Microphone unit and voice input device using same

A microphone unit converts voice into an electric signal based on the vibration of a diaphragm contained in an MEMS chip. The microphone unit includes a substrate on which the diaphragm is mounted (the MEMS chip is mounted); a cover member, having sound holes, that is disposed above the substrate so that the diaphragm is contained within the inner space formed between the cover member and the substrate; and a holding member that holds only the substrate or both of the substrate and the cover member.

TECHNICAL FIELD

The present invention relates to a microphone unit that converts voice into an electric signal and a voice input device that includes such a microphone unit.

BACKGROUND ART

Conventionally, microphone units are employed in voice input devices such as voice communication devices including mobile telephones and transceivers, information processing systems that employ techniques for analyzing inputted voice such as voice authentication systems, and recording devices. Recent years have seen a continuation in the miniaturization of electronic devices, and the development of microphone units that achieve smaller and thinner sizes is in full swing.

MEMS (Micro Electro Mechanical System) microphone devices that are created using semiconductor manufacturing techniques are known as microphone units that achieve smaller and thinner sizes (for example, see Patent Documents 1 through 3). Here, an example of the configuration of a conventional microphone unit will be described.

FIG. 13is a schematic cross-sectional view illustrating an example of the configuration of a conventional microphone unit. As illustrated inFIG. 13, the conventional microphone unit100includes an MEMS chip101that converts an inputted sound wave into an electric signal, a substrate102on which the MEMS chip101is mounted, and a shield case103that covers the MEMS chip101. A sound hole103afor inputting a sound wave from the exterior is formed in the shield case103.

A bottom end103bof the shield case103is electrically connected to a grounding circuit pattern (not shown) formed in the substrate102. Through this, the shield case103can shield the microphone unit100from electromagnetic noise.

CITATION LIST

Patent Documents

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

With the conventional microphone unit100described above, it is necessary, during assembly, to adjust the position of the shield case103so that the bottom end103bof the shield case103is connected to the grounding circuit pattern. In addition, it is also necessary to make adjustments so that the positional relationship between the sound hole103aand the MEMS chip101is a predetermined positional relationship. This positioning operation has been problematic in that it has led to a drop in the efficiency of operations when mass-producing the microphone unit100.

Furthermore, the stated conventional microphone unit100is mounted to a mounting substrate in a voice input device using reflow mounting. For this reason, the microphone unit100is exposed to high temperatures exceeding 200° C. when the microphone unit100is mounted to the mounting substrate, and is then put through a cooling process. Meanwhile, the microphone unit100described above is generally mounted to the surface of the mounting substrate; however, even when mounted to the surface of the mounting substrate, the microphone unit100is exposed to high temperatures exceeding 200° C. and is cooled thereafter.

Normally, the shield case103is formed of a metal, and the substrate102is formed of a non-metal (glass epoxy substrate or the like). For this reason, during reflow mounting, stress easily acts on the MEMS chip101due to a large difference in the thermal expansion coefficient between the substrate102and the shield case103that is affixed thereto. This in turn has been a cause of changes in the properties of the MEMS chip101, thus leading to problems in the properties of the microphone unit100after the reflow mounting has been completed.

Accordingly, it is an object of the present invention to provide a microphone unit that can be assembled in an efficient manner. Furthermore, it is another object of the present invention to provide a microphone unit that is capable of reducing the likelihood of problems in the properties of the microphone unit occurring during mounting to a mounting substrate. Further still, it is another object of the present invention to provide a voice input device that includes such a microphone unit and can be manufactured at high yields.

Means to Solve the Problems

In order to achieve the aforementioned objects, a microphone unit according to the present invention is a microphone unit that converts voice into an electric signal based on the vibration of a diaphragm, and includes: a substrate on which the diaphragm is mounted; a cover member, having a sound hole, that is disposed above the substrate so that the diaphragm is contained within the inner space formed between the substrate and the cover member; and a holding member that holds only the substrate or both the cover member and the substrate.

The microphone unit configured in this manner includes the holding member that holds at least the substrate. By employing such a configuration, in which a holding member that holds the substrate is included, the cover member can be attached with ease while the holding member ensures that the positional relationship between the substrate and the cover member remains a constant positional relationship. In other words, this configuration makes it easy to assemble the microphone unit, and makes it possible to improve the efficiency of operations during assembly.

