Abstract:
The disclosed structure ( 10 ) is provided with: at least three conductors ( 111, 131, 151 ) which face one-another; a through-via ( 101 ) which passes through each of the conductors ( 111, 131, 151 ); openings ( 112, 152 ) which are provided so as to surround the circumference of the through-via ( 101 ); and conductor elements ( 121, 141 ) which are located in different layers to those in which the conductors ( 111, 131, 151 ) are located, and which are connected to the through-via ( 101 ). Facing opening  112  is conductor element  121 , which is larger than said opening ( 112 ), and facing opening  152  is conductor element  141 , which is larger than said opening ( 152 ).

Description:
TECHNICAL FIELD 
     The present invention relates to a structure, a circuit board, and a circuit board manufacturing method. 
     BACKGROUND ART 
     In recent years, it has been known that the propagation characteristics of electromagnetic waves can be controlled by periodically arranging a conductor pattern having a specific structure (hereinafter, referred to as a metamaterial). In particular, a metamaterial constructed to suppress propagation of electromagnetic waves in a specific frequency band is referred to as an electromagnetic bandgap structure (hereinafter, referred to as an EBG structure). The EBG structure is used as a countermeasure against noise propagating in a circuit board or the like. 
     An example of such a technique is described in Patent Document 1 (U.S. Pat. No. 6,262,495). FIG. 2 of Patent Document 1 shows a structure, that is, a mushroom-like EBG structure, in which plural island-like conductor elements are arranged over a sheet-like conductive plane and the respective island-like conductor elements are connected to the conductive plane through vias. 
     Another example of such a technique is described in Patent Document 2 (JP-A-2009-21594). The technique described in Patent Document 2 is a modified example of the mushroom-like EBG structure described in Patent Document 1 and is characterized in that a via corresponding to the stem of a mushroom is formed as a penetration via. Accordingly, it is possible to reduce the number of processes of manufacturing a circuit board (printed circuit board) having the mushroom-like EBG structure. 
     RELATED DOCUMENT 
     Patent Document 
     
         
         [Patent Document 1] U.S. Pat. No. 6,262,495 
         [Patent Document 2] JP-A-2009-21594 
       
    
     DISCLOSURE OF THE INVENTION 
     In general, a circuit board is formed of multiple layers and includes plural penetration vias. For this reason, plural clearance holes through which the penetration vias pass are formed in conductive layers of the circuit board. In the structures disclosed in Patent Documents 1 and 2, an EBG structure is constituted in layers interposed between conductive layers (metal layers) opposed with a conductor element (metal plate) interposed therebetween, but the EBG structure is not constructed in the other layers. Accordingly, it is possible to suppress noise between the conductive layers having the EBG structure formed therein, but electromagnetic waves leak to the other layers not having an EBG structure formed therein through the clearance holes, which causes a problem as a noise countermeasure. 
     The invention is made in consideration of the above-mentioned circumstances and an object thereof is to provide a structure, a circuit board, or a circuit board manufacturing method, in which an EBG structure is constructed between conductive layers using a penetration via in a multi-layered circuit board including at least three conductive layers. 
     According to an aspect of the invention, there is provided a structure including: at least three first conductors that are opposed to each other; a penetration via that penetrates the first conductors; an opening that is formed in at least one of the first conductors so as to surround the penetration via passing through the first conductors and that insulates the penetration via from the at least one first conductor; and a plurality of second conductors that are located in a plurality of layers other than layers in which the first conductors are located and that are connected to the penetration via, wherein the area of the opening is smaller than the area of any of the second conductors. 
     According to another aspect of the invention, there is provided a circuit board having a structure, the structure including: at least three first conductors that are opposed to each other; a penetration via that penetrates the first conductors; an opening that is formed in at least one of the first conductors so as to surround the penetration via passing through the first conductors and that insulates the penetration via from the at least one first conductor; and a plurality of second conductors that are located in a plurality of layers other than layers in which the first conductors are located and that are connected to the penetration via, wherein the area of the opening is smaller than the area of any of the second conductors. 
     According to still another aspect of the invention, there is provided a circuit board manufacturing method including the steps of: (a) arranging at least three first conductors to be opposed to each other, arranging a plurality of second conductors in a plurality of layers other than layers in which the first conductors are located, and stacking the first conductors and the second conductors to be opposed to each other; and (b) forming through-holes that penetrates the first conductors and the second conductors and forming a penetration via that is insulated from at least one of the first conductors and that is connected to the second conductors in the through holes, wherein the area of an opening that is formed in the at least one first conductor insulated from the penetration via in the step of (b) and through which the penetration via passes is smaller than the area of any of the second conductors. 
     According to the aspects of the invention, it is possible to provide a structure, a circuit board, or a circuit board manufacturing method, in which an EBG structure is constructed between conductive layers using a penetration via in a multi-layered circuit board including at least three conductive layers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating an example of a structure according to an embodiment of the invention. 
