A laser processing device and method for creating micro holes by melting the inside of a glass substrate using a laser

Abstract

The present invention relates to a laser processing apparatus and method for creating micro-holes and outer shapes by melting the interior of a glass substrate using a laser. To this end, a laser processing device for creating micro-holes by melting the interior of a glass substrate using a laser according to one embodiment of the present invention comprises: a laser device for generating a laser to melt the interior of the glass substrate; a converging lens for converging and diverging the laser generated by the laser device into a single point; a path splitting unit for passing the laser diverging from the converging lens through a plurality of different optical paths and outputting it in the same direction; and a focusing lens for receiving the laser that has passed through a plurality of different paths output from the path splitting unit to form a melting line or multiple melting spots to melt the interior of the glass substrate, and the laser processing device can realize the internal shape of the micro-hole and the outer C shape of the glass substrate by chemically etching the melted area inside the glass substrate and applying a possible separation method (including mechanical separation, laser separation, etc.).

Description

Technology Field

[0001] The present invention relates to a laser processing apparatus and method for creating micro-holes and outer shapes by melting the interior of a glass substrate using a laser. Background Technology

[0002] Currently, display devices utilize glass-based substrates as base substrates, which are cut to size according to the product specifications. While methods such as diamond tipping or thermal shock cutting are sometimes employed to cut glass substrates to the required dimensions, laser-based cutting devices have recently become the most commonly used.

[0003] A laser cutting device currently in use includes a table on which a glass substrate is placed, and a cutting head equipped with a laser irradiation device that irradiates a laser beam and a coolant spraying device that sprays a coolant, which are movably positioned on the table.

[0004] FIG. 1(a) is an exemplary diagram showing the side view of a glass substrate scribed using a conventional laser processing device. FIG. 1(b) is an exemplary diagram showing the state of chemically etching a glass substrate scribed using a conventional laser processing device.

[0005] Referring to FIG. 1 (a) and (b), since the conventional laser processing device forms a microcrack inside the glass substrate (110) with laser energy and then performs scribing (111) and then performs chemical etching to create a hole (120), there is a possibility that a microcrack (131) exists inside the hole (120) of the glass substrate (110).

[0006] As such, conventional laser-based Through Glass Via (TGV) devices have a problem in that when holes are created through scribing, chemical etching is performed, causing microcracks to form around the holes, which ultimately weakens the strength of the glass substrate.

[0007] Therefore, the need arises for a laser processing device that prevents microcracks from occurring around the hole. Prior art literature

[0008] Korean Published Patent Application No. 10-2014-0022980 The problem to be solved

[0009] Accordingly, the present invention provides a laser processing apparatus and method for creating a hole by melting the interior of a glass substrate using a laser.

[0010] The objects of the present invention are not limited to those mentioned above, and other unmentioned objects and advantages of the present invention may be understood from the following description and will be more clearly understood by the embodiments of the present invention. Furthermore, it will be readily apparent that the objects and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims. means of solving the problem

[0011] To achieve this purpose, a laser processing device according to one embodiment of the present invention, which melts the interior of a glass substrate using a laser to create micro-holes and an outer shape, comprises: a laser device that generates a laser to melt the interior of the glass substrate; a converging lens that converges and diverges the laser generated by the laser device into a single point; a path splitting unit that passes the laser diverging from the converging lens through a plurality of different optical paths and outputs it in the same direction; and a focusing lens that receives the laser that has passed through a plurality of different paths output from the path splitting unit and forms a melting line or multiple melting spots to melt the interior of the glass substrate, wherein the laser processing device can create micro-holes in the melted area inside the glass substrate through chemical etching.

[0012] In addition, according to one embodiment, the laser processing device can form a melting line or a melting spot from the bottom to the top of a glass substrate.

[0013] In addition, according to one embodiment, the diameter of the microhole is characterized to be 5 μm to 500 μm.

[0014] In addition, according to one embodiment, the laser processing device can etch the melted area by spraying a chemical etching solution onto the melted area.

[0015] In addition, according to one embodiment, the chemical etching solution may include hydrogen fluoride and a glass etching solution.

