JP4477466B2 - Electret condenser microphone - Google Patents

Description

  The present invention relates to an electret condenser microphone, and more particularly to a configuration of a conductive member that electrically connects a conductive layer formed on the surface of a circuit board and a back electrode plate.

  In general, an electret condenser microphone includes a capacitor structure portion in which a diaphragm and a back electrode plate are arranged to face each other, an impedance conversion element that converts an impedance of the capacitor structure portion into an electrical impedance, and an impedance conversion element. A circuit board to be mounted and a conductive member electrically connecting the conductive layer formed on the surface of the circuit board and the back electrode plate are housed in a cylindrical metal case.

  In many electret condenser microphones, as described in, for example, “Patent Document 1”, the back electrode plate and the circuit board are arranged to face each other substantially in parallel. The conductive member elastically presses the back electrode plate. As a result, conduction between the back electrode plate and the conductive layer is achieved without impairing the assembly of the electret condenser microphone.

  At that time, in the electret condenser microphone described in the above-mentioned “Patent Document 1”, a coil spring disposed so as to contact the outer peripheral edge of the back electrode plate is used as the conductive member. The plate can be supported stably.

JP 2003-199196 A

  However, in the electret condenser microphone described in the above-mentioned “Patent Document 1”, the coil spring constituting the conductive member is disposed at a position close to the outer peripheral wall of the metal case. There is a problem that stray capacitance (that is, unnecessary capacitance other than the capacitance charged in the capacitor structure portion) is generated, and this reduces the sensitivity of the electret condenser microphone.

  The present invention has been made in view of such circumstances, and has a configuration in which the back electrode plate can be stably supported by the conductive member, and sensitivity reduction due to the generation of stray capacitance is reduced. An object of the present invention is to provide an electret condenser microphone that can be minimized.

  The present invention is intended to achieve the above object by devising the configuration of the conductive member.

That is, the electret condenser microphone according to the present invention is
Capacitor structure part in which a diaphragm and a back electrode plate stretched and fixed to a support ring are arranged opposite to each other, an impedance conversion element for converting the capacitance of the capacitor structure part into electrical impedance, and the impedance conversion element A circuit board on which the circuit board is mounted, a conductive member that electrically connects the conductive layer formed on the surface of the circuit board and the back electrode plate, and a cylindrical structure that houses the capacitor structure, the circuit board, and the conductive member In an electret condenser microphone comprising a metal case,
The back electrode plate and the circuit board are arranged opposite to each other substantially in parallel,
The conductive member is disposed so as to elastically press the back electrode plate between the back electrode plate and the circuit board,
The conductive member is formed so as to concentrically surround a central protruding portion whose tip is in contact with the conductive layer at a substantially central position of the rear electrode plate, and a proximal end portion of the central protruding portion. and the outer annular portion at the outer peripheral edge portion in contact of, Ri Do and a plurality of resilient arm portions connecting the the outer peripheral annular portion and the central projecting portion,
The abutment of the outer peripheral annular portion of the back electrode plate of the conductive member, the support ring that has been done in the depressible position perpendicularly from the circuit board side, it is characterized in.

  The electret condenser microphone according to the present invention may be a foil electret type electret condenser microphone in which an electret layer is formed on a vibrating membrane, or a back electret type electret condenser microphone in which an electret layer is formed on a back electrode plate. There may be.

  The “impedance conversion element” is not limited to a specific element as long as it is capable of converting the change in capacitance of the capacitor structure portion into electric impedance. For example, a junction-type or MOS-type electric field is used. An effect transistor or the like can be used.

  The “conductive member” may be one in which the central projecting portion, the outer peripheral annular portion, and the plurality of elastic arm portions are integrally formed, or a part thereof is formed separately. Also good.

  The specific shape and size of the “center protrusion” is not particularly limited as long as the tip is configured to contact the conductive layer at the approximate center position of the back electrode plate. is not.

  The “circumferential annular portion” is not necessarily required to be formed in an annular shape as long as it is configured to be in contact with the outer peripheral edge portion of the back electrode plate. It may be formed in an annular shape or a rectangular annular shape.

