WO2007007928A1

WO2007007928A1 - Electret microphone include washer spring

Info

Publication number: WO2007007928A1
Application number: PCT/KR2005/002625
Authority: WO
Inventors: Sung Ho Park; Jun Lim
Original assignee: Bse Co., Ltd.
Priority date: 2005-07-08
Filing date: 2005-08-11
Publication date: 2007-01-18
Also published as: KR20070006293A; TW200704264A; TWI381748B; CN1820539A; CN1820539B; KR100673846B1

Abstract

The present invention relates to a condenser microphone which provides a normal operation and an improvement of yield. In order to achieve the above object of the invention, there is provided a electret microphone comprising: a casing; an internally housed components housed by the casing, the components including a vibrating plate, a spacer, a back plate, a first base ring and a second base ring; a printed circuit board for receiving an electrical signal from at least one of the vibrating plate and the back plate; a washer spring for providing an elasticity between the components, and among the components, the casing and the printed circuit board. In accordance with the condenser microphone including the washer spring, the microphone operates normally even an error occurs during a manufacturing process, a uniform product quality is maintained, and reduces a defect rate to remarkably improve a manufacturing yield. In addition, in accordance with the condenser microphone including the washer spring, the washer spring may be easily applied, and an effective and reasonable selection of the microphone and an application of the manufacturing method thereof are possible by showing an effective characteristic and a resulting effect and function.

Description

ELECTRET MICROPHONE INCLUDE WASHER SPRING

Technical Field

[1] The present invention relates to a condenser microphone, and in particular, to a condenser microphone which provides a normal operation and an improvement of yield. Background Art

[2] Recently, multimedia devices that are in everyday use, for example a MP3 player, a camcorder and a mobile device commonly provide a function of recording a sound generated from surroundings. Particularly, one of the reasons for the recording function of the multimedia devices in a trend of a miniaturization and high performance to play its given role is a microphone mounted in the miniaturized multimedia devices.

[3] Typical microphones are an electrodynamic microphone utilizing a magnet and a condenser microphone utilizing a principle of a condenser or capacitor. In case of the electrodynamic microphone, the magnet for generating a magnetic field is housed inside the microphone to use an induced electromotive force. The electrodynamic microphone comprises a coil which is connected to a vibrating plate and moves in the magnetic field. The electrodynamic microphone employs a principle wherein the induced electromotive force generated while the coil is moving in the magnetic field by a vibration is measured to be converted to an electrical signal. The electrodynamic microphone is mechanically robust so that it may be used in a harsh environment. However, the electrodynamic microphone is difficult to be miniaturized because the magnet should be housed inside the microphone, and has an inferior sensitivity characteristic and a slow response time.

[4] In case of the condenser microphone, to the contrary, a mechanical robustness is inferior to that of the electrodynamic microphone. However, the condenser microphone has a superior sensitivity characteristic and a fast response time. The condenser microphone is classified into a non-directional condenser microphone and a directional condenser microphone according to a direction characteristic, and classified into bidirectional and omnidirectional condenser microphone according to the direction charac teristic.

[5] The condenser microphone employs a principle wherein an electric field is generated by a vibrating plate and a back electret, and an amount of change in the generated electric field is then converted to an electrical signal. For this, a power should be supplied to one of the vibrating plate and the back electret of the condenser microphone to generate the electric field. For this reason, a method wherein the power is supplied to the back electret has been used. Recently, a condenser microphone which does not require a separate power supply by an electret in which a charge is accumulated has been developed.

[6] The condenser microphone using the electret is referred to as an electret condenser microphone (hereinafter referred to as "ECM"), and the ECM is classified into a front type and a back type according to a position of the electret and a diaphragm. Operating principles of the back type and the front type are identical except that positions of a dielectric plate having the electret and the diaphragm are different.

