Laser rework for mini-LED chips on flexible PCB for mini-LED backlighting LCD display

In this paper, high-quality and high-speed laser soldering technology for Mini-LED backlighting for LCD display and fully automatic laser repair technology to remove attached tiny fault Mini-LED and attach a new good Mini-LED are introduced. For televisions or monitors, LCD Display technology has been quickly developed and saturated. And new OLED technology is now actively penetrating into this market. However, as an effort of extending LCD market and competing it against OLED quality, LCD technology is now accepting Mini-LED backlighting technology for local dimming applications. In this Mini-LED application, there are two technology huddles such as high-quality soldering and high throughput on ultra-thin flexible PCB. To meet these requirements, advanced soldering technology of LSR (Laser Selective Reflow) bonding technology is developed. LSR technology can make very good bolding quality including high-strength bonding with 1.5 to 2.0 times higher shear strength than conventional mass reflow technology and almost no PCB surface color change which is very important to generate complete black background when it is needed. To perform high-quality and high-speed laser reflow of more than ten-thousand Mini-LEDs on large size PCB substrate, 400mm long line beam using advanced flat-top optic and high-power laser were used. When fault Mini- LED chips are identified or wrong-position or wrong-gesture bonded Mini-LED chips are found, those Mini-LED chips should be repaired not to be throw out expensive whole finished backlight substrate with Mini-LEDs. For this purpose, very nice fully automatic laser repair technology is developed which is introduced in this presentation.