Abstract:
A method of processing an unfired ceramic body or sheet, including the steps of covering, with a cover, a surface of the unfired ceramic body or sheet, such that a portion of the surface of the unfired ceramic body or sheet is exposed, and removing at least a portion of the unfired ceramic body that defines the exposed portion of the surface of the unfired ceramic body, and thereby forming a dent, a dimple, or a through-hole in an exposed portion of the unfired ceramic body or sheet.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method of processing an unfired or unburned ceramic body and particularly to such a method comprising a step of forming a dent, a dimple, or a through-hole in an unfired ceramic body.  
           [0003]    2. Discussion of Related Art  
           [0004]    It has been practiced to form a dent, a dimple, or a through-hole in an unfired ceramic body. For example, Japanese Patent Document No. 7-22734 discloses a method of forming a through-hole through the thickness of an unfired ceramic sheet, i.e., a green sheet that is to be used to produce an electric component such as a multiple-layer ceramic wiring board or a ceramic capacitor. At least one circuit pattern is formed on at least one of opposite surfaces of a green-sheet, and a plurality of green sheets are stacked on each other and then are fired to produce a multiple-layer ceramic wiring board. In this case, it is needed to electrically connect the respective circuit patterns of the green sheets to each other. To this end, an appropriate number of through-holes are formed in respective appropriate portions of each green sheet, through the thickness thereof, and are filled with an electrically conductive material to produce respective electrically conductive portions of the each green sheet through which the circuit patterns are electrically connected to each other.  
           [0005]    In the conventional method, the through-holes are formed by punching of a press machine, cutting of a drill machine, or holing of a laser device. However, the punching needs metallic dies, which leads to increasing the cost; and the sequential formation of through-holes by the drilling or the laser device needs much time. Thus, the conventional method need to be improved.  
         SUMMARY OF THE INVENTION  
         [0006]    It is therefore an object of the present invention to form, using inexpensive equipment and with high efficiency, a dent, a dimple, or a through-hole (hereinafter, referred to as the through-hole or the like) in an unfired ceramic body such as a green sheet. This object may be achieved according to any one of the following modes of the present invention in the form of an unfired-ceramic-body processing method, each of which is numbered like the appended claims and may depend from the other mode or modes, where appropriate, to indicate and clarify possible combinations of technical features. It is, however, to be understood that the present invention is not limited to the technical features or any combinations thereof that will be described below for illustrative purposes only. It is to be further understood that a plurality of elements or features included in any one of the following modes of the invention are not necessarily provided altogether, and that the invention may be embodied without some of the elements or features described with respect to the same mode.  
           [0007]    (1) A method of processing an unfired ceramic body, comprising the steps of covering, with a cover, a surface of the unfired ceramic body, such that a portion of the surface of the unfired ceramic body is exposed, and removing at least a portion of the unfired ceramic body that defines the exposed portion of the surface of the unfired ceramic body, and thereby forming at least a dent in an exposed portion of the unfired ceramic body.  
           [0008]    According to this mode, a portion of a surface of an unfired ceramic body is covered by a cover, and another portion of the surface is not covered by the cover. Thus, a dent, a dimple, or a through-hole can be formed by removing the exposed portion of the unfired ceramic body that is not covered by the cover. For example, in the case where the cover has a number of through-holes, a number of through-holes can be formed in the unfired ceramic body, and at least a portion of those through-holes can be simultaneously formed. Thus, the efficiency of formation of through-holes can be improved. In addition, since it is considerably easy to form a plurality of through-holes in the cover, as will be described later, the cost needed to carry out the present method can be reduced.  
           [0009]    (2) A method according to the mode (1), wherein the step of covering comprises producing the cover separately from the unfired ceramic body, and holding, with a holder, the cover such that the cover is kept in close contact with the surface of the unfired ceramic body.  
           [0010]    The cover may be a mask that is produced by forming one or more through-holes in a metallic plate, and the mask may be held by a holder such that the mask is kept in close contact with the surface of the unfired ceramic body. Thus, only a portion of the surface of the unfired ceramic body is covered by the mask.  
           [0011]    (3) A method according to the mode (1), wherein the step of covering comprises bonding the cover to the surface of the unfired ceramic body, and wherein the method further comprises the step of separating, after the step of removing, the cover from the surface of the unfired ceramic body.  
