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JP2016184794

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DESCRIPTION JP2016184794
Abstract: The present invention provides a unidirectional MEMS microphone suitable for
application of a manufacturing process under a heated atmosphere such as reflow soldering. A
MEMS acoustic chip and an acoustic resistor are accommodated in a casing, and a first sound
hole and a second sound hole are formed in the casing. The MEMS acoustic chip is fixed to the
casing and is formed with a diaphragm electrode for converting sound into an electrical signal.
The acoustic resistor has a communicating sound hole in which the opening edge of the concave
portion having a concave shape is fixed to the casing and the interior portion of the concave
portion communicates with the inside of the casing. The first sound hole communicates with the
inside of the MEMS acoustic chip from the outside of the casing. The second sound hole
communicates with the inside of the recess of the acoustic resistor from the outside of the casing.
The distance from the second sound hole to the communicating sound hole of the acoustic
resistor is set equal to or greater than the distance from the first sound hole to the diaphragm
electrode of the MEMS acoustic chip. [Selected figure] Figure 1
Unidirectional MEMS microphone
[0001]
The present invention relates to a unidirectional MEMS microphone using a MEMS acoustic chip
in which a microphone element is formed.
[0002]
MEMS (Micro Electro Mechanical Systems) means high-performance devices manufactured by
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integrating fine mechanical parts and electronic circuits on a substrate using semiconductor
microfabrication technology applied to the manufacture of ICs.
There is provided a MEMS microphone manufactured by applying the MEMS technology as a
small microphone replacing the conventional electret condenser microphone. MEMS
microphones are widely used in portable information terminals such as cellular phones and
smart phones, and in-vehicle devices. In particular, in order to realize unidirectionality using a
MEMS acoustic chip, conventionally, two MEMS acoustic chips are mounted on a casing as
described in Patent Document 1. Patent Document 2 describes a microphone which achieves a
single directivity by mounting one MEMS acoustic chip on a casing. The MEMS microphone
disclosed therein has a MEMS acoustic chip fixed to a casing, and two incident sound holes are
formed in the casing, one incident sound hole being in communication with the inside of the
MEMS acoustic chip and the other incident The sound holes are in communication with the
inside of the casing, and an acoustic resistance material is provided in any one of the incident
sound holes. Thereby, when the sound from the outside enters the casing, a pressure difference
is formed on the front and back of the diaphragm electrode of the diaphragm of the MEMS
acoustic chip to achieve the effect of the vibration directivity.
[0003]
Japan JP 2013-031146 Gazette China patent publication 102131140 Gazette
[0004]
The inventor examined a unidirectional MEMS microphone using one MEMS acoustic chip.
Although the acoustic resistive material is provided in any one incident sound hole of the MEMS
microphone in Patent Document 2, the acoustic resistive material is a sheet material. The sound
resistance is slightly larger than the size of the sound hole and is disposed close to the sound
hole, since it is presumed that the sound hole is sealed with a sheet material such as cloth or
sponge to make the sound resistance.
[0005]
Here, in manufacturing a unidirectional MEMS microphone using a MEMS acoustic chip, a ferrite
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bead, a capacitive element, a resistive element, and the like for removing noise are mounted on a
substrate on which the MEMS acoustic chip and the signal processing chip are mounted. In
addition, there is also a case where soldering is necessary when the substrate of the MEMS
microphone is covered with a lid. In order to improve the efficiency of soldering at that time, it is
considered preferable to use reflow soldering for the above-mentioned substrate mounting and
the like.
[0006]
However, when the acoustic resistance made of sheet material is adhesively fixed in the vicinity
of the sound hole, the heat of the reflow soldering process causes the acoustic resistance to
deteriorate or the flux scattered around adheres to the acoustic resistance. There is a possibility
that characteristic deterioration may occur. Even if the acoustic resistance is adhesively fixed
after the reflow soldering process, if the soldering is performed at the end of the process of
covering the substrate of the MEMS microphone with a lid, the influence of the scattering of the
flux can not be ignored, and finally the substrate In the process of covering with a lid, adhesion
will have to be used. In the conventional MEMS microphone thus achieving unidirectionality, the
present inventor has found that the problem is caused by the fact that the structure of the
acoustic resistance is not suitable for mounting under a heated atmosphere such as reflow
soldering. It was found.
