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JP2004312323

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DESCRIPTION JP2004312323
The present invention provides a piezoelectric electroacoustic transducer which has stable
frequency characteristics of a diaphragm and is excellent in coating workability of an elastic
adhesive. A housing (10) having a rectangular piezoelectric diaphragm (1), a support (10f) for
supporting the lower surfaces of four corner parts of the piezoelectric diaphragm (1), and a
housing such that an internal connection part is exposed near the support. The fixed terminals
11 and 12, the first elastic adhesive 13 applied between the outer peripheral portion of the
piezoelectric diaphragm and the internal connection portion of the terminal, and the internal
connection portion of the electrode of the piezoelectric diaphragm and the terminal Between the
conductive adhesive 14 applied via the upper surface of the first elastic adhesive, and the second
elastic adhesive sealing the gap between the outer peripheral portion of the piezoelectric
diaphragm and the inner peripheral portion of the housing And 15. The lower portion of the
piezoelectric diaphragm in the inner peripheral portion of the housing, in the region to which the
first elastic adhesive is applied, of the first elastic adhesive lower than the support portion and
between the lower surface of the piezoelectric diaphragm and A pedestal 10g is provided to form
a gap D1 in which the flow can be stopped. [Selected figure] Figure 9
Piezoelectric electroacoustic transducer and method of manufacturing the same
TECHNICAL FIELD The present invention relates to a piezoelectric electroacoustic transducer
such as a piezoelectric receiver or a piezoelectric sounder. Related Art [0002] Patent Document
1: Japanese Patent Application Laid-Open No. 2000-310990 Patent Document 2: Japanese
Patent Application Laid-Open No. 2003-2928 Patent Document 3: Japanese Patent Application
Laid-Open No. 2003-23696 2. Description of the Related Art Piezoelectric electroacoustic
transducers are widely used as piezoelectric sounders or piezoelectric receivers that generate
alarm sounds and operation sounds in products, mobile phones, and the like. In this type of
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piezoelectric electroacoustic transducer, it has been proposed to improve production efficiency,
improve acoustic conversion efficiency, and reduce the size by using a rectangular diaphragm.
[0003] Patent Document 1 has a rectangular piezoelectric diaphragm, a bottom wall portion and
four side wall portions, and a support portion for supporting the diaphragm on the inside of two
opposing side wall portions, and a support portion And the housing provided with the first and
second terminals for external connection, the diaphragm is housed in the housing, and the two
opposing sides of the diaphragm and the support portion are adhesive or elastic adhesive While
being fixed, the gap between the remaining two sides of the diaphragm and the casing is sealed
with an elastic adhesive, and the diaphragm and the first and second terminals are electrically
connected by a conductive adhesive. A piezoelectric electroacoustic transducer is disclosed. The
reason why the diaphragm and the housing are sealed in this way is to isolate the front and back
spaces of the diaphragm and to form an acoustic space on the front and back of the diaphragm.
As the elastic adhesive, a soft elastic material such as a silicone adhesive is used so as not to
suppress the vibration of the diaphragm as much as possible. In order to lower the frequency,
recent diaphragms have become very thin, and thin diaphragms of about several tens to one
hundred μm are used. When such a thin diaphragm is used, the influence of the supporting
structure on the frequency characteristics becomes large. For example, when a diaphragm and a
terminal fixed to a housing are directly connected by a thermosetting conductive adhesive, a
curing shrinkage stress of the conductive adhesive causes distortion in the diaphragm and the
frequency characteristics vary. . In addition, since the Young's modulus of the conductive
adhesive after curing is relatively high, the vibration of the diaphragm may be suppressed, and
conversely, the conductive adhesive may be cracked by the vibration of the diaphragm. there
were. Patent Document 2 discloses a case having a support portion for supporting the lower
surface of two or four sides of the piezoelectric diaphragm on the inner peripheral portion, and
internal connection in the vicinity of the support portion. A first elastic adhesive which is applied
between the exposed terminal and the outer peripheral portion of the piezoelectric diaphragm
and the internal connection portion of the terminal to fix the piezoelectric diaphragm to the
housing, and an electrode of the piezoelectric diaphragm A conductive adhesive which is applied
by bypassing the upper surface of the first elastic adhesive and electrically connects the
electrode of the piezoelectric diaphragm and the internal connection of the terminal between the
terminal and the internal connection of the terminal; There has been proposed a piezoelectric
electroacoustic transducer provided with a second elastic adhesive for sealing a gap between an
outer peripheral portion of a piezoelectric diaphragm and an inner peripheral portion of a
housing.
