JP3389536B2 - Electret condenser microphone - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electret condenser microphone. 2. Description of the Related Art FIG. 6 shows the structure of a conventional electret condenser microphone. It is made of an electret material in which a surface cloth 21 is provided on the top surface of a cylindrical metal case 22 having a sound hole 22a in the center, and a metal layer is formed on the surface by vapor deposition or the like via a film ring 23 inside the top surface. Vibrating membrane 24
It has. The vibration film 24 is fixed to the fixed electrode 26 via the gap spacer 25 and the capacitor gap 32.
The printed circuit board 29 and a concave insulator 27 that accommodates the FET 28 are further disposed below and fixed by the caulking portion 22 b of the metal case 22. The input lead 28a of the FET 28 is connected to the fixed electrode 26, and the output lead 28b passes through the insulator 7 and the printed circuit board 29 and is connected to the soldered portion 9a on the bottom. On the other hand, the vibration film 24 is electrically connected to the metal case 22 by the film ring 23. Now, when sound is input from the sound hole 22a, the vibration film 24 vibrates, which changes the capacitance between the vibration film 24 and the fixed electrode 26. By detecting this, a sound signal is obtained. Can be. However, the above-mentioned conventional electret condenser microphone has the following problems. (1) The electret condenser microphone is required to be small and light, but the conventional one has a large number of parts and the thickness of the caulking portion 22b and the soldered portion 29a cannot be reduced. In addition, because of the presence of the insulator 27 and the printed circuit board 29, the whole could not be reduced in size, weight and thickness. (2) If the size is reduced as described above, the volume in the case is reduced, and the reflected wave due to the vibration of the vibrating membrane 24 collides again with the vibrating membrane 24 to adversely affect the microphone characteristics. There were also problems. Accordingly, the present invention provides a fixed electrode and a vibrating membrane which are arranged at regular intervals, and detects an audio signal given to the vibrating membrane due to a change in capacitance between the two. In the electret condenser microphone described above, the fixed electrode, the vibrating film, and the semiconductor element are housed in a box-shaped case made of an insulating material, and a back chamber is formed on a wall surface of the concave portion. Note that the back chamber in the present invention is a recessed portion that is recessed from other portions on the wall surface of the recess accommodating the semiconductor element and the like, and by forming this back chamber, the inside of the case is formed. In addition to increasing the volume, an escape path for air was created when the vibrating membrane vibrated, so that adverse effects due to reflected waves were prevented. An embodiment of the present invention will be described below with reference to the drawings. The electret condenser microphone shown in FIG. 1A has a stepped portion 9b on the inner wall of a concave portion 9a of a box-shaped case 9 made of ceramics, glass, resin, or an insulator obtained by combining them. Each part is stored and covered with a plate-like lid 2. The cover 2 is a metal plate having a sound hole 2a at the center, and a vibration film 4 made of an electret material having a metal layer formed thereunder via a film ring 3 under the cover. A fixed electrode 6 is provided with a capacitor gap interposed therebetween. The fixed electrode 6 is placed on the step 9b, and is joined to the metallized portion on the step 9b by solder, brazing, conductive adhesive or the like.
