WO2007097520A1

WO2007097520A1 - Electret condenser microphone and assembling method thereof

Info

Publication number: WO2007097520A1
Application number: PCT/KR2006/005864
Authority: WO
Inventors: Kyung-Hwan Kang; Kyoung-Ku Han
Original assignee: Bse Co., Ltd
Priority date: 2006-02-21
Filing date: 2006-12-29
Publication date: 2007-08-30
Also published as: KR100758513B1; KR20070084704A

Abstract

Provided is an electret condenser microphone including a backplate for replacing with a spacer ring. The electret condenser microphone includes a diaphragm, a backplate, and a protrusion. The diaphragm vibrates in response to sound pressure, a backplate is disposed to face the diaphragm, and a protrusion extends from at least one side of the backplate and contacts to one side of the diaphragm. The failure rate of the electret condenser microphone can be reduced by eliminating the tearing of a spacer ring in an insertion process, the generation of burrs on the inside and outside surfaces of the spacer ring, and the non-insertion or duplicate insertion of the spacer rings.

Description

ELECTRET CONDENSER MICROPHONE AND ASSEMBLING

METHOD THEREOF

Technical Field

[1] The present invention relates to an electret condenser microphone, and more particular, to an electret condenser microphone having a backplate capable of replacing a spacer ring. Background Art

[2] With recent development of information communication devices, e.g., mobile phones, telephones, MP3 players, etc., a sound wave device such as an amplifier has been rapidly developed. Thus, extensive research is being conducted to improve the performance of a subminiature electret condenser microphone mounted in the sound wave device.

[3] The electret condenser microphone includes a dielectric plate and a diaphragm and converts an audio signal into an electric signal using an electrostatic field formed between the dielectric plate and the diaphragm. The dielectric plate includes a high polymer film into which a semipermanent electric charge (called an electret) is injected. The diaphragm is manufactured by attaching a metal polar ring to a vibrating membrane formed of a polyethylen terephtalate (PET) film. The electret condenser microphone is classified into a foil type, a back type, and a front type according to the location of the electret.

[4] Such a conventional electret condenser microphone uses a spacer ring to prevent electric contact between the dielectric plate and the diaphragm so as to use them as two terminals of a capacitor, to adjust the sensitivity of the electret condenser microphone through the adjustment of a gap between the two terminals, and to provide a space for the vibration of the diaphragm.

[5] In manuacturing the spacer ring, a film roll formed of an insulating material such as an acrylic resin is cut off in the shape of the spacer ring using a spacer insertion mold and then is inserted into the electret condenser microphone.

[6] The process of inserting the cut-off spacer ring into the electret condenser microphone, however, has problems that causes the breakdown or malfunction of the electret condenser microphone. If the spacer ring is incompletely cut off, for example, it is torn or cut larger than designed, the dielectric plate and the diaphragm do not maintain a constant gap in parallel, causing the electrical contact therebetween and/or noise.

[7] In addition, during the process of cutting the film roll, blurrs are formed in an inner or outer circumference of a cut-off surface of the spacer ring. If the burred spacer ring is inserted between the dielectric plate and the diaphragm, a portion of the diaphragm is deformed or torn. Consequently, the diaphragm may abnormally transmit an external audio signal to the dielectric plate, causing noise or malfunction of the electret condenser microphone.

[8] Finally, when the spacer ring is incompletely cut off from the film roll and therefore still remains in the spacer insertion mold or the film roll during an automatic assembling process, the spacer ring is not inserted into the electret condenser microphone. In this case, both a current electret condenser microphone product and a next electret condenser microphone product may be defective. Disclosure of Invention Technical Problem

[9] Accordingly, the present invention is directed to an electret condenser microphone that substantially obviates one or more problems due to limitations and disadvantages of the related art.

[10] An object of the present invention is to provide an electret condenser microphone having a protrusion formed on a backplate, thereby replacing a spacer ring.

[11] Another object of the present invention is to provide an electret condenser microphone and an assembling method thereof, which can prevent a breakdown of the microphone due to the tearing of a spacer ring during an insertion process, the generation of burrs on the inner and outer circumferences of the spacer ring, and the non-insertion of the spacer ring.

[12] A further object of the present invention is to provide an electret condenser microphone, in the manufacturing process of which, instead of an insertion process of inserting a spacer ring separately manufactured into the microphone, an additional process of forming a protrusion is added to a backplate manufacturing process, such that the simplified manufacturing process is provided.

