TECHNICAL FIELD
The present invention relates to an electro-acoustic transducer such as a microphone and, in particular, to an electro-acoustic transducer that is soldered using the surface mounting art using a reflow furnace, wherein the transducer's cylindrical capsule itself functions as a ground electrode.
BACKGROUND ART
In conventional microphones, a diaphragm ring, a diaphragm, a spacer, a back electrode, a holder, a gate ring, and a substrate, for example, are stacked in a cylindrical metal capsule having sound apertures and the components are fixed by caulking the end of the capsule toward the substrate (Japanese Patent Application Laid Open No. 2003-153392 (Patent Reference 1)). Electrodes are protruded from the substrate for conduction of electricity with an external object. The caulked part has a rounded portion (prominent portion) and the extent to which the portion is rounded (the height of the prominence) varies. That is, the amount of the protrusion of the electrodes with respect to the caulked part varies. Therefore, when such a microphone is soldered using a reflow furnace, the unevenness causes poor soldering in the reflow furnace or a faulty posture (tilt) of the microphone mounted on a wiring board.
To solve the problem, the applicant has previously proposed a structure in which the disposition of components in the cylindrical metal capsule is reversed (Japanese Patent Application No. 2005-121051 filed on Apr. 19, 2005). FIG. 1 shows a cross-sectional view of the microphone previously proposed by the applicant. According to the related art, a ground electrode pattern 114 is formed on the side (bottom 121) in which opening 123 of a capsule 102 is provided. A built-in substrate 112 is provided on the ground electrode pattern 114. The built-in substrate 112 has an output terminal electrode 111 and ground terminal electrode 115 on the same side on which the ground electrode 114 is provided. The terminal electrodes 111, 115 are longer than the thickness of the capsule 102 and protrude outward through the opening 123 of the capsule 102. A conductor pattern 109 is formed on the upper surface of the built-in substrate 112 and an electronic circuit 110 is provided on it. Stacked on the upper surface of the built-in substrate 112 are a gate ring 108, a holder 107, a back electrode 106, a spacer 105, a diaphragm 104, a diaphragm ring 103, and a top plate 130 having sound apertures 131. The end of the capsule is caulked to the top plate 130, thereby fixing each of the components as well. The top plate 130 may be made of the same metal as the capsule 102 and may have the same thickness as the capsule 102, for example.
In this microphone 100, the terminal electrodes 111, 115 can be reliably protruded with respect to the thickness of the bottom 121 without being affected by unevenness of the caulked part 113. Accordingly, defects in soldering using a reflow furnace can be prevented.
However, for example, if the microphone 100 is installed in a cell phone, the microphone 100 picks up touch noise generated when a user touches the cell phone, vibration noise generated by driving of a built-in motor and the like. This problem is unavoidable as long as the microphone is directly mounted on a wiring board.
FIG. 2 shows a circuit configuration of an analog microphone. Contained in a capsule 102 are an acoustic-electric converter 100′ and an electronic circuit 110. The acoustic-electric converter 100′ is formed by the capsule 102 and internal components. The electronic circuit 110 consists of a field-effect transistor (FET) and a capacitor, for example. As can be seen from FIG. 2, the microphone 100 has two terminals: an output terminal and a ground terminal. It should be noted that, the terminal electrode (ground) 115 is shown in two positions in FIG. 1 because FIG. 1 is a cross-sectional view of a toroidal terminal.