           [0012]    The cover may be a protective layer (e.g., a printed layer) that is formed of a material (e.g., an ink) having excellent mechanical or chemical properties, such as impact resistance, wearing resistance, or water resistance, such that the protective layer partly covers the surface of the unfired ceramic body. It is preferred that the protective layer be one that can be, after use, peeled off or dissolved, because it may be needed to form a circuit pattern directly on the surface of the unfired ceramic body. However, the circuit pattern may be formed on the protective layer. In the latter case, the protective-layer removing step can be omitted.  
           [0013]    (4) A method according to any of the modes (1) to (3), wherein the step of removing comprises causing an active medium to act on the exposed portion of the surface of the unfired ceramic body, and at least a portion of the cover that is adjacent to the exposed portion of the surface, and thereby physically removing at least the portion of the unfired ceramic body that defines the exposed portion of the surface.  
           [0014]    According to this mode, an active medium acts on the exposed portion of the surface of the unfired ceramic body, and at least a portion of the cover that is adjacent to the exposed portion of the surface. Thus, the portion of the unfired ceramic body that is covered by the cover is not removed because of protection of the cover, and only the exposed portion is removed to easily form a dent, a dimple, or a through-hole.  
           [0015]    (5) A method according to the mode (4), wherein the active medium comprises a solid.  
           [0016]    A solid active medium may be a shot or a brush. The shot may be mechanically given a kinetic energy by, e.g., a rotary blade, or may be blown with gas from a nozzle, so that the shot hits the cover and the unfired ceramic body. Thus, the shot removes the exposed portion of the unfired ceramic body, thereby forming a through-hole or the like. This process is called “shot blast”. The shot may be provided by any appropriate material. However, it is noted that the greater specific gravity the material has, the greater kinetic energy the shot can be given. If the shot is provided by a material having a small particle diameter, the through-hole or the like can be formed with highly accurate dimensions, but the efficiency of formation thereof is lowered. Thus, it is preferred to use such a shot that is provided by a material having the highest possible specific gravity, so as to improve the efficiency. If the shot is provided by the same sand as the sand as the material of the unfired ceramic body, such an advantage is obtained that a portion of the sand can be left, without any problems, on the unfired ceramic body. Shot blast in which sand is used is called “sand blast”. Shot blast is advantageous in that a plurality of through-holes or the like can be easily formed at once and that the cost needed to carry out it is low.  
           [0017]    (6) A method according to the mode (4) or (5), wherein the active medium comprises a liquid.  
           [0018]    A liquid active medium may be water or a solvent. Water or a solvent is used to remove the exposed portion of the unfired ceramic body. The liquid active medium may be solely applied to the object, or may be blown with gas to be applied to the object. In the latter case, the liquid active medium is used with the gas active medium. The above-described solid active medium may be used with the liquid active medium.  
           [0019]    (7) A method according to any of the modes (4) to (6), wherein the active medium comprises a gas.  
           [0020]    A gas active medium may be a compressed air. The gas active medium may be solely used such that the gas is blown at so high a speed that the gas can remove the exposed portion of the unfired ceramic body. However, for the purpose of improving the efficiency of working, it is preferred to use the gas active medium with the solid or liquid active medium.  
           [0021]    (8) A method according to any of the modes (1) to (7), wherein the unfired ceramic body comprises an unfired ceramic sheet, and wherein the step of removing comprises removing at least one portion of the unfired ceramic sheet that is not covered by the cover, and thereby forming at least one through-hole through a thickness of the unfired ceramic sheet.  
           [0022]    One or more through-holes formed in the unfired ceramic sheet may be one or ones that are used to produce one or more electrically conductive portions in the unfired ceramic sheet; positioning through-holes that are used when a plurality of unfired ceramic sheets are stacked on each other to produce a multiple-layer ceramic wiring board; or an array of through-holes that are used to produce, in the unfired ceramic sheet, a perforated portion that will be described according to the following mode (9). According to this mode, two or all of the through-holes corresponding to the electrically conductive portions, the positioning through-holes, or the array of through-holes corresponding to the perforated portion can be formed in a single step. In the last case, the efficiency of working can be improved.  
           [0023]    (9) A method according to the mode (8), wherein the step of removing comprises forming a plurality of through-holes along a single line in the unfired ceramic sheet, and thereby providing a perforated portion of the unfired ceramic sheet.  
           [0024]    Each of the through-holes may be any sort of hole, such as a circular hole, an elongate hole, or a rectangular hole.  
