JP7166602B2 - MEMS microphone - Google Patents

Description

The present invention relates to a MEMS microphone, and more particularly to a MEMS microphone capable of controlling desired frequency characteristics.

MEMS (Micro Electro Mechanical Systems) are high-performance devices manufactured by integrating fine mechanical parts and electronic circuits on a substrate using semiconductor microfabrication technology applied to the manufacture of ICs (Integrated Circuits). .

A MEMS microphone manufactured by applying MEMS technology is known as a small microphone. MEMS microphones are widely used in personal digital assistants such as mobile phones and smart phones, and in-vehicle equipment.

The structure of a microphone equipped with a MEMS chip is disclosed in Patent Documents 1 and 2.

JP 2010-193120 A JP 2012-39272 A

In a MEMS microphone having a MEMS acoustic chip (MEMS chip), the MEMS acoustic chip is structurally susceptible to dust and foreign matter. In particular, a type of MEMS microphone, called a bottom port, in which a sound hole is formed in a circuit board, has a sound hole directly below the MEMS acoustic chip, and must be handled with the utmost care. In addition, it is known to install a dust filter made of non-woven fabric etc. in the sound hole as a dust prevention measure, but it is difficult to automate the manufacturing process for attaching a dust filter, and there are concerns that the cost will increase due to the increase in parts. be done.

Also, the MEMS acoustic chip may not require a low frequency range depending on the intended use of the microphone. It is possible to cut the low frequency range by designing the MEMS acoustic chip, but since the MEMS acoustic chip requires a lot of cost for development and manufacturing, there is a demand to make it as versatile as possible. On the other hand, a general MEMS microphone has a peak of several tens of decibels in its frequency characteristics in the high frequency range (20 kHz or higher) due to its structure, which may adversely affect performance such as distortion rate and subsequent signal processing.

In other words, in the MEMS microphone, it is a challenge to control the frequency characteristics with high precision at low cost.

Although the structures of the microphones disclosed in Patent Documents 1 and 2 are capable of preventing dust from entering, they all require specially processed parts, which may increase costs. .

SUMMARY OF THE INVENTION An object of the present invention is to provide, in a MEMS microphone, a technology capable of controlling the frequency characteristics with high accuracy and preventing dust and foreign matter from entering from the outside at a low cost.

A brief outline of typical inventions disclosed in the present application is as follows.

A representative MEMS microphone of the present invention includes a MEMS chip that captures sound and converts the sound signal into an electrical signal, is electrically connected to the MEMS chip, and processes the electrical signal transmitted from the MEMS chip. and a signal processing chip. a circuit board having a first surface on which the MEMS chip and the signal processing chip are mounted, and provided with a conductor layer partially exposed on the first surface and an insulating layer covering the conductor layer; and a lid that seals the MEMS chip and the signal processing chip and is bonded to the first surface. The circuit board includes a first hole opened on the first surface, a second hole opened on a second surface opposite to the first surface, the first hole and the a first cavity communicating with the second hole and formed along the first surface, wherein the insulating layer is a photosensitive film bonded to the conductor layer; The cavity is surrounded by the end face of the conductor layer, the photosensitive film forming the ceiling surface, and the base material forming the floor surface, and the height of the first cavity is equal to the thickness of the conductor layer. is equal to

Among the inventions disclosed in the present application, the effects obtained by representative ones are briefly described below.

In a MEMS microphone, it is possible to control the frequency characteristics with high accuracy and prevent dust and foreign matter from entering from the outside at low cost.

1 is a cross-sectional view showing an example of the structure of a MEMS microphone according to Embodiment 1 of the present invention; FIG. 2 is an enlarged partial cross-sectional view showing an example of the structure of a circuit board included in the MEMS microphone shown in FIG. 1; FIG. 2 is an enlarged partial cross-sectional view showing an example of the structure of the first cavity of the MEMS microphone shown in FIG. 1; FIG. (a) is an enlarged partial cross-sectional view showing the structure cut along the line AA shown in FIG. 3, and (b) and (c) each show the structure cut along the line AA shown in FIG. It is an enlarged partial cross-sectional view showing a modification. FIG. 4 is a cross-sectional view showing an example of the structure of a MEMS microphone according to Embodiment 2 of the present invention; FIG. 10 is a cross-sectional view showing an example of the structure of a MEMS microphone according to Embodiment 3 of the present invention; FIG. 4 is a cross-sectional view showing the structure of a MEMS microphone of a comparative example;

(Embodiment 1)
FIG. 1 is a cross-sectional view showing an example of the structure of a MEMS microphone according to Embodiment 1 of the present invention. The MEMS microphone 20 according to the first embodiment shown in FIG. 1 is a small microphone having a MEMS chip for sound (hereinafter also referred to as a MEMS acoustic chip). It is used for in-vehicle equipment. A MEMS is a high-performance device manufactured by integrating minute mechanical parts and electronic circuits on a silicon substrate, for example, using semiconductor microfabrication technology.

