Abstract:
A microphone case includes: a plastic basic frame including a space for housing an electro-acoustic transducing unit; a plastic substrate for closing an opening of the space, the plastic substrate being bonded to the basic frame; conductive layers provided on the bonding surfaces of the basic frame and the substrate respectively, the conductive layers being electrically connected to each other; and exposed portions where the surfaces of the basic frame and the substrate are exposed, wherein the basic frame and the substrate are bonded to each other in the exposed portions.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from a Japanese Patent Application No. 2006-205201 filed on Jul. 27, 2006, and a Japanese Patent Application No. 2006-322998 filed on Nov. 30, 2006, the entire subject matter of which is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a microphone case and a condenser microphone used for various apparatuses such as a cellular phone, a video camera, and a personal computer. 
       BACKGROUND 
       [0003]    An example of a known condenser microphone is disclosed in JP-A-2002-345092. That is, in the known microphone, a unit is constituted by laminating and fixing a circuit substrate mounted with electric components, a lower spacer, a back electrode substrate having a back electrode, an upper spacer, and a vibrating membrane supporting frame in which a vibrating membrane is tightly provided sequentially from a bottom part and the unit is housed in a metal case. 
       SUMMARY 
       [0004]    However, in this kind of condenser microphone, an adhesive agent is interposed between bonding surfaces of the members at the time of laminating and fixing the above-mentioned circuit substrate and the back electrode substrate. In this case, it is necessary to electrically connect conductive patterns provided on the members between the bonding surfaces of the members so as to ensure earth connection. As a result, an adhesive agent layer between the conductive patterns is formed thinner or a conductive adhesive agent containing a conductive binder is used so as not to inhibit conduction between the conductive patterns. 
         [0005]    However, when the adhesive agent layer is very thinner, high bonding strength is not ensured and intensity of the microphone is lowered. When the conductive adhesive agent containing the conductive binder is used, a manufacturing cost is increased due to a high price of the adhesive agent and a gas is generated from the binder due to a heat generated in reflowing, and leakage of electric charges occurs on an electret layer such as the back electrode substrate due to the gas, whereby performance of a condenser microphone is remarkedly lowered. 
         [0006]    In a lamination-structure condenser microphone constituted mainly of three-layer substrates (a circuit substrate, a case substrate, and a top substrate), when the circuit substrate and the top substrate are bonded onto both upper and lower surfaces of the case substrate, respectively, bonding performance of the adhesive agent to the metallic layers is by far inferior to bonding performance of the adhesive agent to a core material (e.g. a glass epoxy resin plate) of the substrate. The reason is as follows. Since a surface of the metallic layer has smoothness better than the core material of the substrate, bonding strength of the adhesive agent decreases. 
         [0007]    Assuming that the heat is applied to the condenser microphone in the same manner as in reflowing at the time of mounting the condenser microphone on the substrate, the core material of a case substrate (e.g. the glass epoxy resin plate) has a coefficient of thermal expansion higher than a metallic layer (e.g. a copper foil), whereby the core material pushes up the metallic layer. In this case, a force is applied to the metallic layer on front and back surfaces of the case substrate which is in communication with a through-hole (a via-hole) in a direction away from the core material by an internal expansion pressure of the core material at the time of applying the heat. As a result, assuming that strength of the through-hole is not enough, the metallic layers on the front and back surfaces are cracked, whereby the metallic layers will not be conducted. 
         [0008]    The invention is made in view of the problems of related art. An object of the invention is to make it possible to acquire a high-strength case of the condenser microphone, to manufacture the high-strength case of the condenser microphone at low cost, and to achieve a high-performance condenser microphone. 
         [0009]    An object of the invention is to provide the condenser microphone and a method of manufacturing the condenser microphone in which the bonding performance between the core material of the case substrate and the circuit substrate and between the core material of the case substrate and the top substrate can be improved at the time of bonding the circuit substrate and the top substrate to the front and back surfaces of the case substrate. 
         [0010]    In order to accomplish the above-mentioned object, according to a first aspect of the invention, there is provided a microphone case including: a plastic basic frame including a space for housing an electro-acoustic transducing unit; a plastic substrate for closing an opening of the space, the plastic substrate being bonded to the basic frame; conductive layers provided on the bonding surfaces of the basic frame and the substrate respectively, the conductive layers being electrically connected to each other; and exposed portions where the resin surfaces of the basic frame and the substrate are exposed, the exposed portions being provided on the bonding surfaces, wherein the basic frame and the substrate are bonded to each other in the exposed portions. 
         [0011]    Accordingly, the basic frame and the substrate are bonded and fixed to each other in the exposed portion having no conductive pattern and are electrically connected to each other by bonding between the conductive patterns. A plurality of substrates constituting the case is strongly bonded to each other and laminated and fixed to each other with the substrates conducted to each other. It is not necessary to use the conductive adhesive agent containing the conductive binder and it is possible to perform bonding with a general adhesive agent, thereby reducing a manufacturing cost. Since it is not necessary to use the conductive adhesive agent, it is possible to prevent a gas from being generated from the conductive binder and to avoid leakage of electric charges occurring due to the gas, thereby achieving a high-performance microphone. 
         [0012]    According to a second aspect of the invention, in the microphone case according to the first aspect, the basic frame and the substrate are made of similar materials, and the basic frame and the substrate are bonded to each other with a bonding member made of the similar materials. 
         [0013]    Accordingly, it is possible to bond and fix the basic frame and the substrate strongly and to prevent occurrence of a difference in an expansion coefficient between the basic frame and the substrate in an expansion coefficient, whereby it is possible to avoid bonding separation. 
         [0014]    According to a third aspect of the invention, in the microphone case according to the second aspect, the bonding member is a heat-resistant bonding sheet. 
         [0015]    The heat-resistant bonding sheet is easy to handle and contributes to promotion of efficiency in a manufacturing process, and since a gas yield is small even though the heat-resistant bonding sheet is subjected to the heat in reflowing, the heat-resistant sheet is effective to prevent the electric charges from being leaked. 
         [0016]    According to a fourth aspect of the invention, in the microphone case according to the second aspect, the bonding member is a curable contractile bonding member. 
         [0017]    Accordingly, the basic frame and the substrate are pulled up by curing contraction of the adhesive agent, whereby it is possible to improve bonding strength and to acquire excellent electric conduction between the conductive patterns. 
         [0018]    According to a fifth aspect of the invention, in the microphone case according to the third aspect, the plastic substrate includes: a first substrate, which is mounted with an electric component and closes one end of the opening of the basic frame; and a second substrate, which includes a sound hole and closes the other end of the opening of the basic frame. 
         [0019]    The microphone case is suitable for a condenser microphone having a condenser section built therein. 
