Abstract:
A laser processing apparatus includes a stage for mounting a workpiece, which moves the workpiece along two axes which are in parallel with the workpiece, the two axes being perpendicular to one other; a laser optical unit including a light source uniting laser light for irradiating the workpiece mounted on the stage with laser light, a stage controller for controlling the movement of the stage in each direction of the two axes, a collecting lens for collecting laser light and irradiating the workpiece with the laser light; a casing for placing the collecting lens on an optical path of the laser light, and a driving unit for moving the casing in a direction parallel to the optical path of the laser light. The driving unit moves the casing and focuses a focal point of the collecting lens on the workpiece.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation of U.S. application Ser. No. 09/631,949, filed Aug. 3, 2000, now U.S. Pat. No. 6,498,319 B1, the subject matter of which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a method and an apparatus for manufacturing electronic circuit boards, and particularly to a multi-layer board manufacturing method and a multi-layer board manufacturing apparatus suitable for manufacturing multi-layer ceramic boards. 
     Recently, the mounting configuration of electronic circuit components such as ICs and LSIs, which are used not only in information equipment but also in household appliances and automobile parts, has become denser. With the increasing density of mounting configuration, there has been a stronger tendency to increase the density and layers of electronic circuit boards for mounting electronic circuit components. Ceramic boards, which are laminated with green sheets and sintered, are becoming dominant as a material for electronic circuit boards. 
     When a ceramic board is manufactured, through holes are formed in green sheets, and circuits are formed by printing. After laminated and bonded by pressing, the green sheets are cut to board size, and then sintered to form a ceramic board. In methods for manufacturing ceramic boards, cutting is performed by methods using cutter blades or stamping methods using dies, as disclosed, for example, in Japanese Patent Laid-Open No. Hei 5-190374, Japanese Patent Laid-Open No. Hei 9-104018, Japanese Patent Laid-Open No. Hei 10-335170, and Japanese Patent Laid-Open No. Hei 11-90894. The methods mentioned above are for mechanical processing. 
     On the other hand, as disclosed in, for example, Japanese Patent Laid-Open No. Hei 9-1369, there is a known method in which a board is laminated with green sheets and sintered, and then the sintered multi-layer board is cleaved by using a laser. A laser cleavage cut is performed by irradiating the surface of the multi-layer board with laser light with a large beam diameter at a position off the focal point, so that thermal stress occurring in the heated part due to the laser light causes the multi-layer board to be cleaved. 
     SUMMARY OF THE INVENTION 
     In methods of cutting a multi-layer ceramic board by mechanical processing, the number of electronic circuit boards manufactured from a green sheet is limited, and therefore it presents a problem of low yields. In order to increase the yields, electronic circuit boards with a plurality of sizes may be arranged on a large green sheet in such a way as to eliminate waste. With mechanical processing methods, it is impossible to cut the plurality of circuit boards arranged close to each other on the green sheet. The reasons for this include a large cut margin resulting from a mechanical processing method and the incapability of mechanical processing methods to perform two-dimensional cutting. Two-dimensional cutting will be described later in detail. One-dimensional cutting means that a sheet is first cut sequentially only in one direction, and then the cut long, narrow sheet is further cut in a direction perpendicular to the above cutting direction. On the other hand, two-dimensional cutting means that after a electronic circuit board is cut along a first side of the electronic circuit board, the cutting is continued along a second side of the electronic circuit board which is perpendicular to the first side. 
     In the method of cleaving a sintered multi-layer board by laser light, irregularities are formed on the cut surfaces, which can cause a crack and therefore present a problem of a low yield. 
     The present invention provides a method and an apparatus for manufacturing multi-layer boards, which will improve yields in the manufacturing of electronic circuit boards. 
     A manufacturing method according to the present invention comprises the steps of: 
     preparing a plurality of green sheets; 
     forming at least one board pattern on each of the plurality of sheets; 
     laminating and bonding each of the plurality of sheets to form a multi-layer board; and 
     cutting the multi-layer board by irradiating the periphery of at least one board pattern on the surface of the multi-layer board with laser light. 
     Thus a section in the multi-layer board where at least one board pattern is formed is cut away from the other section of the multi-layer board. The section of the multi-layer board cut away from the other section of the multi-layer board is sintered. As a result, a multi-layer board is produced. 
     The unsintered multi-layer board is cut by heating and melting with laser light. This makes it possible to improve the yield in the manufacturing of electronic circuit boards. 
     A manufacturing apparatus according to the present invention has a stage for mounting a board. The stage moves a board in the directions of two axes which are in parallel with the board and perpendicular to each other. A laser optical unit is placed above the stage to irradiate the board mounted on the stage with laser light and cut it. The width of the cut portion in the board created by laser light is measured by a width measuring unit. A stage controller, which controls the movement of the stage, controls the velocity at which the stage moves, according to the width measured by the width measuring unit. 