First, the configuration of the MEMS microphone 100 of the comparative example shown in FIG. FIG. 7 is a cross-sectional view showing the structure of a MEMS microphone of a comparative example.

A MEMS microphone 100 of a comparative example shown in FIG. 7 includes a circuit board 1 on which a MEMS acoustic chip (MEMS chip) 2 and a signal processing chip 4 are mounted. A through hole is formed as a sound hole 3 at a position directly below the MEMS acoustic chip 2 mounted on the upper surface 1 a of the circuit board 1 .

A signal processing chip 4 is mounted side by side on the upper surface 1 a of the circuit board 1 next to the MEMS acoustic chip 2 . The MEMS acoustic chip 2 and signal processing chip 4 are electrically connected by metal wires 5 . Further, the signal processing chip 4 is electrically connected to bonding pads 1j exposed on the upper surface 1a of the circuit board 1 by wires 5. As shown in FIG. That is, the signal processing chip 4 is electrically connected to the circuit board 1 through the wires 5 . Note that the wire 5 is, for example, a gold wire.

Further, a lid 7 is provided to cover mounted components such as the MEMS acoustic chip 2 and the signal processing chip 4 described above. The lid 7 covers the mounted parts and is adhered to the peripheral portion of the upper surface 1a of the circuit board 1, forming an internal space 6. As shown in FIG. That is, the MEMS acoustic chip 2 and the signal processing chip 4 are sealed by the lid 7 and the internal space 6 is sealed by the lid 7 .

The connection pattern 1k on the lower surface 1b side of the circuit board 1 is electrically connected to the copper foil pattern 1c (see FIG. 2) on the upper surface 1a side by through-hole wiring or the like (not shown), and the MEMS microphone 100 is mounted on the device. used as a soldering pattern when

In the MEMS microphone 100 of the comparative example shown in FIG. 7, the sound hole 3 is directly below the MEMS acoustic chip 2, and it is necessary to pay close attention to its handling. The inventors have found that providing a dust filter made of non-woven fabric or the like in the sound hole 3 makes it difficult to automate the manufacturing process of the MEMS microphone 100 and increases the number of parts, leading to an increase in cost.

Furthermore, the MEMS acoustic chip 2 may not need a low frequency range depending on the purpose of use of the microphone, but since the MEMS acoustic chip 2 requires a lot of cost for development and manufacturing, it should be as versatile as possible. It is preferable to In addition, due to its structure, the general MEMS microphone 100 has a peak of several tens of decibels in its frequency characteristics in the high frequency range (20 kHz or higher), which may adversely affect performance such as distortion rate and subsequent signal processing. In other words, the inventors of the present invention have found that the MEMS microphone 100 has a problem of controlling the frequency characteristics with high precision at a low cost.

Therefore, in the MEMS microphone 20 according to the first embodiment shown in FIG. It is provided at a shifted position.

The structure of the MEMS microphone 20 of Embodiment 1 will be specifically described with reference to FIGS. 1 to 4. FIG. 2 is an enlarged partial cross-sectional view showing an example of the structure of the circuit board provided in the MEMS microphone shown in FIG. 1, and FIG. 3 is an enlarged partial cross-sectional view showing an example of the structure of the first cavity portion of the MEMS microphone shown in FIG. 4(a) is an enlarged partial cross-sectional view showing the structure cut along the AA line shown in FIG. 3, and (b) and (c) are the structures cut along the AA line shown in FIG. It is an enlarged partial cross-sectional view showing a modification of.

The MEMS microphone 20 of the first embodiment includes a MEMS acoustic chip (MEMS chip) 2 that captures sound and converts the sound signal into an electrical signal, is electrically connected to the MEMS acoustic chip 2, and a signal processing chip 4 for processing the electrical signal transmitted from the chip 2 . The signal processing chip 4 amplifies the electric signal transmitted from the MEMS acoustic chip 2, for example.

