Abstract:
A composite sheet whose product price can be reduced with a smaller number of manufacturing processes. A laser oscillator outputs a pulsed beam at a frequency  f . A mask shapes the outer shape of the beam into a triangular, quadrangular or hexagonal shape. N pieces of time-sharing means time-share the beam to form N beams having a frequency f/N. N pairs of positioning means position the time-shared beams. A condensing lens condenses the beams. A rotating drum displaces a workpiece. A control means controls the time-sharing means, the N pairs of positioning means and a pedestal. The N pairs of positioning means are positioned to irradiate predetermined positions with the beams. The pedestal is moved. The time-sharing means are thereupon operated in predetermined order. The workpiece is machined to make holes whose outer shapes depend on the mask so that distances between sides of adjacent holes are equal to one another.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a composite sheet such as an electromagnetic sheet serving for plasma TV and having a metal conductor layer and an organic compound layer put on top of each other in their thickness direction, a glass sheet (thin-plate glass) serving for liquid crystal TV and having a transparent glass layer coated with acrylic resin or epoxy resin mixed with powder of titanium or carbon, etc., a machining method for such a composite sheet, and a laser machining apparatus for machining such a composite sheet.  
       BACKGROUND OF THE INVENTION  
       [0002]     In a composite sheet serving for plasma TV, holes each having a quadrangular shape or the like are made in a metal conductor layer. In a composite sheet serving for liquid crystal TV, rectangular holes are made in a coating layer applied to the surface of a glass. In the background art, an exposure method or a transfer method has been used as a machining method for making such holes. In recent years, with the advance of a larger screen of plasma TV or liquid crystal TV, a screen size close to a size measuring 600 mm by 1,000 mm has been requested.  
         [0003]     However, when the exposure method is used, a mask fitted to a screen size of plasma TV or the like has to be prepared as a mask for exposure. In addition, the exposure method requires a large number of manufacturing processes. Thus, it takes much time for manufacturing. Further, in respect of handling, it is impossible to increase the dimensions of a sheet or reduce the thickness of the sheet. It is therefore difficult to reduce the price of a product. Furthermore, it is difficult to make the open area ratio of holes (the open area ratio is expressed by dividing the area of a hole by the area of a figure including the dimensions of the hole margined with ½ of a distance to an adjacent hole) not lower than 90%, or to reduce the distance between adjacent ones of the holes. Also in the transfer method, in the same manner as in the exposure method, it is difficult to reduce the price of a product, or it is difficult to make the open area ratio of holes not lower than 90% or to reduce the distance between adjacent ones of the holes.  
       SUMMARY OF THE INVENTION  
       [0004]     An object of the present invention is to provide a composite sheet which can be manufactured in a smaller number of manufacturing processes, whose price as a product can be reduced and in which the open area ratio of holes can be made not lower than 90% and the distance between adjacent ones of the holes can be shortened, a machining method for the composite sheet, and a laser machining apparatus which is suitable for machining the composite sheet.  
         [0005]     In order to solve the foregoing problems, a first configuration of the present invention provides a composite sheet including a first layer and a second layer serving as base layers and put on top of each other in a thickness direction thereof. The first configuration is characterized in that holes having one and the same triangular, quadrangular or hexagonal outer shape and having one and the same size are disposed in the second layer so that distances between sides of adjacent ones of the holes are equal to one another.  
         [0006]     A second configuration of the present invention provides a machining method for a composite sheet including a first layer and a second layer serving as base layers and put on top of each other in a thickness direction thereof. The second configuration is characterized by machining the second layer with a laser beam so that holes having one and the same triangular, quadrangular or hexagonal outer shape and having one and the same size are disposed in the second layer so that distances between sides of adjacent ones of the holes are equal to one another.  
         [0007]     A third configuration of the present invention provides a laser machining apparatus including a laser oscillator which outputs a pulsed laser beam at a frequency f, a mask which shapes an outer shape of the laser beam into one of a triangle, a quadrangle and a hexagon, N pieces of time-sharing means which time-share the laser beam so as to form N laser beams each having a frequency of f/N, N pairs of positioning means which position the time-shared laser beams, a condensing lens which condenses the laser beams, a displacement means for displacing a laser irradiation portion in which the positioning means for the laser beams and the condensing lens are disposed, or a workpiece, and a control means for controlling the time-sharing means, the positioning means and the displacement means. The third configuration is characterized in that the control means makes control to position the N pairs of positioning means so as to irradiate predetermined positions with the laser beams, and to thereafter operate the displacement means, to thereupon operate the time-sharing means in predetermined order, and to machine the workpiece to make holes whose outer shapes depend on the mask, so that distances between sides of adjacent ones of the holes are equal to one another.  
