JP2003189396A - Condenser microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electret type condenser microphone with high sensitivity and that can be sufficiently low-profiled. <P>SOLUTION: Since the condenser microphone 10 uses an insulation ring made of a metal and to which insulation processing is applied in advance, the higher strength than using a resin formed insulation spacer can be obtained and low- profile can be attained. Since the insulation processing is applied in advance, it is not required for processing of insulating a metal being a conductor at assembling, the need for inserting an insulation sheet or the like can be eliminated and insulation mistake attendant on it is not needed. Thus, even when the insulation member is made thinner in the height direction, it is possible to obtain a wide back pressure space of the microphone and the increase in man- hours can be suppressed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electret-type condenser microphone, and more particularly to a structure for increasing the sensitivity of a thin electret-type condenser microphone.

[0002]

2. Description of the Related Art Conventionally, an electret type condenser microphone has been known as one type of microphone.

This electret-type condenser microphone is, for example, as disclosed in Japanese Utility Model Registration No. 2587682, a cylinder whose one end is an end face wall having an opening for a sound hole and whose other end is open. A board on which a capacitor section composed of a vibration plate and a back electrode plate facing each other with a spacer interposed between them and an impedance conversion element (active element) for converting an impedance change of the capacitor section into an electric impedance It is configured to accommodate and.

At this time, as disclosed in the above publication, the capacitor section is housed so that its diaphragm is located at one end side, and the substrate is located at the other end side of the capacitor section. In many cases, the impedance conversion element is housed so as to be positioned on one end side.

This electret-type condenser microphone is relatively easy to be made compact, but
When it is used by being mounted on a mobile phone or the like, which is becoming thinner in recent years, it is desired to make it as thin as possible in addition to being simply downsized.

[0006]

However, when the conventional electret-type condenser microphone is made thin, the condenser portion is made up of various components, and therefore the back space portion, which is a space, is made thinner in the height direction. However, it is often the case to make it thinner. However, when the back space portion is made thin, there is a problem that the sensitivity is lowered. Further, when the back space portion is thinned, the height of the insulating member existing between the back electrode plate and the substrate on which the impedance conversion element is mounted is formed low to achieve a thin shape, but the height is also limited. However, if the insulating member, which is usually made of resin, is made thin to secure a rear space, there is a problem that the insulating member itself is crushed during caulking during assembly. In addition, as in Japanese Patent Laid-Open No. 2000-50394, there is also a cup-shaped back electrode made of a metal material that also serves as an insulating member. However, in such a case, many parts other than the back electrode effective as a capacitor are formed. Therefore, there is a possibility that the efficiency of the capacitor is lowered and the sensitivity is lowered. For this reason, there is a problem in that the condenser microphone cannot be made so thin, and it is not possible to meet the recent demand for thinning.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an electret-type condenser microphone which has high sensitivity and can be sufficiently thinned. is there.

[0008]

The present invention is intended to achieve the above object by using a metallic insulating member whose surface is insulation-processed.

That is, the condenser microphone according to the present invention includes a capacitor portion including a diaphragm and a back plate for converting vibration due to sound into a capacitance change, and a capacitance change converted by the capacitor portion as an electric signal. A circuit board including an impedance conversion element for converting to, an insulating member for maintaining a positional interval between the capacitor section and the circuit board to prevent electrical connection, an internal capacitor section, the insulating member, and the circuit board. In a condenser microphone including a housing for fixing, the insulating member is formed of metal and is subjected to an insulating process in advance. In addition, a ring-shaped spacer is provided in the capacitor portion to form a space between the diaphragm and the back plate to form a space, and the insulating member is the ring-shaped spacer. The back plate is formed in a ring shape so as to abut, and the back plate is arranged so as to be present inside the inner peripheral surface of the insulating member. Further, the back plate is pressed to the diaphragm side by an elastic body arranged on the circuit board. Further, the housing is characterized in that the capacitor portion, the insulating member, and the circuit board are internally fixed by caulking.

The above-mentioned "condenser microphone" may be a foil electret type condenser microphone in which a diaphragm has an electret function.
A back electret-type condenser microphone in which a back electrode plate has an electret function may be used.