           [0025]    (10) A method according to the mode (9), further comprising the step of bonding a support sheet to an opposite surface of the unfired ceramic sheet that is opposite to the surface thereof covered by the cover.  
           [0026]    Since the unfired ceramic sheet is supported by the support sheet, it can be easily handled. The support sheet is separated from the unfired ceramic sheet, i.e., green sheet at an appropriate timing before the green sheet is fired. However, it is possible to form a through-hole or the like in a green sheet that is not supported by a support sheet. In the latter case, a green sheet may be conveyed, or subjected to a hole-forming step, on a green-sheet supporter, such as a conveyor belt.  
           [0027]    (11) A method according to the mode (9) or (10), wherein the step of covering comprises covering, with a first cover having a plurality of first through-holes formed along a single line, the surface of the unfired ceramic sheet, such that the first cover is kept in close contact with the unfired ceramic sheet, wherein the step of removing comprises forming, in the unfired ceramic sheet, an array of through-holes corresponding to the plurality of first through-holes of the first cover, wherein the step of covering further comprises covering, with a second cover having at least one second through-hole corresponding to at least one portion of the first cover that is located between at least one pair of adjacent first through-holes of the plurality of first through-holes, the unfired ceramic sheet having the array of through-holes, such that the second cover is kept in close contact with the unfired ceramic sheet, and wherein the step of removing further comprises removing at least one portion of the unfired ceramic sheet that is located between at least one pair of adjacent through-holes of the array of through-holes, and thereby connecting the array of through-holes with each other so as to form a slit.  
           [0028]    The unfired ceramic sheet may be cut into a plurality of divided sheets. In this case, since the unfired ceramic sheet has the slit, it can be easily separated into the divided sheets. Alternatively, when the slit is formed, the unfired ceramic sheet may be completely separated into the divided sheets. If a plurality of slits are formed in series, the unfired ceramic sheet can be easily separated into the divided sheets; and if a continuous single slit is formed, the unfired ceramic sheet is separated into the divided portions at the same time as the time of formation of the slit. If the unfired ceramic sheet is supported by a support sheet, described according to the following mode (12), the divided sheets are prevented from being apart from each other.  
           [0029]    (12) A method according to the mode (11), further comprising the step of bonding a support sheet to an opposite surface of the unfired ceramic sheet that is opposite to the surface thereof covered by the cover.  
           [0030]    (13) A method according to the mode (9), wherein the step of covering comprises covering, with a first cover having a plurality of first through-holes formed along a single line, the surface of the unfired ceramic sheet, such that the first cover is kept in close contact with the unfired ceramic sheet, wherein the step of removing comprises forming, in the unfired ceramic sheet, an array of through-holes corresponding to the plurality of first through-holes of the first cover, wherein the step of covering further comprises covering, with a second cover having at least one second through-hole corresponding to at least one portion of the first cover that is located between at least one pair of adjacent first through-holes of the plurality of first through-holes, the unfired ceramic sheet having the array of through-holes, such that the second cover is kept in close contact with the unfired ceramic sheet, and wherein the step of removing further comprises forming at least one through-hole in at least one portion of the unfired ceramic sheet that is located between at least one pair of adjacent through-holes of the array of through-holes.  
           [0031]    The less the portion of the unfired ceramic sheet that is located between the pair of adjacent through-holes of the array of through-holes is, the easier the separation of the unfired ceramic sheet into divided sheets is. However, in the case where a single cover is used to form that portion that is very small, the strength or durability of the single cover must lower. According to this mode, however, since the first and second covers are employed, the strength of those covers need not lower, and the separation of the unfired ceramic sheet into the divided sheets can be easily carried out.  
           [0032]    (14) A method according to the mode (9) or (10), wherein, further comprising the step of bonding a support sheet to an opposite surface of the unfired ceramic sheet that is opposite to the surface thereof covered by the cover.  
           [0033]    (15) A method according to any of the modes (8) to (14), further comprising the step of forming, in the unfired ceramic sheet, at least one electrically conductive portion by filling the at least one through-hole of the unfired ceramic sheet with at least one electrically conductive body, and forming an electrically conductive layer on at least one of the opposite surfaces of the unfired ceramic sheet.  
           [0034]    (16) A method according to the mode (15), wherein the step of forming the at least one electrically conductive layer comprises forming, on the at least one of the opposite surfaces of the unfired ceramic sheet, at least one circuit pattern which is electrically connected to the at least one electrically conductive portion of the unfired ceramic sheet.  
