WO2007032579A1

WO2007032579A1 - Electret condenser microphone for surface mounting and main board including the same

Info

Publication number: WO2007032579A1
Application number: PCT/KR2006/000377
Authority: WO
Inventors: Sungho Park; Jun Lim; Chunghee Noh
Original assignee: Bse Co., Ltd.
Priority date: 2005-09-15
Filing date: 2006-02-02
Publication date: 2007-03-22
Also published as: KR20070031524A

Abstract

The present invention relates to an electret condenser microphone and a main board including the same wherein the electret condenser microphone is mounted on a back side of the main board on which relatively large circuit components or parts are mounted so that the electret condenser microphone is easily mounted without preparing a separate space and a manufacturing process thereof is simplified. The electret condenser microphone in accordance with the present invention comprises: a casing; an acoustic processor for converting an external acoustic signal to an electrical signal, the acoustic processor being enclosed by the casing; and a printed circuit board including an acoustic hole, wherein the printed circuit board removes a noise included in the electrical signal and amplifies the electrical signal to generates an acoustic signal, the printed circuit board comprising a pad for delivering the acoustic signal to an outside. The electret condenser microphone and the main board including the same does not employ an interface board for bonding the electret condenser microphone to the main board so that a space required for mounting the electret condenser microphone is minimized and a manufacturing process is simplified, thereby reducing a cost for manufacturing and mounting of the electret condenser microphone.

Description

ELECTRET CONDENSER MICROPHONE FOR SURFACE MOUNTING AND MAIN BOARD INCLUDING THE SAME

Technical Field

[1] The present invention relates to an electret condenser microphone, and in particular, to an electret condenser microphone and a main board including the same wherein the electret condenser microphone is mounted on a back side of the main board on which relatively large circuit components or parts are mounted so that the electret condenser microphone is easily mounted without preparing a separate space and a manufacturing process thereof is simplified. Background Art

[2] Recently, portable multimedia devices such as a camera, a mobile phone, a laptop computer, a PDA (Personal Digital Assistant), a MP3 player, a portable gaming device and a portable DVD player which are capable of recording a sound of surroundings are very popular. The portable multimedia devices include an electret condenser microphone so that a recording function may be provided.

[3] Since the electret condenser microphone is small, operates by a low power, and has a low manufacturing cost, the multimedia device requiring an acoustic input should include the electret condenser microphone.

[4] Fig. 1 is a diagram illustrating an electret condenser microphone mounted on a main board of a multimedia device.

[5] Referring to Fig. 1, a conventional electret condenser microphone comprises a casing 4, an acoustic processor 5 housed in the casing 4 and a printed circuit board 6. The casing 4 blocks an external electromagnetic noise and acoustic noise and protects the inside components from an external shock. Generally, an acoustic hole is formed in the casing 4.

[6] The acoustic processor 5 inside a diaphragm, a spacer ring, a base ring and a back electret plate, and converts an acoustic signal to an electrical signal by vibrating according to the acoustic pressure to vary an electric field.

[7] The printed circuit board 6 amplifies and filters the electrical signal from the acoustic processor 5 and provides the amplified and filtered electrical signal to outside. As shown in Fig. 1, the printed circuit board 6 is connected to an external board by a bonding terminal 7 or a solder ball.

[8] Particularly, as shown in Fig. 1, the electret condenser microphone is manufactured by housing the printed circuit board 6 in the casing 4, and curling an end portion of the casing 4 to surround the printed circuit board 6. It is difficult to apply a heat to the bonding terminal during a separation as well as bonding the printed circuit board 6 to the external board when the curling process is used. More specifically, it is difficult to separate the bonding terminal 7 because the bonding terminal 7 is isolated from outside by a curled portion of the casing 4. In order to solve this problem, a conventional method wherein an interface board 2 is used as shown in Fig. 1 has been proposed. That is, when the conventional electret condenser microphone manufactured by the curling process is defective, the interface board 2 is used to easily separate the electret condenser microphone 3 since it is difficult to separate the electret condenser microphone 3 from a main board 1. Therefore, when the electret condenser microphone 3 is defective, the interface board 2 is removed instead of removing the defective electret condenser microphone 3. The interface board 2 comprises one or more pads 8 for connecting to the main board 1, and the pads 8 is welded by a soldering or a resistance welding to be connected to the main board 1 and the interface board 2.

