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Electronic manufacturing industry PCB/PCBA knowledge
Will COB LED become a trend in the future

COB LED technology is an emerging LED packaging technology, different from the traditional SMD LED package, it is to integrate light-emitting chips in the PCB board, rather than soldering to the PCB one by one. COB has the advantages of high reliability, low cost, small pitch and wear-resistant and anti-collision, which effectively improves the luminous light color of LED display, reduces risk and reduces costs.

Table of Contents

What are the components of LED display

The components of LED display
The components of LED display

1. LED unit board

It is one of the core components of LED display, and the quality of the unit board directly affects the effect of the display display. The unit board is composed of LED module, driver chip and PCB.

2. Control card

Using a low-cost strip screen control card, which can control a 256×16 dot two-color screen with 1/16 scan, and can assemble a cost-advantaged LED screen. The control card can be powered off to save information, and the information stored in it can be displayed without connecting to a PC.

3. Connection

It can be divided into data cable, transmission line and power line. The data cable is the cable used to connect the control card and the LED unit board. The transmission cable is used to connect the control card and the computer. The power cord is used to connect the power supply and control card and the LED unit board, and the diameter of the copper core of the power cord connecting the unit board is not less than 1mm.

4. Power supply

The power supply generally uses switching power supply, 220V input, 5V DC output. Besides, because the LED display screen is a precision electronic device, it is necessary to use switching power supply and cannot use a transformer.

What is a LED display packaging

What is a LED display packaging
What is a LED display packaging

In the production process of LED electronic display, packaging is an indispensable process, what is packaging? It is to package the LED display chip with insulating plastic or ceramic materials to isolate the chip from the outside world to prevent impurities in the air from corroding the chip circuit and causing a decline in electrical performance. And the packaged chip is more convenient for installation and transportation.

Packaging technology is very important, because only packaged products can become terminal products, can be used by users, and the quality of packaging technology directly affects the performance of the LED product itself, good packaging can make LED have better luminous efficiency and heat dissipation environment, and then improve the life of LED, reliable packaging technology is the product to practical and market.

Nowadays, there are three more commonly used LED display packaging methods on the market: DIP, SMD, COB, SIP, three-in-one,…

What is a COB package

COB (chip On board) package is to glue the bare chip to the interconnect with conductive or non-conductive glue, and then bond the wire to realize its electrical connection. COB packaging is bracketless technology, without the soldering pin pin of the bracket, every lamp bead and welding wire is tightly encapsulated in the gel by epoxy resin colloid, without any exposed elements.

Compared with SMD-packaged displays, COB LED displays use integrated packaging technology (eliminating the process of packaging and then patching a single LED device), which can effectively solve many problems of SMD-packaged displays, such as increasing process difficulty, low yield and high cost due to the continuous reduction of point spacing.

However, because COB packaging integrates upstream chip technology, midstream packaging technology and downstream display technology, the application of COB packaging in the display industry has not been widely promoted in recent years. In order to realize large-scale application of COB packaging, it needs to be closely coordinated by upstream, midstream, and downstream enterprises.

What’s the advantage and disadvantage of COB LED

The advantage and disadvantage of COB LED
The advantage and disadvantage of COB LED

LED electronic screen is a kind of display device that uses LED light-emitting diodes as display components, which are widely used in various occasions indoors and outdoors, such as advertising, meetings, performances, rentals, etc. LED packaging technology is an important factor affecting its performance and quality, currently there are mainly two ways of package: SMD packaging and COB packaging two ways.

SMD packaging refers to the LED chip packaged in a plastic shell, and then pasted on the printed circuit board by the placement machine to form a single pixel. The advantage of SMD packaging is that the production process is mature, the cost is low, and it is suitable for large-pitch displays. However, SMD packaging also has some disadvantages, such as easy external damage, poor heat dissipation, serious light decay, rough picture, etc.

