JP2014221491A - Stress cleavage of reinforcement glass plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain strong points of a method for brittle material heat stress cleavage excellent in processing speed and quality as possible and to reduce a weak point of the method that processing of a reinforcement material is difficult by the method.SOLUTION: The cleavage based on release of compression machine stress inherent to a brittle material reinforcement layer having a strong point equivalent to heat stress cleavage has become available by combination with non-linear phenomenon such as specification of a cleavage position generated near a focus of a pulse laser, and cleavage threshold value reduction.

Description

  The present invention relates to a laser processing method and apparatus capable of performing various high-speed and high-precision processing on a tempered glass plate.

In the cutting of glass plates used in information equipment recently, thermal stress cleaving by CO ₂ laser beam irradiation has been used instead of the diamond chip mechanical method that has been used over the past centuries. This technique is shown in Patent Documents 1, 2, and 3 and Non-Patent Documents 1 and 2.

  According to this method, defects inherent in the mechanical cutting method, that is, a reduction in glass strength due to the occurrence of microcracks, contamination due to the occurrence of cullet, low speed processing, existence of a lower limit value of the applied plate thickness, and the like can be eliminated.

  As a result, according to the laser cleaving method, polishing and cleaning, which are subsequent processes of mechanical cutting, are unnecessary, and a mirror surface with a surface roughness of 1 μm or less can be obtained, and the product external dimension accuracy exceeds the industry specification value ± 25 μm. become. This method is currently used for flat panel and touch panel glass having a plate thickness of 0.33 mm to 1 mm, but is expected to be used for a wider range of plate glass in the future.

Kondratenko S. , Method for dividing brittle non-metallic material, Japanese Patent No. 3027768 Kondrenenko Vladimir S. , Method of splitting non-metallic materials, EP 0633867B1 Kondrenenko Vladimir S. , Method of splitting non-metallic materials, USP 5609284.

Karube K. , Karube N. Laser-induced cleavage of LCD glass as full body cutting, Proc. SPIE 6880, 68807-1 2008. Karube K. , Karube N. Laser-induced full body cleavage of flat-panel-display glass, Journal of the SID 17/4, 2009.

  The method was developed by several engineers, including the inventors, inspired by the fact that when mechanical stress is applied to a brittle material such as glass, it breaks instantly. Non-patent documents 1 and 2 show the outline of the principle research results of the technology by the inventors. This technology was initially practical enough for straight cleaving with the simplest shape and succeeded in improving processing quality and speed, but it also worked on processing of general substrate glass for mobile terminals such as actual smartphones and tablets. I couldn't make progress and got stuck.

  The biggest reason is that the thermal stress cleaving technique depends on the thermal and mechanical properties of the material, so that the optimization of the processing conditions must be changed every time the processed glass is changed. Recently, glass manufacturers such as Corning in the United States have begun to offer tempered glass widely, so the processing conditions have changed significantly. And the characteristic of this tempered glass is not suitable for thermal stress cleaving.

  For this reason, expectations have been raised again for glass material removal processing with few such drawbacks. However, the conventional thermal processing such as laser processing has a drawback that the processing quality is insufficient. In order to avoid this, it has been desired to increase the energy density of the irradiation laser extremely and to directly break the molecular bond of the material not by the thermal action but by the nonlinear phenomenon of the laser beam.

  A nanosecond pulse laser or a picosecond pulse laser can be used to realize such a nonlinear phenomenon. The laser beam (wavelength; 1064 nm, 532 nm) is transparent to glass and is absorbed by a nonlinear phenomenon only near the focal point. The former is electric field intensity absorption, and the latter is multiphoton absorption. If processing is performed with the focus in the vicinity of the first back surface and the processing points are sequentially moved to the upper surface, the glass is transparent to beams other than the vicinity of the focus, so imaging is always performed ideally like free space. There is also an advantage that ideal fine processing can be realized in the thickness direction of cracked glass. That is, drilling with a small spot size from the back surface to the front surface is possible.

