JP4040328B2 - Electret condenser microphone - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electret condenser microphone, and more particularly to a configuration that enables surface mounting and supplies a microphone having stable characteristics against electromagnetic noise.
[0002]
[Prior art]
In general, an electret condenser microphone includes an electret condenser unit in which a diaphragm and a back electrode plate are arranged to face each other, an impedance conversion element that converts a change in capacitance of the electret condenser unit into an electrical impedance, and the impedance conversion element. The substrate to be mounted is housed in a cylindrical metal case in a state where the back surface of the substrate can be seen from the outside of the microphone.
[0003]
In this electret condenser microphone, since a plurality of terminal members that are electrically connected to the impedance conversion element are provided so as to protrude in a pin shape from the board, the electret condenser microphone is provided on an external board (for example, a printed board of a mobile phone). It is structurally difficult to mount on the surface.
[0004]
For this reason, when the electret condenser microphone is surface-mounted on an external substrate, for example, as described in JP-A-8-237797, the electret condenser microphone is mounted on a holder having a contact piece for surface mounting, A device for performing surface mounting on an external substrate through this holder has been devised.
[0005]
[Problems to be solved by the invention]
However, in the above conventional electret condenser microphone, since it is necessary to interpose a holder when surface-mounting the external electret condenser microphone on the external substrate, extra parts are required, and the total thickness when surface-mounting is performed. Becomes considerably large, and also becomes unstable in terms of electromagnetic noise.
[0006]
The present invention has been made in view of such circumstances, and is an electret condenser microphone that can be surface-mounted on an external substrate with a small number of parts and reduced in thickness, and further has excellent electromagnetic noise characteristics. Is intended to provide.
[0007]
[Means for Solving the Problems]
In the present invention, the above-described object is achieved by adopting a new configuration of a conventional substrate and terminal member.
[0008]
That is, the electret condenser microphone according to the present invention is
An electret capacitor unit in which a diaphragm and a back electrode plate are arranged to face each other, an impedance conversion element that converts the capacitance of the electret capacitor unit into an electrical impedance, and a case that houses the electret capacitor unit and the impedance conversion element In an electret condenser microphone comprising:
Part of the case is configured as a base member made of synthetic resin,
The base member is opened upward, and at least an electret capacitor portion and an impedance conversion element are mounted in the base member,
A conductive shielding member is provided on the outer surface of the base member.
[0009]
The shield member is constituted by a metal shield plate.
[0010]
Further, the electret capacitor portion is covered with a cylindrical metal cover.
[0011]
Further, the base portion is configured as a synthetic resin base member in which a part of the case is integrally formed with a plurality of terminal members by insert molding, and the shield plate includes a specific terminal member. It is characterized by being conductive.
[0012]
The “electret condenser microphone” may be a foil electret type electret condenser microphone in which the function of the electret is imparted to the vibrating membrane, or a back electret type electret condenser microphone in which the function of the electret is imparted to the back electrode plate. It may be.
In addition, the “electret condenser microphone” may have a configuration in which only the impedance conversion element is accommodated in the case as an electronic component, or other electronic components such as a capacitor are accommodated in addition to the impedance conversion element. It may be a configuration.
The “impedance conversion element” is not limited to a specific element as long as it can convert the change in the capacitance of the capacitor portion into an electrical impedance, and an FET or the like can be employed, for example.
Regarding the portions other than the “base member” in the “case”, the specific configuration such as the material and shape thereof is not particularly limited.
[0013]
[Effects of the invention]
As shown in the above configuration, in the electret condenser microphone according to the present invention, a part of the case that accommodates the electret condenser portion and the impedance conversion element is configured as a synthetic resin base member, and the outer surface of the base member With the configuration in which the conductive shield member is provided, the electret condenser portion can be electromagnetically shielded, and a microphone having excellent noise resistance can be realized.
