Eight points determine the quality of LED full-color display

June 21, 2021

1. Anti-static

The display assembly factory should have good anti-static measures. Dedicated anti-static ground, anti-static floor, anti-static soldering iron, anti-static table mat, anti-static ring, anti-static clothing, humidity control, equipment grounding (especially the foot cutter), etc. are all basic requirements, and should be checked regularly with a static meter .

2. Drive circuit design

The arrangement of the driver IC on the driver circuit board on the display module will also affect the brightness of the LED. Since the output current of the driver IC is transmitted over a long distance on the PCB board, the voltage drop of the transmission path will be too large, which will affect the normal operating voltage of the LED and cause its brightness to decrease. We often find that the brightness of the LEDs around the display module is lower than in the middle, which is the reason. Therefore, to ensure the consistency of the display screen brightness, it is necessary to design the driver circuit distribution diagram.

3. Design current value

The nominal current of the LED is 20mA. Generally, it is recommended that the maximum operating current be no more than 80% of the nominal value. Especially for displays with small dot pitch, the current value should be lowered due to poor heat dissipation conditions. According to experience, due to the inconsistency of the attenuation speed of the red, green, and blue LEDs, the current value of the blue and green LEDs should be reduced in a targeted manner to maintain the consistency of the white balance of the display screen after long-term use.

4. Mixed lights

The LEDs of the same color and different brightness levels need to be mixed, or inserted according to the light insertion diagram designed according to the discrete law to ensure the consistency of the brightness of each color on the entire screen. If there is a problem in this process, the local brightness of the display will be inconsistent, which will directly affect the display effect of the LED display.

5. Control the verticality of the lamp

For in-line LEDs, there must be sufficient process technology to ensure that the LED is perpendicular to the PCB board when passing the furnace. Any deviation will affect the brightness consistency of the LED that has been set, and color blocks with inconsistent brightness will appear.

6. Wave soldering temperature and time

The temperature and time of wave front welding must be strictly controlled. It is recommended that the preheating temperature is 100℃±5℃, and the highest temperature should not exceed 120℃, and the preheating temperature must rise smoothly. The welding temperature is 245℃±5℃. It is recommended that the time should not exceed 3 seconds, and do not vibrate or shock the LED after the furnace until it returns to normal temperature. The temperature parameters of the wave soldering machine should be checked regularly, which is determined by the characteristics of the LED. Overheating or fluctuating temperature will directly damage the LED or cause hidden quality problems, especially for small-sized round and oval LEDs such as 3mm.

7. Welding control

When the LED display does not light up, there is often more than 50% probability that it is caused by various types of virtual soldering, such as LED pin soldering, IC pin soldering, pin header soldering, etc. The improvement of these problems requires strict improvement of the process and strengthened quality inspection to solve. The vibration test before leaving the factory is also a good inspection method.

8. Heat dissipation design

LED will generate heat when it is working, too high temperature will affect the attenuation speed and stability of the LED, so the heat dissipation design of the PCB board and the ventilation and heat dissipation design of the cabinet will affect the performance of the LED.

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