JP2008035159A - Electret capacitor microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent sensitivity deterioration from being generated due to heat in reflow processing in an electret capacitor microphone. <P>SOLUTION: A capacitor structure part 12 is configured so that a vibrating film 32A consisting of a polymer film formed with a conductive thin film 32a on the upper face and a back electrode board 34 formed with an electret layer 34B on the upper face of the electrode board main body 34A are arranged so as to be opposite to each other with the vibrating film 32A faced upward. In this case, the conductive thin film 32a is formed by applying infrared reflecting paint having conductivity to almost the whole region of the upper face of a polymer film. Thus, an infrared ray transmitted through a sound hole 22a formed on a cover board 22 to a capacitor structure part 12 is reflected on the vibrating film 32A on which the infrared reflecting paint has been applied in reflow processing, so that it is possible to prevent the electret layer 34B from being exposed to the heat of the infrared ray. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a back electret type electret condenser microphone.

  In general, an electret condenser microphone has a capacitor structure portion in which a vibrating membrane and a back electrode plate are arranged to face each other as described in, for example, “Patent Document 1”. An impedance conversion element for converting a capacitance change into an electrical impedance is mounted on a circuit board.

  At this time, the condenser structure of the electret condenser microphone described in “Patent Document 1” is a back electret condenser in which an electret layer is formed on the upper surface of the back electrode plate while being arranged with the vibrating membrane facing upward. It is configured as a structural part. In this electret condenser microphone, the capacitor structure portion, impedance conversion element and circuit board are accommodated in a housing that covers them from above, and the upper surface portion of the housing is for guiding sound to the capacitor structure portion. The sound hole is formed.

JP 2006-41575 A

  By adopting an electret condenser microphone as described in the above “Patent Document 1” as the condenser microphone, it can be manufactured at low cost.

  However, when the reflow process is performed on the electret condenser microphone for surface mounting on an external substrate, the electret layer charges are removed to some extent by heat of 200 ° C. or more applied during the reflow process. Therefore, there is a problem that the potential difference of the capacitor structure part becomes smaller than the intended potential difference, which causes a decrease in sensitivity of the electret condenser microphone.

  The present invention has been made in view of such circumstances, and provides an electret condenser microphone that can prevent a decrease in sensitivity due to heat applied during reflow processing. It is the purpose.

  The present invention is intended to achieve the above object by devising the configuration of the vibration membrane.

That is, the electret condenser microphone according to the present invention is
A capacitor structure part in which a vibration film and a back electrode plate are arranged to face each other with the vibration film facing upward, an impedance conversion element for converting the capacitance of the capacitor structure part into an electrical impedance, and the impedance conversion element In an electret condenser microphone comprising: a circuit board to be mounted; and a housing that covers the capacitor structure, the impedance conversion element, and the circuit board so as to cover the circuit board from above.
The capacitor structure part is configured as a back electret type capacitor structure part in which an electret layer is formed on the upper surface of the back electrode plate,
A sound hole for guiding sound to the capacitor structure is formed on the upper surface of the housing,
An infrared reflective paint for reflecting infrared rays is applied to a region including a region located directly below the sound hole on the surface of the vibration film.

  In the above configuration, terms indicating directionality such as “upper” and “upper side” are used for convenience to clarify the positional relationship between members constituting the electret condenser microphone. The directionality when actually using the condenser microphone is not limited.

  The specific configuration of the “impedance conversion element” is not particularly limited, and may be an electronic component such as a field effect transistor, or may be configured as a part of a circuit in an IC chip or the like. Also good.

  The “circuit board” may have a configuration in which only an impedance conversion element is mounted, or may have a configuration in which other electronic components (such as a capacitor and a resistor) are also mounted.

  The specific configuration of the “housing” such as the material, shape and size is not particularly limited.

  The specific arrangement of the “capacitor structure, impedance conversion element, and circuit board” in the housing is not particularly limited.

  The above-mentioned “infrared reflective paint” is not particularly limited as long as it is applied to a region including a region located directly below the sound hole on the surface of the vibration membrane. It may be applied to any of the upper surface, the lower surface, and the upper and lower surfaces.