  Each of the “elastic arm portions” is formed so as to connect the outer peripheral annular portion and the central projecting portion, and can be elastically deformed. There are no particular restrictions on the arrangement, number, etc.

  As shown in the above configuration, in the electret condenser microphone according to the present invention, the conductive member that electrically connects the conductive layer formed on the surface of the circuit board and the back electrode plate is provided between the back electrode plate and the circuit board. The conductive member is arranged so as to elastically press the back electrode plate between the central projection part where the tip end abuts the conductive layer at the approximate center position of the back electrode plate, and the central projection part. It is formed so as to surround the base end concentrically, and comprises an outer peripheral annular portion that contacts the outer peripheral edge of the back electrode plate, and a plurality of elastic arm portions that connect the outer peripheral annular portion and the central protrusion. Therefore, the following effects can be obtained.

  That is, since the conductive member comes into contact with the outer peripheral edge of the back electrode plate at the outer peripheral annular portion, the back electrode plate can be stably supported by the conductive member.

  Further, since the central protrusion and the plurality of elastic arm portions other than the outer peripheral annular portion in the conductive member are disposed at positions sufficiently away from the outer peripheral wall of the metal case, the conductive member is close to the metal case. It is possible to minimize the ratio of the portions arranged at the positions. As a result, the electret condenser microphone can be configured such that stray capacitance is unlikely to occur between the conductive member and the metal case, and the sensitivity reduction can be minimized.

  As described above, according to the present invention, the back electrode plate can be stably supported by the conductive member, and the sensitivity reduction of the electret condenser microphone due to the generation of stray capacitance can be minimized. Can do.

  Moreover, in the electret condenser microphone according to the present invention, since an annular space can be secured around the central protrusion of the conductive member, the degree of freedom in layout of impedance conversion elements and other electronic components mounted on the circuit board is increased. Can be increased.

  In the above configuration, if each elastic arm portion of the conductive member is formed so as to extend in a substantially spiral shape with the central projection portion as the center, the spring constant can be set to a small value, so that the outer circumference with respect to the back electrode plate The pressing force of the annular portion can be suppressed to a relatively small value, and the pressing force can be distributed substantially uniformly over the entire circumference. As a result, the back electrode plate can be more stably supported by the conductive member, and the electret layer of the back electrode plate can be prevented from being accidentally crushed. Therefore, it is possible to prevent the sensitivity characteristic from being changed due to the deformation of the electret layer.

  In the above configuration, the specific shape of the central protrusion is not particularly limited, as described above. However, if this is formed in a cup shape, contact with the conductive layer at the tip thereof over a relatively wide range. Since it can be performed, conduction between the conductive member and the conductive layer can be surely performed, thereby making it difficult to generate noise.

  Further, by forming the central protrusion in a cup shape in this way, the conductive member can be integrally formed as a press-worked product of a metal plate. Then, the conductive member can be manufactured at a low cost by integrally forming the conductive member as a pressed product of a metal plate.

  In the above configuration, if the conductive layer has a ring portion formed at a position facing the tip portion of the central protrusion, the following operational effects can be obtained.

  That is, if the area of the conductive layer is increased, the conductive layer and the tip of the central protrusion can be contacted over a relatively wide range, but the conductive layer and the back surface of the circuit board are electrically connected to the outside. A stray capacitance is generated between the conductive layer formed as an electrode or the like. Therefore, if the conductive layer has an annular portion formed at a position facing the tip of the central protrusion, the conductive layer is not unnecessarily large, and the conductive layer The contact with the tip of the central protrusion can be performed over a relatively wide range. This makes it possible to reliably conduct the conductive member and the conductive layer while effectively suppressing the generation of stray capacitance.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a side sectional view showing an electret condenser microphone 10 according to one embodiment of the present invention in an upwardly arranged state, and FIG. 2 is a sectional view taken along the line II-II in FIG.