[7] The ECM is in trend of a miniaturization due to an employment of the electret, and many technologies are under development. The ECM comprises the diaphragm, the dielectric plate, a spacer ring, an insulation base ring, a conductive base ring and a printed circuit board (hereinafter referred to as "PCB") sequentially stacked in a cylindrical casing having its one end closed. An acoustic hole is formed through the closed end, and a vibration generated by a voice is transmitted through the acoustic hole. When the diaphragm, the dielectric plate, the spacer ring and the base rings are disposed in the cylindrical casing, a remaining portion of the cylindrical casing is curled inward for sealing or the PCB is bonded to the casing by manufacturing the PCB to be larger than the casing to manufacture the ECM. A solder ball for applying a SMD (Surface Mount Device) method is attached to an exposed portion of the PCB, or a terminal for connecting to a main board is formed. The ECM including the solder ball or the terminal is attached to the main board by the SMD method or a solder ball method.

[8] On the other hand, The ECM uses relatively low precision components by considering its manufacturing cost and productivity. Therefore, a margin (or an error) due to a manufacturing process exist among the diaphragm, the spacer, the insulation base rings, the back electret and a printed circuit board. The error results in a poor electrical contact between the internal component and a deformation due to a pressure, and provides a cause for a poor yield.

[9] Specifically, the ECM is manufactured by stacking or inserting the internal components such as the diaphragm, the spacer, the insulation base rings and the back electret in the cylindrical casing and then welding the end portion of the casing to an edge portion or a side surface of the PCB. Or, the PCB is housed in the casing and the end portion of the casing is curled to press the PCB and the internal components.

[10] In case of welding or bonding the PCB to the casing, when the internal components are manufactured to be smaller than a standard size, a small gap is generated, which results in the poor electrical contact between the internal components when bonded without a separate bonding process to degrade the manufacturing yield. On the other hand, when the internal components are manufactured to be larger than a standard size, the internal components protrude above the casing, which raise a difficulty in the bonding process, or a bending of the PCB and a deformation of the components even when the PCB is bonded to the casing to degrade the yield. A similar disadvantage exists in case of using the curling process resulting in an increase in a defect rate and in turn, an increase in the manufacturing cost.

[11] Moreover, the ECM is required to have the diaphragm and the back electret fixed to maintain a distance therebetween so that a normal operation is possible and a high performance and a desired performance can be expected. However, the conventional PCB has above-described problem due to the error in the manufacturing process and the problem also exist in the diaphragm and the back electret, resulting in the bending of the diaphragm, an increase in the distance between the diaphragm and the back electret. The bending and the increase or a decrease in the distance results in a degradation of a sensitivity of the ECM and mal-function, and in turn a reduction of the manufacturing yield. Disclosure of Invention Technical Problem

[12] It is an object of the present invention to provide a condenser microphone wherein a normal operation and an improvement of manufacturing yield are possible.

[13] It is an object of the present invention to provide a condenser microphone by providing an exact inserting position of a washer spring and distinguishing an effect and a function for most effective microphone.

[14] It is another object of the present invention to provide a condenser microphone wherein the number of components is not increased despite an addition of a washer spring to suppress an increase in a manufacturing cost.

[15] In addition, it is an object of the present invention to provide a condenser microphone wherein a thickness of a washer spring and a displacement range are reasonably defined by considering a current manufacturing process so as to be immediately applied to the current manufacturing process.

[16] Finally, it is yet another object of the present invention to prove that a technical idea of the present invention may universally be applied by showing that an effect of using a washer spring is not dependent upon a sealing method of a casing.

Technical Solution

[17] In order to achieve the above object of the invention, there is provided a electret microphone comprising: a casing; an internally housed component housed by the casing, the components including a vibrating plate, a spacer, a back plate, a first base ring and a second base ring; a printed circuit board for receiving an electrical signal from at least one of the vibrating plate and the back plate; a washer spring for providing an elasticity between the components, and among the components, the casing and the printed circuit board.

[18] It is preferable that the washer spring is inserted between the casing and the vibrating plate.

[19] In addition, it is preferable that the vibrating plate comprises a diaphragm and a polar ring for fixing and supporting the diaphragm and for providing a conductive path to the diaphragm, and that the washer spring forms a single body with the polar ring.

