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COB packaging was first used in lighting, and this application has also become a trend. It is understood that COB-packaged bulbs have occupied about 40% of the LED bulb market.
As the LED application market gradually matures, users have higher and higher requirements for product stability and reliability, especially under the same conditions, requiring products to achieve better energy efficiency indicators, lower power consumption, and more competitive product prices. Based on this, compared with traditional LED SMD patch packaging and high-power packaging, the chip-on-board (COB) integrated packaging technology directly encapsulates multiple LED chips on a metal-based printed circuit board. As a lighting module, it directly dissipates heat through the substrate, which can not only reduce the manufacturing process and cost of the bracket, but also has the heat dissipation advantage of reducing thermal resistance. Therefore, it has become a packaging method promoted by lighting companies.
In addition to good heat dissipation performance and low cost, COB light sources can also be personalized. However, technically, COB packaging still has shortcomings such as light decay, short life, and poor reliability. If these shortcomings can be solved, it will be one of the leading directions for future packaging development.
The application of COB in lighting has become a trend. So, can this packaging technology be applied to display screens? In terms of packaging methods, some companies have made new attempts, and this attempt has been verified and has been promoted and applied in the market. At the same time, it has also attracted widespread attention from people in the industry. So why does COB display screen get everyone's attention? There must be a reason.
1. Analysis of the advantages and disadvantages of COB packaging
COB packaging has been used in the field of lighting for many years. It has many advantages in all aspects, so it has been favored by many lighting companies. So what kind of sparks will COB packaging technology create when applied to display screens? Will there be some problems with acclimatization? Let's analyze the advantages and disadvantages of COB packaging. It is understood that COB packaging technology has incomparable advantages over traditional packaging technology when applied to display screens.
1. Ultra-light and thin: According to the actual needs of customers, PCB boards with a thickness of 0.4-1.2mm can be used to reduce the weight to at least 1/3 of the original traditional products, which can significantly reduce the structural, transportation and engineering costs for customers.
2. Anti-collision and anti-pressure: COB products directly encapsulate the LED chip in the concave lamp position of the PCB board, and then use epoxy resin glue to encapsulate and solidify. The surface of the lamp point is raised into a spherical surface, which is smooth and hard, resistant to collision and wear.
3. Large viewing angle: COB encapsulation uses shallow well spherical surface to emit light, with a viewing angle greater than 175 degrees, close to 180 degrees, and has a better optical diffuse color effect.
4. Bendable: Bendability is a unique feature of COB encapsulation. The bending of the PCB will not damage the encapsulated LED chip. Therefore, the use of COB modules can easily make LED curved screens, round screens, and wavy screens. It is an ideal substrate for personalized screens in bars and nightclubs. It can be seamlessly spliced, with a simple production structure, and the price is much lower than the LED special-shaped screens made of flexible circuit boards and traditional display modules.
5. Strong heat dissipation capacity: COB products are lamps packaged on PCB boards, and the heat of the wick is quickly transferred out through the copper foil on the PCB board. In addition, the thickness of the copper foil on the PCB board has strict process requirements. In addition, the gold sinking process will hardly cause serious light attenuation. Therefore, there are few dead lamps, which greatly extends the life of the LED display.
6. Wear-resistant and easy to clean: The surface of the lamp point is raised into a spherical surface, which is smooth and hard, resistant to collision and wear; if there are bad points, they can be repaired point by point; there is no mask, and dust can be cleaned with water or cloth.
7. All-weather excellent characteristics: Triple protection treatment is adopted, and the waterproof, moisture, corrosion, dust, static electricity, oxidation, and ultraviolet effects are outstanding; it meets all-weather working conditions and can still be used normally in a temperature difference environment of minus 30 degrees to plus 80 degrees.
To be honest, COB display packaging has many advantages, especially compared with traditional packaging forms, the contrast effect is more obvious. Since there are so many advantages, why was it not widely used in the early development of LED display screens? Where are the shortcomings of COB packaging? Hu Zhijun, deputy general manager of Shenzhen Weiqiaoshun Optoelectronics Co., Ltd., said: "The only disadvantage of COB packaging is that the screen ink color is difficult to control, that is, when the light is not on, the surface ink color is inconsistent." Yang Rui, marketing director of Shenzhen Aoleida Technology Co., Ltd., also said frankly: "The flaw of COB display packaging is that the surface consistency is not enough. If this problem is not solved, it will be difficult to get customer recognition."
2. Interpretation of COB packaging process
COB packaging technology is classified as a packaging-free or packaging-saving mode, but this packaging method does not save the packaging link, but saves the packaging process. Compared with the patch process, the COB packaging process saves several steps, which saves time and process to a certain extent, and also saves costs to a certain extent. The production process of SMD requires solid crystal, wire bonding, glue dispensing, baking, stamping, light separation and color separation, taping, patching and other links, and the COB process is simplified on this basis. First, the IC is attached to the circuit board and then solid crystal, wire bonding, testing, glue dispensing, baking, and it becomes a finished product.
From the production process alone, several steps are omitted. Industry insiders said that this way, a large part of the cost can be saved. It is worth noting that COB packaging does not require reflow soldering, which is also one of the advantages of COB.
Yang Rui, marketing director of Aoleida, said that conventional packaging is to place the lamp beads on the PCB for soldering. When the lamps become denser and denser, the lamp feet will become smaller and smaller, so the precision requirements for soldering will be higher. How many lamps are there in one square? A lamp has four feet, so there will be many solder joints in one square. At this time, the requirements for solder joints are very high, so the only solution is to reduce the solder joints. Very small solder has poor stability and may fall off if touched casually. This is an unavoidable problem for SMD; COB packaging eliminates processes such as light separation and color separation, drying, etc. The most critical difference is to remove the soldering process. During the soldering process of SMD, it is extremely difficult to control the temperature. If the temperature is too high, it will damage the lamp. If the temperature is too low, the solder will not be completely melted. It is easy to cause false soldering and fake soldering, which is a big challenge for improving the stability of the lamp beads. COB does not have this process, so the stability will be greatly improved.
The processing technology of traditional LED display screens is relatively numerous, especially in the process of reflow soldering, the expansion coefficients of SMD lamp bead brackets and epoxy resins are different under high temperature conditions, which can easily cause the brackets and epoxy resin packaging shells to fall off and gaps to appear. In the later use, the phenomenon of dead lamps gradually appears, resulting in a high defect rate. The reason why COB display screens are more stable is that there is no reflow soldering lamp in the processing technology. Even if there is a later reflow soldering IC process, the diode chip has been encapsulated and cured with epoxy resin glue to protect it, which avoids the problem of gaps between the lamp bead bracket and epoxy resin caused by high-temperature soldering in the welding machine.
3. Challenges faced by COB packaging
The emergence of a new product, new technology, and new process is never smooth sailing. Only by continuous testing and continuous attempts during the research and development and production process can the problem be discovered and solved in real time. The emergence of each problem is a process of research and development personnel tackling it. This process is full of hardships, but it is also accompanied by achievements and satisfaction. The development of all emerging things is improving little by little, and is also approaching success step by step. However, for now, the development of COB packaging technology cannot be called mature. After all, it will take time for new things to mature. At this stage, COB packaging technology still faces some challenges, and these challenges are also gradually improving with the continuous efforts of enterprises.