Future Trend of Small Pixel Pitch LED Display

In the past three years, the supply and sales of small pixel pitch LED large screens have maintained an annual compound growth rate of over 80%. This level of growth not only ranks among the top technologies in today's large-screen industry, but also at the high growth rate of the large-screen industry. The rapid market growth shows the great vitality of small pixel pitch LED technology.

COB: The Rise of "Second Generation" Products

small pixel pitch LED screens using COB encapsulation technology are called "second generation" small pixel pitch LED display. Since last year, this kind of product has shown a trend of high-speed market growth and has become the “best choice” roadmap for some brands that focus on high-end command and dispatch centers.

SMD, COB to MicroLED, Future Trends for Large Pitch LED Screens

COB is an abbreviation of English ChipsonBoard. The earliest technology originated in the 1960s. It is an "electrical design" that aims to simplify the package structure of ultra-fine electronic components and improve the stability of the final product. Simply speaking, the structure of the COB package is that the original, bare chip or electronic component is directly soldered on the circuit board and covered with a special resin.

In LED applications, the COB package is mainly used in high-power lighting systems and small pixel pitch LED display. The former considers the cooling advantages brought by COB technology, while the latter not only makes full use of the stability advantages of COB in product cooling, but also achieves uniqueness in a series of “performance effects”.

The benefits of COB encapsulation on small pixel pitch LED screens include: 1. Provide a better cooling platform. Because the COB package is a particle crystal directly in close contact with the PCB board, it can make full use of the "substrate area" to achieve heat conduction and heat dissipation. The heat dissipation level is the core factor that determines the stability, point defect rate and service life of small pixel pitch LED screens. A better heat dissipation structure naturally means better overall stability.

2. The COB package is a truly sealed structure. Including PCB circuit board, crystal particles, soldering feet and leads, etc. are all fully sealed. The benefits of a sealed structure are obvious - for example, moisture, bump, contamination damage, and easier surface cleaning of the device.

3. The COB package can be designed with more unique "display optics" features. For example, its package structure, the formation of amorphous area, can be covered with black light-absorbing material. This makes the COB package product even better in contrast. For another example, the COB package can make new adjustments on the optical design above the crystal to realize the naturalization of the pixel particles and improve the disadvantages of sharp particle size and dazzling brightness of conventional small pixel pitch LED screens.

4. COB encapsulation crystal soldering does not use surface mount SMT reflow soldering process. Instead, it can use "low temperature soldering process" including thermal pressure welding, ultrasonic welding, and gold wire bonding. This makes the fragile semi-conductor LED crystal particles not subject to high temperatures exceeding 240 degrees. The high-temperature process is the key point of small-gap LED dead spots and dead lights, especially batch dead lights. When the die attach process shows dead lights and needs to be repaired, "secondary high-temperature reflow soldering" will also occur. The COB process completely eliminates this. This is also the key to the COB process's bad spot rate being only one-tenth of the surface-mount products.

Of course, the COB process also has its "weakness." The first is the cost issue. The COB process costs more than the surface mount process. This is because the COB process is actually a encapsulation stage, and the surface mount is the terminal integration. Before the surface mount process is implemented, the LED crystal particles have already undergone the encapsulation process. This difference has caused the COB to have higher investment thresholds, cost thresholds, and technical thresholds from the LED screen business perspective. However, if the "lamp package and terminal integration" of the surface-mounting process is compared with the COB process, the cost change is acceptable enough, and there is a tendency for the cost to decrease with process stability and application scale development.

Second, the visual consistency of COB encapsulation products requires late technical adjustments. Including the gray consistency of the encapsulating glue itself and the consistency of the brightness level of the light-emitting crystal, it tests the quality control of the entire industrial chain and the level of subsequent adjustment. However, this disadvantage is more a matter of “soft experience.” Through a series of technological advancements, most companies in the industry have mastered the key technologies for maintaining the visual consistency of large-scale production.