           [0035]    If a plurality of unfired ceramic sheets each of which has a circuit pattern formed thereon are stacked on each other and are fired, a multiple-layer ceramic wiring board is obtained. If a plurality of unfired ceramic sheets each of which has, in place of a circuit pattern, an electrically conductive layer covering a substantially entire surface thereof are stacked on each other and are fired, a ceramic capacitor is obtained. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0036]    The above and other objects, features, advantages and technical and industrial significance of the present invention will be better understood by reading the following detailed description of preferred embodiments of the invention, when considered in connection with the accompanying drawings, in which:  
         [0037]    [0037]FIG. 1 is an illustrative view for explaining a production line for carrying out the step of producing a green sheet, as part of a multiple-layer ceramic wiring board producing method to which the present invention is applied;  
         [0038]    [0038]FIG. 2 is an illustrative view for explaining another production line for carrying out the step of processing the green sheet into a multiple-layer ceramic wiring board, as part of the multiple-layer ceramic wiring board producing method;  
         [0039]    [0039]FIG. 3 is a partly cross-sectional, illustrative view for explaining the step of forming holes in the green sheet, as part of the multiple-layer ceramic wiring board producing method;  
         [0040]    [0040]FIG. 4 is a plan view for explaining through-holes formed in the hole-forming step;  
         [0041]    [0041]FIG. 5 is a plan view for explaining different through-holes formed in the hole-forming step;  
         [0042]    [0042]FIG. 6 is a partly cross-sectional, illustrative view for explaining a different hole-forming step as part of another multiple-layer ceramic wiring board producing method as a second embodiment of the present invention;  
         [0043]    [0043]FIG. 7 is a plan view of one layer of a multiple-layer ceramic board that is produced in the first embodiment shown in FIGS.  1  to  5  or the second embodiment shown in FIG. 6; and  
         [0044]    [0044]FIG. 8 is a partly cross-sectional, illustrative view for explaining a different hole-forming step as part of yet another multiple-layer ceramic wiring board producing method as a third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0045]    Hereinafter, there will be described an embodiment of the present invention that is applied to production of a multiple-layer ceramic wiring board. The multiple-layer ceramic wiring board is produced in steps shown in FIGS. 1 and 2. FIG. 1 shows a line for producing a green sheet  10  as an example of an unfired or unburned ceramic sheet. More specifically described, a support sheet  12  formed of a synthetic resin such as polyethylene terephthalate (PET) is drawn, in the form of a web, from a supply roll  14 , and a ceramic slurry  18  is applied by a doctor-blade device  16  to an upper surface of the support sheet  12 . The ceramic slurry  18  applied to the support sheet  12  is dried by a drying device  20 , so that the green sheet  10  having a prescribed uniform thickness is formed on the support sheet  12 . The green sheet  10  and the support sheet  12  are taken up by a take-up roll  22 . Before the green sheet  10  is taken up by the take-up roll  22 , an appropriate number of slits are preferably formed in the green sheet  10  such that the slits extend in a lengthwise direction of the sheet  10 , so that the sheet  10  are divided into a plurality of webs. The slurry  18  is, e.g., a mixture of a ceramic powder such as alumina, a binder such as polyvinyl butyral, a dispersant such as ester of phthalic acid, glycol, or ketone or its derivatives, and a solvent.  
         [0046]    The green sheet  10  supported by the support sheet  12 , produced in the above-described manner, is drawn from a supply roller  30 , as illustrated in FIG. 2, and a number of through-holes are formed in the green sheet  10  by a hole-forming device  32 , described later. After the hole-forming step, the green sheet  10  is sent to a printing device  34 , which fills the through-holes of the sheet  10  with electrically conductive paste, thereby forming electrically conductive portions of the sheet  10 , and simultaneously prints an electrically conductive pattern on an upper surface of the sheet  10 . Finally, the green sheet  10  is processed into a ceramic wiring board  36 , shown in FIG. 7. In FIG. 7, the above-described electrically conductive portions are indicated by black circles  38 ; resistance portion formed by printing of resistance paste are indicated by black rectangles  40 ; and the electrically conductive pattern that electrically connects the conductive portions  38  and the resistance portions  40  is indicated by  42 . Hereinafter, the conductive portions  38 , the resistance portions  40 , and the conductive pattern  42  will be referred to as a circuit pattern.  
