Learn about the real MiniLED
Li Xing. MiniLED technology is quickly out of the circle with its powerful advantages. Apple, TCL, Hisense, BOE and other industry giants have launched TVs, displays and other terminal products equipped with MiniLED technology, which has truly pushed MiniLED technology to a new outlet in the industry. As an important town of the LED industry, LED companies in mainland China and Taiwan on both sides of the Taiwan Strait, such as San'an, HC Semitek, Jucan, Funo, Whit, Lite-on, etc., have also greatly enhanced their profitability under the condition of mass production and shipment of MiniLED products.
The reason why the industry is crazy about miniLED technology is because in the early morning of April 21, 2021, miniLED became the biggest highlight at Apple's spring new product launch conference, and its launch of **12The 9-inch iPad Pro is equipped with MiniLED backlit display technology. For Apple, the introduction of MiniLED backlight technology completes the last piece of the puzzle for HDR on all platforms. For the LED industry, the significance is even more significant.
This LiquidRetina XDR display uses more than 10,000 miniLEDs, a total of 2596 local dimming zones, can achieve an ultra-high contrast ratio of 1 million:1, and the peak brightness reaches 1600nits, which is 1000nits higher than the old model, and supports high-end technologies such as P3 wide color gamut, True Tone display and promotion adaptive refresh rate.
From the current point of view, Apple's products are gradually moving away from the traditional side-lit back LCD panel, and MiniLED will become its preferred technology. At this stage, Apple 129-inch iPadPro, **14-inch 16-inch MacBookPro are equipped with Mini LED screens;It is expected that the 11-inch iPad Pro and iMacPro will also be added this year, and the MacBookAir, which has not been updated for two years, is also expected to use a Mini LED screen.
Driven by Apple, Samsung, TCL, Sony, LG, Asus and many other manufacturers have also launched a variety of products such as MiniLED TVs, laptops, and displays, and the penetration of MiniLED technology has accelerated.
The determining factors for evaluating the quality of a display include resolution (number of pixels), PPI (pixel density), viewing distance, etc. Generally speaking, LCDs and LED screens are used above 3 meters, OLEDs are used below 3 meters, 2 3 meters are used for miniLED displays, and microOLED (VR AR field) is used for less than 1 meter.
MiniLED technology can be used directly for RGB displays or for LCD backlight modules. Among them, the LCD screen backlight module mainly uses MiniLED technology to improve the display effect.
What is MiniLED
MiniLED is a type of LED technology, and its LED chip size is between 50 and 200 microns, which is the product of further refinement of small pitch LEDs. Compared with ordinary LEDs, MiniLED has the characteristics of higher resolution, contrast, color gamut range, etc., and is thinner and more energy-saving.
There are also industries that believe that MiniLED refers to LED chips with a size of 100 300 microns and a chip spacing of 01 1mm between the miniature LED device modules in SMD, COB or IMD packages. MiniLED has two innovative paths: MiniLED backlight + LCD and MiniLED display, two-wheel drive. From the perspective of the original components, the application of MiniLED is mainly divided into a backlight scheme using MiniLED chip + LCD and a self-luminous scheme directly using MiniRGB display.
The principle of its MiniLED technology is: MiniLED adopts a direct backlight method, which can be regarded as an upgraded version of an ordinary LCD screen. MiniLED reduces the size of traditional LED backlight beads to achieve finer and denser backlight partitions, and cooperates with localdimming control to improve brightness and contrast, and enhance visual perception. Under the same conditions, MiniLED not only makes up for the shortcomings of OLED's easy screen burn-in, but also is better than OLED in cost, and has a cost advantage while improving the picture.
Compared with traditional LED backlights, the performance of MiniLED backlights has the following improvements:
The small structure of the backlight chip is conducive to making the number of dimming zones (LocalDimmingZones) more detailed, so as to achieve a higher dynamic range (HDR) and achieve a higher contrast effect.
MiniLED can achieve uniform heat dissipation at high brightness (>1000nit).
Compared with the general side-entry backlight solution, the MiniLED backlight can achieve a direct-to-ultra-thin LCD display, shorten the optical mixing distance (OD), and reduce the thickness of the whole machine to achieve the purpose of ultra-thinning.
Compared with the widespread use of OLED screens, the biggest problem is still the longevity of organic light-emitting materials, and because of the series of compromise problems brought about by life. There is no problem of short life under MiniLED backlight technology, MiniLED backlight screen is not lost to OLED screen in contrast, and can surpass OLED in core parameters such as brightness, area light control, life, and color performance.
