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Why is the COB most suitable for display schemes above 100 inches?

Author :ledman Reading :680


  The traditional LED display screen is mainly used in the indoor and outdoor large-screen display market, and the display area ranges from a few square meters to several hundred and thousands of square meters. With the advent of LED small pitch products below P2.5 and the shrinking of dot pitch, LED small pitch products have also been used in the commercial display market of one or two hundred inches. The traditional indoor display technology is mainly based on LCD, laser projection and other technologies. The LED small pitch products have an intersection with LCD and laser projection technologies in the display market of 100 inches or more. LED small pitch products include traditional SMD small pitch products, COB Fine-pitch products, display technology above 100 inches, which technology is the best choice? Below we analyze from the characteristics of various technical solutions.

First look at the LCD technology.

  When the LCD technology is used for display of 100 inches or more, the production yield of a large-sized LCD panel of 100 inches or more is low, and the cost cannot be lowered, and the price is high. Samsung's 98-inch QLED TV released in 2019, close to the price of 1 million yuan, is indeed very expensive.

  LCD technology, another problem with TVs above 100" is the difficulty of transportation and household access. The table below shows the length and width of a 100" to 150" TV.


100 inches or more TV length and width

  It can be seen from the table that when the size of the TV set exceeds 100 inches, the size of the whole machine without the outer packaging is more than 2 meters long and more than 1 meter wide. There are many difficulties in the transportation process. It is extremely difficult for TV to enter the home through elevators.

Next we look at the laser projection technology.

Laser projection television is a large-screen display technology developed in recent years, and also a passive illumination display technology. By using a laser short-throw projector to cast a light-resistant screen, a large-screen display of 100 inches or more can be obtained. There are three congenital shortcomings in laser projection TV, which makes it impossible to achieve the display effect of other display technologies. One is that the anti-light curtain has a very low contrast compared to other display methods. The other is that the color gamut loss is large after the reflection of the light curtain. The third is that the brightness of the projection display is low.


Schematic diagram of the anti-light curtain

  The schematic diagram of the laser projection light-resistant curtain is shown in the figure. The anti-light curtain microstructure is a zigzag optical structure. The upper surface of the sawtooth structure is a light-absorbing layer coated with black material, and the bottom is a white reflective layer coated with a special material. The black layer absorbs ambient light and improves contrast, and the white reflective layer is used to reflect images when projected. From the microstructure of the anti-light curtain, it can be found that the curtain cannot achieve all black, and a considerable part of white, resulting in low contrast of the screen, can not achieve high-quality picture display. 

  In addition to the low contrast ratio of the anti-light curtain, the color gamut of the displayed image will be relatively low, and the color loss is relatively large. Since the curtain is passively reflected, the laser projection is improved by technology, and the color gamut of the projector can be improved, but the anti-light curtain itself is a passive reflection light display mode, which causes a large color loss, and the image color gamut low after the screen reflection .

  The low brightness of the laser projection television is also one of the main reasons for the low display quality. Due to the passive reflection display mode of the laser projection TV, although the nominal brightness of the projector is very high, the brightness of the image reflected by the anti-light curtain is very low, resulting in whitening of the image and loss of sharpness, especially The phenomenon of whitening under ambient light conditions is more obvious. The overall display effect is difficult to achieve the basic needs of people for large screen high display quality.

Let's look at the third SMD LED small pitch display technology.

  SMD LED small-pitch display technology for TVs above 100 inches, with two insurmountable technical barriers, making this technology difficult to become the technology used in TVs over 100 inches. One technical obstacle is the poor anti-collision capability of LED lamp beads and low pixel reliability. The LED small-pitch display made with SMD 1010 device has an impulse that is an order of magnitude smaller than that of the COB display, resulting in low reliability, especially at low P1.0 points. 


Comparison of SMD small pitch Spacing and COB Fine-pitch Spacing Collision Thrust

  From the perspective of failure mechanism, the common non-lighting phenomenon of 1010 small spacing may be caused by the peeling of the outer sealant and the peeling of the bracket or the impact of the external force. To this end, we identified the cause of the failure through failure analysis, and further designed for the sealability of the glue or the mechanical properties of the glue. At the same time, our COB technology cancels the SMD bracket and SMT reflow soldering, no risk of soldering, and higher reliability. In the thrust test, the Ledman COB is at least 10 times more thrust than the SMD, and the lamp bead is more resistant to collision.