         [0047]    The printing device  34  includes a support table  50  formed of a porous material; a screen  52  having through-holes corresponding to the conductive portions  38  and the conductive pattern  42 ; a squeegee device  56  including a squeegee  54  movable along the screen  52 ; a positioning device  58 ; and a suction device  60 . The positioning device  58  includes an elevating and lowering device, not shown, and a plurality of positioning pins  62  that are elevated by the elevating and lowering device to project from an upper surface of the support table  50  and fit in respective positioning pins, not shown, of the green sheet  10 , so as to position the sheet  10 . The suction device  60  sucks air through the porous body of the support table  50 , and applies suction to the support sheet  12  supporting the green sheet  10 , thereby fixing the support sheet  12  to the support table  50 . FIG. 2 shows the single printing device  34 . However, in fact, a plurality of printing devices  34  are employed to print different inks or pastes than the electrically conductive paste; such as the above-described resistance paste.  
         [0048]    After the printing of the printing device  34 , the green sheet  10  is dried by a drying device  64 , and then a separating device  66  separates, from the support sheet  12 , individual sheets each corresponding to a ceramic board, and a take-up roll  68  takes up the support sheet  12  left. A plurality of individual separate sheets, each corresponding to a ceramic board, are stacked on each other. For example, several sheets to several tens of sheets are stacked on one another. In the case of a ceramic capacitor, more than several hundreds of sheets are stacked on one another. The thus stacked sheets are cut as needed, and are fired in a continuous pressure kiln to produce a multiple-layer ceramic wiring board or a ceramic capacitor.  
         [0049]    Next, the above-mentioned hole-forming step will be described in detail. In the present embodiment, the hole-forming device  32  includes a sand-blasting device  70  shown in FIG. 3. Since the sand-blasting device  70  is known in the art, it is not described here. However, the sand-blasting device  70  uses, as sand  72 , the same material as that of the green sheet  10 . the sand-blasting device  70  blows, through a nozzle  74 , the sand  72  with compressed air, toward the green sheet  10 . Alternatively, it is possible to employ a rotary blade or the like that splashes the sand  72  toward the green sheet  10 . In addition, it is possible to employ, as shot, metallic powder or the like. In the present embodiment, the step in which the sand  72  is used to remove a portion of the green sheet  10  is a removing step.  
         [0050]    The green sheet  10  is supported by the support sheet  12 , which in turn is supported by a support table  80 . A mask  82  is placed on an upper surface of the green sheet  10  that is opposite to a lower surface thereof supported by the support table  80 . The mask  82  has through-holes  84  for forming, in the green sheet  10 , through-holes  83  corresponding to the electrically conductive portions  38 , and additionally has through-holes  90  for forming, in the green sheet  10 , a perforation where a portion corresponding to a ceramic board is to be separated from a remaining portion of the green sheet  10 . In the present embodiment, a plurality of shot-blasting devices (e.g., a plurality of sand-blasting devices)  70  are employed and, for example, an upstream-side shot-blasting device  70  is used with the mask  82  having the through-holes  90 , and a downstream-side shot-blasting device  70  is used with another mask  82  having through-holes  92  shown in FIG. 4. The through-holes  92  of the mask  82  are used to form, in the green sheet  10 , through-holes  100  which overlap the through-holes  98  to form a separation groove or slit  88 . That is, the through-holes  92  cooperate with the through-holes  90  to form the separation slit  88  in the green sheet  10 . It is possible to employ two separate masks one of which has the through-holes  84  for forming the through-holes  83  corresponding to the conductive portions  38 , and the other of which has the through-holes  90  for forming the through-holes  98  as part of the separation slit  100 . Each mask  82  is held by a mask holder, not shown, such that the mask  82  is movable to an operative position where the mask  82  is kept in close contact with the green sheet  10  and to a retracted position where the mask  82  is kept away from the sheet  10 . In the present embodiment, the step in which each mask  82  is used to cover the greens sheet  10  is a covering step.  
         [0051]    The masks  82  are formed of metal and accordingly the through-holes  84 ,  90 ,  92  can be easily formed by, e.g., etching. That is, a metallic plate is masked with a chemically stable material except for respective portions corresponding to the through-holes  84 ,  90 ,  92 , and only those portions corresponding to the through-holes  84 ,  90 ,  92  are removed. However, the masks  82  may be formed of any of other known materials, or may be produced in any of other known methods. For example, masks may be mechanically formed of a material that is easily mechanically workable.  