For example, a urethane-based adhesive is used as the first elastic adhesive, and a material
having a lower Young's modulus than the first elastic adhesive, such as a silicone-based adhesive,
is used as the second elastic adhesive. FIG. 13 shows a connection portion between the
piezoelectric diaphragm 30 and the terminal 31 in Patent Document 2. As shown in FIG. The first
elastic adhesive 32 is raised and applied between the piezoelectric diaphragm 30 and the
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internal connection portion of the terminal 31, and the conductive adhesive 33 is applied on the
first elastic adhesive 32. The variation of the frequency characteristic of the diaphragm 30 due to
the cure shrinkage stress, the occurrence of cracks after curing of the conductive adhesive 33
and the like are prevented. However, in this case, since the first elastic adhesive 32 bonds the
support portion 34 and the piezoelectric vibration plate 30, the vibration plate 30 may be
restrained and the vibration thereof may be suppressed. In Patent Document 3, supporting
portions for supporting the lower surfaces of the four corner portions of the piezoelectric
diaphragm are provided in a housing, and a first elastic adhesive is provided between the
piezoelectric diaphragm and the terminal at a position near the supporting portions. And a
conductive adhesive applied thereon. FIG. 14 shows a connection portion between the
piezoelectric diaphragm 30 and the terminal 31 in Patent Document 3. As shown in FIG. In this
case, since the lower part of the diaphragm 30 in the area to which the first elastic adhesive 32 is
applied is hollow, the possibility of the diaphragm 30 being restrained by the first elastic
adhesive 32 is low. When the first elastic adhesive 32 with low viscosity is used, the adhesive 32
flows down to the bottom side of the housing 35 through the gap between the diaphragm 30 and
the housing 35, and the first elastic bonding is performed. The agent 32 can not be raised
between the diaphragm 30 and the terminal 31. As an elastic adhesive, a room temperature
curing type adhesive and a thermosetting type adhesive are generally used. In the case of a cold
setting adhesive, the adhesive (thixotropy) at the time of application is relatively high, and curing
after application is quick, so the adhesive may flow from the gap between the diaphragm and the
case to the bottom side of the case Absent. However, the cold-setting adhesive starts curing in the
middle of coating, and the coating device is easily clogged, and the workability is poor. In
addition, the Young's modulus after curing is relatively high, and there is a problem that the
diaphragm is restrained. On the other hand, in the case of a thermosetting adhesive having a low
viscosity (thixotropy), curing does not start in the middle of coating, and while excellent in
coating workability, the Young's modulus after curing is low. It has the advantage of not binding.
However, when an elastic adhesive having a low viscosity is used, the elastic adhesive flows down
to the bottom side of the housing as described above, and can not be raised between the
diaphragm and the terminal.
Therefore, there is a possibility that the restraining force by the conductive adhesive applied and
cured later acts on the diaphragm to inhibit the vibration. As described above, it is possible to
simultaneously satisfy the three conditions of the conventional structure that the diaphragm can
be held without being strongly restrained, the improvement of the coating workability of the
elastic adhesive can be achieved, and the elastic adhesive can be raised and coated. difficult.
Therefore, an object of the present invention is to provide a piezoelectric electroacoustic
transducer which has stable frequency characteristics of a diaphragm and is excellent in
workability of applying an elastic adhesive. In order to achieve the above object, the invention
according to claim 1 is a rectangular piezoelectric vibrating plate whose area is bent and vibrated
in a thickness direction by applying an alternating signal between electrodes. A casing having a
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support portion for supporting the lower surface of the four corner portions of the piezoelectric
diaphragm on the inner peripheral portion; a terminal fixed to the casing so that the internal
connection portion is exposed in the vicinity of the support portion; A first elastic adhesive which
is applied between the outer peripheral portion of the diaphragm and the internal connection
portion of the terminal and holds the piezoelectric diaphragm with respect to the housing, and
the internal connection portion of the electrode of the piezoelectric diaphragm and the terminal
A conductive adhesive which is applied through the upper surface of the first elastic adhesive to
electrically connect the electrode of the piezoelectric diaphragm and the internal connection
portion of the terminal, the outer peripheral portion of the piezoelectric diaphragm, and the
housing Piezoelectric electroacoustic transducer comprising a second elastic adhesive for sealing
a gap with an inner circumferential portion of In the inner peripheral portion of the housing, the
lower portion of the piezoelectric diaphragm in the region to which the first elastic adhesive is
applied, the lower portion between the support portion and the lower surface of the piezoelectric
diaphragm, and There is provided a piezoelectric electroacoustic transducer characterized in that
a pedestal is provided which forms a gap in which the flow of the elastic adhesive is stopped.
