JP2006109264A - Electret condenser microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electret condenser microphone to which reflow soldering can be applied. <P>SOLUTION: The electret condenser microphone is constituted in such a way that an electret condenser is built in a tubular capsule 11, an opening of the capsule 11 is closed with a circuit board 31, and the circuit board 31 includes terminal electrode patterns 34, 35 on its outer surface and is fixed by a caulked portion 11b by caulking and bending inwards an opening edge of the capsule 11, wherein PTFE with a high fusing point and a high potential holding rate at high temperature is used for an electret 15 used for the electret condenser, and the capsule 11 is made of nickel silver with superior thermal resistance. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electret condenser microphone, and more particularly to an electret condenser microphone that can be favorably subjected to reflow soldering when mounted on a counterpart mounting board or the like.

FIG. 2 shows a configuration described in Patent Document 1 as an example of a conventional configuration of an electret condenser microphone. An electret condenser is built in a cylindrical capsule 11, and a circuit board 12 is formed in an opening of the capsule 11. And the opening is covered with the circuit board 12.
In this example, the electret capacitor is composed of the vibration film 13, the back electrode 14, and the electret 15 disposed on the surface of the back electrode 14 facing the vibration film 13, and the vibration film 13 includes the front plate 11 a of the capsule 11. It arrange | positions so that it may oppose. The vibration film 13 is formed, for example, by forming a metal film such as Ni or Al as a conductive layer on one surface of a polyphenylene sulfide (PPS) film, and the periphery of the metal film is fixed to the vibration film ring 16. Reference numeral 16 denotes the front plate 11 a side and is accommodated in the capsule 11.

A ring-shaped insulating spacer 17 is interposed between the vibrating membrane 13 and the back electrode 14 to form a predetermined interval, and the back electrode 14 is held by a conductive cylindrical body 18 mounted on the circuit board 12. Has been. An insulating ring 19 is fitted to the outer peripheral surfaces of the back electrode 14 and the conductive cylindrical body 18 so that the back electrode 14 and the conductive cylindrical body 18 do not come into contact with the capsule 11.
The circuit board 12 is fixed by caulking the open end of the capsule 11 and bending it inward, and the circuit board 12 is pressed and fixed toward the conductive cylindrical body 18 by the bent caulking portion 11b. An IC element 21 for impedance conversion is mounted on the inner surface of the circuit board 12, and terminal electrode patterns 22 and 23 for external connection are formed on the outer surface. The terminal electrode pattern 22 is an output terminal, and the terminal electrode pattern 23 is a ground terminal.

The connection between the back electrode 14 and the electrode pattern 24 on the circuit board 12 is made through the conductive cylindrical body 18, while the metal film of the vibration film 13 includes the vibration film ring 16, the capsule 11 and the caulking portion 11 b thereof. It is connected to the terminal electrode pattern 23 via. The caulking portion 11 b of the capsule 11 is in pressure contact with the terminal electrode pattern 23. In FIG. 2, 25 indicates a sound hole formed in the front plate 11a of the capsule 11, and 26 indicates a cloth attached to the front plate 11a.
In the above structure, the capsule 11 is made of aluminum, and the electret 15 is made of tetrafluoroethylene-hexafluoropropylene copolymer (FEP).
Japanese Utility Model Publication No. 5-23698

By the way, in soldering and mounting such an electret condenser microphone to a counterpart mounting board or the like, soldering using a reflow device (reflow tank) can be applied as a simple mounting method that can be easily automated. desirable.
However, in the conventional electret condenser microphone described above, FEP is used for the electret 15, and the FEP has a very low electret potential due to a high temperature such as 260 ° C. during reflow soldering, and has a high melting point of 270 ° C. Therefore, it is not suitable for reflow soldering.

Further, since the capsule 11 is made of aluminum, it cannot be said that the capsule 11 is excellent in terms of heat resistance and mechanical strength, and thermal deformation occurs due to the influence of caulking or the like, which causes distortion in the electret condenser microphone, which is remarkable. There was a possibility of causing a sensitivity change (sensitivity reduction).
In view of such a situation, an object of the present invention is to provide an electret condenser microphone capable of performing reflow soldering satisfactorily without impairing performance.