[20] It is preferable that the vibrating plate is electrically connected to the printed circuit board via the washer spring and the casing.

[21] In addition, it is preferable that the washer spring is inserted between the back plate and the second base ring, and the back plate is electrically connected to the printed circuit board by the washer spring and the second base ring.

[22] The washer spring may be a belleville type, a dish type, a cone type, a wave type or a spring pin type.

[23] It is preferable that a thickness of the washer spring ranges from 0.05mm to 0.2mm or from 0. lmm to 0.15mm, a strain of the washer spring in a direction of an elastic force ranges from 0.01mm to 0.09mm.

[24] It is preferable that the printed circuit board is housed inside the casing, and the casing is curled or the casing is welded or bonded to the printed circuit board to be sealed. Advantageous Effects

[25] As described above, in accordance with the condenser microphone including the washer spring, the microphone operates normally even an error occurs during a manufacturing process, a uniform product quality is maintained, and reduces a defect rate to remarkably improve a manufacturing yield.

[26] In addition, in accordance with the condenser microphone including the washer spring, the washer spring may be easily applied, and an effective and reasonable selection of the microphone and an application of the manufacturing method thereof are possible by showing an effective characteristic and a resulting effect and function.

[27] Moreover, in accordance with the condenser microphone including the washer spring, a method and a structure which prevents an increase in the number of components is provided to prevent an increase in a manufacturing cost due to a use of the washer spring.

[28] In accordance with the condenser microphone including the washer spring, a thickness and a displacement range are limited within an actually applicable range, and a range wherein the effect of the present invention is clearly shown is provided to be applied to an actual manufacturing process.

[29] Finally, in accordance with the condenser microphone including the washer spring, various embodiments of the condenser microphone is provided and an application of the washer spring is not dependent upon a minor factor such as a sealing method so as to be universally applied as well. Brief Description of the Drawings

[30] Fig. 1 is cross-sectional view illustrating a back type electret condenser microphone in accordance with a first embodiment of the present invention.

[31] Fig. 2 is a cross-sectional view illustrating an assembled condenser microphone of

Fig. 1.

[32] Fig. 3 is a diagram illustrating a washer spring of Figs. 1 and 2.

[33] Fig. 4 is a diagram illustrating various examples of the washer spring of Fig. 3.

[34] Fig. 5 is a cross-sectional view illustrating an electret condenser microphone in accordance with a second embodiment of the present invention.

[35] Fig. 6 is a cross-sectional view illustrating an electret condenser microphone in accordance with a third embodiment of the present invention.

[36] Fig. 7 is a cross-sectional view illustrating an electret condenser microphone in accordance with a fourth embodiment of the present invention.

[37] Fig. 8 is a cross-sectional view illustrating an electret condenser microphone in accordance with a fifth embodiment of the present invention. Best Mode for Carrying Out the Invention

[38] Fig. 1 is cross-sectional view illustrating a back type electret condenser microphone in accordance with a first embodiment of the present invention, and Fig. 2 is a cross- sectional view illustrating an assembled condenser microphone of Fig. 1.

[39] Referring to Figs. 1 and 2, the ECM in accordance with the present invention comprises a casing 1, a washer spring 2, a vibrating plate 3, a spacer 5, a back plate 6, a first base ring 8, a second base ring 9 and a printed circuit board 10.