According to the fifth aspect of the present invention, there is provided a method of preparing a
rectangular piezoelectric diaphragm which vibrates in the area in the thickness direction by
applying an alternating signal between the electrodes, and four piezoelectric vibrators on the
inner peripheral portion. A support portion for supporting the lower surface of the corner
portion, and a pedestal which is lower than the support portion in the vicinity of the support
portion and on which the flow of the first elastic adhesive is stopped between the lower surface
of the piezoelectric diaphragm A step of preparing a housing to which a terminal having an
exposed internal connection portion is fixed in the vicinity, and between the outer peripheral
portion of the piezoelectric diaphragm and the internal connection portion, between the
piezoelectric diaphragm and the internal connection portion The step of applying and curing the
elastic adhesive of 1 and holding the piezoelectric diaphragm with respect to the housing, and
the upper surface of the first elastic adhesive between the electrode of the piezoelectric
diaphragm and the internal connection portion of the terminal The conductive adhesive is
applied and cured through the internal connection between the electrode and the terminal of the
piezoelectric diaphragm And a step of applying and curing a second elastic adhesive in the gap
between the outer peripheral portion of the piezoelectric diaphragm and the inner peripheral
portion of the housing, and sealing the gap between the two. There is provided a method of
manufacturing a piezoelectric type electroacoustic transducer comprising the above.
In order to hold the diaphragm without holding it strongly and to improve coating workability, it
is necessary to use a first elastic adhesive with low viscosity. When the first low-viscosity elastic
adhesive is applied between the peripheral edge of the diaphragm and the inner surface of the
housing, the elastic adhesive passes through the gap between the diaphragm and the housing to
the bottom wall of the housing Try to flow down to the side. However, a pedestal is provided
below the piezoelectric diaphragm in the application region of the first elastic adhesive, and the
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first elastic adhesive flows into the gap between the pedestal and the diaphragm, and the first
elastic adhesive is applied. Since the flow is stopped by the surface tension of the adhesive, it
does not flow down to the bottom wall side of the housing. Moreover, since the gap between the
pedestal and the diaphragm is set to be narrow, the gap is immediately filled, and the excess
adhesive can be raised. Therefore, when the conductive adhesive is applied on the first elastic
adhesive after curing, the conductive adhesive detours the shortest path between the electrode of
the diaphragm and the internal connection portion of the terminal. The cure shrinkage stress of
the conductive adhesive is relieved by the first elastic adhesive. As a result, distortion of the
diaphragm can be reliably prevented, and at the same time the frequency characteristics are
stabilized, it is possible to prevent the occurrence of cracks and the like of the conductive
adhesive due to the vibration of the diaphragm. According to the second aspect of the present
invention, the inner peripheral portion of the housing is provided with a groove for storing the
second elastic adhesive, and the inner peripheral side of the groove is lower than the support,
and the second elastic adhesive is used. It is preferable to provide a flow-stop wall that restricts
the flow of water into the bottom wall of the housing. Like the first elastic adhesive, the second
elastic adhesive may use a low-viscosity second elastic adhesive, but it is preferable to use a
viscous adhesive between the peripheral portion of the diaphragm and the inner surface of the
housing. When a low elastic adhesive is applied, the elastic adhesive tries to flow down to the
bottom wall side of the housing through the gap between the diaphragm and the housing.
However, since the second elastic adhesive flows into the groove provided in the housing and is
blocked by the flow prevention wall formed on the inner periphery of the groove, the elastic
adhesive is on the bottom wall side of the housing. It is prevented from flowing out. In addition,
since the second elastic adhesive rapidly wraps around along the groove, the periphery of the
diaphragm can be easily sealed. The height of the flow prevention wall does not flow out of the
gap between the wall and the diaphragm due to the surface tension of the second elastic
adhesive toward the bottom wall of the housing, and the vibration of the diaphragm can be made
as small as possible. It is set to the height which does not inhibit. Although the flow control wall
of the second elastic adhesive may have the same height as the pedestal for stopping the flow of
the first elastic adhesive, the flow control wall may be formed from the support. It is desirable to
set it low.
The pedestal is formed at the opposing portion of the piezoelectric diaphragm and the terminal,
that is, in the vicinity of the four corners of the piezoelectric diaphragm, while the flow
prevention wall is provided on substantially the entire periphery of the piezoelectric diaphragm.