[9] A surface mounting technology is mainly used for the electret condenser microphone using the interface board 2 due to the fact that the electret condenser microphone 3 using the interface board 2 may easily be mounted and unmounted. However, the interface board 2 should be separately manufactured and assembled so that the manufacturing process is complicated and a manufacturing cost is increased. Moreover, a space for mounting the interface board 2 in addition to the electret condenser microphone 3 should be secured, thereby degrading a miniaturization of the multimedia devices.

[10] Particularly, in case of the electret condenser microphone 3 wherein the acoustic hole is formed in the main board 1 instead of the casing 4, it is difficult to align the acoustic hole in aligning the printed circuit board 6, the interface board 2 and the main board 1.

Disclosure of Invention Technical Problem

[11] It is an object of the present invention to provide an electret condenser microphone and a main board including the same wherein the electret condenser microphone is mounted on a back side of the main board on which relatively large circuit components or parts are mounted so that the electret condenser microphone is easily mounted without preparing a separate space and a manufacturing process thereof is simplified.

[12] It is another object of the present invention to provide an electret condenser microphone and a main board including the same wherein a pad for a bonding of the electret condenser microphone and an electrical connection is formed for each of the electret condenser microphone and the main board for simplifying and standardizing a manufacturing process.

[13] It is yet another object of the present invention to provide an electret condenser microphone and a main board including the same wherein a sealing ring is inserted between the main board and the electret condenser microphone to minimize a loss, a distortion and a echo phenomenon of an external acoustic signal, thereby improving a performance of the electret condenser microphone.

[14] It is yet another object of the present invention to provide an electret condenser microphone and a main board including the same wherein a washer spring is used to reduce the rate of defective products generated by a manufacturing process margin of the electret condenser microphone, and to guarantee a stable operation after an assembly of the main board. Technical Solution

[15] In order to achieve the above-described object, there is provided an electret condenser microphone comprising: a casing; an acoustic processor for converting an external acoustic signal to an electrical signal, the acoustic processor being enclosed by the casing; and a printed circuit board including an acoustic hole, wherein the printed circuit board removes a noise included in the electrical signal and amplifies the electrical signal to generates an acoustic signal, the printed circuit board comprising a pad for delivering the acoustic signal to an outside.

[16] The first side of the printed circuit board is bonded to the casing, and the pad is disposed on a second side of the printed circuit board, and a sealing ring for surrounding the acoustic hole may be disposed at an edge of the acoustic hole on the second side.

[17] The acoustic processor comprises: a back electret plate for forming a static magnetic field; a diaphragm for forming the static magnetic field with the beck electret plate, wherein the diaphragm vibrating according to the acoustic pressure to vary the static magnetic field whereby the electrical signal is generated; a spacer ring for maintaining a distance between the diaphragm and the back electret plate; an insulation base ring for insulating at least one of the diaphragm and the back electret plate from the casing; and a conductive base ring for providing a path for one of the diaphragm and the back electret plate.

[18] The electret condenser microphone may further comprise a washer spring for providing an elasticity to at least one of the back electret plate, the diaphragm, the spacer ring, the insulation base ring and the conductive base ring.

[19] The electret condenser microphone may further comprise an acoustic resistor for removing or attenuating a portion of the acoustic signal.

[20] There is also provided a main board including an electret microphone, the board comprising: an electret condenser microphone comprising a casing, an acoustic processor for converting an acoustic pressure generated by an external acoustic signal to an electrical signal, the acoustic processor being enclosed by the casing, and a printed circuit board including a first acoustic hole, the printed circuit board being bonded to the casing; and a main board including a second acoustic hole for delivering the acoustic pressure to the first acoustic hole, wherein the main board is bonded to the printed circuit board.

[21] The printed circuit board may comprise a first pad for connecting to the main board disposed thereon; and the main board comprises a second pad disposed on a position corresponding to the first pad.

[22] The printed circuit board may be bonded to the casing via at least one of a laser welding, a high-temperature adhesive, a resistance welding and a soldering.

[23] The main board may further comprise a sealing ring between the printed circuit board and the main board.

[24] The sealing ring connects the first acoustic hole and the second acoustic hole.