[0014]
Further, the shield plate is configured such that a part of the case that accommodates the electret capacitor portion and the impedance conversion element has a metal shield plate mounted on the outer surface of the base member that is configured as a base member made of synthetic resin. Radiant heat is reflected, and the heat conduction to the inside of the electret condenser microphone is lowered by the synthetic resin base member, so that the heat resistance is improved. This makes it possible to directly mount the electret condenser microphone on the external substrate without interposing a holder as in the prior art.
Therefore, according to the present invention, the electret condenser microphone can be surface-mounted on the external substrate with a small number of parts and reduced thickness.
[0015]
Furthermore, since the electret capacitor part inside is covered with a cylindrical metal cover, it is possible to electromagnetically shield the electret capacitor part in combination with a metal shield plate, and it is also resistant to noise. An excellent microphone can be realized.
[0016]
Furthermore, since the shield plate is electrically connected to a specific terminal member (especially a ground terminal) of a synthetic resin base member formed integrally with a plurality of terminal members by insert molding, noise can be released to the outside. As a result, the shielding performance can be improved.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0018]
FIG. 1 is a side cross-sectional view showing an electret condenser microphone according to an embodiment of the present invention in an upwardly arranged state. 2A is a view taken in the direction of arrow IIa in FIG. 1, and FIG. 2B is a view taken in the direction of arrow IIb in FIG. Further, FIG. 3 is an exploded side sectional view showing the electret condenser microphone.
[0019]
As shown in these drawings, the electret condenser microphone 10 according to the present embodiment is a small microphone having a substantially square outer shape with a side of about 4.5 mm in a plan view and a height of about 1.8 mm. An electret capacitor unit 14, FET 16 (impedance conversion element), two capacitors 18 and 20, a coil spring 22, and a contact frame 24 are accommodated therein.
[0020]
The electret capacitor unit 14 includes a vibrating diaphragm subassembly 34, an insulating ring 36, a spacer 38, a back electrode plate 40, and an insulating bush 42 in a short cylindrical metal cover 32 extending in the vertical direction. ing.
[0021]
The metal cover 32 has a sound hole 32 a formed in the upper end wall thereof, and an open lower end portion 32 b thereof is fixed to the insulating bush 42 by caulking.
In the diaphragm sub-assembly 34, the diaphragm 34A is stretched and fixed to the lower surface of the diaphragm support ring 34B. The vibration film 34A is formed by forming a metal vapor deposition film such as nickel on the upper surface of a circular synthetic resin (for example, PPS) film, and a vent hole 34a is formed at the center thereof. The diaphragm support ring 34 </ b> B is configured by a metal ring member having an outer diameter substantially the same as the inner diameter of the metal cover 32.
[0022]
The insulating ring 36 is a ring member having an outer diameter that is substantially the same as the inner diameter of the metal cover 32, and an insulating treatment (alumite coating process) is applied to the aluminum surface.
[0023]
The spacer 38 is formed of a synthetic resin (for example, PPS) thin plate ring having an outer diameter substantially the same as the inner diameter of the insulating ring 36.
The back electrode plate 40 is composed of a stainless steel back electrode plate main body 40A and a synthetic resin (for example, FEP) electret 40B thermally fused (laminated) to the upper surface of the back electrode plate main body 40A. Through-holes 40a are formed. The electret 40B is subjected to a polarization process so as to obtain a predetermined surface potential (for example, about −125 V).
[0024]
In the metal cover 32, the vibration film 34A and the electret 40B are opposed to each other with a predetermined minute interval through the spacer 38, thereby constituting the capacitor portion C.
[0025]
The insulating bush 42 is a synthetic resin molded product (for example, an LCP molded product), and is formed of a ring member having an outer diameter substantially the same as the inner diameter of the insulating ring 36.
In the case 12, a base member 52 made of a synthetic resin (for example, made of LCP) opened upward and a housing member 54 made of a synthetic resin (for example made of LCP) opened downward are fixed by ultrasonic welding. It has become.
[0026]
4 is a cross-sectional view taken along the line IV-IV in FIG. 3, showing the base member 52 in detail. Also,
FIG. 5 is a cross-sectional view showing in detail the outer surface (lower surface) of the base member 52 at the manufacturing stage.