In the case of the same height, the film thickness of the second elastic adhesive interposed in the
gap between the flow prevention wall portion and the piezoelectric vibrating plate becomes thin,
and the restraint force suppresses the vibration of the piezoelectric vibrating plate there is a
possibility. Therefore, by setting the flow prevention wall portion lower than the receiving table,
the second elastic adhesive can be used within a range in which the second elastic adhesive does
not flow out from the gap between the flow prevention wall portion and the piezoelectric
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diaphragm. It is preferable to make the film thickness as thick as possible, and to obtain a reliable
seal while minimizing the restraint force of the second elastic adhesive. As in claim 3, the Young's
modulus after curing of the first elastic adhesive is 500 × 10 <6> Pa or less, and the Young's
modulus after curing of the second elastic adhesive is 30 × 10 <10 6> Pa or less is preferable.
That is, the Young's modulus after curing of the first and second elastic adhesives is set to a value
that is not largely affected by the displacement of the diaphragm, but the Young's modulus after
curing of the first elastic adhesive is 500 × When the Young's modulus of the second elastic
adhesive after curing is 30 × 10 <6> Pa or less, the displacement of the diaphragm may be 90%
or more of the maximum value. Because you can, you do not have a major impact. The reason for
the narrow tolerance of Young's modulus of the second elastic adhesive is that the first elastic
adhesive is partially applied in the vicinity of the corner of the piezoelectric diaphragm, while the
second elastic adhesive is piezoelectric. This is because the piezoelectric diaphragm is easily
affected by the Young's modulus of the second elastic adhesive because it is applied around the
diaphragm. According to a fourth aspect of the invention, a urethane-based adhesive can be used
as the first elastic adhesive, and a silicone-based adhesive can be used as the second elastic
adhesive. As an elastic adhesive, a silicone adhesive is widely used since it has a low Young's
modulus after curing and is inexpensive. However, silicone adhesives have a serious problem that
siloxane gas is generated at the time of heat curing, and this adheres as a film to a conductive
part etc. and causes adhesion failure and conductivity failure when applying a conductive
adhesive etc. . Therefore, the use of silicone adhesives is limited after application and curing of
conductive adhesives. On the other hand, urethane adhesives do not have the same problems as
silicone adhesives. Therefore, as a first elastic adhesive used as a base material of a conductive
adhesive that holds the piezoelectric diaphragm in a housing and electrically connects the
electrode of the piezoelectric diaphragm and the internal connection portion of the terminal, a
urethane type is used. An adhesive is used, and by using a silicone-based adhesive as the second
elastic adhesive that seals the periphery of the piezoelectric diaphragm, a piezoelectric type
having good vibration characteristics without causing adhesion failure or conductivity failure. An
electroacoustic transducer can be obtained.
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of a surface mount
type piezoelectric electroacoustic transducer according to the present invention. The electroacoustic transducer of this embodiment is suitable for use corresponding to a wide range of
frequencies as in a piezoelectric receiver, and includes a piezoelectric diaphragm 1 having a
laminated structure, a case 10, and a cover plate 20. Here, the case 10 and the cover plate 20
constitute a housing. The diaphragm 1 is formed by laminating two layers of piezoelectric
ceramic layers 1 a and 1 b as shown in FIGS. 2 and 3, and main surface electrodes 2 and 3 are
provided on the front and back main surfaces of the diaphragm 1. An internal electrode 4 is
formed between the ceramic layers 1a and 1b. The two ceramic layers 1a and 1b are polarized in
the same direction in the thickness direction as indicated by thick arrows. The main electrode 2
on the front side and the main electrode 3 on the rear side are formed slightly shorter than the
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side length of the diaphragm 1, and one end thereof is connected to the end surface electrode 5
formed on one end surface of the diaphragm 1. Therefore, the main surface electrodes 2 and 3 of
the front and back are mutually connected. The internal electrode 4 is formed substantially
symmetrical with the main surface electrodes 2 and 3, one end of the internal electrode 4 is
separated from the end face electrode 5 and the other end is an end face electrode 6 formed on
the other end face of the diaphragm 1 It is connected. An auxiliary electrode 7 electrically
connected to the end surface electrode 6 is formed on the front and back surfaces of the other
end of the diaphragm 1. Resin layers 8 and 9 covering the main surface electrodes 2 and 3 are
formed on the front and back surfaces of the diaphragm 1. The resin layers 8 and 9 are
protective layers provided for the purpose of preventing a crack of the diaphragm 1 due to a
drop impact. In the resin layers 8 and 9 on the front and back, notches 8a and 9a in which the
main surface electrodes 2 and 3 are exposed and notches 8b and 9b in which the auxiliary
electrode 7 is exposed in the vicinity of the diagonal corner of the diaphragm 1. Is formed.