A semiconductor element 8 such as an ET or an IC is housed therein, and an amplifier circuit and the like are formed in the semiconductor element 8. A concave back chamber 12 is formed on the bottom surface of the recess 9a in the semiconductor element 8 housing portion. Further, the case 9 is provided with a conductive path on the surface and / or inside by printing a conductive paste on the surface, filling the through hole, or laminating a green sheet provided with the conductive paste. . First, lid 2
Is connected to an electrode extraction portion 10a on the bottom surface through the outer wall of the box-shaped case 9. The conductive path 7b provided on the step 9b on which the fixed electrode 6 is placed is connected to the input terminal 8a of the semiconductor element 8, and the conductive path 7c connected to the output terminal 8b is led out of the box case 9. It is connected to the other electrode take-out part 10b. Further, as shown in FIG. 1B, the upper end surface 9c of the box-shaped case 9 is metallized and adhered to the lid 2 with solder, brazing, conductive adhesive or the like. Therefore, the vibrating membrane 4 is connected to the electrode take-out part 10a through the membrane ring 3, the lid 2, and the conductive path 7a. On the other hand, the fixed electrode 6
It is connected to the other electrode extraction portion 10b through the conductive path 7b, the semiconductor element 8, and the conductive path 7c. The conductive paths 7a and 7c can be formed inside through holes. Further, the electrode take-out part 10a is grounded, and the other electrode take-out part 10b also serves as a power supply of the semiconductor element 8 and an output terminal. When a sound is input from the sound hole 2a of the cover 2, the vibrating membrane 4 vibrates, and the capacitance between the vibrating membrane 4 and the fixed electrode 6 changes. An audio signal can be obtained. At this time,
By providing the back chamber 12 on the bottom surface of the concave portion 9a,
Even if the air wave due to the vibration hits the bottom surface of the concave portion 9a, the air escapes to the back room 12, so that the reflected wave does not return to the vibrating film 4 and adversely affects the microphone characteristics. In the electret condenser microphone of the present invention, by using the box-shaped case 9 made of an insulator, the insulator 27 and the printed board 29 can be eliminated as compared with the conventional structure shown in FIG. It is possible to reduce the number of parts and reduce the size. Further, the electret condenser microphone of the present invention only needs to store and fix the components in the concave portion 9a of the box-shaped case 9 in order from the bottom, and finally cover it with the lid 2. The manufacturing process is simplified, and mass production can be easily performed. In addition, since the step-shaped portion 9b is provided inside the box-shaped case 9, the fixed electrode 6 is joined to the step-shaped portion 9b, and the other components are securely joined to the case, it is possible to firmly fix the case. Become. The electret condenser microphone of the present invention has a box-shaped case 9 as shown in FIG.
Since the electrode extraction portions 10a and 10b are provided on both sides of the bottom surface of the substrate, the electrode extraction structure by surface mounting can be facilitated. Further, the box-shaped case 9 has a rectangular shape when viewed in plan. Therefore, when the semiconductor element 8 having a square shape is similarly stored, there is no waste, and the whole can be further reduced in size. Moreover, when the microphone is surface-mounted, it is easy to handle and position easily because of its square shape. Further, as an insulator forming the box-shaped case 9,
In particular, the use of ceramics containing alumina, zirconia, mullite, silicon carbide, silicon nitride, aluminum nitride, or the like as a main component makes it possible to particularly improve vibration damping characteristics. In other words, these ceramics have a greater effect of attenuating vibrations than metal materials and the like, so even when used for applications such as mobile phones, external vibrations can be hardly transmitted to the inside, and the performance of the microphone can be reduced. Can be improved. Further, in the present invention, since the box-shaped case 9 is used, the cover 2 may be a flat plate, which facilitates the processing. Therefore, for example, a structure having a mesh-shaped sound hole 2a may be employed. Normally, it is necessary to cover with a face cloth (not shown) or the like in order to prevent foreign matter from entering through the sound hole 2a. However, by using the mesh-shaped sound hole 2a, it is possible to omit the face cloth. it can. In another embodiment, a box-shaped case 9 is provided.
Alternatively, two step portions 9b may be formed, and the vibrating membrane 4 and the fixed electrode 6 may be placed on each of the step portions 9b. By doing so, the film ring 3 and the gap spacer 5 can be further eliminated. Further, another embodiment of the present invention will be described. The electret condenser microphone shown in FIG. 2 is an example in which the fixed electrode 6 and the cover 2 are also used. That is, the vibration film 4 is provided below the lid 2 covering the upper end surface of the box-shaped case 9 via the gap spacer 5, and the vibration film 4 is fixed to the step 9b. The lid 2 is connected to the conductive path 7.
