Microphone

Provided is a microphone capable of reducing a plane area seen from above, and further increasing a capacity of a back chamber of an acoustic sensor. An interposer 52 is mounted on a top surface of a circuit board 43, and an acoustic sensor 51 is mounted on the top surface thereof. A signal processing circuit 53 is accommodated in a space 70 provided in the interposer 52, and mounted on the circuit board 43. The acoustic sensor 51 is connected to the circuit board 43 through a wiring structure provided in the interposer 52. The acoustic sensor 51, the interposer 52 and the like are covered by a cover 42 put on the top surface of the circuit board 43. In the cover 42, a sound introduction hole 48 is opened in a position opposed to the front chamber of the acoustic sensor 51. The interposer 52 is formed with a ventilation notch 71 for acoustically communicating a space below a diaphragm 56 of the acoustic sensor 51 with a space inside the cover 42 and outside the interposer 52.

TECHNICAL FIELD

The present invention relates to a microphone, and specifically to a microphone with an acoustic sensor mounted inside a package.

BACKGROUND ART

General Microphone

FIG. 1is a sectional view showing a microphone with a conventional general structure. This microphone11is obtained by mounting an acoustic sensor15, a signal processing circuit17inside a package made up of a cover12and a circuit board13. The acoustic sensor15and the signal processing circuit17are mounted in the state of being arranged beside each other on the top surface of the circuit board13, and the signal processing circuit17is covered by a sealing resin21. The acoustic sensor15and the signal processing circuit17are electrically connected by a bonding wire18, and further, the signal processing circuit17is connected to intra-substrate wiring14of the circuit board13by a bonding wire19.

Normally, the under surface of the circuit board13is mounted on a printed wiring board, to be brought into intimate contact with the printed wiring board. For this reason, a sound introduction port20for introducing an acoustic vibration into a package is opened on the top surface of the cover12. The under surface of the acoustic sensor15is bonded to the circuit board13, and the under surface of a back chamber16is blocked by the circuit board13.

The microphone11having such a structure has a problem as described below. In the microphone11, with the acoustic sensor15and the signal processing circuit17arranged beside each other, it is not possible to reduce a projected area to a horizontal plane (hereinafter referred to as plane area) at the time when the microphone11is seen from above. In particular, it is impossible to make the plane area of the microphone11smaller than the sum of a plane area of the acoustic sensor15and a plane area of the signal processing circuit17.

Further, in the microphone11, the acoustic sensor15and the signal processing circuit17are connected by the bonding wire18. In the case of the bonding wire18being stretched and wired, the bonding wire18may break due to vibrations or the like, and hence the bonding wire18is loosened and wired as shown inFIG. 1. Furthermore, in the case of the bonding wire18being loosened downward and wired, the bonding wire18may come into contact with an electrode pad or wiring of the acoustic sensor15or the signal processing circuit17to cause a short-circuit accident, and hence the bonding wire18is loosened upward. As a result, the package needs to have enough a height to accommodate the bonding wire18protruding upward, and associated therewith, the microphone11becomes higher.

There is a correlation between a sensitivity of the microphone and a capacity of the back chamber, and the sensitivity of the microphone decreases with decrease in capacity of the back chamber. In the microphone11, a capacity of the back chamber16inside the acoustic sensor15becomes smaller in the case of providing the sound introduction port20in the cover12, and a sensitivity of the microphone11is thus apt to decrease.

Microphone of Patent Document 1

FIG. 2shows a microphone disclosed in Patent Document 1. In a microphone31of Patent Document 1, the signal processing circuit17is mounted on the top surface of the circuit board13. In a position adjacent to the signal processing circuit17, a spacer32is fixed to the top surface of the circuit board13, and further, the acoustic sensor15is mounted on the top surface of the spacer32. In the spacer32, a vertically penetrating through hole33is opened, and a communication hole34is further formed for alleviating a difference in static pressure between the outside of the spacer32and the inside of the through hole33.

In such a microphone31, since the under surface of the acoustic sensor15is provided with the electrode pad and the acoustic sensor15is electrically connected to the circuit board13via the spacer32, the microphone31is not made higher due to the loosened bonding wire18as in the microphone11ofFIG. 1.

However, this microphone31has the same problem as the microphone11ofFIG. 1. Also in the microphone31, with the acoustic sensor15and the signal processing circuit17arranged beside each other, it is not possible to reduce a plane area of the microphone31. Especially, it is not possible to make the plane area of the microphone31smaller than the sum of a plane area of the acoustic sensor15and a plane area of the signal processing circuit17.