In addition, according to this configuration, the configuration may be such that the holding member is provided between the substrate and the shield cover in the case where the cover member is covered with the shield cover from above in order to shield the microphone unit from, for example, electromagnetic noise. For this reason, in the case where the microphone unit is mounted upon a mounting substrate in a voice input device using reflow mounting, the holding member provided between the substrate and the shield cover can function as a buffer and suppress the occurrence of warping in the substrate, even if there is a large difference in the thermal expansion coefficients of the substrate (the microphone unit substrate) and the shield cover. In other words, it is possible to reduce the likelihood of the occurrence of problems in the properties of the microphone unit when the microphone unit is mounted in a voice input device.

As a specific configuration of the microphone unit configured as described above, the holding member may include a spatial area formed by a base wall and side walls; and the substrate and the cover member may be housed and held within the spatial area. By employing such a configuration, the substrate and the cover member can be positioned relative to each other simply by inserting the substrate and the cover member into the holding member, which makes it very easy to assemble the microphone unit.

In addition, in the microphone unit configured as described above, a depression may be formed in the base wall. More specifically, the sound holes formed in the cover member may include a first sound hole and a second sound hole; and a first sound duct leading from the first sound hole to a first surface of the diaphragm, and a second sound duct leading from the second sound hole through the depression and to a second surface that is the rear surface of the first surface of the diaphragm, may be formed.

By employing such a configuration, the diaphragm of the microphone unit vibrates due to a difference in the sound pressure arising between the first surface and the second surface of the diaphragm. Furthermore, by employing such a configuration, it is easy to obtain an electric signal from which background noise has been eliminated and that contains only a user's voice, which in turn makes it possible to provide a high-performance microphone unit.

In addition, in the microphone unit configured as described above, the diaphragm may be contained in an MEMS chip and the MEMS chip may be mounted upon the substrate. According to this configuration, it is easy to make the microphone unit smaller and thinner, and furthermore, it is possible to mount the microphone unit in a voice input device using reflow mounting.

In addition, the microphone unit configured as described above may further include a conductive shield cover having a sound hole; the sound hole in the cover member and the sound hole in the shield cover may overlap, and the shield cover may be provided so that the holding member is contained within the shield cover. In this configuration, the shield cover and the cover member may be separate members, with the cover member being covered by the shield cover from above, or the shield cover and the cover member may be formed as a single member. Although the shield cover may be attached at the stage in which the microphone unit is mounted in a voice input device, there are also cases where microphone units to which the shield cover has been attached are employed. The present invention is also intended to include such microphone units.

Furthermore, in order to achieve the aforementioned objects, a voice input device according to the present invention includes the microphone unit configured as described above.

Furthermore, in order to achieve the aforementioned objects, a voice input device according to the present invention includes: the microphone unit configured as described above; and a mounting substrate upon which the microphone unit is mounted; the shield cover is electrically connected to a ground formed in the mounting substrate.

As described thus far, with a voice input device that includes the microphone unit configured as described above, the microphone unit can be manufactured in an efficient manner, which makes it possible to reduce the cost of the voice input device. In addition, there is a low likelihood of problems occurring in the properties even in the case where the microphone unit that has been covered by the shield cover is mounted in the voice input device using reflow mounting, and thus the voice input device can be manufactured at high yields.

Advantageous Effects of the Invention

According to the present invention, it is possible to provide a microphone unit that can be assembled in an efficient manner. Furthermore, according to the present invention, it is possible to provide a microphone unit that is capable of reducing the likelihood of problems in the properties of the microphone unit occurring during mounting to a mounting substrate. Further still, according to the present invention, it is possible to provide a voice input device that includes such a microphone unit and can be manufactured at high yields.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of a microphone unit and a voice input device in which the present invention is applied will be described in detail with reference to the drawings.

FIG. 1is a schematic perspective view illustrating the configuration of a microphone unit according to an embodiment of the present invention.FIG. 2is an exploded perspective view illustrating the configuration of the microphone unit according to the present embodiment.FIG. 3is a schematic cross-sectional view taken along the A-A line shown inFIG. 1.FIG. 4is a schematic cross-sectional view taken along the B-B line shown inFIG. 2.FIG. 5is a schematic cross-sectional view illustrating the configuration of an MEMS (Micro Electro Mechanical System) chip provided in the microphone unit according to the present embodiment.FIG. 6is a diagram illustrating the circuit configuration of an ASIC (Application Specific Integrated Circuit) provided in the microphone unit according to the present embodiment.FIG. 7is a schematic plan view illustrating the configuration of a top case provided in the microphone unit according to the present embodiment, viewed from the rear side thereof. Hereinafter, a microphone unit1according to the present embodiment will be described with reference toFIG. 1throughFIG. 7.