[13] A still further object of the present invention is to provide an electret condenser microphone, in which, a backplate with a protrusion, and an integrated base ring having an insulating base ring and a conductive base are inserted into the microphone, such that a back chamber space is enlarged, the sensitivity and the frequency response characteristic are enhanced, and a whole manufacturing process of the microphone is simplified to enhance the production yield. Technical Solution

[14] To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided an electret condenser microphone including: a diaphragm vibrating in response to sound pressure; a backplate disposed to face the diaphragm; and a protrusion extending from at least one side of the backplate, and contacting to one side of the diaphragm. [15] The backplate includes an electret film into which electric charges are injected, and a metal plate with the protrusion. [16] The electret condenser microphone further includes a case having a sound hole on its one side; a conductive base ring disposed on the backplate and providing a conduction path; and a printed circuit board (PCB) for amplifying and filtering an electric signal generated in the backplate. [17] According to another aspect of the present invention, there is provided a method of assembling an electret condenser microphone including: storing a diaphragm in the bottom of a case; placing a backplate with a protrusion on the top of the diaphragm; placing an insulating base ring and a conductive base ring on the top of the backplate; placing a PCB on the top of the conductive base ring; and curling the case at its opening toward interior components. [18] The step of disposing the backplate comprises the step of placing the backplate to contact the protrusion to one side of the diaphragm. [19] It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

Brief Description of the Drawings [20] FIG. 1 is an exploded perspective view of an electret condenser microphone according to an embodiment of the present invention. [21] FIG. 2 is a sectional assembled view of an electret condenser microphone according to an embodiment of the present invention. [22] FIGs. 3 and 4 are perspective views of a backplate according to embodiments of the present invention. [23] FIGs. 5 and 6 are perspective views of a backplate according to other embodiments of the present invention. [24] FIG. 7 is an exploded perspective view of an electret condenser microphone according to another embodiment of the present invention. [25] FIG.8 is a flow diagram illustrating a method of assembling an electret condenser microphone according to an embodiment of the present invention. [26] DESCRIPTION OF THE SYMBOLS IN MAIN PORTIONS OF THE

DRAWINGS>

[27] 100: case 110: sound hole

[28] 200: diaphragm 210: polar ring

[29] 220: vibrating membrane 300: backplate [30] 310: protrusion 320: electret film

[31] 330: metal plate 400: insulating base ring

[32] 500: conductive base ring 600: integrated base ring

[33] 700: PCB

Best Mode for Carrying Out the Invention

[34] Embodiments of the present invention will be described below in detail with reference the accompanying drawings.

[35] FIG. 1 is an exploded perspective view of an electret condenser microphone according to an embodiment of the present invention. FIG. 2 is a sectional assembled view of an electret condenser microphone according to an embodiment of the present invention.

[36] Referring to FIGs. 1 and 2, an electret condenser includes a case 100, a diaphragm

200, a backplate 300, an insulating base ring 400, a conductive base ring 500, and a printed circuit board (PCB) 700.

[37] The case 100 includes a sound hole 110 through which external sound is transmitted to the diaphragm 200, and receives components of the electret condenser microphone, for example, the PCB 700, the insulating base ring 500, the conductive base ring 400, the dielectric plate 300, and the diaphragm 200. Therefore, the case 100 can protect or shield the componets from external impact or external electronic noise. The case 100 provides a conduction path between the PCB 700 and the diaphragm 200. Since the case 100 is curled at an end of its opening, electrical connections between the components are tightened. To this end, the case 100 is formed of a conductive material selected from the group consisting of nickel, copper, aluminum, and an alloy thereof. The case 100 can also be plated with gold so as to increase its conductivity.

[38] The diaphragm 200 vibrates in respond to the sound pressure of an audio signal introduced through the sound hole 110 of the case 100, which leads to the change of an electric field. The diaphragm 200 serves as one terminal of a capacitor for generating an electric field to convert a sound signal into an electric signal. The diaphragm 200 includes a polar ring 210, and a vibrating membrane 220. The polar ring 210 is used to maintain the distance between the vibrating membrane 220 and the bottom surface of the case 100. One side of the polar ring 210 contacts the vibrating membrane 220. The polar ring 210 electrically connects the vibrating membrane 220 to the PCB 700 through the case 100. The polar ring 210 is formed in the shape of a donut or a ring using a metal such as copper or a compound metal. The vibrating membrane 220 contacts an electret film 320. The vibrating membrane 220 vibrates in response to the sound pressure, which leads to the change of the electric field. The vibrating membrane 220 may be formed of the film of insulation material such as polyethylene terephthalate (PET) formed in a thickness of several micrometers.

