Liquid crystal display and its inspecting method

Details Liquid crystal display and its inspecting method Liquid crystal display and its inspecting method

2001-11-19

2002-06-18

Dudek, James (Department: 2871)

Liquid crystal cells, elements and systems

Particular structure

Having significant detail of cell structure only

C349S150000, C349S151000, C349S152000

Reexamination Certificate

active

06407795

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a liquid crystal display for a video monitor such as a television receiver or a display of a computer system, and particularly to a method of fabricating and inspecting the display.
BACKGROUND ART
As liquid crystal displays have recently been improved in a low-voltage operation, low power consumption, and thickness, the displays are widely used as AV devices, OA devices, or house-hold appliances as well as television receivers or monitors. Also, they have an increased screen size.
In such a liquid crystal display, a liquid crystal driving LSI is commonly mounted as a semiconductor chip by a mounting method selected from various techniques. As the method, a tape automated bonding (TAB) method and a chip on glass (COG) method are known.
In the TAB method (also called a TAB mounting), a film circuit board (referred to as a tape carrier package or TCP) on which a driving LSI chip is mounted has an output port connected to a liquid crystal panel and an input port connected to an external circuit board. Although the TAB method is often used for a liquid crystal display, an overall size (outline) of the display may significantly increase.
In the COG method (also called a COG mounting), conductors disposed at an edge of a liquid crystal panel are joined directly to input and output ports (called input/output pads) of liquid crystal driving LSIs of a chip form with an anisotropically conductive adhesive. Thereby, the liquid crystal driving LSIs are located about the liquid crystal panel. More specifically, the liquid crystal driving LSI has the output ports connected to a signal line and a scanning line of the liquid crystal panel, and the input ports connected to a terminal conductor provided at a rim (often an outermost end) of the liquid crystal panel.
Signals including a data signal, clock signal, and source voltage for controlling an operation of the driving LSIs are called control signals. In general, the control signals are transferred via each flexible circuit board (also called flexible printed circuit, FPC), which is equipped with transmission lines (also called bus lines), and received by the terminal conductor.
The transmission of the control signals via the FPC to the driving LSIs is more advantageous than along the transmission lines provided on the liquid crystal panel in respect of the resistance in the transmission lines or the availability of the wiring space. This may also be pertinent to a liquid crystal panel of poly-silicon TFT type which has driving circuits provided at the rim of the panel.
The COG method is more favorable than the TAB method in an operation reliability a reducing of an overall product size.
FIG. 14
illustrates a conventional liquid crystal display having driving LSIs mounted by the COG method. The output and input ports of liquid crystal driving LSIs
5
,
6
are joined to conductors disposed at the outward edge of a liquid crystal panel
1
with an anisotropically conductive adhesive
9
. Flexible circuit boards
101
and
102
are joined to the conductors also with the anisotropically conductive adhesive
9
. The flexible circuit boards
101
and
102
has other end connected to corresponding connectors
104
and
105
on an external circuit board
103
, respectively. In
FIG. 14
, the width of the flexible circuit board
101
and the width of the flexible circuit board
102
are denoted by wy
1
and wx
1
respectively.
FIG. 15
is a schematic overall view of the liquid crystal panel
1
. A pixel is disposed at each intersection
2
between a signal line
3
and a scanning line
4
. A region of the liquid crystal panel
1
where the pixels are arranged is called an image display region, and the other region where pixels are not disposed is called a non-image display region. The signal line driving LSIs
5
for driving the signal line and the scanning line driving LSIs
6
for driving the scanning line are called driving LSIs. The terminal conductors
7
and
8
(also called connector ports) are disposde at the outward edge of the liquid crystal panel
1
. The terminal conductors are classified into signal line terminal conductors and scanning line terminal conductors. The flexible circuit boards
101
and
102
are connected to the signal line terminal conductors and the scanning line terminal conductors, respectively. The circuit board
103
, which often employs a printed circuit board, includes a control circuit generating the control signals.
FIG. 16
is a schematic view of a pattern of wiring on the flexible circuit board
101
or
102
and an arrangement of the terminal conductors
208
on the liquid crystal panel
1
. As shown in
FIG. 16
, each flexible circuit board
202
includes transmission lines (bus lines)
200
for transferring the control signals and connector ports
220
corresponding to the terminal conductors
208
joined to the signal line or scanning line driving LSI, respectively. Reference numerals pi
1
and pi
2
denote the distance between the closest terminal conductors
208
of any two adjacent driving LSIs
206
. The distance is called as an LSI pitch hereinafter. Plural driving LSIs are often disposed at various LSI pitchs, respectively.
As shown in
FIG. 16
, the terminal conductors
210
are connected at least to the input ports of the driving LSI
206
. Other terminal conductors may be provided for connecting to a common electrode to which a reference operational voltage is applied, and to a repair line for replacing a defective signal or scanning lines.
In case that the driving LSIs are replaced with different types or their installation is modified due to a specification change in the liquid crystal panel, the LSI pitch or the number of the terminal conductors may be varied. This requires re-designing of the flexible circuit boards.
FIG. 14
illustrates an extended form of the flexible circuit boards
101
and
102
. The flexible circuit boards
101
and
102
are often used as shown in
FIG. 14
but may be folded to an L-shape or U-shape at the edge of the liquid crystal panel
1
in order to reduce a frame of the liquid crystal display, as not shown.
The flexible circuit boards
101
and
102
are mounted to conductors at the rim of the liquid crystal panel
1
with an anisotropically conductive adhesive
9
which is applied and heated. The board may be heated at a temperature of about 200° C. during the heating, as the flexible circuit board is thermally expanded or contracted, the pitch between the connector ports may be deviated from an original one, that is, a pitch error may be developed. If the pitch error is not negligible, the connector ports and the terminal conductors may be connected inadequately. For reducing the pitch error, the pitch between the connector ports may be thermally compensated. The greater the width of the flexible circuit boards (wy
1
and wx
1
in FIG.
14
), the more accurate thermal compensation for the pitch measurements will be required, and thus, the compensation increases an overall cost.
If the liquid crystal panel
1
changes in a specification or screen size, the flexible circuit boards
101
and
102
has to be modified and re-designed (e.g. the overall dimensions). Such a design modification increases a cost significantly because the number of types of the flexible circuit boards has recently been increasing.
The liquid crystal panel
1
is generally inspected, after the driving LSIs are mounted, through a visual examination with a displayed target. If one of the driving LSIs
5
or
6
is found defective, the flexible circuit boards
101
and
102
is dismounted, the defective driving LSI is then replaced by a new one, and the flexible circuit boards
101
and
102
are then mounted again. That raises a cost.
When plural driving LSIs
5
,
6
are employed, a data shift signal is transferred through the LSIs in sequence. If a defective driving LSI is included in the LSIs, the data shift signal after the defective driving LSI is not transferred to the succeeding LSIs, which can not thus be inspected. Therefore, the LSIs

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