According to the first aspect of the present invention, the electret capacitor is built in the cylindrical capsule, the opening of the capsule is covered with the circuit board, the circuit board has the terminal electrode pattern on the outer surface, and the opening end of the capsule is covered. In the electret condenser microphone fixed by the caulking part by crimping inside, the electret used for the electret condenser is made of polytetrafluoroethylene (PTFE), and the capsule is formed of white and white. Is done.
According to a second aspect of the present invention, in the first aspect of the present invention, the vibration film constituting the electret capacitor is made of a nickel thin film.

According to a third aspect of the present invention, in the first aspect of the present invention, the vibrating membrane constituting the electret capacitor is a polyphenylene sulfide (PPS) film having a metal film formed on one surface, and at a temperature corresponding to the reflow soldering temperature. It is assumed that annealing treatment has been performed.
In the invention of claim 4, in the invention of claim 1, the ring-shaped insulating spacer interposed between the diaphragm and back electrode of the electret capacitor and the holder for holding the back electrode are both made of polyimide or polyphthalamide (PPA). It is supposed to be.

  According to a fifth aspect of the present invention, in the first aspect of the invention, the terminal electrode pattern includes a protruding surface having a height equal to or higher than the caulking portion with respect to the outer surface, and the protruding surface is a reflow soldering surface.

  According to this invention, PTFE having a very high melting point and excellent potential holding ratio at high temperature is used for electrets, and white having excellent heat resistance is used for the constituent material of the capsule. Therefore, heat resistance is greatly improved compared to electret condenser microphones that use conventional FEP for electrets and the capsules are made of aluminum, and reflow soldering can be performed well without losing performance. In this respect, productivity can be improved.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an embodiment of an electret condenser microphone according to the present invention. In this example, the electret condenser microphone is of a back electret type, similar to the conventional electret condenser microphone shown in FIG. 2 corresponding to those in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted.
In this example, the capsule 11 is made of white and the electret 15 is made of polytetrafluoroethylene (PTFE). The vibration film 13 is made of a nickel thin film and has a thickness of 1 μm or less.

In this example, a metal ring 32 is interposed between the circuit board 31 accommodated in the opening of the capsule 11 and covering the opening and the back electrode 14 to form a required space. A ring-shaped holder 33 is arranged on the side. The back pole 14 is positioned and held at its outer corner by a step 33 a provided on the inner periphery of the holder 33.
Although not shown in FIG. 1A on the inner surface of the circuit board 31, a required electrode pattern is formed, and the electrode pattern on the circuit board 31 and the back electrode 14 are electrically connected via a ring 32. Has been.

  On the other hand, a circular terminal electrode pattern 34 forming an output terminal and an annular terminal electrode pattern 35 forming a ground terminal are formed on the outer surface of the circuit board 31 as shown in FIG. , 35 in this example have projecting surfaces 34a and 35a having a height equal to or higher than the height (projection height) of the caulking portion 11b of the capsule 11 with respect to the outer surface of the circuit board 31. The entire surface of the terminal electrode pattern 34 is a protruding surface 34a, and the terminal electrode pattern 35 is provided with an annular protruding surface 35a on the inner peripheral side separated from the caulking portion 11b.

A slit 36 is formed in the projecting surface 35 a in the radial direction, and the inner peripheral side and the outer peripheral side are communicated with each other by the slit 36. Further, three solder bumps 37 are formed on the protruding surface 35a at intervals of 120 °, and one solder bump 37 is formed on the protruding surface 34a at the center thereof.
The caulking portion 11b of the capsule 11 is positioned on the caulking surface 35b on the outer peripheral side where the height of the terminal electrode pattern 35 is low, that is, thin, and is in pressure contact with the terminal electrode pattern 35. The terminal electrode pattern 35 is electrically connected via the capsule 11 and the caulking portion 11b. The terminal electrode patterns 34 and 35 are electrically connected to corresponding electrode patterns on the inner surface side through through holes (not shown).