  Originally, this technology is a material removal process using high energy, and thus has an advantage that it can be applied to all types of glass including tempered glass. Moreover, even if it is minute, there is a cutting allowance, so it is possible to perform hollowing out processing. Further, if the full cut is performed for the entire plate thickness processing, there is an advantage that a post-process is not required and curve processing is possible. Research based on these expectations has continued for several years.

  However, even if the material removal processing with a laser is a small cutting allowance, the glass removal amount is orders of magnitude greater than the cleaving processing, so the processing speed is significantly lower with the same input laser energy ratio, and it is practical in the industry. The level cannot be reached. To that end, the high speed of the cleaving technology must be expected again. At the same time, we want to realize the processing quality and high speed of cutting. However, the cleaving here needs to be free from restrictions on the temperature characteristics and mechanical characteristics of the material as in the previous cleaving.

These problems can be solved by the following method. The tempered glass used in portable information devices has a plate thickness of 1 mm or less, has a chemically strengthened layer with a depth of 30 to 70 μm on the front and back surfaces, and there is strong compressive stress in the same layer in other areas. Has tensile stress. In the conventional thermal stress cleaving, the glass surface is heated by irradiation with a CO ₂ laser beam or cooled by spraying cooling water, and the surface cleaving is realized by the tensile stress generated by the temperature non-uniformity thus created. However, in the case of a tempered glass having a strong compressive stress layer on the surface, even if an attempt is made to generate a tensile stress on the surface by the above-described method, the stress cancels out the compressive stress inherent in the glass and becomes a sufficiently large value. Don't be. Therefore, conventional thermal stress cleaving cannot be realized for tempered glass. In the present invention, the thermal stress is not used as a driving force for the cutting, but the cleaving is performed by the mechanical stress existing in the reinforcing layer. At this time, in order to easily realize cleaving at a desired position, it is necessary to use the following conditions together.

    Such mechanical stress cleaving is applied to the main process that occupies most of the machining time, and non-linear machining using nanosecond or picosecond pulse laser is used for the sub-process necessary for the cleaving. The present invention is possible using either one of these two types of lasers, but in the following technical description, a picosecond pulse laser is used for the sake of simplicity. The first of the conditions is specification of the cleaving position. The second is to reduce the processing threshold for cleaving. The third is the use of the stress intensity phenomenon. When these conditions are met, the glass plate is cleaved by mechanical stress, and the improvement of processing speed, which is an advantage of stress cleaving, and improvement of processing quality are difficult to process with conventional thermal stress cleaving technology. This is possible even with a certain glass plate.

  As described above, according to the present invention, the processing of the substrate glass for portable information devices in which the current trendy surface, which has been difficult to realize the conventional thermal stress cleaving, is processed based on the mechanical stress inherent in the reinforcing layer. It can be realized by cleaving. In that case, high quality and high-speed workability characterized by thermal stress cleaving can be used. Also, the dependence on the temperature characteristics and mechanical characteristics of the material, such as thermal stress cleaving, is not significant. There is no need for post-processing after cleaving and consumption of tools, and industrial gains are immeasurable.

The schematic diagram which shows the structure of the stress cleaving apparatus of the tempered glass board which concerns on one Embodiment of this invention. The figure which shows the residual stress characteristic as a function of the glass plate thickness direction depth of a tempered glass board. Explanatory drawing of the hollow hole processing by the non-linear effect which the image formation characteristic in the glass of the laser beam in this invention and the focus vicinity generate | occur | produces. Explanatory drawing of the stress cleaving phenomenon generate | occur | produced in the laser beam scanning direction in the surface which forms the hollow hole row | line | column by the laser beam nonlinear absorption in the back surface reinforcement layer in this invention, and connects the hollow hole center as a result. In the present invention, the formation of hollow holes by nonlinear absorption of the laser beam on the back surface, the plate thickness intermediate region, and the front surface, and as a result, the stress cleaving phenomenon generated in the laser beam scanning direction on the plane connecting the hollow hole centers and these 3 in the glass plate thickness direction Explanatory drawing of the stress cleaving phenomenon which generates the common single surface which makes a surface continue. Example of glass substrate shape for mobile devices

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The physical principles and application guidelines of thermal stress cleaving, which is the prior art, are introduced in two non-patent documents by the inventors.