         FIG. 2  is a diagram illustrating modified examples of a conductor element. 
         FIG. 3  is a perspective view illustrating an example of a structure according to the embodiment of the invention. 
         FIG. 4  is a perspective view illustrating an example of a structure according to the embodiment of the invention. 
         FIG. 5  is a diagram illustrating modified examples of a conductor. 
         FIG. 6  is a perspective view illustrating an example of a structure according to the embodiment of the invention. 
         FIG. 7  is a perspective view illustrating an example of a structure according to the embodiment of the invention. 
         FIG. 8  is a perspective view illustrating an example of a structure constructed by combining the structures according to the embodiment of the invention. 
         FIG. 9  shows a top view and a cross-sectional view of a circuit board according to an embodiment of the invention. 
         FIG. 10  is a diagram illustrating an arrangement pattern of a structure which can be employed by the circuit board. 
         FIG. 11  is a diagram illustrating an arrangement pattern of a structure which can be employed by the circuit board. 
         FIG. 12  is a diagram illustrating an arrangement pattern of a structure which can be employed by the circuit board. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the invention will be described with reference to the accompanying drawings. In all the drawings, like elements are referenced by like reference numerals and will not be repeatedly described. 
       FIG. 1  is a perspective view illustrating an example of a structure  10  according to an embodiment of the invention. The structure  10  is constructed by various conductive elements formed in a circuit board  100  having at least an A layer  11 , a B layer  12 , a C layer  13 , a D layer  14 , and an E layer  15  (see  FIG. 9 ). 
     The structure  10  includes at least three conductors  111 ,  131 , and  151  (the first conductors) opposed to each other. The structure  10  includes a penetration via  101  that penetrates the conductors  111 ,  131 , and  151  and that is insulated from at least one of the penetrated conductors  111 ,  131 , and  151 . The structure  10  includes an opening  112  formed in the conductor  111  insulated from the penetration via  101  and an opening  152  formed in the conductor  151  insulated from the penetration via  101 . The structure  10  includes conductor elements  121  and  141  (the second conductors) that are located in plural layers other than the layers in which the conductors  111 ,  131 , and  151  are located and that are connected to the penetration via  101 . As shown in the drawing, the penetration via  101  passes through the opening  112  and the opening  152 . The area of the opening  112  is smaller than the area of the conductor element  121  or the conductor element  141 , and the area of the opening  152  is smaller than the area of the conductor element  121  or the conductor element  141 . The opening  112  and the conductor element  121  are opposed to each other without any other conductor interposed therebetween, and the opening  152  and the conductor element  141  are opposed to each other without any other conductor interposed therebetween. A part of the conductor element  121  is opposed to the conductor (a part of the conductor  111 ) around the opening  112 , and a part of the conductor element  141  is opposed to the conductor (a part of the conductor  151 ) around the opening  152 . 
     The structure  10  may include layers other than the A layer  11 , the B layer  12 , the C layer  13 , the D layer  14 , and the E layer  15 . For example, a dielectric layer may be located between the respective layers. The structure  10  may further include holes, vias, signal lines, and the like not shown without conflicting the configuration of the invention. 
     The opening  112  or the opening  152  may not necessarily be hollow, but may be filled with a dielectric. That is, the penetration via  101  may be formed to penetrate the dielectric filled in the opening  112  or the opening  152  and not to come in contact with the conductor  111  or the conductor  151 . 
     In  FIG. 1 , the conductors  111 ,  131 , and  151  and the conductor elements  121  and  141  are all shown as conductive flat plates. In  FIG. 1 , the conductors  111 ,  131 , and  151  are shown as flat plates larger than the conductor elements  121  and  141 . 
     When the structure  10  is repeatedly arranged in the circuit board  100 , the neighboring conductors  111  are connected. The same is true of the conductors  131  and the conductors  151 . The neighboring conductor elements  121  have a gap therebetween and are arranged in an island shape. The same is true of the conductor elements  141 . The sizes of the conductors  111 ,  131 , and  151  and the sizes of the conductor elements  121  and  141  have only to be determined without departing from the above-mentioned principle. Accordingly, in the invention, the conductors  111 ,  131 , and  151  may be smaller than the conductor elements  121  and  141 . 
     In the structure  10 , it is preferable that the conductor connected to the penetration via  101  among the conductors  111 ,  131 , and  151  function as a ground with a reference potential applied thereto. The conductors should be insulated from the penetration via  101  are provided with an opening through which the penetration via  101  passes. 
     Here, the penetration via  101  may not penetrate the conductors located at both ends of the conductors  111 ,  131 , and  151 . That is, at least a part of the penetration via  101  has only to be formed in the conductor  111  or the conductor  151  located at both ends. 