As shown inFIG. 1andFIG. 2, the microphone unit1according to the present embodiment includes: a box-shaped bottom case11; a substrate12on which an MEMS chip14and an ASIC15are mounted; and a top case13that is disposed so as to cover the substrate12. Note that the bottom case11is an embodiment of a holding member according to the present invention. Likewise, the top case13is an embodiment of a cover member according to the present invention.

As shown inFIG. 2, the bottom case11has an approximately cuboid-shaped spatial area (concave space)113that is enclosed by a base wall111and four side walls112. The spatial area113is formed so that the width (that is, the length in the X direction) and the depth (that is, the length in the Y direction) thereof are essentially the same size as the sizes of the substrate12(that is, the sizes in the X direction and the Y direction). It is preferable for the bottom case11to be formed of a resin. Furthermore, in consideration of a case in which the microphone unit1is mounted onto a mounting substrate (not shown) of a voice input device using reflow mounting, it is preferable for the bottom case11to be formed of a thermally-resistive resin such as, for example, an LCP (liquid crystal polymer), PPS (polyphenylene sulfide), or the like.

A depression114is formed in the base wall111of the bottom case11, and is formed in an approximately rectangular shape when viewed from above. In addition, as shown inFIG. 2andFIG. 4, multiple electrode terminals115and116are formed on the inner side and outer side, respectively, of the base wall111in the bottom case11. These electrode terminals115and116include a power source electrode terminal that supplies power to the microphone unit1, an output electrode terminal that outputs an electric signal generated by the microphone unit1, and a ground connection electrode terminal.

Note that it is preferable for the bottom case11that includes the electrode terminals115and116to be formed as a single entity through, for example, insert molding, using a lead frame117(seeFIG. 4) and a resin.

A circuit pattern121is formed on the top and bottom surfaces of the substrate12, and the top and bottom circuit patterns are electrically connected to each other by a via hole (not shown). The circuit pattern on the top surface is formed so that, for example, the MEMS chip14and the ASIC15can be connected, power can be inputted, and electrical signals can be outputted. The circuit pattern on the bottom surface, meanwhile, is provided in order to electrically connect the substrate12to the electrode terminals115formed in the bottom case11when the substrate12is housed within the bottom case12. As a result, the electrical components mounted on the substrate12(the MEMS chip14and the ASIC15) can receive a supply of power, can output electric signals that have been produced to the exterior, and so on.

It should be noted that the substrate12is formed of an insulating material, but the specific material is not particularly limited; for example, the substrate12may be configured of a glass epoxy substrate, a polyamide substrate, a silicon substrate, a glass substrate, or the like. Here, it is preferable for the linear expansion coefficient of the substrate12to be close to the linear expansion coefficient of the MEMS chip14. In the case where the MEMS chip14is formed of silicon, it is preferable for the linear expansion coefficient of the substrate12to be approximately 2.8 ppm/° C. Through this, it is possible to reduce the occurrence of residual stress on the MEMS chip14caused by heating and cooling during reflow mounting.

In addition, as shown inFIG. 2andFIG. 3, a first opening122and a second opening123are formed in the substrate12. These openings are provided in order to form a sound duct for leading sound waves from the exterior to a diaphragm provided in the MEMS chip14. Details of this sound duct will be described later.

The MEMS chip14mounted on the substrate12will now be described with reference toFIG. 5. The MEMS chip14includes an insulating base substrate141, a diaphragm film142, an insulating film143, and a fixed electrode144, and forms a condenser microphone. Note that the MEMS chip14is manufactured using a semiconductor manufacturing technique.

An opening141athat has an approximately circular shape when viewed from above is formed in the base substrate141, and sound waves coming from below the diaphragm film142reach the diaphragm film142through this opening. The diaphragm film142, which is formed upon the base substrate141, is a thin film that vibrates (that is, vibrates up and down) upon being subjected to a sound wave, is conductive, and forms one end of an electrode.

The fixed electrode144is disposed so as to oppose the diaphragm film142with the insulating film143provided therebetween. Through this, the diaphragm film142and the fixed electrode144form a capacitance. Note that multiple sound holes144aare formed in the fixed electrode144so that sound waves can pass through, and thus sound waves coming from above the diaphragm film142can reach the diaphragm film142.