  As shown in these drawings, the electret condenser microphone 10 is a small microphone having an outer diameter of about 4 mm. In the cylindrical metal case 12, a diaphragm subassembly 14, a spacer 16, a back electrode plate 18, The conductive member 20, the insulating bush 22 and the circuit board 24 are accommodated.

  The metal case 12 is formed in a cylindrical shape by pressing a metal plate (for example, an aluminum plate). The metal case 12 has a sound hole 12a formed at the center of the upper end wall thereof, and is caulked and fixed to the circuit board 24 at the open lower end portion 12b of the outer peripheral wall thereof.

  The diaphragm subassembly 14 has a circular diaphragm 26 stretched and fixed to the lower surface of a metal support ring 28, and the outer diameter thereof is set to be substantially the same as the inner diameter of the metal case 12. The vibration film 26 has a metal vapor deposition film formed on the upper surface of a polymer film having a thickness of about 1.5 μm.

  The spacer 16 is formed of a metal thin plate ring having an outer diameter substantially the same as the inner diameter of the metal case 12, and the thickness thereof is set to about 25 μm.

  The back electrode plate 18 includes an electrode plate main body 18A and an electret layer 18B disposed on the upper surface of the electrode plate main body 18A, and a through hole 18a is formed at the center thereof. At that time, the electrode plate body 18A is made of a metal plate having a thickness of about 0.15 mm, and has an outer diameter that is substantially the same as the inner diameter of the insulating bush 22. The electret layer 18B is generated by subjecting an insulating film formed on the upper surface of the electrode plate main body 18A to a thickness of about 12.5 μm with a predetermined charging voltage, whereby a predetermined surface potential is obtained. Is granted.

  In the metal case 12, the electret layer 18 </ b> B and the vibration film 26 are arranged to face each other with a predetermined minute interval through the spacer 16, thereby constituting the capacitor structure portion C. .

  The insulating bush 22 is a cylindrical insulating member having an outer diameter substantially the same as the inner diameter of the metal case 12, and an upper end surface thereof is in contact with the spacer 16 and a lower end surface thereof is in contact with the circuit board 24. The back electrode plate 18 and the conductive member 20 are arranged on the inner peripheral side of the insulating bush 22. At that time, the back electrode plate 18 is elastically pressed toward the spacer 16 by the conductive member 20 as described later.

  The circuit board 24 has an outer diameter that is substantially the same as the inner diameter of the metal case 12, and is arranged in parallel with the back electrode plate 18. On the upper surface of the circuit board 24, an impedance conversion element 34 and three capacitors 36, 38, and 40 are mounted.

  3 and 4 are a plan view and a bottom view showing the circuit board 24.

  As shown in these drawings, the circuit board 24 includes a substrate body 42, four conductive layers 44A, 44B, 44C, 44D formed in a predetermined pattern on the upper surface of the substrate body 42, and the substrate body 42. Three conductive layers 44E, 44F, 44G formed as conductive electrodes to the outside on the lower surface of the substrate, and the conductive layers 44A, 44B, 44C, 44D partially exposed on the upper surface of the substrate body 42 The insulating layer 46 is formed so as to cover them.

  At that time, the conductive layers 44A, 44B, and 44C are electrically connected to the conductive layers 44E, 44F, and 44G through the through-hole portions 44a, 44b, and 44c, respectively. The conductive layer 44D has an annular portion 44d formed in an annular shape at the center of the circuit board 24, and is electrically connected to the conductive member 20 in the annular portion 44d.

  The impedance conversion element 34 is a field effect transistor that includes a power supply terminal 34a, an output terminal 34b, a ground terminal 34c, and a gate terminal 34d, and each of the terminals 34a, 34b, 34c, and 34d includes the conductive layers 46A, 46B, The conduction is fixed to 46C and 46D by soldering. Further, each of the capacitors 36, 38, 40 is conductively fixed to the conductive layers 44B, 44C by soldering.

  FIG. 5 is a perspective view showing the conductive member 20 as a single item.

