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DESCRIPTION JP2010166286

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DESCRIPTION JP2010166286
An object of the present invention is to provide a mounting structure of a silicon microphone
which realizes flattening of frequency characteristics and environmental resistance to light, dust,
speaker's saliva and the like without using nonwoven fabric, mesh and the like. A microphone
chip 4 and an LSI chip 16 are housed and arranged in an internal space 13 of a silicon
microphone 10. A plurality of acoustic holes 24 are formed in front of the silicon microphone 10.
The plurality of acoustic holes 24 are formed on the entire periphery of the lid 22 of the
microphone package 12 at a position immediately above the microphone chip 14 and
surrounding the position immediately above the microphone chip 14. The silicon microphone 10
is disposed on the lower surface of the exterior 28 of the mobile phone 26. A mouthpiece 30 is
formed on the exterior 28. The silicon microphone 10 is disposed in a state in which a region
22a in which the acoustic hole 24 is not formed on the front surface of the silicon microphone
10 faces the mouthpiece 30. [Selected figure] Figure 2
Silicon microphone mounting structure and electronic equipment
[0001]
The present invention relates to a structure for mounting a silicon microphone (also referred to
as "MEMS microphone") on the exterior of an electronic device or the like and an electronic
device provided with the mounting structure, such as non-woven fabric or mesh (mesh of metal,
synthetic resin, etc.) Even without using an acoustic resistance material, it is possible to realize
flattening of frequency characteristics and environmental resistance to light, dust, speaker's
saliva and the like.
[0002]
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The conventional silicon microphone generally has a single acoustic hole formed on the front
surface of the microphone package as described in Patent Document 1 below.
[0003]
Japanese Patent Publication No. 2004-537182 (FIG. 1)
[0004]
According to the conventional silicon microphone in which a single acoustic hole is formed in the
lid of the microphone package, resonance in the lateral direction (opposite direction of the
microphone wall surface) is easily generated in the microphone package internal space.
For this reason, resonance occurs at a relatively low frequency on the high frequency side, and
there is a problem that the range in which the frequency characteristic of the microphone output
is flat is narrow.
In addition, when this silicon microphone is mounted on a device, the resonance frequency is
reduced due to the influence of the device exterior, and the range in which the frequency
characteristic of the microphone output is flat is further narrowed.
[0005]
Heretofore, as a method of flattening the frequency characteristic of the microphone output,
there has been a method of mounting a non-woven fabric, a mesh or the like on the surface of
the microphone.
According to this method, the porous material such as the non-woven fabric or the mesh exhibits
the characteristics of the low pass filter, so that the Q factor of the resonance decreases, and the
frequency characteristics can be flattened. In addition, when non-woven fabric or mesh is
attached to the surface of the microphone, environmental resistance is improved. That is, when
light strikes the microphone chip, noise due to the photoelectric effect occurs in the microphone
output, but since the non-woven fabric or mesh blocks light entering the inside of the
microphone from the outside, generation of noise due to the photoelectric effect in the
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microphone output is suppressed can do. In addition, non-woven fabric and mesh can prevent
dust, speaker's saliva and the like from entering the microphone.
[0006]
With regard to the silicon microphone as well, it is considered that flattening of frequency
characteristics and improvement of environmental resistance can be achieved by attaching a
non-woven fabric or mesh to the front of the microphone package and closing the acoustic hole.
However, attaching a non-woven fabric or mesh to the front of the microphone package has the
problem of requiring extra cost and labor. Also, if it is not a special non-woven fabric or mesh
that is resistant to heat, there is a problem that the adaptability to reflow soldering, which is a
major feature of a silicon microphone, is lost.
[0007]
The present invention has been made in view of the above-mentioned point, and a mounting
structure of a silicon microphone capable of realizing flattening of frequency characteristics and
environmental resistance without using an acoustic resistance material such as non-woven fabric
or mesh It is an object of the present invention to provide an electronic device having a mounting
structure.
