JP2008127223A - Method for cutting flat panel display thin glass sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser scribe technology applicable for manufacturing a flat panel display, which is constituted by sticking thin glass sheets to each other, under a stable condition. <P>SOLUTION: A gas or a liquid having a high thermal conductivity is charged in vacant chambers 18, 181,182 between upper and lower two glass sheets, each of which exists at the lower side of a scribe line. Thereby, the absorption heat generated at the glass surface is conducted to the lower glass sheet through the gas or the liquid being a filling agent. In this case, since the cooling effect is increased by the heat conduction, the thermal characteristics similar to those in the case of thick glass sheets is obtained, and scribing can be performed by the recipe nearly equal to that in the case of the thick glass sheets. When scribing and breaking are simultaneously performed, the cut surface has excellent characteristics of laser scribing and also is made high in quality so as to eliminate the need of a post-treatment process. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for cleaving a thin glass plate used for a thin plate brittle material, especially a flat panel display.

  Conventionally, brittle materials have been cut by a mechanical method using a carbide tool such as a diamond tip. The application of this method to glass is also a method that has been used for a long time over the past century.

  However, such mechanical methods have the following drawbacks. The first is that small pieces called cullet are generated at the time of cutting, and the work surface is soiled. Secondly, there is a risk that a microcrack is generated in the vicinity of the cut surface and the workpiece is cracked starting from the microcrack. Third, there is a cutting margin of about several hundred microns at the minimum, and the existence of this cutting margin cannot be ignored at present when the workpiece size is miniaturized without limit. In addition to this, there are other disadvantages that cannot be ignored in the industry, such as the limit of processing speed and the cost of tools that are consumables.

  Cutting of window glass, etc. is not a problem with conventional technology, but in the case of fine glass cutting used for liquid crystal and plasma flat panel displays, etc., post-processing such as polishing the cut surface to prevent micro cracks and then cleaning is required.

  On the other hand, laser cutting that has recently appeared has the following characteristics. First, the mass loss is zero (no cullet generation), and no post-process such as cleaning is required. Second, since a high-strength cross section is obtained without the occurrence of fracture defects such as microcracks in the vicinity of the split cross section, post-processing such as polishing is unnecessary. Third, a mirror surface having a surface roughness of 1 μm or less is obtained. Fourth, the product external accuracy is ± 25 μm or less. Fifth, it can be used for glass plates with a thickness of up to 0.2 mm and can be used for future flat panel displays. This method is currently being tried in this market and will be introduced into actual production once stability is demonstrated.

When glass is irradiated with a high energy density CO ₂ laser beam, the laser beam is generally absorbed at the irradiation spot, and as a result of rapid heating, radial cracks are generated, and cutting proceeds only in the traveling direction. I can't do that. However, if the energy density of the laser beam is set to be sufficiently lower than that which generates such cracks, the glass is only heated, and neither melting nor cracking occurs. At this time, the glass tends to thermally expand, but because of local heating, expansion is suppressed, and compressive stress is generated in the radial direction around the irradiation point. In addition, there is a tangential component of the stress, which is a compressive stress in a short distance region from the irradiation point, but changes from a certain distance away to a tensile stress due to the Poisson's ratio. When the cooling liquid is sprayed in accordance with the position, this tensile stress is expanded. In particular, stress expansion occurs at the crack tip, and when the same force exceeds the fracture toughness value of the material, the crack expands. The crack can be extended by scanning the irradiation point and the cooling point.

  This is shown in FIG. As shown in the figure, when the cross-sectional shape 1 of the laser beam is formed appropriately, the compressive stress 2 is generated mainly in the direction orthogonal to the light moving direction at the irradiation position, and the tensile stress 4 is generated at the cooling position. In the figure, 1 is an irradiation laser beam, and 3 is a refrigerant spray. The cleavage crack 5 is generated by the action of the tensile stress. In the glass plate 6, if the initial crack 8 is made at the starting point, the cleaving crack 5 can start from this initial crack and advance along the moving direction 7 of the laser beam. In order for such a phenomenon to occur ideally, the energy distribution of the irradiated laser beam needs to be optimal in order to generate such tension. These optimal distributions have been studied in various glass cuttings. The heating laser beam 1 shown in FIG. 1 has been optimized.

In the thermal stress cleaving of glass by CO ₂ laser beam irradiation, as shown in FIG. 2, 99% of the CO ₂ laser beam is absorbed by the glass surface layer having a depth of 3.7 μm and does not transmit through the entire thickness of the glass. The depth of cleaving by laser (referred to as laser scribe) is usually about 100 μm, aided by heat conduction. In the figure, 9 is a laser scribe surface. The mechanical scribe surface shown in FIG. 3 is also usually of a similar depth. Now, since glass is highly brittle, it is easy to cleave by applying mechanical stress in accordance with this scribe line. This process is called a break.