         [0008]     In the first and second configurations, an electromagnetic sheet having a metal conductor layer and an organic compound layer put on top of each other in their thickness direction, or a glass sheet having a transparent glass layer coated with acrylic or epoxy resin mixed with powder of titanium or carbon is used as the composite sheet.  
         [0009]     The manufacturing processes can be reduced on a large scale, and the thickness of the composite sheet can be reduced. Accordingly, when the composite sheet is a composite sheet for plasma TV, the composite sheet can be produced as a windable long sheet. Further, the yield of materials can be improved. It is therefore possible to reduce the price of a product. In addition, when the composite sheet is a composite sheet for liquid crystal TV, the number of manufacturing processes can be reduced. It is therefore possible to reduce the price of a product. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a sectional view of a composite sheet according to an embodiment of the present invention;  
         [0011]      FIGS. 2A-2C  are diagrams showing examples of arrangements of windows which are hexagonal;  
         [0012]      FIGS. 3A-3E  are diagrams showing examples of arrangements of windows which are quadrangular;  
         [0013]      FIG. 4  is a diagram showing a fundamental configuration of an optical system according to the embodiment;  
         [0014]      FIG. 5  is a perspective view showing a configuration of a workpiece displacement unit according to the embodiment;  
         [0015]      FIG. 6  is a diagram for explaining the operation where hexagonal windows are machined out according to the embodiment;  
         [0016]      FIG. 7  is a diagram for explaining the operation where each square window is machined out by a plurality of pulses according to the embodiment;  
         [0017]      FIG. 8  is a diagram showing an applied configuration of an optical system according to the present invention;  
         [0018]      FIG. 9  is a diagram showing a configuration of optical path deflectors of a machining head suitable for the optical system shown in  FIG. 8 ;  
         [0019]      FIG. 10  is a diagram showing another configuration of optical path deflectors in a machining head suitable for the optical system shown in  FIG. 8 ;  
         [0020]      FIG. 11  is a diagram for explaining the operation where equilateral hexagonal windows are machined out when the optical system in  FIG. 8  is used;  
         [0021]      FIG. 12  is a diagram showing an arrangement of beams when square windows in  FIG. 7  are machined out;  
         [0022]      FIG. 13  is a diagram showing an example where the configuration described in  FIG. 8  is expanded and another laser oscillator and another conversion optics in  FIG. 9  are provided additionally;  
         [0023]      FIG. 14  is a diagram showing an example where the reflecting mirror in  FIG. 13  is replaced by a prismatic reflecting mirror provided with two reflecting surfaces;  
         [0024]      FIG. 15  is a diagram showing an example of an arrangement of beams when equilateral hexagonal windows are machined out by a laser machining apparatus shown in  FIG. 13  and  FIG. 14 ;  
         [0025]      FIG. 16  is a diagram showing a configuration of another optical system where two other laser oscillators and two other pieces of conversion optics shown in  FIG. 9  are added;  
         [0026]      FIG. 17  is a diagram showing an example of an arrangement of equilateral hexagonal windows machined out by the optical system in  FIG. 16 ;  
         [0027]      FIG. 18  is a diagram showing a configuration of a laser machining apparatus which can improve the machining efficiency when windows are square;  
         [0028]      FIGS. 19A and 19B  are enlarged views of a workpiece according to the embodiment; and  
         [0029]      FIGS. 20A and 20B  are diagrams showing a modification of  FIG. 19 . 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0030]     Embodiments of the present invention will be described below with reference to the drawings.  
         [0031]      FIG. 1  is a sectional view of a composite sheet according to an embodiment of the present invention.  
         [0032]     A composite sheet A is composed of a metal conductor layer  1  (hereinafter referred to as “conductor layer”) and a transparent organic compound layer  2  (PET in this embodiment). The composite sheet A is about 1,000 mm wide (in a direction perpendicular to the paper) and about 1,000 m long (in the left/right direction of  FIG. 1 ). The material of the conductor layer  1  is copper. The conductor layer  1  is laminated substantially uniformly on one surface of the organic compound layer  2  by sputtering. The conductor layer  1  is 1 μm thick, and the organic compound layer is not thicker than 100 μm.  
         [0033]     Holes  3  (hereinafter referred to as “windows”) are disposed in the conductor layer  1  in the arrangement which will be described later. Hereinafter, portions of the conductor layer  1  excluding the windows  3  will be referred to as “conductor lines  4 ”. The outer shapes of the windows  3  belong to one kind of a triangle, a quadrangle and a hexagon, and the windows  3  are disposed so that distances between adjacent ones of the windows  3  are equal to one another, as will be described in detail later.  