[25]

Advantageous Effects

[26] As described above, in accordance with the electret condenser microphone and the main board including the same, the electret condenser microphone is mounted on a back side of the main board on which relatively large circuit components or parts are mounted so that the electret condenser microphone is easily mounted without preparing a separate space and a manufacturing process thereof is simplified.

[27] In accordance with the electret condenser microphone and the main board including the same, a pad for a bonding of the electret condenser microphone and an electrical connection is formed for each of the electret condenser microphone and the main board for simplifying and standardizing a manufacturing process.

[28] In accordance with the electret condenser microphone and the main board including the same, a sealing ring is inserted between the main board and the electret condenser microphone to minimize a loss, a distortion and an echo phenomenon of an external acoustic signal, thereby improving a performance of the electret condenser microphone.

[29] In accordance with the electret condenser microphone and the main board including the same, a washer spring is used to reduce the rate of defective products generated by a manufacturing process margin of the electret condenser microphone, and to guarantee a stable operation after an assembly of the main board. Brief Description of the Drawings

[30] Fig. 1 is a diagram illustrating an electret condenser microphone mounted on a main board of a multimedia device.

[31] Fig. 2 is a perspective view illustrating a main board including an electret condenser microphone in accordance with the present invention.

[32] Fig. 3 is a cross-sectional view of Fig. 2.

[33] Fig. 4 is a perspective view illustrating a cross-section of an electret condenser microphone, a main board and a sealing ring, wherein the sealing ring is inserted between a printed circuit board and the main board.

[34] Fig. 5 is a diagram illustrating a circular sealing ring.

[35] Fig. 6 is a diagram illustrating a rectangular sealing ring.

[36] Fig. 7 is a diagram illustrating a sealing ring extending to a position where a pad is formed.

[37] Fig. 8 is a diagram illustrating an acoustic processor shown in Figs. 2 through 7.

[38] Fig. 9 is a diagram exemplifying an electret condenser microphone including an acoustic processor wherein a diaphragm is disposed closer to a printed circuit board than a back electret plate.

[39] Figs. 10 through 12 are diagrams exemplifying an electret condenser microphone including an acoustic resistor. Best Mode for Carrying Out the Invention

[40] Fig. 2 is a perspective view illustrating a main board including an electret condenser microphone in accordance with the present invention, and Fig. 3 is a cross-sectional view of Fig. 2.

[41] Referring to Figs. 2 and 3, a main board including an electret microphone in accordance with the present invention comprises an electret condenser microphone 11 comprising a casing 12, an acoustic processor 14 enclosed by the casing 12 for converting an acoustic pressure generated by an external acoustic signal to an electrical signal, and a printed circuit board 13 including a first acoustic hole 15 and having a diameter equal to or larger than that of the casing 12, and a main board 10 including a second acoustic hole 16 for delivering the acoustic pressure to the electret condenser microphone 11 through the first acoustic hole. The main board 10 is bonded to the printed circuit board 13. In addition, a first pad 18for connecting to the main board 10 is disposed on the printed circuit board 13 of the electret condenser microphone 11, and a second pad 19 is disposed on the main board 10 bonded to the first pad 18.

[42] The electret condenser microphone 11 the acoustic pressure by the external acoustic signal to an electrical signal, removes a noise included in the electrical signal and amplifies the electrical signal to be provided to the main board 10. The electret condenser microphone 11 comprises the casing 12, the acoustic processor 14 enclosed by the casing 12 for converting the acoustic pressure to the electrical signal to be provided to the printed circuit board 13, and the printed circuit board 13 for generating an acoustic signal by filtering and amplifying the electrical signal from the acoustic processor 14, and providing the generated acoustic signal to the main board 10. Particularly, the diameter of the printed circuit board 13 is equal to or larger than that of the casing 12 such that the printed circuit board 13 may be bonded to the casing 12 by a resistance welding, a high temperature adhesive, and a laser welding. In addition, the first acoustic hole 15 for delivering the acoustic pressure is formed in the printed circuit board 13. The first pad 18 is formed on a back side, i.e. a surface that is not in contact with the casing 12. The first pad 18 is coupled to 19- formed on the main board 10 to fix the electret condenser microphone 11 to the main board 10 and also to provide a conductive path between the electret condenser microphone 11 and the main board 10. The first pad 18 and the second pad 19 may be bonded using the laser welding, the resistance welding, the high temperature adhesive, and a soldering.