  FIG. 2 shows the magnitude (vertical axis) of the residual stress of the chemically strengthened glass plate as a function of the depth from the glass surface (horizontal axis). On the vertical axis, the upper side shows the region of compressive stress and the lower side shows the region of tensile stress at the zero level. The shaded portion where the residual stress is compressive stress is the reinforcing layer. Internal stress acts in the direction in which the glass expands inside the reinforced layer. However, since the same value is generally smaller than the cleaving fracture threshold, cleaving does not occur.

  FIG. 3 shows a principle diagram of processing using a non-linear phenomenon that is non-thermal processing by a picosecond pulse laser beam in the present invention. Reinforcing layers 9 and 10 exist on the front and back surfaces of the glass plate 7. The laser beam 5 is selected as a wavelength that is transmitted in free space or inside the glass (1064 nm, 532 nm). Its propagation and imaging characteristics are ideal as in free space, and a focal spot 6 having a small optical microscope level can be obtained. ing. In the vicinity, the energy density of the laser beam increases, the glass loses its transparency to the laser beam, the electric field strength and the multiphoton absorption differ depending on the pulse width, and non-thermal processing as shown in the right figure occurs, resulting in a cylindrical shape. A hollow region 11 of shape is produced. For this purpose, if the processing threshold fluence is J and the light condensing spot area is S, the laser pulse output may be selected to be greater than JS. The processing threshold fluence is about 10 J and 5 J in the case of wavelengths of 1064 nm and 532 nm, respectively. The required laser pulse energy is 100 μJ and 50 μJ, and such lasers are commercially available. The smaller the pulse energy, the smaller the focused spot.

  This hollow region is usually chosen starting from the back side of the glass and having a height greater than the reinforcing layer. This can be achieved by adjusting the focal depth of the laser beam (according to the specifications of the condensing optical element) and the focal position (by highly accurate position control of the condensing optical system). If the depth of the reinforcing layer is 50 μm, the focal position, and therefore the positional accuracy of the light collecting system with respect to the glass needs to be 10% ± 5 μm, and such a mechanical specification is available.

  Since the picosecond laser is a pulsed laser, when the laser beam is scanned, the hollow holes form separated rows as shown in FIG. The cleaving fracture threshold in the direction perpendicular to the plane on the plane connecting the centers of these hollow holes will be lower than that at other positions. In the extreme case, if the hollow holes are continuous (the diameter is larger than the center-to-center distance), the fracture threshold is zero. In this case, all processing is removal processing and cleaving processing is zero, so the processing speed is the same as the removal processing and has a low value. Since the removal of the position shifted in the vertical direction from the fractured surface does not contribute to the threshold reduction, it is better that the diameter of the hole is smaller in order to lower the threshold. In order to make this value 1 μm or less, an optical system of an optical microscope may be used. Instead of the circular focus, an oval or rectangular focus that is long in the beam scanning direction may be used. In that case, a combination of a diffractive optical element and a condensing system may be used for the optical system. When the scanning speed of the laser beam is 500 mm / s and the pulse repetition rate is 250 kHz, the hole array pitch is 2 μm. If the hole diameter is 1 μm, the hole occupation ratio is 50%. In order to control the same value, the number of pulse repetitions or the focused spot may be changed. If the pulse width is 10 picoseconds, the movement of the laser beam during this period can be ignored.

  These hollow hole arrays are also necessary for specifying the position of the split cross section inside the reinforcing layer. Without this, if cleaving occurs, the position cannot be controlled, it will only be broken rather than processed.