The above-mentioned "impedance conversion element" is not limited to a specific element as long as it can convert a change in capacitance of the capacitor portion into an electric impedance, and for example, a JFET (junction type) is used. FET) etc. can be adopted.

[0012]

As described above, in the condenser microphone according to the present invention, since the insulating member is made of metal and is pre-insulated, it is stronger than the one made of resin. It can be made thinner and thinner. Furthermore, since the insulation treatment has been performed in advance, there is no need to perform processing to insulate the metal that is the conductor at the time of assembly, there is no need to insert an insulating sheet, and there is no risk of insulation mistakes accompanying this. . In this way, by not using an extra member such as an insulating sheet, the back pressure space of the microphone can be widened even if the insulating member is thinned in the height direction, and an increase in the number of working steps can be suppressed. It becomes possible.

Therefore, according to the present invention, in an electret-type condenser microphone, it is possible to inexpensively achieve high sensitivity and further improve the manufacturing yield.

Further, by disposing the back plate so as to be present on the inner peripheral surface of the insulating member, the floating region in the outer peripheral portion where the back plate and the diaphragm are in contact with each other can be reduced. It is possible to reduce the efficiency, and as a result, it is possible to improve the efficiency without changing the area of the capacitor section. Further, since the thickness of the back plate can be reduced by the thickness of the back plate, it is possible to contribute to the reduction in thickness of the microphone as a whole.

As a result, the electret type condenser microphone can be made more highly sensitive and thinner.

Further, since the back plate is pressed to the diaphragm side by the elastic body arranged on the circuit board, the back plate does not have to be pressed by the insulating member. It is possible to fix the back plate without using a simple design, and it is possible to prevent an increase in the number of work steps and an increase in manufacturing difficulty in reducing the thickness.

Even if the capacitor portion, the insulating member, the circuit board and the like are internally fixed by caulking the casing, the soft resin does not exist in the portion that receives the caulking pressure, so that the contents are crushed below the specified value. This makes it possible to eliminate variations in the location system and improve the yield.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing a condenser microphone according to an embodiment of the present invention in an upwardly arranged state. 2 is a sectional view taken along the line II-II of FIG. 1, and FIG. 3 is a perspective view showing the condenser microphone in an exploded manner.

As shown in these figures, the condenser microphone 10 according to the present embodiment is a small electret type microphone having an outer diameter of about 3.0 mm, and is a short cylindrical case 12 extending vertically. Inside the diaphragm sub-assembly 14, the spacer 16, the insulating ring 20,
The back electrode plate 18, which is a back plate, the coil spring 22, and the JFET board 24 (substrate) are housed in this order from above.

The case 12 is made of a metal (for example, aluminum) whose upper end (one end) is composed of an end wall 12a having a sound hole 30 having an inner diameter of about 0.5 mm and whose lower end (other end) is open. And is formed by press molding or the like. The open end 12b of the case 12 is caulked and fixed to the outer peripheral edge of the JFET board 24 over the entire circumference in a state where the above-mentioned components are accommodated in the case 12. The case 12 is formed with a vent groove 12d at its upper end for adjusting the atmospheric pressure inside and outside the condenser microphone 10. The vent groove 12d has a width of about 0.2 mm and a depth of about 0.02 mm.

Vibration plate sub-assembly 14 (diaphragm)
Is composed of a thin disc-shaped vibrating membrane 26 and a ring-shaped support frame 28 that fixes and supports the vibrating membrane 26. The fixed support of the vibrating membrane 26 by the support frame 28 is
The upper surface of the vibration film 26 is bonded and fixed to the lower surface of the support frame 28 with a conductive adhesive, whereby the support frame 28 and the vibration film 26 are electrically connected.

The outer peripheral portion of the support frame 28 on the case 12 side is chamfered so that it can be fitted and positioned in the case 12. This chamfering process can be performed by etching or the like without distorting the support frame 28.