Further in the microphone31, the through hole33of the spacer32is continued to the back chamber16of the acoustic sensor15to widen a space below a diaphragm, and hence it is substantially possible to expand a capacity of the back chamber16without making the acoustic sensor15larger. As a result, a sensitivity of the microphone31can be expected to improve.

However, even in such a structure, there is a limit on expansion of the capacity of the back chamber16, and it is small as compared with a capacity of the space inside the package made up of the cover12and the circuit board13.

It is to be noted that the communication hole34is opened in a horizontal direction in the spacer32. However, this communication hole34is one for transmitting static pressure between the back chamber16and a space outside the acoustic sensor15and the spacer32(intra-package space), while on the other hand blocking passage of a gas based on pressure fluctuations acting on the diaphragm. That is, the communication hole34is one aimed at removing a difference in static pressure on the inside and the outside of the acoustic sensor15based on generation of an outgas and a height difference.

Microphone of Patent Document 2

Patent Document 2 discloses a microphone in which a tridimensional circuit board is provided on a printed board constituting a package, an acoustic sensor is mounted on the tridimensional circuit board, and a signal processing circuit is accommodated inside an opening formed in a midsection of tridimensional circuit board.

According to such a microphone as in Patent Document 2, with the acoustic sensor arranged above the signal processing circuit, the plane area of the microphone can be made smaller so as to reduce the microphone in size.

In the microphone of Patent Document 2, the acoustic sensor is provided above the tridimensional circuit board, thereby increasing the capacity of the back chamber of the acoustic sensor in a similar manner to Patent Document 1. However, the signal processing circuit is accommodated inside the opening of the tridimensional circuit board, and hence, again, the capacity of the back chamber is small and improving the sensitivity of the microphone is difficult.

PRIOR ART DOCUMENT

Patent Document

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

The present invention was made in view of such technical problems as described above, and has an object to provide a microphone capable of reducing a plane area seen from above, and further increasing a capacity of a back chamber of an acoustic sensor.

Means for Solving the Problem

A microphone according to the present invention is a microphone, including: a circuit board; a supporting member, mounted on a top surface of the circuit board; an acoustic sensor, mounted on the supporting member; a signal processing circuit, accommodated inside a hollow that is formed inside the supporting member, and mounted on the top surface of the circuit board; and a cover, covering the acoustic sensor, the supporting member, and the signal processing circuit and fixed to the top surface of the circuit board, wherein the acoustic sensor is formed with a space to serve as a front chamber on the top surface side and is also provided with a space to serve as a back chamber on the under surface side, and the supporting member is formed with an acoustic transmission path capable of transmitting an acoustic vibration between a space located outside the acoustic sensor and the supporting member and the space to serve as the back chamber inside the acoustic sensor, out of spaces surrounded by the cover and the circuit board.

In the microphone of the present invention, with the acoustic sensor arranged above the signal processing circuit, a plane area of the area for mounting the acoustic sensor and the signal processing circuit can be made smaller, so as to reduce the microphone in size. Further, by providing the acoustic transmission path in the supporting member, the space located outside the acoustic sensor and the supporting member out of spaces surrounded by the cover and the circuit board can be used as the back chamber of the acoustic sensor. This can result in a substantially increased capacity of the back chamber of the acoustic sensor, so as to improve the sensitivity of the microphone.

A microphone according to an embodiment of the present invention has a feature in that a sound introduction hole for introducing an acoustic vibration is opened in the cover, and in the acoustic sensor, a periphery of the space to serve as the front chamber is brought into intimate contact with an area surrounding the sound introduction hole on the inner surface of the cover. According to such an embodiment, an acoustic vibration introduced into the microphone through the sound introduction hole resists leakage to the outside of the front chamber. Therefore, an acoustic vibration having entered through the sound introduction hole resists turning to the back chamber side, and the sensitivity of the microphone thus resists a decrease due to an acoustic vibration turned to the back chamber side.

In a microphone according to another embodiment of the present invention, the supporting member is provided with a wiring structure for electrically connecting the acoustic sensor and the circuit board. According to such an embodiment, since the acoustic sensor and the circuit board can be connected to each other without using a bonding wire, the height of the package made up of the cover and the circuit board can be made smaller than in the case of using the bonding wire, so as to reduce the microphone in height and size.