  As shown in the above configuration, the electret condenser microphone according to the present invention is a back electret condenser in which the condenser structure is disposed with the vibrating membrane facing upward and the electret layer is formed on the upper surface of the back electrode plate. It is configured as a structural part, and a sound hole is formed in the upper surface part of the housing. At that time, infrared rays are reflected to a region including a region located immediately below the sound hole on the surface of the vibration membrane. Since the infrared reflective paint is applied, the following effects can be obtained.

  That is, when the reflow process is performed on the electret condenser microphone, the capacitor structure is exposed to heat of 200 ° C. or more applied during the reflow process. In the furnace, the electret condenser microphone is irradiated with infrared rays.

  At that time, when the capacitor structure is a back electret type capacitor structure as in the electret condenser microphone according to the present invention, the vibration film is disposed above the back electrode plate. The electret layer formed on the upper surface of the plate will be exposed to infrared heat irradiated through the sound hole formed on the upper surface portion of the housing.

  However, in the electret condenser microphone according to the present invention, since the infrared reflective paint is applied to the region including the region located directly below the sound hole on the surface of the diaphragm, the condenser is connected via the sound hole during the reflow process. Infrared rays that reach the structure portion are reflected by the infrared reflecting paint applied to the vibration film. For this reason, it is possible to prevent the electret layer of the back electrode plate from being exposed to the heat of infrared rays, thereby preventing a decrease in sensitivity of the electret condenser microphone.

  As described above, according to the present invention, even when an electret condenser microphone is employed as the condenser microphone, it is possible to prevent the sensitivity from being lowered due to the heat applied during the reflow process.

  In the above configuration, if the infrared reflective coating is applied to the upper surface of the vibration film, the vibration film itself can be prevented from being exposed to infrared heat. As a result, a vibration film having relatively low heat resistance can be used, and the cost can be reduced.

  In the above configuration, if a conductive paint is used as the infrared reflecting paint, one electrode in the capacitor structure can be formed by applying the infrared reflecting paint. As a result, it is not necessary to form a metal vapor deposition film on the surface of the vibration film, and the cost can be reduced.

  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 an embodiment of the present invention in an upwardly arranged state, and FIG. 2 is a view taken in the direction of arrow II in FIG.

  As shown in these drawings, the electret condenser microphone 10 according to the present embodiment is a small microphone having a rectangular outer shape of about 3 × 4 mm in plan view, and includes a capacitor structure portion 12, an IC chip 14, and the like. , The contact spring 16, the base substrate 18, the side substrate 20, and the cover substrate 22. The electret condenser microphone 10 is surface-mounted on an external substrate (not shown) on the lower surface of the base substrate 18.

  The capacitor structure 12 includes a diaphragm subassembly 32 and a back electrode plate 34.

  The vibration membrane subassembly 32 has a vibration film 32A stretched and fixed on the upper surface of a metal support ring 32B formed in a rectangular ring shape. The vibration film 32A is a polymer having a conductive thin film 32a formed on the upper surface. Consists of film. The conductive thin film 32a is formed by applying a conductive infrared reflective paint over substantially the entire area of the upper surface of the polymer film. In this case, a conductive paint containing a tin-containing compound (for example, tin-indium oxide or tin-antimony oxide) as a pigment is used as the infrared reflective paint.

  The back electrode plate 34 includes a metal electrode plate main body 34A and an electret layer 34B heat-sealed to the upper surface of the electrode plate main body 34A, and the electret layer 34B is given a predetermined surface potential by polarization treatment. Has been. The outer diameter of the back electrode plate 34 is set to a value slightly larger than the inner diameter of the support ring 32B.

  In this capacitor structure portion 12, the diaphragm 32A of the diaphragm subassembly 32 and the electret layer 34B of the back electrode plate 34 are spaced at a predetermined minute distance via the support ring 32B of the diaphragm subassembly 32. Thus, a predetermined potential difference is generated between the vibrating membrane 32A and the electret layer 34B.

  In the electret condenser microphone 10 according to the present embodiment, the base substrate 18, the side substrate 20, and the cover substrate 22 constitute a housing that houses the capacitor structure portion 12, the IC chip 14, and the contact spring 16.

  The base substrate 18 includes an insulating substrate 18A, conductive layers 18B1, 18B2, and 18B3 formed on the lower surface of the insulating substrate 18A, and the conductive layers 18B1, 18B2, and 18B3 exposed at the four corners. The insulating layer 18C covers the lower surface in a cross shape, conductive layers 18D1 and 18D2 formed on the upper surface of the insulating substrate 18A, and a conductive layer (not shown). The IC chip 14 is mounted on the base substrate 18 at the center of the upper surface.

