Analysis of fine pitch LED screen technology

With the demand of the market and the rapid progress of LED display technology, the dot pitch of LED displays is getting smaller and smaller. Now the market has launched small-pitch LED displays such as P1.4 and P1.2, and has been used in command and control, video surveillance, etc. field applications. Under the vigorous promotion of manufacturers, the characteristics of fine-pitch LED display, such as high-definition display, high refresh rate, seamless splicing, good cooling system, convenient and flexible disassembly and assembly, have been well known by the majority of industry users. However, further, when it comes to The specific process technology of small-pitch LED screens is rarely known to the general public. “I only know one and do not know the other.” The lack of professional knowledge has directly led to the emergence of blind spots in purchasing.

From a technical point of view, the smaller the pixel pitch of the small-pitch display screen, the higher the requirements for the LED mounting, assembly, splicing process and structure. This article will analyze the various process technologies of fine-pitch LED displays, so that users can have a more thorough understanding of fine-pitch LED products.

1. Packaging technology: Displays with a density above P2 generally use 1515, 2020, and 3528 lamps, and the LED pin shape adopts J or L packaging. If the pins are welded sideways, there will be reflections in the welding area, and the ink color effect will be poor. It is necessary to add a mask to improve the contrast. If the density is further increased, the L or J package cannot meet the application requirements, and the QFN package must be used. The characteristic of this process is that there are no laterally welded pins, and the welding area is non-reflective, which makes the color rendering effect very good. In addition, the all-black integrated design is molded by molding, and the contrast of the screen is increased by 50%, and the image quality of the display application is better than that of the previous display.

2. Printed circuit board technology: With the trend of high density, 4-layer and 6-layer boards are adopted. The printed circuit board will adopt the design of fine vias and buried holes. The mechanical drilling technology used in the technology can no longer meet the requirements. The rapidly developing laser drilling technology will satisfy the micro hole processing.

3. Printing technology: Too much or too little solder paste and printing offset directly affect the welding quality of high-density display lamps. The correct PCB pad design needs to be communicated with the manufacturer and implemented into the design. Whether the opening size of the stencil and the correct printing parameters are directly related to the amount of solder paste printed. Generally, 2020RGB devices use electro-polished laser stencils with a thickness of 0.1-0.12mm, and 1.0-0.8 thickness stencils are recommended for devices below 1010RGB. Thickness and opening size increase in proportion to the amount of tin. The quality of high-density LED soldering is closely related to solder paste printing. The use of functional printers such as thickness detection and SPC analysis will play an important role in reliability.

4. Mounting technology: The slight shift in the position of each RGB device on the high-density display screen will cause uneven display on the screen, which is bound to require higher precision of the mounting equipment.

5. Soldering process: If the reflow soldering temperature rises too fast, it will lead to unbalanced wetting, which will inevitably cause the device to drift during the process of wetting unbalance. Excessive wind circulation can also cause displacement of the device. Try to choose a reflow soldering machine with more than 12 temperature zones, chain speed, temperature rise, circulating wind, etc. as strict control items, that is, to meet the requirements of welding reliability, but also to reduce or avoid the displacement of components, and try to control it within the scope of demand. Generally, 2% of the pixel pitch is used as the control value.

6. Box assembly: The box is spliced with different modules. The flatness of the box and the gap between the modules are directly related to the overall effect of the box after assembly. Aluminum plate processing box and cast aluminum box are the most widely used box types at present. The flatness can reach within 10 wires. The splicing gap between modules is evaluated by the distance between the nearest pixels of the two modules. lines, two pixels too far will result in dark lines. Before assembling, it is necessary to measure and calculate the joint of the module, and then select a metal sheet of relative thickness as a fixture to be inserted in advance for assembly.

7. Screen assembly: The assembled box needs to be assembled into a screen before it can display refined pictures and videos. However, the dimensional tolerance of the box itself and the cumulative tolerance of the assembly cannot be ignored for the assembly effect of the high-density display. If the pixel pitch of the nearest device between the cabinet and the cabinet is too large or too small, dark lines and bright lines will be displayed. The problem of dark lines and bright lines is a problem that cannot be ignored in high-density displays and needs to be overcome urgently. Some companies make adjustments by sticking 3m tape and finely adjusting the nut of the box to achieve the best effect.

8. System card selection: high-density display light and dark lines and uniformity, color difference is the accumulation of LED device differences, IC current differences, circuit design layout differences, assembly differences, etc. Some system card companies can reduce light and dark lines through software correction. and uneven brightness and chromaticity. Nova’s brightness and chromaticity correction system has been applied to various high-density display screens, and has achieved better display effects.