         [0020]    According to a sixth aspect of the invention, in the microphone case according to the fifth aspect, the electric component is fixed to the substrate by a fluxless fixing method. 
         [0021]    Accordingly, production of the gas from a flux is avoided in advance and leakage of electric charges on an electret layer is prevented, whereby it is possible to achieve a high-performance microphone. 
         [0022]    According to a seventh aspect of the invention, there is provided a condenser microphone including: a case substrate including a metallic layer; bonding areas provided on front and back surfaces of the case substrate; a top substrate; and a circuit substrate mounted with electric components, wherein the top substrate and the circuit substrate are bonded and fixed to the bonding areas respectively without using the metallic layer with an adhesive agent. 
         [0023]    According to the seventh aspect of the invention, no metallic layer is provided in the bonding area at the time of bonding the circuit substrate and the top substrate to the front and back surfaces of the case substrate, respectively. As a result, bonding performance between a core material of the case substrate and the circuit substrate and bonding performance between a core material of the case substrate and the top substrate are improved. 
         [0024]    Accordingly, it is possible to a condenser microphone having the above-mentioned advantages. 
         [0025]    As described above, according to an aspect of the invention, a plurality of substrates can be strongly bonded to each other and laminated and fixed to each other with the substrates conducted to each other and leakage of electric charges can be prevented, whereby it is possible to achieve a high-performance microphone. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    In the accompanying drawings: 
           [0027]      FIG. 1  is a cross-sectional view illustrating a condenser microphone according to a first embodiment; 
           [0028]      FIG. 2  is an exploded perspective view of a condenser microphone of  FIG. 1 ; 
           [0029]      FIG. 3  is a partial cross-sectional view enlarging a part of  FIG. 1 ; 
           [0030]      FIG. 4  is a plan view illustrating a bonding structure of a case basic frame to a circuit substrate; 
           [0031]      FIG. 5  is a bottom view illustrating a bonding structure of a case basic frame to a top substrate; 
           [0032]      FIG. 6  is a bottom view illustrating a bonding structure of a vibrating membrane and a spacer to a top substrate; 
           [0033]      FIG. 7  is a partial plan view illustrating a manufacturing process of a condenser microphone; 
           [0034]      FIG. 8  is a partial plan view illustrating a manufacturing process following that of  FIG. 7 ; 
           [0035]      FIG. 9  is a partial plan view illustrating a manufacturing process following that of  FIG. 8 ; 
           [0036]      FIG. 10  is a partial plan view illustrating a manufacturing process following that of  FIG. 9 ; 
           [0037]      FIG. 11  is a partial plan view illustrating a manufacturing process following that of  FIG. 10 ; 
           [0038]      FIG. 12  is a partial plan view illustrating a manufacturing process following that of  FIG. 11 ; 
           [0039]      FIG. 13  is a cross-sectional view illustrating a condenser microphone according to a second embodiment; 
           [0040]      FIG. 14  is an exploded perspective view of a condenser microphone of  FIG. 13 ; 
           [0041]      FIG. 15  is a cross-sectional view illustrating a condenser microphone according to a third embodiment; 
           [0042]      FIG. 16  is an exploded perspective view of a condenser microphone of  FIG. 15 ; 
           [0043]      FIG. 17  is an explanary view illustrating a positional relation between a conductive pattern and a resist on a front surface of a circuit substrate  123 ; 
           [0044]      FIG. 18A  is a plan view of a conductive pattern on a front surface of a circuit substrate  123 ;  FIG. 18B  is a plan view of a conductive pattern;  FIG. 18C  is a plan view of a conductive pattern on a back surface of the circuit substrate  123 ; and 
           [0045]      FIG. 19  is a plan view of a case basic frame  124 . 
       
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
       [0046]    Hereinafter, embodiments of the present invention are described with reference to  FIGS. 1 to 3 . 
         [0047]    As shown in  FIGS. 1 and 2 , a case  22  of a condenser microphone  21  according to the embodiments has a structure in which a tabular circuit substrate  23 , a wholly rectangular case basic frame  24  in which a space is formed, and a tabular top substrate  25  are laminated and fixed with an adhesive agent. The circuit substrate  23 , the case basic frame  24 , and the top substrate  25  are made of electric insulating materials such as an epoxy resin, liquid crystal polymer, and ceramic. In the embodiments, the circuit substrate  23 , the case basic frame  24 , and the top substrate  25  are made of a glass epoxy resin in which a glass fiber is incorporated into the epoxy resin. 
         [0048]    Conductive patterns  23   b  and  23   c  are printed on both upper and lower surfaces of the circuit substrate  23  as a conductive layer made of copper. Electric components such as a field-effect transistor  26  and a capacitance  27  constituting an impedance converting circuit provided in the case  22  are mounted on the circuit substrate  23 . The conductive patterns  24   b  and  24   c  as conductive layers which are arranged in series and made of copper are printed on both upper and lower surfaces and lateral surfaces of the case basic frame  24 . The electric components such as the electric-filed transistor  26  and the capacitance  27  mounted on the circuit substrate  23  is housed in the space of the case basic frame  24 . An insulating film  23   e  is printed in a predetermined position on both upper and lower surfaces of the circuit substrate  23 . Conductive patterns  25   b  and  25   c  as conductive layers made of a copper foil are printed on both upper and lower surfaces and lateral surfaces of the top substrate  25 . A sound hole  28  for taking in sound from an outside is formed in the top substrate  25 . The conductive layers  23   d  and  25   d  which are made of the copper foil are buried in the circuit substrate  23  and the top substrate  25 . The conductive layers  23   d  and  25   d  are laminated between a pair of resin sheets constituting the circuit substrate  23  and the top substrate  25 . 
         [0049]    As shown in  FIGS. 1 to 3  and  6 , a vibrating membrane  29  made of a thin-film sheet material of PPS (polyphenylene sulfide) is tightly bonded onto a lower surface of the lower conductive pattern  25   c  in the top substrate  25  in the case basic frame  24  and a conductive layer not shown is formed on an upper surface of the vibrating membrane  29  by gold deposition. Chip-shaped spacers  30  made of a synthetic resin such as PPS of the similar as the material of the vibrating membrane  29  are bonded and fixed to four locations of a lower periphery of the vibrating membrane  29 . In the case basic frame  24 , a back plate  31  is disposed opposite to the lower surface of the vibrating membrane  29  with the spacers  30  interposed therebetween. In the back plate  31 , a film  31   b  such as PTFE (polytetrafluorethylene) is bonded onto an upper surface of a substrate  31   a  formed of a stainless steel plate. A polarization treatment is performed on the film  31   b  by a corona discharge and the film  31   b  constitutes an electret layer by the polarization treatment. Accordingly, since the back plate  31  constitutes a back electrode, the condenser microphone of the embodiment is a back electret type. The back plate  31  is formed in a substantially elliptic shape in a plan view, which has an outer peripheral shape smaller than an inner peripheral shape of the case basic frame  24 . A clearance is formed between the inner and outer peripheral surfaces. A through-hole  32  for allowing air transfer by vibration of the vibrating membrane  29  is formed in a central part of the back plate  31 . 