         [0034]      FIGS. 2A-2C  and  FIGS. 3A-3E  are diagrams showing examples of arrangements of the windows  3 .  FIG. 2A  shows an arrangement where the outer shape of each window  3  is an equilateral hexagon,  FIG. 2B  shows an arrangement where the outer shape of each window  3  is a hexagon inscribed in a circle and having different sides, and  FIG. 2C  shows an arrangement where the outer shape of each window  3  is a hexagon inscribed in an ellipse.  FIG. 3A  shows an arrangement where the outer shape of each window  3  is a square,  FIG. 3B  shows an arrangement where the outer shape of each window  3  is a parallelogram inscribed in an ellipse,  FIG. 3C  shows a modification of the arrangement shown in  FIG. 3B ,  FIG. 3D  shows an arrangement where the outer shape of each window  3  is a rectangle, and  FIG. 3E  shows an arrangement where the outer shape of each window  3  is a trapezoid inscribed in a circle.  
         [0035]     As is apparent from  FIGS. 2A-2C  and  FIGS. 3A-3E , in each arrangement, the windows  3  can be disposed so that distances between sides of adjacent ones of the windows are fixed. A laser beam is usually adjusted so that any section perpendicular to the optical axis of the laser beam will be formed into a circle. It is therefore possible to use the energy of the laser beam effectively when the outer shape of each window  3  is set as a triangle, a quadrangle or a hexagon inscribed in the circle.  
         [0036]     That is, when R designates the radius of the laser beam incident on the mask which will be described later, the effective utilization of the beam can be expressed by the ratio of the open area of the mask to the area (πR 2 ) of the beam. The area of a mask whose outer shape is an equilateral hexagon inscribed in the beam with the radius R is about 1.5√3R 2 . The area of a square mask is 2R 2 . Therefore, the effective utilization of the beam in the equilateral hexagonal mask is about 83%, while the effective utilization of the beam in the square mask is about 64%. Thus, the effective utilization of the beam in the equilateral hexagonal mask is about 30% higher than the effective utilization of the beam in the square beam, so that the machining speed can be improved by about 30%.  
         [0037]     Assume that the left/right X-direction in  FIGS. 2A-2C  and  FIGS. 3A-3E  is the left/right X-direction of plasma TV. In this case, when the windows  3  are disposed so that one of the sides of each window  3  crosses the X-direction, it is possible to prevent moire fringes from occurring.  
         [0038]     Here, the pitch with which the windows  3  are disposed is kept not longer than 300 μm, the conductor line width is kept not wider than 15 μm, and the open area ratio (open area ratio=[area of an window  3 /(area of the window  3 +area of a figure including dimensions of the window  3  margined with ½ of a distance to an adjacent window  3 ) is kept not lower than 90%. Thus, the permeability of light passing through the windows  3  is enhanced so that the quality of an image can be kept, and harmful light is blocked by the conductor lines  4  so that an electromagnetic shield effect can be provided.  
         [0039]     Particularly in  FIG. 2A , the outer shape of each window  3  is an equilateral hexagon (including a hexagon where a pair of opposite sides is longer or shorter than any other pair of opposite sides). Thus, two pairs of opposite sides are inclined at angles of ±30 degrees with respect to the X-axis while phosphors are disposed like a grid along the coordinate axes. It is therefore possible to reduce occurrence of moire fringes. In the same manner, in  FIG. 3A , due to the windows  3  which are square, opposite sides are inclined at angles of ±45 degrees. It is therefore possible to reduce occurrence of moire fringes.  
         [0040]      FIG. 4  is a diagram showing a fundamental configuration of an optical system in this embodiment.  
         [0041]     In  FIG. 4 , a laser oscillator  8  has a lasing medium of YVO4, YAG or YLF, and outputs a pulsed laser beam  9  with a wavelength of 1,000-1,200 nm. The wavelength of the laser beam  9  is not limited to the aforementioned wavelength, but the laser beam  9  may be a second harmonic, a third harmonic, a fourth harmonic or a fifth harmonic obtained by wavelength conversion of a fundamental wave using a wavelength conversion crystal such as BBO (β·BaB 2 O 4 ), LBO (LiB 3 O 5 ) or CLBO (CsLiB 6 O 10 ).  