The applicant has also proposed previously, in another application, an electret condenser microphone that can be soldered using a reflow furnace and outputs a digital signal (Japanese Patent Application No. 2005-320815 filed on Nov. 14, 2005). FIG. 3 is a cross-sectional view of an exemplary electret condenser microphone outputting a digital signal proposed by the present applicant. The front type electret condenser microphone 200 has an electret polymer film made of a heat-resistant material within an electrically conductive capsule 201. An electrically conductive diaphragm 207, an electrically conductive ring 208, a gate ring 209, and a wiring substrate 202 are provided and are separated from the electret polymer film by a spacer 206 made of an heat-resistant insulator. The end of the electrically conductive capsule 201 is caulked to the wiring substrate 202 and fixes the internal components. An IC device 210 is mounted on the interior side of the wiring substrate 202. Four terminals 204(a-d) are provided on the exterior side of the wiring substrate 202. The terminals 204(a-d) are protruded through an opening 223 of the front type electret condenser microphone 200 for conduction of electricity with an external object. With this configuration, a digital electret condenser microphone capable of resisting high temperatures generated by soldering in a reflow furnace can be implemented.
FIG. 4 shows a circuit configuration of a digital microphone. Provided in an electrically conductive capsule 201 are an acoustic-electric converter 200′ and an IC device 210. The acoustic-electric converter 200′ is formed by the capsule 201 and internal components. The IC device 210 includes an impedance converter/amplifier 210a and a digital sigma modulator 210b. As can be seen from FIG. 4, four terminals, a power supply terminal 204a, a clock input terminal 204b, a digital data output terminal 204c, and a ground terminal 204d, are provided. A problem with this digital microphone is that it is susceptible to high-frequency noise from nearby components because its ground terminal does not have a toroidal shape.
An approach to reducing the number of components of both analog and digital microphones may be to solder the bottom of the capsule directly to a wiring board, thereby omitting the ground terminal. In this case, if a ground electrode can be formed into a toroidal shape, the microphone would be less susceptible to high-frequency noise. However, some measures must be taken against heat transferred to the interior of the microphone during soldering in a reflow furnace. Furthermore, the vibration pickup problem cannot be solved by using the bottom itself as the ground electrode.
BRIEF SUMMARY OF THE INVENTION
Thus, there are various problems with mounting an electro-acoustic transducer directly on a wiring board, and it has been impossible to solve all of those problems at the same time. An object of the present invention is to provide a structure that achieves the following four objects at the same time: a first object is to make the structure resistant to vibration from a wiring board; a second object is to make the structure resistant to high-frequency noise; a third object is to reduce the number of components, and a fourth object is to make the structure resistant to heat generated during soldering in a reflow furnace.
An electro-acoustic transducer (such as a microphone) according to the present invention includes: an electrically conductive capsule having an opening for electrically connecting internal circuitry to an external object; terminals which protrude from the opening to the outside; and a raised part which is a portion of the capsule on the opening side and is spaced with a gap from the internal structure of the capsule. The raised part and the terminals are arranged in such a manner that the raised part and all of the terminals are able to be directly soldered to a wiring board. The raised part may extend toward the terminals in such a manner that the opening is narrowed. Furthermore, the raised part may have a slit extending to the boundary between the raised part and the other part of the capsule.
According to the present invention, there is a gap between the raised part to be soldered to a wiring board and the main structure of the electro-acoustic transducer (such as a microphone). The gap makes the transducer resistive to vibration. Also, a ground electrode of the present invention may be toroidal so that it is not affected by any high-frequency noise. Furthermore, the number of components of the transducer can be reduced because the capsule itself functions as a ground electrode. Moreover, the gap between the raised part and the main structure of the electro-acoustic transducer makes the transducer resistive to heat generated during soldering in a reflow furnace.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a cross-section of a microphone previously proposed by the applicant;
FIG. 2 shows a circuit configuration of an analog microphone;
FIG. 3 is a cross-sectional view of an exemplary electret condenser microphone outputting a digital signal proposed previously by the applicant;
FIG. 4 shows a circuit configuration of a digital microphone;
FIG. 5 is a cross-sectional view showing a structure of a microphone according to a first embodiment;
FIG. 6 is an external perspective view of the microphone 1 in FIG. 5 viewed from the bottom 21;
FIG. 7 is an external perspective view of the microphone 1 in FIG. 5 viewed from the bottom 21;
FIG. 8 is a cross-sectional view of a digital front type electret condenser microphone to which the present invention is applied;
FIG. 9 is a cross-sectional view of a digital back type electret condenser microphone to which the present invention is applied;
FIG. 10 is a cross-sectional view of another digital back type electret condenser microphone to which the present invention is applied;
FIG. 11 is a cross-sectional view of a digital foil type electret condenser microphone to which the present invention is applied;
FIG. 12A is an external perspective view of a digital electret condenser microphone having a front plate with three small sound apertures, viewed from the front-plate side;
FIG. 12B is an external perspective view of a digital electret condenser microphone having a raised part raised near a caulked part, viewed from the opening side;
FIG. 13A is an external perspective view of a digital electret condenser microphone having a front plate with a large circular sound aperture, viewed from the front-plate side;
FIG. 13B is an external perspective view of a digital electret condenser microphone having a raised part extending toward terminals to narrow the opening, viewed from the opening side;
FIG. 14A is an external perspective view of a digital electret condenser microphone having a front plate with a large square sound aperture, viewed from the front-plate side; and
FIG. 14B is an external perspective view of a digital electret condenser microphone having a raised part extending toward terminals to narrow the opening, viewed from the opening side.