     The kerf width can be made almost constant and narrow, by monitoring the kerf width and controlling the cutting velocity by using feedback. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing the process for manufacturing a multi-layer electronic circuit board according to an embodiment of the present invention; 
     FIG. 2 is a perspective view showing the general configuration of an apparatus for manufacturing electronic circuit boards according to an embodiment of the present invention; 
     FIG. 3 is a graph showing the relation between laser power and board thickness when laser cutting is performed; 
     FIG. 4 is a graph showing the relation between cutting velocity and board thickness when laser cutting is performed; 
     FIG. 5 is a graph showing the relation between kerf width and laser power when laser cutting is performed; 
     FIG. 6 is a graph showing the relation between kerf width and cutting velocity when laser cutting is performed; 
     FIG. 7 is a diagram for explaining the conditions of laser light collection and the shape of cut surfaces; 
     FIG. 8 is a diagram for explaining the conditions of laser light collection and the shape of cut surfaces; 
     FIG. 9 is a configuration view of a laser optical system; 
     FIG. 10 is a sectional view showing the relation between the focal point of a laser optical system and the shape of cut surfaces; 
     FIG. 11 is a sectional view of the shape of cut surfaces; 
     FIG. 12 is a diagram of a configuration for removing cutting powder according to an embodiment of the present invention; 
     FIG. 13 is a diagram of a configuration for removing cutting powder according to an embodiment of the present invention; 
     FIG. 14 is a plan view of a multi-layer board; 
     FIG. 15 is a plan view showing a procedure for cutting a multi-layer board; 
     FIG. 16 is a plan view showing a procedure for cutting a multi-layer board; 
     FIG. 17 is a side view of a multi-layer board when it is cut; 
     FIG. 18 is a plan view showing the cut shape of a multi-layer board; 
     FIG. 19 is a plan view showing the cut shape of a multi-layer board; and 
     FIG. 20 is a plan view showing the cut shape of a multi-layer board. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A method and an apparatus for manufacturing electronic circuit boards according to an embodiment of the present invention will now be described with reference to FIGS. 1 to  19 . 
     First, A method for manufacturing a multi-layer electronic circuit board according to the present embodiment will be described with reference to FIG.  1 . 
     FIG. 1 is a diagram showing the process for manufacturing a multi-layer board according to the present embodiment. 
     First, as shown in FIG.  1 (A), holes  12  for through holes and the like are formed in a single-layer green sheet  10  by a mechanical processing method. 
     Next, as shown in FIG.  1 (B), a board pattern  14  is printed on the green sheet  10 . 
     Next, as shown in FIG.  1 (C), a plurality of green sheets on which the board pattern  14  is printed are laminated and bonded by pressing to form a multi-layer board  16 . 
     Next, as shown in FIG.  1 (D), the multi-layer board  16  is cut by using laser light L along a cut line C provided according to the size of the board pattern  14 , to separate into board units. By placing the multi-layer board  16  in the proximity of the focal point of a focusing lens, laser light L is converged in the proximity of the surface of the multi-layer board  16  as laser light with a small beam diameter, to cut the multi-layer board  16  by heating and melting. Incidentally, the position of the cut line C is predetermined by an optical system in order to hold the size of the board pattern  14  within tolerances. 
     Finally, as shown in FIG.  1 (E), the multi-layer board separated by laser light cutting is sintered to complete a multi-layer electronic circuit board  18 . After the completion of the electronic circuit board  18 , tests for conduction and the like are performed. 
     Conventional manufacturing processes have employed methods of stamping the multi-layer board shown in FIG.  1 (C) with dies or methods of cutting the multi-layer board by a cutter blade after sintering. In the present embodiment, on the other hand, the multi-layer board is cut by using laser light, and therefore, as will be described later, the cut margin of the multi-layer board is reduced and it is possible to perform free two-dimensional cutting according to the board pattern of the multi-layer board. 
     It should also be noted that in the present embodiment, an unsintered multi-layer board is cut by using laser light. It is possible to cut a multi-layer board by using laser light after sintering, but in that case, damage such as the occurance of a crack or the adhesion of melt (dross) to the multi-layer board could be caused, which results in a low yield. When an unsintered multi-layer board is cut, on the other hand, stress due to the effects of heat is released and therefore no crack is caused because an unsintered multi-layer board lacks stiffness. In addition, since the melting point of the melt that is produced when an unsintered multi-layer board is heated and melted by laser light is low, the melt becomes powdery matter and thus is blown away without adhering to the cut surfaces. Even if the powder or the binder adheres, it is evaporated and removed because the multi-layer board is heated to a temperature of thousands of degrees in the sintering process following the cutting process. Therefore, the present embodiment can prevent decreases in the quality of a multi-layer board due to damage and thus increase the yield in the manufacturing of electronic circuit boards. Moreover, even when the thickness of a multi-layer board is increased because of the increase in the number of laminated layers, the multi-layer board can be readily cut. 