  As shown in FIG. 4, when cleaving proceeds from the glass end face 12 in the vertical direction of the same surface, the first hollow hole 111 operates as a cleaved initial crack. Since the stress remarkably expands at the crack tip, when the cleaving proceeds continuously from the initial crack, the cleaving easily occurs beyond the cleaving threshold. This cleaving proceeds as long as a hollow hole exists, and if the condition is selected, it stops at the end point of the same hole row.

  Next, the focal position of the laser beam with respect to the glass plate is raised to control the central portion of the glass plate thickness, and the same processing as described above is repeated to create hollow hole arrays 131, 132, 133, etc. When this is completed, the focal position is further raised near the surface, and hollow hole rows such as 141, 142, and 143 are processed. This is shown in FIG. In the laser beam traveling direction, the cleaving proceeds in the same manner as described above to form a continuous cross section. However, the hole series 11 series, 13 series, and 14 series continue to break not only in the thickness direction of the glass plate, but the fractured section advances not only in the laser beam traveling direction but also in the glass plate thickness direction. It becomes a single split section. In this case, it acts as an initial crack with respect to the cleaving in the thickness direction followed by the fractured surface generated earlier. Of course, three or more laser nonlinear processes may be performed in the glass plate thickness direction. Moreover, you may prepare separately the initial stage crack effective for advancing progress. 4 and 5 show the initial crack 15 in this sense. This may be provided not only on the end face of the glass plate but also on the back surface 16 and the front surface 17. Cracks can be prepared by laser beam irradiation as well as mechanical methods.

  It should be noted that the cleaving mechanism is different between the laser beam traveling direction and the glass plate thickness direction. The latter is a cleaving in the tensile stress (mechanical stress) region as in the case of the conventional thermal stress cleaving, and is caused by a tensile stress sandwiched between compressive stress layers that are reinforcing layers. If this tensile stress is greater than the material failure threshold, the cleaving proceeds easily starting from the initial crack and being assisted by the stress expansion. The cleaving was experimentally easier than the former. The cleaving in the same region occurs without any problem because if the cleaving of the back surface and the front surface is realized, they also work as initial cracks.

  Since the former is a cleaving inside the compression layer, it has a mechanism different from that of a normal cleaving. It is wrong to imagine that cleaving does not usually occur within compressive stress. When linear heating is performed with a single glass plate, it can be easily observed that cleavage occurs in the central portion of the heating region. Although this heating region is a compressive stress region, cleaving occurs. In fact, the heated region expands in the linear direction, producing a bimetallic effect on the non-expanded periphery, and cleaves with the resulting orthogonal stress. Thus, cleaving occurs due to the force relationship with the surroundings even as a result of expansion due to compressive stress.

  By the above mechanism, the single mechanical stress split section 18 shown in the rightmost diagram of FIG. 5 is caused by the presence of the compressive stresses 10 and 9 existing on the front and back surfaces of the glass plate, and is assisted by the nonlinear effect by the picosecond pulse laser irradiation. It occurs. This phenomenon has characteristics similar to those of conventional thermal stress cleaving in terms of processing quality and processing speed, and can be used without problems even in tempered glass that is not good at conventional thermal stress cleaving.

  Rather, as can be understood from the above description, the deeper the reinforcing layer and the stronger the strength of the present technology, the more stable and easy it can be achieved.

  The above description has been made for the case where the machining locus is a straight line for convenience, but the technique of the present invention can also be applied to a curved locus or a closed curve machining, and in the latter case, a hollow machining can be performed. Conventional thermal stress cleaving basically has a cutting margin of zero, so a special technique was required for hollowing out. However, according to the technology of the present invention in which the cutting margin is not strictly zero, the machining is compared with that. Easy.