COB packaging refers to the LED chip directly fixed on the printed circuit board, and then completely sealed with epoxy resin to form a uniform light-emitting surface. The advantages of COB packaging are high stability, good heat dissipation, high light efficiency, delicate picture, suitable for small-pitch displays. Specifically, the COB package LED electronic screen has the following advantages and disadvantages:

Advantages of COB LED

● Anti-collision and wear-resistant: Because the device is not exposed, the COB packaged LED can effectively resist the impact of external impact, friction, vibration and other influences, and is not easy to appear dead lights, dropped lights and other phenomena, improving the reliability and durability of the product.

● Fast heat dissipation: Since the heat is directly dissipated through the printed circuit board, the COB LED has a low thermal resistance value and good heat dissipation performance, which can effectively reduce the working temperature and light decay rate, and extend the life of the product.

● Smaller pitch: Since there is no physical barrier and the shell occupies a lot of space, the COB LED can achieve smaller pixel pitch and higher pixel density, thereby improving the resolution and clarity of the display.

● Higher light efficiency: Since there is no light loss caused by lenses and other parts, the COB LED can achieve higher light output and light efficiency ratio, thereby saving energy consumption and operating costs.

● High quality picture: Due to the use of surface light source luminescence and matte coating technology, the COB LED electronic screen can effectively suppress moiré and glare phenomenon, reduce visual fatigue and glare, and improve viewing comfort.

Disadvantages of COB LED

Although the COB LED electronic screen has many advantages, there are also some disadvantages, mainly as follows:

● High cost: Due to the complex process of COB packaging, large equipment investment and low production efficiency, the cost of COB LED electronic screens is higher and is not suitable for large-scale market promotion.

● Uneven brightness: Since the COB LED electronic screen is composed of multiple units, the brightness of each unit may be different, resulting in uneven brightness of the display screen and affecting the display effect.

● Difficult maintenance: Because the COB packaged LED electronic screen is completely sealed on the printed circuit board, if there is a failure, it is difficult to repair and replace, and the entire module or the entire display screen needs to be replaced, which increases the maintenance cost and difficulty.

● Poor compatibility: Since the COB LED electronic screen is a new type of packaging technology, there is no unified standard and specification at present, and the products of different manufacturers may have compatibility problems, which brings difficulties to system integration and application.

Therefore, the LED electronic screen packaged by COB needs further technical improvement and market development to achieve wider application and development.

What’s the process of COB LED display packaging

process of COB LED display packaging
Process of COB LED display packaging

COB LED display has good look, good picture quality, strong protection, all these characteristics are all attributed to its packaging method COB.

COB LED packaging is to package the light-emitting chip directly on the PCB board, a COB display packaging process flow is as follows: clean PCB — drop adhesive— chip paste — test— Seal and heat to cure — test — storage.

1. Clean PCB board: clean board is to improve the quality of bonding, after cleaning the PCB board still has stains or oxide layer, need to test positioning, with brush or air gun to clean before entering the next process.

2. Drop adhesive: the adhesive usually adopts two ways, one is pressure injection method, and the other is needle transfer;

Pressure injection method: the glue is poured into the container, air pressure is applied, and the caliber of the injection is controlled.

Needle transfer: a rapid dispensing method, using a needle to extract glue from the container and apply it to the PCB board;

The drop adhesive is to prevent the chip from falling off during the bond process.

3. Chip pasting: chip pasting is also called solid crystal, the process requires rigorous, must be “stable and positive”, pay attention to the chip can not have reverse phenomenon;

4. Wire bonding: The purpose is to link electrical and mechanical, and the tensile test done by each company is different, and it can be carried out according to the company’s standards. The wire should be handled lightly, and a special person needs to check its correctness every two hours;

5. Sealing: Check whether there is any dew phenomenon during the sealing process, whether there are pores on the surface, and whether the black glue is cured after that. Packaging has strict requirements for technicians, and the process must be strictly controlled;

6. Test: In the bonding process, there may be undesirable phenomena that are not easy to find, so the chip-level packaging must be tested for performance; There are two ways to detect it: non-contact and contact.