         [0052]    The hole-forming device  32  includes, in addition to the sand-blasting devices  70 , a positioning-hole forming device which forms, using, e.g., a punch or a drill, through-holes in both the green sheet  10  and the support sheet  12 . More specifically described, the positioning-hole forming device forms positioning holes in which the positioning pins  62  of the printing device  34  are to fit to position the green sheet  10 ; and positioning holes  104  shown in FIG. 7.  
         [0053]    In the present embodiment, each separation slit  88  is sequentially formed in the web of green sheet  10 , to separate each individual sheet corresponding to a ceramic board. However, as shown in FIG. 5, it is possible to form, in the green sheet  10 , a perforated portion  108  having a first array of through-holes  105  and a second array of through-holes  106  that are not connected to one another to form an elongate slit like the separation slit  88 . To this end, a first mask  110  having through-holes  112 , and then a second mask  110  having through-holes  114  are used, each with sand, to form the through-holes  105  and then the through-holes  106 , respectively. The shape and/or size of the through-holes  112  may be identical with, or different from, those of the through-holes  114 . Likewise, the shape and/or size of the through-holes  90  may be identical with, or different from, those of the through-holes  92 .  
         [0054]    For the purpose of forming the through-holes  83  corresponding to the conductive portions  38 , the through-holes  98 ,  100  corresponding to the separation slit  88 , or the through-holes  105 ,  106  corresponding to the perforated portion  108 , the hole-forming device  32  may employ a brush  120  shown in FIG. 6. The brush  120  includes a rotary shaft  122  and metallic or synthetic-resin fibers  124  extending radially outwardly from an outer circumferential surface of the rotary shaft  122 . When the brush  120  is rotated by a drive device, not shown, tip portions of the fibers  124  act on the green sheet  10  covered with the mask  82 , and a portion of the green sheet  10  that corresponds to the through-hole  84  of the mask  82  is removed to form the through-hole  83 . Likewise, the through-holes  98 ,  100  corresponding to the separation slit  88  and the through-holes  105 ,  106  corresponding to the perforated portion  108  are formed.  
         [0055]    The through-holes  83 ,  98 ,  100 ,  105 ,  106  may be formed in a different method. FIG. 8 shows an example in which a green sheet  130  is supported by a support sheet  132  and is covered by a protection layer  134  as a sort of cover. A hole-forming device  136  includes a nozzle  138  which spouts water  139  as a sort of a liquid medium, so that the water  139  removes portions of the green sheet  130  that correspond to through-holes  140 ,  142  of the protective layer  134 , and thereby forms through-holes  146 ,  148  in the sheet  130 . The protective layer  134  is formed of a material that is resistant to water and is soluble in a solvent and, after the hole-forming step, the protective layer  134  is removed by the solvent. Alternatively, the protective layer  134  may be peeled off the green sheet  130 .  
         [0056]    The perforated portion  108  is defined by the through-holes  105  and the through-holes  106  both of which are formed in a portion of the single green sheet  10  that corresponds a ceramic board. However, it is possible to form the through-holes  105  and the through-holes  106  in respective different portions of the green sheet  10  that correspond to two ceramic boards to be stacked on each other. In this case, it can be said that the thickness of the respective perforated portions  108  of the two ceramic boards stacked on each other is substantially half that of the remaining portions of the same. Therefore, the perforated portions  108  of the two ceramic boards stacked can be easily separated in a subsequent, separating step. The separating step may be carried out after a plurality of ceramic boards stacked on each other are fired into a multiple-layer ceramic wiring board. This method may apply to the separation slit  88  that is defined by the through-holes  98  and the through-holes  100 .  
         [0057]    The foregoing description relates to the embodiment in which the principle of the present invention is applied to the production of electric components such as multiple-layer ceramic wiring boards or ceramic capacitors, particularly, to the formation of through-holes in green sheets in the production of electric components. However, the present invention is applicable to other fields, e.g., to the formation of through-holes in mechanical ceramic components, or the formation of dents or dimples in various things such as electric or mechanical components.  
         [0058]    It is to be understood that the present invention may be embodied with various changes, modifications and improvements, such as those described in SUMMARY OF THE INVENTION, which may occur to a person skilled in the art, without departing from the spirit and scope of the invention defined in the appended claims.