Blogs
on June 1, 2024
The annual Guangzhou International LED Exhibition has come to a perfect conclusion. During the four-day Guangzhou exhibition, all major LED exhibitors in the industry have presented their unique tricks, which can be described as brilliant. And there is an enterprise that has become the only exhibitor of COB small-pitch products in this exhibition-Changchun Xida, showing a mature integrated three-in-one (COB) product display, high contrast, high protection, high system scalability, etc. The advantages make COB small-pitch products attract more and more attention, which has the potential to lead the development of LED display technology in the future.
The mystery of COB small-pitch display technology
COB (Chip On Board) small-pitch display technology is a technical method in which LED light-emitting wafers are directly packaged on a PCB circuit board and combined with CELL units to form a display.
Packaging technology is the soul and life of LED display screens. The pursuit of perfect performance is always the unremitting pursuit in the industry. Integrated packaging technology is undoubtedly the focus of attention from all walks of life. Integrated packaging is a new packaging mode in the field of LED displays, and it is currently classified as the packaging-free mode or packaging-saving mode in the future development direction, that is, chip on board—chip packaging on board, which is to use LED bare chips Conductive or non-conductive adhesives are adhered to the PCB, and wire bonding is used to make its electrical connections. This packaging mode integrates midstream and downstream enterprises, from LED chip packaging to LED display unit module or display production are all completed in one factory. This technology has several characteristics that SMD cannot match: first, the reliability of COB products is much higher than that of surface mount products, and it adopts ultrasonic welding at room temperature, without secondary welding, high temperature shock and electrostatic damage; The smaller it is, the lower its cost, and the closer it is to civilians. These are two very important features, which are enough to support COB products towards a better future.
With the simplicity of "high temperature" as the magic
The most critical component of the LED display is the LED lamp bead. As the component with the highest cost and the largest consumption of the LED display, the LED lamp bead plays a leading role in the quality of the LED display. First, LED is the key component used in the largest number of full-color screens, with thousands to tens of thousands of LEDs per square meter; Third, LED accounts for the largest proportion of the overall cost of the display screen, ranging from 30% to 70%.
Due to the smaller dot pitch, the small-pitch LED display requires 3-4 times as many lamp beads as the ordinary LED display in the same area. Taking P1.6 small-pitch products as an example, there are more than 390,000 lamps per square meter. Beads, nearly 1.6 million leads. These components together constitute a very complex process system problem: and such a complex system must use a process called "reflow soldering" to realize the connection. The reflow soldering process itself means "artificial high temperature" (240 degrees, far exceeding the normal operating temperature of the LED display), and it is difficult to avoid the thermal stress changes due to the different materials in the SMD package of the LED lamp bead during high temperature operation. . This has become the core "culprit" of broken lights and dead lights in small-pitch LED screens.
In related terms, the COB packaging technology can make the LED crystal become the smallest CELL display unit at one time during the packaging process after the chip is split, and no longer needs a second "surface mount" welding, which reduces a high-precision and high-temperature environment operation. , can effectively control the artificial high temperature, reduce the failure rate of the display screen by more than an order of magnitude, and ensure the stability of the electrical and semiconductor structures of the LED crystal to the greatest extent.
Eighteen martial arts of COB technology
It is the housekeeping skill of COB technology to reduce the bad light rate in one step, but COB is not the only skill. It can be said that it is proficient in all kinds of martial arts, and its outstanding advantages are not ordinary.
From the comparison of the collision process of the display unit, the lamp bead of the SMD surface mount product is not seamlessly connected with the PCB board, which makes it easy to cause stress concentration on a single lamp bead during the collision process. However, the transportation and installation of the large-screen system will inevitably have vibrations and collisions, which will cause an "engineering" increase in the failure rate of small-pitch LED displays. The COB packaging technology, through the highly integrated bonding of epoxy resin, chip, and PCB board, can effectively protect the stability of the connection between the chip and chip electrical appliances, and can also avoid broken lights caused by collision and vibration during transportation. Rate.
From the comparison of the temperature uniformity during the working process of the system, the smaller the pitch of the SMD package, the more small-pitch products, the more high-power small-particle LED crystals should be used. At the same time, the gap between the lamp bead and the display panel will hinder the thermal conductivity of the wafer during operation. Due to the adoption of a more integrated overall process for COB packaging, chips with lower power area density and larger crystal particles can be selected in crystal selection, thereby reducing the working intensity of the core luminous point. At the same time, the COB package realizes the all-solid seamless heat dissipation under the full epoxy resin package, which reduces the heat concentration of the LED crystal in the working state, which is beneficial to prolong the product life and improve the system stability.
A new display may start here
The display market has always been advancing in exploration, regardless of whether the situation it is in is good or bad, it is trying its best to be flattered, and to face all praises and criticisms calmly. In the display industry in recent years, countless application technologies have been unearthed and put into display to flourish. Although the LED display has a strong force of small spacing and keeps pace with liquid crystal and projection, the continuous impact of new technologies such as OLED and quantum dots also makes LED display seek new breakthroughs in the advantages of high brightness and colorful colors. The trend of LED display extends from outdoor to indoor video wall display, and gradually penetrates into various market segments.
