Technical differences and difficulties between Mini LED and Micro LED
Mini led and Micro led are very advanced display technologies recently, and now there are two forms: 1. Use small led lamp beads instead of tft display or OLED for direct display. 2. Use LED lamp beads to provide a smarter led backlit for tft display to achieve high contrast and high refresh rate.
Mini led and Micro LED are called the next generation display technology beyond AMOLED. Mini LED refers to “sub-millimeter light emitting diode”, while Micro LED is the abbreviation of “micro light emitting diode”. The boundary between their chip sizes is 100 μm (0.1 mm). The main difference between them is the size of the LED chip. Mini LED is mainly used for direct display, and Micro LED is mainly used for backlight with partition control, but Micro LED can also be used for direct display. Compared with traditional liquid crystal technology and AMOLED technology, Micro LED and Mini LED displays have the advantages of fast response and long service life, but at the same time, they also have the problems of low yield and large thickness.
Classification of Mini led and Micro led
Mini LED and Micro LED are divided into direct display products and backlight products. There is almost no actual mass production of direct display products, and most of them are small-sized and high-resolution products, which are used in the AR/VR field. Backlight products have low requirements on the chip size of LEDs, and there are many mass-produced products, such as Apple’s monitors and flat-panel products. At present, the most important factor for the development of Micro LED and mini led is the mass transfer of LED chips. Direct display products use LED chips as sub-pixels. The pursuit of high resolution means the need for small LED chips, such as HD resolution High-rate products will use 720x1280x3=2,764,800 LED chips, and the large-area, large-quantity LED transfer packaging technology is not yet mature, so most direct display products are products below 1 inch. The difficulty of backlight LED products is lower than that of direct display products. It uses LED lamp beads to provide light source for LCD display screen after uniform light and achieves better display effect by controlling the brightness of LED and LCD screen.
Apple Mini LED backlit product for higher contrast and higher brightness
Difficulties in the development of Min LED and Micro LED
There are high requirements for the mass transfer and packaging speed of Min LED and Micro LED. The transfer speed needs to be millions of pieces per hour, the transfer reliability needs to meet 99.9999%, and the transfer accuracy needs to be controlled within ±5 μm. In recent years, the remarkable progress of mass transfer technology has made it possible to realize the batch integration of Micro LED chips, including the most widely recognized laser transfer technology, contact transfer technology and self-assembly technology. Here, Huang Yong’an’s team from the School of Mechanical Science and Engineering of Huazhong University of Science and Technology and the State Key Laboratory of Digital Manufacturing Equipment and Technology published “Giant Array of Large-area and High-Density Micro LEDs in the International Journal of Extreme Manufacturing (IJEM)”. A review of mass transfer technology, systematically summarizing the research progress of mass transfer technology and emphasizing their potential application value.
Process and application of Micro LED and Mini LED chips
Two methods of LED chip massive transfer
Three problems in the production of Mini led and Micro led
Since the size of the required LED chips is less than 100 µm and the quantity is huge, there are three problems:
1) Products corresponding to ultra-high definition such as 4K and 8K resolution need to selectively pick up more than 100 million chips and place them on the receiving substrate, the traditional pick-and-place technology is difficult to meet the requirements. The current flip-chip bonding equipment can only achieve the assembly throughput of ~8000 chips per hour;
2) It requires high transfer accuracy, generally about 5% of the die size.
3) Very high reliability is required. Even a failure rate of ~0.01% will result in thousands of dead pixels, which is obviously unacceptable. The current large-size LED displays use splicing to reduce the difficulty. When the mass transfer of LED chips becomes mature, Mini LED and Micro LED technologies will shine.