Market outlook for Mini LED.
MiniLED has a wide range of applications in both direct display and backlight markets, and is gradually opening up the market. At present, miniLED display products have begun to be used in large-screen high-definition displays, such as monitoring and command, high-definition studios, high-end cinemas, medical diagnosis, advertising displays, conferences and exhibitions, office displays, virtual reality and other commercial fields. at the same time,With the gradual growth of consumers in the size of the color TV market in recent years,The era of large screens foreseen in the future,It may be coming。
With the introduction of miniLED backlight solutions by mainstream brands such as Samsung and Apple, it has led the innovation boom in the terminal market. TV and tablet terminals are the first to be commercialized, and smartphones, automobiles, and VR are expected to start their first year of commercialization in 2022 and 2023. The miniRGB direct display pays more attention to the market demand such as commercial displays, and has advantages in the fields of commercial displays, electronic product decorative lights, tail lights or atmosphere lights.
With the increase in the penetration rate of new energy vehicles, the development trend of automotive electronics applications will drive the growth of on-board screen area. MiniLED backlight technology is expected to make a big impact in the field of automotive displays, and it seems to be the most feasible and on the eve of application. For the niche application product of miniLED backlight vehicle screen, although the vehicle specification certification time is longer, it also gives the product a longer life cycle, higher industrial barriers and higher single product value, which is the "battleground" of the first chain enterprise.
Challenges faced by Mini LEDs.
The manufacturing cost of MiniLED is still the biggest hurdle to get to market. If you look at Apple's 12 in isolation9"Panel, iPad Pro uses this piece 129"The display is in a MiniLED backlight configuration, with 10,000 MiniLEDs and 2,596 partitions (Chip on Board FPC + BT PCB). According to industry analysis, the 10000 miniLED screens used in this iPad Pro are 12 compared to the backlight BLU (Backlights unit).The cost of a 9-inch traditional side-entry backlight LCD has increased by about 37 times.
In other applications such as TV products and direct displays, the current yield is low, which further pushes up the production cost and becomes a bottleneck for the large-scale application of miniLED. For example, in miniLED direct display products, the blue-green flip chip technology in the chip flip process is relatively mature, and the yield rate is highHowever, the red light chip needs to be substrate transferred and die bonded, and the yield and reliability of the product are still difficult to ensure due to the influence of the process environment and various uncontrollable factors in this process.
In addition, the design of the light angle control scheme also affects the yield of the MiniLED chip, and the size of the light angle can affect a number of optical properties.
According to the industry, although MiniLED backlight technology has begun to be applied to actual products, there are still many technical challenges.
Difficulties in chip technology: The chip used in MiniLED backlight is affected by line width accuracy and electrode shading, and the brightness of the chip itself is reduced, which affects the yield of the chip wafer used in MiniLED backlight. At present, the cutting yield of chip wafers used in MiniLED backlight is generally about 75%.
Difficulties in transfer technology: The transfer of MiniLED chips is realized by high-speed placement machine or die bonding machine, and MiniLED chips are easy to cause the phenomenon of false soldering of solder joints due to their small solder joint area and insufficient detection accuracy of solder paste inspection equipment (SPI) equipment. Both of these transfer methods are unavoidable, especially after reflow soldering, and false soldering is more likely to cause transfer defects. The accuracy and speed of transfer are also technical difficulties faced by Mini LED backlight technology, and these two technical indicators are contradictory. The transfer efficiency and yield directly affect the cost of MiniLED backlight products.
Difficulties in defect management: The concept of defect not only refers to defects in the transfer process, but also includes defects in micro-defects of chips, defects in substrates and pads, and defects in solder paste. Since the consistency and yield requirements of the relevant parts used in the miniLED backlight board are much higher than those of the traditional backlight board, in order to improve the first-pass rate and efficiency of the transfer process as much as possible, it is necessary to be equipped with professional equipment to automatically detect and screen the defects of the related parts.
Difficulties in driver technology: The drive current of Mini LED backlight technology is small (<10mA), which puts forward high requirements for the accuracy of the drive IC control current. Generally, it is necessary to control the driving current accuracy of the Mini LED backlight at 1In the range of 5%, it can provide stable picture output, while the current drive accuracy of traditional LED backlights is only about 10%.
