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DESCRIPTION JPH11266499

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DESCRIPTION JPH11266499
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
electret condenser microphone, and more particularly to an extremely thin electret condenser
microphone.
[0002]
2. Description of the Related Art A conventional example of an electret condenser microphone
(hereinafter referred to as ECM) will be described with reference to FIG. FIG. 3 shows an example
of a back electret condenser microphone. In FIG. 3, the capsule 11 comprises a cylinder of metal
such as aluminum. One end face of the capsule 11 is closed by the front plate 12. At the center of
the front plate 12, a central hole 13 which is a sound hole is bored. In the capsule 11, a vibrating
membrane 16 attached to a vibrating membrane ring 15 made of a metal material is
accommodated, and the vibrating membrane ring 15 is in contact with the front plate 12. An
electret dielectric film 161 is deposited on the upper surface of the back electrode 18. The
vibrating film 16 is positioned opposite to the electret dielectric film 161 on the upper surface of
the back electrode 18 through the insulating spacer 17. 40 'is a metal ring. The metal ring 40 'is
formed with a step 41 at the entire periphery of the upper end thereof, and the back pole 18 is
fitted and held there. A back chamber 28 is formed at the center of the metal ring 40 '. The metal
ring 40 ′ and the capsule 11 are electromechanically separated with an insulating ring 401
interposed. 70 is a printed wiring board. An IC chip 50 in which a high amplification factor
amplifier with an extremely large gain is integrated with an impedance conversion circuit is
formed on the inner surface of the printed wiring board 70 as a measure to reduce the influence
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of external noise of the ECM.
[0003]
Referring also to FIG. 4, in the above ECM, the back electrode 18 having the electret dielectric
film 161 formed on the upper surface constitutes one electrode, and the vibrating film 16
constitutes the other electrode. The back electrode 18, which is one of the electrodes, is
connected to the surface of the printed wiring board 70 through the metal ring 40 ', and
connected to the gate of the field effect transistor 54 constituting the impedance conversion
circuit through the gate end 53'. The other electrode, the vibrating membrane 16, is electrically
connected to the grounding terminal 52 through the vibrating membrane ring 15 made of a
metal material, the capsule 11, and a lead (not shown). Here, when the acoustic vibration enters
through the center hole 13, the ECM vibrates the vibrating film 16 due to this, and the
capacitance change between the vibrating film 16 and the back electrode 18 corresponding to
the vibration is It can be output across the resistor 56 as an audio signal.
[0004]
In the above-mentioned prior art ECM, the metal ring 40 'fixes and holds the back electrode 18,
but at the same time, the back electrode 18 which is one of the electrodes and the printed wiring
board 70. It also plays a role of electrically connecting with the surface of the However, this
metal ring 40 'has a minute external dimension, and it is necessary to form the step 41 at the
entire periphery of the upper end thereof, and for other reasons because the mechanical strength
needs to be somewhat high. , Processing is not always easy. And, the ratio of the weight of the
metal ring 40 'to the weight of the ECM is relatively large.
[0005]
In addition, since the conductive metal ring 40 'is used as a holder for fixing and holding the
back electrode 18, the insulating ring 401 for electromechanically separating between the metal
ring 40' and the capsule 11 accompanying it is used. To reach the need. If the number of parts is
increased by one, the number of assembling steps will be increased accordingly, and the
possibility of missing parts or the occurrence of errors or other failures will be increased.
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[0006]
Furthermore, with regard to the IC chip 50 that constitutes the impedance conversion circuit,
there is no conventional general package product whose height is less than 0.6 mm, which limits
the thinning of the ECM. In addition, a high amplification factor amplifier is integrated in the IC
chip 50 to reduce the influence of external noise of the ECM.
[0007]
The present invention provides an ECM that solves the above-mentioned problems.
[0008]
According to a first aspect of the present invention, there is provided a holder for supporting a
diaphragm ring made of a metal material with a back electrode having an electret dielectric film
attached to the upper surface thereof or a diaphragm attached to the diaphragm. In the electret
condenser microphone having the printed wiring board 70 to which the IC chip 50 including the
impedance conversion circuit is attached, the IC chip 50 is a bare chip 50 'and the holder 18 is
made of an insulating material and extends from the upper end face to the lower end face A
conductive layer 42 is formed on the inner surface, and an electret condenser microphone in
which the back electrode 18 or the diaphragm ring 15 and the printed wiring board 70 are
electrically connected by the conductive layer 42 is configured.
[0009]
In a second aspect of the present invention, in the electret condenser microphone according to
the first aspect, the electret condenser in which the bump 501 formed on the lower surface of
the bare chip 50 'and the printed wiring board 70 are connected via the anisotropic conductive
film 61. I configured a microphone.
According to a third aspect of the present invention, in the electret condenser microphone
according to the first aspect, the bump formed on the lower surface of the bare chip and the
wiring pattern of the printed wiring board are connected by ultrasonic welding.