BEST MODE FOR CARRYING OUT THE INVENTION
In the following description, components having like functions are labeled like reference numerals and redundant description of which will be omitted.
First Embodiment
FIG. 5 is a cross-sectional view showing a structure of a microphone according to a fist embodiment. An electrically conductive capsule 2 has, on the bottom face, a bottom 21 with which internal components are in contact, an opening 23 through which a terminal electrode is exposed, and raised parts 21b raised from the bottom 21. The capsule 2 may be made of albata or aluminum. A built-in substrate 112 is in contact with the bottom 21. The built-in substrate 112 has a ground electrode pattern 114 electrically connected to the bottom 21, and a conductor pattern 109 provided on the side opposite to the bottom 21. A terminal electrode (output) 11 for providing electrical contact with an external object through an opening 23 is provided on the surface of the built-in substrate 112 on the bottom 21 side. An electronic circuit 110 is mounted on the surface of the built-in substrate 112 on the side opposite to the bottom 21. The terminal electrode 11 may be formed as an integral part of the built-in substrate 112 or may be formed by plating or the like on the built-in substrate 112. Stacked on the built-in substrate 112 on the side opposite to the bottom 21 are a gate ring 108, a holder 107, a back electrode 106, a spacer 105, a diaphragm 104, a diaphragm ring 103, and a top plate 130 having sound apertures 131. The end of the capsule 2 is caulked to the top plate 130, thereby fixing the internal components. The lower end of the raised part 21b is substantially in the same plane as the lower end of the terminal electrode (output) 11. The purpose of this is to ensure that the terminal electrode (output) 11 and the raised part 21b are evenly soldered when the microphone is soldered to a wiring board and that the microphone is firmly mounted on the wiring board without tilting with respect to the wiring board.
With this configuration, a gap of approximately 50 μm-100 μm is created between the raised part 21b and the built-in substrate 112. The size of the gap depends on the size of the microphone in practice. Because of the gap between the raised part 21b and the built-in substrate 112, the raised part 21b functions as a member that absorbs vibration from an external vibration source. Accordingly, vibration transferred to the microphone 1 can be reduced. Furthermore, because only the raised part 21b, rather than the entire bottom 21, is in contact with the wiring board, the contact area is reduced and therefore less vibration is transferred to the microphone 1. In addition, the gap can prevent heat conduction to the interior of the microphone even when the portion (raised part 21b) to be soldered is exposed to a high temperature, for example 260° C., in a reflow furnace. It should be noted that if the raised part 21b is reduced in length in the radial direction, heat transferred from the raised part 21b to the built-in substrate 112 can also be reduced because the area in contact with solder (heated area) is reduced. Furthermore, the need for the terminal electrode (ground) 115 shown in FIG. 1 can be eliminated because the raised part 21b functions as a ground electrode. Moreover, the raised part 21b can be formed into a toroidal shape, thereby resolving the high-frequency noise problem.