     The penetration via  101 , the conductor  111 , the conductor element  121 , the conductor  131 , the conductor element  141 , and the conductor  151  may be formed of the same material or different materials, as long as they are formed of a conductive material. 
     It is assumed that the conductor  111  is located in the A layer  11 , the conductor element  121  is located in the B layer  12 , the conductor  131  is located in the C layer  13 , the conductor element  141  is located in the D layer  14 , and the conductor  151  is located in the E layer  15 . The relative positional relationship of the A layer  11 , the B layer  12 , the C layer  13 , the D layer  14 , and the E layer  15  can be changed and thus the relative positional relationship of the conductor  111 , the conductor element  121 , the conductor  131 , the conductor element  141 , and the conductor  151  can be changed. 
     By employing the above-mentioned configuration, a parallel plate including the conductor  111  and the conductor  131  can constitute at least a part of an electromagnetic bandgap structure along with the conductor element  121  and the penetration via  101 . A parallel plate including the conductor  131  and the conductor  151  can constitute at least a part of an electromagnetic bandgap structure along with the conductor element  141  and the penetration via  101 . By adjusting the gap between the conductor  111  and the conductor element  121 , the gap between the conductor element  121  and the conductor  131 , the gap between the conductor  131  and the conductor element  141 , the gap between the conductor element  141  and the conductor  151 , the thickness of the penetration via  101 , the mutual gap of the conductor element  121  or the conductor element  141 , and the like, it is possible to set the frequency band (bandgap range), in which the propagation of electromagnetic waves should be suppressed, to a desired value. This will be described in more detail later. 
     In the structure  10  shown in  FIG. 1 , the conductor  111 , the conductor element  121 , the conductor  131 , the conductor element  141 , and the conductor  151  are sequentially arranged in this order from the upper side of the drawing. The conductor  131  is connected to the penetration via  101 . The conductor  111  and the conductor  151  are opposed to each other with the conductor  131  interposed therebetween. The conductor  111  has the opening  112  through which the penetration via  101  passes and is insulated from the penetration via  101 . The conductor  151  has the opening  152  through which the penetration via  101  passes and is insulated from the penetration via  101 . 
     The conductors  111 ,  131 , and  151  and the conductor elements  121  and  141  are shown in a rectangular shape, but is not limited to this shape and may have various modified examples. 
       FIG. 2  is a diagram illustrating modified examples of the conductor element  121  or the conductor element  141  of the structure  10  shown in  FIG. 1 .  FIG. 2(A)  is a top view of the conductor element  121  or the conductor element  141  used in the structure  10  shown in  FIG. 1 . The conductor element  121  or  141  has a rectangular shape and can constitute a so-called mushroom-like structure  10 . Specifically, the penetration via  101  corresponds to the stem part of a mushroom and forms inductance. On the other hand, the conductor element  121  corresponds to the head part of the mushroom and forms capacitance along with the conductor  111  opposed thereto. The conductor element  141  corresponds to the head part of a mushroom and forms capacitance along with the conductor  151  opposed thereto. 
     The conductor element  121  or the conductor element  141  constituting the mushroom-like structure  10  is not limited to the rectangular shape, but may have a polygonal shape such as a triangular shape or a hexagonal shape or a circular shape. 
     The mushroom-like EBG structure can be expressed by an equivalent circuit in which a parallel plate is shunted with a serial resonance circuit including the capacitance and the inductance and the resonance frequency of the serial resonance circuit gives the central frequency of a bandgap. Accordingly, it is possible to achieve the fall in the frequency of the bandgap range by causing the conductor element  121  to approach the opposed conductor  111  forming the capacitance to increase the capacitance. However, even when the conductor element  121  is not made to approach the opposed conductor  111 , the substantial effect of the invention is not affected at all. It is possible to achieve the fall in the frequency of the bandgap range by causing the conductor element  141  to approach the conductor  151  forming the capacitance to increase the capacitance. Even when the conductor element  141  is not made to approach the opposed conductor  151 , the substantial effect of the invention is not affected at all. 
       FIG. 2(B)  is a top view illustrating an example of the conductor element  121  or the conductor element  141  in the structure  10  shown in  FIG. 1 . The conductor element  121  or the conductor element  141  shown in the drawing is a spiral transmission line formed in a planar direction, where one end thereof is connected to the penetration via  101  and the other end thereof is an open end. By employing the conductor element  121  or the conductor element  141  shown in the drawing, the structure  10  can constitute an open stub type EBG structure in which a microstrip line including the conductor element  121  or the conductor element  141  serves as an open stub. The penetration via  101  forms inductance. On the other hand, the conductor element  121  is electrically coupled to the conductor  111  to forma microstrip line having the conductor  111  as a return path. The conductor element  141  is electrically coupled to the conductor  151  to form a microstrip line having the conductor  151  as a return path. 