[40] The casing 1 houses the washer spring 2, the vibrating plate 3, the spacer 5, the back plate 6, the first base ring 8 and the second base ring 9 and protects internal components from an external shock. In addition, the casing 1 blocks indrafts of acoustic noise and an electro-magnetic interference noise from outside so that a conversion of a sound to an electrical signal is smoothly carried out. The casing 1 electrically connects the vibrating plate 3 and the printed circuit board 10. For this, the casing 1 is manufactured to have a cylinder shape, and has a structure wherein one end portion is closed except an acoustic hole 11 (sound input hole) and the other end portion is open (opening). The washer spring 2, the vibrating plate 3, the spacer 5, the back plate 6, the first base ring 8 and the second base ring 9 are sequentially stacked inside surface of the casing 1 where the acoustic hole 11 is formed. The opening of the casing 1 is sealed by bonding or welding to a side surface and an edge portion of the side surface of the printed circuit board 10 or an end portion of the opening of the casing 1 is curled to be sealed after housing the printed circuit board 10 inside the casing 1. The casing 1 is manufactured using a metal having high conductivity such as aluminum or copper to block a noise, and gold or nickel may be electroplated on the casing 1 to improve an electrical conductivity and to prevent a corrosion.

[41] The washer spring 2 prevents movements of the spacer 5, the vibrating plate 3, the back plate 6, and the first and the second base rings 8 and 9 due to a margin generated during a manufacturing process of the ECM, and electrically connects the vibrating plate 3 and the printed circuit board 10 together with the casing 1. For these, the washer spring 2 is inserted between the casing 1 and the vibrating plate 3. Through this, the washer spring 2 eliminates an unnecessary gap generated during the manufacturing process among the vibrating plate 3, especially a polar ring 3a, the first base ring 8 and the casing 1, and presses the components to be adhered as well. In addition, the washer spring 2 enables an adjustment of a process pressure or a bonding pressure generated during an assembly or a sealing of the components stacked in a small space, and minimizes a damage of the component such as an deformation of the vibrating plate 3 during an curling process of the casing 1 and an assembly of the printed circuit board 10. A description in detail will be described below with reference to Figs. 3 and 4.

[42] The vibrating plate 3 vibrates according to an acoustic pressure of a sound transmitted through the acoustic hole 11 of the casing 1 to generate a variation of an electric field. In addition, the vibrating plate 3 serves as an electrode for generating the electric field for converting an acoustic signal to an electrical signal. For this, the vibrating plate 3 includes a diaphragm 3b and the polar ring 3a. The diaphragm 3b varies the electric field according to the vibration by the acoustic pressure. For this, the diaphragm 3b is manufactured by sputtering nickel (Ni) or gold (Au) for a conductive characteristic on a film such as PET (Polyethylene Terephthalate) having a thickness of a few micrometers. The polar ring 3a is used to separate and maintain a gap between the diaphragm 3b and an inner sidewall of the casing 1, and is in contact with the diaphragm 3b on one side and the washer spring 2 on the other side. In addition, the polar ring 3a electrically connects the printed circuit board 10 and the diaphragm 3b via the casing 1 and the washer spring 2. The polar ring 3a is manufactured to have a donut or a ring shape using a metal such as copper and an alloy thereof.

[43] The spacer 5 is disposed between the vibrating plate 3 and the back plate 6, and serves a function of maintaining a distance and parallel between the vibrating plate 3 and the back plate 6. In addition, the spacer 5 electrically isolates the vibrating plate 3 and the back plate 6, and is manufactured to have a donut or a ring shape using a material having a superior insulating characteristic such as an acrylic resin.

[44] The back electret (or dielectric plate) 6 forms a static electric field along with the vibrating plate 3 to convert the acoustic pressure by the acoustic signal into the electrical signal. For this, the back electret 6 comprises an electret high molecular film 6a and a metal plate (or electret) 6b. An electric charge is semi-permanently charged in the electret high molecular film 6a, and the static electric field is formed by the charged electric charge. The back electret 6 is formed by pressurizing and thermal bonding a high molecular film such as PTFE (Poly Tetra Fluoro Ethylene), PFA (Perfluoroalkoxy), FEP (Fluoroethylenepropylene) to the conductive electret 6b and then injecting the charge using a charge injector. The electret 6b consists of a metal such as copper, bronze, brass and phosphor bronze.