The vibrating membrane 26 has a thickness of P of about 1.5 μm.
A metal vapor deposition film 26B of, for example, nickel (Ni) is formed on the upper surface of the ET (Polyethylene Terephthalate) film 26A, and the outer diameter thereof is the inner diameter (2.8 mm) of the case 12.
(about 2.75 mm).

On the other hand, the support frame 28 is made of metal (for example, stainless steel) and has an outer diameter substantially the same as the vibrating membrane 26 and an inner diameter of about 2.0 mm. In the state where the diaphragm sub-assembly 14 is housed in the case 12, the metal vapor deposition film 26B of the diaphragm 26 is in pressure contact with the case 12 via the support frame 28 by a pressing force described later, so that the electrical Will be connected to.

The spacer 16 is a frame-shaped member having an outer diameter substantially equal to the inner diameter of the case 12, and has a plate thickness of 25 μm.
A large opening 16a is formed in the center of a circular resin film PET having a size of about m by pressing or the like.

The back electrode plate 18 (back plate) includes a back electrode plate body 180, an electret 182 formed on the upper surface of the back electrode plate body 180, and a plurality of back electrode plate bodies 180 and electrets 182. Through hole 188
It consists of

The back electrode plate body 180 is made of a metal plate (for example, a stainless steel plate) having a circular outer shape and a plate thickness of about 0.15 mm.

On the other hand, the electret 182 has a thickness of 2
FEP (Fluorinated Ethylene Propyle) of about 5 μm
ne) It consists of film.

The through holes 188 are round holes having a diameter of about 0.4 mm, and four through holes 188 are formed at equal intervals. This through hole 18
The vibrating membrane 26 and the back space of the back electrode plate 18 can be communicated with each other by means of 8, and the vibration plate sub-assembly 14 and the back electrode plate 1
The resistance component of the thin fluid layer formed between No. 8 and No. 8 is reduced, which contributes to the improvement of the frequency response in the high frequency range (5 KHz or higher band). Further, it is possible to adjust the frequency response in the high frequency range by adjusting the hole diameter and the number of the through holes 188 at the design stage.

In the back electrode plate 18, a film-shaped electret 182 is heat-sealed (laminated) in advance,
A through hole 188 is formed on the surface of the metal plate that constitutes the back electrode plate body 180 by pressing, etching, or the like, and at the same time, the outer shape is circular.

After that, the electret 182 is subjected to a polarization treatment and is set so as to have a predetermined surface potential (for example, about -300 V). The back electrode plate 18 is concentric with the case 12 and accommodated in an insulating ring 20 inside the case 12.

In the case 12, the back electrode plate 18 and the vibrating membrane 26 have a plate thickness of 25 with the spacer 16 interposed therebetween.
The capacitors are opposed to each other with an interval of about μm, and thereby the capacitor section C is configured.

The insulating ring 20, which is an insulating member, is a ring-shaped member having an outer diameter substantially the same as the inner diameter of the case 12, and a metal ring 220 made of aluminum or the like has a thickness of 10 μm.
It is an insulating ring that has been subjected to some alumite treatment.
The thickness of the insulating ring 20 is set to a thickness (about 0.1 mm) in which the back electrode plate 18 can be contained. In addition, SUS or the like may be used for the metal ring 220 constituting the insulating ring 20, and a resin film treatment (for example, Parylene C coating manufactured by Nippon Parylene Co., Ltd.) may be applied to the insulating treatment.

The coil spring 22, which is an elastic body, is formed of a coil spring made of metal such as SUS and electrically connects the connection portion on the JFET board 24 and the back electrode plate 18. In addition, the coil spring 22 has a pressing force of about 0.4 N (1.35 mm when expanded, compressed when compressed) so that the diaphragm sub-assembly 14, the spacer 16, the back electrode plate 18, etc. are fixed to the case 12 while exerting a pressing force when assembled. The time is set to 0.75 mm).

The JFET board 24 includes a circular board body 32 and a JFET (Junction Field-Effect Transistor).
or) chip 34 and a noise filter 38 such as a chip capacitor for cutting carrier wave noise of communication equipment such as a mobile phone are mounted. Board body 3
2 has an outer diameter substantially the same as the inner diameter of the case 12, and predetermined conductive patterns 36 are formed on both upper and lower surfaces thereof.

