Abstract:
It is possible by use of a disclosed cutter wheel to obtain deep vertical cracks inside brittle materials while suppressing generation of horizontal cracks. Such a cutter wheel for brittle materials comprises a disk with two side planes and an outer periphery between them, outer periphery comprising two bevel portions and a ridge portion between them. The ridge portion comprises a plurality of peaks aligned along a circumferential line. For example, the ridge portion comprises a straight line connecting two adjacent peaks in the plurality of peaks. Alternatively, the ridge portion comprises a depression between two adjacent peaks in the plurality of peaks, and the depth of the depression is deeper than the straight line connecting between the two adjacent peaks. Preferably, the peaks are arranged at an equal distance between them.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a scribing method for forming scribe lines on a brittle plate such as a glass plate, a semiconductor wafer or a ceramic plate, a cutter wheel used for such a method by rotating on a brittle sheet, and an apparatus provided with such a cutter wheel.  
           [0003]    2. Description of Prior Art  
           [0004]    A cutter wheel for brittle materials is fabricated by working a disk made of a cemented carbide alloy, sintered diamond or the like. The disk is ground at the outer periphery obliquely on the two sides to form an edge having a V-character-like shape. A rotational shaft is fixed to a shaft hole provided at the center of the disk, and the shaft is mounted rotatively in a manual cutter or in a cutter head of an automatic scriber or the like. Accordingly, the cutter wheel is rotated on a brittle plate such as a glass sheet, a semiconductor wafer or a ceramic plate under a pressure to form scribe lines thereon.  
           [0005]    However, such a conventional cutter wheel cannot generate deep vertical cracks inside a brittle sheet. Further, it is liable to slip on a brittle sheet on scribing, and this abrades the edge. Residual stress is remained along scribe lines. Further, when the brittle sheet is cut along the scribe lines, unnecessary defects due to horizontal cracks are liable to be generated at the sections subjected to the cutting. This is a problem on the quality of brittle cutting.  
           [0006]    Deep vertical cracks can be obtained by the cutter wheel disclosed in the U.S. Pat. No. 5,836,229 assigned to the same assignee of this application. As shown in FIG. 1, the cutter wheel  1  has a disk with V-character-like bevel portions  2 , and an edge  3  between the bevel portions  2  having depressions  4  of microscopic sizes formed at an equal distance between them to provide protrusions  5  between them which contact a brittle sheet. It is possible by use of the cutter wheel  1  to generate deep vertical cracks into a brittle sheet. Further, the residual stress is decreased, and the generation of unnecessary defects due to horizontal cracks along the scribe lines is not increased.  
           [0007]    One of main uses of the cutter wheel for brittle materials is cutting of glass sheets used for flat panel displays (FPD&#39;s for abbreviation) such as liquid crystal display (LCD for abbreviation) panels. Recently, there is a high demand for LCD panels of high quality. Therefore, it is required to suppress the generation of unnecessary horizontal cracks as much as possible.  
         SUMMARY OF THE INVENTION  
         [0008]    An object of the present invention is to provide a scribing method for brittle materials which generates deep vertical cracks while more suppressing generation of horizontal cracks.  
           [0009]    Another object of the present invention is to provide a cutter wheel for brittle materials which generates deep vertical cracks while suppressing generation of unnecessary horizontal cracks.  
           [0010]    A further object of the present invention is to provide a scribing apparatus which suppresses generation of horizontal cracks by using the cutter wheel as a scribing means.  
           [0011]    A cutter wheel for brittle materials in accordance with the present invention comprises a disk with two side planes and an outer periphery between them, the outer periphery provided with two bevel portions, and a ridge portion between them of a polygon. The ridge portion comprises a plurality of peaks aligned along a circumferential line. For each pair of two adjacent peaks in the plurality of peaks, the ridge portion except the peaks extends along or lower than a straight line connecting the two adjacent peaks. Preferably, the peaks are arranged at an equal distance between them. For example, for each pair of two adjacent peaks, the ridge portion is a polygon form with vertices along the straight line connecting the two adjacent peaks. Thus, the edge portion has a polygon shape. Alternatively, for each pair of two adjacent peaks, the ridge portion has a depression between the two adjacent peaks, and the depression extends lower than the straight line connecting the two adjacent peaks.  