[0016] In addition, a method for creating micro-holes and outer shapes by melting the interior of a glass substrate using a laser according to an embodiment of the present invention may include: a laser device generating a laser to melt the interior of the glass substrate; a converging lens converging the laser generated by the laser device into a single point and diverging; a path splitting unit passing the laser diverging from the converging lens through a plurality of different optical paths and outputting it in the same direction; a focusing lens receiving the laser that has passed through a plurality of different paths output from the path splitting unit and forming multiple melting spots or melting lines to melt the interior of the glass substrate; and a process of creating micro-holes in the melted area of ​​the glass substrate through chemical etching.

[0017] In addition, the process of melting the interior of a glass substrate according to one embodiment of the present invention may include the process of forming a melting spot from the bottom to the top of the glass substrate.

[0018] In addition, the process of creating microholes according to one embodiment of the present invention may include the process of etching the melted area by spraying a chemical etching solution onto the melted area. Effects of the invention

[0019] The laser processing device of the present invention outputs an emitted laser onto a glass substrate to melt the interior of the glass substrate, and then creates a hole by removing the melted area through chemical etching, thereby fundamentally preventing microcracks that may occur when creating a hole in a glass substrate.

[0020] In addition, the present invention can ensure the manufacturing reliability of a display by producing a glass substrate in which no microcracks occur.

[0021] In addition, the present invention can secure mass production economics by producing a glass substrate without microcracks, thereby improving yield and reducing the workforce required for the mass production process.

[0022] In addition to the effects described above, the specific effects of the present invention are described together with the specific details for implementing the invention below. Brief explanation of the drawing

[0023] Figure 1 (a) is an example diagram showing the side of a glass substrate scribed by forming microcracks using a conventional laser processing device. Figure 1(b) is an example diagram showing the state of chemically etching a glass substrate scribbled by a conventional laser processing device. FIG. 2 is an exemplary diagram showing a laser processing apparatus that creates micro-holes by melting the interior of a glass substrate using a laser according to one embodiment of the present invention. FIG. 3 is a flowchart illustrating the process of a laser processing device according to one embodiment of the present invention using a laser to melt the interior of a glass substrate and create micro-holes. FIG. 4(a) is an exemplary diagram showing the upper surface of a glass substrate on which a melting line is formed by a laser processing device according to one embodiment of the present invention. Figure 4(b) is an exemplary diagram showing the side of a glass substrate in which a melting line is created by a laser processing device according to one embodiment of the present invention. Figure 4(c) is an exemplary diagram showing the state in which a laser processing device according to one embodiment of the present invention creates micro-holes in a glass substrate. FIG. 5 is an exemplary diagram of a laser processing device according to one embodiment of the present invention using a laser to create an outer shape of a glass substrate. FIG. 6 is an exemplary diagram showing a cross-section of a sample chemically etched from a melted region inside a glass substrate according to one embodiment of the present invention. Specific details for implementing the invention

[0024] The aforementioned objectives, features, and advantages are described in detail below with reference to the attached drawings, thereby enabling those skilled in the art to easily implement the technical concept of the present invention. In describing the present invention, detailed descriptions of known technologies related to the present invention are omitted if it is determined that such descriptions would unnecessarily obscure the essence of the invention. Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the attached drawings. In the drawings, the same reference numerals are used to indicate the same or similar components.

[0025] Although terms such as "first," "second," etc., are used to describe various components, it goes without saying that these components are not limited by these terms. These terms are used merely to distinguish one component from another, and unless specifically stated otherwise, the first component may also be the second component.

[0026] In the following, the statement that any configuration is placed on the "upper (or lower)" of a component or on the "upper (or lower)" of a component may mean not only that any configuration is placed in contact with the upper (or lower) surface of said component, but also that another configuration may be interposed between said component and any configuration placed on (or below) said component.

[0027] In addition, where it is stated that one component is "connected," "combined," or "connected" to another component, it should be understood that while the components may be directly connected or connected to each other, another component may be "interposed" between each component, or each component may be "connected," "combined," or "connected" through another component.

[0028] Throughout the specification, unless specifically stated otherwise, each component may be singular or plural.

[0029] Singular expressions used in this specification include plural expressions unless the context clearly indicates otherwise. In this application, terms such as "composed of" or "comprising" should not be interpreted as necessarily including all of the various components or steps described in the specification, and should be interpreted as meaning that some of the components or steps may be omitted or additional components or steps may be included.