  An example of the glass substrate shape for portable terminals, such as a smart phone, is shown in FIG. The external shape is also determined by the emphasis on design and the grip feeling when holding the smartphone in your hand, especially considering that smartphones are often used by women and children. Considering these requirements, as the dimensions of the glass substrate 19 shown in FIG. 6, the thickness of the substrate is about 0.2 to 1.0 mm, the size is 100 mm or less in the long side, and the width is 50 mm or less, The outer shape needs to be processed into a free curve as shown at 20 in FIG. Further, as shown in FIG. 6, it is necessary to process large and small hollow through holes 21 and 22 and slits 23 having semicircular ends on the glass substrate 19 of the smartphone for the purpose of assembling a speaker / microphone or a substrate. is there. These through holes and slits are determined by the function of the apparatus. Unlike the conventional thermal stress cleaving, the technology of the present invention can process these shapes.

According to the embodiment of the present invention, the following effects can be realized.
1) Prior art thermal stress cleaving has perfect machining quality. The technology of the present invention provides processing quality equivalent to the technology.
2) The processing speed is far superior to that of material removal processing using the nonlinear effect of picosecond pulse laser, and it can be used as a mass production technology for smartphones.
3) Unlike thermal stress cleaving, the processing conditions do not depend on the thermal and mechanical properties of the material. Accordingly, it is possible to change the type of material to be processed and change the material characteristics without drastically changing the processing conditions. Tempered glass used in smartphones can also be processed. Rather, the deeper the reinforcement depth and the greater the reinforcement degree, the easier the processing.
4) Not only the peripheral processing of brittle materials but also hollowing out is possible.
5) No post-process such as polishing and cleaning after cutting is required.
6) The occurrence of microcracks near the cut surface is small, and the material strength of the workpiece is high.
7) Cutting position accuracy is high.
8) The cut surface is sufficiently perpendicular to the glass surface.
9) The roughness of the cut surface is good.
10) The laser is non-contact processing and there is no tool wear.
11) Laser machining can also be used for complex shape machining, allowing direct product machining from a large glass plate.
12) Laser is non-contact energy processing and can be applied to materials other than glass.

  Next, examples of the present invention will be described.

  An embodiment for realizing the above conditions will be described. Glass cutting according to the invention can be carried out using the apparatus schematically shown in FIG. The laser oscillator 1 uses a YAG laser fundamental wave or a second harmonic nanosecond pulse laser or picosecond pulse laser. The specifications of this laser relating to the technology of the present invention are described in [0019] [0021]. Control of the oscillator and laser beam characteristics necessary for the present invention is performed by a laser control apparatus not shown in the figure.

  The laser beam 2 from the oscillator is guided to a condensing and laser beam shaping optical system 4 by a reflecting mirror 3. The outgoing light 5 from that has the specifications described in [0021]. The optical system 4 is a combination of an optical microscope class condensing system and, in some cases, a diffraction grating optical element system that changes the beam cross-sectional shape.

  The laser beam 5 propagates in the free space and the inside of the transparent glass plate 6 in the same manner as in the free space, is imaged, and forms a focal point 6 at a predetermined position. As a result of nonlinear phenomena due to high laser energy density for the first time near the focal point, the material processing described in [0019] [0021] occurs. The place must be a predetermined place. For this purpose, the processing table 8 on which the glass plate is mounted moves in the X and Y directions in the glass surface and in the Z direction perpendicular to the same surface with a predetermined speed and accuracy. . The above is an explanation of the case where there is a motion of the processing table with respect to the stationary optical system, but what is required here is the relative movement of the focal point position with respect to the glass plate, so a moving optical system such as a scanner with respect to the stationary glass plate is used. Also good.

