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What is COB?

Its full name is chip-on-board, that is, chip on board packaging, which is a new packaging method different from SMD sticker packaging technology, specifically, the bare chip is attached to the PCB with conductive or non-conductive adhesive, and then the lead bond to achieve its electrical connection, and the chip and the bond lead are wrapped with adhesive.

Advantages of COB packaging

1. Ultra-thin and light: according to the actual needs of customers, the thickness of the PCB board from 0.4-1.2mm thickness is used, so that the weight is reduced to at least 1/3 of the original traditional products, which can significantly reduce the structure, transportation and engineering costs for customers.

2. Anti-collision and anti-pressure: COB products directly package the LED chip in the concave lamp position of the PCB board, and then package and cure with epoxy resin adhesive, the surface of the lamp point is raised into a sphere, smooth and hard, crash-resistant and wear-resistant.

3. Large viewing Angle: The COB package uses the foreground spherical light, the viewing Angle is greater than 175 degrees, close to 180 degrees, and has a better optical diffuse color muddy light effect.

4. Bendability: bendability is the unique characteristic of COB package, PCB bending will not cause damage to the packaged LED chip, so the use of COB module can easily make LED curved screen, circular screen, wave screen. It is the ideal base material for personalized modeling in bars and nightclubs. It can be seamless splicing, the production structure is simple, and the price is much lower than the LED shaped screen made by the flexible circuit board and the traditional display module.

5. Strong heat dissipation: The COB product is to package the lamp on the PCB board, and quickly transfer the heat from the wick through the copper foil on the PCB board, and the copper foil thickness of the PCB board has strict process requirements, and the gold sinking process, almost will not cause serious light attenuation. As a result, deaths are rare and life expectancy is greatly extended.

6. Wear-resistant and easy to clean: the surface of the lamp is convex into a sphere, smooth and hard, crash-resistant and wear-resistant; There are bad points, can be repaired point by point; No mask, dust can be cleaned with water or cloth.

7, all-weather excellent features: triple protection treatment, waterproof, tide, rot, dust, electrostatic, oxidation, UV effect is outstanding; Meet the all-weather working conditions, the temperature difference between minus 30 degrees to 80 degrees can still be used normally.

Years of actual cases and data have proved that COB products are powerful, and the industry's vigorous promotion has also given COB products greater space for development. At present, COB packaging technology mainly has the following three development directions

(A) single lamp bead COB packaging technology

This technology follows the idea of traditional packaging technology, has a lower technical threshold, and the entire process route and industrial chain layout have not changed much. Display factory or purchase packaging factory packaging COB lamp beads, and then through the SMT process to the LED display panel

(2) Limited integration of COB packaging technology

In order to improve production efficiency and reduce pixel failure rate, while avoiding significantly increasing the difficulty of packaging technology, some manufacturers began to try limited integration COB packaging technology. The display factory no longer purchases a single COB lamp bead from the packaging factory, but a COB module with a stand in a limited integrated package, and then these modules are installed on the LED display panel through the SMT process

(3) COB integrated packaging technology

COB integrated packaging technology refers to COB packaging technology with a high degree of integration, generally should have at least 0.5k of integration, the current technology has broken through the integration of 2k. The lamp bead integration of the entire LED display panel is completed in the packaging link and no longer requires the SMT process.

The most significant difference between COB integrated packaging technology and the other two COB packaging technologies lies in the following aspects.

(1) No support.

(2) Have a high integration of at least 0.5k.

(3) There is no display factory link in the industrial chain structure

(4) The LED display panel is integrated in the packaging link rather than through the SMT process after packaging

Second, COB packaging process interpretation

The packaging technology of COB is classified as packaging free or packaging mode, but this packaging method is not to save the packaging link, but to save the packaging process, compared with the patch process, the packaging process of COB to save several steps, to a certain extent, saving time and technology, but also to a certain extent, saving costs. SMD production process needs to go through solidification, welding wire, dispensing, baking, stamping, splitting color separation, ribbon, patch and other links, and COB process on this basis to simplify, first paste the IC on the circuit board and then solidification, welding wire, testing, dispensing, baking, become a finished product.

Third, the challenges of COB packaging

1, the one-time pass rate of the packaging process

COB package because of its characteristics, COB package is to be on a large board, the board has a maximum of 1024 lights, SMD if the seal is broken, only need to change one on the line, but COB package of 1024 lights after the completion of the package, to test, all lights confirmed that there is no problem, before sealing. How to ensure that the whole board of 1024 lights are completely intact, a pass rate is a very big challenge.

2. One-time pass rate of finished products

The COB product is to seal the lamp first, after sealing the lamp, the IC driver device should be reflow processing, how to ensure that the lamp surface in the reflow processing, the high temperature of 240 degrees in the furnace will not cause damage to the lamp. This is another big challenge. Compared with SMD, COB saves the processing of over-reflow on the lamp surface, but the device surface needs to be over-reflow as well as SMD, that is, SMD needs to be reflow twice. The difference is that when SMD is over-reflow, the temperature in the furnace will cause two kinds of damage to the lamp surface, one is the welding wire, the temperature is too high. It will expand rapidly, causing the filament to break, the second is the heat in the furnace through the four pins of the support quickly transferred to the wick, the wick may cause small fragmentation damage, this damage is very deadly, detection is often difficult to find, including aging test is difficult to detect, but the crystal of this small damage subtle cracks, after a period of time

Such shortcomings will be prominent, which will lead to the failure of the bulb. COB is to ensure that when the lamp surface is reflow welded, the high temperature in the furnace does not cause damage to it and ensure the yield, which is also a very important level.

3, the whole lamp maintenance

For the maintenance of COB lights, professional repair and maintenance is required. One of the biggest problems with single lamp maintenance is that after repair, there will be a circle around the lamp, repair a lamp, and the surrounding circle will be smoked by the welding torch, and the maintenance difficulty is relatively high.

There are challenges that need to find out the corresponding solutions, at present, COB packaging in the packaging and maintenance process of the problems encountered, the company has come up with the corresponding solutions, such as when the lamp surface reflow, using a certain way to protect the lamp surface, reduce damage; In the maintenance process, point-by-point correction technology is used to ensure the consistency between the lamp beads.

Fourth, the development trend of COB packaging

One advantage of COB packaging is that it is directly packaged on the PCB board and is not limited by the lamp beads, so, for COB, the point spacing is not scientific, in theory, COB packaging wants to achieve high-density, it is very easy. To borrow a word from the industry, COB packaging is tailored for small spacing.