[45] The first base ring 8 (or insulation base ring) is disposed between back electret 6 the casing 1 to electrically insulate back electret 6 and the casing 1. The first base ring 8 has a cylindrical or a hollow polygonal pillar shape, a surface of the cylinder or the pillar is in contact with the casing 1. The first base ring 8 houses the second base ring

9. in addition, one of a bottom surface or a top surface of the first base ring 8 not only supports the spacer 5 but also firmly fixes other components by the casing 1, the spacer

5 and the washer spring 2.

[46] The second base ring 9 (or conductive base ring) electrically connects back electret

6 and the printed circuit board 10. an outside diameter of the second base ring 9 is proportional to an inside diameter of the first base ring 8 to prevent a vibration of the second base ring 9 by an external shock. In addition, the second base ring 9 also has a shape of the cylindrical or the hollow polygonal pillar shape, and a bottom surface and a top surface thereof are in contact with back electret 6 and the printed circuit board

10, respectively.

[47] The printed circuit board 10 (hereinafter referred to as "PCB") includes a circuit and terminal for amplifying and filtering the electrical signal generated by the variation of the electric field to transmit to outside. For this, the PCB 10 includes an amplifying element such as a field effect transistor (hereinafter referred to as "FET") for amplifying the variation of the electrical field, and a filter circuit such as Multilayer Ceramic Capacitor (hereinafter referred to as "MLCC") including one or more capacitor for filtering. The amplifying element, the filter circuit and a circuit pattern for connecting the amplifying element, the filter circuit are formed on a first side of the PCB 10, and a terminal for connecting to an external device or board, and a solder ball are formed on a second side of the PCB 10. In addition, the PCB 10 is electrically connected to the vibrating plate 3 and back electret 6 by the second base ring 9 and the casing 1. when the FET was used as an the amplifying element, a gate terminal of the FET is connected to back electret 6 by the second base ring 9, a source terminal is connected to the vibrating plate 3 by the casing 1, and a drain terminal is connected to

MLCC.

Mode for the Invention

[48] Fig. 3 is a diagram illustrating a shape and an operation of the washer spring of

Figs. 1 and 2.

[49] Fig. 3 illustrates a C-washer spring 2 of a basic shape. As shown in Fig. 3, the washer spring 2 is manufactured to have a ring shape wherein two ends of a metal plate having a predetermined thickness deviate from each other so that the ends are not in contact. In addition, a spring-pin type may be used as well as the C-washer spring 2. Although Fig. 3 shows the washer spring 2 having only one bent end, a washer spring having two ends bent in opposite direction may be used. An arrow A of Fig. 3 illustrates a direction to which an external pressure is applied, and an arrow B illustrates a direction to which a force of the washer spring 2 is applied against the external pressure. That is, when the casing 1 is disposed under the washer spring 2 (downward direction in Fig. 3) and the polar ring 3a and the spacer 5 apply pressure from the top (upward direction in Fig. 3), the washer spring 2 reacts to the pressure in the direction of the arrow A. Therefore, the washer spring 2 is compressed in the direction A to generate a repellent force in the direction of arrow B. That is, only a displacement height d2 is reduced without any changes in an outside diameter d3 and thickness dl of the washer spring 2. Therefore, in case the first base ring 8, the spacer 5 and the vibrating plate 3 are inserted in the casing 1 and the casing 1 is then curled, the internal components, the casing 1, the spacer 5 and the vibrating plate 3 in particular, are adhered together by the washer spring 2 even when an unnecessary space is formed due to a manufacturing process. In addition, the washer spring 2 is contracted due to an elasticity to form a housing space for the spacer 5, the first base ring 8 and the vibrating plate 3 even when a required space is small. As described above, in order to obtain an shock absorbing and pressurizing effect, it is sufficient that a thickness of the polar ring 3a is reduced or extending a length of the casing 1 by the displacement height d2 of the washer spring 2 within an error limit.