         [0050]    As shown in  FIGS. 1 to 3 , in the case basic frame  24 , a holding member  33  formed of a plate spring material is interposed between the back plate  31  and the circuit substrate  23  in a compression state. The back plate  31  is compressed in a direction abutting lower surfaces of the spacers  30  from an opposite side of the vibrating membrane  29  by a resilient force of the holding member  33 . Accordingly, a predetermined clearance as thick as a thickness of the spacer  30  is held between the vibrating membrane  29  and the back plate  31  and a condenser section having a predetermined capacity is formed therebetween. The holding member  33  is formed by gold-plating both front and back surfaces of the stainless steel plate. The back-plate  31  is electrically connected to terminals  44  of the impedance converting circuit on the circuit substrate  23  with the holding member  33  interposed therebetween. 
         [0051]    As shown in  FIG. 1 , a plurality of through-holes  34  and  35  are formed on the circuit substrate  23  and the top substrate  25 , respectively. Conductive patterns  34   a  and  35   a  in series with the conductive patterns  23   b  and  23   c  and the conductive patterns  25   b  and  25   c  are provided on inner peripheral surfaces of the through-holes  34  and  35 , respectively. The through-holes  34  and  35  are filled with conductive materials  36  and  37 . Conductive sections  57  and  58  are formed of the conductive materials  36  and  37  and the conductive patterns  34   a  and  35   a . A conductive path is formed to an earth terminal not shown from the conductive section  58  including the conductive patterns  25   b  and  25   c  and the through-hole  35  of the top substrate  25  via the conductive patterns  24   b  to  24   d  on the case basic frame  24  and the conductive section  57  including the conductive patterns  23   b  and  23   c  and the through-hole  34  of the circuit substrate  23 . 
         [0052]    Next, the circuit substrate  23 , the case basic frame  24  and the top substrate  25  constituting the case  22 , and a laminated and fixed structure thereof will be described in detail. 
         [0053]    As shown in  FIGS. 1 to 5 , exposed portions  38  and  39  of a basic frame body  24   a  in which the conductive patterns  24   c  and  24   b  are not provided are formed as a whole being a perimeter shape in inner peripheries of a lower surface and an upper surface of the case basic frame  24 . A plurality of exposed portions  40  of a substrate body  23   a  in which the conductive pattern  23   b  is not provided is arranged on an upper surface of the circuit substrate  23  along a perimeter-shaped zone in correspondence with a lower exposed portion  38  of the case basic frame  24 . A plurality of exposed portions  41  of a substrate body  25   a  in which the conductive pattern  25   c  is not provided is arranged on a lower surface of the top substrate  25  along the perimeter-shaped zone in correspondence with an upper exposed portion  39  of the case basic frame  24 . 
         [0054]    An adhesive agent  42  made of an epoxy resin as a bonding member is interposed between the exposed portions  40  of the circuit substrate  23  and the lower exposed portion  38  of the case basic frame  24 . The circuit substrate  23  and the case basic frame  24  are bonded and fixed to each other with the adhesive agent  42  in the exposed portions  40  and  38  of the substrate body  23   a  and the basic frame body  24   a , which are made of electric insulating materials. In sections other than the exposed portions  40  and  38 , the conductive pattern  23   b  on the upper surface of the circuit substrate  23  and the conductive pattern  24   c  on the lower surface of the case basic frame  24  are directly bonded with each other and the circuit substrate  23  and the case basic frame  24  are electrically connected to each other. 
         [0055]    Similarly, an adhesive agent  43  made of the epoxy resin as the bonding member is interposed between the exposed portions  41  of the top substrate  25  and the upper exposed portion  39  of the case basic frame  24 . The top substrate  25  and the case basic frame  24  are bonded and fixed to each other in the exposed portions  41  and  39  of the substrate body  25   a  and the basic frame body  24   a  with the adhesive agent  43 . In sections other than the exposed portions  41  and  39 , the conductive pattern  25   c  on the lower surface of the top substrate  25  and the conductive pattern  24   b  on the upper surface of the case basic frame  24  are directly bonded with each other and the top substrate  25  and the case basic frame  24  are electrically connected to each other. 
         [0056]    A heat-resistant sheet such as a bonding sheet mainly made of epoxy and a thermoplastic resin, a sheet made of high heat-resistant acrylic adhesive agent, or a bonding sheet made of a polyolefin resin is adapted as the bonding member, i.e., the adhesive agent. 
         [0057]    In the condenser microphone  21  of the embodiment configured as above, when a sound wave from a sound source reaches the vibrating membrane  29  through the sound hole  28  of the top substrate  25 , the vibrating membrane  29  vibrates depending on a frequency, an amplitude, and a waveform of the sound. A gap between the vibrating membrane  29  and the back plate  31  is varied from a set value with vibration of the vibrating membrane  29  and thus, an impedance of the condenser is varied. The variation of the impedance is converted into a voltage signal by the impedance converting circuit. 
         [0058]    Next, a manufacturing method of the condenser microphone  21  having the above configuration will be described. 
         [0059]    However, in manufacturing the condenser microphone  21 , first, a vibrating formation sheet  46  for separately forming plural pieces of vibrating membranes  29  and a spacer formation sheet  47  for separating plural sets of spacers  30  formed of one set of four spacers are bonded and fixed with the adhesive agent and thus, a vibrating membrane assembly  48  is prepared, as shown in  FIG. 7 . A plurality of through-holes  47   a  is arranged in the spacer formation sheet  47  and convex portions  47   b  for separately forming the four spacers  30  are provided in inner peripheries of the through-holes  47   a . The vibrating formation sheet  46  is tightly provided in each of the through-holes  47   a  of the spacer formation sheet  47  in a properly tight state with the both sheets  46  and  47  bonded to each other. 