[39] The capacitance of the backplate 300 is changed due to the change of the vibration, i.e., the change of the distance between the vibrating membrane 220 and the backplate 300, transmitted from the diaphragm 200. Thus, the amount of accumulated electric charge on the backplate 300 is changed according to this capacitance change. That is, the current of the backplate 300 varies according to the change of the audio signal, such that the audio signal is converted into the electric signal. As illustrated in FIG. 3, a space between the backplate 300 and the diaphragm 200 is required to form a electric field such that the backplate 300 includes a metal plate 330 with a protrusion 310 formed for the space. The backplate 300 is provided by thermally laminating the electret film 320 on one side of the metal plate 330 using a laminating machine, and injecting an electric charge into the electret film 320 using a charge injector. The backplate 300 has semipermanent electric charges, forms a static electric field, and serves as the other terminal of the capacitor by connecting to the PCB 700 through the conductive base ring 500.

[40] The electret film 320 may be formed of a polymer film such as one of fluoronate ethylen ppropyylen (FEP), polytetrafluorethylene (PTFE), and perfluoroalkoxy (PFA).

[41] The metal plate 330 may be formed of at least one of gold, bronze, brass, and phosphor bronze. One or more protrusions 310, which are formed on the edge region of the metal plate 330 at regular intervals, may be formed by heating one side of the metal plate 330 and forging it using a press die. As illustrated in FIG. 4, the protrusions 310 are formed over the whole edge of the metal plate 330. The width of the protrusions 310 contacting the vibrating membrane 210 may be smaller than the width of the polar ring 210. The height of the protrusion 310 may be in the range from 0.01 to 0.04 D. Although only the forging method for forming the protrusion 310 has been described herein, a molding method can also be used.

[42] FIGs. 5 and 6 are perspective views of a backplate 300 according to other embodiments of the present invention.

[43] Referring to FIG. 5, a backplate 300 may be formed in a polygon shape, e.g., a rectangular shape. One or more protrusions 310 are formed on the edge region of one side of the backplate 300 formed in a rectangular shape. Referring to FIG. 6, a backplate 300 may be formed by providing a metal plate 330 formed in a polygon shape, and a protrusion 310 formed over the whole edge region of the metal plate 300.

[44] The insulating base ring 400 insulates the backplate 300 formed as a conductor and the case 100, and protects the backplate 300 from outside physical impact and heat. The insulating base ring 400 may be formed of a thermosetting plastic material.

[45] The conductive base ring 500 provides a conduction path through which the electric signal of the backplate 300 is transmitted to the PCB 700. The conductive base ring 500 may be formed of a metal material such as copper, silver, and nickel. In the embodiment of the present invention, copper is suitable because of its cost efficiency and easy processability.

[46] The PCB 700 receives the electric signal generated in the backplate 300 through the conductive base ring 500. The PCB 700 includes a field effect transistor (FET) for amplifying the received electric signal to be rectified and transmitted to external devices, a multilayer ceramic capacitor (MLCC) for filtering the amplified signal, and a circuit pattern for providing electric paths therebetween. The PCB 700 is electrically connected to the backplate 300 through the conductive base ring 500, and to the diaphragm 200 through the case 100, so that the electret condenser microphone operates as a capacitor.

[47] FIG. 7 is an exploded perspective view of an electret condenser microphone including a backplate with a protrusion, and an integrated base ring according to another embodiment of the present invention.

[48] Except for an insulating base ring and a conductive base ring, all components in

FIG. 7 are identical to those of the embodiment in FIG. 1, and thus their detailed description will be omitted for conciseness.

[49] Referring to FIG. 7, an electret condenser microphone includes a case 100, a diaphragm 200, a backplate with a protrusion 310, an integrated base ring 600, and a PCB 700.

[50] The integrated base ring 600 is formed by a PCB fabrication technique. More specifically, conductive layers 620 are formed on the top and bottom ends of a hollow cylindrical nonconductive ring 610 using metal plating, and a conductive pattern is formed on the inside surface of the nonconductive ring 610 to electrically connect the conductive layers 620 to each other, which completes the integrated base ring 600 integrating the insulating base ring 400 and the conductive base ring 500. The non- conductive ring 610 may be an insulating substrate formed of a glass epoxy based material, a resin based material, a polyvinyl chloride (PVC) based material, or the like.

[51] FIG.8 is a flowchart illustrating an assembling method of an electret condenser microphone according to an embodiment of the present invention.

[52] Referring to FIG. 8, in step SlOl, a diaphragm is placed on the base of a case with a sound hole, and a vibrating membrane is attached to a polar ring.

[53] In step S 102, a backplate is placed on the diaphragm.

[54] The process of inserting spacer ring is omitted, and the backplate with a protrusion is disposed on the diaphragm.

[55] In step S 103, an insulating base ring and conductive base ring, or an integrated base ring are(is) placed.