           [0012]    An advantage of the present invention is that generation of horizontal cracks is remarkably suppressed while generating deep vertical cracks. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    These and other objects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, and in which:  
         [0014]    [0014]FIG. 1 is a diagram for explaining a prior art cutter wheel;  
         [0015]    [0015]FIG. 2 is a diagram of a cutter wheel of a first embodiment of the invention;  
         [0016]    [0016]FIG. 3 is a diagram of a cutter wheel of a second embodiment of the invention;  
         [0017]    [0017]FIG. 4 is a schematic front view of a machine for fabricating cutter wheels;  
         [0018]    [0018]FIG. 5 is a diagram of a cutter wheel of a third embodiment of the invention;  
         [0019]    [0019]FIG. 6 is a diagram of a cutter wheel of a fourth embodiment of the invention;  
         [0020]    [0020]FIG. 7 is a schematic front view of an automatic scriber for brittle materials having a general mechanism;  
         [0021]    [0021]FIG. 8 is a side view of the automatic scriber;  
         [0022]    [0022]FIG. 9 is a partially broken front view of a manual cutter for brittle materials.  
         [0023]    [0023]FIG. 10 is a schematic front view of a device using a cutter wheel; and  
         [0024]    [0024]FIGS. 11A and 11B are schematic front views of other cutter wheels with shafts. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    Referring now to the drawings, wherein similar reference numerals and characters designate similar or corresponding parts throughout the several views, FIG. 2 shows a cutter wheel  11  of a first embodiment of the invention. FIG. 2 includes a side view on the left side, a front view in the center and a cross sectional view on the right side. The cutter wheel  11  has a disk with two side planes made of a cemented carbide alloy and the outer periphery thereof. The outer periphery has two bevel portions  12  and a V-character-like ridge  13  between them. The ridge  13  has a peak in contact with a brittle sheet for forming scribe lines. The ridge  13  has a shape of a regular polygon of sixty vertices when observed from a side of the wheel. For simplicity in FIG. 2, the ridge  13  has a shape of a regular polygon of eighteen vertices. The two bevel portions  12  extending from a side of the polygon of the ridge  13  make an angle θ of 125° in a section perpendicular to the disk. Any section in the bevel portions  12 , including the ridge  13 , has a form of a regular polygon of sixty vertices. FIG. 2 shows on the right side a cross sectional view of a polygon corresponding to a cross section obtained after cutting the cutter wheel along Q-Q′ line in the front view situated in the center of FIG. 2. The cutter wheel  11  has a central hole for inserting a rotational shaft (not shown).  
         [0026]    As will be explained below, the bevel portions  12  are formed by grinding, and this results in the above-mentioned ridge  13  having the form of the regular polygon of sixty vertices.  
         [0027]    [0027]FIG. 3 shows a cutter wheel  11 ′ of a second embodiment in accordance with the present invention. FIG. 3 includes a side view of the cutter wheel  11 ′ on the left side, a front view of the same in the center and a cross sectional view thereof on the right side. The cross sectional view of a circle corresponds to the cross section obtained after cutting the cutter wheel  11 ′ along R-R′ line in the front view. The cutter wheel  11 ′ has a center hole for inserting a rotational shaft (not shown). The cutter wheel  11 ′ is obtained by working only the circular ridge of a normal cutter wheel to form a polygon shape at the ridge with many flat planes  15  and vertices  16  between them alternately along the ridge. The cutter wheel  11 ′ has sixty (for simplicity, eighteen in FIG. 3) flat planes  15  and vertices  16  alternately between them along the ridge.  
         [0028]    The dimensions of the cutter wheel  11  (and  11 ′) are as follows.  
                                                       Wheel diameter:   2.5 mm.           Wheel thickness:   0.65 mm.           Edge angle (θ);   125°.                      
 
         [0029]    By using the cutter wheel  11  (and  11 ′), scribing is performed according to following scribing conditions.  
                                                       Edge load:   2.0 Kgf.           Scribing speed:   300 mm/sec.           Thickness of glass plate:   0.7 mm.                      
 
         [0030]    When the cutter wheel  11  (and  11 ′) is used according to the scribing data, the depth of vertical cracks is of the same order as that generated by the prior art cutter wheel  1  shown in FIG. 1, while the generation of horizontal cracks is suppressed more. As to the prior art cutter wheel shown in FIG. 1, it is understood that deep vertical cracks are generated due to impacts repeatedly generated many times when the protrusions  5  along the ridge strike the brittle plate at scribing. However, the protrusions  5  themselves are parts of a circumferential line which contacts the brittle plate, and it is further understood that portions  4   a  and  4   b  in FIG. 1 formed at the depressions  4  generate horizontal cracks. On the other hand, the generation of horizontal cracks is small for the cutter wheel  11  (and  11 ′) of the first (and second) embodiment, and the reason is assumed as follows. The cutter wheel  11  (and  11 ′) gives an impact to the brittle plate at each vertex (peak) of the regular polygon along the ridge, but the vertex itself does not have a length along the direction of the ridge. Further, because the ridge except the vertices consists of straight lines or sides of the regular polygon, the crack depth into the brittle plate by the linear portions becomes smaller. Thus, the generation of horizontal cracks is suppressed.  