     The open stub type EBG structure can be expressed by an equivalent circuit in which a parallel plate is shunted with a serial resonance circuit including the open stub and the inductance and the resonance frequency of the serial resonance circuit gives the central frequency of a bandgap. Accordingly, by increasing the stub length of the open stub including the conductor element  121  or the conductor element  141 , it is possible to achieve a fall in the frequency of the bandgap range. 
     It is preferable that the conductor element  121  constituting the microstrip line and the opposed conductor  111  be located close to each other. It is preferable that the conductor element  141  constituting the microstrip line and the opposed conductor  151  be located close to each other. This is because as the distance between the conductor element and the opposed plane becomes smaller, the characteristic impedance of the microstrip line becomes lower, thereby widening the bandgap range. However, even when the conductor element  121  is not made to approach the opposed conductor  111 , the substantial effect of the invention is not affected at all. Even when the conductor element  141  is not made to approach the opposed conductor  151 , the substantial effect of the invention is not affected at all. 
       FIG. 2(C)  is a top view illustrating an example of the conductor element  121  or the conductor element  141  in the structure  10  shown in  FIG. 1 . The conductor element  121  or the conductor element  141  is a rectangular conductor and has an opening. In the opening, a spiral inductor of which an end is connected to the edge of the opening and the other end is connected to the penetration via  101  is formed. By employing the conductor element  121  or the conductor element  141  shown in the drawing, the structure  10  can constitute an inductance-increased EBG structure in which inductance is increased by forming an inductor in the head part of a mushroom in a mushroom-like EBG structure as a basic structure. More specifically, the conductor element  121  corresponds to the head part of a mushroom and forms capacitance along with the opposed conductor  111 . The conductor element  141  corresponds to the head part of the mushroom and forms capacitance along with the opposed conductor  151 . 
     The inductance-increased EBG structure can be expressed by an equivalent circuit in which a parallel plate is shunted with a serial resonance circuit including the capacitance and the inductance and the resonance frequency of the serial resonance circuit gives the central frequency of a bandgap. Accordingly, by causing the conductor element  121  to approach the conductor  111  forming the capacitance to increase the capacitance or extending the length of the inductor to increase the inductance, it is possible to achieve a fall in the frequency of the bandgap range. However, even when the conductor element  121  is not made to approach the opposed conductor  111 , the substantial effect of the invention is not affected at all. By causing the conductor element  141  to approach the conductor  151  forming the capacitance to increase the capacitance or extending the length of the inductor to increase the inductance, it is possible to achieve a fall in the frequency of the bandgap range. However, even when the conductor element  141  is not made to approach the opposed conductor  151 , the substantial effect of the invention is not affected at all. 
       FIG. 3  is a perspective view illustrating an example of the structure  10  according to this embodiment. In the structure  10  shown in  FIG. 3 , the conductor  111  or the conductor  151  located at both ends of the conductors  111 ,  131 , and  151  has the opening  112  or the opening  152  through which the penetration via  101  passes and is insulated from the penetration via  101 . The conductor  131  located therebetween is connected to the penetration via  101 . The conductor element  121  is located above the conductor  111  and the conductor element  141  is located below the conductor  151 . 
     The structure shown in  FIG. 3  is a modified example of a mushroom-like EBG structure. Specifically, the penetration via  101  corresponds to the stem part of a mushroom and forms inductance. On the other hand, the conductor element  121  or the conductor element  141  corresponds to the head part of the mushroom and forms capacitance along with the opposed conductor  111  or the opposed conductor  151 . 
     Similarly to the mushroom-like EBG structure, the structure shown in  FIG. 3  can be expressed by an equivalent circuit in which a parallel plate is shunted with a serial resonance circuit including the capacitance and the inductance and the resonance frequency of the serial resonance circuit gives the central frequency of a bandgap. Accordingly, it is possible to achieve the fall in the frequency of the bandgap range by causing the conductor element  121  or the conductor element  141  to approach the conductor  111  or the conductor  151  forming the capacitance to increase the capacitance. However, even when the conductor element  121  or the conductor element  141  is not made to approach the opposed conductor  111  or the opposed conductor  151 , the substantial effect of the invention is not affected at all. 
     The conductor element  121  or the conductor element  141  in the structure  10  shown in  FIG. 3  may have the shape shown in  FIG. 2(B) . Here, the structure  10  similarly has the characteristics of the above-mentioned open stub type EBG structure. The conductor element  121  or the conductor element  141  in the structure  10  shown in  FIG. 3  may have the shape shown in  FIG. 2(C) . Here, the structure  10  similarly has the above-mentioned characteristics of the inductance-increased EBG structure. 