[43] A circuit pattern for carrying out a function of the multimedia device is formed on the main board 10, and various circuit components are also mounted on the main board 10. Particularly, the electret condenser microphone 11 is mounted on the main board 10. For this, the second acoustic hole 16 is formed on the main board 10, and the second pad 19 is formed around the second acoustic hole 16.

[44] As shown in Fig. 3, the first acoustic hole 15 and the second acoustic hole 16 disposed such that centers of the acoustic holes 15 and 16 are almost aligned. Since the electret condenser microphone 11 is not a precision component, a small process error may occur during a manufacturing and a mounting of the electret condenser microphone 11 and a formation process of the second acoustic hole 16. While the positions of the first acoustic hole 15 and the second acoustic hole 16 may be not aligned due to the process error, it is preferable that the centers of the first acoustic hole 15 and the second acoustic hole 16 are aligned when it is assumed that the process error do not occur. In addition, it is preferable that shapes and diameters of the first acoustic hole 15 and the second acoustic hole 16 are identical in order to prevent a loss and a distortion of the acoustic pressure. Mode for the Invention

[45] Fig. 4 is a perspective view illustrating a cross-section of an electret condenser microphone, a main board and a sealing ring, wherein the sealing ring is inserted between a printed circuit board and the main board.

[46] A space is formed between the printed circuit board 13 and the main board 10 even when the centers of the first acoustic hole 15 and the second acoustic hole 16 are aligned in case of Figs. 2 and 3. When the acoustic signal is delivered to the space between the printed circuit board 13 and the main board 10 during a transmission process of the acoustic signal, a negative effect such as a resonance, an echo, and the loss of acoustic signal may occur. Therefore, a method for transmitting the acoustic signal passed through the second acoustic hole 16 to the first acoustic hole 15 without the loss or distortion is required. In order to achieve this, in accordance with the present invention, a sealing ring 27 is inserted between a printed circuit board 24 and a main board 20 as shown Fig. 4. The sealing ring 27 is inserted between the printed circuit board 24 and the main board 20 to provide an acoustic path between a first acoustic hole 25 and a second acoustic hole 28, and prevents the acoustic signal from reaching the space between the printed circuit board 24 and the main board 20. In addition, the sealing ring 27 may serve as an adhesive layer. The sealing ring 27 may fix the second local oscillator 21 to the main board 20 more firmly by bonding the printed circuit board 24 and the main board 20 when adhesive layers are formed on top and bottom surfaces of the sealing ring 27 or when the sealing ring 27 provides an adhesive strength by a pressure, a heat or an ultraviolet ray.

[47] Figs. 5 through 7 are diagrams illustrating various forms of the sealing ring, wherein Fig. 5 is a diagram illustrating a circular sealing ring, Fig. 6 is a diagram illustrating a rectangular sealing ring, and Fig. 7 is a diagram illustrating a sealing ring extending to a position where a pad is formed.

[48] Referring to Fig. 5, a seal ring 30 may be manufactured to have a donut shape. In addition, the seal ring 30 may be manufactured to have a rectangular shape as shown in Fig. 6. That is, the shape of the seal ring 30 does not have a significant meaning, and the seal rings 30 and 31 may have any shape as long as the seal ring 30 is in contact with the printed circuit board 24 and the main board 20 so as to prevent the acoustic signal from reaching the space between the printed circuit board 24 and the main board 20.

[49] Particularly, a seal ring 32 shown in Fig. 7 extends to a pad 33. When the seal ring

32 is as large as a printed circuit board 34, a manufacturing process may be simplified. In addition, it is preferable that the seal ring 32 extends without overlapping an area of the printed circuit board 34 where the pad 33 is formed to induce a contact between the printed circuit board 34 and a main board.

[50] Fig. 8 is a diagram illustrating an acoustic signal processor shown in Figs. 2 through 7.

[51] Referring to Fig. 8, the above described acoustic processor comprises a back electret plate 43 for forming a static electric field, a diaphragm 41 for forming the static electric field with the back electret plate 43 and vibrates according to the acoustic pressure, a spacer ring 42 for maintaining a distance between the diaphragm 41 and the back electret plate 43, a insulation base ring 45 and a conductive base ring 46. In addition, the acoustic processor further comprises a washer spring 44 for providing an elasticity to the back electret plate 43, the diaphragm 41, the spacer ring 42, the insulation base ring 45 or the conductive base ring 46.

