Difference between COB and COG LCD Module Technology

COG modules are thinner and more compact than COB modules, and are often used in portable machines and handheld products. COG technology is often preferred for applications where space constraints are critical, such as in handheld devices and automotive displays.

 

An LCD Module (LCM) consists of four main components: the LCD screen, LED backlight, IC, and PCB (sometimes encased in a plastic shell). For simplicity, it can be viewed as having two primary parts: the LCD screen and the LED backlight, as these are the most visible elements. LCMs can be categorized based on the chip position into COB (chip on board), COG (chip on glass), and COF (chip on film). Additionally, they can be classified into graphic LCD modules and character LCD modules according to their resolution and character count.

 

COB LCD Module

 

COB, short for "Chip On Board," is the most common method for processing the drive circuit board of an LCM. The IC is directly attached to a specific location on the PCB with a piece of adhesive plastic, with the IC located under the black plastic in the image below. The chip's electrodes are connected to the corresponding pads on the PCB using aluminum wire by a soldering machine, and they are covered with a piece of adhesive plastic.

 

The COB LCD module is highly reliable, requiring precision equipment and a complex processing procedure. It uses PIN or a conductive rubber strip to connect and secure the LCD screen, LED backlight, and PCB together, making it impossible to disconnect without causing damage. While very reliable under normal circumstances, if damaged, it cannot be repaired. This technology is considered obsolete due to its size and is being replaced by the more compact COG LCD module.

 

COG LCD Module

 

COG, short for "Chip On Glass," involves bonding the IC directly to the ITO glass, as shown in the picture below. This method significantly reduces the size of the LCD module, making it ideal for mass production of consumer electronic products such as mobile phones, PDAs, and other portable devices.

 

Unlike COB, the COG LCD module does not require a PCB, which might suggest it is cheaper. However, this is not the case. COG technology necessitates dedicated glass molds and LCD FPC molds, which COB does not require. Additionally, it may require special molds for the light guide plate and backlight FPC due to its unique structure. As a result, the tooling fees for COG are the highest among the three types. For small quantities, such as 1,000 pieces, the unit price is extremely high due to these tooling costs. Conversely, for large orders, such as 100,000 or 1 million pieces, the tooling fee becomes almost negligible.

 

Is it reliable? Absolutely. While COB is the most reliable, COG is also highly dependable. Its popularity stems from its ability to save space by integrating all functions into a single IC and its cost-effectiveness for large quantities. This space-saving feature is crucial for modern portable electronic products that require compact designs.

 

In traditional LCD modules, the LCD driver is usually situated on a PCB located behind the module, which increases the display's overall thickness. Connection to the driver is established using either fixed pins or elastomer connectors, requiring multiple bonds for each drive input to the LCD. Since LCDs typically demand multiple drive inputs (even with multiplex drive techniques), the quality of these bonds significantly impacts reliability.

 

In contrast, COG modules position the LCD driver directly onto an overlapping edge of one of the glass plates composing the LCD. This design reduces the display's thickness to less than 3 mm, with all connections from the LCD driver to the LCD being completely shielded from the external environment. Each connection in COG modules requires only a single bond, ensuring optimal reliability.

 

This design eliminates the need for a separate PCB, resulting in incredibly thin and lightweight displays.

 

COG displays are smaller, more cost-effective, and highly customizable compared to typical LCD modules. They also offer improved image quality and lower power consumption. COG modules are thinner and more compact than COB modules, and are often used in portable machines and handheld products.

 

COG technology is often preferred for applications where space constraints are critical, such as in handheld devices and automotive displays.

 

 

COB LCD Module:

 

Involves mounting chips directly onto the PCB.

Compact but slightly larger due to the inclusion of a separate PCB.

May be prone to issues related to PCB connections.

Generally lower cost due to simpler assembly.

Commonly used in applications where size is not a primary concern, such as industrial displays, instrumentation panels, and consumer electronics like microwave ovens.

 

Advantages of COB:

 

Enhanced Durability: The secure placement of the driver IC on the PCB makes COB displays resistant to shock, vibration, and extreme temperatures, making them ideal for industrial settings.

Cost-Effective for Large Quantities: Despite higher initial tooling costs, COB displays become highly cost-effective when produced in large quantities.

 

Applications of COB:

 

Industrial control systems

Automotive dashboards

Medical equipment

 

COG LCD Module:

 

ICs are mounted directly onto the glass substrate.

Extremely compact and suitable for space-constrained applications.

Offers enhanced reliability due to direct chip attachment to the glass.

While requiring a higher initial investment, COG modules potentially offer cost savings over the product lifecycle due to improved reliability.

Ideal for compact devices where space is limited, including smartphones, wearables, medical devices, and automotive displays.

 

Advantages of COG:

 

Ultra-Thin Design: COG displays are ideal for modern electronic devices like smartphones and tablets, where minimizing thickness is crucial.

High-Quality Display: Direct bonding of the driver IC often results in superior image quality and reduced signal interference.

 

Applications of COG:

 

Smartphones and tablets

Ultraportable laptops

Wearable technology

 

Choosing Between COB and COG:

 

The decision between COB and COG hinges on your development and application needs:

 

- For Ruggedness and Reliability in Remote Conditions: COB is the preferred choice.

- For Thinness, Sleekness, and Stylish Design: COG is the ideal option.

 

By understanding the distinct characteristics and features of COB and COG technologies, you can effectively choose the best LCD solution for your project.

 

Conclusion:

 

In summary, we have discussed the differences between COB and COG LCD technologies in detail. COB offers simplicity and cost-effectiveness, while COG provides compactness and enhanced reliability. Armed with this understanding, designers and engineers can make informed decisions based on their project's specific requirements. Whether optimizing space, improving reliability, or managing costs, selecting the right LCD technology is crucial for achieving success in display-based applications.