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What Are COB LED & Why Choose COB LED Displays

by | Nov 8, 2023 | Blogs | 0 comments

The development history of LED display is a history of changes in display technology. From monochrome to full color, from large pixel pitch outdoor displays to micro-pitch, COB, with the continuous innovation of display technology, LED displays have become more excellent in visual effects, and becoming more affordable. Compared with other display products, LED displays have more significant advantages.

 

The development of COB LED display.

 

Nowadays, as 5G+8K technology becomes increasingly mature, the public has higher requirements and expectations for display effects. The LED display industry has entered the ultra-high-definition display era of “fine pitch and high refresh.”

 

As the mainstream in the future display field, COB LED fine-pitch display not only has a huge market scale, but has also attracted investments from the LED display industry and consumer electronics manufacturers.

 

Under the goal of ultra-high-definition display, COB LED displays meet the needs of various pixel densities and various sizes of displays with its characteristics of low energy consumption, high brightness, high contrast and high reliability, and is becoming driving force for the transformation and construction of display technology.

 

The media predicts that by 2025, the Mini / COB LED market will reach US$5.3 billion, with a compound annual growth rate of more than 85%; the global Micro / COB LED market will exceed US$3.5 billion. The global Micro / COB LED market size is expected to exceed the US$10 billion mark in 2027.

 

The era of COB / Micro LED display has arrived, and the support for further market expansion must be the technological progress of ultra-fine pitch in the industry and the cost reduction of large-scale mass production.

The future of Mini LED has arrived. Can COB LED be the main driver of cost reduction?

 

The LED display industry is continuously optimizing COB LED technical solutions to help reduce mass production costs. As far as packaging technology is concerned, since the advent of LED display devices, various types such as DIP direct plug-in, dot matrix module, single-color CHIP type, full-color TOP type, full-color CHIP type, multi-light integrated packaging, MIP, COB, etc. have been produced.

 

In the field of small-pitch LED displays, SMD packaging technology is still the mainstream at this stage. However, as micro-pitch competition further intensifies, traditional SMD single-lamp packaging technology makes it difficult to meet the needs of small-pitch LED displays below P0.9.

 

COB technology breaks through the physical size limitations of packaging light-emitting chips into lamp beads and attaching lamp beads to PCB boards. With its high stability and ultra-high-definition display technology characteristics, it has become an emerging display technology in the current market.

 

What Are COB Technology and Their Benefits?

 

COB (chip-on-board) is chip-on-board packaging technology. It is a new packaging method that is different from SMD surface-mount packaging technology. Specifically, the bare chip is adhered to the PCB with conductive or non-conductive glue, and then wire bonded. The electrical connections are made together, and the chip and bonding wires are encapsulated with glue.

 

First of all, the LED display screen using COB packaging quickly dissipates heat directly through the PCB board and has a small thermal resistance, so the display screen can work at a lower temperature and has the characteristics of strong heat dissipation, low power consumption, and long life.

 

Secondly, there is no physical barrier between the light-emitting chips, the LED display using COB packaging can show more pixels per unit, so it can achieve smaller spacing, clearer pictures, and more colors; features include smaller spacing, better image quality, and wider viewing angles.

 

Furthermore, due to the integrated module design, the COB-packaged LED display screen eliminates the multiple processes and components required by the SMD-packaged LED electronic screen, reduces the installation space and weight, simplifies the installation steps and methods, and with lower costs. It is easier to install and more convenient to maintain.

 

DOIT VISION’s COB LED displays adopt a bracket large module design and have ultra-high flatness; it uses four-chip multiplexing technology to achieve higher resolution, and it uses a full flip-chip process to achieve higher stability.

 

It uses a balanced design with low power consumption for higher reliability, while the unique design with a wide viewing angle makes the display more consistent.

 

Ultimately, the product can achieve better display effects while being more cost-effective.

 

DOIT VISION’s COB LED displays make the picture cleaner, and have ultra-high contrast to make the display clearer. It also adopts complete front-end maintenance for simple and quick maintenance. And through the full flip-chip process, the light emission is more uniform and can prevent surface reflection; while full grayscale correction makes the picture more realistic.

 

Why Choose COB LED Display

 

The modular design of the COB LED display is quick to assemble, easy to extend, and conducive to personalized customization. Once it was launched, it was accepted and recognized by the market and users.

 

However, due to the thickness tolerance of PCB substrates in the same batch or different batches, the flow rate of the sealing material in the mold at different times and different batches is different, which can easily lead to modularization of the COB display. Different areas of the same LED diode board have different colors, and different LED diode boards in the same LED panel have different colors. There may also be reflection problems on the display surface.

 

In order to solve the modularization problem of COB LED display, the following surface treatment technologies are commonly used to achieve consistent display effects.

