COG LCD Display Modules

COG (Chip-On-Glass)

Chip-On-Glass (COG) is a flip chip bonding method which is used for connect assembly of bare integrated circuits (ICs) on glass substrate directly by using Anisotropic Conductive Film (ACF). The pitch of the IC bumps (footprint) can be scaled down according to customers' requirements (contact pitch of glass substrate). This method reduces the assembly area to the highest possible packing density, which especially important to those applications that space saving is crucial. It allows a cost-effective mounting of driver chips because integrating flex PCB is no longer required. The IC is bonded directly onto the glass substrate and is suitable for handling high-speed or high-frequency signals.

COG technology is one of the high-tech mounting methods which use Gold Bump or Flip Chip IC's, and implemented in most compact applications. Chip-On-Glass integrated circuits were first introduced by Epson. In flip-chip mounting, the IC chip is not packaged but is mounted directly onto the PCB as a bare chip. Because there is no package, the mounted footprint of the IC can be minimized, along with the required size of the PCB. This technology reduces the mounting area and is better suited to handling high-speed or high frequency signals.

COG is primarily used for source driver ICs within TFT display technologies where they are used for LCD, plasma, e-ink, OLED or 3D technologies. This is essential for consumer electronic products such as notebooks, tablets, cameras or mobile phones with the need for small size and light-weight components.

Advantages: 

Very economical on size. Chip-On-Glass LCD modules can be as thin as 2 mm. 

Cost effective over COB, especially in graphic LCD modules, because reduces the number of IC's. 

More reliable than TAB due to TAB's weakness in the bond area. 

Disadvantages: 

COG can only be used at a certain resolution level where the lines are not too fine. At very fine pitches COG becomes difficult to test, and TAB would be the preferred approach. 

It may be more cost-effective to use TAB or COB, if a designer has to integrate a keypad or indicator around the display. 

The active area is not centered within the outline but offset, because of the area where the circuits are.