         [0042]     The energy (power) of the laser beam  9  is adjusted by an acoustooptical beam distributor  10  so as to form a beam  14 ′. The energy distribution of the beam  14 ′ is made flat (into a so-called top-hat beam) by a beam mode shaper  11 . The outer diameter of the beam  14 ′ is adjusted by a collimator  12  for beam diameter adjustment. Further, the outer shape of the beam  14 ′ is shaped (for example, into an equilateral hexagon) by a mask  13  so as to form a beam  14 . Hereinafter, the beam distributor  10 , the beam mode shaper  11 , the collimator  12  and the mask  13  will be collectively referred to as “conversion optics B”. The beam  14  is introduced onto a fixed reflecting mirror  15  of a machining head C. The shape of the mask  13  is scaled down and projected onto a surface  17  of the composite sheet A by a condensing lens  16 . Thus, windows  3  are formed in the metal conductor layer  1  of the composite sheet A.  
         [0043]      FIG. 5  is a perspective view showing a configuration of a workpiece displacement unit.  
         [0044]     A rotatable rotating drum  18  has a sheet suction mechanism (not shown) of a vacuum system on its surface so as to displace the composite sheet A. A rotatable let-off unit  22  holds the composite sheet A which has been wound like a coil and which has not been machined. A rotatable take-up unit  23  holds the composite sheet A which has been machined. The surface of the rotating drum  18  and the uppermost layer of the composite sheet A wound around the let-off unit  22  and the take-up unit  23  are positioned in the rotation direction with a positioning accuracy of 2 μm.  
         [0045]     The rotating drum  18 , the let-off unit  22  and the take-up unit  23  are retained on a pedestal  19  movably in the illustrated X-direction. The position of the pedestal  19  is controlled by a scale  20  and a sensor  21 . The pedestal  19  is positioned with a positioning accuracy not longer than 2 μm. Three cameras  24  monitor the shape of each window, the condition of the window and the condition of the sheet.  
         [0046]     Next, a machining procedure will be described.  
         [0047]      FIG. 6  is a diagram for describing the operation where hexagonal windows are machined out. The upper half of  FIG. 6  depicts the arrangement of the windows, and the lower half of  FIG. 6  depicts a velocity diagram of the pedestal  19 .  
         [0000]     (1) First, the rotating drum  18  to which the composite sheet A has been fixed by the suction mechanism is fixed to a predetermined position. In addition, the pedestal  19  is positioned at a start position Z 0 .  
         [0000]     (2) A machining start command is issued. In response thereto, the pedestal  19  begins to move while the laser oscillator  8  is turned on.  
         [0048]     (3) As soon as the pedestal  19  arrives at a position Z 1 , a laser beam is radiated. Till then the laser beam has reached a pulse frequency domain where the pulse energy is stable. That is, the start position Z 0  is defined on the basis of the position Z 1  in concert to the time for the laser beam to reach the pulse frequency domain where the pulse energy is stable. The pedestal  19  moves at a constant velocity when the pedestal  19  has reached the position Z 01 .  
         [0049]     (4) After that, the laser beam is radiated whenever the pedestal  19  moves a distance (√3r+w). Here,  r  designates the radius of a circle where each window is inscribed, and w designates a distance between windows (between sides of adjacent windows). (See  FIGS. 2A-2C )  
         [0000]     (5) The pedestal  19  is braked at a position Z 02 .  
         [0000]     (6) Machining the first line is terminated at a position Z 2 . By the aforementioned operation, windows (the reference numeral  25  in  FIG. 6 ) in the first line in  FIG. 6  are machined out.  
         [0050]     (7) The rotating drum  18 , the let-off unit  22  and the take-up unit  23  are operated (rotated) so that the composite sheet A is displaced in the Y-direction (the up/down direction in  FIG. 6 ) by a distance (1.5r+a). Here, the relation a=w/cos 30° is established. (See  FIGS. 2A-2C )  
         [0000]     (8) The pedestal  19  is positioned at a start position Z 3 .  
         [0000]     (9) A machining start command is issued. In response thereto, the pedestal  19  begins to move while the laser oscillator  8  is turned on.  
         [0051]     (10) As soon as the pedestal  19  arrives at a position Z 4 , a laser beam is radiated. Till then the laser beam has reached a pulse frequency domain where the pulse energy is stable. That is, the start position Z 3  is defined on the basis of the position Z 4  in concert to the time for the laser beam to reach the pulse frequency domain where the pulse energy is stable. The pedestal  19  moves at a constant velocity when the pedestal  19  has reached the position Z 02 .  
         [0000]     (11) After that, the laser beam is radiated whenever the pedestal  19  moves a distance (√3r+w). (See  FIGS. 2A-2C )  
         [0000]     (12) The pedestal  19  is braked at the position Z 01 .  