[0007]
An object of the present invention is to provide a unidirectional MEMS microphone suitable for
application of a manufacturing process under a heating atmosphere such as reflow soldering.
[0008]
The above and other objects and novel features of the present invention will become apparent
from the description of the present specification and the accompanying drawings.
[0009]
The outline of representative ones of inventions disclosed in the present application will be
briefly described as follows.
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Note that reference numerals in the drawings and the like described in parentheses in this
section are examples for facilitating the understanding.
[0010]
[1] <To obtain unidirectionality using acoustic resistance in which the front and back of the
concave portion are communicated with the communicating sound hole> The unidirectional
MEMS microphone (1) according to the present invention has a casing (2) and a MEMS acoustic
chip (6), the signal processing chip (5), and the acoustic resistor (4) are accommodated, and the
first sound hole (7) and the second sound hole (8) are formed in the casing.
The MEMS acoustic chip is fixed to the casing and a diaphragm electrode (20A) is formed to
convert sound into an electrical signal. The signal processing chip processes electrical signals
from the MEMS acoustic chip. The acoustic resistor has a communicating sound hole (9) which is
fixed to the casing at the opening edge of the recess (4A) having a recess shape and which
communicates with the inside of the casing at the back of the recess. The first sound hole
communicates with the inside of the MEMS acoustic chip from the outside of the casing. The
second sound hole communicates with the inside of the concave portion of the acoustic resistor
from the outside of the casing. The distance from the second sound hole to the communicating
sound hole of the acoustic resistor is set equal to or greater than the distance from the first
sound hole to the diaphragm electrode of the MEMS acoustic chip.
[0011]
According to this, the sound generated at the rear first enters the second sound hole and then
enters the first sound hole. In this case, a sound coming from the second sound hole earlier and
delayed by the acoustic resistor to reach the back of the diaphragm electrode of the MEMS
acoustic chip, and a sound coming from the first sound hole behind the diaphragm electrode of
the MEMS acoustic chip The phase difference with the sound to be reached is reduced. If the
phase difference is small, the sound transmitted to the front and back of the diaphragm electrode
is offset as substantially the same amount of energy generated simultaneously on the front and
back of the diaphragm electrode, so that the electric signal output can not be obtained. On the
other hand, the sound generated in the front enters the second sound hole after entering the first
sound hole first. In this case, compared to the sound reaching the surface of the diaphragm
electrode of the MEMS acoustic chip earlier from the first sound hole, the sound entering behind
from the second sound hole is further delayed by the acoustic resistor and the back of the
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diaphragm electrode Reaching The acoustic energy on the front and back of the diaphragm
electrode is output as an electrical signal without being offset by the phase difference of the
sound reaching the front and back of the diaphragm electrode. This makes it possible to obtain
directivity from the front first sound hole to the rear second sound hole. At this time, the distance
from the first sound hole to the diaphragm electrode of the MEMS acoustic chip is at least equal
to the distance between the first sound hole and the flux at the time of fixing the MEMS acoustic
chip to the substrate. An equivalent distance is set between the second sound hole and the
communicating sound hole of the acoustic resistor. Therefore, it is possible to avoid the
possibility that the flux at the time of fixing the acoustic resistor to the casing blocks the
communicating sound hole and the acoustic resistance deviates from the design value. In this
respect, it is suitable for application of the manufacturing process under a heating atmosphere
such as reflow soldering.
[0012]
[2] <Squeezed Metal Acoustic Resistor> In the item 1, the acoustic resistor is a metal formed by
drawing.
[0013]
According to this, the formation of the recessed portion is easy, and moreover, it is suitable for
soldering.
[0014]
[3] <The acoustic resistor is soldered and fixed to the substrate by reflow> In paragraph 2, the
casing has the substrate and a lid for covering the substrate to form an inner section, and the
substrate is formed with a metal pattern The acoustic resistor is soldered to the substrate by
reflow.
[0015]
According to this, it is suitable for the reflow soldering to the board | substrate of an acoustic
resistor.
[0016]
[4] <The lid is soldered to the substrate by reflow> In Section 3, the lid is made of a substrate
material on which a metal pattern is formed, and the lid is soldered to the substrate by reflow.