The MEMS microphone 20 has a top surface (first surface) 1a on which the MEMS acoustic chip 2 and the signal processing chip 4 are mounted. and a lid body 7 that covers and seals the MEMS acoustic chip 2 and the signal processing chip 4 and is bonded to the upper surface 1a.

The MEMS acoustic chip 2 includes a hollow portion (cavity portion) 2a and a diaphragm (not shown) provided in the hollow portion 2a. ing. Then, the MEMS acoustic chip 2 captures sound waves, converts the sound signal into an electrical signal, and transmits the electrical signal to the signal processing chip 4 . The MEMS acoustic chip 2 and the signal processing chip 4 are electrically connected via wires 5 such as gold wires. Therefore, an electrical signal output from the MEMS acoustic chip 2 is transmitted to the signal processing chip 4 via the wire 5. FIG.

The signal processing chip 4 amplifies and outputs the electric signal transmitted from the MEMS acoustic chip 2 , and is electrically connected to the circuit board 1 via a plurality of wires 5 . Specifically, a plurality of wires 5 electrically connected to the signal processing chip 4 are electrically connected to a plurality of bonding pads 1j on the upper surface 1a of the circuit board 1, respectively.

The lid 7 is joined to the peripheral portion of the upper surface 1 a of the circuit board 1 via a conductive paste or the like, forms a sealed space 6 inside, and seals the MEMS acoustic chip 2 and the signal processing chip 4 . is stopping. The lid 7 is a cap made of metal or resin.

A plurality of connection patterns 1k are provided on the lower surface (second surface) 1b of the circuit board 1 . The plurality of connection patterns 1k are electrically connected to the conductor layer on the upper surface 1a side by through-hole wiring (not shown) or the like.

The circuit board 1, as shown in FIG. 2, is a printed board having a base material 1f made of glass epoxy material or the like. Conductor layers are laminated on both the front and back sides of the substrate 1f. The conductor layer is a copper foil pattern 1c formed of copper foil.

An insulating layer is formed on the copper foil pattern 1c on the upper surface 1a side. The insulating layer is a photosensitive film 1e that is laminated to a copper foil pattern 1c formed by etching. That is, the insulating layer is a solder resist covering the copper foil pattern 1c, and the photosensitive film 1e is provided as the solder resist. However, as shown in FIG. 1, part of the copper foil pattern 1c is exposed from the photosensitive film 1e as a bonding pad 1j for connecting the wire 5. As shown in FIG. That is, after the formation of the copper foil pattern 1c, the photosensitive film 1e is pasted (laminated) on the copper foil pattern 1c, and the photosensitive film 1e is exposed and developed to expose the bonding pads 1j on the photosensitive film 1e. forming an opening in the Thereby, the bonding pads 1j are exposed from the openings of the photosensitive film 1e.

On the other hand, in the circuit board 1 shown in FIG. 2, a liquid solder resist 1n is formed by printing on the copper foil pattern 1c on the lower surface 1b side.

That is, the circuit board 1 includes a base material 1f, a copper foil pattern 1c on the upper surface 1a side formed on the upper layer of the base material 1f, and a top layer (solder resist) formed on the copper foil pattern 1c on the upper surface 1a side. a photosensitive film 1e, a copper foil pattern 1c on the lower surface 1b side formed on the lower layer of the substrate 1f, and a solder resist 1n formed as the lowest layer on the lower layer of the copper foil pattern 1c on the lower surface 1b side. ing.

As an example, the thickness of each layer of the circuit board 1 is 200 μm for the substrate 1f, 35 μm for each of the copper foil patterns 1c on the upper surface 1a side and the lower surface 1b side, and 25 μm for the uppermost photosensitive film 1e. The thickness of the lower layer solder resist 1n is 20 μm, but it is not limited to these numerical values.

Moreover, as shown in FIG. 3, the circuit board 1 of the MEMS microphone 20 of Embodiment 1 has a first hole portion 1g opened at the upper surface 1a and a second hole portion 1g opened at the lower surface 1b opposite to the upper surface 1a. and an acoustic flow path (first hollow portion) 1i formed along the upper surface 1a and connecting the first hole portion 1g and the second hole portion 1h. That is, the first hole portion 1g on the upper surface 1a side and the second hole portion 1h on the lower surface 1b side are connected via the acoustic flow path 1i.