[0008]
In the mounting structure of the silicon microphone according to the present invention, the
microphone chip is accommodated and disposed in the internal space of the microphone package
having the first acoustic hole formed on the front surface, and the sound in the external space of
the microphone package is from the first acoustic hole The microphone chip receives the sound
through the internal space of the microphone package, and the microphone chip has a plurality
of first acoustic holes, and the plurality of first acoustic holes are generally at the front of the
microphone package. A silicon microphone is formed around the entire circumference of the
microphone chip at a position immediately above the microphone chip, and the silicon
microphone is disposed inside, and a second acoustic hole is formed on the front surface. And a
sheath for taking in the sound of the external space from the second acoustic hole and entering
the first acoustic hole, the second acoustic hole being the silicon mass. Formed to be smaller than
the front surface of Kurohon, in which the first region of the central portion is sound hole not
formed of the front surface of the silicon microphone becomes so arranged as to face each other
in the second sound hole.
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[0009]
According to the present invention, a plurality of acoustic holes are formed on the entire surface
of the front surface of the microphone package at a position substantially immediately above the
microphone chip, surrounding the position directly above the microphone chip, thereby forming
a single lid. The frequency characteristics can be flattened compared to the case of forming the
acoustic holes.
This is because, in the case where a single acoustic hole is formed in the lid, resonance is likely to
occur in the lateral direction (opposite direction of the inner wall of the microphone package) in
the microphone package internal space as described above. It is considered that lateral resonance
is less likely to occur by forming the acoustic hole on the front surface of the microphone
package at a position approximately immediately above the microphone chip and surrounding
the position just above the microphone chip on the entire circumference. .
Further, according to the present invention, the acoustic hole of the exterior is formed smaller
than the front surface of the silicon microphone, and the area of the central portion of the front
surface of the silicon microphone where the acoustic hole is not formed is made to face the
acoustic hole of the exterior The acoustic hole of the silicon microphone is hidden at the
periphery of the acoustic hole of the sheath. Therefore, light from the outside is less likely to be
incident into the microphone package, and generation of noise due to the photoelectric effect in
the microphone output can be suppressed. In addition, it is possible to suppress that the garbage,
the saliva of the speaker, etc. get into the microphone package. This provides environmental
resistance. Therefore, it is not necessary to attach a non-woven fabric or a mesh to the front of
the microphone package, and unnecessary cost and labor can be saved. In addition, since it is not
necessary to use a non-woven fabric or mesh, the adaptability to reflow soldering can be
maintained.
[0010]
In the present invention, the plurality of first acoustic holes can be formed, for example, along a
position close to the inner wall surface of the internal space of the microphone package. Further,
according to the present invention, it is possible to sandwich a gasket which surrounds the first
acoustic hole and the second acoustic hole and allows the two acoustic holes to communicate
with each other between the silicon microphone and the exterior.
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[0011]
The electronic device of the present invention comprises the mounting structure of the silicon
microphone of the present invention.
[0012]
It is the top view and sectional drawing which show embodiment of the silicon microphone used
with the mounting structure of this invention.
It is a figure which shows embodiment of the mounting structure of this invention, and it is the
top view and sectional drawing which show the structure which mounted the silicon microphone
of FIG. 1 in the mobile telephone. It is a top view which shows the comparative example of a
silicon microphone. (A) is a plan view showing a design example (model A) of the single silicon
microphone 10 of FIG. 1 according to the embodiment of the present invention and its mounting
structure, and (b) is a single silicon microphone 44 of FIG. FIG. 16 is a plan view showing a
design example (model B) of the mounting structure thereof. It is a figure which shows each
frequency characteristic in the silicon microphone 10 single-piece | unit in the design of the
model A of Fig.4 (a), and its mounting structure. It is a figure which shows each frequency
characteristic in design of the design of the silicon microphone 44 single-piece | unit in the
design of the model B of FIG.4 (b), and its mounting structure.