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[0017]
According to this, it is also possible to carry out the assembly of the casing and the mounting of
the acoustic resistor on the substrate together in the reflow soldering process.
[0018]
The effects obtained by the typical ones of the inventions disclosed in the present application will
be briefly described as follows.
[0019]
That is, it is possible to provide a unidirectional MEMS microphone suitable for application of a
manufacturing process under a heating atmosphere such as reflow soldering.
[0020]
FIG. 1 is a side cross-sectional view illustrating an embodiment of a unidirectional MEMS
microphone according to the present invention.
FIG. 2 is a cross-sectional view schematically showing an A-A cross section of FIG.
FIG. 3 is a plan view illustrating a metal pattern formed on the surface of a substrate.
FIG. 4 is a cross sectional view schematically showing a longitudinal cross section of the MEMS
acoustic chip.
[0021]
An example of a unidirectional MEMS microphone according to the present invention is shown in
FIG.
In the unidirectional MEMS microphone 1 shown in the figure, the MEMS acoustic chip 6, the
signal processing chip 5, and the acoustic resistor 4 are housed in the casing 2, and the first
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sound hole 7 and the second one are formed in the casing 2. Sound holes 8 are formed.
[0022]
The casing 2 has a substrate 2A and a lid 2B which covers the substrate 2A to form an internal
space, and although not particularly limited, the substrate 2A and the lid 2B are made of a
substrate material on which a predetermined metal pattern is formed.
For example, a glass epoxy resin substrate can be adopted as the substrate material.
As illustrated in FIG. 3 showing the surface of the substrate 2A viewed from the bottom side of
FIG. 1, a ring-shaped metal pattern 11 is formed concentrically around the first sound hole 7 of
the substrate 2A. A ring-shaped metal pattern 12 is formed concentrically around the second
sound hole 8 of the substrate 2A.
13 is an output pad and 14 is a power supply pad.
At four corners of the surface of the substrate 2A, square ground patterns 10 are formed.
Although not particularly shown, a ground terminal connected to the ground pad 10 through a
through hole, a power supply terminal connected to the power supply pad 14, and an output
terminal connected to the output pad 13 are provided on the back of the substrate 2A. The same
metal pattern is also formed on the back side of the metal pattern 12. Although not shown, metal
patterns on which ferrite beads for removing noise and the like, capacitive elements, resistive
elements and the like are mounted are formed on the back surface of the substrate. Furthermore,
a metal pattern (not shown) is formed on the periphery of the back surface of the substrate 2A,
and this metal pattern faces a metal pattern (not shown) formed on the end face of the lid 2B,
and the metal pattern is soldered to both The two are closely fixed to each other to form an
internal space. The two members may be adhered and fixed not only by solder but also by using
a thermosetting adhesive or the like.
[0023]
As illustrated in FIG. 4, the MEMS acoustic chip 6 is provided with a silicon substrate 20 made of
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single crystal silicon, a diaphragm 20A, a spacer 21, and a plurality of through holes 23
manufactured using semiconductor microfabrication technology. A back electrode 22 is provided
to form a capacitive microphone element. A bias voltage is applied to the back electrode 22 from
the bias electrode of the signal processing chip 5 through the bonding wire 15, and the
diaphragm 20 A is coupled to the input electrode of the signal processing chip 5 through the
bonding wire 16.
[0024]
The signal processing chip 5 is composed of a MOS transistor or the like having a predetermined
signal amplification characteristic, and the output terminal of the amplification signal is
connected to the output pad 13 via the bonding wire 19 of FIG.
[0025]
The acoustic resistor 4 has an opening edge of a recess 4A in the form of a recess fixed to the
substrate 2A, and has a plurality of communicating sound holes 9 communicating with the inside
of the casing 2 at the back of the recess 4A.
The acoustic resistor 4 is made of, for example, a metal formed by drawing a copper alloy plate
having a thickness of about 0.05 mm. The communicating sound hole 9 is formed with a
diameter of 60 μm by pressing, though it is not particularly limited. As illustrated in FIG. 2, a
plurality of communicating sound holes 9 are arranged in the circumferential direction of a
predetermined diameter.
[0026]
The first sound hole 7 communicates with the inside of the MEMS acoustic chip 6 from the
outside of the casing 2 and faces the diaphragm electrode 20A from the chip substrate 20 side.
