Assembly types refers to
how LCD controller/driver IC chips are mounted. The most common types are
SMT, COB, TAB and COG. There are also other variants based on the these
types.SMT (Surface Mount Technology)
Using quad flat packages on printed
circuit boards is the most popular in LCD industry, and is available for
mass production of most LCD modules. It remains the most reliable and robust
method for LCD assembly.
Plastic Quad Flat Package (QFP)
represents itself as a flat rectangular integrated circuit package with its
leads projecting from all four sides of the package.
COB (Chip On Board)
COB is a popular IC mounting method
that provides wire bonding as the direct attachment of bare die to laminated
printed circuit boards. The LCD driver is formatted into an area on the PCB.
Electrical connections are made by micro diameter gold wires. The entire
area is then covered with epoxy. Most of our LCD modules use COB mounting
method.
Advantages
- Very compact
- Space savings over SMT assembly.
- Cost savvy compared with SMT, since there is no plastic
package
TAB (Tape Automated Bonding)
LCD controller and/or driver
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.
TAB mounting method uses the same type of integrated circuits
as COG technology - Gold Bumped Flip Chips. After this type of IC chip is
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.
Advantages
- Offers compactness (IC and its interfacing circuitry
can be bent behind the LCD glass panel).
- Some times more cost-effective than COG, if a designer
has to integrate a keypad or indicator around the display.
- The active area is centered (differently from COG).
- Can provide interfacing at very fine pitches.
Disadvantages
- The bonding area is weak. Less reliable than COG.
- More expensive than COG. Even though TAB LCD modules
use the same type of IC as COG, tape automated bonding requires a package.
COG (Chip On Glass)
COG is one of the high-tech mounting methods that uses gold bump or flip
chip ICs, and implemented in most compact applications. COG 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.
Advantages
-
Very space economical. COG LCD modules can be as thin
as 2 mm.
-
Cost effective over COB, especially in graphic LCD
modules, because much less IC's are required.
-
More reliable than TAB, because of the weakness in the
bond area of TAB.
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 is 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.
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