The Production Process of Small-pitch LED Display Wall

With the rapid development of display technology, small-pitch LED screens have become increasingly popular in applications such as command and control and video surveillance. However, to achieve HD and stable effects, it is inseparable from the powerful manufacturing process behind it. Today, Doitvision will introduce you to the small-pitch LED video walls production process technology.

Market trends and advantages of small-pitch LED screens

In the indoor monitoring large-screen market, DLP splicing and LCD splicing technologies once dominated. However, both technologies have an obvious shortcoming- there are seams in the display unit. The seams not only affect the overall coherence, but also reduce the visual experience. The small-pitch LED display screen has the inherent advantage of seamless splicing.

Nowadays, Due to the resolution is increasing, They can also present a clearer and more delicate display picture. Taking the current mainstream P1.5 and P1.2 LED display screens as an example, they can easily meet most high-definition resolution requirements. With the gradual reduction in the price of high-density LEDs and the new packaging technology breakthrough, the market share of small-pitch LED screens is expected to increase further.

Next, let’s take a look at these manufacturing processes.

In-depth analysis of the manufacturing process of small-pitch LED video screens

LED lamp beads

Conventional LED lamp selection

For LED display above P2, LED display manufacturers usually use 1515, 2020, 3528 and other LEDs. The pin shape of these LEDs mostly adopts J or L packaging. However, there is an obvious problem with this packaging method. The side welding pins will cause reflection in the welding area, which will affect the ink color effect. In order to make up for this defect and improve the contrast of the picture, an additional mask is required.

Packaging upgrade under reduced pixel pitch

With the continuous increase in the density of LED display screens, the L or J packaging method can no longer meet the requirements of the minimum electrical performance spacing. At this time, the QFN packaging method came into being. Both Nationstar’s 1010 and Kingligt’s 0505 use this advanced packaging technology.

QFN packaging has a unique welding process. It abandons the side welding pins, so that there is no reflection problem in the welding area. This design can greatly improve the color rendering effect, making the colors more vivid and realistic.

In addition, the QFN package also uses an all-black integrated design molding technology to increase the contrast of the picture by 50%. Compared with previous LED display screens, the small-pitch LED screens using QFN packages have made a qualitative leap in picture quality.

Printed circuit board process

PCB Board layer and hole design under high-density trend

As small-pitch LED displays develop towards high density, the requirements for printed circuit boards are getting higher and higher. In order to meet the needs of high-density circuit layout, 4-layer and 6-layer boards have gradually become the mainstream choice.

At the same time, PCBs have begun to adopt micro-via and buried hole designs, and the wires of printed circuit graphics have become thinner, with a clear trend of micro-holes and narrow pitches.

Introduction of laser drilling technology

The traditional mechanical drilling process technology is no longer able to process these micro-holes. The rapid development of laser drilling technology provides an effective way to solve this problem. Laser drilling has the characteristics of high precision and high efficiency. It can accurately process micro-holes to meet the strict requirements of small-pitch LED screens for circuit board processing, thereby ensuring the stability and reliability of the circuit.

Printing technology

The influence of solder paste amount and printing offset

In the production process of small-pitch LED video wall, the amount of solder paste and the offset of printing have a crucial impact on the welding quality of small-pitch LED display screen lamps.

• If the amount of solder paste is too much, it may cause the lamp to short-circuit;
• if the amount of solder paste is too little, the welding will be unstable and affect the normal operation of the lamp.
• If the printing offset is too large, the position of the lamp will be inaccurate, which will affect the display effect of the entire display.

PCB pad design and stencil parameter optimization

In order to ensure printing quality, correct PCB pad design is essential. At the same time, the opening size and printing parameters of the stencil are also directly related to the amount of printed solder paste. Generally speaking, 2020RGB devices use an electropolished laser steel mesh with a thickness of 0.1-0.12MM, while devices below 1010RGB are recommended to use a steel mesh with a thickness of 1.0-0.8. In addition, the thickness and opening size increase proportionally with the amount of tin.

In addition, the use of printers with functions such as thickness detection and SPC analysis can monitor and adjust the printing process in real time, further improving the printing quality.

Mounting technology

The importance of precision requirements

The position accuracy requirements of each RGB device of the small-pitch LED video screen are extremely high. Even a slight offset can cause uneven display, color deviation or inconsistent brightness. Therefore, the mounting equipment must have higher precision to meet production needs.

