COB LED Display Technology

What Is a COB LED?

COB (Chip on Board) is a packaging method in which red, green, and blue LED chips are mounted directly onto a printed circuit board and then the entire surface is coated with epoxy resin. Since the chips are not housed separately, there are no exposed components on the module’s surface.

This structure differs from the traditional surface-mount (SMD) method in two key ways. First, the wires connecting the chips to the circuit board are eliminated; second, the protective resin layer encapsulates the entire module as a single unit. The result is a module that allows for both a higher pixel density and greater resistance to external factors.

The Difference Between SMD and COB Packaging

In SMD technology, each LED chip is packaged within its own housing, and this package is soldered to the surface of the circuit board. Since the housing and solder joints take up a certain amount of space, the distance between chips cannot be reduced below a certain value. In the COB method, since the chips are placed directly onto the board, more pixels can fit into the same area.

The second difference lies in durability. In SMD modules, the chip housings protrude from the surface and can therefore be damaged by impact, friction, or contact. In COB modules, the resin layer covers these components, resulting in a flat and protected surface.

Advantages of COB LED Technology

Applications

COB modules are preferred for indoor applications where the viewer is several meters away from the screen. The protected surface offers an additional advantage in areas with heavy foot traffic.

• Control and Monitoring Rooms
• Boardrooms and meeting rooms
• Corporate reception and lobby areas
• Broadcast studio backdrops
• Showroom and sales office presentation walls

The COB Module Manufacturing Process

COB module production begins with the placement of chips onto the contact points on the printed circuit board. After the chips are positioned with micron-level precision, electrical connections are established, and the entire module is coated with epoxy resin. When the coating process is performed under vacuum, no air pockets form; if air pockets remain, moisture buildup and pixel loss may occur over time.

After coating, the module surface undergoes a matte finish treatment. This process reduces the reflection of ambient light, thereby enhancing contrast. The final step in the production process is measuring and recording the color and brightness values of each module; this data forms the basis for the calibration performed when the modules are assembled.

Limitations of COB Technology

The advantages offered by COB modules must be evaluated in conjunction with specific cost and service conditions. This technology may not be the right choice for every project.

• Individual pixel repair is limited. Since the chips are encapsulated in resin, replacing a single pixel—as is possible with SMD modules—is impractical; in the event of a failure, the entire module must be replaced.
• The module cost is high. It is significantly higher than that of SMD modules for the same surface area.
• It offers no benefit at long distances. On screens viewed from eight meters or farther, the difference in resolution is imperceptible; the budget spent does not yield a corresponding visual benefit.
• Spare module planning is required. To ensure color consistency, it is recommended that spare modules be sourced from the same production batch.

The Relationship Between COB and MicroLED

MicroLED is a production approach in which the chip size is reduced to the micrometer level and is used in conjunction with COB packaging. Since COB defines a packaging method and MicroLED defines the chip scale, the two concepts are not alternatives to one another.

Screens with pixel pitches of P0.9 and below on the market are generally produced by packaging MicroLED chips using the COB method. This segment is geared toward applications requiring very close viewing distances, such as control rooms and broadcast studios.