     Next, the configuration of an apparatus for manufacturing electronic circuit boards according to the present embodiment will be described with reference to FIGS. 2 to  6 . 
     First, the general configuration of the manufacturing apparatus will be described with reference to FIG.  2 . 
     An unsintered multi-layer board  16  is fixed and held by a fixing jig  20 . The fixing jig  20  is mounted on an X-axis stage  30  and a Y-axis stage  32 . The movement of the X-axis stage  30  and the Y-axis stage  32  in the X-axis direction and the Y-axis direction is controlled by a stage controller  34 . 
     A laser light source  40  is provided above the multi-layer board  16 . Laser light L emitted from the laser light source  40  is collected by a collecting lens  42  and irradiated on the multi-layer board  16 . The laser light L forms a kerf G on the multi-layer board  16  to cut the multi-layer board  16 . In the example shown in the figure, the stage controller  34  in this case drives the Y-axis stage  32  in the Y-axis direction to cut the multi-layer board  16  in the Y-axis direction. 
     When the materials for the multi-layer board  16  are mullite type ceramic materials or glass type ceramic materials, a laser in the infrared wavelength region, such as a YAG laser (wavelength of 1.06 μm) and a CO 2  laser (wavelength of 10.6 μm), for example, is suitable as the laser light source  40 . A CO 2  laser is suitable especially for high-speed, high-quality cutting. According to data on the infrared absorption spectrum of a green sheet of ceramic material, the absorption factor of the green sheet at 10.6 μm is about 85%, which is especially high among infrared wavelengths, and therefore a CO 2  laser emitting laser light with a wavelength of 10.6 μm is suitable. In addition, a CO 2  laser is suitable because it operates in single mode even when the output is high. On the other hand, a YAG laser can also be used to emit laser light with infrared wavelengths to be absorbed by a green sheet, but it is not quite suitable to use for high output because it changes from single mode to multimode when the output is high. 
     Continuous oscillation (CW) is suitable as a laser oscillation method. Although a pulse method is often used as a normal laser oscillation method, the continuous oscillation method provides better cut surfaces with less irregularities. 
     In addition, a CCD camera  50  is provided above the multi-layer board  16  to pick up the image of the kerf G. The image of the kerf G picked up by the CCD camera  50  is displayed on a monitor  52  after magnified by about 100 to 200 times. An image processing unit  54  recognizes and measures the width Wg of the kerf G displayed on the monitor  52 . The stage controller  34  controls the Y-axis stage  32  in such a way that the the width Wg of the kerf G measured by the image processing unit  54  is kept constant. Incidentally, when the multi-layer board  16  is cut in the direction of the X-axis, the stage controller  34  controls the X-axis stage  30 . The control method of the stage controller  34  will be described later in detail. 
     Next, the relations between laser power, cutting velocity, and board thickness when laser cutting is performed will be described with reference to FIGS. 3 and 4. 
     FIG. 3 shows the relation between board thickness and laser power when laminated green sheets are cut by using a continuous-oscillation CO 2  laser. In FIG. 3, the axis of ordinates denotes laser power (W), while the axis of abscissas denotes board thickness (mm). Here, the cutting velocity of the continuous-oscillation CO 2  laser is set to be constant at 30 mm/s, while the beam diameter of the continuous-oscillation CO 2  laser is set to be constant at φ200 μm. 
     It is clear from the graph that when the diameter of the collected beam is set to be constant, the laser power is almost in a proportional relation with the board thickness. For example, in order to cut a board with a thickness of 5 mm, the laser power needs to be set at about 600 W. Thus, in order to cut a board with a thickness of 10 mm at a cutting velocity of 30 mm/s, for example, the laser power needs to be set at 1 kW or more. 
     On the other hand, FIG. 4 shows the relation between board thickness and cutting velocity when laminated green sheets are cut by using a continuous-oscillation CO 2  laser. In FIG. 4, the axis of ordinates denotes cutting velocity (mm/s), while the axis of abscissas denotes board thickness (mm). Here, the laser power of the continuous-oscillation CO 2  laser is set to be constant at 100 W, while the beam diameter of the continuous-oscillation CO 2  laser is set to be constant at φ200 μm. 
     It is clear from the graph that when the diameter of the collected beam is set to be constant, the cutting velocity is almost in an inversely proportional relation with the board thickness. For example, in order to cut a board with a thickness of 5 mm, the cutting velocity needs to be set at 3 to 4 mm/s. Thus, in order to cut a board with a thickness of 10 mm at a laser power of 100 W, for example, the cutting velocity needs to be set at about 1 mm/s. 