With this MEMS chip14, when a sound wave enters into the MEMS chip14, a sound pressure pf is applied to the top surface142aof the diaphragm film142and a sound pressure pb is applied to the bottom surface142bof the diaphragm film142. As a result, the diaphragm film142vibrates in accordance with the difference between the sound pressure pf and the sound pressure pb, thus causing a gap Gp between the diaphragm film142and the fixed electrode144to change; this in turn causes the electrostatic capacitance between the diaphragm film142and the fixed electrode144to change. In other words, the MEMS chip14, which functions as a condenser microphone, is capable of obtaining an electric signal from a sound wave that has entered.

Although the diaphragm film142is located below the fixed electrode144in the present embodiment, it should be noted that the configuration may be such that this relationship is inverted (that is, the diaphragm film is above and the fixed electrode is below).

The ASIC15mounted on the substrate12will now be described with reference toFIG. 6. The ASIC15is an integrated circuit that outputs an electric signal based on vibrations of the diaphragm film142in the MEMS chip14. The ASIC15according to the present embodiment is configured so as to use a signal amplifier circuit153to amplify an electric signal based on a change in the capacity of the condenser formed by the MEMS chip14, and output the amplified signal. In addition, the ASIC15is configured so as to include a charge pump circuit151and an op-amp152, so that the change in the electrostatic capacitance of the condenser (that is, the MEMS chip14) can be accurately obtained. Furthermore, the ASIC15is configured so as to include a gain adjustment circuit154so that the amplification factor (gain) of the signal amplifier circuit153can be adjusted. The electric signal that has been amplified by the ASIC15is outputted to and processed by, for example, a voice processing unit that is mounted on a mounting substrate (not shown) on which the microphone unit1is also mounted.

Note that in the present embodiment, both the MEMS chip14and the ASIC15are mounted on the substrate12using a flip chip process. The MEMS14and the ASIC15are electrically connected by a wiring pattern121formed in the substrate12. Although the present embodiment employs a configuration in which the MEMS chip14and the ASIC15are mounted using a flip chip process, it should be noted that the configuration is not limited thereto, and a configuration in which the mounting is carried out using, for example, die bonding, wire bonding, or the like may be employed as well.

As shown inFIG. 2, the top case13has an approximately rectangular outer shape when viewed from above, and two sound holes132and133, having approximately ellipsoidal shapes when viewed from above, are formed in an upper plate131of the top case13. As shown inFIG. 7(a diagram in which the top case13is viewed from the rear side thereof), an approximately cuboid-shaped first space portion134and an approximately elliptical column-shaped second space portion135are formed inside of the top case13.

Note that the top case13is formed so that the width (that is, the length in the X direction) and the depth (that is, the length in the Y direction) thereof essentially match the sizes of the substrate12(that is, the sizes in the X direction and in the Y direction). In other words, the outer shape of the top case13has essentially the same width and depth as the spatial area113of the bottom case11.

Meanwhile, it is preferable to form the top case13using a resin. Furthermore, in consideration of a case in which the microphone unit1is mounted onto a mounting substrate (not shown) of a voice input device using reflow mounting, it is preferable for the top case13to be formed of a thermally-resistive resin such as, for example, an LCP (liquid crystal polymer), PPS (polyphenylene sulfide), or the like.

The substrate12onto which the MEMS chip14and the ASIC15have been mounted is inserted into the bottom case11, and the top case13is then inserted into the bottom case11so as to cover the substrate12, thus configuring the microphone unit1.

Note that in the present embodiment, the electrode terminals115in the bottom case11and the circuit pattern (electrode terminals) formed on the bottom surface of the substrate12are electrically affixed to each other through soldering, a conductive paste, or the like. The circuit pattern formed on the top surface of the substrate12and the circuit pattern formed on the bottom surface of the substrate12are electrically connected to each other using through wiring (not shown) that passes through the substrate12. Furthermore, the substrate12and the top case13are affixed to each other using an adhesive. Further still, in order to prevent sound leakage from occurring in the microphone unit1, a sealing resin18, as shown inFIG. 1, is applied to the upper portions of the side walls in the bottom case13after the top case13has been inserted into the bottom case11, so that gaps between the bottom case11and the top case13are covered. An epoxy-based resin, for example, is used as the sealing resin.

Next, the configuration of the microphone unit1according to the present embodiment will be described in further detail with reference primarily toFIG. 3. As shown inFIG. 3, an inner space134is formed between the top case13and the substrate12when the top case13is installed over the substrate12(note that the same reference numeral as the aforementioned first space portion of the top case13is used for the inner space). The MEMS chip14and the ASIC15are disposed within this inner space134.

