Electric heating – Metal heating – By arc
Reexamination Certificate
2001-09-14
2003-05-13
Elve, M. Alexandra (Department: 1725)
Electric heating
Metal heating
By arc
C219S121760, C219S121770, C219S121820
Reexamination Certificate
active
06563082
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser cutting method and a laser cutting apparatus for cutting two substrates disposed one over the other and bonded to each other, such as a liquid crystal panel, and a method and an apparatus for manufacturing a liquid crystal device.
2. Description of the Related Art
In a manufacturing process for a liquid crystal panel, a large number of products are taken out of one glass substrate. In this case, the glass substrate must be cut and separated to fit a liquid crystal panel to a product size.
FIG. 14
is an explanatory view for illustrating a conventional cutting method for fitting a liquid crystal panel to a product size. On the surface of one glass substrate
1
of two glass substrates
1
and
2
, which are bonded to each other via a sealing material
3
for sealing liquid crystal, a scribe line
5
is formed with, for example, a diamond tip. After the two glass substrates
1
and
2
are turned over, a bending stress is applied from the surface of the other glass substrate
2
by using a jig such as a rubber roller so as to cut two glass substrates
1
and
2
.
However, in the conventional cutting method as described above, the start point of a crack on the scribe line appears unstably, and the glass substrates are cut discontinuously, so that many chippings are produced. If many chippings are produced, cleaning must be performed to remove the chippings. Also, because this method is of a contact cutting mode, any foreign matter sticking on the rubber roller may scratch the glass substrate
2
. Also, because the destructive power by the rubber roller is low, the glass substrates including the sealing material
3
cannot be cut, so that cutting must be performed at an area without the sealing material
3
. Therefore, as shown in portion A of
FIG. 15
, a cleaning solution (liquid for cleaning liquid crystal which wets the glass substrates when it is enclosed) remains undesirably between the glass substrate
1
and the glass substrate
2
in the vicinity of the sealing material
3
. Since the cleaning solution reacts with wiring of the liquid crystal panel, it is necessary to remove the cleaning solution.
Also, a method in which a laser beam is employed to cut a glass substrate etc. has been proposed (for example, Japanese Patent Laid-Open No. 11-104869 specification). However, this cutting method has been premised to cut one substrate, not to cut two substrates. Even if an attempt is made to cut two substrates by this method, they cannot be cut under the same conditions. Although they can be cut by increasing laser power (or decreasing cutting speed), such a method has problems of low cutting accuracy (linearity) and no reproducibility. These problems will be explained in further detail.
In the case of cutting one substrate with a laser beam, an internal stress due to heat is utilized. In the case of cutting two substrates, the following problems arise:
(1) A thermal stress acts in the upper glass substrate only. This is because glass has a high light absorption coefficient, so that only the upper glass substrate is heated, and the lower glass substrate is not heated.
(2) The upper and lower glass substrates are connected to each other by the sealing material (see FIG.
14
), and so that when the upper glass substrate is going to crack, the lower glass substrate serves to restrain the cracking of the upper glass substrate. Accordingly, two substrates cannot be cut under the same conditions of cutting one glass substrate.
(3) Although force to cut the upper glass substrate can be increased by increasing thermal energy, the lower glass substrate is cut by receiving the force via the sealing material. However, the received force depends on the construction of panel, the bonding state of sealing material, etc. and has no reproducibility.
SUMMARY OF THE INVENTION
The present invention has been achieved to solve the above problems, and accordingly an object thereof is to provide a laser cutting method and a laser cutting apparatus, and a method and an apparatus for manufacturing a liquid crystal device, in which a plurality of substrates disposed one over another, especially two substrates disposed one over the other and bonded to each other, can be cut with higher accuracy.
(1) One mode of the present invention provides a laser cutting method in which a laser beam is applied to a pair of opposed substrates to cut the paired substrates, including at least the steps of applying a first laser beam from a first surface side of one substrate of the paired substrates; and applying a second laser beam from a second surface side of the other substrate of the paired substrates. In the present invention, laser beams are applied to both surfaces of the paired substrates. When a laser beam is applied, the temperature of the irradiated location rises, so that a thermal stress developed by the temperature gradient increases. Therefore, a crack is generated on each of the substrates in the thickness direction, so that a high cutting accuracy (linearity) and excellent reproducibility is provided. Also, since the substrates are cut in a non-contact mode, there is no fear of scratching the substrates like the prior art. In this case, if the step of applying the first laser beam and the step of applying the second laser beam are carried out at the same time, the working time can be shortened.
(2) In the laser cutting method in accordance with another mode of the present invention, scribe lines are formed in advance at cutting locations on the substrates, and the laser beams are applied to the scribelines. In the present invention, when the laser beams are applied to the scribe lines, the temperature of the irradiated location rises, so that a thermal stress developed by the temperature gradient increases. Therefore, cracks originating at the scribe lines develop in the thickness direction to break the substrates, so that the cutting accuracy (linearity) is further enhanced.
(3) In the laser cutting method in accordance with still another mode of the present invention, the pair of substrates and the laser beams are moved relatively to cut the pair of substrates. To do this, there can be used a method in which a position of the pair of substrates is fixed and the laser beams are moved along the scribe lines, or a method in which locations irradiated with the laser beams are fixed and a work support section supporting the pair of substrates is moved. In the present invention, cracks originating at the scribe lines develop in the thickness direction, and the cracks propagate along with the relative movement of the laser beams, by which the pair of substrates is cut along the scribe lines.
(4) In the laser cutting method in accordance with still another mode of the present invention, further in the laser cutting method of the above item (3), correlation between a relative moving speed of the laser beams to the pair of opposed substrates and a power density of the laser beams is set in a predetermined range. If the relative speed of the laser beams is low and the power density of the laser beams is high, the substrate is destroyed. If the relative speed of the laser beams is high and the power density of the laser beams is low, the substrate cannot be cut. In the present invention, therefore, the relative speed of the laser beams and the power density of the laser beams are set so that the correlation therebetween is in a predetermined range in order for the substrate to be cut properly.
(5) In the laser cutting method in accordance with still another mode of the present invention, further in the laser cutting method of any one of the above items (1) to (4), upper and lower substrates are cut including another member, for example, a sealing material, interposed between the pair of opposed substrates. In the present invention, since a laser beam is applied to each of both surfaces of the two substrates, the substrates having another member (including the later-described sealing material and bonding layer) interpose
Ito Hidehiro
Masuda Kenji
Terada Shoichi
Yoshimura Kazuto
Elve M. Alexandra
McHenry Kevin
Oliff & Berridge PLC.
Seiko Epson Corporation
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