         [0000]     (13) Machining the second line is terminated at a position Z 5 . By the aforementioned operation, windows (the reference numeral  26  in  FIG. 6 ) in the second line in  FIG. 6  are machined out.  
         [0000]     (14)  
         [0052]     After that, the operations (1) to (13) are repeated till the pedestal  19  arrives at a machining end point in the longitudinal direction of the composite sheet A.  
         [0053]     The window shift amount between the first line and the second line is (√3r+w)/2.  
         [0054]     As shown in  FIGS. 3A-3E , an window matrix which is √2r square can be machined out in a procedure similar to the aforementioned procedure. In this case, when  w  designates a distance between windows and the relation b=w/cos 45° is established, the X-direction pitch is (2r+w) and the Y-direction pitch is (r+b).  
         [0055]     Here, specific description will be made about the relationship between the thickness of a conductor layer and the size of each window when the window is formed by one pulse.  
         [0056]     A conductor layer was perforated by a UV laser with a wavelength of 355 nm, a pulse frequency of 30 KHz and a machining portion average output of 2.75 W, using a hexagonal mask whose circumcircle has the same diameter as that of a laser beam. When the conductor layer was 0.5 μm thick, hexagonal windows each having an opposite side distance of about 155 μm and a width across corner of about 175 μm were obtained.  
         [0057]     When the conductor layer was 0.3 μm thick or 0.1 μm thick, hexagonal windows each having an opposite side distance of about 160 μm and a width across corner of about 180 μm were obtained.  
         [0058]     In the same manner, a square mask whose circumcircle has the same diameter was used. When the conductor layer was 0.5 μm thick, square windows each having an opposite side distance of about 147 μm were obtained.  
         [0059]     When the conductor layer was 0.3 μm thick or 0.1 μm thick, square windows each having an opposite side distance of about 150 μm were obtained.  
         [0060]     That is, the thicker the conductor layer is, the smaller the windows are. Accordingly, in order to form large windows in a thick conductor layer, it is necessary to perform machining on each window with a plurality of pulses using beams for machining small partial windows.  
         [0061]     In the aforementioned test, proper energy density was 0.2-0.4 J/cm 2 . That is, when the energy density was lower than 0.2 J/cm 2 , there was a case where the metal conductor layer survived partially in the surface of the organic compound layer. When the energy density was higher than 0.4 J/cm 2 , there was a case where the surface of the organic compound layer was damaged.  
         [0062]     When the composite sheet was a liquid-crystal composite sheet (glass sheet) coated with acrylic resin mixed with titanium powder so as to be 1 μm thick, the energy density high enough to form each window measuring 100 μm by 150 μm was about 1 J/cm 2 , and the number of pulses required for the window was 10. In the same manner, when the composite sheet was a liquid-crystal composite sheet (glass sheet) coated with epoxy resin mixed with titanium powder so as to be 1 μm thick, the energy density high enough to form each window measuring 100 μm by 150 μm was about 1 J/cm 2 , and the number of pulses required for the window was 10.  
         [0063]      FIG. 7  is a diagram for explaining the operation where each square window is machined by a plurality of pulses. The upper half of  FIG. 7  depicts the arrangement of windows, and the lower half of  FIG. 7  depicts a velocity diagram of the pedestal  19 .  
         [0064]     Hereinafter, an window which can be machined out by one pulse will be referred to as “partial window”. Assume that a partial window and another partial window are laid to overlap each other by a distance  s  (=3 μm).  
         [0065]     Also in this case, machining can be performed in the procedure described in  FIG. 6 , but machining must be performed doubly in each even line as compared with machining in each odd line. As shown in  FIG. 7 , after windows (the reference numeral  25  in  FIG. 7 ) in the first line are machined out, one-side windows (the reference numeral  26  in  FIG. 7 ) in the second line are machined out in the leftward travel in the second line. In the left end, the line to be machined is not changed, but machining is performed rightward at that position so as to form the other windows (the reference numeral  27  in  FIG. 7 ) in the second line. Distances among partial windows etc. are shown in  FIG. 7 . That is, when w designates a distance between windows and the relation b=w/cos 45° is established, windows can be finally formed at a pitch  2 (2r−s)+b both in the X-direction and in the Y-direction.  
         [0066]     Next, description will be made about a case where the number of beams is increased.  