The inner space134communicates with the external space via a first sound hole132formed in the upper plate131of the top case13(seeFIG. 2). In other words, a sound that has occurred outside of the microphone unit1passes through the first sound hole132and the inner space134, and reaches the top surface (a first surface)142aof the diaphragm film142provided in the MEMS chip14(seeFIG. 5). In this sense, it can be said that the inner space134and the first sound hole132form a sound duct (a first sound duct16).

As described above, the two openings122and123are formed in the substrate12. Of these, the first opening122is provided so that the second space portion135in the top case13and the depression114formed in the bottom case11communicate with each other when the substrate12has been covered by the top case13. The first opening122has the same shape and the same size as the second sound hole133in the top case13. Furthermore, when the substrate12has been covered by the top case13, a side surface of the second space portion135and a side surface of the first opening122form a single surface and communicate with the depression114.

The second opening123formed in the substrate12is formed so that the diaphragm film142of the MEMS chip14mounted upon the substrate12and the depression114in the bottom case11communicate with each other. The second opening123has a size and shape that matches the vibrating area of the diaphragm film142(that is, has an approximately circular shape when viewed from above).

Note that the width (that is, the length in the X direction; seeFIG. 2) of the depression114in the bottom case11is set so that the first opening122and the second opening123in the substrate12communicate with the depression114when the substrate12is housed and held within the bottom case11. In addition, the depression114in the bottom case11is formed so that the depth (that is, the length in the Y direction; seeFIG. 2) thereof is greater than the diameter of the vibrating area of the diaphragm film142.

As described thus far, a sound that has occurred outside of the microphone unit1passes through the second sound hole133, the second space portion135, the first opening122, the depression114, and the second opening123, and then reaches the bottom surface (second surface)142bof the diaphragm film142in the MEMS chip14(seeFIG. 5). In this sense, it can be said that the second sound hole133, the second space portion135, the first opening122, the depression114, and the second opening123form a sound duct (a second sound duct17).

Note that the first sound duct16and the second sound duct17are formed so that the time required for a sound wave to move from the first sound hole132to the top surface142aof the diaphragm film142is the same as the time required for a sound wave to move from the second sound hole133to the bottom surface142bof the diaphragm film142. It is preferable for the volume of the space that forms the first sound duct16and the second sound duct17to be 30 mm3or less, and further preferable for this volume to be 10 mm3or less (for example, approximately 7 to 8 mm3). Furthermore, it is preferable for the volume of the space that forms the first sound duct16and the second sound duct17to be such that the volumes of the two sounds ducts are equal to within an error of ±30%.

In addition, it is preferable for the first sound hole132and the second sound hole133to have an area of greater than or equal to an area of a circle of ø0.5 mm and for the two sound holes to be formed having the same shape; the length of the ellipse in the lengthwise direction (that is, the Y direction inFIG. 2) and the length of the ellipse in the widthwise direction (that is, the X direction inFIG. 2) are set to that end. In order to prevent degradation in the acoustic properties, it is preferable for the width of the sound ducts to be greater than or equal to 0.1 mm, and preferable for the stated length in the widthwise direction to be greater than or equal to 0.1 mm. Note that in the same sense, it is preferable for the depth of the depression114provided in the bottom case11(seeFIG. 3) to be greater than or equal to 0.1 mm.

Incidentally, it is not absolutely necessary for the first sound hole132and the second sound hole133to have approximately elliptical shapes (long-hole shapes) when viewed from above; the configuration thereof can be changed, and the shapes may be, for example, approximately circular shapes. However, it is easier to reduce the size of the microphone unit1and advantageous in terms of acoustical properties to employ a long-hole shape in which the lengthwise axis is vertical relative to the direction in which the first sound hole132and the second sound hole133are arranged, as in the present embodiment, and thus the long-hole shape is preferable.

The center distance L between the first sound hole132and the second sound hole133will now be discussed. If the distance between the first sound hole132and the second sound hole133is too small, the difference in the sound pressure that is applied to the top surface142aand the bottom surface142bof the diaphragm film142drops, leading to a drop in the amplitude of the diaphragm film142; as a result, the SNR (S/N ratio) of the electric signal outputted from the ASIC15worsens. For this reason, it is preferable for the distance between the first sound hole132and the second sound hole132to be great to a certain degree. On the other hand, if the center distance L between the first sound hole132and the second sound hole133is too great, the difference between the amount of time required for sound wave emitted from a sound source to pass through the first sound hole132and reach the diaphragm film142and the amount of time required for the sound wave to pass through the second sound hole133and reach the diaphragm film142, or in other words, the phase difference, will increase; this leads to a drop in the noise-canceling performance. For this reason, it is preferable for the center distance L between the first sound hole132and the second sound hole133to be not less than 4 mm and not more than 6 mm, and it is further preferable for the center distance L to be approximately 5 mm.