  At that time, the conductive layer 18B1 constitutes a power supply terminal, the conductive layer 18B2 constitutes an output terminal, and the conductive layer 18B3 constitutes a ground terminal. The conductive layer 18B1 is electrically connected to a conductive layer (not shown) formed on the upper surface of the insulating substrate 18A through a through hole (not shown), and is electrically connected to the power supply terminal 14a of the IC chip 14 in this conductive layer. The conductive layer 18B2 is electrically connected to a conductive layer (not shown) formed on the upper surface of the insulating substrate 18A through a through hole (not shown), and is electrically connected to the output terminal 14b of the IC chip 14 in this conductive layer. Further, the conductive layer 18B3 is electrically connected to a conductive layer (not shown) formed on the upper surface of the insulating substrate 18A through a through hole (not shown), and is electrically connected to the ground terminal 14c of the IC chip 14 in this conductive layer.

  The side substrate 20 is placed and fixed on the base substrate 18 so as to surround the IC chip 14.

  The side substrate 20 includes an insulating substrate 20A formed in a rectangular ring shape having an inner diameter slightly larger than that of the back electrode plate 34, and conductive layers 20B and 20C formed on the lower surface and the upper surface of the insulating substrate 20A, respectively. Yes. At this time, the conductive layers 20B and 20C are electrically connected to each other through a through hole (not shown).

  The cover substrate 22 has an insulating substrate 22A having the same outer shape as the base substrate 18 in plan view, a conductive layer 22B formed in a rectangular ring shape on the lower surface of the insulating substrate 22A, and a substantially entire surface on the upper surface of the insulating substrate 22A. The conductive layer 22 </ b> C is formed, and is placed and fixed on the side substrate 20 via the vibration film subassembly 32.

  At this time, in the cover substrate 22, the conductive layers 22 </ b> B and 22 </ b> C are electrically connected to each other through a through hole (not shown), whereby the metal vapor deposition film of the vibration film 32 </ b> A is located on the upper surface of the cover substrate 22. The conductive layer 22B is electrically connected to the ground terminal of the external substrate.

  A sound hole 22 a penetrating the cover substrate 22 in the vertical direction is formed at a position slightly deviated from the center of the cover substrate 22.

  The contact spring 16 is formed with a pair of projecting pieces projecting in parallel with each other at each corner portion of the frame portion formed in a square shape in plan view, and each pair of projecting pieces at two locations on the frame portion. In addition, it is composed of a metal leaf spring formed so as to be bent downward. The contact spring 16 is disposed in a state where the contact spring 16 is bent to some extent so as to surround the IC chip 14 in the frame portion. At this time, the contact spring 16 contacts the lower surface of the electrode plate body 34A of the back electrode plate 34 at the frame portion, and contacts the four conductive layers 18D1 of the insulating substrate 18A at the four protruding pieces. Yes. The electrode plate body 34A of the back electrode plate 34 and the input terminal 14d of the IC chip 14 are electrically connected via the contact spring 16 and the conductive layer 18D1.

  In the electret condenser microphone 10 according to the present embodiment, an impedance conversion element for converting the capacitance of the capacitor structure 12 into an electrical impedance is incorporated in the IC chip 14 as an impedance conversion circuit.

  Next, the effect of the electret condenser microphone 10 according to the present embodiment will be described.

  When the electret condenser microphone 10 according to the present embodiment is surface-mounted on an external substrate, a reflow process is performed on the electret condenser microphone 10, and this reflow process is performed on the electret condenser microphone 10 in the reflow furnace. It is performed by irradiating. At this time, the capacitor structure 12 is exposed to heat of 200 ° C. or higher by infrared irradiation, and the vibration film 32A has a conductive thin film 32a formed in substantially the entire area of the upper surface of the polymer film. Since 32a is formed by application of an infrared reflecting paint, the infrared rays reaching the capacitor structure 12 through the sound hole 22a during the reflow process are reflected by the infrared reflecting paint applied to the vibration film 32A. Can do. As a result, it is possible to prevent the electret condenser microphone 10 from being deteriorated in sensitivity so that the electret layer 34B of the back electrode plate 34 is not exposed to infrared heat.