         [0067]      FIG. 8  is a diagram showing an applied configuration of an optical system according to the present invention. The beam distributor in  FIG. 4  is replaced by four distributors while the conversion optics B is replaced by four pieces of conversion optics. Constituent parts in  FIG. 8  are referenced by three-digit numerals where 1 to 4 are suffixed to the reference numerals in  FIG. 4  respectively. Each beam  141 ,  142 ,  143 ,  144  is designed to be positioned, for example, by optical path deflectors (a pair of optical scanners) which will be described later, so that the beams  141 ,  142 ,  143  and  144  are incident on one condensing lens  16 . In this optical system, beam distributors  101 ,  102 ,  103  and  104  are, for example, controlled so that the beams  141 ,  142 ,  143  and  144  can be made incident on the condensing lens  16  in that order.  
         [0068]      FIG. 9  is a diagram showing a configuration of optical path deflectors of a machining head suitable for the optical system shown in  FIG. 8 .  
         [0069]     The beams  141  to  144  are introduced into the machining head individually. The beam  141  passing through an optical scanner  291  and an optical scanner  301  which position their own mirrors rotatably, and a reflecting mirror  311  and a reflecting mirror  15 , is introduced into an fθ lens  32  whose pupil diameter D is 50 mm. The beam  141  is scaled down and projected onto the surface  17  of the composite sheet A individually. In the same manner, the beams  142 - 144  passing through optical scanners  292 - 294 , optical scanners  302 - 304 , reflecting mirrors  312 - 314  and the reflecting mirror  15 , are introduced into the fθ lens  32  whose pupil diameter D is 50 mm, respectively. The beams  142 - 144  are scaled down and projected onto the surface  17  of the composite sheet A individually. The reflecting mirrors  311 ,  312 ,  313  and  314  are disposed symmetrically with respect to the center of the reflecting surface of the reflecting mirror  15 .  
         [0070]     When  f  designates the focal length of the fθ lens  32  and θ designates the incident angle of each beam  141 - 144  on the fθ lens  32 , the beam  141 - 144  goes out to a position at a distance fθ from the central axis of the fθ lens  32  in the focal plane. Accordingly, when the incident angle θ is small and even when an offset length L of each of the four beams is large on the incident side, the beam can be condensed near the central axis of the fθ lens  32  if the beam including the beam diameter  d  falls into the pupil, that is, if D&gt;2L+d. For example, assume that f=150 mm. In this case, if d&lt;15 when L=15 mm, and if d&lt;10 when L=20, each beam can be positioned in a desired position in an area measuring 5 mm by 5 mm centering the central axis of the fθ lens in the X- and Y-directions by controlling the optical scanner  291 ,  292 ,  293 ,  294  and the optical scanner  301 ,  302 ,  303 ,  304 .  
         [0071]      FIG. 10  is a diagram showing another configuration of optical path deflectors in a machining head suitable for the optical system shown in  FIG. 8 .  
         [0072]     In this embodiment, the beams  142  and  143  are converted into P waves by not-shown polarizing means before they are incident on polarizing beam splitters  331  and  332 . The beams  142  and  143  are then introduced into the machining head. The beams  142  and  143  passing through optical scanners  292 ,  302 ,  293  and  303  penetrate the polarizing beam splitters  331  and  332  disposed in positions where the reflecting mirrors  311  to  314  are disposed in  FIG. 9 . The beams  142  and  143  are then introduced into the fθ lens  32  via the reflecting mirror  15 .  
         [0073]     On the other hand, the beams  141  and  144  are converted into S waves halfway in their optical paths. The beams  141  and  144  are then introduced into the machining head. The beams  141  and  144  passing through optical scanners  291 ,  301 ,  294  and  304  are reflected by the beam splitters  331  and  332 . The beams  141  and  144  are then introduced into the fθ lens  32  via the reflecting mirror  15 .  
         [0074]      FIG. 11  is a diagram showing an example of an arrangement of windows when the optical system in  FIG. 8  is used.  FIG. 11  shows the case where equilateral hexagonal windows are machined out.  
         [0075]     In this optical system, the laser beams  141  to  144  can be positioned in different positions respectively. For example, the optical axes of the laser beams  141 - 144  are positioned in the Y-direction so that the windows  25 ,  26 ,  27  and  28  can be machined out with the beams  141 ,  142 ,  143  and  144  respectively. There is a lag in irradiation time. For example, the optical axes of laser beams corresponding to the second to fourth lines are positioned to be shifted by a distance (√3r+w)/4 in the X-direction with respect to those in the first line. Irradiation is carried out by one of the beams  141  to  144  by a not-shown controller whenever the pedestal  19  moves the distance (√3r+w)/4. Thus, an window having a width of 4 (1.5r+a) in the Y-direction can be machined out whenever the pedestal  19  is moved once. The pulse oscillating frequency of the laser oscillator  8  and the operating frequencies of the beam distributors  101  to  104  are much higher than the moving velocity (machining pulse frequency×laser irradiation pitch) of the pedestal  19 . It is therefore possible to shorten the machining time. Redundant description of specific operations will be omitted because the specific operations can be understood easily from the aforementioned case in  FIG. 6 .  