[0013]
A first embodiment of the present invention is shown in FIG. The silicon microphone 10 is
configured by housing and arranging the MEMS chip 14 that constitutes the microphone body
and the LSI chip 16 that performs signal processing such as impedance conversion on the output
acoustic signal of the MEMS chip 14 in the internal space 13 of the microphone package 12. .
The LSI chip 16 is sealed with a potting material as needed. The microphone package 12 includes
a circuit board 18 constituting a bottom plate, a frame-like side wall 20 fixed to the upper
surface of the circuit board 18, and a lid 22 (front plate) fixed to the upper surface of the side
wall 20. It is comprised by the rectangular parallelepiped which has square front shape. The
outer dimensions of the microphone package 12 are, for example, 4 mm in the longitudinal
direction, 3 mm in the short side direction, and 1 mm in thickness when viewed from the front
side. The MEMS chip 14 and the LSI chip 16 are fixed on the circuit board 18. A sound receiving
surface 15 made of a diaphragm (membrane) is disposed on the surface 14 a of the MEMS chip
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14 so as to face the back surface of the lid 22. An output signal of the LSI chip 16 is output to
the outside from a terminal (not shown) disposed on the lower surface of the circuit board 18.
The lid 22 is formed with a plurality of acoustic holes (first acoustic holes) 24 of the same
diameter continuously arranged side by side. The acoustic holes 24 can be formed, for example,
by etching if the lid 22 is made of metal. No holes are formed in the circuit board 18 and the side
wall 20. The sound in the external space is taken from the acoustic hole 24, passes through the
internal space 13 of the microphone package 12, and is received by the sound receiving surface
15 of the MEMS chip 14.
[0014]
The configuration and arrangement of the plurality of acoustic holes 24 in the lid 22 will be
described. Each acoustic hole 24 is configured as a straight hole made perpendicular to the
surface of the lid 22. Each acoustic hole 24 is formed in a circular shape (or square shape or the
like) having the same diameter in the cross-sectional direction in the direction perpendicular to
the axis. The diameter of the acoustic hole 24 is, for example, 0.25 mm. The acoustic holes 24
can also be configured with finer holes (e.g., 0.1 mm in diameter). Each acoustic hole 24 is
formed on the entire circumference along a position close to the inner wall surface 13 a of the
internal space 13 of the microphone package 12 so as to surround the position just above the
MEMS chip 14 at a position away from the position just above the MEMS chip 14. ing. In this
embodiment, the internal space 13 of the microphone package 12 is formed in a rectangular
shape as viewed from the front side, and a plurality of acoustic holes 24 are provided along each
of the four sides of the internal space 13 adjacent to the inner wall 13a. It is formed by arranging
them one by one continuously.
[0015]
A structure in which the silicon microphone 10 of FIG. 1 is mounted on a mobile phone is shown
in FIG. A mouthpiece (second acoustic hole) 30 is formed on the exterior 28 (casing) of the
mobile phone 26. A substrate 34 on which the silicon microphone 10 of FIG. 1 is mounted is
accommodated and disposed inside the exterior 28. The mouthpiece 30 is formed in a
rectangular shape smaller than the front surface of the silicon microphone 10. The silicon
microphone 10 is disposed on the lower surface of the exterior 28 in a state in which the central
region 22a in which the acoustic hole 24 is not formed is made to face the mouthpiece 30 on the
front surface. A long square annular gasket 36 is sandwiched between the front outer edge of the
silicon microphone 10 and the rear surface of the exterior 28. The gasket 36 airtightly encloses
all of the plurality of acoustic holes 24 and the mouthpiece 30 to airtightly block the interior 32
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of the exterior 28 and the exterior space 38, and the front surface of the silicon microphone 10
and the exterior 28 are The all acoustic holes 24 and the mouthpiece 30 are mutually
communicated via the gap 40 formed between the back side. As a result, the voice of the speaker
emitted in the external space 38 is taken in from the mouthpiece 30 and enters the acoustic hole
24 of the silicon microphone 10 through the gap 40, and the MEMS chip 14 disposed inside the
silicon microphone 10. Received at. In the acoustic path from the mouthpiece 30 to the acoustic
hole 24 through the gap 40, no acoustic resistance material such as a non-woven fabric or a
mesh that prevents the passage of sound is disposed.