The traditional LED display system is mostly used for outdoor display and long-distance viewing display, and its requirements for viewing angle and visual comfort are not obvious. However, with the popularity of small-pitch LED applications and the emergence of a large number of indoor display systems and close-up viewing systems, how to improve the viewing comfort of LED displays has become a major industry problem.
Compared with SMD packaging, small-pitch LED products under COB technology are naturally "non-granular display", and the uniformity of image quality, color curve, and viewing angle effects have been improved to varying degrees. After adopting the built-in point-by-point tuning technology of the PCB cell board, COB has also made great progress in the uniformity of crystal and unit effects. The combination of these changes makes COB packaging the best technical route to realize the "visual comfort" and "experience effect improvement" of small-pitch LED TVs.
New opportunities for the development of small-pitch LEDs in the city of wisdom
With the continuous development of information technology, the level of informatization application is also constantly improving, and the concept of smart city has emerged as the times require, and has gradually become a new trend in urban development, and has received strong support from policy and industry levels. Building a smart city is not only necessary to achieve sustainable urban development, but also to respond to the needs of the development of information technology, and it is also a strategic choice to enhance my country's comprehensive competitiveness.
Smart city construction includes all aspects of urban life, such as transportation, security, energy, medical care, education, etc., so it will also bring more attractive application prospects for the application of information technology. Among them, the application of small-pitch LED display technology It is favored by many people in the industry.
In recent years, the COB small-pitch LED display screen, which has performed well in the field of indoor high-end applications, has gradually emerged in the field of traditional large-screen projects represented by command and control centers due to its advantages such as no seam, good color, flexible use, energy saving and environmental protection. And set foot in the fields of studio, meteorological bureau, meeting room, exhibition hall and so on.
The goal of smart city construction is to achieve a more intelligent and efficient urban management method. Among them, timely grasp of the real-time status of various urban systems has become an essential means for many industry departments. The command center with the large-screen monitoring system as the core, Needless to say, the importance of the scheduling room. Many LED displays using COB technology have been successfully applied in other fields and achieved good application results. For example, Aureida COB LED display has been used in Beijing Science and Technology Museum, Hong Kong Cyberport project and so on.
At present, there are 290 pilot smart cities in my country. With the advancement of new urbanization with Chinese characteristics, the concept of "smart" will further penetrate into all aspects of urban life, and it will create new technologies for display technology that carries the core task of efficient communication of information. More business opportunities, with the upgrading of technology and the continuous reduction of prices, small-pitch LED screens will also enjoy more dividends from the construction of smart cities. This will also become a "useful place" for COB small-pitch LED displays.
New standard COB walking
Thanks to the advantages of COB display technology, such as good full-color color consistency, large visual angle, low thermal resistance, waterproof, moisture-proof, and UV-proof, the display effect of small-pitch LEDs is becoming more and more high-definition and high-quality, and the industry is also optimistic about COB as a substitute for traditional SMD in the future. Technology becomes the core of small spacing.
The emergence of a new technology and process will never go smoothly, and it must be constantly tested and tried in the process of research and development and production. Compared with traditional SMD technology, COB can be described as a new member of the market. Although COB display technology has become a rising star in the small-pitch LED industry, this does not mean that COB technology is perfect.
Due to its characteristics, the COB packaging method is to ensure that all lamp beads on the same board are tested and there are no dead lights before sealing, instead of sealing the damaged part like SMD. Carefully replaced. How to ensure that the entire board of lamp beads is completely intact, the one-time pass rate is a very big challenge, otherwise the entire board will be discarded due to a broken lamp, which will increase the cost instead.
For COB products, the lamp is sealed first. After the lamp is sealed, the IC drive device must be processed by reflow soldering process. How to ensure that the lamp surface will not be damaged by the high temperature of 240 degrees in the furnace during the reflow soldering process. This is another big challenge. Compared with SMD, COB saves the processing of reflow soldering on the lamp surface, but the device surface, like SMD, needs to be reflow soldered, that is to say, SMD needs to go through two reflow soldering. The most important thing is that when SMD is reflowed, the temperature in the furnace will cause two kinds of damage to the lamp surface. One is the welding wire. If the temperature is too high, it will expand rapidly and cause the filament to break. The second is The heat in the furnace is quickly transferred to the wick through the four pins of the bracket, which may cause small fragmentation damage on the wick, which is fatal and difficult to detect, but such small damage and tiny cracks on the crystal , After a period of use, this disadvantage will be highlighted, and then cause the lamp to fail. And COB is to ensure that when the lamp surface is reflow soldered, the high temperature in the furnace will not damage it and ensure the yield rate, which is also a very important aspect.
At the same time, COB packaging technology itself started relatively late, and has long been used in high-end high-brightness light source and customized light source markets. In the field of small-pitch LED screen display, the accumulation of process technology and material technology is not as good as that of SMD technology. As a result, COB is still inferior to traditional SMD technology in terms of extremely small pitch products and overall cost. Some industry research institutions predict that the key to COB technology in 2017 is to make more technological breakthroughs and cost breakthroughs in P1.5, P1.2 and P1.0 products.
Technological innovation is always on the road. COB has been successfully applied to small-pitch LED displays, and gradually shows the advantages of breaking through the tradition. Now that it is available and usable, the biggest opportunity and development of COB display technology in the future should be to use Good, excellent, and easy to use in detail, creating a new era of display.