Although the cutaway portions 8a, 8b, 9a, 9b may be provided on only one of the front and back,
in order to eliminate the directivity of the front and back, they are provided on the front and back
in this example. Further, the auxiliary electrode 7 does not have to be a band-shaped electrode
having a fixed width, and may be provided only at the portion corresponding to the cutouts 8 b
and 9 b. Here, a 10 mm × 10 mm × 40 μm PZT-based ceramic was used as the ceramic layers
1 a and 1 b, and a polyamide-imide resin having a thickness of 3 to 10 μm was used as the resin
layers 8 and 9. As shown in FIGS. 4 to 10, the case 10 is formed of a resin material in a
rectangular box shape having a bottom wall portion 10a and four side wall portions 10b to 10e.
As the resin material, a heat-resistant resin such as LCP (liquid crystal polymer), SPS (syndiotactic
polystyrene), PPS (polyphenylene sulfide), epoxy or the like is desirable.
The bifurcated inner connection portions 11a and 12a of the terminals 11 and 12 are exposed to
the inside of the two opposing side walls 10b and 10d among the four side walls 10b to 10e. The
terminals 11 and 12 are insert-molded in the case 10. The outer connection portions 11b and
12b of the terminals 11 and 12 exposed to the outside of the case 10 are bent toward the bottom
of the case 10 along the outer surfaces of the side wall portions 10b and 10d (see FIG. 6). At four
corners inside the case 10, support portions 10f for supporting the lower surface of the corner
portion of the diaphragm 1 are formed. The support portion 10 f is formed one step lower than
the exposed surface of the inner connection portions 11 a and 12 a of the terminals 11 and 12.
Therefore, when the diaphragm 1 is placed on the support portion 10f, the top surface of the
diaphragm 1 and the top surfaces of the inner connecting portions 11a and 12a of the terminals
11 and 12 have substantially the same height. In the vicinity of the support portion 10 f, a
pedestal 10 g which is lower than the support portion 10 f and which forms a predetermined gap
D 1 with the lower surface of the diaphragm 1 is formed. That is, in the gap D1 between the
upper surface of the pedestal 10g and the lower surface of the diaphragm 1 (the upper surface of
the support portion 10f), the first elastic adhesive 13 flows out by the surface tension of the first
elastic adhesive 13 described later. Is set to the dimensions that can be stopped. When the
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viscosity of the first elastic adhesive 13 at the time of application is 6 to 10 Pa · s, the gap D1 is
preferably about 0.1 mm to 0.2 mm. In this embodiment, the gap D1 is set to 0.15 mm. In
addition, a groove 10 h for filling a second elastic adhesive 15 described later is provided on the
periphery of the bottom wall 10 a of the case 10, and the flow lower than the support 10 f is
provided inside the groove 10 h. A stop wall 10i is provided. The flow prevention wall portion
10i regulates the flow of the second elastic adhesive 15 to the bottom wall portion 10a, and the
upper surface of the wall portion 10i and the lower surface of the diaphragm 1 (the upper
surface of the support portion 10f) The gap D2 is set such that the second elastic adhesive 15
can stop the flow by its surface tension. When the viscosity at the time of application of the
second elastic adhesive 15 is 0.5 to 2.0 Pa · s, the gap D2 is preferably 0.15 to 0.25 mm. In this
embodiment, the gap D2 is set to 0.20 mm. In this embodiment, the bottom surface of the groove
10 h is located higher than the upper surface of the bottom wall 10 a, and the groove 10 h is
filled with a relatively small amount of the second elastic adhesive 15 and rapidly wraps around.
The groove 10 h is formed in a shallow bottom.