     It is shown from the above descriptions that when the thickness of a multi-layer board is about 1 mm, the multi-layer board can be cut in a satisfactory manner by setting the output of the CO 2  laser at about 120 W and setting the cutting velocity of the CO 2  laser at 30 mm/s or more. The kerf width can be reduced to 150 to 190 μm by using a 1-inch (25.4 mm) collecting lens. 
     Next, a control method for kerf width according to the present embodiment will be described with reference to FIGS. 5 and 6. 
     FIGS. 5 and 6 show changes in kerf width according to cutting conditions. 
     When a board is cut by using a laser light, the kerf width of the board is constant unless cutting conditions change. However, if the tolerance accuracy must be a few μm, the kerf width of the board needs to be controlled in such a way that it is held constant. 
     FIG. 5 shows the dependence of kerf width on laser power. 
     In FIG. 5, the axis of ordinates denotes kerf width (μm), while the axis of abscissas denotes laser power (W). FIG. 5 shows the relation of kerf width to laser power in two cases where cutting velocity is 25 mm/s and where cutting velocity is 30 mm/s. When the cutting velocity is the same, a 10 W change in the laser power does not cause a wide range of change in the kerf width. The changes in the kerf width in this case are within 5 μm. 
     On the other hand, FIG. 6 shows the dependence of kerf width on cutting velocity. 
     In FIG. 6, the axis of ordinates denotes kerf width (μm), while the axis of abscissas denotes cutting velocity (mm/s). FIG. 6 shows the relation of kerf width to cutting velocity in two cases where laser power is 65 W and where laser power is 80 W. It is clear from the figure that when the laser power is the same, a 10 mm/s change in the cutting velocity causes a wide range of change in the kerf width. The changes in the kerf width in this case are about 10 to 30 μm. 
     In order to deal with this, the image processing unit  54  in the manufacturing apparatus as shown in FIG. 2 recognizes and measures the width of the kerf G picked up by the CCD camera  50 . The image of the kerf G picked up by the CCD camera  50  is also displayed on the monitor  52 . The stage controller  34  controls the Y-axis stage  32  in such a way that the the width of the kerf G measured by the image processing unit  54  is kept constant. As shown in FIG. 6, the kerf width is decreased as the the cutting velocity is increased. Therefore, the stage controller  34  controls the moving velocity of the Y-axis stage  32 , that is, the cutting velocity by using feedback in such a way that the cutting velocity is increased when the comparision of a target kerf width with the measured kerf width shows that the measured kerf width is larger than the target kerf width, whereas the cutting velocity is decreased when the comparision of a target kerf width with the measured kerf width shows that the measured kerf width is smaller than the target kerf width. The target kerf width is determined by the stage controller  34  from the beam diameter (focused diameter) of laser light irradiated on the multi-layer board. Or the target kerf width may be preset in the stage controller  34 . Or the stage controller  34  may recognize the target kerf width by other methods. Incidentally, when the multi-layer board is cut in the direction of the X-axis, the stage controller  34  controls the moving velocity of the X-axis stage  30  by using feedback. 
     The feedback control of the cutting velocity by the stage controller  34  allows the kerf width to be kept constant. Since the kerf width is made almost constant, the cut line of the multi-layer board after cutting can be made almost linear. 
     Next, a laser optical system used in the manufacturing apparatus will be described with reference to FIGS. 7 to  11 . 
     First, the conditions of laser collection and the shape of cut surfaces will be described with reference to FIGS. 7 and 8. 
     When laser cutting is performed, the manufacturing apparatus uses a collecting lens  42  to collect and irradiate a multi-layer board  16  with laser light L. In the case of a multi-layer board  16  with a thickness of about 1 mm, the multi-layer board  16  can be cut in a satisfactory manner even when the focal length Lfl of the collecting lens  42  is about 1 inch (25.4 mm), and the shape of cut surfaces is straight, and not tapered. In general, the shorter the focal length Lfl of the collecting lens  42  is, the smaller the focused diameter of the laser light can be made, which therefore results in a smaller cut width. 
     However, as shown in FIG. 8, if the thickness Tl of the multi-layer board  16  becomes 5 mm or more, the cut surface of the multi-layer board  16  aquires a tapered shape and the amount of taper Tt of the cut surface increases in proportion to the thickness Tl of the multi-layer board  16 . In order to solve this problem, the focal length Lfl of the collecting lens  42  shown in FIG. 7 should be increased, and the focal depth df of the collecting lens  42  should also be increased. Inventors considered the focal length of the collecting lens that can reduce the amount of taper of a cut surface by changing the thickness of a multi-layer board. As a result, it was shown that the amount of taper Tt of the cut surface is made to be 10 μm or less by setting the focal length of the collecting lens at 3.5 inches when the thickness of the multi-layer board is about 2 mm, by setting the focal length of the collecting lens at 5 inches when the thickness of the multi-layer board is about 5 mm, and by setting the focal length of the collecting lens at 7 inches when the thickness of the multi-layer board is about 10 mm. Incidentally, the focal depth df of the collecting lens is the distance between the points where the beam diameter of the laser light becomes twice as large as the focused diameter of the laser light at the focal point. For example, if the focused diameter of the laser light is 200 μm, the focal depth df of the collecting lens is the distance between the points where the beam diameter of the laser light becomes 400 μm. 
