The led display is the same as other items, and it is inevitable to encounter such problems or precautions during use. When using a full-color led large screen, there may be eight problems that cause difficulty or affect the use of the large screen and extend its useful life.
1, heat dissipation design
When the led work, it will be hot. If the temperature is too high, it will affect the decay speed and stability of the LED. Therefore, 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.
2, mixed lights
LEDs of the same color with different brightness levels need to be mixed with lights, or inserted into the light pattern according to the discrete pattern to ensure the consistency of the brightness of each color of the whole screen. If there is a problem in this process, there will be a phenomenon that the local brightness of the large screen is inconsistent, which directly affects the display effect of the large screen of the LED.
3, design current value
The nominal current of the LED is 20mA. It is generally recommended that the maximum current used is not more than 80% of the nominal value. Especially for large screens with small dot spacing, the current value should be reduced due to poor heat dissipation conditions. According to experience, due to the inconsistency of the red, green and blue LED attenuation speeds, the current values ​​of the blue and green LEDs are purposely reduced to maintain the consistency of the white balance after long-term use of the large screen.
4, drive circuit design
The arrangement of the driver board driver IC on the large screen module also affects the brightness of the LED. Since the driving IC output current is too far away on the PCB, the voltage drop of the transmission path is too large, which affects the normal operating voltage of the LED and causes its brightness to decrease. We often find that the brightness of the LEDs around the large screen module is lower than the middle, which is why. Therefore, to ensure the consistency of the brightness of the large screen, it is necessary to design the drive circuit distribution map.
5, control the verticality of the lamp
For in-line LEDs, there must be enough process technology to ensure that the LEDs are perpendicular to the PCB. Any deviation will affect the brightness consistency of the already set LEDs, and the color blocks with inconsistent brightness will appear.
6, virtual welding control
When the LED large screen is not bright, there are often more than 50% probability caused by various types of virtual soldering, such as LED pin soldering, IC pin soldering, pin rowing and soldering. Improvements in these problems require rigorous improvements in the process and enhanced quality inspections. The vibration test before leaving the factory is also a good test method.
7, over wave soldering temperature and time
The temperature of the wave front welding and the furnace time must be strictly controlled. The recommended temperature is: preheating temperature 100 °C ± 5 °C, maximum not exceeding 120 °C, and the preheating temperature rise is required to be stable, the welding temperature is 245 °C ± 5 °C, welding The time is recommended not to exceed 3 seconds. After the furnace is over, avoid vibrating or impacting 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. The overheated or fluctuating temperature will directly damage the LED or cause LED quality hazard, especially for small and thin LEDs such as 3mm.
8, anti-static
Led large screen assembly factory should have good anti-static measures. Special anti-static grounding, anti-static floor, anti-static soldering iron, anti-static mat, anti-static ring, anti-static clothing, humidity control, equipment grounding (especially cutting machine) are basic requirements, and should be regularly tested by static electricity meter. . For more information, please continue to visit the LED display of the China Information Network's industry information channel.
Mixed Assembly
What is PCB SMT assembly?
With the development of electronic technology, the demand for HDI PCB and High Frequency Board has increased. In order to reduce the cost of PCBA Manufacturing, more SMT chip technology is now being purchased. SMT patch refers to the abbreviation of a series of technological processes that are processed on the basis of PCB, and PCB (Printed Circuit Board) is a printed circuit board. SMT is surface mount technology (Surface Mounted Technology) (abbreviation for Surface Mounted Technology), and it is the most popular technology and process in the electronics assembly industry. It is a kind of surface assembly Electronic Components (SMC/SMD for short, chip components in Chinese) that are mounted on the surface of a printed circuit board (Printed Circuit Board, PCB) or other substrates without leads or short leads. Circuit assembly technology in which reflow soldering or dip soldering is used for soldering and assembly. Under normal circumstances, the electronic products we use are designed by PCB plus various Electronic Components such as Electronic Resistor And Capacitor according to the designed circuit diagram, so all kinds of electrical appliances need various smt patch processing techniques to process.
1. Silk screen: Its function is to leak solder paste or patch glue onto the PCB pads to prepare for the soldering of components. The equipment used is a screen printing machine (screen printing machine), located at the forefront of the SMT production line.
2. Dispensing: It is to drip glue onto the fixed position of the PCB board, and its main function is to fix the components on the PCB board. The equipment used is a glue dispenser, located at the forefront of the SMT production line or behind the testing equipment.
3. Mounting: Its function is to accurately mount the surface mount components to the fixed position of the PCB. The equipment used is a placement machine, located behind the screen printing machine in the SMT production line.
5. Reflow soldering: Its function is to melt the solder paste, so that the surface assembly components and the PCB board are firmly bonded together. The equipment used is a reflow oven, located behind the placement machine in the SMT production line.
6. Cleaning: Its function is to remove the solder residues such as flux that are harmful to the human body on the assembled PCB board. The equipment used is a washing machine, and the location may not be fixed, it may be online or offline.
7. Inspection: Its function is to inspect the welding quality and assembly quality of the assembled PCB board. The equipment used includes magnifying glass, microscope, online tester (ICT), flying probe tester, automatic optical inspection (AOI), X-RAY inspection system, functional tester, etc. The location can be configured in a suitable place on the production line according to the needs of the inspection.
8. Rework: Its function is to rework the PCB boards that have failed to detect faults. The tools used are soldering irons, rework stations, etc. Configured at any position in the production line.
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