There are many reasons for LED electronic display screen pixels out of control, and the most important reason is “led failure”. The main causes of LED failure can be divided into two aspects: one is the poor quality of LED itself; the other is the improper use of LED. Through the analysis, we conclude the corresponding relationship between LED failure mode and the above two main factors.
As mentioned above, many led failures can not be found in the regular inspection and testing of LEDs. In addition to the improper use of electrostatic discharge, high current (resulting in high junction temperature), external strength and other improper use, many led failures are caused by the difference of thermal expansion coefficient of LED chip, epoxy resin, bracket, inner lead, solid crystal glue, PPA cup and other materials under high temperature, low temperature, rapid temperature change or other harsh conditions It is a very complex work to detect the quality of the product.
Furthermore, for GaN based LEDs, electrostatic discharge is the biggest cause of failure. The mechanism of LED failure caused by electrostatic discharge is very complex. Equipment, tools, utensils and human body may carry static electricity and discharge it. The static electricity is hundreds of volts less, tens of thousands of volts high, and the discharge time is at nanosecond level. The blue-green tube failure in the production, installation and use of the display screen is often caused by the electrostatic discharge of the led-pn junction.
The international electrostatic Association strictly stipulates the standard ESD modes, which are mainly divided into human body discharge mode (HBM) and machine discharge mode (mm). The ESD sensitivity (ESDs) of devices in China can be divided into three levels (human mode): Level 1 is 0-1999v; Level 2 is 2000-3999v; Level 3 is above 4000V.
In general, the ESD sensitivity of LED is in the range of hundreds to tens of thousands of volts in human mode, but only tens to 500 volts in machine mode. Due to the complicated production process of LED display screen, it is difficult to prevent ESD. Therefore, the sensitivity of LED ESD should be 2 or above (human body mode), and electrostatic protection must run through the whole production process. [LED display manufacturer]