[0027]
As shown in these figures, the base member 52 includes a substantially square bottom wall portion 52A and a peripheral wall portion 52B extending upward from the outer peripheral edge portion of the bottom wall portion 52A, and four terminal members are formed by insert molding. 56A, 56B, 56C, and 56D are integrally formed. These four terminal members 56A, 56B, 56C, and 56D are formed as inserts by punching and bending a strip-shaped conductive member.
[0028]
One end of each of the terminal members 56A, 56B, 56C, and 56D is exposed as four land portions 56Aa, 56Ba, 56Ca, and 56Da that constitute a part of the conductive pattern P on the inner surface (upper surface) of the bottom wall portion 52A. Yes. On the other hand, the other end portions of the terminal members 56A, 56B, 56C, and 56D are exposed as four external connection terminal portions 56Ab, 56Bb, 56Cb, and 56Db on the outer surface of the bottom wall portion 52A. Each of these external connection terminal portions 56Ab, 56Bb, 56Cb, 56Db is formed in an L shape so as to go from the bottom surface of the bottom wall portion 52A to the outer surface of the peripheral wall portion 52B in the vicinity of each corner portion of the bottom wall portion 52A. . At that time, each of the external connection terminal portions 56Ab, 56Bb, 56Cb, 56Db is formed flush with the lower surface of the bottom wall portion 52A by insert molding with respect to the bottom wall portion 52A. Is formed so as to protrude from the outer surface of the peripheral wall portion 52B by the thickness by cutting and bending after insert molding.
[0029]
Of the four terminal members 56A, 56B, 56C, and 56D, the terminal member 56A is an output terminal that is connected to a power source via a load resistor when mounted on an external board, and the terminal member 56B is a ground terminal. The remaining two terminal members 56C and 56D are dummy terminals.
[0030]
In the bottom wall portion 52A of the base member 52, a plurality of hollow portions 52a are formed by insert support pins at the time of insert molding.
Then, after insert molding, a pin is inserted into the hollow portion 52a so as to pierce the conductive pattern P from above (or by laser light irradiation or the like), so that the conductive pattern P is divided and the through hole 52b is formed. It comes to form. As a result, a new land portion 58 electrically separated from the land portion 56Aa is formed on the inner surface of the bottom wall portion 52A of the base member 52.
[0031]
The FET 16 and the capacitors 18 and 20 are mounted on the base member 52 at predetermined portions of the conductive pattern P.
The FET 16 is an element that converts the change in electrostatic capacitance of the electret capacitor portion C into an electrical impedance. The drain electrode D is electrically connected to the land portion 56Aa of the terminal member 56A, and the source electrode S is the land portion 56Ba of the terminal member 56B. And the gate electrode G is mounted so as to be electrically connected to the land portion 58. Capacitors 18 and 20 are two types of capacitors having different electrostatic capacities provided for noise removal, and are arranged in parallel so as to straddle land portion 56Aa of terminal member 56A and land portion 56Ba of terminal member 56B. Implemented in.
[0032]
On the inner surface of the bottom wall portion 52 </ b> A of the base member 52, a spring mounting boss 52 c is formed that protrudes upward at the formation portion of the land portion 58. A coil spring 22 is mounted on the spring mounting boss 52c. The coil spring 22 is made of metal, and when the electret condenser microphone 10 is assembled, the coil spring 22 is compressed and elastically deformed in a state in which both end portions thereof are in contact with the land portion 58 and the back electrode plate body 40A. It has become. As a result, the gate electrode G of the FET 16 is electrically connected to the back electrode plate body 40A via the land portion 58 and the coil spring 22.
[0033]
The contact frame 24 is formed by punching a stainless steel plate into a substantially L-shape and bending a part thereof, and three terminal contact pieces 24a, 24b, 24c projecting obliquely downward at three locations. Is formed. The contact frame 24 has an outer shape that is substantially the same as the inner surface shape of the peripheral wall portion 52B of the base member 52. When the contact frame 24 is mounted in the base member 52, the terminal contact pieces 24a, 24b, 24c comes into contact with the land portions 56Ba, 56Ca, 56Da of the respective terminal members 56B, 56C, 56D.