The acoustic channel 1i is a channel formed along the upper surface 1a (or the lower surface 1b) of the circuit board 1, and connects a hole opening to the outside of the MEMS microphone 20 and a hole opening to the inside. flow path. Therefore, the sound channel formed by the first hole portion 1g, the acoustic channel 1i, and the second hole portion 1h (sound hole 3) is It is formed in a crank shape (non-linear shape).

In other words, in the circuit board 1, the first hole portion 1g on the upper surface 1a side and the second hole portion 1h on the lower surface 1b side, which are connected by the acoustic flow path 1i, are flat as shown in FIG. It is arranged in a position that is shifted when viewed visually. Further, as shown in FIG. 1, in the MEMS microphone 20, the first hole 1g opens in a chip mounting area 1m, which is a mounting area for the MEMS acoustic chip 2 on the upper surface 1a.

Therefore, in the MEMS microphone 20 , the sound wave entering from the sound hole 3 (second hole portion 1 h ) reaches the MEMS acoustic chip 2 through the acoustic flow path 1 i and further through the first hole portion 1 g.

Incidentally, as shown in FIG. 3, the height T1 of the acoustic flow path 1i is equal to the thickness T2 of the copper foil pattern 1c (T1=T2). This is because the acoustic flow path 1i is formed as a copper foil pattern 1c by etching and removing a part of the copper foil. It is equal to the thickness T2 of 1c.

Furthermore, since the acoustic channel 1i is formed as a cavity by removing a part of the copper foil by etching, the side wall of the acoustic channel 1i is formed by the end face 1d of the copper foil pattern 1c. ing. That is, the end surface 1d of the patterned copper foil (copper foil pattern 1c) on the circuit board 1 becomes the wall surface of the acoustic flow path 1i, and therefore the height T1 of this wall surface corresponds to the thickness T2 of the copper foil pattern 1c. do.

In other words, in the copper foil pattern 1c, the end face 1d left after being scraped off by etching serves as the side wall of the acoustic flow path 1i. Therefore, as shown in FIG. 4(a), the acoustic channel 1i is surrounded by the end face 1d of the copper foil pattern 1c, which is the side wall (wall face) thereof.

As shown in FIG. 3, the acoustic flow path 1i has a photosensitive film 1e as its ceiling surface and a substrate 1f as its floor surface. Thus, the acoustic flow path 1i in the circuit board 1 is formed by the end surface 1d of the copper foil pattern 1c, the photosensitive film 1e provided as a solder resist on the upper surface 1a side, and the base material 1f.

As described above, the sound hole 3 of the MEMS microphone 100 shown in FIG. 7, which the present inventors compared and studied, is provided directly below the MEMS acoustic chip 2, and the acoustic flow path is formed linearly. In contrast, in the MEMS microphone 20 according to the first embodiment shown in FIG. 1, the sound hole 3 is provided at a position shifted from directly below the MEMS acoustic chip 2 inside.

In the MEMS microphone 20, the sound wave entering from the sound hole 3 has the end surface 1d of the patterned copper foil (copper foil pattern 1c) of the circuit board 1 as the side wall, and the photosensitive film 1e as the ceiling surface. It reaches the MEMS acoustic chip 2 through the acoustic channel 1i formed with the material 1f as a floor surface. At this time, since the acoustic flow path 1i is formed by removing a part of the copper foil pattern 1c by etching, the height T1 of the side wall of the acoustic flow path 1i, that is, the wall surface, is equal to that of the copper foil pattern 1c. It corresponds to thickness T2.

Furthermore, the ceiling surface of the acoustic flow path 1i is a photosensitive film 1e joined to the copper foil pattern 1c by lamination. That is, the photosensitive film 1e is bonded onto the copper foil pattern 1c by lamination after etching for forming the copper foil pattern 1c. It is different from the resist formation method. That is, a cavity can be formed in the lower part of the laminated photosensitive film 1e. Therefore, the end surface 1d of the copper foil pattern 1c after etching can be used as the side wall (wall surface) of the acoustic flow path 1i, and the height T1 of the acoustic flow path 1i can be formed with high accuracy.

In addition, as shown in FIG. 4A, the side wall of the acoustic channel 1i is surrounded by the end surface 1d of the copper foil pattern 1c (the dot portion in the figure), so the width of the acoustic channel 1i is also formed with high accuracy. be able to. That is, since the height and width of the acoustic flow path 1i are determined by the copper foil pattern 1c formed by etching, the height and width of the acoustic flow path 1i can be formed with high accuracy.