Technical difficulties of backplane: According to the material of the backplane, it can be divided into glass substrate and printed circuit board (PCB). These two substrates have their own advantages and disadvantages, and at present, they are mainly printed circuit boards, and glass substrates may become mainstream in the future. However, there are still several problems with glass substrates that need to be solved urgently. The first is the problem of current line loss (IRDROP), due to the low line mobility of the TFT substrate, the line resistance of the current is large, resulting in uneven current distribution between the current input and output terminals, resulting in a large difference in brightness. Secondly, TFT-LCD generally uses voltage drive, while Mini LED backlight technology uses current drive, and the small voltage fluctuation in the voltage drive mode has little impact on the display performance of TFT-LCD, but when the voltage fluctuation is converted into current fluctuation, it has a greater impact on brightness. In addition, there are a series of problems such as temperature rise and reliability.
Technical difficulties in color formation: When using blue light chips in MiniLED backlight, due to the influence of wavelength consistency, driving voltage and current fluctuations, the problem of uneven white field brightness or chromaticity often occurs in the full white field detection of the backlight. Therefore, the problem of light color non-uniformity is generally used to increase the number of layers and diffusion of the diaphragm, or to use D-Mura technology, but these methods will sacrifice the brightness of the Mini LED backlight, increase power consumption, and then easily cause problems such as heat concentration.
Who should choose OLED and MiniLED?
The main difference between Mini LED and OLED is:
The unique advantage of OLED, that is, pixel self-illumination, compared with the traditional liquid crystal with a rear backlight and a color that blocks the light, the highest brightness and contrast ratio (the brightest and darkest contrast) are much better, and the colors are more vivid at the same technical level, while the same brightness and other parameters are relatively power-saving, and because there is no backlight layer, it is thinner.
Who should choose OLED and MiniLED?
The difference between MiniLED and OLED is mainly due to the unique advantages of OLED, that is, the pixel is self-luminous, compared with the traditional liquid crystal with a rear backlight and a color by blocking the light, the highest brightness and contrast (the brightest and darkest contrast) are much better, and at the same technical level, the color is more vivid, while the same brightness and other parameters are relatively power-saving, and because there is no backlight layer, it is thinner.
OLED uses an electric current to directly excite the color substances in the pixel to emit light and produce colors, which also brings a problem, that is, the consumption of these substances. If you maintain the color of a pixel for a long time, these substances may be excessively consumed, resulting in a decrease in color and luminescence ability, and the perception is that the color of this pixel or even all the colors and brightness are gradually dimmed, if there is a problem with a pixel, it is the so-called "screen burning".
To put it bluntly, MiniLED has changed the original unified brightness backlight into a zoned brightness that can be adjusted by partition, of course, the premise is to use LED dot matrix backlight. Now the common miniLED will be divided into 512 to thousands of backlight zones, each partition is about (tens x dozens) pixel area, with LCD control, you can adjust the pixel brightness and darkness faster and better, and can also present more vivid colors and better contrast.
However, it also has an unavoidable problem, that is, there are a small number of pixels with a huge difference in brightness in a certain partition, such as when the sky is starry. If the brightness of the partition is lowered according to the color of the sky at night, then the starlight is too dim and distorted, and conversely, if the brightness of the backlight partition is increased to ensure the brightness of the stars, then the surrounding dark pixels are likely to be illuminated, resulting in the so-called glow, and the background color of the starry sky will be distorted.
When the granularity of MiniLED local dimming is relatively coarse (i.e., the number of backlight zones is small), it is easy to observe "halos", which are caused by the leakage of light from a certain zone to the adjacent non-emitting zone (or darker zone). If you look closely, you might even be able to distinguish the different areas of backlight with the naked eye.
*：prospects and challenges of mini-led and micro-led displays*
The essence of Mini LED is to make this backlight partition more, or make each LED backlight smaller, to achieve more accurate backlight and picture brightness control (so Mini LED obviously belongs to LCD). For example, in the image above, when showing a candle, only the backlit part required for the display is illuminated, and there are different gray levels (although its accuracy is not comparable to OLED).
Take a brief look at the characteristics of the two products, in fact, you can have a basic understanding of the most suitable scenarios, such as more inclined to fixed scenes, such as always using a software, an interface for a long time to work, design, and read, you should pay attention to the problem of OLED screen burning in the fixed display area, MiniLED is more suitable. If you are inclined to entertainment, such as gaming, **, or have a wide range of interests, then OLED with excellent color, high-speed response, and no small area display "worry" is more suitable.