         [0076]     When the laser beams are radiated sequentially in the column direction (X-direction), the period with which adjacent windows are machined out can be extended to 4/F seconds (F designate the laser oscillating frequency), and the adjacent windows can be prevented from being machined successively. It is therefore possible to relieve the conductor layer from deterioration due to heat affection or scattered debris.  
         [0077]      FIG. 12  is a diagram showing an arrangement of the beams  141 - 144  when square windows described in  FIG. 7  are machined out with the beams  141 - 144 .  
         [0078]     In the case of  FIG. 12 , the optical axes of the laser beams  141 - 144  are positioned in the Y-direction so that the partial windows  25 ,  26 ,  27  and  28  can be machined out with the beams  141 ,  142 ,  143  and  144  respectively. There is a lag in irradiation time. For example, the optical axes of laser beams corresponding to the second to fourth lines are positioned to be shifted by a distance (2r−s)/4 in the X-direction with respect to those in the first line. Irradiation is carried out by one of the beams  141  to  144  by a not-shown controller whenever the pedestal  19  moves the distance (2r−s)/4. Thus, an window can be machined out in substantially half an area within a region of 2(2r−s)+b in the Y-direction width whenever the pedestal  19  is moved once. The pulse oscillating frequency of the laser oscillator  8  and the operating frequencies of the beam distributors  101  to  104  are much higher than the moving velocity of the pedestal  19 . It is therefore possible to shorten the machining time. Redundant description of specific operations will be omitted because the specific operations can be understood easily from the aforementioned case in  FIG. 6 .  
         [0079]     As is apparent from the aforementioned description, the machining speed can be improved as the number of beams which can be positioned in different positions is increased.  
         [0080]      FIG. 13  shows an expansion of the configuration described in  FIG. 8 . In  FIG. 13 , another laser oscillator and another conversion optics in  FIG. 9  are provided additionally so that 8 beams can be made incident on the reflecting surface of the reflecting mirror  15  of the machining head.  
         [0081]      FIG. 14  shows an example where the reflecting mirror  15  in  FIG. 13  is replaced by a prismatic reflecting mirror  34  provided with two reflecting surfaces.  
         [0082]     Redundant description of specific operations will be omitted because the specific operations can be understood easily from the aforementioned case in  FIG. 6 .  
         [0083]      FIG. 15  shows an example of an arrangement of beams when equilateral hexagonal windows are machined out by the laser machining apparatus shown in  FIG. 13  and  FIG. 14 .  
         [0084]     As shown in  FIG. 15 , when the number of beams is 8, an area twice as wide as that when the number of beams is 4 can be machined at a time by one-time movement of the pedestal  19 . It is therefore possible to improve the machining efficiency better.  
         [0085]      FIG. 16  is a configuration diagram of another optical system according to the present invention.  
         [0086]     This configuration can be implemented by adding two other laser oscillators and two other pieces of conversion optics shown in  FIG. 9 .  
         [0087]      FIG. 17  shows an example of an arrangement of equilateral hexagonal windows machined out by the optical system in  FIG. 16 .  
         [0088]     Redundant description of specific operations will be omitted because the specific operations can be understood easily from the aforementioned case in  FIG. 6 .  
         [0089]     Though not shown, the machining head may be replaced by an X-direction scanning optics constituted by a polygon mirror with a number P of surfaces and a semi-cylindrical fθ lens. The X-direction scan by the polygon mirror and the Y-direction drum rotation are synchronized to condense beams into a machining portion of the fθ lens. In this case, accuracy in window dimensions, window shape and conductor line width deteriorates. Thus, the frequency of occurrence of a change in open area ratio or moire fringes increases slightly.  
         [0090]     When regions to be irradiated with N laser beams are disposed in a straight line and a workpiece is moved relatively to the regions, the following conditions can be generally set. That is:  
         [0091]     (1) If irradiation with the laser beams is carried out whenever the workpiece moves a fixed distance, the ratio between an acceleration period and a deceleration period in one traveling cycle becomes smaller relatively as the distance where the workpiece travels at a constant velocity is longer. It is therefore possible to improve the machining efficiency in a fixed time.  