  As shown in the figure, the conductive member 20 includes a central projection 20A formed in a cup shape, and an outer peripheral annular portion 20B that concentrically surrounds the base end portion (that is, the upper end portion) of the central projection 20A. The outer peripheral annular portion 20B and the central projecting portion 20A are composed of three elastic arm portions 20C. At that time, the outer peripheral annular portion 20B is formed in an annular shape, and the three elastic arm portions 20C are formed on the same plane at a position one step lower than the outer peripheral annular portion 20B.

  The conductive member 20 has a central protrusion 20A, an outer peripheral annular portion 20B, and three elastic arm portions 20C as a pressed product of a metal plate having a spring property (for example, a phosphor bronze plate having a thickness of about 60 to 70 μm). It is integrally formed. The outer diameter of the conductive member 20 is set to substantially the same value as the inner diameter of the insulating bush 22, and the height of the conductive member 20 is the distance between the lower surface of the back electrode plate 18 and the upper surface of the circuit board 24. It is set to a value slightly larger than.

  The conductive member 20 is disposed between the back electrode plate 18 and the circuit board 24, and the front end portion (that is, the lower end portion) 20 a of the central protrusion 20 A is formed in a ring shape of the conductive layer 44 D of the circuit board 24. The outer peripheral annular portion 20B is in contact with the outer peripheral edge portion of the electrode plate main body 18A of the back electrode plate 18, and the three elastic arm portions 20C are bent and deformed so that the back electrode plate 18 is deformed. It is designed to be elastically pressed.

  At this time, since the tip 20a of the central protrusion 20 is formed in a flat shape, the contact between the tip 20a and the annular portion 44d of the conductive layer 44D is an annular surface along the annular portion 44d. It is done by contact.

  Each elastic arm portion 20C is formed so as to extend in a substantially spiral shape with the central protrusion 20A as the center. Thus, each elastic arm portion 20C is formed as long as possible, and its spring constant is set to a sufficiently small value. These elastic arm portions 20C are formed in the same shape at equal intervals in the circumferential direction.

  These three elastic arm portions 20C are formed by punching substantially L-shaped long holes 20b at three locations when a metal plate is pressed. The width of each of the long holes 20b is set to a value smaller than the outer diameter of the distal end portion 20a of the central protrusion 20A, whereby the center of the conductive member 20 is between the plurality of manufactured conductive members 20. The protruding portion 20 </ b> A is prevented from entering the long hole 20 b of the other conductive member 20.

  As described in detail above, the electret condenser microphone 10 according to the present embodiment includes the conductive member 20 that electrically connects the conductive layer 44D formed on the top surface of the circuit board 24 and the back electrode plate 18 with the back electrode. The conductive member 20 is disposed between the plate 18 and the circuit board 24 so as to elastically press the back electrode plate 18, but the conductive member 20 has a conductive layer 44 </ b> D having a tip 20 a at a substantially central position of the back electrode plate 18. A central projecting portion 20A that contacts the outer peripheral annular portion 20B, a peripheral annular portion 20B that is formed so as to concentrically surround the base end portion of the central projecting portion 20A, and that contacts the outer peripheral edge of the back electrode plate 18; Since the three elastic arm portions 20C for connecting the central projection portion 20A and the central projection portion 20A, the following operational effects can be obtained.

  That is, since the conductive member 20 comes into contact with the outer peripheral edge portion of the back electrode plate 18 at the outer peripheral annular portion 20B, the back electrode plate 18 can be stably supported by the conductive member 20. it can.

  In addition, the central protrusion 20A other than the outer peripheral annular portion 20B and the three elastic arm portions 20C in the conductive member 20 are arranged at positions sufficiently away from the outer peripheral wall of the metal case 12, so that the conductive member The ratio of the part arrange | positioned in the position close | similar to the metal case 12 in 20 can be suppressed to the minimum. As a result, the electret condenser microphone 10 can be configured such that stray capacitance is unlikely to occur between the conductive member 20 and the metal case 12, and the sensitivity reduction can be minimized.