Next, operations of the microphone unit1will be described. Before describing these operations, the properties of sound waves will be discussed. The sound pressure of a sound wave (that is, the amplitude of the sound wave) is in inverse proportion with the distance from the sound source. Furthermore, the sound pressure attenuates drastically at locations that are close to the sound source, and attenuates gradually the further from the sound source.

For example, in the case where the microphone unit1is applied in a close-talking voice input device, the user's voice is emitted in the immediate vicinity of the microphone unit1. For this reason, the user's voice is significantly attenuated between the first sound hole132and the second sound hole133, and thus a large difference appears between the sound pressure that is applied to the top surface142aof the diaphragm film142and the sound pressure that is applied to the bottom surface142bof the diaphragm film142.

Meanwhile, the sound sources of noise components such as background noise are present in locations that are farther from the microphone unit1than the user's voice. For this reason, the sound pressure of the noise undergoes almost no attenuation between the first sound hole132and the second sound hole133, and thus almost no difference appears between the sound pressure that is applied to the top surface142aof the diaphragm film142and the sound pressure that is applied to the bottom surface142bof the diaphragm film142.

The diaphragm film142of the microphone unit1vibrates due to a sound pressure difference between the sound waves that enter into the first sound hole132and the second sound hole133at the same time. As described above, because the difference in the sound pressure of noise that strikes the top surface142aof the diaphragm film142and the bottom surface142bof the diaphragm film142is extremely low, that sound pressure is canceled out by the diaphragm film142. As opposed to this, the difference in the sound pressure of the user's voice that strikes the top surface142aof the diaphragm film142and the bottom surface142bof the diaphragm film142is large, and thus the user's voice causes the diaphragm film142to vibrate without being canceled out by the diaphragm film142.

Accordingly, with the microphone unit1, it can be thought that the diaphragm film142will vibrate only in response to the user's voice. For this reason, the electric signal outputted from the ASIC15of the microphone unit1can be thought of as a signal from which noise (background noise and the like) has been eliminated and that contains only the user's voice. In other words, according to the microphone unit1of the present embodiment, it is possible to obtain an electric signal from which noise has been eliminated and that contains only the user's voice, using a simple configuration.

As described thus far, the microphone unit1according to the present embodiment has a configuration that is not conventionally employed, in which the bottom case11is prepared, and the substrate12and the top case13are housed and held in the bottom case13. With this configuration, the positional relationship between the substrate12and the top case13can be set to a desired relationship simply by inserting the substrate12and the top case13into the bottom case11. Accordingly, it is possible to increase the efficiency of operations when assembling the microphone unit1.

FIG. 8is a diagram illustrating an embodiment of the schematic configuration of a voice input device in which the microphone unit according to the present embodiment is applied.FIG. 9is a schematic cross-sectional view taken along the C-C line shown inFIG. 8. The configuration of a voice input device2in which the microphone unit1is applied will now be described with reference toFIG. 8andFIG. 9. Here, a case in which the voice input device2is a mobile telephone will be described as an example, but the voice input device is of course not limited to a mobile telephone.

As shown inFIG. 8, two sound holes211and212are provided in a lower area of a housing21of the voice input device2, and the user's voice is inputted into the microphone unit1, which is disposed within the housing21, via these sound holes211and212. The microphone unit1disposed in the voice input device2is, as shown inFIG. 8andFIG. 9, covered by a conductive shield cover19in order to suppress the influence of electromagnetic noise. Here, the microphone unit that is covered by the shield cover19is indicated by the reference numeral1.

Note that the shield cover19may be formed of any material that has an electromagnetic shielding function, and therefore may be formed of a metallic material such as Kovar (an alloy in which nickel and cobalt are mixed with iron; an example of the component weight percent is 29% Ni, 17% Co, 0.2% Si, 0.3% Mn, and 53.5% Fe), alloy 42 (an Fe-42% Ni alloy), or the like.

The shield cover19contains an inner space that is surrounded by an upper plate191and four side walls192. The shield cover19covers the top case13from above so that the shield cover19houses, in its inner space, the bottom case11that houses and holds the substrate12and the top case13. In the present embodiment, the width (that is, the length in the horizontal direction inFIG. 9) and the depth (that is, the length in the vertical direction inFIG. 9) of the inner space of the shield case19are set so as to be approximately the same as the width and the depth, respectively, of the bottom case11. For this reason, the shield case19is held by simply covering the top case13with the shield case19from above. In addition, the shield case19is formed so that bottom ends192aof the side walls192and the bottom surfaces11aof the bottom case11form a single surface when the top case13is covered by the shield case19.