     Next, a laser optical system used in the manufacturing apparatus will be described with reference to FIG.  9 . 
     Two collecting lenses  42 L and  42 S are placed inside the casing  44  of the laser optical system. The collecting lens  42 L has a long focal length. The focal length of the collecting lens  42 L is 7 inches, for example. The collecting lens  42 S has a short focal length. The focal length of the collecting lens  42 S is 5 inches, for example. The casing  44  is provided with a housing  44 L for the collecting lens  42 L and a housing  44 S for the collecting lens  42 S. The collecting lens  42 L can be made to move between a position in the housing  44 L and a position on the optical axis by using a revolver or the like, which is not shown in the figure. Similarly, the collecting lens  42 S can be made to move between a position in the housing  44 S and a position on the optical axis by using a revolver or the like, which is not shown in the figure. Either the collecting lens  42 L or the collecting lens  42 S is placed on the optical axis of the laser light L emitted from the laser light source. 
     The casing  44  can be moved in the direction of the arrow Z by a vertical driving mechanism  46 . Also, the casing  44  is externally supplied with air assist gas G from its sides in the Z direction. The casing  44  is designed to blow the supplied air assist gas on the portion being cut by the laser. 
     In addition, the laser optical system is provided with a contact height sensor  48 . The contact height sensor  48  comes in contact with the surface of the multi-layer board  16  to measure the thickness of the multi-layer board  16 . 
     The relation between the focal point of the laser optical system and the shape of cut surfaces will be described with reference to FIGS. 10 and 11. 
     FIG. 10 shows the relation between the focal point of the laser optical system and the shape of cut surfaces when the thickness of the multi-layer board  16  is large. 
     FIG.  10 (A) shows the shape of cut surfaces when the focal point Pf of a collecting lens is located at a point on the surface of the multi-layer board  16 . As shown in the figure, the cut surfaces are tapered when the focal point Pf of the collecting lens is located at a point on the surface of the multi-layer board  16 . 
     On the other hand, FIG.  10 (B) shows the shape of cut surfaces when the focal point Pf of the collecting lens is located at a point inside the multi-layer board  16 . As shown in the figure, the cut surfaces have a convex shape with the middle parts of the cut surfaces projecting when the focal point Pf of the collecting lens is located at a point inside the multi-layer board  16 . 
     On the other hand, FIG.  10 (C) shows the shape of cut surfaces when the focal point Pf of the collecting lens is located at a point 0.1 to 0.2 mm above the surface of the multi-layer board  16 . As shown in the figure, the cut surfaces have a straight shape with little taper when the focal point Pf of the collecting lens is located at a point way above the surface of the multi-layer board  16 . When the focal point Pf of the collecting lens is located at a point 0.1 to 0.2 mm above the surface of the multi-layer board  16 , the beam shape of the laser light is trapezoidal, with a small beam diameter on the upper surface side of the multi-layer board and a large beam diameter on the lower surface side of the multi-layer board. Since the energy density of the laser light is high on the upper surface side of the multi-layer board, however, the multi-layer board tends to be heated and melted more easily on the upper surface side. As a result, the cut surfaces have a straight shape with little taper. Thus, according to the present embodiment, the manufacturing apparatus locates the the focal point Pf of the collecting lens at a point 0.1 to 0.2 mm above the surface of the multi-layer board  16 . 
     On the other hand, FIG. 11 shows the shape of cut surfaces when the thickness of the multi-layer board  16  is small. When the thickness of the multi-layer board  16  is small, either a collecting lens with a long focal length or a collecting lens with a short focal length can be used to make the shape of cut surfaces straight. 
     However, if a lens with a long focal length is used, the kerf width results in Wg 1 , as shown in FIG.  11 (A). On the other hand, if a lens with a short focal length is used, the kerf width results in Wg 2 , as shown in FIG.  11 (B). Here, the kerf width Wg 1  is larger than the kerf width Wg 2 . This is because the beam diameter at the focal point of the lens with a long focal length is larger than the beam diameter at the focal point of the lens with a short focal length. For example, the beam diameter at the focal point of a collecting lens with a focal length of 1 inch is about 200 μm, while the beam diameter at the focal point of a collecting lens with a focal length of 5 inches is about 250 to 300 μm. 