  As described above, according to the present embodiment, the back electrode plate 18 can be stably supported by the conductive member 20, and the sensitivity reduction of the electret condenser microphone 10 due to the generation of stray capacitance is minimized. To the limit.

  Moreover, in the electret condenser microphone 10 according to the present embodiment, since an annular space can be secured around the central protrusion 20A of the conductive member 20, the impedance conversion element 34 and the three capacitors mounted on the circuit board 24 can be secured. The layout freedom of 36, 38, and 40 can be increased.

  In particular, in the present embodiment, each elastic arm portion 20C of the conductive member 20 is formed so as to extend in a substantially spiral shape with the central protrusion portion 20A as the center, so that the spring constant can be set to a small value. Thus, the pressing force of the outer peripheral annular portion 20B against the back electrode plate 18 can be suppressed to a relatively small value, and the pressing force can be distributed substantially uniformly over the entire circumference. As a result, the back electrode plate 18 can be supported more stably by the conductive member 20, and the electret layer 18B of the back electrode plate 18 can be prevented from being accidentally crushed. . Therefore, it is possible to prevent the sensitivity characteristic from being changed due to the deformation of the electret layer 18B.

  Further, in the present embodiment, since the central protrusion 20A of the conductive member 20 is formed in a cup shape, the tip 20a can be in contact with the conductive layer 44D over a relatively wide range, thereby Conduction between the conductive member 20 and the conductive layer 44D can be reliably performed. This makes it difficult to generate noise.

  In addition, since the central protrusion 20A is formed in a cup shape in this way, the conductive member 20 can be integrally formed as a pressed product of a metal plate as in this embodiment. Then, the conductive member 20 can be manufactured at low cost by integrally forming the conductive member 20 as a pressed product of a metal plate.

  Further, in the present embodiment, since the conductive layer 44D has the annular portion 44d formed at a position facing the tip portion 20a of the central protrusion 20A, the area of the conductive layer 44D does not become unnecessarily large. In addition, the contact between the conductive layer 44D and the tip 20a of the central protrusion 20A can be performed over a relatively wide range. As a result, the conductive member 20 and the conductive layer 44D can be reliably connected to each other while the generation of stray capacitance is effectively suppressed.

  In the electret condenser microphone 10 according to the present embodiment, since the conductive member 20 has no protrusions or notches, it is possible to prevent the plurality of conductive members 20 from being entangled with each other in the manufacturing process. be able to. The conductive member 20 has a central protrusion 20A and three long holes 20b. The width of each long hole 20b is set to a value smaller than the outer diameter of the tip 20a of the central protrusion 20A. Therefore, the central protrusion 20A of the conductive member 20 can be prevented from entering the long hole 20b of the other conductive member 20 in advance.

  In the above-described embodiment, the conductive member 20 has been described as including three elastic arm portions 20C. However, it is of course possible to have two or four or more elastic arm portions 20C.

  Next, a modification of the above embodiment will be described.

  FIG. 6 is a side sectional view showing an electret condenser microphone 110 according to this modification.

  As shown in the figure, the electret condenser microphone 110 has the same basic configuration as the electret condenser microphone 10 according to the above embodiment, but the configuration of the conductive member 120 is different from that in the above embodiment. Yes.

  That is, while the conductive member 20 of the above embodiment is integrally formed as a pressed product of a metal plate, a part of the conductive member 120 of this modification is configured as a separate member.

  Specifically, the conductive member 120 has an outer peripheral annular portion 120B and three elastic arm portions 120C configured as a pressed product of a metal plate, but the central protrusion 120A is a separate member as a metal column. It is configured. In the conductive member 120, the central protrusion 120 A is inserted into the through hole 120 b formed in the central portion of the three elastic arm portions 120 C, and the central protrusion 120 A is caulked in the central portion. It is fixed.

  The central projection 120A is formed in a columnar shape, and the tip 120a is configured as a circular plane. The contact between the front end portion 20a of the central protrusion 120A and the annular portion 44d of the conductive layer 44D is performed by annular surface contact along the annular portion 44d.