[52] The back electret plate 43 forms the electric field with the diaphragm 41, and converts the acoustic pressure to the electrical signal. The back electret plate 43 comprises an electret high molecular film 43 a and a metal plate 43b. The electret high molecular film 43a is semi-permanently charged with a charge, and an electric field is formed by the charge. The electret high molecular film 43a may be formed by heating and pressing a high molecular film such as PTFE (Poly Tetra Fluoro Ehtylene), PFA (Perfluoroalkoxy) or FEP (Fluoroethylenepropylene) to the metal plate 43b, and then injecting the charge using an electron injector. In addition, the back electret 43b is manufactured using metals such as copper, bronze, brass or phosphor bronze.

[53] The diaphragm 41 vibrates according to the acoustic pressure of the acoustic signal transmitted through an acoustic hole 49. For this, the diaphragm 41 serves as a pair of electrodes with the back electret plate 43. The diaphragm 41 comprises a vibrating film 41b and a polar ring the polar ring 41a. Particularly, the vibrating film 41b is manufactured using a film such as a PET (Polyethylene Terephthalate) having a thickness of a few micrometers so that the vibrating film 41b vibrates according to a small acoustic pressure. The vibrating film 41b is coated with metals such as nickel, silver or gold using a sputtering in order to have a conductivity. The polar ring 41a maintains a distance between the vibrating film 41b and other components, and also provides a conductive path with a casing 40.

[54] The spacer ring 42 is disposed between the diaphragm 41 and the back electret plate 43, and maintains that the diaphragm 41 is parallel to the back electret plate 43 having a predetermined distance therebetween. In addition, the spacer ring 42 is manufactured using a material having a high insulation characteristic such as an acrylic resin so that the diaphragm 41 is electrically insulated from the back electret plate 43.

[55] The insulation base ring 45 is disposed between the back electret plate 43 and the casing 40 to insulate the back electret plate 43 form the casing 40. The insulation base ring 45 is manufactured to have a circular or polygonal shape cylinder having a space therein. An outer surface of the cylinder is in contact with an inner wall of the casing 40, and the conductive base ring 46 is housed therein.

[56] The conductive base ring 46 provides a conductive path between the back electret plate 43 and the printed circuit board 47. An outer diameter of the conductive base ring 46 is manufactured to accord to that of the insulation base ring 45 so that the insulation base ring 45 is not moved by an external shock.

[57] The washer spring 44 provides the elasticity for preventing a movement of the spacer ring 42, the diaphragm 41, the back electret plate 43, the insulation base ring 45 and the conductive base ring 46 due to a marginal error generated during the manu- facturing process of the electret condenser microphone. In addition, the washer spring 44 shown in Fig. 8, is inserted between the back electret plate 43 and the conductive base ring 46 to form a conductive path with the conductive base ring 46. The washer spring 44 applies pressure to the housed components to maintain contacts between the components as well as preventing the movement of the housed components due to the marginal error generated during the manufacturing process.

[58] The casing 40 houses the washer spring 44, the diaphragm 41, the spacer ring 42, the back electret plate 43, the insulation base ring 45 and the conductive base ring 46 to protect the same from an external shock. In addition, the casing 40 blocks an external acoustic noise and electromagnetic noise. The casing 40 also provides a conductive path to the diaphragm 41 or the back electret plate 43. Therefore, the casing 40 is manufactured to have a polygon or a circular cylinder shape such as a container (vessel) having a one open end portion. The open end of the casing 40 is bonded to the printed circuit board 47 by resistance welding, laser welding or bonding. The casing 40 consists of highly conductive metals such as aluminum, copper or the highly conductive metals having gold or nickel plated thereon to improve an electrical conductivity and prevent a corrosion. In addition, an acoustic hole may be formed in the casing 40.

[59] The printed circuit board 47 amplifies and filters a change in the electric field generated by the diaphragm 41 and the back electret plate 43. The change is then converted to the electrical signal and provided to outside. For this, the printed circuit board 47 comprises an amplifying device such as a field effect transistor, and a multilayer ceramic capacitor 40 consisting of one or more capacitors for filtering the noise. As described above, the acoustic hole 49 and the pad 50 are formed in the hole 47.