[0016]
The environmental resistance by the mounting structure of FIG. 2 will be described. Of the light
42 such as sunlight incident on the mouthpiece 30 from the outside in FIG. 2B and electric light
such as a fluorescent lamp, the light 42a incident on the mouthpiece 30 straight (at right angle)
is silicon. Since the acoustic hole 24 of the lid 22 of the microphone 10 is blocked by hitting the
central area 22 a where the acoustic hole 24 is not formed, it is not incident on the internal space
13 of the microphone package 12. Further, even if light 42b obliquely incident on the
mouthpiece 30 is incident in the direction away from the MEMS chip 14 even if it is incident on
the internal space 13 of the microphone package 12 from the acoustic hole 24 of the silicon
microphone 10, the MEMS chip 14 is not directly irradiated. Therefore, generation of noise due
to the photoelectric effect in the microphone output is suppressed. Further, since the acoustic
hole 24 of the silicon microphone 10 is hidden by the peripheral portion 30 a of the mouthpiece
30 of the exterior 28 when viewed from the front of the exterior 28, dust, saliva of the speaker,
etc. Entry to 13 is suppressed. Thus, environmental resistance is secured.
[0017]
Next, the frequency characteristic of the microphone output will be described. Here, a silicon
microphone 44 shown in FIG. 3 is assumed as a comparative example. This silicon microphone
44 is different from the silicon microphone 10 of FIG. 1 only in the arrangement of the acoustic
holes 24. That is, while the acoustic hole 24 of the silicon microphone 10 in FIG. 1 is formed on
the entire circumference at a position away from the position directly above the MEMS chip 14
and surrounding the position immediately above the MEMS chip 14, the silicon microphone 44
in FIG. The acoustic hole 24 is formed at a position deviated from the position directly above the
MEMS chip 14 but at a position deviated to the position directly above the LSI chip 16 (that is, a
position not surrounding the position immediately above the MEMS chip 14).
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[0018]
With regard to the silicon microphone 10 of FIG. 1 and the silicon microphone 44 of FIG. Here,
both silicon microphones 10 and 44 alone and their mounting structure are designed as shown
in FIG. 4A shows the design of the silicon microphone 10 alone in the embodiment of the present
invention shown in FIGS. 1 and 2 and the mounting structure thereof (hereinafter referred to as
“model A”), and FIG. The design of the silicon microphone 44 alone and its mounting structure
(hereinafter “model B”) in FIG. The dimensions of each part are as follows. "The mouthpiece 30
of the exterior 28" <Model A> · La (length of one side of the mouthpiece 30) = 1.5 mm · Lb
(length of the other side of the mouthpiece 30) = 2.5 mm Model B La La (length of one side of the
mouth 30) = 2.35 mm Lb (length of the other side of the mouth 30) = 1. 65 mm Thickness of the
exterior 28 = 0.5 mm Common to models A and B) << Internal space 13 of microphone package:
Common to models A and B >> Lc (the length in the minor axis direction of the internal space 13)
= 2.35 mm Ld (the length in the major axis direction of the internal space 13 Volume) of internal
space 13 = 1.85 × 10 <3> mm << Gasket 36: Common to models A and B >> Le (inner dimension
in the direction of short axis of gasket 36) = 2.55 mm Lf (inner size in the longitudinal direction
of the gasket 36) = 3.36 mm Thickness of the gasket = 0.2 mm Sound hole 24: Model A, B
common ", radius = 0.1 mm, numerical aperture of the lid 22 by sound hole 24 = 13% (a state in
which the lid removed 22 to 100%)
[0019]
FIG. 5A shows the frequency characteristics of the silicon microphone 10 of model A alone.