     Therefore, when the multi-layer board  16  with a small thickness is to be cut by laser light, either a collecting lens with a long focal length or a collecting lens with a short focal length can be used; however, in order to narrow the kerf width, it is desirable to use a collecting lens with a short focal length. On the other hand, when a multi-layer board  16  with a large thickness is to be cut by laser light, it is required to use a collecting lens with a long focal length. Therefore, as described in FIG. 9, the laser optical system switches between the collecting lens  42 L with a long focal length and the collecting lens  42 S with a short focal length, according to the thickness of the multi-layer board. 
     Next, the operation of the laser optical system will be described. 
     First, after a multi-layer board  16  is fixed and held by the fixing jig  20  as shown in FIG. 2, the contact height sensor  48  comes in contact with the surface of the multi-layer board  16  to measure the thickness of the multi-layer board  16 . If the thickness of the multi-layer board  16  is larger than a specified thickness, the collecting lens  42 L with a long focal length is set on the optical axis. Then the casing is moved in the Z direction by the vertical driving mechanism  46  so as to locate the focal point of the collecting lens  42 L at a point 0.1 to 0.2 mm above the surface of the multi-layer board  16 . 
     If the thickness of the multi-layer board  16  is smaller than the specified thickness, the collecting lens  42 S with a short focal length is set on the optical axis. Then the casing is moved in the Z direction by the vertical driving mechanism  46  so as to locate the focal point of the collecting lens  42 S at a point 0.1 to 0.2 mm above the surface of the multi-layer board  16 . 
     Next, the configuration of the unit for removing cutting powder will be described with reference to FIGS. 12 and 13. Incidentally, identical numerals in FIGS. 2 and 9 denote identical parts. 
     As shown in FIG. 12, the fixing jig  20  that holds the multi-layer board  16  comprises a fixing suction unit  22  which fixes the multi-layer board  16  by suction, a space box  24  which has space inside and is placed in such a way as to cover the fixing suction unit  22 , and a hose  26  connected to a dust absorb cleaner not shown in the figure. The space box  24  has an approximately rectangular parallelepiped shape, and has an opening on the upper surface. The fixing suction unit  22  is placed at the opening of the space box  24 . When the multi-layer board  16  is sucked and fixed by the fixing suction unit  22 , the opening of the space box  24  is closed by the multi-layer board  16 , and the space inside the space box  24  is brought almost to a sealed state. 
     When the multi-layer board  16  is cut by laser light L, cutting powder is produced. Since the inside of the space box  24  connected with the hose  26  is sucked by the dust absorb cleaner, the cutting powder produced is absorbed from the space box  24  to the outside via the hose  26 . The space inside the space box  24  is brought nearly to a sealed state by fixing and holding the multi-layer board  16  to the fixing suction unit  22 , thereby resulting in a high dust absorbing efficiency. 
     As shown under magnification in FIG. 13, the casing  44  that holds the collecting lens  42  has a triple nozzle structure comprising three nozzles  44 A,  44 B, and  44 C each placed on the same axis. The nozzle  44 A holds the collecting lens  42 . In addition, the nozzle  44 A has at least one gas leader and blows the air assist gas G 1  led in from the outside through the gas leader onto the portion of the multi-layer board  16  being cut by laser light L. The cutting powder produced in the proximity of the portion of the multi-layer board  16  being cut by laser light L is blown away by the air assist gas G 1 , and at least part of the cutting powder is blown into the space box  24 . The nozzle  44 B has at least one absorber. The space between the innermost nozzle  44 A and the intermediate nozzle  44 B is sucked by an absorbing means, which is not shown in the figure, via the absorber. Another part of the cutting powder blown away the air assist gas G 1  is absorbed by the absorbing means. Furthermore, the nozzle  44 C has at least one gas leader, and air assist gas G 2  is led into the space between the outermost nozzle  44 C and the intermediate nozzle  44 B from the outside through the gas leader. The air assist gas G 2  is blown onto the multi-layer board  16  in such a way that the cutting powder blown away by the air assist gas G 1  will not fly to the outside. As a result, the part of the cutting powder that did not enter the space box  24  is absorbed into the space between the nozzle  44 B and the nozzle  44 A. 
     When the gas pressure of the air assist gas G 1  is 5 kg/cm 2 , for example, the gas pressure of the air assist gas G 2  is set to be 2 kg/cm 2 , for example. By making the gas pressure of the air assist gas G 2  lower than the gas pressure of the air assist gas G 1 , the air assist gas G 2  can be used as an air curtain. 
     Next, the method of cutting a multi-layer board will be described with reference to FIGS. 14 to  16 . 
     In the example shown in FIG. 14, four board print patterns  14 A,  14 B,  14 C, and  14 D are formed on a multi-layer board  16  laminated with green sheets. Also, pads  14 A 11 ,  14 A 12 ,  14 A 21 ,  14 A 22 ;  14 B 11 ,  14 B 12 ,  14 B 21 ,  14 B 22 ;  14 C 11 ,  14 C 12 ,  14 C 21 ,  14 C 22 ;  14 D 11 ,  14 D 12 ,  14 D 21 , and  14 D 22  are formed on the multi-layer board  16  in such a way that the pads surround each of the board print patterns  14 A,  14 B,  14 C, and  14 D. Each pad is individually formed on the outside of each corner of each of the board print patterns. A center position pad  14 E is formed at the center of the multi-layer board  16 . 