[0034]
The contact frame 24 is configured such that when the electret condenser microphone 10 is assembled, the terminal contact pieces 24a, 24b, and 24c are slightly bent and deformed by contact with the metal cover 32 of the electret condenser unit 14. It has become. Thus, the source electrode S of the FET 16 is electrically connected to the vibration film 34A via the land portion 56Ba of the terminal member 56B, the contact frame 24, the metal cover 32, and the vibration film support ring 34B, and the land of the terminal members 56C and 56D. The portions 56Ca and 56Da are also electrically connected so that these terminal members 56C and 56D can also be used as ground terminals.
[0035]
A shallow circular recess 52d having an inner diameter substantially the same as the outer diameter of the electret capacitor unit 14 is formed on the outer surface (lower surface) of the bottom wall portion 52A of the base member 52. The circular recess 52d includes the circular recess 52d. A shield plate 60 made of metal, which is a shield member, which is thinner than the depth of is attached and fixed.
[0036]
The shield plate 60 is a stainless steel disk-shaped shield plate having a thickness of about 80 μm. The shield plate 60 is preferably made of a metal with high radio wave shielding properties (for example, stainless steel, copper, aluminum, etc.). It is also desirable to use a metal having a low thermal conductivity (for example, stainless steel, titanium, etc.) for reflecting radiant heat.
[0037]
The shield plate 60 is conductively bonded to the GND terminal E by a conductive adhesive. Thereby, the shielding property is further enhanced.
The shield plate 60 and the GND terminal E are bonded by pouring a conductive adhesive into a square or triangular square gate hole 61 formed on the outer surface (lower surface) of the bottom wall portion 52A of the base member 52. Is going. In addition, there is a round gate hole 62, which is not used for conduction. At this time, the round gate hole 62 may be sealed with an insulating adhesive or the like in order to improve the airtightness inside the electret condenser microphone 10. In this way, the gate hole is divided into shapes to improve workability. Also, image recognition is possible due to the difference in the shape of the gate hole, and automation is also possible.
[0038]
When the base member 52 is in a single product state, the upper end surface of the peripheral wall portion 52B is formed in a substantially conical shape, so that ultrasonic welding with the housing member 54 can be easily performed.
[0039]
The housing member 54 includes a top wall portion 54A having the same shape as the bottom wall portion 52A of the base member 52, a peripheral wall portion 54B extending downward from an outer peripheral edge portion of the top wall portion 54A, and an upper wall so as to surround the electret capacitor unit 14. It consists of an annular wall portion 54C extending downward from the portion 54A. A plurality of sound emission holes 54 a are formed in the ceiling wall portion 54 </ b> A of the housing member 54. Each corner portion of the housing member 54 is formed with a concave space 54b communicating with the internal space of the base member 52 by the peripheral wall portion 54B and the annular wall portion 54C.
[0040]
In this embodiment, the shield plate 60 is used as the conductive shield member. However, the present invention is not limited to this. For example, a conductive adhesive or conductive resin is poured into the circular recess 52d to form the shield member. Alternatively, the shield member may be formed of a conductive resin or the like at the position of the shield plate 60 by two-color molding. Further, a resin film or the like laminated with a metal foil may be used instead of the shield plate 60, and an effect on noise due to electromagnetic waves can be obtained as long as it is a conductive substance.
[0041]
As described above in detail, in the electret condenser microphone 10 according to the present embodiment, a part of the case 12 that houses the electret condenser C, the FET 16, and the capacitors 18 and 20 is configured as a base member 52 made of synthetic resin. Further, the configuration in which the metal shield plate 60 is mounted on the outer surface of the base member 52 can reduce noise due to electromagnetic waves, and the shield plate 60 reflects the radiant heat generated by the reflow process at the time of surface mounting. Since the base member 52 made of synthetic resin reduces heat conduction into the electret condenser microphone 10, heat resistance is improved. Further, by providing the metal shield plate 60 on the synthetic resin base member 52, the rigidity of the electret condenser microphone 10 is also improved.