In addition, the acoustic flow path 1i has an effect of suppressing the peak of the high frequency range of the acoustic characteristics as its acoustic resistance. For example, it acts on the acoustic flow path 1i as acoustic resistance and inertance. Inertance mainly affects the frequency characteristics of high-pitched sounds because it affects the action of sound that tries to propagate quickly. The degree to which the peak is suppressed can be controlled by the width, height, and length of the acoustic channel 1i.

Here, each of FIGS. 4(b) and 4(c) shows a modified example of the shape of the acoustic flow path 1i, and the patterning of the copper foil (copper foil pattern 1c: dot portion in the figure). Depending on the shape, the width and length of the acoustic channel 1i can be easily changed.

For example, the acoustic flow path 1i of the modified example of FIG. 4B is formed to have a narrower width (thinner) than the acoustic flow path 1i of FIG. 4A. 4(c) has a longer length and a narrower width than the acoustic channel 1i shown in FIG. 4(a). It is visually bent at two points.

As a result, peaks in the high frequency range of the frequency characteristics can be suppressed as necessary. That is, in the MEMS microphone 20, the frequency characteristics of captured sound can be controlled with high precision.

Moreover, in the MEMS microphone 20 of the first embodiment shown in FIG. 1h) are formed in a crank shape (non-linear shape) in the thickness direction of the circuit board 1 to prevent dust and foreign matter from reaching the MEMS acoustic chip 2 directly. can be prevented.

Note that the acoustic flow path 1i of the modified example of FIG. 4(c) described above is bent at two points even in a plan view, so that dust and foreign matter enter more easily than the acoustic flow path 1i of FIG. 4(a). It can be quiet.

In addition, the acoustic flow path 1i in the MEMS microphone 20 is composed of the copper foil pattern 1c of the circuit board 1, the photosensitive film 1e, and the base material 1f, and the photosensitive film 1e also functions as a solder resist. Since there are no additional parts or steps, the MEMS microphone 20 can be produced at low cost with excellent mass productivity.

Therefore, according to the MEMS microphone 20 of the first embodiment, it is possible to control the frequency characteristics with high accuracy and prevent dust and foreign matter from entering from the outside at low cost.

In addition, since various frequency characteristics of sound can be obtained simply by changing the shape of the copper foil pattern 1c, MEMS microphones 20 with many different characteristics can be produced at the lowest cost.

(Embodiment 2)
FIG. 5 is a cross-sectional view showing an example of the structure of the MEMS microphone according to Embodiment 2 of the present invention. A MEMS microphone 30 according to the second embodiment will be described with reference to FIG.

The difference between the MEMS microphone 30 of the second embodiment and the MEMS microphone 20 of the first embodiment is that the other first hole portion 1q in the circuit board 1 is located on the upper surface 1a of the circuit board 1, and the MEMS acoustic chip 2 and the lid The point is that the space 6 in the region (non-chip mounting region 1p) between the side wall 7a of the body 7 is also opened.

The first hole portion 1q communicates with the second hole portion 1h, which is the sound hole 3. As shown in FIG. Specifically, an acoustic channel (first cavity) 1r extending along the upper surface 1a like the acoustic channel 1i and having a structure similar to that of the acoustic channel 1i is formed. A first hole portion 1q that opens in the region 1p and a second hole portion 1h that opens in the lower surface 1b communicate with each other via an acoustic flow path 1r.

The acoustic channel 1r has the same structure as the acoustic channel 1i. That is, the ceiling surface is the photosensitive film 1e, the floor surface is the substrate 1f, and the side surface (side wall) is the end surface 1d of the copper foil pattern 1c. Therefore, the height of the acoustic flow path 1r is equal to the thickness of the copper foil pattern 1c.

In addition, in the MEMS microphone 30 shown in FIG. 5, the acoustic channel 1r also communicates with the acoustic channel 1i. That is, the first hole portion 1q and the second hole portion 1h communicate with each other through the acoustic flow path 1r, and furthermore, the first hole portion 1g and the second hole portion 1g and the second hole 1h which open toward the hollow portion 2a of the MEMS acoustic chip 2 are connected. 1h are in communication with each other via the acoustic flow path 1i, and the acoustic flow path 1r is also connected to the acoustic flow path 1i.