         [0000]     (2) When the capacity of the laser oscillator is secured to be enough large and the moving velocity of the workpiece is fixed, the machining efficiency can be improve as the interval of laser irradiation is shortened.  
         [0092]     The same thing can be applied to the case where the workpiece is fixed and the regions to be irradiated with the laser beams are moved relatively to the workpiece.  
         [0093]     Accordingly, when the windows are equilateral hexagonal, it will go well if the windows are disposed so that a pair of opposite sides of each window are put at right angles with the traveling direction of the composite sheet as shown in  FIG. 11  (each window is shifted from a second adjacent window by ½ of the distance between two opposing sides when the windows are equilateral hexagonal, but the windows can be regarded as disposed substantially in a straight line).  
         [0094]     On the other hand, when windows are square, the aforementioned conditions (1) and (2) can be satisfied in the following manner. Thus, the machining efficiency can be improved.  
         [0095]      FIG. 18  is a configuration diagram of a laser machining apparatus which can improve the machining efficiency when windows are square. Parts the same as those in  FIG. 4  are referenced correspondingly, and redundant description thereof will be omitted.  FIGS. 19A and 19B  are enlarged views of a workpiece.  FIG. 19A  shows a general view, and  FIG. 19B  shows an arrangement of windows as a product.  
         [0096]     In  FIG. 18 , a laser irradiation portion including an fθ lens  32  is mounted on a table  60  which can move in the illustrated up/down direction on a linear guide  62  disposed on a base  61 . Thus, the laser irradiation portion can move in the illustrated up/down direction. On the other hand, a composite sheet A is wound and positioned by a main positioning driving roll  51  and an accessory positioning driving roller  52 . The main positioning driving roll  51  is disposed at one end of a flat sheet backup  50  having a sheet suction mechanism (not shown) of a vacuum system on its surface. The accessory positioning driving roller  52  is disposed to the other end of the sheet backup  50  (hereinafter the main positioning driving roll  51 , the sheet backup  50  and the accessory positioning driving roller  52  will be collectively referred to as “table T”).  
         [0097]     Laser beams (four beams in the illustrated case) are positioned to be arrayed in a straight line K which is at an angle of 45 degrees with the moving direction of the table  60 . The table T is positioned in a direction where the composite sheet A can be wound in the direction of the straight line K. The table  60  reciprocates a machining width (distance obtained by adding distances required for acceleration and deceleration to an area to be irradiated with the laser beams).  
         [0098]     The oscillating frequency of the laser oscillator is usually 20 kHz or higher. In the aforementioned manner, the machining speed can be made 1.4 times as high as that in the case where the winding direction of the composite sheet A is set at right angles with the moving direction of the table  60 . In addition, the mass of the table  60  can be made smaller than the mass of the table T. Accordingly the moving velocity can be made higher than that in the case where the table  60  is moved in the illustrated up/down direction. As a result, the machining efficiency can be improved as compared with that in the case where the table T is moved.  
         [0099]     The table T may be designed to be moved in the illustrated up/down direction. Alternatively the table T may be designed to be mounted on a rotationally positioning mechanism so that the angle of the table T with the table  60  can be changed.  
         [0100]     In the laser machining apparatus shown in  FIG. 18 , the distance between the laser oscillator  8  and the fθ lens  32  changes correspondingly to the machining width. Therefore, when a relay lens is disposed between each beam distributor  10  and each beam mode shaper  11 , the laser beam diameter and the beam mode (laser intensity distribution) can be fixed. As a result, the machining quality can be made uniform.  
         [0101]     Here, as shown in  FIGS. 20A and 20B , positions of windows may be shifted in the row direction between upper and lower columns if the shifted distance is within a range having no trouble in practical use (illustrated distance  g ).  
         [0102]     The number of beams may be more increased.  
         [0103]     When a hole cannot be machined out by one pulse, for example, in  FIG. 18  the number of times of reciprocating of the table  60  may be increased so that the hole can be machined out by a plurality of pulses.  
         [0104]     Further, for example, a diffraction-type or aspherical beam shaper or the like may be used to shape the outer shape of a laser beam, for example, into a shape similar to and slightly larger than a beam shape serving for irradiation, and shape the shaped beam into a final shape by use of a mask. In this manner, the use efficiency of the beam can be improved.  
         [0105]     Description has been made about the case where a composite sheet is machined. When a plate-like composite  
         [0106]     Description has been made about the case where windows are formed in a composite sheet. However, a laser machining apparatus according to the present invention can be also applied to the case where places scattered regularly on the sheet to be heated, such as the case in the step of forming organic transistors in the flat panel.