[0042]
Therefore, according to the present embodiment, it is possible to make the electret condenser microphone 10 suitable for surface mounting on an external substrate after reducing the number of parts and reducing the thickness (specifically, for example, with respect to the external substrate). Thus, the electret condenser microphone 10 can be directly mounted on the external substrate without interposing a holder as in the prior art.
[0043]
In particular, in this embodiment, since the internal electret capacitor unit 14 is covered with the cylindrical metal cover 32, the electret capacitor unit 14 is electromagnetically shielded by the combination with the metal shield plate 60. Therefore, the electret condenser microphone 10 having excellent noise resistance can be realized.
[0044]
Furthermore, in the present embodiment, the shield plate 60 is electrically connected to the GND terminal E of the synthetic resin base member 52 integrally formed with the plurality of terminal members 56A, 56B, 56C, and 56D by insert molding. , Noise can be released to the outside, and the shielding performance against noise is improved. In addition, since the external connection terminal portions 56Ab, 56Cb, and 56Db serve as the GND terminal E via the shield plate 60, when the electret condenser microphone 10 is attached to a mobile phone or the like, the degree of freedom in design on the attachment side is increased.
[Brief description of the drawings]
FIG. 1 is a side cross-sectional view showing an electret condenser microphone according to an embodiment of the present invention arranged in an upward direction. FIG. 2 is a view taken in the direction of arrows IIa (a) and IIb in FIG.
3 is an exploded side cross-sectional view of the electret condenser microphone. FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. 3 showing the base member of the electret condenser microphone in detail. Sectional view showing the outer surface (lower surface) of the base member in detail at the manufacturing stage [Explanation of symbols]
10 Electret condenser microphone 12 Case 14 Electret condenser unit 16 FET (impedance conversion element)
18, 20 Capacitor 22 Coil spring 24 Contact frame 24a, 24b, 24c Terminal contact piece 32 Metal cover 32a Sound hole 32b Open lower end 34 Vibration membrane subassembly 34A Vibration membrane 34B Vibration membrane support ring 34a Vent hole 36 Insulating ring 38 Spacer 40 Back electrode plate 40A Back electrode plate main body 40B Electret 42 Insulating bush 52 Base member 52A Bottom wall portion 52B Peripheral wall portion 52a Hollow portion 52b Through hole 52c Spring mounting boss 52d Circular recess 54 Housing member 54A Top wall portion 54B Peripheral wall portion 54C Annular Wall part 54a Sound emission hole 54b Recessed space 56A, 56B, 56C, 56D Terminal members 56Aa, 56Ba, 56Ca, 56Da Land part 56Ab, 56Bb, 56Cb, 56Db External connection terminal part 58 Land part 60 Shield play 61 square gate hole 62 round the gate hole C electret capacitor portion D drain electrode G gate electrode P conductive pattern S source electrode E GND terminal

Claims (4)

An electret capacitor unit in which a diaphragm and a back electrode plate are arranged to face each other, an impedance conversion element that converts the capacitance of the electret capacitor unit into an electrical impedance, and a case that houses the electret capacitor unit and the impedance conversion element In an electret condenser microphone comprising:
A part of the case is configured as a base member made of synthetic resin,
The base member is opened upward, and at least an electret capacitor unit and an impedance conversion element are mounted in the base member,
An electret condenser microphone, wherein a conductive shielding member is provided on an outer surface of the base member.   2. The electret condenser microphone according to claim 1, wherein the shield member is made of a metal shield plate.   The electret condenser microphone according to claim 1 or 2, wherein the electret condenser section is covered with a cylindrical metal cover.   The base portion is configured as a synthetic resin base member in which a part of the case is integrally formed with a plurality of terminal members by insert molding, and the shield plate is electrically connected to the specific terminal member. The electret condenser microphone according to any one of claims 1 to 3, wherein the electret condenser microphone is provided.

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