       FIG. 4  is a perspective view illustrating the structure  10  according to this embodiment. In the structure  10  shown in  FIG. 4 , the conductor  111 , the conductor element  121 , the conductor  131 , the conductor element  141 , and the conductor  151  are sequentially arranged in this order from the upper side of the drawing. The conductors  111  and  151  located at both ends of the conductors  111 ,  131 , and  151  are connected to the penetration via  101 . The conductor  131  located therebetween has the opening  132  through which the penetration via  101  passes and is insulated from the penetration via  101 . The conductor element  121  is located between the conductor  111  and the conductor  131  and the conductor element  141  is located between the conductor  131  and the conductor  151 . 
     The structure shown in  FIG. 4  is a modified example of a mushroom-like EBG structure. Specifically, the penetration via  101  corresponds to the stem part of a mushroom and forms inductance. On the other hand, the conductor element  121  or the conductor element  141  corresponds to the head part of the mushroom and forms capacitance along with the opposed conductor  131 . 
     Similarly to the mushroom-like EBG structure, the structure shown in  FIG. 4  can be expressed by an equivalent circuit in which a parallel plate is shunted with a serial resonance circuit including the capacitance and the inductance and the resonance frequency of the serial resonance circuit gives the central frequency of a bandgap. Accordingly, it is possible to achieve the fall in the frequency of the bandgap range by causing the conductor element  121  or the conductor element  141  to approach the conductor  131  forming the capacitance to increase the capacitance. However, even when the conductor element  121  or the conductor element  141  is not made to approach the opposed conductor  131 , the substantial effect of the invention is not affected at all. 
     The conductor element  121  or the conductor element  141  in the structure  10  shown in  FIG. 4  may have the shape shown in  FIG. 2(B) . Here, the structure  10  similarly has the characteristics of the open stub type EBG structure described with reference to  FIG. 2(B) . 
     The conductor element  121  or the conductor element  141  in the structure  10  shown in  FIG. 4  may have the shape shown in  FIG. 2(C) . Here, the structure  10  similarly has the characteristics of the inductance-increased EBG structure described with reference to  FIG. 2(C) . 
       FIG. 5  is a top view illustrating an example of the conductor  111  or the conductor  151  in the structure  10  shown in  FIG. 4 . The conductor  111  or the conductor  151  shown in the drawing has an opening. In the opening, a spiral inductor of which an end is connected to the edge of the opening and the other end is connected to the penetration via  101  is formed. The conductor  111  or the conductor  151  shown in  FIG. 5  is used along with the conductor element  121  or the conductor element  141  shown in  FIG. 2(A) . By employing the conductor element  121  or the conductor element  141  shown in  FIG. 2(A)  along with the conductor  111  or the conductor  151  shown in  FIG. 5 , the structure  10  can constitute an inductance-increased EBG structure in which inductance is increased by forming an inductor in the conductor  111  or the conductor  151  in a mushroom-like EBG structure as a basic structure. More specifically, the conductor element  121  corresponds to the head part of a mushroom and forms capacitance along with the opposed conductor  131 . The conductor element  141  corresponds to the head part of the mushroom and forms capacitance along with the opposed conductor  131 . On the other hand, the penetration via  101  corresponds to the stem part of the mushroom and forms inductance along with the inductor formed in the conductor  111  or the conductor  151 . 
     The inductance-increased EBG structure can be expressed by an equivalent circuit in which a parallel plate is shunted with a serial resonance circuit including the capacitance and the inductance and the resonance frequency of the serial resonance circuit gives the central frequency of a bandgap. Accordingly, by causing the conductor element  121  or the conductor element  141  to approach the conductor  131  forming the capacitance to increase the capacitance or extending the length of the inductor to increase the inductance, it is possible to achieve a fall in the frequency of the bandgap range. However, even when the conductor element  121  or the conductor element  141  is not made to approach the opposed conductor  131 , the substantial effect of the invention is not affected at all. 
       FIG. 6  is a perspective view illustrating an example of the structure  10  according to this embodiment. In the structure  10  shown in  FIG. 6 , the conductor  151  is connected to the penetration via  101 . The conductor  111  and the conductor  131  are located on the same side with respect to the conductor  151 . The conductor  111  has the opening  112  through which the penetration via  101  passes and is insulated from the penetration via  101 . The conductor  131  has the opening  132  through which the penetration via  101  passes and is insulated from the penetration via  101 . The conductor element  121  is located between the conductor  111  and the conductor  131 , and the conductor element  141  is located between the conductor  131  and the conductor  151 . The conductor element  121  and the conductor element  141  are connected to the penetration via  101 . 
     By employing the configuration shown in  FIG. 6 , the number of layers (the B layer  12  and the D layer  14 ) in which the conductor element  121  or the conductor element  141  is located is equal to the number of layers (the A layer  11  and the C layer  13 ) in which the conductor  111  or the conductor  131  is located. More specifically, the number of the conductor elements  121  is equal to the number of the openings  112  formed in the conductors  111 . The number of the conductor element  141  is equal to the number of the opening  132  formed in the conductors  131 . 