The terminal electrode patterns 34 and 35 having the above structure are formed by, for example, copper plating, and the protruding surfaces 34a and 35a are formed by increasing the plating thickness. In this example, both the insulating spacer 17 and the holder 33 are made of polyimide or polyphthalamide (PPA), and the back electrode 14, the diaphragm ring 16 and the ring 32 are all made of brass.
According to the electret condenser microphone described above, the electret 15 has a very high melting point of 327 ° C. compared to FEP, a high potential holding ratio at high temperatures, and a large potential even at the reflow soldering temperature (about 260 ° C.). PTFE that does not decrease is used, and the capsule 11 has excellent heat resistance and mechanical strength, so it should be reflow soldered without losing performance. Will be able to.

Further, both the insulating spacer 17 and the holder 33 are made of polyimide or PPA having excellent heat resistance, and the vibration film 13 is made of a nickel thin film whose resonance frequency is not changed by heating. Good reflow soldering is possible.
In addition, in this example, the projecting surfaces 34a and 35a formed on the terminal electrode patterns 34 and 35 of the circuit board 31 are used as reflow soldering surfaces, so that the crimping portions 11b of the capsule 11 are in pressure contact with each other. A step 35c exists between the caulking surface 35b of the pattern 35 and the reflow soldering surface (projecting surface 35a). The presence of the vertical step 35c and the creeping surface from the reflow soldering portion to the caulking portion 11b due to the step 35c. By increasing the distance, the reflow solder can be prevented from flowing into the capsule 11 from the caulking portion 11b, and the propagation of reflow heat can be suppressed.

Since the annular projecting surface 35a of the terminal electrode pattern 35 is provided with a slit 36, the space between the terminal electrode patterns 34 and 35 is not sealed during reflow, and therefore solder due to thermal expansion of air. No improper attachment or deformation of the circuit board 31 occurs.
In the above-described example, a nickel thin film is used for the vibration film 13. However, for example, a film in which a metal film is formed on one surface of a PPS film may be used as in the conventional case. In this case, the vibration film 13 using the PPS film changes in resonance frequency due to reflow heat, and the change is not uniform due to factors such as the assembly accuracy and component accuracy of each electret condenser microphone, that is, propagation of reflow heat. Since it is not uniform due to the difference in condition and a stable performance cannot be obtained, a material which has been previously annealed at a temperature (260 ° C.) corresponding to the reflow soldering temperature is used. By doing so, it is possible to realize an electret condenser microphone having a stable performance with little change in sensitivity, even if the resonance frequency passes through the reflow device.

  The back electret type has been described above as an example, but the present invention is not limited to the back electret type, and can also be applied to a front electret type or a foil electret type electret condenser microphone.

The figure which shows one Example of the electret condenser microphone by this invention, A is sectional drawing, B is a bottom view. Sectional drawing which shows the example of a conventional structure of an electret condenser microphone.

Claims (5)

An electret capacitor is built in the cylindrical capsule, the opening of the capsule is covered with a circuit board, the circuit board has a terminal electrode pattern on the outer surface, and the opening end of the capsule is crimped and bent inward, In the electret condenser microphone fixed by the caulking part,
The electret used in the electret condenser is made of polytetrafluoroethylene (PTFE),
An electret condenser microphone, wherein the capsule is made of white and white. The electret condenser microphone according to claim 1,
An electret condenser microphone, wherein the vibration film constituting the electret condenser is made of a nickel thin film. The electret condenser microphone according to claim 1,
The vibration film that constitutes the electret capacitor is one in which a metal film is formed on one surface of a polyphenylene sulfide (PPS) film and annealed at a temperature corresponding to the reflow soldering temperature. An electret condenser microphone characterized by The electret condenser microphone according to claim 1,
An electret condenser microphone, characterized in that a ring-shaped insulating spacer interposed between a diaphragm and a back pole of the electret condenser and a holder for holding the back pole are both made of polyimide or polyphthalamide (PPA). The electret condenser microphone according to claim 1,
The electret condenser microphone according to claim 1, wherein the terminal electrode pattern includes a protruding surface having a height equal to or higher than the caulking portion with respect to the outer surface, and the protruding surface is a reflow soldering surface.

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