoresist, exposure, development, etching, removing the photoresist, etc. Generally, it needs to repeat 5 to 7 times.

▶ Cell Layer process

This process takes the output from the previous process as the top and bottom substrates, drips liquid crystals in between, and then bonds them together as a whole.

The combined glass made in this process is called an LCD panel.

In the LCD industry, these two processes, TFT-array and cell layer, are finished by the same LCD manufacturer. In another word, those LCD factories supply LCD panels.

After that, the big ‘glass’ can be cut into pieces as needed in different sizes.

▶ LCD module (LCM) assembly

Using the cut-size LCD panel as the basic materials, LCM manufacturers proceed with the bonding of the backlight unit, and electrical components (like driver IC, FPC, etc.) onto the ‘glass’ panel, then assemble it with the outer frames (or bezel) for protection.

In the TFT display, it is common to do the custom in the LCM stage.

The size of the screen, the backlight unit, and the electrical system provides choices to cope with the requirement of the main system of the terminals.

Now you have known how the LCD and LCD module is produced in a factory in different steps.

Moreover, you still should understand some basic concepts and features of LCD, which are related to the display quality and the setting of your devices.

Actually, in the communication and development of a display, display manufacturers will provide specifications of the LCD as a basis for further discussion.

Here are the key concepts in the specification:

II. 8 Key Concepts of LCD and TFT-LCD

● Size of Screen

Display size uses the diagonal length of the actual visible area, the unit is an inch (1 inch =2.54 cm) in common.

● Aspect Ratio

The aspect ratio is the proportional relationship and ratio of the width to the height of the visible area of the LCD, also called the screen ratio.

The aspect ratio of LCD is mainly 4:3, 5:4, 16:10, and 16:9, the ratio of 16:9 is closer to the golden section ratio, which is more comfortable for human eyes to watch.

In the design of the TFT LCD module, H (horizontal) is usually used to represent the length, and V (vertical) represents the width.

● Active Area (AA)

The active area is the total area of the TFT LCD screen that can be displayed.

But in common, factories mark only the length and width of the area on the draw for easy understanding.

Through the display size (diagonal length) and aspect ratio of the LCD screen, the specific length and width of the effective display area can be calculated by using the Pythagorean theorem.

● Pixel

Pixel, one of the small dots that make up a screen display, is used as a unit of resolution.

● Pixel Pitch

PPI is the pixel density of a display, the number of pixels per inch size.

The display providing clearer images has a high PPI value.

Figure7 is the PPI calculation formula. (X: the number of pixels in length, Y: the number of pixels in width, Z: the size of the screen)

● Resolution

Resolution is a measure of the image display, which depends on the size of the dots that make up the image.