Issues to be paid attention to in the design and production of full-color LED display screens

LED display screens, like other items, will inevitably encounter various problems and precautions during use.

1. Anti-static

LED display assembly factories should have good anti-static measures. Special anti-static ground, anti-static floor, anti-static soldering iron, anti-static mat, anti-static ring, anti-static clothing, humidity control, equipment grounding (especially the foot cutting machine), etc. are all basic requirements, and they should be tested regularly with an anti-static meter.

2. Design current value

The nominal current of LED is 20mA. It is generally recommended that the maximum current used should not exceed 80% of the nominal value. Especially for displays with small dot pitch, the current value should be reduced due to poor heat dissipation conditions. According to experience, due to the inconsistency of the attenuation speed of red, green and blue LEDs, the current values ​​of blue and green LEDs should be reduced in a targeted manner to maintain the consistency of white balance after long-term use of the display.

3. Heat dissipation design

LED generates heat when working. Too high temperature will affect the attenuation speed and stability of LED. Therefore, the heat dissipation design of PCB board and the ventilation and heat dissipation design of the box will affect the performance of LED.

4. Driving circuit design

The arrangement of the driver IC on the driver circuit board of 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 in the transmission path will be too large, which will affect the normal working voltage of the LED and reduce its brightness. We often find that the brightness of the LEDs around the display module is lower than that in the middle. This is the reason. Therefore, to ensure the consistency of the brightness of the display, it is necessary to design a good distribution diagram of the driver circuit.

5. Mixed lights

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

6. Control the verticality of the light

For direct-plug LEDs, sufficient process technology must be used to ensure that the LED is perpendicular to the PCB board during the furnace. Any deviation will affect the brightness consistency of the already set LEDs, resulting in color blocks with inconsistent brightness.

7. Wave soldering temperature and time

The temperature and furnace time of wave soldering must be strictly controlled. The recommended temperature is: preheating temperature 100℃±5℃, the maximum temperature should not exceed 120℃, and the preheating temperature should rise steadily. The welding temperature is 245℃±5℃, and the welding time is recommended not to exceed 3 seconds. After the furnace, do not vibrate or impact the LED 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 temperatures will directly damage the LED or cause quality risks for the LED, especially for small sizes such as 3mm round and oval LEDs.

8. Control of cold solder joints

When the LED display screen fails to light up, there is often a 50% chance that it is caused by various types of cold soldering, such as cold soldering of LED pins, cold soldering of IC pins, cold soldering of pin headers, etc. To improve these problems, strict process improvement and enhanced quality inspection are required. Vibration testing before leaving the factory is also a good inspection method.