         [0031]    [0031]FIG. 4 shows a machine for fabricating the cutter wheel  11 . A disk-like wheel  20  made of a cemented carbide alloy has a shaft (not shown) and the shaft is set rotatively. When a bevel plane is formed on the left side of the V-character-like ridge, the wheel  20  is fixed, and a grinder  22  is moved in a direction along the bevel plane to form a plane  23  including a side of the regular polygon with sixty vertices, and the plane  23  is ground. This is repeated each time the wheel  20  is rotated by 6° (=360/60), and sixty planes are formed on the left side of the V-character-like ridge. Thereafter, in order to form the other bevel planes on the right side, the wheel  20  is removed and reversed. Then, it is set again rotatively, and the position of the wheel  20  is determined according to working conditions by using an image processing system (not shown). Then, the grinder  22  is moved again similarly to form a plane  25  (represented by a dotted line) including a side of the regular polygon on the right side of the V-character-like ridge. This is repeated each time the wheel  20  is rotated by 6°. Thus, a cutter wheel  11  is obtained to have the edge with a shape of a polygon with sixty vertices.  
         [0032]    It is also possible to produce the cutter wheel  11  by using a prior art cutter wheel provided with a circular V-shaped ridge at an outer periphery. The prior art wheel is worked by the machine shown in FIG. 4 to grind the bevel portions including the ridge portion as explained above. It is similarly possible to produce the cutter wheel  11 ′ by using a prior art cutter wheel having a circular V-shaped ridge at an outer periphery. The prior art cutter wheel is similarly worked by a machine disclosed in the U.S. Pat. No. 5,836,229 to grind only the ridge portion.  
         [0033]    Alternatively, electro-discharge machining may be used to fabricate the cutter wheel  11 ,  11 ′ instead of grinding carried out by the above-mentioned machine.  
         [0034]    In the first and second embodiments (FIGS. 2 and 3), as explained above, the ridge has a shape of a polygon when observed from a side of the cutter wheel. Therefore, an impact is given at each vertex of the polygon to a brittle plate thereby generating deep vertical cracks, while generation of unnecessary horizontal cracks is suppressed except the vertices. This results in that the generation of horizontal cracks can be decreased while vertical cracks are deeply generated inside the brittle materials.  
         [0035]    [0035]FIG. 5 shows a cutter wheel  31  of a third embodiment of the invention. FIG. 5A is a side view of the cutter wheel  31  and FIG. 5B is a front view of the same. A depression  14  is formed along the ridge for each side of the regular polygon with 60 vertices, similarly to the depressions  4  of the prior art wheel shown in FIG. 1. The depressions  14  are formed to have a depth below a line or a side connecting adjacent two vertices of the regular polygon. For example, the depth of the depression  14  is about 0-20% of the length of the side of the regular polygon. Thus, the cutter wheel  31  does not have linear portions along the ridge. The depressions  14  may be formed by using a thin disk-like grinder moved in a direction perpendicular to the disk, as disclosed in the U.S. Pat. No. 5,836,229.  
         [0036]    [0036]FIG. 6 shows a cutter wheel  31 ′ of a fourth embodiment of the invention. FIG. 6A is a side view of the cutter wheel  31 ′ and FIG. 6B is a front view of the same. The cutter wheel  31 ′ is provided with sixty vertices (edges) at the ridge (a polygon shape with eighteen vertices is shown in FIG. 6A for simplicity).  
         [0037]    The cutter wheel  31 ′ is obtained by working the ridge of the cutter wheel  11 ′ in FIG. 3 with sixty flat planes  15  and vertices  16  along the ridge, and round bevel planes  12 ′ . The cutter wheel  31 ′ is obtained after forming depressions  14  between the vertices  16  along the ridge. The depressions  14  are formed to have a depth below a line or a side connecting adjacent two vertices of the regular polygon. For example, the depth of the depression  14  is about 0-20% of the length of the side of the regular polygon. Thus, the cutter wheel  31 ′ does not have linear portions along the ridge. The depressions  14  may be formed by using a thin disk-like grinder moved in a direction perpendicular to the disk, as disclosed in the U.S. Pat. No. 5,836,229.  