  Conventionally, glass is broken by a combination of mechanical scribe and break. In the case of mechanical scribing, as shown in FIG. 3, since there are a large number of microcracks near the scribe surface, the break is relatively easy. However, as shown in FIG. 12, the break surface after mechanical scribing does not necessarily constitute one plane orthogonal to the glass surface. In order to remove the microcrack layer and improve the accuracy of the break surface, in the case of mechanical scribe, the fractured surface is polished and cleaned after the break.

  On the other hand, in the case of laser scribing, there are no microcracks in the vicinity of the scribe surface, so the break surface is ideal as shown at 10 in FIG. In that case, polishing cleaning can be omitted.

  Such a laser scribe has reached a practical level when the glass plate thickness is 0.7 mm for a liquid crystal TV or 2.8 mm for a plasma TV and the technology has progressed and has passed the stage of technical evaluation. . The problem is with LCD mobile flat panel displays. In this case, the thickness of the glass plate to be used is gradually reduced for weight reduction, and is 0.2 mm in the current product, and is said to approach 0.155 mm in the future. In the case of such a plate thickness, stable laser scribing cannot be realized under conditions (hereinafter referred to as a recipe) that can be used with a plate thickness greater than that (0.3 mm is the boundary value). Furthermore, since the glass plate for mobile use is not a single plate but needs to be laser scribed after being mounted on a flat panel display, the heat conduction depends on the structure of the cell below the glass surface, not the process in the single plate, and it is cleaved. It spurs difficulties.

  Considering that the cause of the above difficulties is rooted in the difference in the heat conduction mechanism between the thick and thin plates and the difference in the same phenomenon between the single plate and the laminated glass, the latter also helps stabilize the laser scribe. We decided to realize the phenomenon.

  This will be described with reference to FIG. FIG. 1A shows the case of thick glass. Reference numeral 1 denotes an irradiation laser beam, all of which is absorbed by a region 13 having a depth of 3.7 μm on the surface of the glass plate. Some of the absorbed heat is cooled by the refrigerant 3, while others are cooled by heat conduction 14, 141, 142, 143, 144, etc. to the inside of the glass. Laser scribing occurs due to the balance between heating and cooling. The condition for realizing the balance is a recipe.

  Even in the case of the thin glass shown in FIG. 2 (2), heating in the region 13 by laser irradiation and cooling by the refrigerant are surface phenomena, and thus are equal to the above case. The difference is cooling by heat conduction inside the glass. Since the heat capacity in the case of FIG. 2B is smaller than that in FIG. 1A, the effects of heat conduction 15, 151, 152, 153, 154 and the like are also small. In this case, the region 13 becomes hotter than before, and the optimum recipe is different from the previous one.

  As a means for preventing this, it is conceivable to optimize the laser irradiation condition and the cooling condition by the refrigerant so that the temperature characteristics of the region 13 are the same. Conditions that can be changed in this case include laser intensity (lower output for thin plate), irradiation shape (same magnification), scanning speed (same speed), refrigerant capacity (same increase), refrigerant position, and the like. However, in this case, the recipe must be changed each time the glass-side conditions change. The glass side conditions include the glass type, the same thickness, the structure below the glass surface, and the glass heat history. Since these change for each design of the cell, a new recipe is required each time. Moreover, these recipes are narrow in stability and reduce process reliability. Even in the case of the same design, when dividing a large number of cells from one large plate glass, usually about 10 sets of recipes must be used, which is also a problem.

  On the other hand, in the flat panel display structure, if the glass scribe position structure has the same effect as the case of thick plate veneer, the glass scribe position structure is stable only by applying the plate veneer recipe. Laser scribe can be realized and is convenient.

According to the present invention, stable laser scribing can be performed using a common recipe even in a flat panel display composed of thin plates. Glass cleaving with a laser has the following technical advantages over conventional mechanical cleaving methods.
1) Cutting position accuracy is high.
2) The fractured surface is a mirror surface and the surface roughness is good.
3) Split section inclination is highly accurate.
4) There is no adhesion of cullet on the cut surface and it is clean.
5) Both scribe and break can be automated.
6) Both scribe and break can be performed at high speed.
7) Subsequent processes such as polishing and cleaning can be omitted.

  Thus, laser laser breaking is a significant advance over conventional mechanical methods such as using a diamond cutter. If glass cleaving by laser becomes widespread, there are things that cannot be measured in terms of processing speed, processing quality, economy, and overcoming difficulty.

  The glass mounted on the flat panel display can be expected to have the same heat capacity as the thick plate even if the plate thickness is as thin as 0.2 mm if the heat conduction reaches the entire lower part at the scribe position. Recipe can be applied.