Specifically, the height D3 from the bottom of the groove 10h to the lower surface of the
diaphragm 1 (the upper surface of the support 10f) is set to 0.33 mm. The groove 10h and the
wall 10i are provided on the periphery of the bottom wall 10a except for the pedestal 10g, but
continuously along the entire circumference of the bottom wall 10a via the inner circumferential
side of the pedestal 10g. You may provide. The end of the groove 10h in contact with the support
10f and the pedestal 10g is formed wider than the other portions. Therefore, it is possible to
absorb the excess adhesive 15 at this wide portion and prevent the adhesive 15 from overflowing
on the diaphragm 1. On the inner surfaces of the side wall portions 10 b to 10 e of the case 10,
tapered protrusion portions 10 j for guiding the four sides of the piezoelectric vibration plate 1
are provided. Two protrusions 10 j are provided on each of the side walls 10 b to 10 e. On the
inner surface of the upper edge of the side wall portions 10b to 10e of the case 10, a recessed
portion 10k for restricting the rising of the second elastic adhesive 15 is formed. Further, a first
sound output hole 10l is formed in the bottom wall 10a near the side wall 10e. On the top
surfaces of the corner portions of the side wall portions 10b to 10e of the case 10, a
substantially L-shaped positioning convex portion 10m for fitting and holding the corner portion
of the lid plate 20 is formed. A tapered surface 10 n for guiding the lid plate 20 is formed on the
inner surface of the convex portion 10 m. The diaphragm 1 is housed in the case 10, and the
corner portion thereof is supported by the support portion 10f. At this time, since the peripheral
portion of the diaphragm 1 is guided by the tapered projections 10j provided on the inner
surfaces of the side walls 10b to 10e of the case 10, the corner portion of the diaphragm 1 is
exactly on the support 10f. Placed on In particular, by providing the tapered protrusion 10j, the
clearance between the diaphragm 1 and the case 10 can be narrowed more than the accuracy of
inserting the diaphragm 1, and as a result, the product size can be reduced. In addition, since the
contact area between the projection 10 j and the peripheral portion of the diaphragm 1 is small,
the vibration of the diaphragm 1 can be prevented from being impeded. After the diaphragm 1 is
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housed in the case 10, the first elastic adhesive 13 is applied to four places as shown in FIG. It is
held at 12a. That is, between the main surface electrode 2 exposed to the notched portion 8a at
the diagonal position and one inner connecting portion 11a of the terminal 11, and one inner
connecting portion of the auxiliary electrode 7 and the terminal 12 exposed to the notched
portion 8b. The first elastic adhesive 13 is applied between 12a and 12a.
In addition, the first elastic adhesive 13 is applied also to the remaining two diagonal positions.
In addition, although the 1st elastic adhesive 13 was apply | coated to a laterally long ellipse or
oval, the application | coating shape is not restricted to this. As the first elastic adhesive 13, an
adhesive having a relatively low Young's modulus after curing of 500 × 10 <6> Pa or less is
used. This is because, as shown in FIG. 11, from the relationship between the displacement of the
center of the diaphragm and the Young's modulus after curing of the first elastic adhesive 13, the
displacement of the center of the diaphragm is after curing of the first elastic adhesive 13. It is in
the range which is not much influenced by the Young's modulus. In this example, a urethanebased adhesive of 3.7 × 10 6 Pa was used. After the first elastic adhesive 13 is applied, heat
curing is performed. Since the viscosity is low when the first elastic adhesive 13 is applied, the
first elastic adhesive 13 flows down to the bottom wall portion 10 a through the gap between the
piezoelectric diaphragm 1 and the terminals 11 and 12. There is a fear. However, as shown in
FIG. 9, a pedestal 10 g is provided under the piezoelectric diaphragm 1 in the area to which the
first elastic adhesive 13 is applied, and the gap D 1 between the pedestal 10 g and the
piezoelectric diaphragm 1 is narrow. Since it is set, the surface tension of the first elastic
adhesive 13 stops the flow, and the outflow to the bottom wall 10a is prevented. Moreover, since
the gap D1 is quickly filled, the surplus elastic adhesive 13 is formed between the piezoelectric
diaphragm 1 and the terminals 11 and 12 so as to be raised. In addition, since the layer of the
elastic adhesive 13 for the gap D1 is present between the pedestal 10g and the piezoelectric
diaphragm 1, the piezoelectric diaphragm 1 is not restrained more than necessary. After curing
the first elastic adhesive 13, the conductive adhesive 14 is applied in an oval or elongated shape
so as to cross over the first elastic adhesive 13. The conductive adhesive 14 is not particularly
limited, but in this embodiment, a urethane-based conductive paste having a Young's modulus of
0.3 × 10 <9> Pa after curing was used. After the conductive adhesive 14 is applied, the main
surface electrode 2 and the inner connection portion 11 a of the terminal 11 and the auxiliary
electrode 7 and the inner connection portion 12 a of the terminal 12 are connected by heating
and curing the conductive adhesive 14. The application shape of the conductive adhesive 14 is
not limited to the elliptical shape, and the main surface electrode 2 and the inner connection
portion 11a, and the auxiliary electrode 7 and the inner connection portion 12a are connected
via the upper surface of the first elastic adhesive 13. It should be possible. Since the first elastic
adhesive 13 is formed to be raised, the conductive adhesive 14 is applied in the form of an arch
on the top surface of the first elastic adhesive 13 so as to bypass the shortest path (see FIG. 9).