[60] Positions of the diaphragm 41 and the back electret plate 43 may be varied contrary to Fig. 8. The diaphragm 41 may be disposed on top of the conductive base ring 46 of Fig. 8, and the back electret plate 43 may be disposed on top of the spacer ring 42. In this case, a third base ring may be disposed between the back electret plate 43 and the casing 40 additionally to secure a space for a back chamber and provide a conductive path to the back electret plate 43.

[61] In addition, the insulation base ring 45 may be extended to an inner surface of the casing 40. when the insulation base ring 45 is in contact with both the casing 40 and the printed circuit board 47, that is, when a height of the insulation base ring 45 is almost identical to that of the electret condenser microphone, outer diameters of the diaphragm 41, the spacer ring 42 and the back electret plate 43 are almost the same as an inner diameter of the insulation base ring 45.

[62] While Fig. 8 illustrates an example wherein the washer spring 44 is disposed between the back electret plate 43 and the conductive base ring 46, the washer spring 44 may be disposed at other positions. For instance, the washer spring 44 may be disposed at the various positions such as between the casing 40 and the diaphragm 41, between the conductive base ring 46 and the printed circuit board 47 and between the insulation base ring 45 and the printed circuit board. In addition, the polar ring 41a of the diaphragm 41 may be replaced with the washer spring 44. The washer spring 44 may be selected from various washer springs such as a washer spring having "V" or "U" shaped cross-section, a wave type washer spring, a C-washer spring and a pin type washer spring.

[63] Fig. 9 is a diagram exemplifying an electret condenser microphone including an acoustic signal processor wherein a diaphragm is disposed closer to a printed circuit board than a back electret plate.

[64] The electret condenser microphone of Fig. 9 comprises a casing 60, an insulation base ring 63 housed in the casing 60, a washer spring 61, a conductive base ring 62, a back electret plate 65, a spacer ring 66, a diaphragm 67 and a integrated base ring 64 stacked in the insulation base ring 63. The insulation base ring 63 insulates the casing 60 and the diaphragm 67. The conductive base ring 62 supports the back electret plate 65 and also provides a conductive path to the back electret plate 65. The conductive base ring 62 may be replaced with the washer spring 61. Particularly, the integrated base ring 64 comprises a conductive layer 64c for providing a conductive path to the diaphragm 67, an insulating layer 64b for insulating the conductive layer 64c and the casing 60, and a base ring 64a for supporting the insulating layer 64b and the conductive layer 64c and the insulating layer 64b. The conductive layer 64c provides a conductive path to the diaphragm 67 and a printed circuit board 68, and may be manufactured as a single body with the polar ring of the diaphragm 67. In addition, since the insulating layer 64b and the base ring 64a should maintain the conductivity between the conductive layer 64c and the casing 60, the insulating layer 64b and the base ring 64a are manufactured using an insulating material. While Fig. 9 illustrates an example wherein the insulating layer 64b and the base ring 64a are separate, it is preferable that the insulating layer 64b and the base ring 64a are manufactured as the single body so as to reduce a manufacturing cost and to simplify a manufacturing process. Moreover, the integrated base ring 64 may be used with the insulating layer 64b omitted. The conductive base ring 62 may also be omitted and only the washer spring 61 may be used. The washer spring 61 may be disposed at various positions in case of Fig. 9, and an embodiment of the electret condenser microphone having the acoustic resistor is also possible.

[65] Figs. 10 through 12 are diagrams exemplifying an electret condenser microphone including an acoustic resistor, wherein Fig. 10 illustrates an electret condenser microphone having the acoustic resistor on an outer surface of a casing, Fig. 11 illustrates an electret condenser microphone having the acoustic resistor inserted in an acoustic hole of a casing, and Fig. 12 illustrates an electret condenser microphone having the acoustic resistor inserted between an electret and a casing.