Non-contact detection is mainly visual inspection, and it is also the basic detection technology that must be mastered by COB process personnel, but whether it is non-contact or contact, the relationship between the two should be complementary, not alternative.

What is the difference between SMD LED and COB LED packaging technology

LED display is packaged into a screen, when it comes to packaging technology, the most commonly used in the LED display industry is SMD technology and COB technology, so what is the difference between these two packaging technologies?

● The meaning is different

SMD packaging technology is to package the light-emitting chip into a lamp bead, solder the lamp bead to the PCB board to form a unit module, and finally spliced into a whole LED screen.

COB packaging technology is to solder the light-emitting chip directly on the PCB board, and then the overall film is coated to form a unit module, and finally spliced into a whole LED screen.

● The image is displayed differently

COB screen is a surface light source, SMD screen is a point light source, so COB screen visual perception is better, and no grain, more suitable for long-term close viewing. COB screen has higher contrast than SMD screen, and the viewing effect of COB screen is closer to LCD screen when viewed frontally, with vivid colors and better details. However, the COB screen cannot sort the similar optical performance of the single lamp beads like the SMD screen, so the COB LED screen is prone to chromatic aberration when squinting.

● Stability, maintainability are different

SMD LED screen, the overall protection is weak, and easy to knock the lamp off, waterproof, moisture-proof, dustproof performance is poor, can not be wiped, but the site maintenance is convenient, conducive to later maintenance.

The COB LED screen has good overall protection, the front protection level can reach IP65, and it can be cleaned with a wet towel, but because the overall lamination site cannot be repaired, it needs to be returned to the factory for repair.

● Power consumption, energy efficiency is different

The luminescent wafer in the lamp bead of the mainstream product SMD screen is mostly a formal installation process, and there are leads above the light source, while the COB screen is mostly a flip process, and the light source is not occluded, so when the same brightness is achieved, the power consumption of the COB screen is lower and has a better economic type. In addition, due to the low permeability of epoxy resin used in SMD lamp bead packaging, the overall film permeability of the COB screen is higher, which further improves the use economy of the COB screen.

● The cost is different

The production process of SMD is relatively complex, but the technical threshold is low, and the vast majority of manufacturers in the country adopt SMD technology, and the technology development is relatively mature. COB production process threshold is high, less than 20 manufacturers in the country have R & D production and manufacturing capabilities. Although the theoretical cost of COB technology is lower than that of SMD screen, the actual cost is not very low at present due to the low product yield.


Since the advent of LED devices for display purposes, it has experienced DIP in-line, dot matrix module, monochrome CHIP type, full-color TOP type, full-color CHIP type, multi-lamp integrated packaging, COB and other packaging types. The emergence of each new packaging form enriches the application types of LED display products. The emergence of COB LED will also bring a large number of new products and applications.

Although the price of the COB package display is not dominant, the COB package LED module is installed with multiple LED chips on the bottom plate, and the use of multiple chips can not only improve the brightness, but also help to achieve the reasonable configuration of the LED chip, reduce the input current of a single LED chip to ensure high efficiency. In the future, COB LED displays may be more widely used.


COB LED is called COB LED source,COB LED module, meaning that the chip is directly bound to the entire substrate, and all the chips are integrated together for packaging.

COB LED packaging is to package the light-emitting chip directly on the PCB board, a COB display packaging process flow is as follows: clean PCB --- drop adhesive--- chip paste --- test--- Seal and heat to cure --- test --- storage.

● Anti-collision and wear-resistant
● Fast heat dissipation
● Smaller pitch
● Higher light efficiency
● High quality picture

● High cost
● Uneven brightness
● Difficult maintenance
● Poor compatibility

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