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Therefore, the cure shrinkage stress of the conductive adhesive 14 is relieved by the first elastic
adhesive 13 and the influence on the piezoelectric diaphragm 1 is reduced. After the conductive
adhesive 14 is applied and cured, the second elastic adhesive 15 is applied to the gap between
the entire periphery of the diaphragm 1 and the inner periphery of the case 10, and the front
side of the diaphragm 1 Prevent air leakage between the rear and the rear. After the second
elastic adhesive 15 is applied in a ring shape, heat curing is performed. As the second elastic
adhesive 15, a thermosetting adhesive having a low Young's modulus after curing of not more
than 30 × 10 <6> Pa and a low viscosity of, for example, about 0.5 to 2 Pa · s before curing. Is
used. This is because, as shown in FIG. 12, from the relationship between the displacement of the
center of the diaphragm and the Young's modulus after curing of the second elastic adhesive 15,
the displacement of the center of the diaphragm is after curing of the second elastic adhesive 15.
The Young's modulus of the In addition, the silicone type adhesive agent of 3.0 * 10 <5> Pa was
used here. When the second elastic adhesive 15 is applied, since the viscosity is low, there is a
possibility that the second elastic adhesive 15 may flow down to the bottom wall portion 10 a
through the gap between the piezoelectric diaphragm 1 and the case 10. is there. However, as
shown in FIG. 10, a groove portion 10h for filling the second elastic adhesive 15 is provided on
the inner peripheral portion of the case 10 facing the peripheral portion of the diaphragm 1, and
the flow stops inside the groove portion 10h. Since the wall portion 10i is provided, the second
elastic adhesive 15 enters the groove 10h and spreads around. Since a gap D2 is formed between
the diaphragm 1 and the flow prevention wall 10i in which the second elastic adhesive 15 is
stopped by its surface tension, the second elastic adhesive 15 flows down to the bottom wall 10a.
Is prevented. In addition, since the layer of the elastic adhesive 15 corresponding to the gap D2
is present between the wall portion 10i and the piezoelectric diaphragm 1, it is possible to
prevent the vibration of the piezoelectric diaphragm 1 from being suppressed. In this
embodiment, the gap D2 is slightly larger than the gap D1 (D1 = 0.15 mm, D2 = 0.20 mm). The
reason is that while the first elastic adhesive 13 is partially applied to the opposing portion of the
piezoelectric diaphragm 1 and the terminals 11 and 12, the second elastic adhesive 15 is
substantially the same as that of the piezoelectric diaphragm 1. Since the coating is applied to the
entire circumference, the gap D2 is made as large as possible within the range in which the
second elastic adhesive 15 does not flow out in order to minimize the restraint force on the
piezoelectric diaphragm 1 by the second elastic adhesive 15. It is. On the other hand, since the
application position of the first elastic adhesive 13 is limited for the gap D1, even if D1 is made
small, the influence by the restraining force is low, and the piezoelectric diaphragm 1 and the
terminal 11 are as small as possible. A gap D1 is set so that a raised portion can be formed
between them.
When the second elastic adhesive 15 is applied, a part of the second elastic adhesive 15 may rise
up the side wall portions 10 b to 10 e of the case 10 and adhere to the top surface of the side
wall portion. In the case where the second elastic adhesive 15 is a releasable sealant such as a
silicone adhesive, the adhesion strength is reduced later when the lid plate 20 is adhered to the
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top surfaces of the side wall portions 10b to 10e. There is a fear. However, since the recess 10k
for restricting the rise of the second elastic adhesive 15 is formed on the inner surface of the
upper edge of the side wall 10b to 10e, the second elastic adhesive 15 is formed on the top
surface of the side wall. It can be prevented from adhering. After the diaphragm 1 is attached to
the case 10 as described above, the lid plate 20 is adhered to the top surface of the side wall
portion of the case 10 by the adhesive 21. As the adhesive 21, a known adhesive such as epoxy
may be used, but when the second elastic adhesive 15 is a silicone adhesive, the coating by the
siloxane gas is the top of the side wall of the case 10. In this case, a silicone-based adhesive may
be used as the adhesive 21 because there is a possibility of adhesion to the surface. The cover
plate 20 is formed of a material similar to that of the case 10 in a flat plate shape. The peripheral
edge portion of the cover plate 20 is engaged with the inner tapered surface 10n of the
positioning convex portion 10m provided on the top surface of the side wall portion of the case
10, and the positioning is accurately performed. By bonding the cover plate 20 to the case 10, an
acoustic space is formed between the cover plate 20 and the diaphragm 1. In the cover plate 20,
a second sound output hole 22 is formed. As described above, the surface mount type
piezoelectric electroacoustic transducer is completed. In the electro-acoustic transducer of this
embodiment, by applying a predetermined alternating voltage (AC signal or rectangular wave
signal) between the terminals 11 and 12, the diaphragm 1 can be subjected to area bending
vibration. The piezoelectric ceramic layer in which the polarization direction and the electric field
direction are the same direction is contracted in the plane direction, and the piezoelectric
ceramic layer in which the polarization direction and the electric field direction are opposite is
expanded in the plane direction, and therefore the film is bent as a whole. In this embodiment,
the diaphragm 1 is a laminated structure of ceramics, and a bimorph structure in which two
vibration regions (ceramic layers) arranged in order in the thickness direction vibrate in opposite
directions to each other. Compared to the above, a large amount of displacement, that is, a large
sound pressure can be obtained. The present invention is not limited to the above embodiment,
and can be modified without departing from the spirit of the present invention. The application
area of the second elastic adhesive is not limited to the entire periphery of the diaphragm 1 as in
the embodiment, and may be applied to an area that can seal the gap between the diaphragm 1
and the case 10.