     When the multi-layer board  16  held by the fixing jig  20  as shown in FIG. 2 is mounted on the Y-axis stage  32 , the CCD camera  50  picks up the image of the upper surface of the multi-layer board  16 . The CCD camera  50  picks up the image of each section of the upper surface of the multi-layer board  16  by moving the CCD camera  50 , or the Y-axis stage  32  and the X-axis stage  30 . When each of the pads  14 A 11 ,  14 B 12 ,  14 C 21 ,  14 D 22  is picked up by the CCD camera  50 , the image processing unit  54  detects the position of each of the pads in the X-Y coordinate system, and calculates the position of the center of gravity of the four pads. Then, after the center position pad  14 E is picked up by the CCD camera  50 , the image processing unit  54  detects the position of the center position pad in the X-Y coordinate system, and calculates the difference between the position of the center position pad and the above-mentioned position of the center of gravity of the four pads. The stage controller  34  operates the Y-axis stage  32  and the X-axis stage  30  according to the calculated difference to correct the position of the multi-layer board  16 . 
     Next, the method of cutting a section in the multi-layer board where a board print pattern is formed will be described. 
     When the section in the multi-layer board  16  where the board print pattern  14 A is formed is to be cut by laser light, for example, the pads  14 A 11 ,  14 A 12 ,  14 A 21 , and  14 A 22  are picked up by the CCD camera  50 . The image processing unit  54  detects the position of each of the pads in the X-Y coordinate system. Then the image processing unit  54  calculates the position  14   g  of the center of gravity of the four pads. With the position  14   g  of the center of gravity set to be the center, positions away from the center by a distance Lx in the lateral direction (x direction) and positions away from the center by a distance Ly in the vertical direction (y direction) form cutting lines. If the size of the section to be cut is 65 mm×70 mm, for example, Lx is set to be 32.5 mm and Ly is set to be 35 mm. In order to irradiate a start point S with laser light L as shown in FIG. 15, the stage controller  34  operates the X-axis stage and the Y-axis stage, putting the multi-layer board  16  in place. The laser light source  40  begins to irradiate the start point S with laser light L. The stage controller  34  first drives the X-axis stage  30  to irradiate the multi-layer board  16  with laser light L along the cutting line C 1 . The laser light L cuts the multi-layer board  16  along the cutting line C 1 , starting at the start point S. When the point where the laser light L is irradiated reaches the point where the cutting line C 1  and the cutting line C 2  cross each other, the stage controller  34  stops the operation of the X-axis stage  30 , and drives the Y-axis stage  32  to irradiate the multi-layer board  16  with laser light L along the cutting line C 2 . This allows the multi-layer board  16  to be cut along the cutting line C 2  continuously from the point where the cutting line C 1  and the cutting line C 2  cross each other. Similarly, the multi-layer board  16  is cut in the manner of one stroke writing along the cutting line C 3  and along the cutting line C 4  in that order. As a result, the board print pattern  14 A is cut off. 
     Incidentally, if the multi-layer board  16  is cut at a high cutting velocity of 30 mm/s or more, the corner sections of the multi-layer board  16  that should have a rectangular cut shape (or the sections where the cutting lines cross each other; for example, the corner section Z in FIG. 15) may be rounded, and therefore the right angle formed at the corner sections may be decreased. Therefore when the cutting velocity is high, cutting is performed along the cutting lines C 1 , C 3 , C 2 , and C 4  in that order, as shown in FIG.  16 . Specifically, the multi-layer board  16  is cut along the cutting line C 1  and then is cut along the cutting line C 3 . Next the multi-layer board  16  is cut along the cutting line C 2  and then is cut along the cutting line C 4 . Since the four sides of the multi-layer board  16  are cut independently of each other, the right angles of the corner sections that should have a rectangular cut shape are improved. 
     Next, the side shape of the multi-layer board when it is cut will be described with reference to FIG.  17 . 
     When the multi-layer board  16  is cut along the cutting line C by heating and melting with laser light, the shape of the multi-layer board  16  viewed from the side of the cut portion has arcs with a radius of R at the edge on the upper side and at the edge on the lower side, as shown in FIG.  17 . For example, if a multi-layer board with a thickness of 1 mm is cut by laser light, the radius R is about 5 to 7 μm. In general, if a cutter or a die is used for cutting, the sharp cutting edge allows the edges of the cut portion to form right angles. On the other hand, when laser light is used for cutting, the edges of the cut portion are rounded because the multi-layer board is cut by the heat of laser light. The rounded edges present no problem in terms of size accuracy, and they are rather free from problems such as the chipping of the edges during handling work with multi-layer boards after cutting. This improves yields in the manufacturing of electronic circuit boards. 