The second sound hole 8 communicates with the inside of the recess 4 A of the acoustic resistor
4 from the outside of the casing 2. According to this, the sound generated at the rear (right side
in the X direction in FIG. 1) first enters the second sound hole 8 and then enters the first sound
hole 7. In this case, the sound coming from the second sound hole 8 earlier and reaching the
back (the back electrode 23 side) of the diaphragm electrode 20A of the MEMS acoustic chip 6
delayed by the acoustic resistor 4 and the back sound from the first sound hole 7 Thus, the phase
difference with the sound reaching the front (the chip substrate 20 side) of the diaphragm
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electrode 20A of the MEMS acoustic chip 6 is reduced. If the phase difference is small, the sound
transmitted to the front and back of the diaphragm electrode 20A will not be an electrical signal
output to the signal processing chip 5 because it is offset as approximately the same amount of
energy generated simultaneously on the front and back of the diaphragm electrode 20A. . On the
other hand, the sound generated forward (on the left side in the X direction in FIG. 1) first enters
the first sound hole and then enters the second sound hole. In this case, as compared with the
sound reaching the surface of the diaphragm electrode 20A of the MEMS acoustic chip earlier
than the first sound hole, the sound entering later from the second sound hole is further delayed
by the acoustic resistor 4 and the diaphragm electrode It reaches the back of 20A. The acoustic
energy on the front and back of the diaphragm electrode 20A is output as an electrical signal to
the signal processing chip 5 without being offset by the phase difference of the sound reaching
the front and back of the diaphragm electrode 20A. Thereby, it is possible to obtain unidirectivity
in the arrow X direction from the front first sound hole to the rear second sound hole.
[0027]
As illustrated in FIG. 1, the distance D2 from the second sound hole 8 to the communicating
sound hole 9 of the acoustic resistor 4 is not less than the distance D1 from the first sound hole
7 to the diaphragm electrode 20A of the MEMS acoustic chip 6. The distances D1 and D2 which
are set or both are substantially equal. For example, assuming that the outer dimensions of the
MEMS acoustic chip 6 and the acoustic resistor 4 are about 0.6 mm to 1.2 mm, the distance D1
of the MEMS acoustic chip 6 is 0.2 mm to 0.5 mm, and the distance D2 of the acoustic resistor 4
is 0.1. The above relationship is satisfied in the range of dimensions such as 2 mm to 0.6 mm.
The distance D1 from the first sound hole 7 to the diaphragm electrode 20A of the MEMS
acoustic chip 6 (the depth of the hole formed in the frame electrode 20 by etching) D1 occurs
when the MEMS acoustic chip 6 is fixed to the substrate 2A Then, the flux is expected to be
sufficiently dimensioned to avoid the risk of damaging the diaphragm electrode 20. This
dimension D1 is practically expected to have such an effect, and the dimension D1 is not
determined considering only that. In fact, since a thin silicon substrate is etched to form a thinner
diaphragm 20A, the substrate 20 needs to have a thickness necessary to secure a certain degree
of rigidity as a whole compared to the thickness of the diaphragm 20A. When D1 is determined
according to the difference, it is sufficient if the dimension D1 is a distance necessary to avoid
damage to the diaphragm electrode 20 due to the flux.
[0028]
Since the distance D2 at least equal to the distance D1 is set between the second sound hole 8
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and the communicating sound hole 9 of the acoustic resistor 4, when the acoustic resistor 4 is
fixed to the substrate 2A by solder or the like It is possible to avoid the possibility that the flux
which is expected to be generated in the air may block the communicating sound hole 9 and the
acoustic resistance may deviate from the design value. In this respect, it is preferable to use an
assembly process under a heating atmosphere such as reflow soldering.
[0029]
Here, a method of assembling the unidirectional MEMS microphone 1 will be described. The
necessary patterns 10 to 14 are formed on the surface of the substrate 2A as illustrated in FIG. 3,
and the first sound hole 7 and the second sound hole 8 are formed. Although not particularly
limited, all the patterns 10 to 14 are made of copper, aluminum or the like. The MEMS acoustic
chip 6 is fixed to the back surface of the pattern 11 using, for example, a heat-resistant adhesive.
