The advantages and disadvantages of COB packaged LED display and its development difficulties

COB packaging integrates upstream chip technology, midstream packaging technology and downstream display technology. Therefore, COB packaging requires close cooperation between upstream, midstream and downstream companies to promote the large-scale application of COB LED displays.

As shown in the figure above, it is a COB integrated package LED display module. The front side is composed of LED lamp modules to form pixels, and the bottom side is an IC driving element. Finally, each COB display module is spliced ??into a design-sized LED display.

Theoretical advantages of COB:

1. Design and development: Without the diameter of a single lamp body, it can be made smaller in theory;

2. Technical process: reduce bracket cost and simplify manufacturing process, reduce chip thermal resistance, and realize high-density packaging;

3. Engineering installation: From the application side, the COB LED display module can provide manufacturers of display screen users with a simpler and faster installation efficiency.

4. Product features:

(1) Ultra-light and thin: According to the actual needs of customers, PCB boards with a thickness from 0.4 to 1.2 mm can be used to reduce the weight at least to 1/3 of the original traditional products, which can significantly reduce the structure, transportation and engineering costs.

(2) Anti-collision and compression: COB products directly encapsulate the LED chip in the concave lamp position of the PCB board, and then encapsulate and cure it with epoxy resin. The surface of the lamp point is convex into a spherical surface, which is smooth and hard, and is resistant to crash. 

(3) Large viewing angle: the viewing angle is greater than 175 degrees, close to 180 degrees, and has a better optical diffuse color haze effect.

(4) Strong heat dissipation capability: COB products encapsulate the lamp on the PCB board, and quickly transfer the heat of the wick through the copper foil on the PCB board. Moreover, the thickness of the copper foil of the PCB board has strict process requirements, plus the sink that the gold process hardly causes serious light attenuation. So there are few dead lights, which greatly extends the life of the LED display.

(5) Wear-resistant and easy to clean: The surface is smooth and hard, impact-resistant and wear-resistant; there is no mask, and it can be cleaned with water or cloth when there is dust.

(6) Excellent all-weather characteristics: triple protection treatment, outstanding waterproof, moisture, corrosion, dust, static electricity, oxidation, and ultraviolet effects; meeting all-weather working conditions, and the temperature difference environment of minus 30 degrees to minus 80 degrees can still be used normally.

It is for these reasons that COB packaging technology has been pushed to the forefront in the display field.

Current COB technical problems:

At present, COB's accumulation in the industry and process details need to be improved, and some technical problems are also facing.

1. The one-time pass rate of the package is not high, the contrast is low, and the maintenance cost is high;

2. The color uniformity is far inferior to the display screen after the SMD device with light and color separation.

3. The existing COB package still uses the formal chip, which requires die bonding and wire bonding. Therefore, there are many problems in the wire bonding process and the process difficulty is inversely proportional to the pad area.

4. Manufacturing cost: Due to the high defect rate, the manufacturing cost far exceeds the small pitch of SMD.

Based on the above reasons, although the current COB technology has made certain breakthroughs in the display field, it does not mean that SMD technology has completely withdrawn and declined. In the field of dot pitch above 1.0mm, SMD packaging technology relies on its mature and stable product performance. Extensive market practice and perfect installation and maintenance guarantee system are still the leading role, and they are also the most suitable selection direction for users and the market.

With the gradual improvement of COB product technology and the further evolution of market demand, the large-scale application of COB packaging technology in the interval of 0.5mm to 1.0mm will reflect its technical advantages and value. To borrow a word from the industry saying: "COB package is tailor-made for 1.0mm and below dot pitch."