         [0038]    In the above-mentioned ridge of the cutter wheel  11  or  11 ′ shown in FIG. 2 or  3 , the linear portions are provided except the vertices of the polygon, and the generation of the horizontal cracks on the brittle plate is decreased. On the other hand, in the cutter wheel  31  or  31 ′ shown in FIG. 5 or  6 , the depressions  14  are provided deeper than the linear portions in the cutter wheel  11  or  11 ′. Thus, the cutter wheel  31  in FIG. 5 (or  31 ′ in FIG. 6) is not in close contact with portions between the vertices resulting in that the generation of the horizontal cracks is suppressed more than the case of the cutter wheel with the linear lines  13  in FIG. 2 (or the flat planes  15  in FIG. 3).  
         [0039]    The above-mentioned dimensions of the cutter wheels  11 ,  11 ′,  31 ,  31 ′ are exemplified data. Recommended dimensions of a general cutter wheel are given below.  
                                                       Wheel diameter:   1-20 mm.           Wheel thickness:   0.6-5 mm.           Edge angle (θ)   90-160°.                      
 
         [0040]    General scribing conditions are as follows.  
                                                       Edge load:   0.8-60 Kgf.           Scribing speed:   50-1,000 mm/sec.                      
 
         [0041]    In the third or fourth embodiment, depressions are formed between the vertices, as explained above. Therefore, necessary vertical cracks can be obtained by a smaller scribing load impressed at the ridge, while the generation of horizontal cracks can be decreased more than the cutter wheel of the first or second embodiment.  
         [0042]    The cutter wheel explained above is suitable for an automatic scriber and a manual cutter for brittle materials.  
         [0043]    [0043]FIGS. 7 and 8 are a front view and a side view of a general automatic scriber for brittle materials. A table  41  for setting a brittle plate is rotated by a rotation table  42  in a horizontal plane, and it is moved along a rail  45  in Y direction (or left-to-right direction in FIG. 7) by a ball screw  44 . On the other hand, a cutter head  46  is moved in X direction (or left-to-right direction in FIG. 8) along rails  47 . The cutter head  46  has the cutter wheel  11 ,  11 ′,  31 , or  31 ′ with a shaft fitted at the center thereof, and the shaft is supported rotatively at a lower end of the cutter head  46 .  
         [0044]    On scribing, each time the table  41  is moved in Y direction by a predetermined pitch, the cutter head  46  is moved in X direction. Thus, the brittle plate is scribed in X direction. Then, after the table  41  is rotated by 90°, scribing is performed similarly. Accordingly, the brittle plate is also scribed in Y direction.  
         [0045]    The automatic scriber for brittle materials explained above is one example of a scriber. The cutter wheel of the invention can also be used in other types of scribers. For example, the cutter head  46  is fixed, and the table is moved in X and Y directions. Alternatively, the table  41  is fixed, and the cutter head  46  is moved in X and Y directions.  
         [0046]    [0046]FIG. 9 shows the cutter wheel  11 ,  11 ′,  31 , or  31 ′ mounted in a manual glass cutter disclosed in Japanese Utility Model Publication 62-23, 780/1987. The glass cutter has a cylindrical handle  61  for grip and a head  62  provided at a lower side thereof. The glass cutter wheel  11 ,  11 ′,  31 , or  31 ′ with a shaft is mounted to the head rotatively around the shaft. Further, an oil chamber  63 , a cap  64  thereof and a relevant mechanism  65 - 93  are provided in order to supply oil to the glass cutter wheel  11 ,  11 ′,  31 , or  31 ′, but detailed explanation thereon is omitted here.  
         [0047]    [0047]FIG. 10 shows the head  62  shown in FIG. 9. A shaft  11   a  is inserted through the hole of the glass cutter wheel  11 ,  11 ′,  31 , or  31 ′, and two ends of the shaft  11   a  are supported at a two-fork type member of the head  62 . A cap  62   a  stops the shaft  11   a    
         [0048]    The cutter wheel  11 ,  11 ′,  31 , or  31 ′ is provided as an element as shown in FIGS. 2, 3,  5  and  6 . When it is used, a shaft  11   a  shown in FIG. 10 is inserted to the center hole provided in the wheel  11 ,  11 ′,  31 , or  31 ′. However, because the outer diameter of the wheel is very small, the diameter of the shaft  11   a  may become equal to or smaller than 1 mm, and it is difficult to handle the shaft. Therefore, as shown in FIG. 11A, a shaft  11   a ′ may be integrated with the main body of the cutter wheel to form a single unit  11 ″. Alternatively, as shown in FIG. 11B, a pivot shaft  11   a ″ may be integrated with the main body of the cutter wheel to form a single unit  11 ″. The shape of the shaft depends on the structure of the bearing at the cutter head  62 .  
         [0049]    In the above-mentioned embodiments of the invention, a cutter wheel has a shape of a regular polygon. However, a cutter wheel of a polygon in shape has a similar advantage.  
         [0050]    Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.