In a microphone according to still another embodiment of the present invention, the acoustic transmission path is formed by recessing a top surface section of the supporting member into concave form or groove form. According to such an embodiment, processing of the acoustic transmission path can be performed with ease.

In a microphone according to yet another embodiment of the present invention, the hollow for accommodating the signal processing circuit vertically penetrates through the supporting member. According to such an embodiment, since the hollow for accommodating the signal processing circuit becomes part of the back chamber of the acoustic sensor, the capacity of the back chamber of the acoustic sensor can be further increased, so as to improve the sensitivity of the microphone.

In a microphone according to yet another embodiment of the present invention, the hollow for accommodating the signal processing circuit is provided in concave form on the under surface of the supporting member, and the hollow and the acoustic transmission path are partitioned by the supporting member. According to such an embodiment, a short-circuit accident does not occur between the acoustic sensor and the signal processing circuit. Further, the signal processing circuit can be protected from moisture, dust and the like.

It is to be noted that the means for solving the above problems in the present invention has features in appropriate combination of the above described constitutional elements, and the present invention enables a large number of variations by combination of such constitutional elements.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the following embodiments of the present invention are not restrictive, and a variety of changes in design can be made within the range not deviating from the gist of the present invention.

First Embodiment

A microphone according to Embodiment 1 of the present invention will be described with reference toFIGS. 3 to 5.FIG. 3is a sectional view showing a structure of a microphone41according to Embodiment 1.FIG. 4(A)is a perspective view of an interposer52(supporting member) used for the microphone41, andFIG. 4(B)is a perspective view showing a state where the interposer52has been vertically inverted.FIGS. 5(A) and 5(B)are sectional views of the interposer52, andFIG. 5(A)is a cross section taken along line X-X ofFIG. 4(A)whileFIG. 5(B)is a cross section taken along line Y-Y ofFIG. 4(A).

In the microphone41, a package is formed of a cover42and a circuit board43. An acoustic sensor51, the interposer52and a signal processing circuit53are accommodated inside this package.

On the top surface of the circuit board43constituting part of the package, there are provided a plurality of top-surface electrode pads44for joining the interposer52and the signal processing circuit53. On the under surface of the circuit board43, there are provided a plurality of under-surface electrode pads45for connecting the microphone41to the printed wiring board and the like at the time of mounting the microphone41on the printed wiring board and the like. The cover42has a box form with the under surface thereof open, and an electromagnetic shield47made of a metal plated film is formed on the inner surface of a cover body46made of an insulating material (e.g., plastic). Further, a sound introduction hole48for introducing an acoustic vibration into the package is opened at least one place in the cover42.

In addition, the cover body46may be made of metal, and in that case, there is no need for separately providing the electromagnetic shield47since the cover body46has a function of electromagnetic shield.

The acoustic sensor51is a capacitance type element produced by use of a MEMS technique. As shown inFIG. 3, the whole of the acoustic sensor51is held by a silicon substrate54. In the silicon substrate54, a front chamber55is opened so as to vertically penetrate therethrough. On the under surface of the silicon substrate54, a thin film-like diaphragm56is provided so as to cover an under-surface opening of a front chamber55. The diaphragm56is formed by polysilicon having conductivity. Therefore, the diaphragm56itself serves as a movable electrode plate. A plurality of places at an outer edge of the diaphragm56are supported by anchors (not shown), so that the diaphragm56is stretched in film form on the under surface of the silicon substrate54, and a vent hole (narrow gap) is formed between the anchors and between the outer edge of the diaphragm56and the under surface of the silicon substrate54.

A back plate57is provided below the diaphragm56so as to form an air gap58(void) between the back plate57and the diaphragm56, and an outer periphery of the back plate57is fixed to the under surface of the silicon substrate54. Further, on the top surface of the back plate57, a fixed electrode plate59is provided so as to be opposed to the diaphragm56. The back plate57is formed of insulating SiN, and a fixed electrode plate59is formed of conductive polysilicon. As a result, the diaphragm56and the fixed electrode plate59, which are opposed to each other via the air gap58, constitute a capacitor for acoustic vibration sensing.

In almost the whole of the back plate57and the fixed electrode plate59, a large number of acoustic holes60are punched for allowing passage of an acoustic vibration after vibration of the diaphragm56.

