CHIP-ON-GLASS (COG)
Chip-On-Glass is one of the high-tech mounting methods that uses Gold Bump or Flip Chip ICs, 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 a mounting area and is better suited to handling high-speed or high-frequency signals. Currently, there are 12 standard C.O.G. LCD modules available with the regular mass production delivery time.
Advantages:
o Very space economical. Chip-On-Glass LCD modules can be as thin as 2 mm.
o Cost effective over COB, especially in graphic LCD modules, because much less IC's are required.
o More reliable than TAB because of the weakness in the bond area of TAB.
Disadvantages:
o 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 is the preferred approach.
o It may be more cost-effective to use TAB or COB, if a designer has to integrate a keypad or indicator around the display.
o The active area is not centered within the outline but offset, because of the area where the circuits are.
o Since the Chip-On-Glass integrated circuit has been invented by Epson, COG technology became very popular due to the demand for more compact applications. In the near future we will see this IC mounting method finding its applications in many other equipment than cellular phones, PDA's, computer network servers, satellite receivers, etc.
TAPE AUTOMATED BONDING (TAB)
Tape Automated Bonding (TAB) LCD driver or controller electronics are encapsulated in a thin, hard bubble package, of which the drive leads extend from the bubble package on a thin plastic substrate. The adhesive along the edges is used to attach the TAB to the LCD glass and/or PCB.
Tape Automated Bonding IC mounting method uses the same type of integrated circuits as Chip-On-Glass technology - Gold Bumped Flip Chips. After this type IC chip has been produced, a gold bump is placed on the IC chip and then sealed onto the polymide board. (This procedure is called ILB or Inner Lead Bonding) and is how the TCP IC is produced. TAB LCD modules are always custom made.
Advantages:
o Offers compactness (IC and its interfacing circuitry can be bent behind the LCD glass panel).
o Some times more cost-effective than Chip-On-Glass, if a designer has to integrate a keypad or indicator around the display.
o The active area is centered (differently from COG).
o Can provide interfacing at very fine pitches.
Disadvantages:
o The bonding area is weak. Less reliable than COG.
o More expensive than COG. Even though TAB LCD modules use the same type of IC as COG, tape automated bonding requires a package