         [0060]    Next, as shown in  FIG. 8 , the vibrating membrane assembly  48  is bonded with the adhesive agent on a lower surface of a top substrate formation member  49  for separately forming plural pieces of top substrates  25 . In this case, the conductive patterns  25   b  and  25   c  and the sound hole  28  for separately forming the plurality of top substrates  25  are formed in the top substrate formation member  49  at predetermined intervals. The only conductive pattern  25   c  on the lower surface is shown in  FIG. 8 . Circular-shaped through-holes  49   a  for fixing four corners of each of the top substrates  25  are formed in the top substrate formation member  49  in correspondence with four corners of each of the conductive patterns  25   c . As shown by a two-dot chain line in a lower part of  FIG. 8 , the adhesive agent is applied only to a predetermined bonding area  50  on the conductive pattern  25   c  inside of the exposed portion  41  of each of the conductive patterns  25   c  of the top substrate formation member  49 , whereby the vibrating membrane formation sheet  46  and the conductive pattern  25   c  are bonded to each other only in the bonding area  50 . 
         [0061]    Subsequently, as shown by a two-dot chain line in an upper part of  FIG. 8 , the vibrating membrane assembly  48  is fixed to each of the through-holes  47   a  of the spacer formation sheet  47  and a the plurality of vibrating membranes  29  having a size in which the vibrating membranes  29  can be housed in the case basic frame  24  and four chip-shaped spacers  30  which are bonded to the vibrating membranes  29  are formed by punching and cutting the vibrating membrane assembly  48  along a virtual cutting line  51  matching with the bonding area  50  with a laser beam. In this case, since the virtual cutting line  51  is set to be positioned in correspondence with each of the conductive patterns  25   c  made of metallic materials on the top substrate formation member  49 , there is no possibility for damaging the top substrate formation member  49  even though punching and cutting the vibrating membrane assembly  48  with the laser. 
         [0062]    Subsequently, as shown in  FIG. 9 , the top substrate formation member  49  to which the vibrating membranes  29  are bonded is laminated on a case basic frame formation member  52  for separately forming a plurality of case basic frames  24  and the top substrate formation member  49  and the case basic frame formation member  52  are bonded and fixed to each other as described below. In this case, a plurality of through-holes  52   a  serving as an internal surface of the case basic frame  24  are formed in the case basic frame formation member  52  at predetermined intervals. Circular-shaped through-holes  52   b  for settling four corners of each of the case basic frames  24  and long hole-shaped through grooves  52   c  and  52   d  for settling an external surface of each of the case basic frames  24  which are formed slightly away from the through-hole  52   b  are formed in the case basic frame formation member  52 . The conductive patterns  24   b  to  24   d  of the case basic frame  24  are formed on both front and back surfaces of the case basic frame formation member  52 , inner peripheral surfaces of the through-holes  52   b , and inner peripheral surfaces of the through-holes  52   c  and  52   d.    
         [0063]    An epoxy adhesive agent made of the similar material as the top substrate formation member  49  and the case basic frame formation member  52  is applied to any one of the exposed portion  41  in each of the conductive patterns  25   c  in the top substrate formation member  49  and the exposed portion  39  in an upper peripheral edge of each of the through-holes  52   a  in the case basic frame formation member  52 , whereby the top substrate formation member  49  and the case basic frame formation member  52  are incorporated with each other and strongly bonded and to each other in the exposed portions  41  and  39  of the substrate body  25   a  and the basic frame body  24   a . In this case, since the adhesive agent is not interposed between the conductive patterns  25   c  and  24   b  of the top substrate formation member  49  and the case basic frame formation member  52 , the conductive patterns  25   c  and  24   b  thereof are directly bonded with each other and electrically conducted. 
         [0064]    As shown in  FIG. 10 , the back plate  31  and the holding member  33  are put in each of the through-holes  52   a  of the case basic frame formation member  52  and inserted and attached. Subsequently, as shown in  FIG. 11 , a circuit substrate formation member  53  for forming the plurality of circuit substrates  23  in the case basic frame formation member  52  is laminated and bonded and fixed as described below, thereby forming a microphone assembly  54 . In this case, the conductive patterns  23   b  and  23   c , and the insulating film  23   e  for the circuit substrate  23  are formed in the circuit substrate formation member  53  and the electric components such as the field-effect transistor  26  and the capacitance  27  are loaded on the conductive pattern  23   b  by using laser welding precedently. The laser welding is performed by radiating the laser beam to a boundary between the electric components and the conductive patterns  23   b  and  23   c .  FIG. 11  illustrates only a part of the conductive pattern  23   c  on a lower surface. Circular-shaped through-holes  53   a  for settling four corners of each of the circuit substrates  23  are formed in the circuit substrate formation member  53  in correspondence with four corners of each of the conductive patterns  23   c . Arc welding, fluxless soldering, or flux washing soldering may be used instead of the laser welding. 
         [0065]    An epoxy adhesive agent made of the similar material as the case basic frame formation member  52  and the circuit substrate formation member  53  is applied to any one of the exposed portion  38  in a lower peripheral edge of each of the through-holes  52   a  in the case basic frame formation member  52  and the exposed portion  40  on each of the conductive patterns  23   b  in the circuit substrate formation member  53 , whereby the case basic frame formation member  52  and the circuit substrate formation member  53  are incorporated with each other and strongly bonded and fixed to each other in the exposed portions  38  and  40  of the basic frame bodies  24   a  and  23   a . In this case, since the adhesive agent is not interposed between the conductive patterns  24   c  and  23   b  of the case basic frame formation member  52  and the circuit substrate formation member  53 , the conductive patterns  24   c  and  23   b  are electrically bonded with each other and thus, it is possible to obtain excellent electric conduction. 
         [0066]    Thereafter, as shown in  FIG. 12 , the microphone assembly  54  are cut and separated along virtual crisscross cutting lines  55  and  56  passing through the through-holes  49   a ,  52   b , and  53   a , and the through grooves  52   c  and  52   d  by a dicing saw and a plurality of condenser microphones  21  is formed at the same time. Here, each of the cutting lines  55  and  56  is positioned on a straight line linking centers of the through-hole  49   a  of the top substrate formation member  49 , the through-hole  52   b  and the through grooves  52   c  and  52   d  of the case basic frame formation member  52 , and the through-hole  53   a  of the circuit substrate formation member  53 . As a result, a cut resistance can be reduced and thus, a cutting work can be performed at low load. Even though a burr is produced on four corners of the condenser microphone  21  at the time of cutting and separating the plurality of condenser microphones  21  from the microphone assembly  54 , the burr is positioned in the through-holes  49   a ,  52   b , and  53   a  of the four corners of each of the condenser microphones  21 , whereby it is possible to prevent the burr from protruding from external surfaces on sides of the condenser microphone  21 . Even when the adhesive agent  42  and an adhesive agent  43  are spilled, the adhesive agents  42  and  43  may be overspilled into the through-holes  49   a ,  52   b  and  53   a , whereby it is possible to maintain constant thickness accuracy of case  22 . 
         [0067]    The condenser microphone  21  of the embodiment configured as above has the following advantages. 