The signal processing chip 5 is fixed to the central portion of the substrate 2A using, for example,
a heat-resistant adhesive. The signal input electrode and the bias electrode of the signal
processing chip 5 are connected to the MEMS acoustic chip 6 by wire bonding. The ground
electrode, the signal output electrode and the power supply electrode of the signal processing
chip 5 are electrically coupled to the predetermined pads 10, 13 and 14 on the surface of the
substrate 2A by bonding wires 17, 18 and 19 through through holes not shown. It is connected
to the electrode on the back surface of the substrate 2A. For example, cream solder is applied to
the metal pattern on the back surface of the pattern 12, and the acoustic resistor 4 is placed on it
and temporarily attached. In addition, on the back surface of the substrate 2A, ferrite beads for
removing noise and the like, capacitive elements, resistive elements and the like are attached to
corresponding metal patterns for mounting. In addition, a metal pattern made of copper or
aluminum or the like is formed on the end face of the lid 2B facing the substrate 2A, for example,
cream solder is applied on the surface, and the lid 2B is covered on the substrate 2A. Then, the
whole is heated and so-called reflow soldering is performed. As a result, the acoustic resistance 4
and ferrite beads for removing noises, etc. are fixed to the substrate 2A, and the cap 2B is fixed to
the substrate 2A. During the reflow soldering, foreign matter such as flux scatters from the cream
solder and adhesive due to the heat, but as described above, the height up to the diaphragm
electrode 20 in the MEMS acoustic chip 6 and the acoustic resistor 4 penetrate Since the height
to the sound hole 9 is secured to a predetermined size, there is no risk of damage to the
diaphragm electrode 20 or clogging of the through sound hole 9 due to scattering of foreign
matter such as flux, etc. There is no possibility that the unidirectional property will deteriorate.
[0030]
Furthermore, although reflow soldering is performed when the MEMS microphone is mounted on
a device, there is no possibility that the unidirectionality will be deteriorated in the mounting
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process as well as the above-mentioned assembly process.
[0031]
The unidirectional MEMS microphones 1 may be individually manufactured one by one, but may
be manufactured in a so-called multiple-piece manner.
For example, assuming that n × m multiple-pieces are taken, n × m substrates 2A are formed on
the base material, and the MEMS acoustic chip 6 and the acoustic resistor 4 are mounted on the
respective substrates. Thereafter, a lid member on which n × m lids 2B are formed is positioned
and covered on the base material after component mounting, and in this state, both are heated
and reflow soldering is performed. The parts are soldered onto each base material base plate, and
the base plate and the lid are respectively soldered to each other. After this, the unidirectional
MEMS microphones may be cut out by dicing, respectively.
[0032]
Although the invention made by the inventor has been specifically described based on the
embodiments, it is needless to say that the present invention is not limited thereto, and various
modifications can be made without departing from the scope of the invention.
[0033]
For example, in the assembly procedure, after fixing the acoustic resistor 4, the ferrite bead, the
capacitive element, the resistive element and the like by reflow soldering, the MEMS acoustic
chip 6 and the signal processing chip 5 are bonded and necessary bonding wires are performed.
Finally, the lid 2B may be adhered.
In addition, the desired effect can be obtained because the distance from the second sound hole
to the communicating sound hole of the acoustic resistor is set to be equal to or more than the
distance from the first sound hole to the diaphragm electrode of the MEMS acoustic chip. Even if
the distance relationship is slightly reversed in the range, it may be considered as a
manufacturing error. Further, although bonding is partially used for wiring, the electrode bumps
of the chip may be bonded and fixed to the wiring pattern on the substrate 2A by reflow
soldering. Also, the MEMS acoustic chip is not limited to the bias type, and may be an electret
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type.
[0034]
DESCRIPTION OF SYMBOLS 1 unidirectional MEMS microphone 2 casing 2A substrate 2B lid 4
acoustic resistor 4A recessed part 5 signal processing chip 6 MEMS acoustic chip 7 first sound
hole 8 second sound hole 9 communicating sound hole 10 ground pad 11 conductive pattern 12
Conductive pattern 13 Output pad 14 Power supply pad 15, 16, 17, 18, 19 Bonding wire 20
Frame substrate 20A Diaphragm 21 Spacer 22 Back electrode 23 Through hole
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