A leading wire61is extended out from the end of the diaphragm56. The end of the leading wire61is electrically connected with an electrode section62embedded in the back plate57. Further, a leading wire63is extended out from the end of the fixed electrode plate59. The end of the leading wire63is electrically connected with an electrode section64embedded in the back plate57. The under surface of the electrode section62is protruded from any one place out of four corners of the under surface of the acoustic sensor51, and a bump67is provided on the under surface of the electrode section62. The under surface of the electrode section64is protruded from another corner out of the four corners of the under surface of the acoustic sensor51, and the bump67is provided on the under surface of the electrode section64. Dummy electrodes (not shown) are provided at corners not provided with the electrode sections62,64out of the four corners of the under surface of the acoustic sensor51. The dummy electrode is an electrode for mechanical fixing the under surface of the acoustic sensor51by means of a solder or the like, the electrode having no electrical function. The dummy electrode is also provided with a bump.

The interposer52has such a structure as shown inFIGS. 4(A),4(B),5(A) and5(B). The interposer52is formed of an insulating material in rectangular form, and a hollow70, which vertically penetrates therethrough and is capable of accommodating the signal processing circuit53, is formed inside the interposer52. Further, a ventilation notch71(acoustic communication path) is formed in the upper portion of the wall surface of the interposer52.

The interposer52is provided with a structure for electrically connecting the acoustic sensor51and the circuit board43. That is, a through electrode65is embedded at any one place out of four corners of the interposer52, a pad section65aconducted with the through electrode65is provided on the top surface of the interposer52, and a pad section65bconducted with the through electrode65is provided on the under surface of the interposer52. Similarly, a through electrode66is embedded at another place out of the four corners of the interposer52, a pad section66aconducted with the through electrode66is provided on the top surface of the interposer52, and a pad section66bconducted with the through electrode66is provided on the under surface of the interposer52. Further, at corners not provided with the through electrodes65,66out of the four corners of the interposer52, dummy electrodes72aare provided on the top surface of the interposer52, and dummy electrodes72bare provided on the under surface of the interposer52. The dummy electrodes72a,72bare electrodes for fixing the interposer52by mechanical connection, and the dummy electrode72aon the top surface and the dummy electrode72bon the under surface are not electrically conducted to each other.

It is to be noted that, although the ventilation notch71is formed in the upper portion of the wall surface of the interposer52inFIGS. 4 and 5, the ventilation notch71may be provided in the lower portion of the wall surface of the interposer52. Further, a ventilation opening (acoustic transmission path) may be opened in window form on the wall surface of the interposer52. However, the acoustic transmission paths such as the ventilation notch and the ventilation opening are each required to have a path sectional area large enough to transfer a dynamic pressure change due to an acoustic vibration.

Further, the signal processing circuit53(ASIC) is a circuit that amplifies an acoustic sensing signal outputted from the acoustic sensor51, further converts the signal to a digital signal, and outputs the converted signal. An electrode section69for inputting a signal from the acoustic sensor51and an electrode section69for outputting a signal subjected to signal processing are provided on the under surface of the signal processing circuit53.

The microphone41is assembled in such a manner as follows. The acoustic sensor51is placed on the interposer52, the bump67provided on the under surface of the electrode section62is bonded to the top surface (pad section65a) of the through electrode65, and the bump67provided on the under surface of the electrode section64is joined to the top surface (pad section66a) of the through electrode66. Further, the bump67of the dummy electrode provided on the under surface of the acoustic sensor51is joined to the dummy electrode72aon the top surface of the interposer52. This results in mechanical fixing of the acoustic sensor51to the top surface of the interposer52by the bumps67at the four places. Further, the electrode sections62,64of the acoustic sensor51are respectively conducted to the lower surface (pad sections65b,66b) of the interposer52through the through electrodes65,66.

The pad sections65b,66band the dummy electrodes72bprovided on the under surface of the interposer52are joined to the top-surface electrode pads44of the circuit board43by a conductive material68such as solder or a conductive adhesive. The electrode section69of the signal processing circuit53is also joined to the top-surface electrode pads44of the circuit board43by the conductive material68such as the solder or the conductive adhesive.

The cover42is superposed on the top surface of the circuit board43so as to cover the acoustic sensor51, the interposer52and the signal processing circuit53which are superposed on the top surface of the circuit board43. At this time, a sound introduction hole48of the cover42is arranged so as to border the inside of the front chamber55of the acoustic sensor51. The whole periphery of the top surface of the acoustic sensor51(top surface of the silicon substrate54) is bonded to the inner surface of the cover42by use of an adhesive resin50, to seal the whole of the top surface. The under surface of the cover42is bonded to the top surface of the circuit board43by the conductive adhesive, and the electromagnetic shield47is conducted to a ground electrode of the circuit substrate43.