  Even in the case of adopting the configuration of this modified example, as in the case of the above-described embodiment, the back electrode plate 18 can be stably supported by the conductive member 120, and the stray capacitance is generated. The decrease in sensitivity of the electret condenser microphone 110 to be performed can be minimized.

  In addition, the conductive member 120 of the present modification example includes the central protrusion 120A, the outer peripheral annular portion 120B, and the three elastic arm portions 120C, which are separate members. In addition, it is possible to eliminate the need to form the central protrusion 20A in a cup shape by deep drawing, and thus the conductive member 120 can be easily manufactured.

  In the present modification, the upper end 120c of the central protrusion 120A has been described as being caulked and fixed to the center of the three elastic arm portions 120C while being inserted into the through hole 120b. It is also possible to adopt the fixed structure. For example, the conductive member 120 may be configured by joining the central protruding portion 120A to the central portion of the three elastic arm portions 120C by welding or brazing, or the central protruding portion 120A may be formed by a screw member. The conductive member 120 may be configured by configuring and screwing it into the through hole 120b.

The sectional side view shown in the state where the electret condenser microphone concerning one embodiment of the invention of this application was arranged upwards II-II sectional view of Fig. 1 The top view which shows the circuit board of the said electret condenser microphone Bottom view showing the circuit board The perspective view which shows the electrically-conductive member of the said electret condenser microphone by a single item The figure similar to FIG. 1 which shows the modification of the said embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,110 Electret condenser microphone 12 Metal case 12a Sound hole 12b Opening lower end part 14 Vibration membrane subassembly 16 Spacer 18 Back electrode plate 18A Electrode plate main body 18B Electret layer 18a Through-hole 20, 120 Conductive member 20A, 120A Central protrusion part 20B, 120B Outer peripheral annular portion 20C, 120C Elastic arm portion 20a, 120a Tip portion 20b Long hole 22 Insulating bush 24 Circuit board 26 Vibration film 28 Support ring 34 Impedance conversion element 34a Power supply terminal 34b Output terminal 34c Earth terminal 34d Gate terminals 36, 38, 40 Capacitor 42 Substrate body 44A, 44B, 44C, 44D, 44E, 44F, 44G Conductive layer 44a, 44b, 44c Through-hole portion 44d Annular portion 46 Insulating layer 120b Hole 120c upper part C Capacitor structure

Claims (5)

Capacitor structure part in which a diaphragm and a back electrode plate stretched and fixed to a support ring are arranged opposite to each other, an impedance conversion element for converting the capacitance of the capacitor structure part into electrical impedance, and the impedance conversion element A circuit board on which the circuit board is mounted, a conductive member that electrically connects the conductive layer formed on the surface of the circuit board and the back electrode plate, and a cylindrical structure that houses the capacitor structure, the circuit board, and the conductive member In an electret condenser microphone comprising a metal case,
The back electrode plate and the circuit board are arranged opposite to each other substantially in parallel,
The conductive member is disposed so as to elastically press the back electrode plate between the back electrode plate and the circuit board,
The conductive member is formed so as to concentrically surround a central protruding portion whose tip is in contact with the conductive layer at a substantially central position of the rear electrode plate, and a proximal end portion of the central protruding portion. and the outer annular portion at the outer peripheral edge portion in contact of, Ri Do and a plurality of resilient arm portions connecting the the outer peripheral annular portion and the central projecting portion,
Abutment against the outer peripheral annular portion of the back electrode plate of the conductive member, the support ring that has been done in the depressible position perpendicularly from the circuit board side, an electret condenser microphone, characterized in that.   2. The electret condenser microphone according to claim 1, wherein each of the elastic arm portions is formed so as to extend in a substantially spiral shape with the central projection portion as a center.   The electret condenser microphone according to claim 1, wherein the central projection is formed in a cup shape.   4. The electret condenser microphone according to claim 3, wherein the conductive member is integrally formed as a pressed product of a metal plate.   The electret condenser microphone according to any one of claims 1 to 4, wherein the conductive layer has an annular portion formed at a position facing a tip portion of the central protrusion.

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