FIGS. 6 and 7 are perspective views of the microphone 1 shown in FIG. 5, viewed from the bottom 21. While both FIGS. 6 and 7 show examples in which the raised part 21b is split into three, the raised part 21b may be split into any other number of sections. The difference between the examples in FIGS. 6 and 7 lies in the width of the slit 24. With this configuration, the elasticity of the raised part 21b can be controlled by adjusting the width of the raised part 21b. That is, the ability of the raised part 21b to absorb vibration can be controlled by adjusting the number of sections into which the raised part 21b is split and by adjusting the width of the slit 24. Heat conduction can also be controlled by adjusting the width of the raised part 21b. However, if the slit 24 is too wide, the raised part 21b which also functions as a ground electrode would lose the shape of toroid and would become susceptible to high-frequency noise.
As has been described, the provision of the raised part 21b allows for the effects of absorbing vibration and high-frequency noise, reducing the number of components, and preventing heat conduction. The number of sections of the raised part 21b, the radial length of the raised part 21b, and the width of the slit 24 should be chosen to be appropriate to the environment in which the microphone 1 is used because the effects of absorbing vibration and high-frequency noise and preventing heat conduction can be in a trade-off relationship with one another.
It should be noted that the position of the terminal electrode (output) 11 does not change even if the microphone is rotated because the electrode 11 is positioned in the center of the built-in substrate 112 and the raised part 21b is provided around it in toroidal form. Therefore, when mounting the microphone, the microphone can be positioned in place merely by aligning the terminal electrode (output) 11. Furthermore, the slit 24 dividing the raised part 21b extends to the boundary 21c between the raised part 21b and a marginal portion 21 a. Accordingly, the opening is not completely sealed when the microphone is soldered on a wiring board. That is, the slit 24 at the boundary 21c let the gas escape during soldering. The slit 24 must have a sufficient width for releasing gas.
Second Embodiment
FIG. 8 is a cross-sectional view of a digital front type electret condenser microphone to which the present invention is applied. The differences of the microphone in FIG. 8 from that in FIG. 3 lie in the shape of the electrically conductive capsule and the number of the terminals 204. The electrically conductive capsule 41 of the present invention has a raised part 41c on the opening 42 side. Accordingly, a caulked part 43 is not an end of the electrically conductive capsule 41. The raised part 41c acts as a ground terminal and therefore eliminates the need for the ground terminal 204d shown in FIG. 3.
FIG. 9 is a cross-sectional view of a digital back type electret condenser microphone to which the present invention is applied. The electrically conductive capsule 51 has a raised part 51c on the opening 52 side. A heat-resistive cylindrical synthetic-resin molded member 211 is provided on the internal sidewall of the electrically conductive capsule 51. Stacked inside the electrically conductive capsule 51 are a front plate 51a, an electrically conductive ring 208, an electrically conductive diaphragm 207, a spacer 206, an electret polymer film 205, a fixed electrode 212 having sound apertures 212a, a gate ring 209, and a wiring substrate 202 having an IC device 210 and terminals 204a-204c, in this order.
FIG. 10 is a cross-sectional view of another digital back type electret condenser microphone to which the present invention is applied. The electrically conductive capsule 61 has a raised part 61c on the opening 62 side. A heat-resistive cylindrical synthetic-resin molded member 211 is provided on the internal sidewall of the electrically conductive capsule 61. Stacked inside the electrically conductive capsule 61 are a front plate 61a, a dust-preventive metallic mesh 213 having pores 213b, a fixed electrode 212 having sound apertures 212a, an electret polymer film 205, a spacer 206, an electrically conductive diaphragm 207, a gate ring 209, an electrically conductive ring 208, and a wiring substrate 202 having an IC device 210 and terminals 204a-204c, in this order.