[50] Considering a currently available manufacturing process, it is preferable that a thickness of the washer spring 2 is determined within a range of 0.05mm to 0.5mm. When the thickness of the washer spring 2 is too thin, since the elasticity is too small for the current material, it is difficult to obtain a desirable shock absorbing and pressurizing effect and a manufacturing cost is greatly increased in order to obtain the desirable shock absorbing and pressurizing effect. In addition, considering that thicknesses of ECMs having a diameter of 4mm, 6mm and 8mm, namely heights of the cylinder are 1.5mm, 2.87mm and 3.5mm respectively, and that the internal components inside the condenser microphone are manufactured using materials such as a thin copper alloy or a resin, the thickness of the washer spring 2 should be determined to be not more than 0.5mm. Moreover, considering that a margin generated during the manufacturing of the ECM is about 0.2mm, it is preferable that the thickness of the washer spring 2 is determined to be in a range of 0.1mm to 0.15mm. Moreover, it is preferable that the displacement height of the washer spring 2 is determined to be in a range of 0.01mm to 0.08mm.

[51] Fig. 4 is a diagram illustrating various examples of the washer spring of Fig. 3.

[52] Referring to Fig. 4, Fig. 4a illustrates a ring type washer spring 22 wherein in a portion between an inside and an outside diameter is concaved. That is, a case a cross- section of the washer spring has a "v" shape is exemplified. In addition, Fig. 4b illustrates a wave washer spring 23 wherein one or more portion is bent to have a shape of a wave. Fig. 4c illustrates a belleville washer spring having a elongated portion along an outside diameter of plate washer spring. Contrary to Fig. 4a, Fig. 4d illustrates a washer spring 25 wherein the washer spring 25 itself is bent to have a "V" shape. Moreover, a cone type washer spring, and a saw-toothed washer spring having a sawtooth-shaped wing may be applied to the embodiment of the present invention.

[53] Fig. 5 is a cross-sectional view illustrating an electret condenser microphone in accordance with a second embodiment of the present invention. Since the second embodiment is similar to the first embodiment in its configuration and operation except that a washer spring 32 is inserted between a second base ring 39 and a back electret 36, a description in detail is omitted.

[54] The washer spring 32 in accordance with the second embodiment electrically connects the PCB 40 and the back electret 36 via the second base ring 39. In addition, the washer spring 32 is inserted between the back electret 36 and the second base ring 39 to absorb a shock or to apply a pressure. Through this, a connection between the second base ring 39 and the PCB 40 is secured. Moreover, since the shock is absorbed and the pressure is applied from below the back electret 36, a contact of the back electret 36, a spacer 35, a vibrating plate 33 and a casing 31 is firm and a damage of the back electret 36, the spacer 35, the vibrating plate 33 and the casing 31 is prevented by dispersing the pressure applied thereto.

[55] Fig. 6 is a cross-sectional view illustrating an ECM in accordance with a third embodiment of the present invention, wherein a foil type ECM having an electret in a vibrating plate is shown.

[56] The foil type ECM in accordance with the third embodiment of the present invention comprises a casing 51, a washer spring 52, a electret vibrating plate 53, a spacer 55, a back electret 56, a first base ring 58, a second base ring 59 and a PCB 60. [57] A description regarding an operation and characteristic identical to the first or the second embodiment will be omitted in a description of the third embodiment.

[58] The back electret 56 generates a static electric field with the electret vibrating plate

53 and converts an acoustic pressure to an electrical signal to be provided to the PCB 60. The back electret 56 is electrically connected to the PCB 60 by the second base ring 59. in addition, a pressure is applied in a direction of the electret vibrating plate 53 by the washer spring 52 inserted between the back electret 56 and the second base ring 59, thereby maintaining a constant distance to the electret vibrating plate 53.

[59] The second base ring 59 electrically connects the PCB 60 and the back electret 56 having the washer spring 52 therebetween, the second base ring 59 supports the washer spring 52, the back electret 56 and the electret vibrating plate 53 along with the PCB 60 so that the components housed in the casing 51 are firmly fixed.

