With rapid advances in technology LED display, LED display dot pitch getting smaller and smaller, and now the market has launched P1.4, P1.2 high density LED display, and began to use in command and control and video surveillance.
Large-screen monitor in the indoor market DLP and LCD splicing splicing LCD display technology both occupy the market opportunities, although they have their own advantages, but they are nothing but there is a common problem, that is, between the patchwork unit display. High density LED display has inherent advantages can be achieved seamless. High density screen pixels become smaller and smaller, more and more high-resolution display screen is sharp and detailed. When displaying standard definition images, you can fully meet the requirements of the resolution. If the high-density lamp lower and lower prices, is bound to high-density LED display will occupy a larger market for indoor video surveillance.
High density LED display with high-definition display, high refresh rate, seamless, good cooling system, easy accessibility and flexible features. With the increasingly smaller pixel pitch of LED placement, assembly, splicing process and structure raised higher and higher requirements. In this paper, some research on technological issues.
1, LED choice: more than P2 density screen the general 1515,2020,3528 lights, LED pin shape with J or L package. Lateral welding pin pads have reflective ink is poor, will be needed to increase the mask to improve contrast. Density to further improve, L or J package does not meet the minimum needs of the electrical properties of the pitch must be used QFN package. 1010 and 0505 the country star Crystal stations are used for this package.
Original QFN package unique welding process, this process is characterized by welding without lateral pin pads non-reflective, so that the color is very good. Further integration of all-black design molding, screen contrast increased by 50%, indicating that the application quality results contrast previous screen better.
2, the printed circuit board process selection: With the trend of high-density, 4-layer, 6-layer is employed, the printed circuit board will use micro vias and buried vias design, printed circuit pattern thin wire, microporation narrow spacing, mechanical processing used in the drilling process technology can not meet the requirements. Rapidly developing laser drilling technology will meet the micropores processing.
3, printing technology: too much, too little solder paste volume and offset printing directly affect the quality of welding high density screen lamp. After the correct PCB pad design needs to communicate with the manufacturers to implement the design, the size of the opening screen and printing parameters correct or not directly related to the amount of solder paste printing. General 2020RGB device uses laser 0.1-0.12mm thickness of electro-polished steel, 1010RGB following devices are recommended stencil thickness 1.0-0.8. Thickness, the opening size is proportional to the increasing amount of tin. High-density LED welding quality solder paste printing closely with thickness testing, SPC analysis and other functions will use the press plays an important significance reliability.
4. Mount Technology: High-density screen each RGB component placement subtle shift will result in Screen display unevenness, it will require a more precision placement equipment, Panasonic NPM equipment placement accuracy (QFN ± 0.03mm) to P1.0 meet the above requirements mount.
5, welding technology: reflow soldering temperature will cause excessive wetting is not balanced, it will inevitably cause the device leads to offset the imbalance in the wetting process. Excessive wind circulation can also cause displacement of the device. Try to choose more than 12-zone reflow soldering machine, chain speed, temperature, wind and other circulation as strict control of the project, that is, to meet the reliability requirements of welding, but also to reduce or prevent the device from the shift, try to control into the range of needs. Generally in the range of 2% as the pixel pitch control value.
6, box assembly: Box is different splicing module, the cabinet is directly related to the gap between flatness and modules assembled cabinet overall effect. Aluminum processing box, aluminum box is the current widely box type, flatness can be achieved within 10 silk. Module splicing gap between the two modules to assess the closest pixel pitch after the two-pixel lighting is too bright line, two pixels too far can cause dark lines. Need to be calculated before the measurement modules assembled patchwork, and then choose the relative thickness of the metal sheet is inserted as a rule be assembled in advance.
7, assembled Screen: assembled cabinet needs before they can be assembled into Screen display fine picture, video. But the box itself, dimensional tolerances and assembly tolerances cumulative effect of high density screen assembly can not be ignored. Between the cabinet and the cabinet recently pixel pitch of the device is too large, too small, dark line display, bright lines. Dark lines, bright lines issue is now high density screen can not be ignored, urgent need to overcome the problem. Some companies through posted 3m tape, box fine adjustment nut can be adjusted to achieve the best results.
8, the system card options: high density and uniformity of light and dark lines display, color LED device is different, accumulated current difference IC circuit design layout differences, differences in assembly criticism, some of the system card company through software correction reduces light and dark lines and luminance, chromaticity unevenness. Nova launched brightness, color correction system has been applied to various high-density screen, and achieved good display.
High density screen display with fine results, we must proceed from the various aspects of material selection, circuit design, temperature control, and crafts. We believe high density screen with the progress of technology, the price of the public of, will achieve greater and broader market share.