[0010]
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In a fourth aspect of the present invention, in the electret condenser microphone according to
the first aspect of the present invention, there is provided an electret condenser microphone in
which the bumps formed on the lower surface of the bare chip and the wiring pattern of the
printed wiring board are connected by solder.
In a fifth aspect of the present invention, in the electret condenser microphone according to any
of the first to fourth aspects, the bare chip 50 'is configured as an impedance converting and
amplifying circuit by adding an amplification circuit.
[0011]
In the electret condenser microphone according to any one of claims 1 to 4, the impedance
conversion circuit constitutes an electret condenser microphone configured as an emitter
follower or a source follower.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will
be described with reference to FIG.
FIG. 1 is a view for explaining an embodiment of a back electret type ECM. In FIG. 1, the capsule
11 comprises a cylinder of metal such as aluminum. One end face of the capsule 11 is closed by
the front plate 12. At the center of the front plate 12, a central hole 13 which is a sound hole is
bored.
[0013]
In the capsule 11, a vibrating membrane 16 attached to a vibrating membrane ring 15 made of a
metal material is accommodated, and the vibrating membrane ring 15 is in contact with the front
plate 12. An electret dielectric film 161 is deposited on the upper surface of the back electrode
18. The vibrating film 16 is positioned opposite to the electret dielectric film 161 on the upper
surface of the back electrode 18 through the insulating spacer 17. Reference numeral 40 denotes
a holder formed by molding a synthetic resin, and the bottom of the holder is removed to form a
ring. Reference numeral 42 denotes a conductive metal layer formed on the inner side surface of
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the holder 40 from a part of the upper end surface of the holder 40 to a part of the lower end
surface. The holder 40 may be made of light metal with low density, and the outer surface
thereof may be covered with an insulating coating. The holder 40 is formed with a step 41 at the
entire periphery of the upper end thereof, and the back pole 18 is fitted and held here. A back
chamber 28 is formed at the center of the holder 40.
[0014]
70 is a printed wiring board. Attached to the inner surface of the printed wiring board 70 is an IC
chip 50 integrated with an impedance conversion circuit and a high amplification factor amplifier
with extremely large gain. Here, referring also to FIG. 4, the impedance conversion circuit is
constituted of a field effect transistor 54, a resistor 55, and a resistor 56, and further, a
semiconductor element constituting a high amplification factor amplifier is also integrated into
an IC and connected. It is a chip 50. The high amplification factor amplifier is integrated in the IC
chip 50 to reduce the influence of the external noise of the ECM.
[0015]
Here, referring to FIG. 2, this is a diagram for explaining bare chip flip chip bonding to a printed
wiring board. As IC chip 50, bare chip 50 'before being packaged is used. Then, on the lower
surface of the bare chip 50 ', bumps 501 made of metal such as gold or solder are formed as
terminals, to which the gate and other element electrodes of the bare chip 50' are connected. A
wiring pattern and an output end 51 ', a ground end 52', a gate end 53 ', and a power supply end
57' are formed on the printed wiring board 70, and corresponding bumps 501 are oppositely
connected to these. The connection of the bumps 501 of the bare chip 50 'to the wiring pattern
of the printed wiring board 70 is performed by applying the anisotropic conductive film 61
between the two. The bonding material for forming the anisotropic conductive film 61 is made of
a thermosetting synthetic resin 611 in which minute gold balls 612 are dispersed. The bonding
material is applied to a region of the printed wiring board 70 where the bare chip 50 'is to be
bonded, the bare chip 50' is mounted on this region, and the bare chip 50 'is pressed against the
printed wiring substrate 70 while being heated. In this case, the minute gold balls 612 dispersed
in the thermosetting synthetic resin 611 between the bump 501 to which the pressing force is
applied and the gate end 53 'reach cohesive contact while excluding the thermosetting synthetic
resin. Eventually, the bumps 501 and the gate ends 53 'are electrically connected via the micro
gold balls 612 in cohesive contact.
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[0016]
Here, when acoustic vibration enters through the center hole 13, the vibrating film 16 vibrates
due to this, and the change in electric capacity between the vibrating film 16 and the back
electrode 18 corresponding to this vibration is used as an electric signal. Output. The connection
of the bumps 501 of the bare chip 50 'to the wiring pattern of the printed wiring board 70 was
carried out using the anisotropic conductive film 61, but in addition, it may be connected by
ultrasonic welding or connected by solder. it can.