         [0068]    The exposed portions  38  to  41  exposing a resin surface which does not include the conductive patterns  23   b ,  24   b ,  24   c , and  25   c  are provided on parts of bonding surfaces of a plurality of substrates  23  and  25 , and the basic frame  24  constituting the case  22  laminatedly. The substrates  23  and  25  opposed to each other and the basic frame  24  are bonded and fixed in the exposed portions  38  to  41 . As a result, a thin bonding layer is provided between smooth metal planes such as conductive patterns and thus, it is possible to obtain a bonding strength stronger than that of a known configuration in which the members such as the basic frame and the substrate are bonded and fixed. 
         [0069]    The conductive patterns  23   b ,  24   b ,  24   c , and  25   c  are directly bonded with each other in sections other than the exposed portions  38  to  41  on the bonding surfaces of the substrates  23  and  25  and the basic frame  24 , it is possible to ensure excellent electric conduction between each of the substrates  23  and  25  and the basic frame  24 . It is not necessary to use a high-priced conductive adhesive agent containing a conductive binder and it is possible to perform bonding with a general adhesive agent, whereby a manufacturing cost may be reduced. 
         [0070]    Since the adhesive agent which does not include the conductive binder is used and the electric components are fixed by the laser welding, the arc welding, the fluxless soldering, or flux washing soldering, it is possible to prevent a gas from being produced from the conductive binder or flux of the soldering in reflowing. As a result, it is possible to prevent the leakage of the electric charge on the electret layer in advance, thereby obtaining the high-performance condenser microphone. 
         [0071]    Since the epoxy resin made of the similar material as the substrates  23  and  25  and the basic frame  24  is used as the adhesive agent for bonding the substrates  23  and  25  and the basic frame  24 , it is possible to increase the bonding strength between the substrates  23  and  25  and the basic frame  24  and expansion coefficients between the substrates  23  and  25  and the basic frame  24  and the adhesive agent are substantially the same, whereby it is possible to prevent peeling of a bonding portion, which is caused by a difference in the expansion coefficient. 
         [0072]    Since an epoxy resin as a curing contractive adhesive agent, which has a high curing contraction rate, is used as the adhesive agent, the same adhesive agent is remarkedly contracted with curing. As the result, the substrates  23  and  25  and the basic frame  24  are pulled up each other, whereby a strength of the condenser microphone  21  is improved and contact pressures of the conductive patterns  23   b ,  24   b ,  24   c , and  25   c  increase, thereby ensuring the electric conduction more surely and improving a hermetic property of the case  22 . 
         [0073]    Since the entire case  22  is formed of three layers and the spacer is not interposed therebetween unlike the known configuration, it is possible to contribute a decrease in size of the microphone and since the spacer is separated into four chips, the case  22  has little to thermal deformation. Accordingly, it is possible to prevent the vibrating membrane from being excessively tight or loose by deformation of the spacer, thereby obtaining an excellent sensitivity of the microphone. 
         [0074]    The substrate bodies  23   a  and  25   a  of the substrate  23  and the top substrate  25  are made of the electric insulating material such as the epoxy resin and have a multilayer structure in which the conductive layers  23   d  and  25   d  made of the copper foil are buried substantially in a center portion in a thickness direction. As the result, it is possible to improve a mechanical strength of the entire case  22  by improving strengths of the circuit substrate  23  and the top substrate  25  and it is possible to improve reliability of the microphone by improving electromagnetic shield property of the case  22 . 
         [0075]    In a method of manufacturing the condenser microphone  21 , it is possible to discharge the adhesive agent spilled between the bonding surfaces to the through-holes  49   a ,  52   b , and  53   a  and the through grooves  52   c  and  52   d . As the result, it is possible to prevent the adhesive agent from flowing into the case  22 , thereby preventing an inconvenience such as variation of an electrostatic capacitance. 
         [0076]    Since the through-holes  49   a ,  52   b , and  53   a  are positioned on four corners of each of the condenser microphones  21 , whereby it is possible to prevent the burr occurring at the time of cutting and separating the condenser microphone  21  from protruding to external surfaces of the sides, it is possible to prevent a trouble from occurring in handling of the condenser microphone  21  at the time of the condenser microphone  21  on a substrate of a cellular phone. 
         [0077]    The heat-resistant bonding sheet formed of a bonding sheet mainly made of the epoxy resin and the thermoplastic resin is adapted as the adhesive agent for bonding between the exposed portions  40  of the circuit substrate  23  and the lower exposed portion  38  of the case basic frame  24  and between the exposed portions  41  of the top substrate  25  and the upper exposed portion  39  of the case basic frame  24 . Since the heat-resistant sheet is easy to handle and a gas production amount is small by a heat in reflowing, it is possible to effectively prevent the leakage of the electric charge. 
       Second Embodiment 
       [0078]    Next, a second embodiment according to the invention will be described focusing on parts other than the parts of the first embodiment. 
         [0079]    However, in the second embodiment, as shown in  FIGS. 13 and 14 , the exposed portion  40  is formed in the outer peripheral part including four corner portions on an upper surface of the substrate body  23   a  of the circuit substrate  23  and the exposed portion  39  is formed in the outer peripheral part including four corners on both upper and lower surfaces of the basic frame body  24   a  of the case basic frame  24 , and the exposed portion  41  is formed in the outer peripheral part including four corners on a lower surface of the substrate body  25   a  of the top substrate  25 . The circuit substrate  23  and the case basic frame  24  and the case basic frame  24  and the top substrate  25  are bonded between the exposed portions  40  and  39  and between the exposed portions  39  and  41  with the adhesive agents  42  and  43  made of the similar material. 
         [0080]    Meanwhile, the spacer  30  made of stainless steel is formed in a cup shape and the vibrating membrane  29  is bonded and fixed onto an upper surface of the spacer  30 . An assembly of the vibrating membrane  29  and the spacer  30  is laminated between the top substrate  25  and the case basic frame  24  and it is bonded and fixed therebetween. In the spacer  30 , oblique side portions  30   a  are formed four corners and the exposed portion  39  of the case basic frame  24  and the exposed portion  41  of the top substrate  25  are bonded to each other in positions corresponding to the oblique side portions  30   a  with the adhesive agents  43  and  43  made of the similar material as described above. 
         [0081]    Accordingly, even in the second embodiment, it is possible to acquire substantially the same advantage as the advantage disclosed in the first embodiment. 
         [0082]    In the second embodiment, a gold deposition surface is formed on the lower surface of the vibrating membrane  29  and a folding-back portion  30   b  is formed on vibrating membrane  29  upwardly. As the result, the gold deposition surface of the vibrating membrane  29  in the folding-back portion  30   b  ensures the electric conduction between the vibrating membrane  29  and the conductive pattern  25   c  and the electric conduction between the spacer  30  and the electric conduction between the conductive pattern  24   b  of the case basic frame  24 . 