  Another of SMD's small-pitch display technology is a technical obstacle, which is that the resolution cannot meet the display requirements. With the continuous development of 4K and 8K display requirements, the requirements for sharpness are getting higher and higher, and SMD small pitch technology can only achieve P1.0 or higher dot pitch display. It is very difficult to mass production below P1.0.


SMD small pitch display and COB Fine-pitch display can achieve the range of point spacing

Finally, let's look at COB Fine-pitch LED display technology.

  COB Fine-pitch display technology, called Micro LED display technology in foreign countries, Samsung released a 146-inch Micro LED TV product - The Wall in 2018. This is the first product released by the global display giant Samsung in the LED TV video wall market. Another international display giant, Sony, released Crystal Black with Micro LED as early as 2016.

  COB Fine-pitch display is integrated with LED packaging technology and LED display technology. 70% of the technology belongs to packaging technology, so packaging technology is the main technical difficulty of COB Fine-pitch display. Ledman has accumulated packaging patents since fifteen years ago. COB integrated packaging technology has overcome nearly 100 technical difficulties in substrate, chip transfer, sealing, online maintenance, reliability, splicing, consistency, and correction algorithms. Growing up to be the leader of domestic COB Fine-pitch display.

  More than 100 inches COB Fine-display TV, compared with LCD TVs, due to the use of splicing technology, there is no problem of transport and home of LCD TVs over 100 inches. Compared with liquid crystal display technology and laser projection technology, COB Fine-pitch display technology has higher brightness and overwhelming advantages in display quality. The figure below shows the measured gamut range of the COB Fine-pitch display technology.


COB Fine-pitch display measured color gamut

  As can be seen from the figure, the color gamut of COB Fine-pitch display technology is much wider than the current DCI-P3 standard and ITU-R BT.709 standard adopted by the film industry. Compared with liquid crystal display and laser projection, the ability to express color is stronger.

  Compared with SMD LED small-pitch display technology, COB Fine-pitch display technology has high reliability in terms of pixel reliability. The pixel failure rate is less than 10PPM when used by the user, which is one to two orders of magnitude lower than the SMD small-pitch display technology. 

  In terms of achieving smaller dot pitch, COB Fine-pitch display technology can achieve dot pitches above P0.5. SMD small-pitch display technology is generally used for dot pitches above P1.0, and COB technology can achieve clearer display.

Therefore, COB Fine-pitch LED display technology has a very obvious technical advantage compared with SMD small pitch technology.

  With the popularity of 4K TV, 8K TV has begun to come to us. 4K and 8K TVs have higher requirements for resolution, and also call for the emergence of larger ultra-high-definition large-size panels. Samsung, Sony and other international display giants in the display technology of more than 100 inches, have chosen to adopt the COB Fine-pitch display technology route, which is not a coincidence, but with the market demand for more than 100 inches of ultra-high-definition large-size display continues to develop, requirements The international display giant needs to propose a technical solution that can meet the market requirements. With the continuous maturity of Mini LED and Micro LED using COB display technology, COB Fine-pitch display technology is also an inevitable choice.

  Looking at the domestic market, as of now, Ledman has successfully realized the mass production of P1.9, P1.5, P1.2, P0.9 and other Fine-pitch products, and its products are in more than 20 industries in China and ten countries in the world have achieved batch application, and the technology level is leading in the industry. In the process of developing COB Fine-pitch display products, Ledman also obtained a large amount of intellectual property rights. As of the first quarter of 2019, COB Fine-pitch display technology has obtained about 30 technical patents.

  Through the above analysis, COB Fine-pitch LED display technology is indeed the best technology for large-screen TVs of 100 inches or more, and is the best choice for large-screen TVs of 100 inches or more. As the mainstream manufacturer of COB Fine-pitch displays in China, Ledman currently uses the same technical route as Samsung and Sony. For the large screen display market of 100 inches or more, Ledman will gradually introduce 100-300 inches standard large screen products for customers. Provide customers with solutions for oversized displays over 100 inches.

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