Accordingly, upon entering of an acoustic vibration into the microphone41through the sound introduction hole48, the acoustic vibration is guided into the front chamber55of the acoustic sensor51. Since the acoustic vibration vibrates the diaphragm56, it changes a capacitance of the capacitor configured by the diaphragm56and the fixed electrode plate59, and this change in capacitance is outputted from the electrode sections62,64as acoustic sensing signals. The acoustic sensing signals outputted from the acoustic sensor51are transmitted to the top-surface electrode pads44through the through electrodes65,66. The top-surface electrode pads44, joined with the pad sections65b,66bof the through electrodes65,66, are conducted to the top-surface electrode pads44joined with the electrode section69for signal input of the signal processing circuit53by means of a wiring pattern (not shown) provided on the top surface of the circuit board43or on the inside thereof. Hence the acoustic sensing signals of the acoustic sensor51are each inputted from the electrode section69for signal input into the signal processing circuit53. Further, the top-surface electrode pad44, joined with the electrode section69for signal output, is connected to the under-surface electrode pad45of the circuit board43by a wiring structure (not shown) provided inside the circuit board43. Therefore, an output signal processed in the signal processing circuit53is outputted from the under-surface electrode pad45of the circuit board43to the outside.

It is to be noted that, since the electrical connection form between the acoustic sensor51and the signal processing circuit53, the number of through electrodes in the interposer52, and the like change depending on the configurations of the acoustic sensor51and the signal processing circuit53, the above description represents one example.

In the acoustic sensor51with such a configuration, it is possible to obtain such function effect as follows. In the acoustic sensor51, the signal processing circuit53is connected with the acoustic sensor51through the through electrodes65,66provided in the interposer52. This eliminates the need for considering a loosened portion of the bonding wire as in the case of connection by use of the bonding wire, thereby preventing the acoustic sensor51from being made unnecessarily high.

Further, since the acoustic sensor51and the signal processing circuit53are vertically arranged, there is eliminated the need for the area for mounting the signal processing circuit53apart from the area for mounting the acoustic sensor51, and it is thereby possible to make the plane area of the microphone41very small as compared with the case of those being arranged beside each other as in a conventional manner. Therefore, even in a case where the acoustic sensor51or the signal processing circuit53cannot be reduced in size, the microphone41can be reduced in size.

In this acoustic sensor51, a space surrounded by the silicon substrate54between the sound introduction hole48and the diaphragm56serves as a front chamber55. On the other hand, a space on the under surface side of the diaphragm56serves as the back chamber of the acoustic sensor51. However, the acoustic vibration after passage of the diaphragm56passes through the acoustic holes60, expands to the hollow70inside the interposer52, further passes through the ventilation notch71, and expands to an intra-package space49. Herein, the intra-package space49refers to a space on the outsides of the acoustic sensor51and the interposer52out of spaces surrounded by the cover42and the circuit board43. Accordingly in the acoustic sensor51, a space in combination of the space below the diaphragm56of the acoustic sensor51, the hollow70inside the interposer52and the intra-package space49substantially serves as the back chamber. That is, in this microphone41, almost all the spaces out of the spaces inside the package, except for the front chamber55, serve as the back chamber.

A sensitivity of the acoustic sensor51improves more with a larger capacity of the back chamber. In this microphone41, most of the space inside the package can be used as the back chamber, and hence the sensitivity of the acoustic sensor51can be improved.

In addition, the microphone31shown in Patent Document 1 is formed with the communication hole34in the horizontal direction in the spacer32. However, differently from the ventilation notch71of the present embodiment, this is one to alleviate a difference in static pressure between the inside and the outside of the back chamber which is generated due to thermal expansion, a pressure change or the like, and is not one to transfer an acoustic vibration. In the microphone31of Patent Document 1, when the path sectional area of the communication hole34is made large enough to transfer an acoustic vibration, the capacity of the back chamber of the acoustic sensor15increases. However, when the path sectional area of the communication hole34is increased in the microphone31, the front chamber and the back chamber of the acoustic sensor15are communicated with each other, and hence the sensitivity of the acoustic sensor15cannot be obtained. Further, although the ventilation hole is also formed between the tridimensional circuit board and the printed board in Patent Document 2, this ventilation hole is provided for the same purpose as the communication hole in Patent Document 1.