[56] The insulating base ring is inserted between the side of the backplate and the inside surface of the case, and insulates the backplate from the case. The conductive base ring is disposed on the backplate and transmits an electric signal generated in the backplate to a PCB. The integrated base ring is inserted instead of the insulating base ring and conductive base ring.

[57] In step S 104, the PCB is placed on the conductive base ring, or the integrated base ring.

[58] The top surface of the conductive base ring or integrated base ring contacts a circuit pattern of the PCB. The electric signal transmitted from the top surface is amplified by an FET, filtered through an MLCC, and transmitted to external devices.

[59] In step S 105, the case is curled inward at its opening such that inner components are packed closely.

[60] In the structure of a backplate with a protrusion and an assembling method of electret condenser microphones according to embodiments of the present invention, the method of forming the protrusion on a metal plate of the backplate is described for replacing a spacer ring herein, however, the present invention is not limited there to. That is, various changes in form, material, and process are possible.

[61] A back plate and integrated base ring can be applied to not only a back type electret condenser microphone but also a front type and foil type electret condenser microphone. Industrial Applicability

[62] As described above, in an electret condenser microphone according to an embodiment of the present invention, a spacer ring is replaced by a backplate with a protrusion.

[63] The present invention can prevent the tearing of the spacer ring during the insertion process, the generation of burrs on the inner and outer circumferences of the spacer ring, and the non-insertion of the spacer ring or duplicate insertion of the spacer rings, thereby reducing the failure rate of the electret condenser microphone.

[64] The process of inserting the spacer ring into the electret condenser microphone can be omitted by an additional process of forming the protrusion to a backplate manufacturing process. Thus, the manufacturing process of the electret condenser microphone can be simplified.

[65] The process of inserting the spacer ring into the electret condenser microphone can be omitted by an additional process of forming the protrusion to a backplate manufacturing process. Thus, the manufacturing process of the electret condenser microphone can be simplified.

[66] The integrated base ring forming process is added to the protrusion forming process on the backplate to replace the spacer ring. The integrated base ring includes the insulating base ring and the conductive base ring. Accordingly, a whole manufacturing process of the microphone can be simplified, thereby enhancing the production yield. In addition, a back chamber space is enlarged, thereby improving the sensitivity and frequency response characteristics of the electret condenser microphone. [67]

Claims

[I] An electret condenser microphone comprising: a diaphragm vibrating in response to sound pressure; a backplate disposed to face the diaphragm; and a protrusion extending from at least one side of the backplate, and contacting one side of the diaphragm. [2] The electret condenser microphone of claim 1, wherein the backplate includes: an electret film into which electric charges are injected; and a metal plate having the protrusion. [3] The electret condenser microphone of claim 2, wherein one or more protrusions are formed with a predetermined height at the edge region of the metal plate. [4] The electret condenser microphone of claim 2, wherein the protrusion is formed with a predetermined height at the whole edge region of the metal plate. [5] The electret condenser microphone of claims 3 or 4, the protrusion has the height of 0.01 to 0.04D from the metal plate. [6] The electret condenser microphone of any one of claims 1 to 5, wherein the backplate is formed in a circular shape, an oval shape, or a polygonal shape. [7] The electret condenser microphone of claim 1, further comprising: a case having a sound hole on its one side; a conductive base ring disposed on the backplate and providing a conduction path; and a printed circuit board (PCB) for amplifying and filtering an electric signal generated in the backplate. [8] The electret condenser microphone of claim 7, further comprising an insulating base ring for preventing electric contact between the conductive base ring and the case by storing the conductive base ring therein. [9] The electret condenser microphone of claims 7 or 8, wherein the conductive base ring and the insulating base ring are integrally formed into an integrated base ring. [10] The electret condenser microphone of claim 9, wherein the integrated base ring includes at least one of a first metal plated layer formed on the top and bottom ends thereof, a second metal plated layer formed on the inside surface thereof, and a via hole formed therein.

[I I] The electret condenser microphone of claim 9, wherein the integrated base ring has a hollow cylindrical shape or a hollow polygonal shape, and the outer diameter of the first metal plated layer is smaller than that of the integrated base ring. [12] A method of assembling an electret condenser microphone, comprising the steps of: storing a diaphragm in the bottom of a case; placing a backplate with a protrusion on the top of the diaphragm; placing an insulating base ring and a conductive base ring on the top of the backplate; placing a PCB on the top of the conductive base ring; and curling the case at its opening toward interior components. [13] The method of claim 12, wherein the step of disposing the backplate comprises the step of placing the backplate to contact the protrusion to one side of the diaphragm. [14] The method of claim 12, wherein the insulating base ring and the conductive base ring are integrally formed into an integrated base ring.