That is, in the MEMS microphone 30 of the second embodiment, the space 6 inside the MEMS microphone 30 (internal volume of the lid 7) and the outside of the MEMS microphone 30 pass through the acoustic channel 1r connected to the acoustic channel 1i. Further, the first hole portion 1g opening to the hollow portion 2a of the MEMS acoustic chip 2 is also connected to the outside via the acoustic flow path 1i.

In the structure shown in FIG. 5, sound taken in from the second hole 1h enters the cavity 2a of the MEMS acoustic chip 2 from the first hole 1g through the acoustic flow path 1i, and reaches the bottom surface of the diaphragm (not shown). Reportedly. At the same time, the sound enters the space 6 through the first hole 1q through the acoustic flow path 1r and is transmitted to the upper surface of the diaphragm (not shown). Since the lower the frequency of the sound, the more likely it is to wrap around, the same-phase sound enters from both sides of the diaphragm, canceling out the movement of the diaphragm, so that low-pitched sounds can be cut. In other words, it is possible to increase the cut-off frequency of the low range acoustic characteristics. The cutoff frequency can be controlled by the length, width and height of the channel and the diameter of the small holes in the diaphragm. Then, similarly to the MEMS microphone 20 of the first embodiment, by changing the width and length of the acoustic channel 1r, the frequency characteristics of the bass range can be controlled with high accuracy.

The acoustic flow path 1r for controlling low-frequency characteristics may be provided separately so as not to communicate with the acoustic flow path 1i for high-frequency characteristics.

In addition, since the first hole 1g that opens to the cavity 2a of the MEMS acoustic chip 2 is connected to the second hole 1h that opens to the outside through the acoustic flow path 1i, the MEMS microphone 30 of the first embodiment Similar to the effect obtained, it is possible to suppress peaks in the high frequency range of the frequency characteristics (cut high sounds).

Therefore, according to the MEMS microphone 30 of the second embodiment, similarly to the MEMS microphone 20 of the first embodiment, the frequency characteristics of captured sound can be controlled with high accuracy. Also in the MEMS microphone 30, it is possible to control the frequency characteristics with high accuracy and prevent dust and foreign matter from entering from the outside at low cost. Other effects obtained by the MEMS microphone 30 of the second embodiment are the same as the effects of the MEMS microphone 20 of the first embodiment, so redundant description thereof will be omitted.

(Embodiment 3)
FIG. 6 is a cross-sectional view showing an example of the structure of the MEMS microphone according to Embodiment 3 of the present invention. The third embodiment describes an example of a directional MEMS microphone having an acoustic channel.

The MEMS microphone 40 shown in FIG. 6 has a first hole portion 1g that opens toward the cavity portion 2a of the MEMS acoustic chip 2 on the front side of the circuit board 1, and a front a second hole portion 1h, which is the sound hole 3 on the side, and an acoustic flow path on the front side formed along the upper surface (first surface) 1a and communicating between the first hole portion 1g and the second hole portion 1h 1i are formed. Further, the MEMS microphone 40 is opened in the space 6 in the area (non-chip-mounted area 1v) on the circuit board 1 opposite to the area where the MEMS acoustic chip 2 is mounted with respect to the signal processing chip 4 (back side). and a fourth hole 1t, which is a sound hole 8 on the rear side and is opened on the lower surface (second surface) 1b. In addition, the circuit board 1 includes a rear-side acoustic flow path (second hollow portion) 1u formed along the upper surface 1a so as to allow the third hole portion 1s and the fourth hole portion 1t to communicate with each other.

In other words, the MEMS microphone 40 of the third embodiment has sound holes 3 and 8 at two locations on the front side and the back side, and two acoustic channels 1i and 1u communicating with the respective holes. The acoustic flow path 1 i on the front side, which is connected to the sound hole 3 on the side, communicates with the lower side of the MEMS acoustic chip 2 toward the hollow portion 2 a of the MEMS acoustic chip 2 . As a result, the front-side acoustic flow path 1i connected to the front-side sound hole 3 mainly contributes to the suppression of the entry of dust and foreign matter and the control of the frequency characteristics in the high-pitched range.