The JFET chip 34 is an impedance conversion element for converting the change in the electrostatic capacitance between the vibrating membrane 26 and the back electrode plate 18 (that is, the electrostatic capacitance of the capacitor C) into an electrical impedance, and is the board body 32. Is mounted on the conductive pattern 36 formed on the upper surface of the.

The conductive pattern 36 has the JFET chip 3
Drain electrode D, source electrode S, and gate electrode G, which are electrically connected to and correspond to the drain electrode, the source electrode, and the gate electrode of No. 4, respectively, and the drain electrode D and the source electrode of the conductive pattern 36 are formed. Between S,
A noise filter 38 is mounted. The drain electrode D is electrically connected to the drain electrode D of the conductive pattern 36 on the back surface of the mounting surface of the JFET chip 34 by a through hole (not shown). The source electrode S is electrically connected to the source electrode S of the conductive pattern 36 on the back surface of the mounting surface of the JFET chip 34 by a through hole (not shown).
It is formed in a ring shape so as to be securely electrically connected to the open end portion 12b when the caulking is performed. Also, JFE
The gate electrode of the T-chip 34 is electrically connected to the back electrode plate 18 via the coil spring 22 from the gate electrode G of the conductive pattern 36.

FIG. 4 is a perspective view for explaining a method of assembling the condenser microphone 10 according to this embodiment.

As shown in the figure, when assembling the condenser microphone 10, the case 12 is arranged downward (the end wall 12a is arranged downward), and the case 1 is assembled.
2, the diaphragm sub-assembly 14, the spacer 16, the insulating ring 20, the back electrode plate 18, the coil spring 22 and the JFE.
The T board 24 is inserted from above in this order, and then the open end 12b of the case 12 is caulked.

That is, first, the diaphragm sub-assembly 14
And the spacer 16 is sequentially inserted into the case 12. At this time, the diaphragm sub-assembly 14 is positioned with respect to the case 12 by fitting the chamfered outer peripheral surface of the support frame 28 with the inner peripheral surface of the case 12.

Next, the insulating ring 20 is fitted and inserted into the case 12. Then, the back electrode plate 18 is fitted and inserted into the inner peripheral surface of the insulating ring 20. Further, the coil spring 22 is arranged on the lower surface side of the back electrode plate 18.

After that, the JFET board 24 is attached to the case 12
Insert inside. At this time, the gate electrode G of the conductive pattern 36 connected to the gate electrode of the JFET chip 34 is
As will be described later, the coil spring 22 is brought into contact with the pressing force of the coil spring 22.

Finally, the open end 12b of the case 12 is
The JFET board 24 is caulked and fixed to the outer peripheral edge of the board body 32 over the entire circumference. This caulking and fixing is performed by pressing the open end 12b of the case 12 from above with a caulking jig (not shown) and bending the open end 12b toward the inner peripheral side. And acts on the insulating ring 20 via. As a result, the back electrode plate 18 is positioned with respect to the case 12 while being electrically insulated from the case 12. Further, this ensures the sealing property between the insulating ring 20, the case 12, and the JFET board 24, and enhances the airtightness of the space defined by the diaphragm sub-assembly 14 and the JFET board 24.

With the condenser microphone 10 assembled, the spacer 16 and the JFET board 2 are
The distance from the board body 32 of No. 4 is defined by the height of the insulating ring 20, and its value is about 0.98 mm,
The total height of the condenser microphone 10 is about 1.5 mm. Further, the elastic deformation amount of the coil spring 22 is defined by the height of the insulating ring 20, and the pressing amount of the back electrode plate 18 and the like is also defined by the height of the insulating ring 20.

As described above in detail, since the condenser microphone 10 according to the present embodiment uses the insulating ring 20 which is made of metal and which is previously subjected to insulating processing, an insulating spacer made of resin is used. The strength can be obtained and the thickness can be reduced. Further, since the insulation treatment is performed in advance, it is not necessary to perform a treatment for insulating the metal that is the conductor at the time of assembly, there is no need to insert an insulating sheet or the like, and there is no fear of insulation mistakes accompanying this. . In this way, by not using an extra member such as an insulating sheet, the back pressure space of the microphone can be widened even if the insulating member is thinned in the height direction, and an increase in the number of working steps can be suppressed. It becomes possible.