  FIG. 5 shows an embodiment of the present invention. Here, since a flat panel display in the middle of manufacture is shown instead of a single plate, there are two glass plates, 6 on the upper surface and 61 on the lower surface. These are now alkali-free glass with a thickness of 0.2 mm. The two are bonded with adhesives 17, 171, 172, 173 and the like. A color filter (CF) or transistor (TFT) film is formed on the inner surface of the glass, but is omitted in the figure. The adhesive layers between the glass are empty bunches 18, 181, 182 and the like.

  In the present invention, heat conduction is generated by filling vacancies, and heat generated in the region 13 is transmitted not only inside the glass plate 6 but also to the lower glass plate 61 via the vacancies by heat conduction. . At this time, heat conduction occurs over a thickness of about 0.5 mm, which is the total thickness of the two sheets of glass and the airborne layer, eliminating the difficulty of cleaving the thin glass.

  If possible, a filler having a large heat capacity is desirable as a filler for the empty chamber. One is the liquid crystal itself. However, it would not be possible to provide a cutting line where the liquid crystal is.

  If it is liquid, it can be removed after processing. Water can be used as a low possibility of contamination. The thermal conductivity of water is 0.56 W / m · K, which is not much different from the equivalent value of 0.6 W / m · K of soda glass. If the empty chamber is filled with water, heat conduction occurs over the entire thickness of 0.5 mm, which is ideal because it is the same as the processing of the thick plate.

  Considering drying after processing, alcohol can be selected. The thermal conductivity of alcohol is 0.19 W / m · K, which is lower than water but has its effect.

If it is filled with gas, the possibility of contamination is very low. He gas has a thermal conductivity of 0.142 W / m · K, which is quite high in the gas. Although it is lower than solid and liquid, the effect is remarkable when compared with 0.024 W / m · K of air. H ₂ gas also has a high thermal conductivity of 0.168 W / m · K and is promising. When these gases are used, the workpiece may be placed in an airtight chamber and the used gas may be sealed in the chamber. Further, since the thermal conductivity of the gas does not depend on the pressure, the enclosure pressure may be 1 atm.

  Thus, what is necessary is just to implement the break by well-known techniques, such as a mechanical or thermal means, to the workpiece | work which performed laser scribe.

  As described above, according to the present invention, it is possible to perform laser cleaving of a thin glass constituting a flat panel display with ease and stability similar to that of a single plate, and in that case, advantages of laser cleaving over conventional mechanical methods. Can be realized.

  What has been described above is a few examples of mechanisms for realizing the functions of the present invention, and it goes without saying that the spirit of the present invention can be realized in many other ways.

  Cleaving of thin glass for flat panel displays such as liquid crystal displays and plasma displays used in mobile and car navigation systems is currently performed with a diamond cutter, and the need for a cleaning process after cutting and the presence of microcracks, etc. Presents a problem. Such a problem can be solved by the laser cutting of the present invention.

  Thus, the advent of laser technology for improving glass breaking is a solution to various problems demanded by modern society.

Explanatory drawing of the thermal stress scribe by a laser. Glass laser scribe. Glass mechanical scribe. Difference in heat conduction mechanism between thick and thin glass. Explanatory drawing of this invention.

Explanation of symbols

1 Irradiation laser beam
2 Compressive stress inside glass 3 Refrigerant spray 4 Tensile stress inside glass 5 Scribe surface generated in glass 6 Glass plate 61 Same 7 Laser beam and refrigerant moving direction 8 Initial crack 9 Laser scribe surface 10 Break surface after laser scribe
11 Mechanical scribing surface 12 Break surface after mechanical scribing 13 Heating region 14 by laser beam absorption 14 Heat conduction 141 Same 142 Same 144 Same 15 Same 151 Same 152 Same 153 Same 154 Same 16 Same 161 Same 162 Same 163 Same 164 Same 17 Adhesive 171 Same 172 Same 173 Same 18 Empty 181 Same 182 Same

Claims (3)

  The combined use of laser beam irradiation that precedes the movement of the laser and the cooling means that uses the subsequent coolant generates a crack (laser scribe) due to thermal stress in the glass surface layer constituting the flat panel display, along the scribe plane. In a cleaving method that breaks the entire thickness direction of a material by mechanical means or thermal means, the laser absorption heat on the glass surface is actively cooled by heat conduction to the lower structure of the workpiece. .   2. A liquid having high thermal conductivity is filled in an air chamber surrounded by two sheets of glass and an adhesive layer constituting a flat panel display below a laser scribe planned line to generate heat conduction via the liquid. thing.   2. A gas having high thermal conductivity is filled in an air chamber surrounded by two sheets of glass and an adhesive layer constituting a flat panel display below a laser scribe planned line to generate heat conduction via the gas. thing.

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