On the other hand, the acoustic channel 1u connected to the sound hole 8 on the back side communicates with the space (internal volume of the lid 7) 6 of the non-chip mounting area 1v on the back side inside the MEMS microphone 40 . As a result, sound taken in through the sound hole 8 on the rear side enters the space 6 through the third hole 1s through the acoustic flow path 1u, and is transmitted to the upper surface of the diaphragm (not shown) of the MEMS acoustic chip 2. FIG. The balance between this sound pressure and the sound pressure taken in from the sound hole 3 on the front side and transmitted to the lower surface of the diaphragm contributes to the formation of the directional characteristics of the microphone.

As described above, in the MEMS microphone 40 of the third embodiment, it is possible to obtain various directivity characteristics by appropriately setting the shape of the acoustic flow path.

The acoustic channel 1u has the same structure as the acoustic channel 1i. That is, the ceiling surface is the photosensitive film 1e, the floor surface is the substrate 1f, and the side surface (side wall) is the end surface 1d of the copper foil pattern 1c.

Therefore, as in the MEMS microphone 20 of the first embodiment, the height of the acoustic channel 1u is equal to the thickness of the copper foil pattern 1c.

As a result, in the MEMS microphone 40 of the third embodiment, similarly to the MEMS microphone 20 of the first embodiment, the frequency characteristics of captured sound can be controlled with high accuracy. Also in the MEMS microphone 40, it is possible to control the frequency characteristics with high accuracy and prevent dust and foreign matter from entering from the outside at low cost. Other effects obtained by the MEMS microphone 40 of the third embodiment are the same as the effects of the MEMS microphone 20 of the first embodiment, so redundant description thereof will be omitted.

Although the invention made by the present inventor has been specifically described based on the embodiments, the invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the described configurations.

In the above embodiment, the circuit board 1 is a board having one wiring layer (copper foil layer forming the copper foil pattern 1c) on each of the upper layer and the lower layer of the base material 1f. , the circuit board 1 may be a multilayer wiring board having a plurality of wiring layers in each of the upper layer and the lower layer of the base material 1f.

1 circuit board 1a upper surface (first surface)
1b lower surface (second surface)
1c Copper foil pattern (conductor layer)
1d end face (side wall)
1e photosensitive film (insulating layer)
1f base material 1g first hole 1h second hole 1i acoustic flow path (first cavity)
1j bonding pad 1k connection pattern 1m chip mounting area 1n solder resist 1p non-chip mounting area 1q first hole 1r acoustic flow path (first cavity)
1s Third hole 1t Fourth hole 1u Acoustic flow path (second cavity)
1 v Non-chip mounting area 2 MEMS acoustic chip (MEMS chip)
2a cavity 3 sound hole 4 signal processing chip 5 wire 6 space 7 cover 7a side wall 8 sound hole 20, 30, 40, 100 MEMS microphone

Claims (5)

a MEMS chip that captures sound and converts the sound signal into an electrical signal;
a signal processing chip electrically connected to the MEMS chip and processing the electrical signal transmitted from the MEMS chip;
a circuit board provided with a first surface on which the MEMS chip and the signal processing chip are mounted, a conductor layer partially exposed on the first surface, and an insulating layer covering the conductor layer;
a lid that seals the MEMS chip and the signal processing chip and is bonded to the first surface;
has
The circuit board includes a first hole that opens on the first surface, a second hole that opens on a second surface opposite to the first surface, and the first hole and the second hole. a first cavity communicating with the hole and formed along the first surface;
The insulating layer is a photosensitive film bonded to the conductor layer,
The first cavity is surrounded by an end surface of the conductor layer, the photosensitive film forming a ceiling surface, and a base material forming a floor surface,
A MEMS microphone, wherein the height of the first cavity is equal to the thickness of the conductor layer. The MEMS microphone of claim 1 , wherein
The conductor layer is a copper foil pattern formed of copper foil,
The MEMS microphone, wherein the side wall of the first cavity is an end surface of the copper foil pattern. The MEMS microphone of claim 1, wherein
The MEMS microphone, wherein the first hole opens toward a cavity provided in the MEMS chip on the first surface. The MEMS microphone of claim 1, wherein
The MEMS microphone, wherein the first hole opens toward a space in a region between the MEMS chip and a side wall of the lid on the first surface. The MEMS microphone of claim 1, wherein
The circuit board has a third hole that opens into a space in a region opposite to the region where the MEMS chip is mounted with respect to the signal processing chip, a fourth hole that opens in the second surface, a second hollow portion communicating with the third hole portion and the fourth hole portion and formed along the first surface;
A MEMS microphone, wherein the height of the second cavity is equal to the thickness of the conductor layer .

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