LED screen yin and yang screen problem analysis and technical solutions

With the development of small pitch LED display technology, the viewing distance continues to shorten, the LED chip, PCB board and patch process precision requirements are increasing. Once in the large pitch era imperceptible manufacturing defects, now in close viewing exposed, yin and yang screen problem has become an important factor affecting the quality of the display.

1.What is the LED yin and yang screen phenomenon?

LED screen yin and yang screen problem, refers to different sides of the screen from the observation, the brightness of the visual difference between dark or light. Commonly seen in the left look darker right look brighter or the opposite situation, affecting the overall picture consistency and display effect.

2.The main reasons for yin and yang screen

2.1 LED lamp bead selection problems

small pitch LED screen commonly used CHIP-type and TOP-type lamp beads. TOP-type lamp beads if the 90 ° right-angle bending pin, in the uneven distribution of solder paste is likely to lead to tilt lamp beads. Preferred hook angle design pin LED lamp beads, and strictly control the pin flatness and size differences, can effectively reduce the risk of tilt, improve the mounting flatness and screen display quality.

2.2 Improper control of the placement process

stencil printing and furnace temperature control directly affects the uniformity of solder paste and reflow soldering quality. Small size LED pins are easy to block the stencil, through the introduction of new coating materials to reduce drawing, and regularly clean the stencil. At the same time, accurate control of the furnace temperature curve to ensure the consistency of reflow soldering for each production shift is an important means of preventing yin and yang screen.

2.3 PCB Manufacturing Precision Problems

Unreasonable PCB pad design or insufficient printing precision can also trigger uneven solder paste distribution. Reasonable optimization of the size of the pad and window ratio, to avoid ink accumulation phenomenon, strengthen the PCB production process of size and flatness control, is to improve the patch quality, eliminate the key to the phenomenon of yin and yang screen.

3.Technical solutions for yin and yang screen

• To effectively solve the problem of LED display yin and yang screen, we should start from the following aspects:
• Select high quality LED lamp beads, give priority to the use of hook and corner pin design, reduce the tilt caused by uneven solder paste.
• Strengthen the SMD process control, optimize the stencil material and design, the implementation of accurate furnace temperature curve monitoring.
• Improve the PCB board manufacturing precision, optimize the layout of pads and open windows, to eliminate the impact of ink accumulation.

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