         [0083]    The present embodiment may be realized by the following modification. 
         [0084]    The invention may be realized by an electret-type condenser microphone of a foil electret type in which a function of an electret is granted to the vibrating membrane  29  instead of the back plate  31 . 
         [0085]    Further, the invention may be realized by a charge pump-type condenser microphone in which a voltage is applied to the back plate  31  and the vibrating membrane  29  by a charge pump circuit. 
         [0086]    Further, the invention may be realized by an MEMS (micro electro mechanical systems) microphone in which a microphone prepared by a semiconductor process is housed in the case. 
       Third Embodiment 
       [0087]    Hereinafter, a third embodiment according to the invention will be described focusing on parts other than those of the first and second embodiments with reference to  FIGS. 15 to 19 . 
         [0088]    As shown in  FIGS. 15 and 16 , a case  122  of a condenser microphone  121  according to the embodiment has a structure in which a tabular circuit substrate  123  serving as a mounting substrate, a rectangular case basic frame  124  serving as a case substrate, and a tabular top substrate  125  serving as a top cover are laminated and they are integrally fixed by a bonding sheets  127 A and  127 B. The circuit substrate  123 , the case basic frame  124 , and the top substrate  125  are made of the electric insulating material such as the epoxy resin. In the embodiment, the member is made of a glass fabric-based epoxy resin and is not limited to the epoxy resin. 
         [0089]    As shown in  FIG. 18A , conductive patterns  123   a ,  123   b , and  123   c  made of the copper foil as a conductive member are formed on an upper surface (alternatively, also referred to as a surface of the circuit substrate  123 ) of the circuit substrate  123 . In the specification, the upper surface represents a surface facing an upside and the lower surface represents a surface facing a downside when the circuit substrate  123  is disposed in a lower side, the case basic frame  124  is disposed in a center, and the top substrate  125  is disposed in an upper side. The conductive patterns  123   a ,  123   b , and  123   c  are shown by hatching for easy description in  FIGS. 17 and 18A . 
         [0090]    As shown in  FIG. 18A , in the conductive pattern  123   a , a first edge is positioned near one edge side in a longer direction and near one edge side in a shorter direction on the upper surface of the circuit substrate  123  and a second edge  151  is extends toward a center side on the upper surface of the circuit substrate  123 . The first edge of the conductive pattern  123   a  is formed of a conductive section  150 . 
         [0091]    Here, on the upper surface of the circuit substrate  123 , an axis in a shorter direction represents an x axis and an axis in a longer direction represents a y axis, which are orthogonal to each other on a central axis o (see  FIG. 18A ) penetrating in a thickness direction of the circuit substrate  123 . 
         [0092]    On the upper surface of the circuit substrate  123 , a line symmetric area P 1  of the conductive section  150  in which the x axis serves as a symmetric axis, a line symmetric area P 2  of the conductive section  150  in which the y axis serves as the symmetric axis, and a point symmetric area P 3  of the conductive section  150  in which the central axis o serves as a central point are included in an area (hereinafter, referred to as a nonconductive pattern area) in which the conductive pattern is not provided. The nonconductive pattern area represents an area surrounded by the conductive patterns  123   c  and excluding the conductive patterns  123   a  and  123   b  on the surface of the circuit substrate  123 . The plurality of conductive patterns  123   b  (four conductive patterns in the embodiment) is provided in the embodiment. 
         [0093]    The conductive pattern  123   c  as an earth conductive pattern is formed in a cup shape so as to face a cup shape of the case basic frame  124 . The conductive patterns  123   a  and  123   b  serves as power input or a value signal fetching as a conductive pattern for component connection. 
         [0094]    As shown in  FIGS. 17 and 18B , a surface including the areas P 1  to P 3  is covered with a resist  152  on a part of the upper surface of the conductive patterns  123   a  to  123   c  and in the nonconductive pattern area. The resist  152  is shown by hatching in  FIG. 18B  for easy description. 
         [0095]    The resist  152  as an insulating member is made of the epoxy resin, but it is not limited to the material and all insulating synthetic resins can be used. The resist  152  is formed in an even film thickness throughout an entirety thereof (i.e. an entirety including the areas P 1  to P 3 ) and has the same thickness as the conductive section  150 . In other words, the resist  152  positioned in the areas P 1  to P 3  has the same height (i.e. thickness) as the conductive sections  150  on the basis of the upper surface of the circuit substrate  123 . The thicknesses of the conductive section  150  and the resist  152  are generally set approximately to 20 μm to 40 μm. In the embodiment, the thicknesses of the conductive section  150  and the resist  152  are set to 30 μm. In the resist  152 , a notch  152   a  is formed around the conductive section  150  and the conductive section  150  is exposed. In the resist  152 , windows  152   b  are provided in a second edge  151  of the conductive pattern  123   a , edges of the conductive patterns  123   b , and a portion corresponding to a part of the conductive pattern  123   c  and thus, the portions are exposed through the window  152   b.    
         [0096]    A cup-shaped peripheral portion of the conductive pattern  123   c  is formed of an exposed portion which is not covered with the resist  152  and faces the case basic frame  124 . 
         [0097]    As shown in  FIG. 18C , a plurality of conductive patterns  123   d  and  123   e  (only one conductive pattern  123   d  is shown in  FIG. 15 ) made of the copper foil is formed on the lower surface (alternatively, also referred to as a back surface) of the circuit substrate  123 . In  FIG. 18C , the conductive patterns  123   d  and  123   e  are shown by hatching for easy description. 
         [0098]    A plurality of through-holes  123   g  is provided in the circuit substrate  123  and conductive layers not shown is formed in inner peripheries of the same through-holes  123   g . The conductive pattern  123   c  is connected to the conductive pattern  123   d  on the lower surface of the circuit substrate  123  via the conductive layers of several through-holes  123   g  out of the plurality of the same through-holes. A part of the conductive pattern  123   d  serves as an earth terminal. 
         [0099]    The conductive patterns  123   a  and  123   b  are connected to the conductive pattern  123   e  connected to a signal output terminal (not shown) or a power input terminal (not shown) on the lower surface of the circuit substrate  123  via the conductive layers of the other through-holes out of the plurality of the same through-holes. 
         [0100]    As shown in  FIG. 15  a interlayer  123   f  made of the copper foil is provided in the circuit substrate  123  and thus, the interlayer  123   f  is electrically connected to the through-hole  123   g  electrically connecting the conductive patterns  123   c  and the conductive pattern  123   d.    