[0030] Throughout the specification, "A and / or B" means A, B, or A and B unless specifically stated otherwise, and "C to D" means C or more and D or less, unless specifically stated otherwise.

[0031] Hereinafter, a laser processing apparatus and method for creating micro-holes and outer shapes by melting the interior of a glass substrate using a laser according to some embodiments of the present invention will be described.

[0032] FIG. 2 is an exemplary diagram showing a laser processing apparatus that uses a laser according to an embodiment of the present invention to melt the interior of a glass substrate to create micro-holes and an outer shape.

[0033] Referring to FIG. 2, a laser processing device (200) that creates micro-holes by melting the interior of a glass substrate using a laser according to one embodiment of the present invention may include a laser device (210), a converging lens (220), a path splitting unit (230), and a focusing lens (240).

[0034] The configuration of the laser processing device (200) that creates micro-holes and outer shapes by melting the interior of a glass substrate using the laser shown in FIG. 2 is according to one embodiment, and the components of the laser processing device (200) are not limited to the embodiment shown in FIG. 2, and some components may be added, changed, or deleted as needed.

[0035] According to one embodiment, the laser device (210) can generate a laser to melt the interior of the glass substrate (250). For example, the laser device (210) can generate a laser having an intensity that melts the interior of the glass substrate. For example, the melting point of glass is generally 600 o C or higher. The laser device (210) can generate a laser with an intensity for melting the interior of glass having such a melting point in the direction of the converging lens (220).

[0036] This laser device (210) can generate group pulses that can adjust the pulse energy value per sub-pulse and the intensity profile of the pulse train.

[0037] The glass substrate (250) described in the present invention may include a hole display, a HIAA (Hole In Active Area) display, an IT organic light-emitting diode (IT OLED), and a glass OLED. Additionally, the laser device (210) according to the present invention may be applied to a glass product including a semiconductor TGV (Through Glass Via), a glass core, and a display.

[0038] In addition, the laser processing device (200) according to the present invention can, for example, create a plurality of micro-holes with a diameter of 5 μm to 500 μm in such a glass substrate (250). These values ​​can be variably adjusted.

[0039] Additionally, the laser processing device (200) can form micro-holes such that the size of the incident hole and the size of the exit hole are the same (or nearly similar).

[0040] According to one embodiment, the converging lens (220) can converge and diverge the laser generated from the laser device (210) into a single point.

[0041] In this way, the laser generated from the laser device (210) converges at a point in the converging lens (220) and diverges to the path splitting section (230).

[0042] According to one embodiment, the path splitting unit (230) can output a laser emitted from a converging lens (220) in the same direction by passing it through multiple optical paths having different distances. That is, the path splitting unit (230) receives a beam that is converged and then diverged from the converging lens (220) and directs it to a focusing lens (240) via optical paths of different distances (e.g., first optical path (231a), second optical path (233a), third optical path (235a), fourth optical path (237a)).

[0043] According to one embodiment, the path splitting unit (230) may include a first polarizing beam splitter (PBS1) (231) that receives a beam that is converged and then diverged by a converging lens (220), transmits a portion of it through a first optical path (231a), and reflects a portion of it, and a second polarizing beam splitter (PBS2) (232) that transmits the beam transmitted from the first polarizing beam splitter (PBS1) (231) and also reflects a beam incident through a plurality of other optical paths toward a focusing lens (240) in the same direction as the transmitted beam.

[0044] Additionally, the path splitter (230) may include first and third beam splitters (BS1, BS3) (233, 234) installed at predetermined intervals on the path of the beam reflected from the first polarizing beam splitter (PBS1) (231), wherein a portion of the incident beam is transmitted through the second optical path (233a) and the third optical path (235a), respectively, and a portion is reflected; a first reflector (M1) (237) that reflects the beam transmitted through the third beam splitter (BS3) (235); and a second reflector (M2) (238) that reflects the beam reflected from the first reflector (M1) through the fourth optical path (237a) toward the back of the second polarizing beam splitter (PBS2).

[0045] Additionally, the path splitting section (230) may include second and fourth beam splitters (BS2, BS4) (234, 236) that transmit and reflect the reflected beam of the second mirror (M2) (238) and the beams reflected through the second and third optical paths (233a, 235a) from the first and third beam splitters (BS1, BS3) (233, 236), respectively, and cause them to be incident on the back surface of the second polarizing beam splitter (PBS2) (232).