[60] The electret vibrating plate 53 generates the static electric field with the back e lectret 56, and includes a polar ring 53a and the electret diaphragm 53b. As described above, the electret vibrating plate 53 vibrates according to the acoustic pressure to convert the acoustic signal to the electrical signal. The electret vibrating plate 53, contrary to a back type ECM, also serves as an electret generating the static electric field. That is, the electret diaphragm 53b of the electret vibrating plate 53 is manufactured using a high molecular film which can maintain an electrical charge by charging although the high molecular film has a slightly poor vibration characteristic. The electret vibrating plate 53 faces the back electret 56 having the spacer 55 disposed therebetween. A surface of the electret vibrating plate 53 facing the back electret 56 is charged with the electrical charge to form the static electric field for generating the electrical signal.

[61] Fig. 7 is a cross-sectional view illustrating another example of the ECM in accordance with a fourth embodiment of the present invention.

[62] A structure, an operation and a function of the fourth embodiment are similar to the third embodiment except that an inserting position of a washer spring 63 is changed. In addition, since an action of the washer spring 63 is almost identical to the first embodiment, a detailed description is omitted.

[63] A foil type ECM shown in Fig. 7 includes a washer spring 62 inserted between a polar ring 63a of a vibrating plate 63 and a casing 61. Through this, along with a first base ring 68, a second base ring 69 and the casing 61, a back electret 66, a spacer 65 and the vibrating plate 63 are more firmly fixed, and protected form an excessive pressure applied thereto.

[64] In addition, a distance between the vibrating plate 63 and the back electret 66 is constantly maintained by the washer spring 62 even when an error due to a process occurs. [65] On the other hand, as can be seen from the first to fourth embodiments, the washer ring of the present invention may be inserted between vibrating plate and the casing, and between the second base ring and the back electret simultaneously. That is, two polar rings may be disposed inside one ECM. However, in this case, it is not desirable because of an increase in a manufacturing cost, manufacturing time due to an increase in the number of components as well as an increase in the thickness of the ECM. Moreover, a method of inserting the washer spring between the second or the first base ring and the PCB may be considered. In this case, however, since a partial deformation and damage of the PCB may occur, inserting positions described in the first through fourth embodiments is the most suitable.

[66] Fig. 8 is a cross-sectional view illustrating an electret condenser microphone in accordance with a fifth embodiment of the present invention, wherein the washer spring is used instead of the polar rings of the first through fourth embodiments.

[67] A description regarding a configuration and effect similar to the first through fourth embodiments will be omitted in a description of the fifth embodiment, and only an operation and characteristic of a configuration different from the first through fourth embodiments will be described.

[68] Referring to Fig. 8, the ECM in accordance with the fifth embodiment of the present invention comprises a casing 71, a washer spring 72, a vibrating plate 73, a spacer 75, a back plate 76, a first base ring 78, a second base ring 79 and a PCB 80.

[69] The washer spring 72 electrically connects the spacer 75 and the PCB 80 and also supports and fixes the spacer 75. In addition, the washer spring 72 absorbs and disperses an excessive pressure applied to the vibrating plate 73, the spacer 75 and the back plate 76 to prevent a damage or a deformation of the vibrating plate 73, the spacer 75, the back plate 76, the first base ring 78 and the second base ring 79 due to the excessive pressure. Moreover, the washer spring 72 compensates insufficient pressure to firmly fix the internal components, resulting in a normal operation of the ECM.

[70] The spacer 75 generates a vibration according to an acoustic pressure to generate an electrical signal. The generated electrical signal is transmitted to the PCB 80 via the washer spring 72 and the casing 71. For this, the washer spring 72 is formed by a thin high molecular film having an excellent vibration characteristic. In addition, in case of the foil type ECM, the washer spring 72 also serves as an electret.

[71] The back plate 76 is connected to the PCB 80 by the second base ring 79, and generates an electrical signal to the PCB 80 along with the washer spring 72. The back plate 76 further comprises an electret high molecular film for generating a static electric field in case of a back type ECM.

[72] Rest of the configuration is described through the first through the fourth embodiment. Therefore, a detailed description is omitted. In accordance with the fifth embodiment, the washer spring is used instead of the polar ring disposed in the vibrating plate. Through this, the fifth embodiment provides a substantially the same effect as the first through the fourth embodiments while reducing the number of components.

