The display with density above P2 generally uses 1515, 2020, and 3528 lights, and the LED pin shape adopts J or L package. 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 increased, and the L or J package cannot meet the application requirements. A QFN package must be used. The characteristics of this process are no lateral welding pins and no reflection in the welding area, which makes the color rendering effect very good. In addition, the all-black integrated design is LED used for compression molding, and the screen contrast has been increased by 50%.
A slight shift in the position of each RGB device of a micro-pitch display will cause uneven LED parts of the screen, which will inevitably require higher accuracy of the mounting equipment.
Excessive temperature rise in reflow soldering will cause uneven wetting, 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 cost, 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.
Printed Circuit Board Process
With the development trend of micro-pitch displays, 4-layer and 6-layer boards have been adopted. Printed circuit boards will use micro-via and buried-hole designs, printed circuit pattern wires will be fine, and micro-holes will be narrowed. The mechanical drilling technology can no longer meet the requirements, and the rapidly developing laser drilling technology will meet the fine hole processing.
Too much and too little solder paste and printing offset directly affect the welding quality of micro-pitch display tube. 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. Micro-pitch 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 of role in reliability.
Screen Body 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 cabinet itself and the cumulative tolerance of the assembly can not neglect the effect of assembling the micro-pitch display. The pixel pitch of the nearest device between the cabinet and the cabinet is too large or too small for house, which will cause dark lines and bright lines to be displayed. The problem of dark lines and bright lines is a problem that cannot be ignored in current micro-pitch display screens 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 box is formed by splicing different modules. The flatness of the box and the gap between the modules directly affect 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 10 wires. The stitching gap between modules is evaluated by the distance between the nearest pixels of the two modules. The two pixels are too bright when they are lit. Line, two pixels too far can 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.
System Card Selection
Micro-pitch display light and dark lines and uniformity, chromatic aberration are the accumulation of LED device differences, IC current differences, circuit design layout differences, assembly differences, etc., some system card companies can reduce the light and dark lines and brightness, chroma Both. The high-performance system card is selected to correct the brightness and chrominance of the micro-pitch LED display, so that the display achieves better brightness and chromaticity uniformity, and achieves better display results.