  As described above, according to the present embodiment, even when the electret condenser microphone 10 is employed as the condenser microphone, it is possible to prevent the sensitivity from being lowered due to the heat applied during the reflow process.

  In addition, in the present embodiment, since the infrared reflective paint is applied to the upper surface of the vibration film 32A, the vibration film 32A itself can be prevented from being exposed to infrared heat. As a result, a vibration film 32A having a relatively low heat resistance can be used, and the cost can be reduced.

  Furthermore, in this embodiment, since the conductive paint is used as the infrared reflective paint, one electrode in the capacitor structure portion 12 can be configured by applying the infrared reflective paint. As a result, it is not necessary to form a metal vapor deposition film on the surface of the vibration film 32A, and the cost can be reduced.

  In the electret condenser microphone 10 according to the above-described embodiment, the vibration film 32A has a configuration in which a conductive infrared reflective paint is applied to substantially the entire region of the upper surface of the polymer film. Instead, a metal vapor deposition film is formed on almost the entire upper surface of the polymer film, and the non-conductive infrared reflective coating is directly below the sound hole 22a on the upper or lower surface of the polymer film. It is also possible to adopt a configuration in which the coating is applied to a region including a region located in the region. Even in this case, it is possible to prevent the electret layer 34B of the back electrode plate 34 from being exposed to infrared heat.

  In the electret condenser microphone 10 according to the above-described embodiment, if the infrared reflective paint is applied to the surface of the cover substrate 22 and the surface of the conductive layer 22C, the heat inside the housing of the electret condenser microphone 10 can be obtained. It becomes possible to suppress entry effectively. Further, when a filter member is additionally disposed on the surface of the cover substrate 22 so as to block the sound hole 22a with respect to the electret condenser microphone 10 according to the above embodiment, an infrared reflective paint is applied to the filter member. With the applied configuration, it becomes possible to effectively prevent the heat from entering the housing of the electret condenser microphone 10.

  In the electret condenser microphone 10 according to the above-described embodiment, it has been described that the electrical impedance conversion is performed by the impedance conversion circuit incorporated as a part of the IC chip 14, but instead of doing this, a field effect transistor is used. Of course, it is also possible to adopt a configuration in which electrical impedance conversion is performed by a single impedance conversion element such as.

  Further, in the above embodiment, the base substrate 18, the side substrate 20 and the cover substrate 22 constitute a housing for housing the capacitor structure 12, the IC chip 14 and the contact spring 16. It is also possible to comprise by 18 and the metal case with which it was attached.

  In addition, the numerical value shown as a specification in the said embodiment is only an example, and of course, you may set these to a different value suitably.

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 direction view of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electret condenser microphone 12 Capacitor structure part 14 IC chip 14a Power supply terminal 14b Output terminal 14c Ground terminal 14d Input terminal 16 Contact spring 18 Base board 18A, 20A, 22A Insulation board 18B1, 18B2, 18B3, 18D1, 18D2, 20B, 20C, 22B, 22C Conductive layer 18C Insulating layer 20 Side substrate 22 Cover substrate 22a Sound hole 32 Vibration membrane subassembly 32A Vibration membrane 32a Conductive thin film 32B Support ring 34 Back electrode plate 34A Electrode plate body 34B Electret layer

Claims (3)

A capacitor structure part in which a vibration film and a back electrode plate are arranged to face each other with the vibration film facing upward, an impedance conversion element that converts the capacitance of the capacitor structure part into an electrical impedance, and the impedance conversion element In an electret condenser microphone comprising: a circuit board to be mounted; and a housing that covers the capacitor structure, the impedance conversion element, and the circuit board so as to cover the circuit board from above.
The capacitor structure part is configured as a back electret type capacitor structure part in which an electret layer is formed on the upper surface of the back electrode plate,
A sound hole for guiding sound to the capacitor structure is formed on the upper surface of the housing,
An electret condenser microphone, characterized in that an infrared reflecting paint for reflecting infrared rays is applied to a region including a region located directly below the sound hole on the surface of the vibrating membrane.   2. The electret condenser microphone according to claim 1, wherein the application of the infrared reflecting paint is performed on an upper surface of the vibration film.   The electret condenser microphone according to claim 1, wherein a conductive paint is used as the infrared reflective paint.

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