     Next, the cut shape of the multi-layer board will be described with reference to FIGS. 18 to  20 . 
     As shown in FIG.  18 (A), six board print patterns  14 A,  14 B,  14 C,  14 D,  14 E, and  14 F are formed on a multi-layer board  16 . When the six board print patterns are to be cut by laser light, the multi-layer board  16  is cut by laser light along the cutting lines C 1 , C 2 , C 3 , C 4 , C 5 , C 6 , and C 7 . Since the cutting width Wg according to the present embodiment is about 200 μm, the cutting between the board print patterns  14 A and  14 B, for example, is completed in a single cutting operation along the cutting line C 2 . In addition, if the distance between the board print patterns  14 A and  14 B is made equal to the cutting width Wg of 200 μm, then the number of board print patterns that can be cut off from a single multi-layer board  16  will be increased. 
     For reference, the cut shape of the multi-layer board when it is cut by means other than laser light will be described with reference to FIG.  18 (B). 
     Four board print patterns  14 A,  14 B,  14 C, and  14 D are formed on a multi-layer board  16 ′. In order to cut the four board print patterns by using a cutter, for example, the multi-layer board is cut along the cutting lines C 1 ′, C 2 ′, C 3 ′, C 4 ′, C 5 ′, C 6 ′, C 7 ′, and C 8 ′. When the multi-layer board is cut by a cutter, a cutting portion for the cutter is required. Therefore, the width Wc between the the board print pattern  14 A and the board print pattern  14 B, for example, is required to be about 5 mm. As a result, the number of patterns that can be cut off from a single multi-layer board  16  is limited. Also, when board print patterns are stamped by a die, a similar problem is presented. Specifically, the width Wc between the the board print pattern  14 A and the board print pattern  14 B is required to be at least about 5 mm because the stiffness of the stamping die needs to be maintained. 
     FIG. 19 shows other examples of cut shapes. 
     As shown in FIG. 19, four board print patterns  14 G,  14 H,  14 I, and  14 J are formed on a multi-layer board  16 ′. These four board print patterns have shapes of different sizes from one another. Cutters cannot be used for such board print patterns with shapes of different sizes from one another. On the other hand, laser light is able to cut the multi-layer board  16 ′ along each of the circumferences of the board print patterns  14 G,  14 H,  14 I, and  14 J in the manner of one stroke writing as shown in FIG.  15 . Therefore, laser light can be applied to various types of board print patterns. 
     Next, FIG. 20 shows other examples of cut shapes. 
     As shown in FIG. 20, four board print patterns  14 K,  14 L,  14 M, and  14 N are formed on a multi-layer board  16 ″. These four board print patterns have a shape of the same size; however, the board print patterns are arranged in such a way as to increase the number of patterns that can be cut off from a single multi-layer board  16 ″. Cutters cannot be used for board print patterns with such two-dimensional shapes. On the other hand, laser light is able to cut the multi-layer board  16 ″ along each of the circumferences of the board print patterns  14 K,  14 L,  14 M, and  14 N in the manner of one stroke writing as shown in FIG.  15 . Therefore, laser light can also be applied to board print patterns with two-dimensional shapes. 
     As described above, an unsintered multi-layer board is cut by heating and melting with laser light. This improves yields in the manufacturing of electronic circuit boards. 
     In addition, optimum cut shape and kerf width can be obtained according to the thickness of the multi-layer board by switching between a lens with a long focal length and a lens with a short focal length. 
     Moreover, a thick multi-layer board can be readily cut by changing the output of laser light or the cutting velocity of the laser according to the thickness of the multi-layer board. 
     Furthermore, the manufacturing apparatus monitors the kerf width of the multi-layer board and controls the cutting velocity of the laser by feedback, thereby holding the kerf width of the multi-layer board almost constant and narrowing the kerf width of the multi-layer board. 
     Furthermore, the manufacturing apparatus is provided with a laser optical system having a triple nozzle structure, and a fixing jig  20 , and therefore cutting powder is removed effectively. As a result, decreases in yields due to the adhesion of powder to multi-layer boards after cutting can be prevented. 
     Furthermore, when a cutter or a die is used for cutting, the sharpness of the cutter or the die is reduced because of wear, which may result in irregularities or a crack in the shape of cut surfaces. As a result, defective products are produced. On the other hand, when the multi-layer board is cut by using laser light, defective products are reduced, thereby resulting in improved yields. 
     Furthermore, laser light is able to cut a plurality of multi-layer boards with shapes of different sizes from one another, and is able to perform two-dimensional cutting, therefore resulting in improved yields.