     The structure  10  shown in  FIG. 6  is a modified example of a mushroom-like EBG structure. Specifically, the penetration via  101  corresponds to the stem part of a mushroom and forms inductance. On the other hand, the conductor element  121  corresponds to the head part of the mushroom and forms capacitance along with the opposed conductor  111 . The conductor element  141  corresponds to the head part of the mushroom and forms capacitance along with the opposed conductor  131 . 
     Similarly to the mushroom-like EBG structure, the structure shown in  FIG. 6  can be expressed by an equivalent circuit in which a parallel plate is shunted with a serial resonance circuit including the capacitance and the inductance and the resonance frequency of the serial resonance circuit gives the central frequency of a bandgap. Accordingly, it is possible to achieve the fall in the frequency of the bandgap range by causing the conductor element  121  to approach the conductor  111  forming the capacitance to increase the capacitance. However, even when the conductor element  121  is not made to approach the opposed conductor  111 , the substantial effect of the invention is not affected at all. It is possible to achieve the fall in the frequency of the bandgap range by causing the conductor element  141  to approach the conductor  131  forming the capacitance to increase the capacitance. Even when the conductor element  141  is not made to approach the opposed conductor  131 , the substantial effect of the invention is not affected at all. 
     In the structure  10  shown in  FIG. 6 , the conductor element  121  is arranged to oppose the bottom surface of the conductor  111 , but may be arranged to oppose the top surface of the conductor  111 . In the structure  10  shown in  FIG. 6 , the conductor element  141  is arranged to oppose the bottom surface of the conductor  131 , but may be arranged to oppose the top surface of the conductor  131 . 
     The conductor elements  121  and  141  in the structure  10  shown in  FIG. 6  may have the shape shown in  FIG. 2(B) . Here, the structure  10  similarly has the above-mentioned characteristics of the open stub type EBG structure. 
     The conductor elements  121  and  141  in the structure  10  shown in  FIG. 6  may have the shape shown in  FIG. 2(C) . Here, the structure  10  similarly has the characteristics of the inductance-increased EBG structure described with reference to  FIG. 2(C) . In the structure  10  shown in  FIG. 6 , the shape shown in  FIG. 5  may be employed as an example of the conductor  151 . At this time, the structure  10  similarly has the characteristics of the inductance-increased EBG structure. 
       FIG. 7  is a perspective view illustrating an example of the structure  10  according to this embodiment. In the structure  10  shown in  FIG. 7 , all of the conductor  11 , the conductor  131 , and the conductor  151  are insulated from the penetration via  101 . The conductor  111  has an opening  112  through which the penetration via  101  passes. The conductor element  121  is arranged to oppose to the opening  112 . The conductor  131  has an opening  132  through which the penetration via  101  passes. The conductor element  141  is arranged to oppose to the opening  132 . The conductor  151  has an opening  152  through which the penetration via  101  passes. The conductor element  161  is arranged to oppose to the opening  152 . It is assumed that the conductor element  161  is located in the F layer  16 . 
     By employing the configuration shown in  FIG. 7 , the number of layers (the B layer  12 , the D layer  14 , and the F layer  16 ) in which the conductor element  121 , the conductor element  141 , or the conductor element  161  is located is equal to the number of layers (the A layer  11 , the C layer  13 , the E layer  15 ) in which the conductor  111 , the conductor  131 , or the conductor  151  is located. More specifically, the number of the conductor elements  121  is equal to the number of the openings formed in the conductors  111 . The number of the conductor elements  141  is equal to the number of the openings formed in the conductors  131 . The number of the conductor elements  161  is equal to the number of the openings formed in the conductors  151 . 
     The structure  10  shown in  FIG. 7  is a modified example of a mushroom-like EBG structure. Specifically, the penetration via  101  corresponds to the stem part of a mushroom and forms inductance. On the other hand, the conductor element  121  corresponds to the head part of the mushroom and forms capacitance along with the opposed conductor  111 . The conductor element  141  corresponds to the head part of the mushroom and forms capacitance along with the opposed conductor  131 . The conductor element  161  corresponds to the head part of the mushroom and forms capacitance along with the opposed conductor  151 . Since the conductor element  121  and the conductor  111  are opposed to each other to form capacitance and the opening  112  formed in the conductor  111  is included in the region in which both are opposed to each other, it is possible to almost prevent the leakage of noise from the opening  112 . Since the conductor element  161  and the conductor  151  are opposed to each other to form capacitance and the opening  152  formed in the conductor  151  is included in the region in which both are opposed to each other, it is possible to almost prevent the leakage of noise from the opening  152 . 