[0017]
In the back electret type ECM described above, the back electrode 18 made of a metal material
whose electret dielectric film 161 is formed on the upper surface constitutes one electrode, and
the vibrating film 16 made of a metal material constitutes the other electrode. The back electrode
18 which is one of the electrodes is formed on the surface of the printed wiring board 70 via the
conductive metal layer 42 formed on the inner side surface of the holder 40 from a part of the
upper end face of the holder 40 to a part of the lower end face. It connects and connects to the
gate of the field effect transistor 54 which comprises an impedance conversion circuit via gate
end 53 '. The other electrode, the vibrating membrane 16, is electrically connected to the
grounding terminal 52 through the vibrating membrane ring 15 made of a metal material, the
capsule 11, and a lead (not shown). In particular, referring to FIGS. 1 (b) and 1 (c), the power
supply end 57 'of the IC chip 50 is connected to the power supply terminal 57 via the printed
wiring, and the output end 51' is outputted via the printed wiring It is connected to the terminal
51, and the ground end 52 'is connected to the ground terminal 52 through printed wiring. Then,
the back electrode 18 can be in contact with the gate end 53 ′ of the printed wiring through the
conductive metal layer 42, and the gate end 53 ′ is further connected to the gate 53 of the IC
chip 50 through the bonding wire 59. Here, the rear end of the capsule 11 is bent and crimped to
the lower surface of the printed wiring board 70. By doing this, the diaphragm ring 15, the
diaphragm 16, the spacer 17, the back electrode 18, and the printed wiring board 70 are
mechanically accommodated and fixed in the capsule 11.
[0018]
When bending and crimping the rear end of the capsule 11, a part thereof is expanded to form a
ground surface on the lower surface of the printed wiring board 70, and the ground terminal 52
is fixed thereto. Then, an output terminal surface is further formed on the lower surface of the
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printed wiring board 70 and the output terminal 51 is fixed thereto, and a power terminal
surface is formed and the power terminal 57 is fixed thereto. Reference numeral 58 denotes a
thick film gain adjustment resistor of the high amplification factor amplifier of the IC chip 50.
The thick film gain adjusting resistor 58 is formed in advance to have a wider width on the
output terminal formation surface. The sensitivity of the microphone can be easily set to an
appropriate sensitivity by adjusting the width of the thick film gain adjusting resistor 58 which
has been formed widely in advance. In this process, a sound pressure of 1 pa (1 kHz) is applied to
an electret microphone whose sensitivity is to be adjusted, and a thick film gain adjustment
resistor formed widely while monitoring the output value of the microphone in operation While
cutting off the width of 58 by laser processing or other cutting, change the resistance value and
set the sensitivity to the specified value. By doing this, it is possible to omit the manufacturing
process of the microphone such as selection of resistance, soldering, terminal alignment, and
bending adapted to the specified sensitivity, and at the same time, make the microphone thinner,
smaller and yield the product. Can be improved. Although FIG. 1 shows an embodiment of the
back electret microphone, this can be applied to a front electret microphone.
[0019]
In the above embodiment, the layer electrically connecting the back electrode 18 which is one
electrode to the surface of the printed wiring board 70 extends from a part of the upper end
surface of the holder 40 to a part of the lower end surface on the inner surface The conductive
metal layer 42 was formed by plating, but as another example, instead of plating to form a
conductive metal layer, a conductive resin is coated to form a conductive resin layer. Depending
on the situation, the effect is almost the same.
[0020]
Although the previous embodiment incorporated the high amplification factor amplifier into the
impedance conversion circuit to reduce the influence of external noise of the ECM, in another
embodiment, the impedance conversion circuit is configured as an emitter follower or source
follower. Can reduce the output impedance of the ECM and reduce the influence of external
noises of the ECM.
The above description of the present invention has been about the back electret type ECM, but
this forms the electret dielectric film 161 on the inner surface of the front plate 12 of the capsule
11, and the diaphragm 16 is disposed opposite to it. The same applies to the front electret type
ECM.
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[0021]
As described above, according to the present invention, a metal ring is not used to electrically
connect the back electrode or the vibrating film, which is one of the electrodes, to the surface of
the printed wiring board. By forming a conductive layer on the inner surface of the holder
formed by molding a synthetic resin to obtain continuity, the number of parts resulting from the
use of metal rings increases, the number of assembling steps increases, and parts are forgotten to
be incorporated Alternatively, it is possible to reduce the weight of the ECM while eliminating the
possibility of built-in errors and other failures.
[0022]
And as for the IC chip that constitutes the impedance conversion circuit, there are no general
package products of which the height is less than 0.6 mm as described above, and thus the
thinning of the ECM has been limited. By adopting a bare chip as the chip and flip chip bonding
it, the semiconductor element itself can be thinned to about 0.3 mm, and the thickness of the
bare chip including the printed wiring board can be about 0.8 mm. .
As a result, it contributes greatly to thickness reduction of the whole ECM.
[0023]
In addition, by configuring the impedance conversion circuit as an emitter follower circuit or a
source follower circuit to reduce the output impedance of the ECM, the influence of external
noises of the ECM can be reduced more easily than when an amplifier circuit is added. can do.
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