[66] Referring to Figs. 10 through 12, the electret condenser microphone of Figs. 2, 3, 8 and 9 may further comprise acoustic hole in the casing in addition to the acoustic hole of the printed circuit board. The electret condenser microphone having the acoustic holes in the casing and the printed circuit board has a bi-directional characteristic. Particularly, when the acoustic holes are formed in both the casing and the printed circuit board, and the acoustic resistor is disposed at one of the acoustic holes, the unidirectional electret condenser microphone may be manufactured. Figs. 10 through 12 are diagrams exemplifying the uni-directional electret condenser microphone including the acoustic resistor for describing various arrangements of the acoustic resistor. The electret condenser microphone shown in Figs. 10 through 12 is an electret condenser microphone wherein an insulation base ring is in contact with the printed circuit board and the inner surface of the casing for exemplifying another structure of the electret condenser microphone. While a form of the insulation base ring slightly differs from those of the above-described insulation base rings, it will be described together since the arrangement of the acoustic resistor is more or less irrespective of the form of the insulation base ring. In addition, the acoustic resistor is not only applicable to the structure of the electret condenser microphone shown in Figs. 10 through 12, but also generally applicable to the electret condenser microphones described above. Moreover, a description will be given based on the electret condenser microphone having the insulation base ring omitted.

[67] Referring to Fig. 10, the electret condenser microphone comprising an acoustic resistor 80 disposed on an outer surface of a casing 70 comprises a insulation base ring 76 disposed in a space between the casing 70 and the printed circuit board 77 and extending from the printed circuit board 77 to an inner surface of the casing 70, a washer spring 71, an electret 72, a spacer ring 73, a diaphragm 74, and a conductive base ring 75 sequentially stacked in the insulation base ring 76. In addition, a first acoustic hole 78 is formed in the printed circuit board 77 and a second acoustic hole the second acoustic hole 79 is formed in the casing 70. Since the insulation base ring 76, the washer spring 71, the electret 72, the spacer ring 73, the diaphragm 74 and the conductive base ring 75 are described above in detail, a detailed description is hereby omitted.

[68] Fig. 10 illustrates an example wherein the acoustic resistor is attached to the outer surface of the casing 70. Therefore, an acoustic signal coming through the first acoustic hole 78 reaches the diaphragm 74 and the electret 72 without any delay and attenuation to be converted to an electrical signal. On the other hand, most of the acoustic signal cannot pass through the second acoustic hole the second acoustic hole 79 due to the acoustic resistor 80 disposed around the second acoustic hole 79. Therefore, the electret condenser microphone of Fig. 10 has the uni-directional characteristic. In addition, a method wherein the acoustic resistor 80 is disposed on the outer surface of the casing 70 may be applied to the printed circuit board 77. That is, when the acoustic resistor 80 is disposed on a surface whereon a terminal or a pad is formed, only a direction of a directional characteristic is changed and almost identical uni-directional characteristic may be obtained.

[69] Fig. 11 illustrates the electret condenser microphone having the uni-directional characteristic. The electret condenser microphone of Fig. 11 differs from that of Fig. 10 in that the acoustic resistor 81 attached on the outer surface of the casing 70 is inserted in the second acoustic hole 79. The acoustic resistor 81 may also be inserted in the first acoustic hole 78. While inserting the acoustic resistor 81 in the acoustic holes 78 and 79 requires an accuracy in a manufacturing process, the electret condenser microphone having the uni-directional characteristic may be manufactured without increasing a size of the electret condenser microphone.

[70] Fig. 12 illustrates an example wherein the acoustic resistor is disposed in the electret condenser microphone such that the acoustic resistor is disposed on inner surface of the casing. As shown in Fig. 12, the acoustic resistor is disposed between the electret 72 and the inner surface of the casing 70. In this case, an effect identical to that of the case the acoustic resistor is attached to the outer surface of the casing 70 may be obtained. In accordance with another example with reference to Fig. 12, the acoustic resistor may be inserted between the diaphragm 74 and the printed circuit board 77 to allow a manufacture of the uni-directional electret condenser microphone. However, when the acoustic resistor is inserted closer to the first acoustic hole 78 of the printed circuit board 77 than the second acoustic hole 79 of the casing 70, it is preferable that the diaphragm 74 is disposed close to the casing 70 and the electret 72 is disposed close to the printed circuit board similar to a structure shown in Fig. 8.