Two sound holes193and194are formed in the shield cover19. To be more specific, the two sound holes193and194are formed so as to overlap with the two sound holes132and133, respectively, that are formed in the top case13. In addition, the microphone unit1is disposed so that the two sound holes193and194formed in the shield cover19overlap with the two sound holes211and212, respectively, formed in the housing21. For this reason, sound that has occurred outside of the housing21passes through the two sound ducts16and17provided in the microphone unit1and reaches the top surface142aand the bottom surface142b(for both, refer toFIG. 5) of the diaphragm film142.

Note that in the voice input device2according to the present embodiment, an elastic member22is disposed between the housing21and the microphone unit1. Openings221and222are formed in the elastic member22so that sound that has occurred outside of the housing21passes through the two sound ducts16and17provided in the microphone unit1and reaches the top surface142aand the bottom surface142bof the diaphragm film142. It is not absolutely necessary to provide this elastic member22. However, disposing the microphone unit1in the housing21with the elastic member22provided therebetween makes it difficult for vibrations from the housing21to be transmitted to the microphone unit1, thereby increasing the operational accuracy of the microphone unit1. For this reason, it is preferable to provide the elastic member22, as is the case in the present embodiment.

As shown inFIG. 9, the microphone unit1disposed within the housing21is mounted upon a mounting substrate23provided within the housing21. The mounting substrate23is configured so as to supply power to the microphone unit1, process electric signals outputted from the microphone unit1, and so on.

The microphone unit1is mounted upon the mounting substrate23using reflow mounting (a process carried out at, for example, 250° C.). Through this, the electrode terminals16(seeFIG. 4) formed in the bottom case11of the microphone unit1and a circuit pattern formed in the mounting substrate23are affixed to and electrically connected to each other through soldering, a conductive paste, or the like. In addition, a side surface bottom end192aof the shield case19and a ground (GND) formed in the mounting substrate23are soldered to and electrically connected to each other. Through this, the shield cover19acts as a shield against electromagnetic noise.

The foregoing has described the schematic configuration of the voice input device2in which the microphone unit1according to the present embodiment is applied; hereinafter, the effects of such a configuration will be described.

In the case where the microphone unit1is mounted on the mounting substrate23, the mounting is carried out through reflow mounting at a high temperature (for example, approximately 200 to 250° C.), as described above. The various elements of which the microphone unit1is configured experience thermal expansion when processed at high temperatures in this manner. With respect to this point, as described earlier, in the conventional microphone unit100(seeFIG. 13), the thermal expansion coefficients of the shield cover, which is formed of a metal, and the substrate (the substrate on which the MEMS chip is mounted), which is formed of a non-metal, differ significantly, which has led to cases in which the substrate has become warped and stress is applied to the MEMS chip as a result. There have been cases where the MEMS chip has been damaged due to this stress.

However, with the microphone unit1according to the present embodiment, the substrate12is held by the bottom case11, which is formed using a resin such as LCP or the like. In this case, the bottom case11functions as a buffer material, which makes it unlikely that the substrate12will experience warping during a reflow mounting, even if the shield cover19is formed of a metal and the substrate12is formed of a non-metal. For this reason, with the voice input device2according to the present embodiment, the amount of stress applied to the MEMS chip14that is mounted on the substrate12can be reduced during reflow mounting, which makes it possible to reduce the possibility of problems in the properties occurring during assembly. In other words, it can be said that the voice input device2according to the present embodiment can be manufactured at high yields.

The aforementioned embodiment is merely an example, and the microphone unit and voice input device according to the present invention are not limited to the configurations described in the aforementioned embodiment. Many variations can be carried out on the configuration described in the aforementioned embodiment without departing from the essential scope of the present invention.

For example, in the aforementioned embodiment, the configuration is such that the top case13is formed of a resin such as LCP or the like, and the shield cover19is placed thereupon from above to act as a shield from electromagnetic noise. However, the present invention is not limited to this configuration. The configuration may be such that the top case13is formed so as to include a conductive member that has electromagnetic shielding properties, and the top case13is electrically connected to a GND formed in the substrate12. In this case, it is not necessary to further cover the top case13from above with the shield cover19. Furthermore, the effect in which the efficiency of operations when assembling the microphone unit is improved as described above can be achieved in this case as well.

