LED display manufacturers reveal eight aspects of the small spacing production process

In the indoor monitoring large screen market, DLP splicing and LCD LCD splicing these two display technologies occupy the market leader, although they have their own advantages, but they all have a common problem, that is, the seam between the display unit.High-density LED displays have the inherent advantage of seamless stitching. The pixel of high-density display is getting smaller and smaller, the resolution is getting higher and higher, the display picture is clearer and finer. In the display of standard hd images, can fully meet the resolution requirements. If the price of high-density lamp tube is lower and lower, it is inevitable that high-density LED display will occupy a larger market in the field of indoor video surveillance.

The high-density LED display features high-definition display, high refresh frequency, seamless stitching, good heat dissipation system, convenient and flexible disassembly. With the smaller and smaller pixel spacing, the mounting, assembly, splicing process and structure of LED put forward higher and higher requirements. In this paper, some technical problems are discussed.

1, LED selection: P2 above the density of the display generally use 1515, 2020, 3528 lights, LED pin shape using J or L packaging. Side welding pin, welding area will be reflective, poor ink effect, it is necessary to increase the mask to improve contrast. When the density is further increased, the packaging of L or J cannot meet the requirement of minimum electrical performance spacing, so QFN packaging mode must be adopted. Nationstar 1010 and Crystal 0505 are used in this package.

Unique QFN package welding process, this process is characterized by no side welding pin, welding area without reflection, so that the color effect is very good. In addition, the use of black integrated design molding, screen contrast increased by 50%, display application picture quality effect is better than the previous display.

Unique QFN package welding process, this process is characterized by no side welding pin, welding area without reflection, so that the color effect is very good. In addition, the use of black integrated design molding, screen contrast increased by 50%, display application picture quality effect is better than the previous display.

3, printing technology: too much, too little solder paste amount and printing offset directly affect the welding quality of high density display lamp. The correct PCB pad design needs to be implemented in the design after communication with the manufacturer. The opening size of the screen and the correct printing parameters are directly related to the amount of solder paste printed. Generally, electropolishing laser stencil of 0.1-0.12mm thickness is used for 2020RGB devices, and 1.0-0.8 thickness stencil is recommended for devices below 1010RGB. Thickness and opening size increase in proportion to tin content. High density LED welding quality is closely related to solder paste printing, and the use of printing machines with thickness detection, SPC analysis and other functions will play an important role in reliability.

4. Mounting technology: the slight deviation of the position of the RGB components in the high-density display will lead to the uneven display of the screen body, which will inevitably require the mounting equipment to have higher accuracy. The mounting accuracy of Panasonic NPM equipment (QFN±0.03mm) will meet the mounting requirements of P1.0 and above.

5. Welding process: Excessive temperature rise of reflow welding will lead to unbalance of wetting, which will inevitably lead to deviation of the device in the process of unbalance of wetting.

Excessive wind circulation can also cause device displacement. Try to select the reflow welding machine above the temperature zone of 12, chain speed, temperature rise, circulating wind power and other items as strict control, namely to meet the welding reliability requirements, but also to reduce or avoid the displacement of devices, as far as possible to control to the demand range.

Generally, the 2% range of pixel spacing is used as the control value.

6. Box assembly: The box is composed of different modules. The flatness of the box and the gap between the modules are directly related to the overall effect of the box assembly.

Aluminum plate processing box, cast aluminum box is now widely used box type, flatness can reach 10 wire. Splicing gaps between modules are evaluated by the distance between the nearest pixels of the two modules. If two pixels are too close, a bright line will be lit, and if two pixels are too far, a dark line will be created. Before assembling, it is necessary to measure and calculate the joint of the module, and then select the metal sheet of relative thickness as the fixture to insert in advance for assembling.

7. Screen body assembly: The assembled box needs to be assembled into a screen body before fine pictures and videos can be displayed. But the size tolerance of the box itself and the cumulative tolerance of assembly can not be ignored for the assembly effect of high density display.

If the pixel spacing between the box and the nearest device is too large or too small, dark and bright lines will be displayed. The problem of dark line and bright line is the problem of high density display screen which can not be ignored and needs to be solved urgently. Some companies use 3M tape and small adjusting nuts to adjust the box to achieve the best results.

8, system card selection: high density display light and shade line and uniformity, color difference is LED device difference, IC current difference, circuit design layout difference, assembly difference and other accumulated criticism, some system card companies through software correction can reduce light and shade line and brightness, color imbalance. Nova launched brightness, chromaticity correction system has been applied to all high density display, and achieved good display effect.

Conclusion: High density display screen has fine display effect, so we must start from material selection, circuit design, temperature rise control, process and other aspects. It is believed that with the progress of technology and the popularization of the price of high-density display, it will gain a larger and wider market share.