The vibration film 4 is connected to the electrode take-out portion 10b through the conductive path 7b, the semiconductor element 8, and the conductive path 7c. Further, a back chamber 12 is provided on the bottom surface of the recess 9a. In this embodiment, the lid 2 also serves as the fixed electrode 6, and detects a change in capacitance between the lid 2 (fixed electrode 6) and the diaphragm 4. for that reason,
The number of parts can be further reduced as compared with that of FIG. Next, the mounting structure of the semiconductor element 8 will be described. In the example of FIGS. 1 and 2, the input lead 8a and the output lead 8b of the semiconductor element 8 are placed on the conductive paths 7b and 7c, respectively, and are joined with solder, a solder, a conductive adhesive or the like. As yet another embodiment, as shown in FIG. 3A, only the box-shaped case 9 and the semiconductor element 12 are shown, two recesses 9b and 9b 'are formed in the recess 9a, and the recess 9a is formed in the recess 9a'. The semiconductor element 8 can also be mounted. Or Figure 3
(B) As shown in (c), the connection can be made by wire bonding 11 using a semiconductor element 8 having no lead. Next, various examples of the planar shape of the back chamber 12 will be described. As shown in FIGS. 4A and 4C, the back chamber 12 is formed in a rectangular shape on the bottom surface of the concave portion 9a.
As shown in (b), it can be formed in a circular shape. In any case, the back chamber 12 is formed so as to be spatially continuous with the recess 9a without being completely covered with the semiconductor element 8. The back chamber 12 may be provided on any of the wall surfaces of the concave portion 9a, but is preferably formed on the bottom surface facing the vibration film 4. By providing the back chamber 12, when the semiconductor element 8 is joined with a solder, a solder, a conductive adhesive or the like, it can also act as a flow stopper for the semiconductor element 8 and reduce the overall weight. Also contributes. Alternatively, other electronic components can be mounted in the back room 12. However, in view of the strength of the box-shaped case 9, the thickness of the box-shaped case 9 in the portion where the back chamber 12 is formed needs to be 0.1 mm or more. As still another embodiment, as shown in FIG. 5, by forming the step 9b 'of the box-shaped case 9 on only one side, the volume of the concave portion 9a is increased, and the step 9b' is formed. By forming it in two, the space 9d between the two step portions 9b 'can be used as a back room. The shape and the like of the back chamber 12 are not limited to the above embodiment, but may be various. For example, a through hole communicating from the back chamber 12 to the outside of the box-shaped case 9 may be provided. . When the electret condenser microphone of the present invention is manufactured, mass production can be performed by using a multi-cavity method. According to the present invention, the fixed electrode and the vibrating membrane are arranged at regular intervals, and a sound signal given to the vibrating membrane is detected by a change in capacitance between the two. In the electret condenser microphone, the fixed electrode, the vibrating membrane, and the semiconductor element are housed in a box-shaped case made of an insulating material, and the back wall is provided on the wall surface of the concave portion. As a result, it is possible to prevent adverse effects due to reflected waves during vibration and to improve microphone characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an electret condenser microphone of the present invention, wherein (a) is a longitudinal sectional view, (b) is a plan view,
(C) is a bottom view. FIG. 2 is a longitudinal sectional view showing another embodiment of the present invention. FIGS. 3A to 3C are cross-sectional views showing another embodiment of the electret condenser microphone of the present invention. FIGS. 4A to 4C are plan views showing the shape of the back room in the electret condenser microphone of the present invention. 5A is a cross-sectional view showing another embodiment of the electret condenser microphone of the present invention, and FIG. 5B is a perspective view showing only the wire bonding portion of FIG. FIG. 6 is a longitudinal sectional view showing a conventional electret condenser microphone. [Explanation of Symbols] 2: Lid 2a: Sound hole 3: Membrane ring 4: Vibrating membrane 5: Gap spacer 6: Fixed electrodes 7a, 7b, 7c: Conductive path 8: Semiconductor element 9: Box-shaped case 9a: Recess 9b : Step 9c: Upper end surface 10a, 10b: Electrode take-out part 12: Back chamber

Claims (1)

(57) [Claims] [Claim 1] A fixed electrode and a vibrating membrane are arranged at regular intervals,
In the electret condenser microphone configured to detect an audio signal given to the vibrating membrane due to a change in capacitance between the two, the fixed electrode,
An electret condenser microphone which houses a semiconductor element on which a vibration film, an amplifier circuit and the like are formed, and has a back chamber on a wall surface of the concave portion.