However, in the case where this configuration is employed, there is a higher likelihood of stress being applied to the MEMS chip when mounting the microphone unit onto the mounting substrate of the voice input device and problems in the properties thereof occurring as a result. For this reason, it is preferable to employ a configuration in which the shield cover19is provided separately from the top case13, and the substrate12and the shield cover19are not directly connected (that is, are separated from each other), as in the embodiment.

Meanwhile, as another configuration, the shield cover19may be formed integrally with the top case13, as shown inFIG. 10. This makes it possible to reduce the overall number of components and simplify the manufacturing process, while at the same time maintaining the aforementioned advantages of an improvement in the efficiency of operations during assembly and a reduction in the occurrence rate of problems in the properties during mounting onto the voice input device. Furthermore, with this configuration, the side walls of the bottom case11are sandwiched between and held by the shield cover19and the top case13using the metallic spring force of the shield cover19, which makes it possible to fix the top case13to the bottom case11. Note that it is possible to adjust the stated spring force by providing a slit in a part of the side walls of the shield cover19, and thus a slit may be provided in the side walls of the shield cover19as appropriate.

In addition, the aforementioned embodiment describes a case in which the microphone unit is configured so that the diaphragm film (diaphragm)142vibrates based on a difference in the sound pressures applied to the top surface142aand the bottom surface142bthereof. However, the configuration of the microphone unit in which the present invention is applied is not limited to the configuration described in the aforementioned embodiment. For example, as shown inFIG. 11, the microphone unit may have a configuration in which the diaphragm (provided in the MEMS chip14) vibrates from the sound pressure applied to only one of the surfaces of the diaphragm. In the case of this configuration, it is not necessary to provide the depression114in the bottom case11as described in the aforementioned embodiment, and furthermore, only one sound duct is necessary.

In addition, in the aforementioned embodiment, the configuration is such that the microphone unit1includes the bottom case11. However, if the configuration includes a holding member that holds only the substrate12or both the substrate12and the top case13, the efficiency of operations during assembly can be improved, and a configuration such as that shown in, for example,FIG. 12may be employed.

The configuration shown inFIG. 12includes a holding member11′ that grips and holds the substrate12, instead of the bottom case11. Even in this case, the top case13is guided to the covering position by the holding member11′, and thus the top case13can be attached without carrying out troublesome positional adjustments. In other words, the efficiency of operations during the assembly of the microphone unit can be improved beyond that of the conventional microphone unit. Furthermore, because the holding member11′ is provided, it is easier to implement a configuration in which the substrate12and the shield cover19(connected to the GND of the mounting substrate onto which the microphone unit is mounted) are not connected, as shown inFIG. 12, in the case where the top case13is covered by the shield cover19from above. Further still, if this configuration is employed, the holding member11′ acts as a buffer material when the microphone unit is mounted onto the voice input device using reflow mounting, which in turn makes it possible to reduce the likelihood of problems occurring in the properties of the MEMS chip14.

In addition, although the MEMS chip14and the ASIC15are configured of separate chips in the aforementioned embodiment, the integrated circuit provided in the ASIC15may be formed monolithically upon the silicon substrate of which the MEMS chip14is formed.

In addition, although the aforementioned embodiment describes a configuration in which the microphone chip for converting voice into an electric signal is the MEMS chip14, which is formed using a semiconductor manufacturing technique, the configuration of the embodiment is not limited thereto. Furthermore, in the aforementioned embodiment, a so-called condenser microphone is employed as the configuration of the microphone chip (this corresponds to the MEMS chip14according to the embodiment) provided in the microphone unit1. However, the present invention can also be applied in a microphone unit that employs a configuration aside from a condenser microphone. For example, the present invention can also be applied in a microphone unit that employs a dynamic microphone, a magnetic microphone, a piezoelectric microphone, or the like.

Furthermore, the shape of the microphone unit is not intended to be limited to the shape described in the aforementioned embodiment, and can of course be changed to various shapes. Moreover, in addition to mobile telephones, voice communication devices such as transceivers, voice processing systems that employ techniques for analyzing inputted voice (voice authentication systems, voice recognition systems, command generation systems, electronic dictionaries, translation devices, voice-activated remote controllers, and so on), voice recording devices and amplification systems (amplifiers), microphone systems, and the like can be given as other examples of voice input devices in which the present invention can be applied.

INDUSTRIAL APPLICABILITY

The present invention is useful in voice communication devices such as mobile telephones, transceivers, or the like, information processing systems that use techniques for analyzing inputted voice, such as voice authentication systems, and so on, voice recording devices, and so on.