     Similarly to the mushroom-like EBG structure, the structure shown in  FIG. 7  can be expressed by an equivalent circuit in which a parallel plate is shunted with a serial resonance circuit including the capacitance and the inductance and the resonance frequency of the serial resonance circuit gives the central frequency of a bandgap. Accordingly, it is possible to achieve the fall in the frequency of the bandgap range by causing the conductor element  121  to approach the conductor  111  forming the capacitance to increase the capacitance. However, even when the conductor element  121  is not made to approach the opposed conductor  111 , the substantial effect of the invention is not affected at all. It is possible to achieve the fall in the frequency of the bandgap range by causing the conductor element  141  to approach the conductor  131  forming the capacitance to increase the capacitance. Even when the conductor element  141  is not made to approach the opposed conductor  131 , the substantial effect of the invention is not affected at all. It is possible to achieve the fall in the frequency of the bandgap range by causing the conductor element  161  to approach the conductor  151  forming the capacitance to increase the capacitance. Even when the conductor element  161  is not made to approach the opposed conductor  151 , the substantial effect of the invention is not affected at all. 
     In the structure  10  shown in  FIG. 7 , the conductor element  121  is arranged to oppose the top surface of the conductor  111 , but may be arranged to oppose the bottom surface of the conductor  111 . In the structure  10  shown in  FIG. 7 , the conductor element  141  is arranged to oppose the top surface of the conductor  131 , but may be arranged to oppose the bottom surface of the conductor  131 . In the structure  10  shown in  FIG. 7 , the conductor element  161  is arranged to oppose the top surface of the conductor  151 , but may be arranged to oppose the bottom surface of the conductor  151 . 
     The conductor elements  121 ,  141 , and  161  in the structure  10  shown in  FIG. 7  may have the shape shown in FIG.  2 (B). Here, the structure  10  similarly has the above-mentioned characteristics of the open stub type EBG structure. 
     The conductor elements  121 ,  141 , and  161  in the structure  10  shown in  FIG. 7  may have the shape shown in  FIG. 2(C) . Here, the structure  10  similarly has the characteristics of the inductance-increased EBG structure described with reference to  FIG. 2(C) . 
     The structures  10  constituting the EBG structure using three sheet-like conductors  111 ,  131 , and  151  and the penetration via  101  are described above with reference to  FIGS. 1 to 7 . Another structure constituting the EBG structure using four or more sheet-like conductors and a penetration via may be constructed by combining the structures  10  shown in  FIGS. 1 to 7 . For example, the structure shown in  FIG. 8  is obtained by combining the structures shown in  FIGS. 1 to 6 . The individual elements are the same as described above and thus will not be repeated. 
     All the structures  10  described with reference to  FIGS. 1 to 7  include the penetration via  101  as a constituent. The structures  10  are manufactured through the following manufacturing processes. 
     First, (a) the conductor  111 , the conductor  131 , the conductor  151 , the conductor element  121 , and the conductor element  141  are stacked to oppose each other and to be located in different layers. Then, (b) a through-hole is formed which penetrates the conductor  111 , the conductor  131 , the conductor  151 , the conductor element  121 , and the conductor element  141  and the penetration via  101  that is insulated from at least one of the conductors  111 ,  131 , and  151  and that connects the conductor element  121  and the conductor element  141  is formed in the through-hole. Here, the constituents are arranged in the process of (a) so that at least one conductor element is opposed to the openings that is disposed in the conductor insulated from the penetration via  101  formed through the process of (b) and through which the penetration via  101  passes. 
     When there is any constituent not shown, the constituent is preferably arranged appropriately in the process of (a). In the process of (b), the method of forming the through-hole is not particularly limited as long as it is applicable, and for example, the through-hole may be formed with a drill. In the process of (b), the method of forming the penetration via  101  is not particularly limited as long as it is applicable, and for example, the connection member may be formed by plating the inner surface of the through-hole. 
       FIG. 9  shows a top view and a cross-sectional view of the circuit board  100  according to this embodiment. More specifically,  FIG. 9(A)  is a top view of the circuit board  100  and  FIG. 9(B)  is a cross-sectional view taken along the indicated sectional line in  FIG. 9(A) . In  FIG. 9(A) , squares indicated by dotted lines represent the conductor elements  121  formed in the B layer  12  or the conductor elements  141  formed in the D layer  14  in each of the structures  10  which are repeatedly arranged. In  FIG. 9(A) , circles in the squares indicated by dotted lines represent the penetration via  101  formed in each of the structures  10  which are repeatedly arranged. In  FIG. 9 , it is assumed that the structure  10  described with reference to  FIG. 5  is repeatedly arranged and the structures  10  are illustrated with black in  FIG. 9(B) . 
     As shown in  FIG. 9 , the conductor elements  121  located in the B layer  12  are connected to different penetration vias  101 . The conductor elements  141  located in the D layer  14  are connected to different penetration vias  101 . 