Moreover, in the microphone41of the present embodiment, since the electromagnetic shield47is formed on the inner surface of a cover42(an electromagnetic shield may be provided inside the circuit board43), the acoustic sensor51and the signal processing circuit53can be shut off from foreign noise, leading to improvement in S/N ratio of the microphone41.

Manufacturing Method for Microphone of First Embodiment

Next, a process for manufacturing the microphone41of Embodiment 1 will be described with reference toFIGS. 6 to 10. A plurality of interposers52are produced at once.FIG. 6(A)is a plan view showing the plurality of integrally produced interposers52.FIG. 6(B)is a sectional view taken along line Z-Z ofFIG. 6(A). The plurality of interposers52are produced in such a manner as follows. The under surface of an insulating Si wafer73is subjected to metal plating or vapor deposition, to form the pad sections65b,66band the dummy electrodes72bat respective predetermined positions. Subsequently, through holes are formed in the Si wafer73at the positions of the pad sections65b,66b. A metal material is deposited by plating or the like inside the through holes, to produce the through electrodes65,66. Further, the pad sections65a,66aare formed by metal plating or vapor deposition on the top surface of the Si wafer73at the positions of the through electrodes65,66. Simultaneously with this, the dummy electrodes72aare formed at predetermined positions on the top surface of the Si wafer73. Subsequently, a midsection of an area surrounded by a set of the pad sections65a,66aand the dummy electrodes72ais etched so as to open the vertically penetrating hollow70. Further, the top surface of the Si wafer73is etched into groove form, to form the ventilation notches71.FIGS. 6(A) and 6(B)represent the plurality of interposers52as thus integrally produced.

A plurality of acoustic sensors51are also produced at once.FIG. 7(A)is a sectional view showing the plurality of integrally produced acoustic sensors51. On the top surface of a Si wafer74, the polysilicon-made diaphragm56is provided in each area to serve as the acoustic sensor51. A sacrifice layer75is formed on the diaphragm56, and the fixed electrode plate59and the back plate57are provided on the top surface of the sacrifice layer75. Further, the electrode sections62,64and the dummy electrodes are provided at the respective corners of each area to serve as the acoustic sensor51.

As shown inFIG. 7(B), the acoustic sensor51produced as inFIG. 7(A)is vertically inverted and superposed on the top surface of the interposer52ofFIG. 6, and the electrode section62, the electrode section64and the dummy electrodes are respectively joined with the pad section65a, the pad section66aand the dummy electrodes72aby the bumps67. As a result, the Si wafer74which is configured by the plurality of acoustic sensors51and the Si wafer73which is configured by the plurality of interposers52are integrally bonded together.

Subsequently, as shown inFIG. 8(A), the top surface of the acoustic sensor51is polished to decrease a thickness of the Si wafer74. If the acoustic sensor51formed in one Si wafer74is singly provided, polishing the Si wafer74to reduce the thickness thereof causes occurrence of clapping or chipping in the Si wafer74in the polishing step or a subsequent step, thereby decreasing a yield of the acoustic sensor51. However, in the manufacturing method described herein, the Si wafer74is polished in the state of the two Si wafers, namely the Si wafer73and the Si wafer74, being bonded together, and it is thereby possible to perform the polishing while enhancing the rigidity of the Si wafer74so as to polish the Si wafer74with ease and a favorable yield.

Thereafter, as shown inFIG. 8(B), the sacrifice layer75of the acoustic sensor51is removed by etching, to form the air gap58between the diaphragm56and the fixed electrode plate59. This results in formation of the diaphragm56into the form of a vibratable film. Subsequently, the Si wafers74,73are subjected to dicing along a cutting line indicated by a dashed line inFIG. 8(B). As a result, as shown inFIG. 9(A), the acoustic sensor51and the interposer52are separated one by one while remaining vertically bonded.

Next, the signal processing circuit53is flip-chip mounted on the top surface of the circuit board43, and the electrode sections69of the signal processing circuit53are joined to the top-surface electrode pads44of the circuit board43by the conductive material68. In such a manner, the signal processing circuit53mounted on the circuit board43is shown inFIG. 9(B).