[73] As described above, the ECMs provided by the first through the fifth embodiments reduce a mal-function, a quality degradation, and a defect due to unavoidable margin generated during the manufacturing process thereof.

[74] Firstly, when a gap between the components is excessively increased because of the process margin, a defective product is manufactured due to a poor electrical contact or a distance variation between the diaphragm and the back electret or a sensitivity characteristic is degraded. However, the excessive gap is removed through the washer spring to prevent the defect due to the poor electrical contact and also prevent an increase in the distance between the diaphragm and the back electret, thereby maintaining substantially the same sensitivity characteristic for most of the ECM products.

[75] In addition, when a gap between the components are very small, the washer spring is deformed by an elasticity to provide a gap to be maintained between the components, resulting in a remarkable reduction of a defect due to a failure of adjustment of the margin.

[76] Moreover, since a manufacturing error may be sufficiently considered by reflecting the height of the washer spring, a precision processing is not necessary, resulting in a reduction in the manufacturing cost.

[77] The drawings for describing the first through the fifth embodiments illustrate examples wherein the internal components are sealed by a curling process. However, the first through the fifth embodiments may be applied to an ECM wherein the ECM is sealed by welding or bonding the PCB to the casing, namely a welding type. The welding type is identical to the first through the fifth embodiments except the bonding method of the casing and the PCB. Therefore, a detailed description is omitted. Industrial Applicability

[78] A condenser microphone wherein a normal operation and an improvement of manufacturing yield are possible is provided. In addition, a condenser microphone having a most effective form is provided by providing an exact inserting position of a washer spring and distinguishing an effect and a function for most effective microphone. A condenser microphone wherein the number of components is not increased despite an addition of a washer spring to suppress an increase in a manufacturing cost is provided. A condenser microphone wherein a thickness of a washer spring and a displacement range are reasonably defined by considering a current manufacturing process so as to be immediately applied to the current manufacturing process is provided. Finally, a technical idea of the present invention may be universally applied by showing that an effect of using a washer spring is not dependent upon a sealing method of a casing.

[79]

[80]

[81]

Claims

[ 1 ] A electret microphone comprising : a casing; an internally housed components housed by the casing, the component including a vibrating plate, a spacer, a back plate, a first base ring and a second base ring; a printed circuit board for receiving an electrical signal from at least one of the vibrating plate and the back plate; a washer spring for providing an elasticity between the components, and among the components, the casing and the printed circuit board. [2] The electret microphone in accordance with claim 1, wherein the washer spring is inserted between the casing and the vibrating plate. [3] The electret microphone in accordance with claim 1, wherein the vibrating plate comprises: a diaphragm; and a polar ring for fixing and supporting the diaphragm and for providing a conductive path to the diaphragm. [4] The electret microphone in accordance with claim 3, wherein the washer spring forms a single body with the polar ring. [5] The electret microphone in accordance with one of claims 2 and 4, wherein the vibrating plate is electrically connected to the printed circuit board via the washer spring and the casing. [6] The electret microphone in accordance with claim 1, wherein the washer spring is inserted between the back plate and the second base ring. [7] The electret microphone in accordance with claim 6, wherein the back plate is electrically connected to the printed circuit board by the washer spring and the second base ring. [8] The electret microphone in accordance with claim 1, wherein the washer spring is a belleville type, a dish type, a cone type, a wave type or a spring pin type. [9] The electret microphone in accordance with claim 1, wherein a thickness of the washer spring ranges from 0.05mm to 0.2mm or from 0.1mm to 0.15mm. [10] The electret microphone in accordance with claim 1, a strain of the washer spring in a direction of an elastic force ranges from 0.01mm to 0.09mm. [11] The electret microphone in accordance with claim 1, wherein the printed circuit board is housed inside the casing, and the casing is curled. [12] The electret microphone in accordance with claim 1, the casing is welded or bonded to the printed circuit board to be sealed.