[0046] According to one embodiment, the focusing lens (240) can receive a laser that has passed through a plurality of different paths output from the path splitting unit (230) and output it to the glass substrate (250). Then, a melting line (251) is formed on the glass substrate (250) by the laser, and a melted area adjacent to the melting line (251) is created.

[0047] Alternatively, the focusing lens (240) may receive a laser that has passed through multiple different paths output from the path splitting unit (230) and form multiple melting spots at different distances to melt the interior of the glass substrate (250). Then, an area melted by the laser is created on the glass substrate (250).

[0048] The laser processing device (200) according to the present invention forms a primary focus by placing a converging lens (220) after a laser beam emitted in parallel, and then divides the beam path into four paths (e.g., first optical path (231a), second optical path (233a), third optical path (235a), fourth optical path (237a)) at the beam path splitting unit (230), and then combines them and sends them to a focusing lens (240). This is a principle that makes the distance (object distance) between the primary focus and the focusing lens (240) different, that is, the distance of the diverging beam different, thereby forming a different width of light incident on the focusing lens (240), and thus making the points (e.g., melting spots) of the four optical paths (e.g., first optical path (231a), second optical path (233a), third optical path (235a), fourth optical path (237a)) different.

[0049] In this way, the laser processing device (200) according to the present invention can form a melting line (251) because the image distance (focus position) focused by different optical paths (e.g., first optical path (231a), second optical path (233a), third optical path (235a), fourth optical path (237a)) is formed at different positions. And, a melted area is formed adjacent to the melting line.

[0050] Additionally, the laser processing device (200) according to the present invention may form multiple spots because the focused image distance (focus position) is formed at different locations due to different optical paths (e.g., first optical path (231a), second optical path (233a), third optical path (235a), fourth optical path (237a)). For example, the laser processing device (200) may form a melting line or a melting spot from the bottom to the top of a glass substrate (250). And, a melted area is formed at a location adjacent to the melting line or the melting spot by the melting line or the melting spot.

[0051] And, the laser processing device (200) can create micro-holes through chemical etching to remove the melted area inside the glass substrate (250).

[0052] In this case, the melted region is a region with lower strength than the glass substrate (250). In the etching process of the melted region (i.e., chemical etching process), microcracks do not occur because the melted region has relatively lower strength (or higher ductility) than the glass substrate. Also, this melted region is formed around the melting spot. The solution used in this chemical etching process may include hydrogen fluoride and a glass etching solution.

[0053] FIG. 3 is a flowchart illustrating the process of a laser processing device according to an embodiment of the present invention using a laser to melt the interior of a glass substrate and create micro-holes. FIG. 4(a) is an exemplary diagram showing the top surface of a glass substrate on which a melting line has been created by a laser processing device according to an embodiment of the present invention. FIG. 4(b) is an exemplary diagram showing the side surface of a glass substrate on which a melting line has been created by a laser processing device according to an embodiment of the present invention. FIG. 4(c) is an exemplary diagram showing the state in which a laser processing device according to an embodiment of the present invention has created micro-holes in a glass substrate. FIG. 5 is an exemplary diagram showing a laser processing device according to an embodiment of the present invention creating an outer shape of a glass substrate using a laser. FIG. 6 is an exemplary diagram showing a cross-section of a sample in which a melted area inside a glass substrate has been chemically etched according to an embodiment of the present invention.

[0054] Hereinafter, with reference to FIGS. 3 to 6, the process of a laser processing device according to one embodiment of the present invention melting the interior of a glass substrate using a laser to create micro-holes is described in detail as follows.

[0055] According to one embodiment, a laser processing device (200) (e.g., a laser device (210)) can generate a laser to melt the interior of a glass substrate (S310). The laser device (210) can generate a laser (e.g., a plasma laser) having an intensity greater than a certain magnitude so as to melt the interior of the glass substrate. For example, the melting point of glass is generally 400 o C to 500 o C. The laser device (210) can generate a laser with an intensity for melting the inside of the glass in the direction of the converging lens (220).

[0056] According to one embodiment, a laser processing device (200) (e.g., a converging lens (220)) can converge a laser to a single point and diverge (S312). The converging lens (220) can converge a laser generated from a laser device (210) to a single point and diverge it to a polarizing beam splitter (e.g., a first polarizing beam splitter (PBS1) (231)) within a path splitting section (230).