Subsequently, as shown inFIG. 10(A), the interposer52and the acoustic sensor51are superposed on the circuit board43so as to cover the signal processing circuit53, and the signal processing circuit53is accommodated inside the hollow70of the interposer52. At this time, the pad sections65b,66band the dummy electrodes72bof the interposer52are respectively joined to the top-surface electrode pads44of the circuit board43by the conductive material68.

Thereafter, as shown inFIG. 10(B), the cover42is superposed on the circuit board43so as to cover the acoustic sensor51, the interposer52and the signal processing circuit53. The sound introduction hole48has previously been opened in the cover42, and when the cover42is superposed on the circuit board43, the sound introduction hole48is accommodated inside the upper-surface opening of the front chamber55. Subsequently, the under surface of the cover42is joined to the circuit board43by the conductive adhesive. Simultaneously with this, the top surface of the acoustic sensor51is bonded to the inner surface of the cover42by the adhesive resin50, to seal the space between the whole periphery of the top surface of the acoustic sensor51and the inner surface of the cover42, so as to prevent an acoustic vibration having entered through the sound introduction hole48from leaking through a gap between the acoustic sensor51and the cover42.

When the microphone41is manufactured in such a manner, the Si wafer74resists occurrence of crapping and chipping at the time of polishing the Si wafer74, thereby leading to improvement in yield in the manufacturing process for the microphone41. Further, with the Si wafer74resisting occurrence of crapping or chipping in the Si wafer74, the Si wafer74can be reduced in thickness by polishing, so as to reduce the acoustic sensor51in height. When the acoustic sensor51can be reduced in height, the cover42with a small height can be used, so that the microphone41can be reduced in height and size.

Second Embodiment

FIG. 11is a sectional view showing a microphone81according to Embodiment 2 of the present invention. This microphone81differs from the microphone41of Embodiment 1 only in the shape of the interposer52. Therefore, descriptions of the microphone81of Embodiment 2 will be omitted except for a description of the interposer52.

In the interposer52used for the microphone81, the hollow70for accommodating the signal processing circuit53is formed in box form with the under surface thereof open and the top surface thereof closed, as shown inFIGS. 12(A) and 12(B). On the other hand, ventilation notches71in the form of one or a plurality of grooves are provided on the top surface of the interposer52.

Therefore, the space (back chamber) below the diaphragm56of the acoustic sensor51is communicated with the intra-package space49through the ventilation notch71, not via the hollow70for accommodating the signal processing circuit53. This enables the capacity of the back chamber to substantially increase, so as to improve the sensitivity of the microphone81.

Further, in this microphone81, the vertically arranged acoustic sensor51and the signal processing circuit53are partitioned by the interposer52, and it is thereby possible to prevent a short-circuit accident between the acoustic sensor51and the signal processing circuit53, and the like. Moreover, with the signal processing circuit53covered by the interposer52, it is possible to protect the signal processing circuit53from moisture and dust having entered through the sound introduction hole48.

Other Embodiments

The interposer52can be formed with a variety of structures other than the structures as described in Embodiments 1, 2. For example, in an embodiment shown inFIGS. 13(A) and 13(B), in the interposer52where the hollow70and the ventilation notch71are separated as in Embodiment 2, a ventilation notch82for communicating the hollow70and the intra-package space49is provided in the lower portion of the interposer52so that the inside of the hollow70can also be used as the back chamber.

Further, in an embodiment shown inFIGS. 14(A) and 14(B), the ventilation notch71provided on the top surface of the interposer52separately from the hollow70is formed into the form of a crossed groove.

One shown inFIGS. 15(A) and 15(B)is still another embodiment. In this interposer52, an extended electrode section83ais extended out from the pad section65aalong the top surface of the interposer52while an extended electrode section83bis extended out from the pad section65balong the under surface of the interposer52, and the tip of the extended electrode section83aand the tip of the extended electrode section83bare connected by the through electrode65. Similarly, an extended electrode section84ais extended out from the pad section66aalong the top surface of the interposer52while an extended electrode section84bis extended out from the pad section66balong the under surface of the interposer52, and the tip of the extended electrode section84aand the tip of the extended electrode section84bare connected by the through electrode66. According to such an embodiment, it is possible to provide the through electrodes65,66at free positions.

DESCRIPTION OF SYMBOLS

43: circuit board

48: sound introduction hole

53: signal processing circuit

55: front chamber

57: back plate

59: fixed electrode plate

66,66: through electrode

65a,65b,66a,66b: pad section

83a,83b,84a,84b: extended electrode section