FIG. 11 is a cross-sectional view of a digital foil type electret condenser microphone to which the present invention is applied. The electrically conductive capsule 71 has a raised potion 71c on the opening 72 side. A heat-resistive cylindrical synthetic-resin molded member 211 is provided on the internal sidewall of the electrically conductive capsule 71. Stacked inside the electrically conductive capsule 71 are a front plate 71a, an electrically conductive ring 208, an electrically conductive diaphragm 207, a spacer 206, a fixed electrode 212 having sound apertures 212a, a gate ring 209, and a wiring substrate 202 having an IC device 210 and terminals 204a-204c, in this order.
FIGS. 12A, 13A, and 14A are external perspective view of digital electret condenser microphones viewed from their front-plate side. FIG. 12A shows a microphone with a front plate 41a, 51a, 71a having three small sound apertures 41b, 51b, 71b. FIG. 13A shows a microphone with a front plate 61a having a large circular sound aperture 61b. FIG. 14A shows a microphone with a front plate 61a having a large square sound aperture 61b. FIGS. 12B, 13B, and 14B are external perspective view of the digital electret condenser microphones viewed from the opening side. The digital electret condenser microphones have only three terminals, a power supply terminal 204, a clock input terminal 204b, and a digital data output terminal 204c, because their raised part 41c, 51c, 61c, 71c also functions as a ground terminal. In FIG. 12B, the raised part 41c, 51c, 71c is raised near the caulked part 43, 53, 73. The internal structure may be any of the structures shown in FIGS. 8, 9, and 11. In FIGS. 13B and 14B, the raised part 61c extends toward the terminals to narrow the opening 62. The internal structure is as shown in FIG. 10. Microphones having the structures shown in FIGS. 8, 9, and 11 also can be modified to have any of the exterior appearances shown in FIGS. 13A and 14A by attaching a metallic mesh 213 on the front plate 41a, 51a, 71a. While the front plate of the three microphones is generally square, it may be a circle as shown in FIGS. 6 and 7.
The height of the raised parts 41c, 51c, 61c, 71c is substantially the same as the height of the protruded portion of the terminals 204a-204c. The purpose of this is to ensure that the terminals 204a-204c and the raised part 41c, 51c, 61c, 71c are evenly soldered when the microphone is soldered to a wiring board and that the microphone is firmly mounted on the wiring board without tilting with respect to the wiring board.
With this configuration, a gap of approximately 50 μm-100 μm is created between the raised part 41c, 51c, 61c, 71c and the wiring substrate 202. The size of the gap depends on the size of the microphone in practice. Because of the gap, the raised part 41c, 51c, 61c, 71c functions as a member that absorbs vibration from an external vibration source. Accordingly, vibration transferred to the electret condenser microphone 40, 50, 60, 70 can be reduced. In addition, the gap can prevent heat conduction to the interior of the microphone even when the portion (raised part 41c, 51c, 61c, 71c) to be soldered is exposed to a high temperature, for example 260° C., in a reflow furnace. It should be noted that if the area of the raised part is reduced, heat transferred to the wiring substrate 202 can also be reduced because the area in contact with solder (heated area) is reduced. Furthermore, because the raised part 41c, 51c, 61c, 71c surrounds the terminals 204a-204c, the high-frequency noise problem is eliminated.
In addition, the elasticity and heat conduction of the raised part can be controlled by adjusting the width of the raised part 41c, 51c, 61c, 71c. However, if the width of the raised part 41c, 51c, 61c, 71c is too small, the raised part would no longer surround the terminals and the microphone would become susceptible to high-frequency noise.
As has been described, the provision of the raised part 41c, 51c, 61c, 71c allows for the effects of absorbing vibration and high-frequency noise, reducing the number of components, and preventing heat conduction. The width of the raised part 41c, 51c, 61c, 71c and the length of its extension toward the terminals should be chosen to be appropriate to the environment in which the microphone is used because the effects of absorbing vibration and high-frequency noise and preventing heat conduction can be in a trade-off relationship with one another.
Patent Application
20060285707
