Analysis of various process problems of high-density LED display?
With the rapid progress of LED display technology, the dot pitch of LED display screens is getting smaller and smaller. Now the market has launched high-density LED display screens of P1.4 and P1.2, and it has begun to be applied in the field of command control and video surveillance.
In the indoor monitoring large-screen market, two display technologies, DLP splicing and LCD liquid crystal splicing, dominate the market. Although they have their own advantages, they have a common problem: the seam between display units. High-density LED displays have inherent advantages to achieve seamless splicing. The pixels of the high-density display are getting smaller and smaller, the resolution is getting higher and higher, and the display picture is clearer and more delicate. When displaying standard high-definition images, the resolution can be fully met. If the price of high-density lamps is getting lower and lower, high-density LED displays are bound to occupy a larger market in the field of indoor video surveillance.
The high-density LED display has high-definition display, high refresh frequency, seamless splicing, good heat dissipation system, convenient and flexible disassembly and so on. With the ever-smaller pixel pitch, higher and higher requirements are placed on the mounting, assembly, splicing process and structure of LEDs. This article makes some discussions on process issues.
1. LED selection: 1515, 2020, and 3528 lights are generally used for displays with a density of P2 or higher. The LED pin shape is packaged in J or L. Side welding pins, the welding area will be reflective, the ink effect is poor, it is necessary to add a mask to improve the contrast. The density is further improved. The package of L or J cannot meet the minimum electrical performance spacing requirements, and QFN packaging must be used.
Unique QFN package welding unique process, this process is characterized by no side welding pins, no reflection in the welding area, so that the color rendering effect is very good. In addition, the all-black integrated design is used for compression molding, and the screen contrast is increased by 50%. The display application quality is better than the previous display.
2. Printing technology: Too much and too little solder paste and printing offset directly affect the welding quality of high-density display lamp tubes. The correct PCB pad design needs to be implemented in the design after communicating with the manufacturer. The correct opening size of the screen and the printing parameters are directly related to the amount of solder paste printed. Generally, 2020RGB devices use 0.1-0.12mm electro-polished laser stencils. Devices below 1010RGB are recommended to use 1.0-0.8 thickness stencils. Thickness and opening size increase in proportion to the amount of tin. High-density LED soldering quality is closely related to solder paste printing. The use of functional printing machines with thickness detection and SPC analysis will play an important role in reliability.
3. Printed circuit board process selection: With the high-density trend, 4-layer and 6-layer boards are used. The printed circuit board will use micro-via and buried-hole design, and the printed circuit pattern conductors will be fine and the micro-holes will be narrowed. The mechanical drilling technology used in processing has been unable to meet the requirements. The rapid development of laser drilling technology will meet micro-hole processing.
4. Box assembly: The box is formed by splicing 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 boxes and cast aluminum boxes are widely used at present, and the flatness can reach within 10 wires. The stitching gap between modules is evaluated based on the distance between the nearest pixels of the two modules. If the two pixels are too close to light, they will be bright lines. If the two pixels are too far away, they will cause dark lines. Before assembling, it is necessary to measure and calculate the module seam, and then use a metal sheet with a relative thickness as a jig to insert it in advance for assembly.
5. Mounting technology: A slight shift in the position of each RGB device on a high-density display will cause uneven display of the screen body, which will inevitably require higher accuracy of the placement equipment. The placement accuracy of Panasonic NPM equipment (QFN ± 0.03mm) will Meet the requirements of P1.0 and above.
6. 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 and other accusations. Some system card companies can reduce the light and dark lines through software correction. And uneven brightness and chromaticity. Nova launched the brightness and chromaticity correction system that has been applied to various high-density displays and achieved good display results.
7. Soldering process: If the reflow soldering temperature rises too quickly, wetting will be uneven, which will inevitably cause the device to shift during the wetting imbalance process. Excessive wind cycles can also cause device displacement. Try to choose a reflow soldering machine with a temperature of 12 or more. Chain speed, temperature rise, circulating wind, etc. are strictly controlled items, that is, to meet the reliability requirements of welding, and to reduce or avoid the displacement of components, try to control to within the required range. Generally, the 2% range of the pixel pitch is used as the control value.
8. Assembly of the screen body: The assembled box needs to be assembled into a screen body before it can display fine pictures and videos. However, the dimensional tolerance of the cabinet itself and the cumulative tolerance of the assembly can not be ignored in the assembly effect of the high-density display. The pixel pitch of the nearest device between the cabinet and the cabinet is too large or too small, which will cause dark lines and bright lines to be displayed. The problem of dark lines and bright lines is a problem that can not be ignored in high-density displays, and needs to be overcome urgently. Some companies adjust by applying 3m tape and fine adjustment nuts on the box to achieve the best results.
The high-density display has a refined display effect, which must start from various links such as material selection, circuit design, temperature rise control, and technology. It is believed that with the advancement of technology and the popularization of prices, high-density displays will achieve a larger and wider market share.
If you want to know more, our website has product specifications for the LED display, you can go to ALLICDATA ELECTRONICS LIMITED to get more information