         [0101]    An electric-field transistor  126  constituting an impedance converting element, as a field-effect component provided in the case  122 , is mounted on the circuit substrate  123 . The field-effect transistor  126  is electrically connected to a second edge  151  of the conductive pattern  123   a  and ends of several conductive patterns  123   b  out of the plurality of conductive patterns  123   b.    
         [0102]    The case basic frame  124  has opening portions on both upper and lower ends thereof and the conductive patterns  124   a ,  124   b , and  124   c  made of the copper foil, which are arranged in series are formed on the both upper and lower end surfaces and an external surface of a side wall as shown in  FIG. 15 . As shown in  FIGS. 16 and 19 , the conductive patterns  124   a  and  124   b  are formed in a perimeter shape in both peripheral edges of both upper and lower opening portions of the case basic frame  124 . In  FIGS. 16 and 19 , the only conductive pattern  124   a  is shown and the conductive pattern  124   b  is also formed in the same shape as the conductive pattern  124   a  shown in  FIGS. 16 and 19 . 
         [0103]    The conductive pattern  124   c  is formed on the external surface of the side wall of the case basic frame  124  by applying a conductive paste including a metal such as a copper is applied onto an inner surface of a concave portion  124   i  provided in a part other than an external surface of four corner parts C of the same case basic frame  124  or by performing metal foil plating such as copper plating on the inner surface of the concave  124   i , whereby the conductive pattern  124   c  electrically connects the conductive patterns  124   a  and  124   b  (see  FIG. 15 ). The conductive pattern  124   c  corresponds to a metallic layer. 
         [0104]    A metal plating layer may be formed on the conductive patterns  124   a  and  124   b  in a final step of forming the conductive pattern or the through-hole in the case basic frame  124 . Accordingly, since the conductive patterns  124   a  and  124   b  protrude to the surface from a through-hole filled with the resin, a clearance into which a bonding sheet  127 A are input is enlarged, thereby improving the bonding strength. When a metal plating layer is formed on the conductive patterns  124   a  and  124   b , thicknesses of the conductive patterns  124   a  and  124   b  are preferably approximately in the range of 25 μm to 40 μm. 
         [0105]    In  FIG. 19 , Q 1  represents a range of the conductive pattern  124   c  provided in the concave portion  124   i  of the case basic frame  124 . The conductive pattern  124   c  is provided in the concave portion  124   i  provided on the external surface of the side wall of the case basic frame  124 , thereby producing an electromagnetic shield. A portion in which the conductive pattern  124   c  is provided corresponds to an electromagnetic shield section. 
         [0106]    As shown in  FIG. 19 , on the external surface of the case basic frame  124 , portions  154   a  in which the conductive pattern  124   c  is not provided are provided in the corner portions C of the case basic frame  124 . The portions  154   a  in which the conductive pattern  124   c  is not provided constitute a part of a connecting section  154  described in a manufacturing method described below and external surfaces of the same portions  154   a  corresponds to a nonelectromagnetic shield section. In  FIG. 19 , Q 2  represents a range of the nonelectromagnetic shield section. As shown in  FIG. 15 , the conductive pattern  124   b  on the lower surface is connected to the conductive pattern  123   d  on the lower surface of the circuit substrate  123  via the conductive pattern  123   c  on the circuit substrate  123 . 
         [0107]    A filling portion  124   j  filled with an insulating synthetic resin such as the epoxy resin is formed in the concave portion  124   i  (see  FIG. 15 ). The insulating synthetic resin such as the epoxy resin corresponds to a filler and a resin filler. 
         [0108]    In the case basic frame  124 , substantially rectangular cup-shaped bonding areas SRa and SRb are formed of both upper and lower surfaces of the portions  154   a  in which both upper and lower surfaces of the filling section  124   j  and the conductive pattern  124  are not provided. In  FIG. 19 , the only bonding portion SRa provided on the upper surface of the case basic frame  124  is shown. The bonding areas are not limited to a rectangular cup shape, but the bonding areas may have other shapes. Consequently, the bonding areas may have shapes similar to the cup shape of the case basic frame  124 . 
         [0109]    As shown in  FIGS. 15 and 16 , a peripheral edge of an opening portion in a lower part of the case basic frame  124 , i.e., the bonding area SRb is integrally bonded and fixed to the circuit substrate  123  by the bonding sheet  127 A as a rectangular perimeter-shaped adhesive agent disposed outside the conductive pattern  123   c . The bonding sheet  127 A is made of the same material as the resin filler used in the filling section  124   j . Electric components of the field-effect transistor  126  on the circuit substrate  123  is housed and disposed in the case basic frame  124 . 
         [0110]    The material of the bonding sheet  127 A may have the same configuration as a resin material part used in a substrate of the case basic frame  124  of the bonding sheet  127 A. Accordingly, assuming that the bonding sheet  127 A, the circuit substrate  123 , and the top substrate  125  have the same material as the resin material part, they can obtain the same advantage as the resin material part. 
         [0111]    As shown in  FIG. 15 , conductive patterns  125   a  and  125   b  made of the copper foil are formed on both upper and lower surfaces of the top substrate  125 . A sound hole  128  for taking in sound from an outside is formed in the top substrate  125 . 
         [0112]    As shown in  FIGS. 15 and 16 , a peripheral edge of an opening portion in an upper part of the case basic frame  124 , i.e., the bonding area SRa is integrally bonded and fixed to the top substrate  125  by the bonding sheet  127 B as a rectangular perimeter-shaped adhesive agent disposed outside the conductive pattern  124   a . The bonding sheet  127 B is made of the same material as the resin filler used in the filling section  124   j . The peripheral edge of the opening portion in the upper part of the case basic frame  124  is integrally connected to the top substrate  125  via a spacer  129  and a vibrating membrane  130 . 
         [0113]    As shown in  FIGS. 15 and 16 , the perimeter-shaped spacer  129  formed of an insulating film is interposed and fixed between the case basic frame  124  and the top substrate  125 . The spacer  129  is bonded to the conductive pattern  124   a  by the conductive adhesive agent. The vibrating membrane  130  formed of a synthetic resin thin film having insulation property such as a PPS (polyphenylene sulfide) film is tightly provided by bonding on an upper surface of the spacer  129  and a conductive layer  130   a  formed by gold deposition is formed on a lower surface of the vibrating membrane  130 . 
         [0114]    Through-holes not shown are provided in the vibrating membrane  130  and the spacer  129  and the conductive layer  130   a  can be conducted to the conductive pattern  124   a  via the conductive paste filled in the same through-holes and a conductive adhesive agent (not shown) between the spacer  129  and the case basic frame  124  (exactly, the spacer  129  and the conductive pattern  124   a ). 