[71] On the other hand, in accordance with the electret condenser microphone of the present invention, the internal components of the electret condenser microphone may be arranged in various ways to manufacture various electret condenser microphones. The electret condenser microphones disclosed by description of the present invention are merely examples. Therefore, it will be understood by those skilled in the art that various changes in form and details may be effected therein. In addition, while the sealing ring is omitted in Figs. 8 through 12, the seal ring connecting the acoustic hole formed in the main board and the acoustic hole of the electret condenser microphone may be used when the electret condenser microphones described with reference to Figs. 8 through 12 is mounted on the main board.

[72] Moreover, the condenser microphone and the main board including the same in accordance with the present invention employs the washer spring to reduce the rate of defective products generated by a manufacturing process margin of the electret condenser microphone, and to guarantee a stable operation after an assembly of the main board. Industrial Applicability

[73] In accordance with the electret condenser microphone and the main board including the same, the electret condenser microphone is mounted on a back side of the main board on which relatively large circuit components or parts are mounted so that the electret condenser microphone is easily mounted without preparing a separate space and a manufacturing process thereof is simplified, thereby preventing a degradation of the electret condenser microphone.

[74]

[75]

Claims

[1] A main board including an electret microphone, the board comprising: an electret condenser microphone comprising a casing, an acoustic processor for converting an acoustic pressure generated by an external acoustic signal to an electrical signal, the acoustic processor being enclosed by the casing, and a printed circuit board including a first acoustic hole, the printed circuit board being bonded to the casing; and a main board including a second acoustic hole for delivering the acoustic pressure to the first acoustic hole, wherein the main board is bonded to the printed circuit board. [2] The main board in accordance with claim 1, wherein the printed circuit board comprising a first pad for connecting to the main board disposed thereon; and the main board comprises a second pad disposed on a position corresponding to the first pad. [3] The main board in accordance with claim 2, wherein the printed circuit board is bonded to the casing via at least one of a laser welding, a high-temperature adhesive, a resistance welding and a soldering. [4] The main board in accordance with claim 3, further comprising a sealing ring between the printed circuit board and the main board. [5] The main board in accordance with claim 4, wherein the sealing ring connects the first acoustic hole and the second acoustic hole. [6] The main board in accordance with one of claims 1 and 2, wherein the acoustic processor comprises: a back electret plate for forming a static magnetic field; a diaphragm for forming the static magnetic field with the beck electret plate, wherein the diaphragm vibrating according to the acoustic pressure to vary the static magnetic field whereby the electrical signal is generated; a spacer ring for maintaining a distance between the diaphragm and the back electret plate; an insulation base ring for insulating at least one of the diaphragm and the back electret plate from the casing; and a conductive base ring for providing a path for one of the diaphragm and the back electret plate. [7] The main board in accordance with claim 6, further comprising a washer spring for providing an elasticity to at least one of the back electret plate, the diaphragm, the spacer ring, the insulation base ring and the conductive base ring. [8] An electret condenser microphone comprising: a casing; an acoustic processor for converting an external acoustic signal to an electrical signal, the acoustic processor being enclosed by the casing; and a printed circuit board including an acoustic hole, wherein the printed circuit board removes a noise included in the electrical signal and amplifies the electrical signal to generates an acoustic signal, the printed circuit board compri sing a pad for delivering the acoustic signal to an outside. [9] The microphone in accordance with claim 8, wherein the first side of the printed circuit board is bonded to the casing, and the pad is disposed on a second side of the printed circuit board. [10] The microphone in accordance with claim 9, further comprising a sealing ring for surrounding the acoustic hole, wherein the sealing ring is disposed at an edge of the acoustic hole on the second side. [11] The microphone in accordance with claim 8, wherein the acoustic processor comprises: a back electret plate for forming a static magnetic field; a diaphragm for forming the static magnetic field with the beck electret plate, wherein the diaphragm vibrating according to the acoustic pressure to vary the static magnetic field whereby the electrical signal is generated; a spacer ring for maintaining a distance between the diaphragm and the back electret plate; an insulation base ring for insulating at least one of the diaphragm and the back electret plate from the casing; and a conductive base ring for providing a path for one of the diaphragm and the back electret plate. [12] The microphone in accordance with claim 11, further comprising a washer spring for providing an elasticity to at least one of the back electret plate, the diaphragm, the spacer ring, the insulation base ring and the conductive base ring. [13] The microphone in accordance with claim 8, further comprising an acoustic resistor for removing or attenuating a portion of the acoustic signal.