According to this, Resonant frequency: The sensitivity difference with the low band at
approximately 55 kHz and 20 kHz: approximately 1 dB.
[0020]
FIG. 5 (b) shows the frequency characteristics of the model A in the mounted state. According to
this, Resonant frequency: The sensitivity difference from the low band at approximately 35 kHz
and 20 kHz: approximately 5 dB.
[0021]
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FIG. 6A shows the frequency characteristics of the silicon microphone 44 of model B alone.
According to this, Resonant frequency: The sensitivity difference with the low band at
approximately 32.5 kHz and 20 kHz: approximately 5 dB.
[0022]
FIG. 6 (b) shows the frequency characteristics in the mounted state of model B. According to this,
Resonant frequency: The sensitivity difference with the low band at approximately 22.5 kHz and
20 kHz: approximately 16 dB.
[0023]
According to FIG. 5 and FIG. 6, the following can be said. [A] Comparing FIG. 5A and FIG. 6A, the
silicon microphone 10 of the model A can shift the resonance frequency to the high frequency
side compared to the silicon microphone 44 of the model B. This is because in the case of the
silicon microphone 44 of the model B in which the acoustic hole 24 is formed at a biased
position, resonance in the lateral direction (opposite direction of the wall surface of the
microphone package) is easily generated in the microphone package internal space 13 In the
case of the silicon microphone 10 of model A, which is formed on the entire circumference, it is
considered that the resonance in the lateral direction is less likely to occur. [B] Comparing (a) and
(b) in FIG. 5 and FIG. 6 respectively, when the silicon microphones 10 and 44 are mounted on the
exterior 28 compared to the silicon microphones 10 and 44 alone, the resonance frequency is
lower shift. [C] Therefore, in the state of being mounted on the exterior 28, the resonance
frequency occurs near 20 kHz in the model B, whereas the model A can realize sufficiently flat
frequency characteristics up to around 20 kHz. Therefore, according to the model A, flat
frequency characteristics can be obtained over a wide band as compared with the model B in a
state of being mounted on the exterior 28.
[0024]
In the above embodiment, the acoustic holes 24 are formed in a line along the position of the lid
22 of the microphone package 12 close to the inner wall surface 13a of the internal space 13 of
the microphone package 12, but the invention is not limited thereto. For example, the diameter
of the acoustic holes 24 may be smaller, and the acoustic holes 24 may be formed in a plurality
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of rows (for example, two rows) along the position close to the inner wall 13a of the internal
space 13 of the microphone package 12. In addition to forming the acoustic hole 24 along the
position close to the inner wall surface 13a of the internal space 13 of the microphone package
12, the acoustic hole 24 can be additionally formed immediately above the LSI chip 16. In this
way, the aperture ratio of the lid 22 can be increased. In this case, the mouthpiece 30 of the
exterior 28 is formed so as to hide the acoustic hole 24 formed immediately above the LSI chip
16 as well. Further, the planar shape of the microphone package 12, the planar arrangement
shape of the acoustic holes 24, and the planar shape of the mouthpiece 30 are not limited to
quadrilateral, and may be circular or polygonal other than quadrilateral.
[0025]
In the above embodiment, the mounting structure of the present invention is applied to a
portable telephone. However, the mounting structure of the present invention is not limited to
portable telephones, and can be applied to cameras, personal computers and other electronic
devices.
[0026]
DESCRIPTION OF SYMBOLS 10 ... Silicon microphone, 12 ... Microphone package, 13 ... Internal
space, 13a ... Inner wall surface of the internal space of a microphone package, 22 ... Lid of a
microphone package, 22a ... The central part in which the acoustic hole of the lid of a
microphone package is not formed Region 24 24 acoustic hole (first acoustic hole) 26 mobile
phone (electronic device) 28 exterior 30 second microphone (second acoustic hole) 32 exterior
of interior 38 external space , 36 ... gaskets.
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