[0057] According to one embodiment, a laser processing device (200) (e.g., a path splitter (230)) can pass a laser through multiple optical paths of different distances and output it in the same direction (S314). The path splitter (230) receives a beam emitted by a converging lens (220) through a first polarizing beam splitter (PBS1) (231), transmits a portion of the beam through a first optical path (231a) toward a second polarizing beam splitter (PBS2) (232), and reflects a portion of the beam.

[0058] Additionally, the path splitter (230) transmits the beam transmitted from the first polarizing beam splitter (PBS1) (231) through the first optical path (231a) to the focusing lens (240) via the second polarizing beam splitter (PBS2) (232), and can also reflect the beam incident through a plurality of other optical paths (e.g., second optical path (233a), third optical path (235a), fourth optical path (237a)) toward the focusing lens (240) in the same direction as the transmitted beam.

[0059] Additionally, the path splitter (230) is installed at predetermined intervals on the path of the beam reflected from the first polarizing beam splitter (PBS1) (231) through the first and third beam splitters (BS1, BS3) (233, 234) so ​​as to transmit a portion of the incident beam through the second optical path (233a) and the third optical path (235a), respectively, and reflect a portion of the beam.

[0060] Additionally, the path splitter (230) can reflect the beam that has passed through the third beam splitter (BS3) (235) through the first reflector (M1) (237) to the second reflector (M2) (238) through the fourth optical path (237a), and reflect the beam incident on the second reflector (M2) (238) in the direction of the back of the second polarizing beam splitter (PBS2).

[0061] Additionally, the path splitter (230) can transmit and reflect the reflected beam of the second mirror (M2) (238) through the second and fourth beam splitters (BS2, BS4) (234, 236) and the beam reflected through the second and third optical paths (233a, 235a) from the first and third beam splitters (BS1, BS3) (233, 236), respectively, so that they are incident on the back of the second polarizing beam splitter (PBS2) (232).

[0062] According to one embodiment, a laser processing device (200) (e.g., a focusing lens (240)) can melt a glass substrate by forming multiple melting spots at a melting line (251) or at different distances (S316). The laser processing device (200) can melt the interior of a glass substrate (250) by using a focusing lens (240) to receive a laser that has passed through multiple different paths output from a path splitting unit (230) and forming multiple melting spots at a melting line (251) or at different distances.

[0063] For example, the laser processing device (200) can form a melting line (251) or a melting spot from the bottom to the top of the glass substrate (250). Alternatively, the laser processing device (200) can form a melting line (251) or a melting spot from the top to the bottom of the glass substrate (250).

[0064] In this way, the glass substrate (250) may include a melted region inside, and this melted region has lower strength than the glass substrate.

[0065] Referring to FIG. 4(a), the laser processing device (200) can operate the path splitting part (230) to form a melting line (251) in a vertical direction on the plane (250) of the glass substrate (250). Around this melting line (251), an area (411) is formed where the glass substrate is melted by the heat of the laser.

[0066] According to one embodiment, the laser processing device (200) can create micro-holes by removing a melted area (S318). The laser processing device (200) can create micro-holes (420) in a melted area (411) of a glass substrate (250) through chemical etching. The solution used to perform chemical etching may include hydrogen fluoride and a glass etching solution.

[0067] Referring to FIG. 4 (b) and (c), the laser processing device (200) can form micro-holes (420) by removing the melted area through chemical etching.

[0068] According to one embodiment, the laser processing device (200) operates the path splitting part (230) to form a micro hole (420) on a single melting line (251), such as on the front surface (340) of the glass substrate (250). The laser processing device (200) can form a micro hole (420) by chemically etching the melted area on the plane (330) of the glass substrate (250).

[0069] The laser processing device (200) according to the present invention can create a plurality of micro-holes on a glass substrate (250) by repeatedly performing the process described above.

[0070] Referring to FIG. 5, a laser processing device (200) according to the present invention can form a plurality of micro-holes on the edge portion of a glass substrate (250). The laser processing device (200) can form micro-holes (530) by melting the interior of the edge portions (501, 502) of the glass substrate (250) and then removing the melted area through chemical etching. These micro-holes (530) can be formed through the edge line (510) of the glass substrate (250).