Advantages of Panasonic NPM equipment

Panasonic NPM equipment performs well in the mounting small-pitch LED screens. Its mounting accuracy (QFN±0.03mm) can meet the mounting requirements of P1.0 and above. The equipment uses advanced mounting technology and a precise control system to ensure that each RGB device is accurately mounted in the specified position. So it provides a strong guarantee for the uniform display of the display screen.

Soldering process

Challenges of reflow soldering

Reflow soldering is a key link in the production of small-pitch LED screens. In this process, excessive temperature rise will lead to uneven wetting, causing the device to shift during the wetting imbalance process. Excessive wind circulation will also cause displacement of components and affect welding quality.

Strict control of process parameters

In order to ensure welding quality, it is necessary to choose a reflow soldering machine with more than 12 temperature zones as much as possible, and strictly control parameters such as chain speed, temperature rise, and circulating wind force. The setting of these parameters must not only meet the welding reliability requirements, but also minimize or avoid the displacement of components. Generally speaking, taking the 2% range of pixel pitch as the control value can effectively ensure the welding quality and ensure the stability and reliability of the display.

Cabinet assembly:

Cabinet type and flatness

The cabinet is spliced by different LED modules. The cabinet  flatness and the gap between modules are directly related to the overall effect after the cabinet is assembled. At present, aluminum plate processing cabinets and cast aluminum cabinets are the most widely used cabinet types. Their flatness can reach within 10 silks, which can provide a flat and stable installation foundation for the display.

Control of module joints

The control of the joint gap between modules is the key to cabinet assembly. It is usually evaluated by the spacing between the closest pixels of the two modules. If two pixels are too close, bright lines will appear after lighting up; if two pixels are too far, dark lines will appear. In order to solve this problem, LED screen manufacturers need to make precise measurements before assembly, calculate the module joints, and then select metal sheets of relatively thick thickness as jigs to be inserted in advance for assembly, so that the joint gaps between modules can meet the requirements.

Screen assembly

The influence of tolerance on assembly effect

The assembled cabinet needs to be assembled into a screen to achieve refined picture and video display. However, the size tolerance of the cabinet itself and the cumulative tolerance of assembly have an important influence on the assembly effect of small-pitch LED display screens. If the pixel spacing of the nearest device between the cabinets is too large or too small, it will cause dark or bright line problems.

Exploration of adjustment methods

The problem of dark and bright lines is a difficult problem that small-pitch LED display screens are currently facing and need to be overcome. Some LED screen manufacturers make adjustments by sticking 3M tape and fine-tuning nuts on the cabinet to reduce the appearance of dark and bright lines, thereby achieving the best display effect. Although these methods can improve the assembly effect to a certain extent, continuous exploration and innovation are still needed to find a more perfect solution.

System card selection

The root cause of the problem of light and dark lines and uniformity

If the small-pitch LED display has problems such as light and dark lines, uniformity, and color difference, it is often caused by the accumulation of multiple factors such as LED device differences, IC current differences, circuit design layout differences, and assembly differences. These problems seriously affect the display effect of the display and reduce the user’s visual experience.

Correction effect of the system card

In order to solve these problems, some LED system card companies use software correction technology to reduce light and dark lines and uneven brightness and chromaticity. For example, the Nova brightness and chromaticity correction system has been applied to various small-pitch  LED display screens. It has achieved good display effects. Nova’s point-by-point correction system can accurately adjust the brightness and chromaticity of each pixel according to the actual situation of the display, making the display effect of the entire display more uniform and consistent.

Conclusion:

Small-pitch LED screens have huge commercial potential in the indoor displays. However, in order to keep the small-pitch LED screens good, LED display manufacturers must start from material selection, circuit design, temperature rise control, process and other aspects, and strictly control every detail.

Doitvision has a strict quality control system in small-pitch LED display manufacturing, which makes our screens have good quality at a reasonable price.

With the continuous advancement of technology, the performance of small-pitch LED screens will continue to improve and the price will gradually decrease. For example, the latest COB LED screens will achieve a larger and wider market share, bringing a more exciting visual experience. If you need a HD small-pitch LED display screen, you can contact us at will.