Further, even when the case 12 is caulked, the soft resin does not exist in the portion that receives the caulking pressure, so that the contents are not crushed below the specified value, and the variation in the positional accuracy can be eliminated. And the yield is improved.

Moreover, in the present embodiment, the back electrode plate 18
By arranging so as to be present on the inner peripheral surface of the insulating ring 20, the floating region of the outer peripheral portion where the back electrode plate 18 and the diaphragm sub-assembly 14 are in contact with each other can be reduced, so that the region that does not function as a capacitor is It is possible to reduce the efficiency, and as a result, it is possible to improve the efficiency without changing the area of the capacitor section. Further, since the thickness of the back electrode plate 18 can be reduced in the height direction, the microphone as a whole can be reduced in thickness.

As a result, in the electret type condenser microphone 10, it is possible to achieve further miniaturization, higher sensitivity, and thinner thickness.

Further, in the present embodiment, the back electrode plate 18 is configured to be pressed to the diaphragm sub-assembly 14 side by the coil spring 22 which is an elastic body disposed on the JFET board 24. 18 does not have to be pressed by the insulating ring 20, and the back electrode plate 18 can be fixed in the insulating ring 20 without using a special design, which results in an increase in the number of work steps due to the reduction in thickness. It is possible to prevent an increase in manufacturing difficulty.

Further, the conduction between the JFET board 24 and the back electrode plate 18 of the condenser microphone 10 according to the present embodiment is constituted by the coil spring 22, but it is not limited to this, and the JFET board 24 and the back electrode 18 are not limited to this. Any material can be used as long as it can be electrically connected to the plate 18. In addition, back plate 18 and J
It is more preferable if a pressing force is exerted between the FET boards 24. For example, instead of the coil spring 22, another spring such as a leaf spring may be used, and conductive rubber may be used.
It is particularly preferable that the conduction can be ensured while exerting a pressing force between the back electrode plate 18 and the JFET board 24.

[Brief description of drawings]

FIG. 1 is a perspective view showing a condenser microphone according to an embodiment of the present invention in an upwardly arranged state.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is an exploded perspective view showing the condenser microphone.

FIG. 4 is a perspective view for explaining a method of assembling the condenser microphone.

[Explanation of symbols]

10 condenser microphone 12 cases 12a End wall 12b open end 12c inner surface 12d vent groove 14 Vibration plate sub-assy 16 spacers 16a opening 18 back plate 180 Back plate body 182 electret 188 through hole 20 insulating ring 22 coil spring 24 JFET board (substrate) 26 Vibration film 26A PET film 26B metal vapor deposition film 28 Support frame 30 sound holes 32 board body 34 JFET chip 36 Conductive pattern 38 Noise filter C capacitor section D drain electrode G gate electrode S source electrode

Claims (4)

[Claims] 1. A capacitor section including a diaphragm and a back plate for converting vibration due to sound into a capacitance change, and an impedance conversion element for converting the capacitance change converted by the capacitor section into an electric signal. A circuit board including, an insulating member for maintaining a positional gap between the capacitor section and the circuit board to prevent electrical connection, and a housing for internally fixing the capacitor section and the insulating member and the circuit board, In a provided condenser microphone, the insulating member is made of metal and is previously subjected to insulation processing. 2. A ring-shaped spacer for interposing a predetermined distance between the diaphragm and the back plate to form a space in the capacitor portion,
The insulating member is formed in a ring shape so as to abut the ring-shaped spacer, and the back plate is arranged so as to be present inside the inner peripheral surface of the insulating member. 1. The condenser microphone described in 1. 3. The condenser microphone according to claim 2, wherein the back plate is pressed toward the diaphragm by an elastic body arranged on the circuit board. 4. The condenser microphone according to claim 1, wherein the housing is internally fixed to the capacitor portion, the insulating member, and the circuit board by caulking.