 

PCB surface treatment

 

For COB LED package displays using PCB substrates, due to differences in the base color of the substrate, the LED diode board will show color difference.

 

In order to improve the contrast of the COB LED diode board, black PP can be used during the production process of the PCB substrate or black solder-resist oil can be used to cover non-functional areas. It is also a practical method to spray ink in the chip space area after solidification. Taking the PCB board of DOIT VISION’s current formal chip as an example, the black ratio before the bonding wires is solidified is about 45%.

 

After inkjet comparison, the black ratio increases to 75%. Depending on the chip, a space 100% larger than the chip is reserved for die bonding. After processing, the proportion of black in the entire screen (hereinafter referred to as the black ratio) is up to 80% (the proportion of chips that require bonding wires is smaller), far less than 99%. High-speed and precise spraying technology can achieve precise positioning.

 

Even the tiny gaps between chips can be sprayed with ink. No screen printing is required, shortening the work process, ink recycling, no loss, UV light curing light source can be installed, and long life. Energy saving and environmental protection.

 

LED diode board/LED panel surface treatment technology

 

Using ion sputtering equipment, a uniform black paint is sprayed on the surface of the COB LED diode board to achieve the effect of a black surface; a black adhesive film can also be made to closely fit on the surface of the unit board of the box, which can greatly improve the contrast.

 

Display image contrast refers to the measurement of different brightness levels between the brightest white and the darkest black in the light and dark areas of an image, that is, the size of the grayscale contrast of an image. The larger the difference range, the greater the contrast, and the smaller the difference range, the smaller the contrast. Spray the darkest substance on the surface of the unit board to minimize the darkest black value and the contrast ratio can reach 10000:1.

 

Calibration Consistency Technology

 

For COB LED displays, the dot pitch is getting smaller and smaller, and the actual distance between lamps is getting smaller and smaller, which leads to increasingly obvious phenomena such as crosstalk between pixels and image blur and overlap. In addition, the packaging process of COB makes the three-color light to be reflected inside the colloid, causing interference, which affects the accuracy of collecting the brightness and chromaticity of the lamp beads.

 

Comparison of COB module before and after correction

COB LED

There is a significant difference between low gray performance and high gray performance, and the problem of display inconsistency in low gray segments is highlighted.

 

The display effect of the screen under different gray levels

COB LED

The low grayscale effect is related to circuit design, chip selection, and hardware control; low grayscale is easily affected by the above conditions and causes inaccurate color realization, resulting in poor display effects.

 

Display calibration system

COB LED

The correction effect can be improved through the following aspects.

 

Use the scientific-grade camera to improve measurement accuracy.

 

It adopts CIE-XYZ filter that conforms to the perception characteristics of the human eye, reflecting the true perception of the human eye.

 

Due to cost considerations, conventional cameras usually use simple Bayer filters. However, the Bayer filter spectrum is unstable and has the problem of uneven burr transition, which can lead to serious spectral measurement errors. Through years of innovation in filter design and continuous iteration, the calibration camera adopts CIE-XYZ filter technology and is iterated into a CIE-XYZ scientific-grade camera.

 

The high-standard camera introduces a filter calibration algorithm designed for LED measurement and uses multiple sets of wheels. , take multiple measurements to ensure the accuracy of the measurement and obtain measurement data that conforms to the characteristics of the human eye, making the correction closer to the picture effect perceived by the human eye.

 

2Improve the correction process and add light mixing elimination processing

 

Process the collected image twice, restore its own brightness data, and re-count the correction data under true brightness. Improving the uniformity of the screen body and making the display effect more delicate is the new mixed light elimination technology of the COB display.

 

3Full grayscale correction technology improves grayscale performance accuracy.

 

The grayscale data is collected through the light gun CA-410, and then the correction coefficient is calculated through the grayscale correction tool to compensate for each grayscale and improve the nonlinear response. Finally, through hardware coding, the grayscale display step problem is optimized on the receiving card.

 

Conclusion:

 

In terms of COB LED display, traditional PCB surface treatment technology, LED diode board and LED panel surface treatment technology are used to improve the display consistency. DOIT VISION adopts a display correction system and full grayscale correction technology to improve the accuracy of grayscale performance.

Comparing the effects before and after full grayscale correction, you will find that compared with before correction, the problems of pitting, color blocks, and color casts in the display screen after correction have been significantly improved, and the uniformity and picture fineness have been greatly improved.

 

About the Author

Kris Liang

Kris Liang

Founder/LED display expert

Kiris Liang is the founder of Doitvision. 12 + years in LED visual industry. Full passion of LED, product designer & chief salesman. Looking for teammate of technical/ marketing / sales.

Connecting people relative with LED displays.

Email: kris@doitvision.net