  When the mutual movement and beam control of these glass plates and the laser beam focus are realized, the cleaving described in [Best Mode for Carrying Out the Invention] is realized. The laser beam scanning speed is 500 mm / s, the spot diameter is 1 μm, the object to be processed is a tempered glass plate having a thickness of 1 mm shown in FIG. Since the total cutting length is 500 mm or less, the direct processing time is a maximum of 3 seconds for three times of laser processing and stress cleaving. In fact, system time such as material handling is added to this. The processing quality is ideal because about 70% of the cut surface is purely cleaved. In the other 30%, streaks with a diameter of about 10 μm remain on the fractured surface. If it is about this level, a post-process such as polishing is unnecessary. The above processing time and processing quality are acceptable for glass processing for portable information equipment. In addition, the hollowing out of the closed curve can be performed by adding a little taper to the cut section or pressurizing the hole surface to the glass surface.

  What has been described above is a representative embodiment for realizing the functions of the present invention, and it is needless to say that the spirit of the present invention can be realized in many other ways.

  If the mechanical stress cleaving technology of tempered glass sheet induced by nonlinear glass processing technology such as picosecond pulse laser of the present invention is introduced as means for cutting tempered glass substrate for mobile terminals such as smartphones and tablets, the processing speed In improving the processing quality and economy, and overcoming the weaknesses of the prior art, the effects are immeasurable. These processes are currently performed by a mechanical method such as a diamond cutter, which presents problems such as the necessity of a cleaning step after cutting for generating cullet and a decrease in material strength due to the presence of microcracks. This problem can be eliminated by the advancement of the mechanical stress cleaving technique in a broad sense according to the present invention.

DESCRIPTION OF SYMBOLS 1 Laser oscillator 2 Injected laser beam 3 Reflecting mirror 4 Condensing and / or beam shaping optical system 5 Condensed and / or beam-shaped laser beam 6 Laser beam focus 7 Glass plate 8 Processing table 9 Reinforcement layer (rear surface)
10 Strengthening layer (surface)
11 Hollow hole 111 generated by nonlinear effect One of the hole array on the back 112 Same 113 Same 114 Same -------
12 Glass end surface 131 One of the middle hollow hole rows 132 Same 133 Same 134 Same -------
141 One of the hollow hole arrays on the surface 142 Same as 143 Same as 144 Same as above -------
15 Initial crack 16 on the glass end face 16 Initial crack on the back surface 17 Initial crack on the surface 18 Single section 19 Glass substrate 20 for mobile terminal Same outer periphery 21 Same hole size 22 Same hole small 23 Same slit

Claims (8)

In a fragile brittle material with a reinforcing layer on the front and back surfaces of the plate, the cleaving based on the release of the compressive mechanical stress inherent in the reinforcing layer is divided into holes by forming a hole array due to a nonlinear phenomenon that occurs near the focal point of the pulse laser beam. In the laser processing method for reducing the specific and cleaving threshold, the laser beam focus scanning is first performed in the vicinity of the back surface of the plate and sequentially performed in multiple layers while approaching the vicinity of the front surface, and cleaving is performed in the laser beam scanning direction and the plate thickness direction. It is characterized by being expanded to include a split section. The cross-sectional shape at the focal point of the laser beam according to claim 1 is elongated in the beam traveling direction. In Claim 1, there is an initial crack at a cleaved position at any one of the plate end surface, the same surface, and the same back surface. In the case of the closed curve cleaving in claim 1, the same surface is tapered. In a fragile brittle material with a reinforcing layer on the front and back surfaces of the plate, the cleaving based on the release of the compressive mechanical stress inherent in the reinforcing layer is divided into holes by forming a hole array due to a nonlinear phenomenon that occurs near the focal point of the pulse laser beam. In a laser processing device that aims to specify and reduce the cleaving threshold, laser beam focus scanning is first performed in the vicinity of the back surface of the plate and sequentially performed in multiple layers while approaching the vicinity of the front surface, and cleaving is performed in the laser beam scanning direction and the plate thickness direction. It is characterized by being expanded to include a split section. 6. The cross-sectional shape at the focal point of the laser beam is made longer in the beam traveling direction. In Claim 5, there is an initial crack at the cleaved position at any of the plate end surface, the same surface, or the same back surface. In the case of the closed curve cleaving in claim 5, the same surface is tapered.

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