What is COB? Its full name is chip-on-board, which is a chip-on-board package. It is a new type of package that is different from SMD surface-mount package technology. Specifically, the LED bare chip is adhered to the PCB with conductive or non-conductive glue, and then Wire bonding enables electrical connection and encapsulation of the chip and bond wires with glue.
This kind of packaging is not a package, but it integrates upstream and downstream enterprises. The production from LED chip package to LED display unit module or display screen is completed in one factory, which integrates and simplifies the production of packaging companies and display manufacturers. Process, production process is easier to organize and control, product point spacing can be smaller, reliability is multiplied, and cost is closer to civilians.
COB packaging was first used in Lighting, and this application has also become a trend. It is understood that COB-packaged bulbs already occupy about 40% of LED bulbs.
With the gradual maturity of the LED application market, users are increasingly demanding product stability and reliability, especially under the same conditions, requiring products to achieve better energy efficiency indicators, lower power consumption, and more competition. Product price. Based on this, compared with the traditional LEDSMD chip package and high power package, the on-chip (COB) integrated package technology directly encapsulates multiple LED chips on a metal-based printed circuit board as a lighting module directly through the substrate. Heat dissipation not only reduces the manufacturing process and cost of the bracket, but also has the advantage of reducing the thermal resistance of the thermal resistance, thus becoming a kind of packaging method promoted by the lighting enterprise.
In addition to good heat dissipation and low cost, COB light source can be personalized. However, in terms of technology, COB package still has shortcomings such as light decay, short life, and poor reliability. If it can be solved, it will be one of the leading directions for future package development.
The application of COB in lighting has become a trend and trend. Can this packaging technology be applied to the display? In terms of packaging methods, some companies have made new attempts, and such attempts have been verified and promoted and applied in the market. At the same time, it has also attracted widespread attention from people in the industry. So, why is the COB display getting everyone's attention? There must be a reason in it.
I. Analysis of advantages and disadvantages of COB packaging
The application of COB package has been applied in the field of lighting for many years. It has many advantages in various aspects, so it has been favored by many lighting companies. So what kind of spark will COB packaging technology be applied to the display screen? Will there be some levels of acclimatization? Let's analyze the advantages and disadvantages of COB packaging. It is understood that COB packaging technology is applied to the display screen, which has the incomparable advantages of traditional packaging technology.
1. Ultra-thin: According to the actual needs of customers, PCB board with thickness from 0.4-1.2mm can be used to reduce the weight to 1/3 of the original traditional products, which can significantly reduce the structural, transportation and engineering costs for customers.
2. Anti-collision and compression: The COB product directly encapsulates the LED chip in the concave lamp position of the PCB board, and then is cured by epoxy resin. The surface of the lamp point is convex into a spherical surface, which is smooth and hard, and is resistant to collision and wear.
3. Large viewing angle: The COB package uses shallow well spherical illumination, the viewing angle is greater than 175 degrees, close to 180 degrees, and has a better optical diffuse color dimming effect.
4. Bendable: Bendability is a unique feature of COB packages. PCB bending does not cause damage to packaged LED chips. Therefore, LED arc screens, circular screens, and wavy screens can be easily fabricated using COB modules. . It is an ideal substrate for personalized screens in bars and nightclubs. It can be seamlessly spliced, the production structure is simple, and the price is far lower than the LED shaped screen made by the flexible circuit board and the traditional display module.
5. Strong heat dissipation: COB products are packaged on the PCB board, and the heat of the wick is quickly transmitted through the copper foil on the PCB board. The thickness of the copper foil of the PCB board has strict technical requirements, plus the immersion gold process. Hardly causing severe light attenuation. Therefore, there are very few dead lights, which greatly extend the life of the LED display .
6, wear-resistant, easy to clean: the surface of the lamp point is convex into a spherical surface, smooth and hard, collision-resistant and wear-resistant; there are dead spots, you can repair point by point; no mask, dust can be cleaned with water or cloth.
7, all-weather excellent characteristics: the use of triple protection treatment, waterproof, moisture, corrosion, dust, static electricity, oxidation, UV effect is outstanding; to meet all-weather working conditions, the temperature difference of minus 30 degrees to zero 80 degrees can still be used normally.
To put it bluntly, the advantages of the COB display package are really quite a lot, especially when compared with the traditional package form, the contrast effect is more obvious. Since there are many advantages, why not get a large-scale application in the early development of LED display? What are the inadequacies of COB packaging? Hu Zhijun, deputy general manager of Shenzhen Weiqiaoshun Optoelectronics Co., Ltd. said: "The only shortcoming of COB packaging is that the screen ink color is not well controlled, that is, when the lamp is not lit, the surface ink color is inconsistent." Shenzhen Aolida Technology Co., Ltd. Yang Rui, the company's marketing director, said frankly: "The scarcity of the COB display package is that the surface consistency is not enough. If this problem is not solved, it will be difficult to get the customer's approval."
Second, the interpretation of COB packaging process
The COB packaging technology is categorized as a package-free or provincial-saving package. However, this package does not eliminate the packaging process, but saves the packaging process. Compared with the SMT process, the COB packaging process is saved. Going to a few steps saves time and process to a certain extent, and also saves costs to a certain extent. SMD's production process needs to undergo solid crystal, wire bonding, dispensing, baking, stamping, splitting, color separation, tape, and patch. The COB process is simplified on this basis. First, the IC is attached to the circuit board. Then solid crystal, wire bonding, testing, dispensing, baking, and become a finished product.
In terms of the production process alone, several steps have been omitted, and industry insiders say that this can save a large part of the cost. It is worth noting that the COB package does not require reflow soldering, which is one of the advantages of COB.
Array's marketing director Yang Rui said that the conventional package is to place the lamp bead on the PCB for soldering. When the lamp is getting denser and denser, the lamp pin will become smaller and smaller, so the precision of soldering will be higher. How many lamps in a square, one lamp has four feet, then there will be many solder joints in one square. At this time, the requirements for solder joints are very high, then the only solution is to reduce the solder joints. Very small solder stability is very poor, it may be accidentally touched, it may fall off, this is a problem that SMD can not avoid; COB package eliminates the process of splitting, color separation, drying, etc. The most critical difference is to remove the solder. Process, SMD in the process of soldering, the temperature control is extremely difficult to master, the temperature is too high, will cause damage to the lamp, too low, the solder does not completely melt. It is easy to cause the phenomenon of virtual welding, false welding, etc., which is a great challenge to the stability of the lamp bead. And COB does not have this process, then the stability will be greatly improved.
The processing technology of the traditional LED display screen is quite numerous, especially in the process of reflow soldering. Under the high temperature state, the expansion coefficient of the SMD lamp bead holder and the epoxy resin is different, which easily causes the bracket and the epoxy resin encapsulation to fall off. In the gap, the dead light phenomenon gradually appears in the later use, resulting in a high defect rate. The reason why the COB display is more stable is because there is no reflow soldering lamp in the processing technology. Even if there is a post-reflow soldering IC process, the diode chip has been cured and cured with epoxy resin, thus avoiding soldering. There is a problem of gaps between the lamp holder and the epoxy resin caused by high-temperature soldering in the machine.
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