     The A layer  11 , the B layer  12 , the C layer  13 , the D layer  14 , and the E layer  15  may further include constituents other than the constituents shown in the drawing, such as transmission lines transmitting electrical signals. The circuit board  100  may include layers other than the A layer  11 , the B layer  12 , the C layer  13 , the D layer  14 , and the E layer  15 , and these layers may include the constituents other than the above-mentioned constituents, such as transmission lines. Here, when the transmission lines are disposed in a region in which the structure  10  is repeatedly arranged in the circuit board  100  and in the vicinity of the region, the characteristics of the EBG structures constituted by the structures  10  vary and thus it is preferable to avoid this arrangement. 
     In the circuit board  100 , it is possible to suppress the propagation of electromagnetic waves of the bandgap range in the region in which the structure  10  is repeatedly arranged. That is, the structures  10  have only to be arranged to surround a noise source generating the electromagnetic waves of the bandgap range or elements to be protected from the electromagnetic waves of a specific frequency band and the arrangement pattern thereof may include various examples. 
       FIGS. 10 to 12  are diagrams illustrating the arrangement patterns of the structures  10  which can be employed by the circuit board  100 . Here, the meshed members in  FIGS. 10 to 12  are a semiconductor package  161  and a semiconductor package  162 . As shown in  FIG. 10 , the structures  10  may be arranged in a band shape between the semiconductor package  161  and the semiconductor package  162 . The structures  10  may be arranged to surround the semiconductor package  161  as shown in  FIG. 11  or the structures  10  may be arranged to surround the semiconductor package  162  as shown in  FIG. 12 . 
     Even when electromagnetic waves to be suppressed propagate in any direction, it is possible to more effectively suppress the propagation of the electromagnetic waves by arranging the plural structures  10  so as to pass the electromagnetic waves therethrough. Accordingly, like the arrangement pattern shown in  FIG. 10  or  11 , the arrangement pattern in which the plural structures  10  are arranged in parallel in the direction from one semiconductor package to the other semiconductor package is more desirable than the arrangement pattern shown in  FIG. 12 . 
     The effects of this embodiment will be described below. The structure  10  can constitute the EBG structures by the use of the conductors  111 ,  131 , and  151 , the conductor elements  121  and  141 , and the penetration via  101 . Accordingly, in the structure  10 , it is possible to suppress noise propagating in a first parallel plate including the conductor  111  and the conductor  131  and noise propagating in a second parallel plate including the conductor  131  and the conductor  151 . Accordingly, even when there is noise leaking from the first parallel plate to the second parallel plate or noise leaking from the second parallel plate to the first parallel plate, it is possible to suppress such noise. 
     In the circuit board  100 , it is possible to suppress noise propagating between the A layer  11  and the C layer  13  and noise propagating between the C layer  13  and the E layer  15  by arranging the structures  10  in a region in which noise should be prevented from propagating. Accordingly, even when noise propagating between the A layer  11  and the C layer  13  leaks into the layer between the C layer  13  and the E layer  15  through the C layer  13 , or even when noise leaks in the reverse direction, it is possible to suppress such noise. 
     All the structures  10  used in this embodiment include the penetration via  101 . Accordingly, compared with a case in which a non-penetration via is employed, it is possible to reduce the number of manufacturing processes and to reduce the manufacturing cost. 
     While the embodiment of the invention has been described with reference to the accompanying drawings, the embodiment is only an example of the invention, and various configurations not described above may be employed. 
     For example, the number of the first conductors (the conductors  111 ,  131 , and  151  in the above-mentioned embodiment) of the invention is set to three in the above-mentioned embodiment, but may be set to four or more. As the number of the first conductors increases, the number of layers of the structure or the circuit board increases. Here, when the number of parallel plates in which the propagation of noise should be suppressed increases, the number of layers in which the conductor elements corresponding to the second conductors of the invention should be formed may be made to increase. 
     In any structure described in the above-mentioned embodiment, it has been stated that at least one conductor element is opposed to the respective openings through which the penetration via, but the invention is not limited to this configuration. That is, some of the conductor elements may be removed from the above-mentioned structure. It should be noted that the EBG structure is not constructed between the parallel plates in which the conductor elements are moved. 
     In the above-mentioned embodiment, all the structures  10  have a single penetration via  101 , but the invention is not limited to this configuration. That is, a configuration in which plural structures  10  described in the above-mentioned embodiment are connected may be considered as a single structure. Accordingly, in this structure, plural penetration vias are repeatedly arranged and the conductor elements located in the same layer are connected to different connection members, respectively. 
     The above-mentioned embodiment and the modified examples thereof can be combined without conflicting each other. In the above-mentioned embodiment and the modified examples, the functions and the like of the constituents are specifically described above, but the functions and the like can be modified in various forms without departing from the concept of the invention. 
     Priority is claimed on Japanese Patent Application No. 2010-051086, filed Mar. 8, 2010, the content of which is incorporated herein by reference.