[0071] Since the micro holes (530) according to the present invention have a smaller diameter compared to conventional holes (510), the laser processing device (200) according to the present invention is advantageous for a delicate process of forming fine micro holes in a glass substrate (250).

[0072] Referring to FIG. 6, the laser processing device (200) according to the present invention can realize a melted region formed inside a VMB glass substrate (250) in a C shape, and then, through chemical etching and the application of a possible separation method (including mechanical separation, laser separation, etc.), form a micro hole with an internal shape and realize an outer C shape of the glass substrate.

[0073] As described above, the laser processing device (200) according to the present invention generates a laser through a laser device (210), converges the generated laser to a single point through a converging lens (220) and diverges, outputs the laser diverging from the converging lens (220) onto a glass substrate (250) through a path splitting unit (230), and can melt the interior of the glass substrate (250) using the laser through a focusing lens (240) and can create a hole by removing the melted area.

[0074] Through this, the present invention can form a melting line in a vertical direction even when the laser is irradiated once.

[0075] In addition, the present invention can fundamentally prevent microcracks that may occur inside the glass substrate (250) by melting the inside of the glass substrate (250) and then creating holes through chemical etching.

[0076] Each step in each of the flowcharts described above may be operated independently of the illustrated order or may be performed simultaneously. Additionally, at least one component of the present invention and at least one operation performed by said at least one component may be implemented in hardware and / or software.

[0077] Although the present invention has been described above with reference to the illustrated drawings, the present invention is not limited by the embodiments and drawings disclosed in this specification, and it is obvious that various modifications can be made by a person skilled in the art within the scope of the technical concept of the present invention. Furthermore, even if the effects of the configuration of the present invention were not explicitly described while explaining the embodiments of the present invention above, it is natural to acknowledge that the effects predictable by said configuration should also be recognized. Explanation of the symbols

[0078] 200: Laser processing device 210: Laser device 220: Converging lens 230: Path splitter 240: Focusing lens

Claims

Claim 1 A laser processing device (200) for creating micro-holes and outer shapes by melting the interior of a glass substrate (250) using a laser, comprising: a laser device (210) for generating a laser to melt the interior of the glass substrate (250); a converging lens (220) for converging and diverging the laser generated from the laser device (210) into a single point; and a path splitting unit (230) for passing the laser diverging from the converging lens through multiple optical paths of different distances and outputting them in the same direction. The laser processing device (200) includes a focusing lens (240) that receives a laser passing through a plurality of different paths output from the path splitting unit (230) to form a melting line and melt the interior of the glass substrate (250), and the laser processing device (200) melts the interior of the glass substrate (250) through the laser emitted through the focusing lens (240) to form the melting line from the bottom to the top of the glass substrate (250), and then creates a micro-hole by chemical etching a melted area adjacent to the melting line by the laser, wherein the melting line is formed in a direction perpendicular to the plane of the glass substrate (250). Claim 2 A laser processing device according to claim 1, characterized in that the diameter of the micro-hole is 5 μm to 500 μm. Claim 3 In claim 1, the laser processing device (200) is a laser processing device that etches the melted area by spraying a chemical etching solution onto the melted area. Claim 4 In claim 3, the chemical etching solution is a laser processing device containing hydrogen fluoride. Claim 5 A method for creating micro-holes and outer shapes by melting the interior of a glass substrate (250) using a laser, comprising: a laser device (210) generating a laser to melt the interior of the glass substrate (250); a converging lens (220) converging the laser generated from the laser device (210) into a single point and diverging; a path splitting unit (230) passing the laser diverging from the converging lens (220) through multiple different optical paths and outputting it in the same direction; a focusing lens (240) receiving the laser that has passed through multiple different paths output from the path splitting unit (230) to form a melting line and melt the interior of the glass substrate (250); and a process of forming the melting line from the bottom to the top of the glass substrate (250) by melting the interior of the glass substrate (250) through the laser diverging through the focusing lens (240). A method comprising the process of creating micro-holes in a melted area adjacent to the melting line by chemical etching by the laser, wherein the melting line is formed in a direction perpendicular to the plane of the glass substrate (250). Claim 6 In claim 5, the process of creating the micro-holes comprises a method of etching the melted area by spraying a chemical etching solution onto the melted area.

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