Third, COB encapsulation on products with large pixel spacing greatly increases the "production complexity" of the product. In other words, COB technology is no better, it does not apply to products with P1.8 spacing. Because at a greater distance, COB will bring more significant cost increases. - This is just like the surface-mounting process can not completely replace the LED display, because in the p5 or more products, the complexity of the surface-mount process leads to increased costs. The future COB process will also be mainly used in P1.2 and below pitch products.

It is precisely because of the above advantages and disadvantages of COB encapsulation small pixel pitch LED display that: 1.COB is not the earliest route selection for small pixel pitch LED display. Because the small pixel pitch LED is gradually progressing from the large-pitch product, it will inevitably inherit the mature technology and production capacity of the surface-mounting process. This also formed the pattern that today's surface-mounted small pixel pitch LEDs occupy the majority of the market for small pixel pitch LED screens.

2. COB is an "inevitable trend" for small pixel pitch LED display to further transition to smaller pitches and to higher-end indoor applications. Because, at higher pixel densities, the dead-light rate of the surface-mount process becomes a "finished product defect problem." COB technology can significantly improve the dead-lamp phenomenon of small pixel pitch LED display. At the same time, in the higher-end command and dispatch center market, the core of the display effect is not the "brightness" but the "comfortability and reliability" that dominates. This is precisely the advantage of COB technology.

Therefore, since 2016, the accelerated development of COB encapsulation small pixel pitch LED display can be considered as a combination of “smaller pitch” and “higher-end market”. The market performance of this law is that LED screen companies that do not engage in the market of command and dispatch centers have little interest in COB technology; LED screen companies that mainly focus on the market of command and dispatch centers are particularly interested in the development of COB technology.

Technology is endless, large-screen MicroLED is also on the road

The technical change of LED display products has experienced three phases: in-line, surface-mount, COB, and two revolutions. From in-line, surface-mount, to COB means smaller pitch and higher resolution. This evolutionary process is the progress of LED display, and it has also developed more and more high-end application markets. So will this kind of technological evolution continue in the future? The answer is yes.

LED screen from the inline to the surface of the changes, mainly integrated process and lamp beads package specifications changes. The benefits of this change are mainly higher surface integration capabilities. LED screen in the small pixel pitch phase, from the surface-mount process to the COB process changes, in addition to the integration process and package specifications changes, COB integration and encapsulation integration process is the process of the entire industry chain re-segmentation. At the same time, the COB process not only brings smaller pitch control capability, but also brings better visual comfort and reliability experience.

At present, MicroLED technology has become another focus of forward-looking LED large-screen research. Compared with its previous generation COB process small pixel pitch LEDs, the MicroLED concept is not a change in integration or encapsulation technology, but emphasizes the "miniaturization" of lamp bead crystals.

In the ultra-high pixel density small pixel pitch LED screen products, there are two unique technical requirements: First, high pixel density, itself requires a smaller lamp size. COB technology directly encapsulates crystal particles. Compared with surface mount technology, the lamp bead products that have already been encapsulation are soldered. Naturally, they have the advantage of geometric dimensions. This is one of the reasons why COB is more suitable for smaller pitch LED screen products. Second, the higher pixel density also means that the required brightness level of each pixel is reduced. Ultra-small pixel pitch LED screens, mostly used for indoor and near viewing distances, have their own requirements for brightness, which have decreased from thousands of lumens in outdoor screens to less than one thousand, or even hundreds of lumens. In addition, the increase in the number of pixels per unit area, the pursuit of luminous brightness of a single crystal will fall.

The use of MicroLED's micro-crystal structure, that is to meet the smaller geometry (in typical applications, MicroLED crystal size can be one to one ten-thousandth of the current mainstream small pixel pitch LED lamp range), also Meet the characteristics of lower brightness crystal particles with higher pixel density requirements. At the same time, the cost of LED display is largely composed of two parts: the process and the substrate. Smaller microcrystalline LED display mean less substrate material consumption. Or, when the pixel structure of a small pixel pitch led screen can be simultaneously satisfied by large-size and small-size LED crystals, adopting the latter means lower cost.

In summary, the direct benefits of MicroLEDs for small pixel pitch LED large screens include lower material cost, better low-brightness, high grayscale performance, and smaller geometry.

