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How to make LED Backlight

2021-03-08

The development of the LED backlight can be traced back to the Second World War. At that time, ultra-small tungsten filament lamps were used as the backlight of aircraft instruments. This is the initial stage of backlight development. After half a century of development, the backlight has now become an independent subject of electronics, and has gradually formed a research and development hotspot.


The service life of LED backlight is longer than that of cold light cathode tube (more than 5,000 hours), and it uses DC voltage. It is usually used in small monochrome displays, such as telephones, remote controls, microwave ovens, air conditioners, instrumentation, stereo audio equipment, etc. . However, its brightness is currently not enough to provide a back light source for large transmissive displays.


The structure of LED backlight and CCFL backlight is basically the same. The main difference is that LED is a point light source, while CCFL is a line light source. From a long-term trend, the existence of LED backlight technology as a replacement technology product will certainly slowly spread. The service life of LED backlight is longer than EL (more than 5000 hours), and it uses DC voltage. It is usually applied to small monochrome displays, such as telephones, remote controls, microwave ovens, air conditioners, instrumentation, stereo audio equipment, etc. However, its brightness is currently not enough to provide a back light source for large transmissive displays.


Next, get a preliminary understanding of the production process of LED backlight:


A. Cleaning: Use ultrasonic to clean PCB or LED lead frame and dry.


B. Mounting: After preparing the electrode on the bottom of the LED chip (large wafer) with silver glue, expand it, and place the expanded chip (large wafer) on the crystal piercing table, and use the crystal pen to move the die one by one under the microscope. It is installed on the corresponding pad of the PCB or LED bracket, and then sintered to cure the silver glue.


C, pressure welding: use aluminum wire or gold wire welding machine to connect the electrode to the LED die for the lead of current injection. The LED is directly mounted on the PCB, generally using an aluminum wire welding machine. (A gold wire welding machine is required to make white light TOP-LED)


D. Package: The LED die and the bonding wire are protected by epoxy through dispensing. Dispensing glue on the PCB has strict requirements on the shape of the glue after curing, which is directly related to the brightness of the finished backlight. This process will also take on the task of phosphor (white LED).


E. Soldering: If the backlight is SMD-LED or other packaged LEDs, the LED needs to be soldered to the PCB board before the assembly process.


F, film cutting: use a punch to die-cut various diffusion films and reflective films required by the backlight.


G. Assembly: According to the drawing requirements, manually install the various materials of the backlight in the correct position.


H. Test: Check whether the photoelectric parameters of the backlight source and the uniformity of the light are good.


I. Packaging: The finished products are packaged and stored as required.

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