         [0115]    As shown in  FIG. 15 , a plurality of through-holes  136  is formed in the top substrate  125  and a conductive pattern  125   c  arranged in series with the conductive patterns  125   a  and  125   b  is provided on inner peripheral surfaces of the through holes  136 . A conductive adhesive agent  137   a  is filled in the through-holes  136  and a conductive section  137  is formed of the conductive adhesive agent  137   a  and the conductive pattern  125   c . The conductive section  137  is electrically connected to the conductive layer  130   a  of a folding-back portion  130   b  (see  FIG. 15 ) formed by folding back the lower surface of the vibrating membrane  130 . Even though the conductive adhesive agent  137   a  is not filed in the through-holes  136 , the conductive pattern  125   c  may be formed and when the conductive pattern  125   c  is not formed in the through-holes  136 , the conductive adhesive agent  137   a  may be filled therein. Both the conductive pattern  125   c  and the conductive adhesive agent  137   a  are formed, thereby improving conductivity and shield property. 
         [0116]    A conductive path from the conductive patterns  125   a  and  125   b  of the top substrate  125  reaching the earth terminal on the circuit substrate  123  is formed through the conductive section  137 , the conductive layer  130   a , the conductive pastes of the through-holes not shown provided in the vibrating membrane  130 , the conductive adhesive agent between the spacer  129  and the conductive pattern  124   a , and the conductive patterns  124   a  to  124   c  on the case basic frame  124  is formed. 
         [0117]    In the case basic frame  124 , the back plate  131  as a polar plate is opposed to the lower surface of the vibrating membrane  130  with the spacer  129  interposed therebetween. In the back plate  131 , a film  131   b  such as PTFE (polytetrafluorethylene) is bonded and fixed to an upper surface of a back plate body  131   a  formed of stainless steel. The polarization treatment is performed on the film  131   b  by the corona discharge and the film  131   b  constitutes the electret layer by the polarization treatment. In the embodiment, since the back plate  131  constitutes the back electrode, the condenser microphone of the embodiment is the back electret type. 
         [0118]    The back plate  131  is formed in a substantially elliptic shape in a plan view, which has an outer peripheral shape smaller than an inner peripheral shape of the case basic frame  124 . A clearance P is formed between the inner and outer peripheral surfaces. A through-hole  132  for allowing the air transfer by vibration of the vibrating membrane  130  is formed in a central part of the back plate  131 . The back plate  131  is formed by punching a stainless steel plate material to which the film  131   b  is bonded from the film  131   b , i.e., an upper side of  FIG. 16  to a lower side by a punching blade (not shown). 
         [0119]    As shown in  FIGS. 15 and 16 , in the case basic frame  124 , a holding member  133  formed of a plate spring material is interposed between the back plate  131  and the circuit substrate  123  in a compression state. The back plate  131  is compressed in a direction abutting lower surfaces of the spacers  129  from an opposite side of the vibrating membrane  130  by a resilient force of the holding member  133 . Accordingly, a predetermined clearance is held between the vibrating membrane  130  and the back plate  131  and a condenser section having a predetermined capacity is formed therebetween. 
         [0120]    The holding member  133  is formed by punching and molding a plate material formed by gold-plating both front and back surfaces of the stainless steel plate. The holding member  133  has a substantially perimeter-shaped frame portion  133   a  and four legs portions  133   b  protruding toward both lower sides on four corners of the frame portion  133   a . Accordingly, a space S is formed between the leg portions  133   b  in a lower side of the frame portion  133   a . In the embodiment, as shown in  FIG. 15 , the field-effect transistor  126  on the circuit substrate  123  is disposed between a pair of leg portions  133   b  in the space S. 
         [0121]    Four sphere-shaped contact portions  134  as a protruding portion, which abut a lower surface of the back plate  131  protrude on an upper surface of the frame portion  133   a  of the holding member  133  and four sphere-shaped contact portions  135  as the protruding portion protrude on a front lower surface of each of the leg portions  133   b.    
         [0122]    One leg portion  133   b  selected from a plurality of leg portions  133   b  is contacted to the conductive section  150  via the contact portion  135  and the other leg portions  133   b  is contacted to the upper surface of the resist  152  positioned in the areas P 1  to P 3  included in the nonconductive pattern area via the contact portion  135  on the upper surface of the circuit substrate  123 . 
         [0123]    However, in the condenser microphone  121 , when a sound wave from a sound source reaches the vibrating membrane  130  through the sound hole  128  of the top substrate  125 , the vibrating membrane  130  vibrates depending on a frequency, an amplitude, and a waveform of the sound. A gap between the vibrating membrane  130  and the back plate  131  is varied from a set value with vibration of the vibrating membrane  130  and thus, an impedance of the condenser is varied. The variation of the impedance is converted into a voltage signal by the impedance converting element. 
         [0124]    The condenser microphone according to the embodiment has the bonding areas SRa and SRb on front and back surfaces of the case basic frame  124  and the top substrate  125  and the circuit substrate  123  mounted with the electric components are bonded to all bonding areas SRa and SRb on the front and back surfaces of the case basic frame  124  with the adhesive agent without using the metallic layer. As the result, the bonding performances between an insulating substrate Kc (the core material) of the case basic frame  124  and the circuit substrate  123  and between the insulating substrate Kc (the core material) of the case basic frame  124  and the top substrate  125  are improved. 
         [0125]    Since the both upper and lower surfaces of the filling section  124   j  positioned in the bonding areas SRa and SRb, the top substrate  125 , the circuit substrate  123 , and the filling section  124   j  are made of the same material as the adhesive agent, the bonding performance is not damaged. 
         [0126]    The present embodiment may be realized by the following modification. 
         [0127]    In the embodiment, the back plate body  131   a  is formed of the stainless steel, but it may be formed of a brass plate or a titanium plate. 
         [0128]    Further, the invention may be realized in a method of manufacturing the foil electret-type condenser microphone in which the vibrating membrane  130  is formed of an electret polymer film. 
         [0129]    Further, the invention may be realized in a method of manufacturing a charge pump-type condenser microphone having a booster circuit. When the microphone is configured as above, the vibrating membrane  130  is changed into the electret layer and electrodes opposed to each other are provided in the vibrating membrane  130  and the back plate  131 . 
         [0130]    In the embodiment, an electret condenser microphone of a back electret type is described, but the invention may be applied to an electret condenser microphone of a front electret type. 
         [0131]    The impedance converting element mounted on the circuit substrate  123  of the embodiment is exemplified. As long as it is a known impedance converting element, any impedance converting element in which variation of an electrostatic capacitance can be detected employs any one of analog and digital operating modes may be used.