The piezoelectric vibration plate 1 of the above embodiment is a laminate of two piezoelectric
ceramic layers, but may be a laminate of three or more piezoelectric ceramic layers. Further, as
the piezoelectric vibrating plate, not only a laminate of piezoelectric ceramic layers, but also a
known unimorph or bimorph vibrating plate in which a piezoelectric plate is attached to one side
or both sides of a metal plate may be used. The housing according to the present invention is not
limited to the case having the concave cross-sectional shape as in the embodiment and the lid
plate 20 bonded to the upper surface opening portion, and for example, a cap-shaped case whose
lower surface is open And a substrate adhered to the lower surface of the case. As is apparent
from the above description, according to the invention described in claim 1, the piezoelectric
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vibration in the application region of the first elastic adhesive is an inner peripheral portion of
the case. When a pedestal is provided in the lower part of the plate and the first elastic adhesive
is applied between the diaphragm and the terminal, the first elastic adhesive flows into the gap
between the pedestal and the diaphragm, and the surface tension of the elastic adhesive Since
the flow is stopped by this, the flow does not fall to the bottom wall side of the housing even with
the use of the low-viscosity first elastic adhesive. Moreover, since the gap between the pedestal
and the diaphragm is set to be narrow, the gap is immediately filled, and the excess adhesive can
be raised. Therefore, when the conductive adhesive is applied on the first elastic adhesive after
curing, the conductive adhesive detours the shortest path between the electrode of the
diaphragm and the internal connection portion of the terminal. The cure shrinkage stress of the
conductive adhesive is relieved by the first elastic adhesive. As a result, distortion of the
diaphragm can be reliably prevented, and at the same time the frequency characteristics are
stabilized, it is possible to prevent the occurrence of cracks and the like of the conductive
adhesive due to the vibration of the diaphragm. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1
is an exploded perspective view of a first embodiment of a piezoelectric electroacoustic
transducer according to the present invention. FIG. 2 is a perspective view of a piezoelectric
diaphragm used in the piezoelectric electroacoustic transducer of FIG. 1; 3 is a cross-sectional
view taken along the line AA of FIG. 4 is a plan view of a case used for the piezoelectric
electroacoustic transducer of FIG. 1; 5 is a cross-sectional view taken along line XX in FIG. 4; 6 is
a cross-sectional view taken along line YY of FIG. 4; 7 is a plan view of the case shown in FIG. 4 in
which the diaphragm is held (before application of a second elastic adhesive); 8 is an enlarged
perspective view of a corner portion of the case shown in FIG. 4; 9 is an enlarged cross-sectional
view taken along the line B-B in FIG. 7; 10 is an enlarged sectional view taken along the line C-C
in FIG. 7; FIG. 11 is a view showing the relationship between diaphragm displacement and
Young's modulus of the first elastic adhesive.
FIG. 12 is a view showing a relationship between diaphragm displacement and Young's modulus
of a second elastic adhesive. 13 is a cross-sectional view of a connection portion between a
piezoelectric diaphragm and a terminal in Patent Document 2. FIG. 14 is a cross-sectional view of
a connection portion between a piezoelectric diaphragm and a terminal in Patent Document 3.
FIG. Explanation of code 1 Piezoelectric diaphragm 10 Case 10a Bottom wall 10f Support 10g
Support 10h Groove 10i Flow prevention wall 11, 12 Terminal 13 1st elastic adhesive 14
Conductive adhesive 15 2nd elasticity adhesive
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