Electric heating – Metal heating – By arc
Reexamination Certificate
2002-02-28
2003-07-08
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121670, C219S121770
Reexamination Certificate
active
06590181
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention generally relates to cutting of a substrate, and more particularly to apparatus and method for cutting a brittle object such as a glass substrate for use of an LCD panel using a laser.
(b) Description of the Related Art
Liquid crystal display (LCD) devices are a well known form of flat panel display. Especially, the smaller, lighter and less power consumptive characteristics make the LCD devices considered as one of the most contending display devices to replace the cathode ray tube (CRT).
LCD devices include two pieces of glass substrates, and a liquid crystal inserted between the two glass substrates. The liquid crystal acts as an optical shutter for an incident light by changing its alignment state by applying an electric field, and thereby an image is displayed on the LCD screen.
To enhance a productivity in manufacturing such LCD devices, methods for making a plurality of panels in a single process have been proposed. One method is using a glass substrate having a size corresponding to those of a plurality of unit panels, for example, 6 unit cells.
When a thin film transistor (TFT) LCD is manufactured using two substrates of the above-mentioned large 6 unit LCD panel size, a gate line, a data line, a thin film transistor, a pixel electrode, an alignment film and other components necessary for 6 unit TFT substrates are formed on the inner surface of one of substrates, while a color filter layer, a counter electrode, a black matrix and the like which are necessary for 6 unit color filter substrates are formed on the inner surface of the other.
The two glass substrates are produced as a unit panel after undergoing a process of attaching two glass substrates using a sealant, a cutting process, a liquid injecting process, an end seal process, and a process of attaching a polarizing film.
FIG. 1
is a plan view of a mother glass substrate
1
for cutting, where cutting keys
20
are formed on each corner of LCD unit cells
6
, and scribe lines
4
a
,
4
b
are defined along the cutting keys
20
.
During the cutting process, a preliminary cutting groove having a selected depth is formed along the scribe lines
4
a
,
4
b
on the mother glass substrate
1
using a diamond cutter. Then, an impact is added onto the glass substrate
1
so as to separate LCD unit cells
6
from the mother glass substrate
1
.
However, a cutting apparatus such as the diamond requires an impact for a complete separation after the preliminary cutting groove is formed, which scatters small glass chips all around the cutting line. Therefore, an additional dust collection device is needed in order to prevent a failure caused by those fine glass chips.
Moreover, a plurality of rough edges as shown in
FIGS. 2A and 2B
, which are expanded views of portions E1, E2 of
FIG. 1
, are generated when the mother glass substrate
1
is cut by a diamond cutter. A high stress is concentrated on the rough edges, and a higher stress is concentrated on a portion
8
that is extremely rough. Therefore, when the unit panel
6
is separated by an impact which is added after the preliminary cutting groove is formed, the unit panel
6
is separated along the portion
8
where a high stress is concentrated on, not along the preliminary cutting groove (marked as a dotted line). This failure may cut out an active area.
Such a problem occurs frequently while manufacturing a tiled LCD panel for a large screen display.
FIG. 3
is a plan view of an LCD panel
20
where the four unit panels (A to D) are tiled, and
FIG. 4
is an expanded view of the portion E4 shown in FIG.
3
.
As shown in
FIGS. 3 and 4
, assume that the unit panels cut by the diamond cutter are bonded by an optical bond
22
. When the two LCD unit glasses A and B having rough cut faces
24
and
25
are bonded, a seam line
22
becomes at least 2 mm wide, due to the prominence and depression margin of cut faces
24
and
25
of LCD unit glass A and B. Therefore, the black matrix at the bonding boundary of the glass A and B also becomes at least 2 mm wide to cover the seam line
22
. The black matrix at the bonding boundary is much wider compared with that of the black matrix on the surfaces of the two LCD unit glasses A and B. As a result, the seam line
22
distinguishes itself on a screen of the tiled LCD panel
20
during operation and it appears that the image is divided by the seam line. To prevent this, a minimum seam line width that can be achieved is calculated beforehand. Then, the width between the pixels of the LCD panel is designed to be the same as the calculated minimum width of the seam line, so that the seam line may serve as a black matrix, which prevents the split appearance of screen.
That is, an overall resolution of the tiled LCD module is determined by the width of the seam line. Therefore, to enhance the overall resolution of the tiled LCD module, the width of the seam line
22
needs to be narrowed.
However, narrowing the seam line
22
is extremely difficult to achieve due to the margin of error when cuffing the LCD unit glass by a diamond cutter. Therefore, a large tiled LCD module with a low resolution is used for an outdoor projects which do not require a high resolution, despite of its high cost.
When the glass substrate
1
is cut along the scribe line
4
a
, i.e., a first cutting line, and is cut along the scribe line
4
b
, i.e., a second cutting line, the failure as shown in
FIGS. 2A and 2B
may frequently occur in the cross point where the scribe lines
4
a
and
4
b
cross each other.
If the substrate is cut by laser, even a minute crack is not generated at the cut surface. This is more important when the cross point is a panel pad or an active area.
A conventional cutting apparatus using a laser beam has following problems.
Coolant sprayed for cooling down the highly heated glass hinders the laser beam's cutting force of the glass substrate by dispersing the beam's radiation.
If gas is employed as coolant, the cooling gas becomes hot while cooling down the glass substrate. Thus, molecule of the gas moves actively, and the cooling gas is diffused into the laser beam output from a focusing lens housing, thereby scattering the laser beam.
If liquid is employed as coolant, the laser beam is also scattered due to vapors generated when the cooling liquid cools down the glass substrate.
If the laser beam is so-scattered, the heated area of the glass substrate becomes wider while the heating temperature becomes low. Thus, the crack may not be generated or may not propagate to inner surface of the glass substrate, which prevents complete cutting of the LCD unit cell from the glass substrate.
Another problem is that the LCD unit cell may be spotted and the liquid crystal injection opening of the LCD unit cell may be blocked when the coolant dries up.
Moreover, the coolant sprayed from the cooling unit is splashed, which causes an impediment of the laser cutting apparatus and scattering of the laser beam.
The aforementioned laser cuffing process of the glass substrate is performed in a dark chamber, and the laser beam at an infrared ray band having approximately a wavelength of 1300 mm. Therefore, a worker cannot see whether the cutting laser beam is proceeding straight along the scribe line.
The crack moves along the direction in which the laser beam proceeds. Therefore, if the cutting laser beam goes out of the scribe line and turns to the inside of the LCD unit cell, the crack is also propagated toward the inside of the LCD unit cell. Thus, if the scanning line of the laser beam cannot be seen by the worker, all the LCD unit cells cut from the glass substrate may fail.
Any failure in the process of cutting one piece of glass substrate may in sequence cause another failure in the process of cutting a number of glass substrates in the subsequent process, which may result failures in a large number of LCD unit cells.
This is because a worker cannot individually confirm the cutting state of the glass substrate coming out of the chamber after finishing t
Choo Dae-ho
Jung Sung-uk
Kim Bum-soo
Kim Byeong-ill
Lee Woo-shik
Evans Geoffrey S.
McGuireWoods LLP
Park Hae-Chan
LandOfFree
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