At the same time, MicroLEDs have some additional advantages for small pixel pitch LED screens: 1. Smaller crystal grains mean that the reflective area of crystalline materials has dropped dramatically. Such a small pixel pitch LED screen can use light-absorbing materials and techniques on a larger surface area to enhance the black and dark grayscale effects of the LED screen. 2. Smaller crystal particles leave more room for the LED screen body. These structural spaces can be arranged with other sensor components, optical structures, heat dissipation structures, and the like. 3. The small pixel pitch LED display of MicroLED technology inherit the COB encapsulation process as a whole and have all the advantages of COB technology products.

Of course, there is no perfect technology. MicroLED is no exception. Compared with conventional small pixel pitch LED display and common COB-encapsulation LED display, the main disadvantage of MicroLED is "a more elaborate encapsulation process." The industry calls this "a huge amount of transfer technology." That is, the millions of LED crystals on a wafer, and the single crystal operation after the splitting, cannot be completed in a simple mechanical manner, but require specialized equipment and processes.

The latter is also the "none bottleneck" in the current MicroLED industry. However, unlike the ultra-fine, ultra-high-density MicroLED displays used in VR or mobile phone screens, MicroLEDs are first used for large-pitch LED displays without the "pixel density" limit. For example, the pixel space of P1.2 or P0.5 level is a target product that is easier to "achieve" for "giant transfer" technology.

In response to the problem of huge amounts of transfer technology, Taiwan's enterprise group created a compromise solution, namely 2.5 generations of small pixel pitch LED screens: MiniLED. MiniLED crystal particles larger than the traditional MicroLED, but still only one-tenth of conventional small pixel pitch LED screen crystals, or a few tens of. With this technology-reduced MiNILED product, Innotec believes that it will be able to achieve “process maturity” and mass production in 1-2 years.

On the whole, MicroLED technology is used in the small pixel pitch LED and large-screen market, which can create a “perfect masterpiece” of display performance, contrast, color metrics, and energy-saving levels that far exceed existing products. However, from surface-mounting to COB to MicroLED, the small pixel pitch LED industry will be upgraded from generation to generation, and it will also require continuous innovation in process technology.

Craftsmanship Reserve Tests the "Ultimate Trial" of small pixel pitch LED Industry Manufacturers

LED screen products from the line, the surface to the COB, its continuous improvement in the level of integration, the future of MicroLED large-screen products, "giant transfer" technology is even more difficult.

If the in-line process is an original technology that can be completed by hand, then the surface-mounting process is a process that must be mechanically produced, and the COB technology needs to be completed in a clean environment, a fully automated, and numerically controlled system. The future MicroLED process not only has all the features of the COB, but also designs a large number of "minimal" electronic device transfer operations. The difficulty is further upgraded, involving more complicated semiconductor industry manufacturing experience.

At present, the huge amount of transfer technology that MicroLED represents represents the attention and research and development of international giants such as Apple, Sony, AUO and Samsung. Apple has a sample display of wearable display products, and Sony has achieved mass production of P1.2 pitch splicing LED large screens. The goal of the Taiwanese company is to promote the maturation of huge amounts of transfer technology and become a competitor of OLED display products.

In this generational advancement of LED screens, the trend of progressively increasing process difficulty has its advantages: for example, increasing the industry threshold, preventing more meaningless price competitors, increasing industry concentration, and making industry core companies “competitive”. Advantages "significantly strengthen and create better products. However, this kind of industrial upgrading also has its disadvantages. That is, the threshold for new generations of upgrading technology, the threshold for funding, the threshold for research and development capabilities are higher, the cycle for forming popularization needs is longer, and the investment risk is also greatly increased. The latter changes will be more conducive to the monopoly of the international giants than to the development of local innovative companies.

Whatever the final small pixel pitch LED product can look like, new technological advances are always worth the wait. There are many technologies that can be tapped in the technology treasures of the LED industry: not only COB but also flip-chip technology; not only can MicroLEDs be QLED crystals or other materials.

In short, the small pixel pitch LED large screen industry is an industry that continues to innovate and advance technology.

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