JPH0933560A - Piezoelectric sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable piezoelectric sensor which can be properly seated in any position while changing the posture according to the direction of a sensitivity axis which is requested when mounting on a printed circuit board. SOLUTION: In a piezoelectric sensor 1 where a band-shaped piezoelectric element 2 with a specific sensitivity axis is enclosed in a package 3, the outer shape of the package 3 is formed in the shape of parallelepiped and at the same time the aspect ratio of the length to the width of the end face is set to nearly 1:1 and an external lead-out electrode 4 of the piezoelectric element 2 is formed at least on the end face, thus always making nearly the same posture of the piezoelectric sensor 1 even in any surface out of the four surface of the package 3 face upward and stabilizing seating in any case. Also, the direction of the sensitivity axis can be specified depending on the posture of the piezoelectric sensor 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric sensor for detecting acceleration or vibration.

[0002]

2. Description of the Related Art Among piezoelectric sensors, an acceleration sensor for detecting acceleration is mounted on a printed circuit board by setting a sensitivity axis of the acceleration sensor substantially parallel to the printed circuit board and substantially perpendicular to the printed circuit board. There are cases.

Normally, the acceleration sensor is fixed to the printed board by soldering or the like. However, if the acceleration sensor falls down during the soldering process and the posture changes,
Since the direction of the sensitivity axis of the acceleration sensor is deviated, it is necessary to prevent the posture of the acceleration sensor from collapsing during the soldering process.

For this reason, the outer shape of the acceleration sensor is formed into a flat rectangular parallelepiped shape, and the mounting posture of the acceleration sensor is such that its rectangular end face is horizontally long.
By the way, the dimensional ratio of the length and width of the end surface of the conventional acceleration sensor is generally set to about 0.5 to 0.7: 1.

Conventionally, two types of acceleration sensors are manufactured, each having a flat rectangular parallelepiped outer shape and different structures depending on the direction of the sensitivity axis. That is, there are a structure in which the direction of the sensitivity axis is set parallel to the long side of the rectangular end face and a structure in which the direction is set perpendicular to the long side.

[0006]

By the way, in the above-mentioned conventional acceleration sensor, since it is necessary to manufacture two kinds of structures having different structures depending on the direction of the sensitivity axis, not only the manufacturing cost is high, but also after the manufacturing. Product costs are inevitably rising due to high storage costs.

Therefore, the present invention provides a piezoelectric sensor which can be seated well in any posture and has high stability while being capable of responding only by changing the posture according to the direction of the sensitivity axis required for mounting on a printed circuit board. It is an object.

[0008]

According to the present invention, a piezoelectric sensor having a structure in which a piezoelectric element having a specific sensitivity axis is surrounded by a package has the following structure.

In the first piezoelectric sensor of the present invention, the package has an outer shape of a rectangular parallelepiped, and
The vertical and horizontal dimensional ratios of the end faces are set to approximately 1: 1 and the external lead electrode of the piezoelectric element is formed at least on the end faces.

In a second piezoelectric sensor of the present invention, the piezoelectric element is composed of a pair of strip-shaped piezoelectric ceramic plates which are vertically joined, and the package has at least one end portion along the longitudinal direction of the piezoelectric element. The package includes two sandwiching parts that sandwich the piezoelectric element from above and below to support the piezoelectric element in a bridge shape, and two lid parts that are attached to both sides of the sandwiching part and cover both side surfaces of the piezoelectric element. Is formed in a rectangular parallelepiped shape, and the longitudinal and lateral dimension ratios of its end faces are set to approximately 1: 1, and at least the end faces are formed with external lead electrodes of the piezoelectric element.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the embodiments shown in FIGS. Here, an acceleration sensor that detects acceleration is used as an example of the piezoelectric sensor. 1 to 5 relate to an embodiment of the present invention,
FIG. 1 is a perspective view showing a partially broken acceleration sensor, FIG.
4 is an exploded perspective view of the sensor, FIG. 3 is an explanatory view schematically showing a deformed state of a piezoelectric element when an acceleration acts, and FIG.
FIG. 5 is an explanatory diagram showing a posture of the acceleration sensor when mounted on a printed circuit board, and FIG. 5 is an explanatory diagram showing a tape carrier relating to the acceleration sensor.

The acceleration sensor 1 shown in the figure comprises a piezoelectric element 2 called a bimorph type, a package 3, and external extraction electrodes 4 and 4. The direction of the sensitivity axis is a piezoelectric element as indicated by an arrow. 2 is parallel to the thickness direction (see below).

The piezoelectric element 2 is provided with a pair of piezoelectric ceramic plates 5 and 5 each having a strip shape and having signal extraction electrodes 6 and 6 and intermediate electrodes 7 and 7 formed on the main surface thereof. It is a 7-face-to-face joint. Here, the stacking direction of the piezoelectric ceramic plates 5 and 5 is set to the piezoelectric element 2
Is called the thickness direction. Each of the piezoelectric ceramic plates 5 and 5 has three parts 5a, 5b and 5b which are divided by a boundary line L in the longitudinal direction.
In 5b, the stress generated by the action of the acceleration G is different between "tensile" and "compressed". Each of the central portion 5a and the end portions 5b, 5b is polarized along the plate thickness direction of each piezoelectric ceramic plate 4 in directions opposite to each other (indicated by arrows A, B and C, D in the figure). At the same time, the polarization directions A and C in each of the central portions 5a are inward toward each other, while the polarization directions B and D in the end portions 5b and 5b are outward from each other.

The package 3 is mounted on both left and right sides of the sandwiching parts 8 and 9 which are substantially U-shaped in side view and sandwiches both ends along the longitudinal direction of the piezoelectric element 2 from above and below. It is composed of two lid parts 10 and 11 having a substantially U-shaped vertical and horizontal cross section, which covers the left and right side surfaces of the piezoelectric element 2. The overall outer shape of the package 3 is formed in a rectangular parallelepiped shape, and the longitudinal and lateral dimension ratios of its end faces are set to approximately 1: 1 or substantially square. When the vertical dimension of the end face is A and the lateral dimension is B, it is ideal to set A / B to "1", that is, A = B.
It also includes the case where / B is set in the range of "0.9 to 1.1".

The external extraction electrodes 4 and 4 are formed in layers on both end faces in the longitudinal direction of the package 3 including both end faces in the longitudinal direction of the piezoelectric element 2, and also on the peripheral faces on both end sides in the longitudinal direction of the package 3. Is formed in. The one external extraction electrode 4 is connected to one of the signal extraction electrodes 6 and 6 formed on each piezoelectric ceramic plate 5 and 5, and the other external extraction electrode 4 is connected to the remaining signal extraction electrodes 6, respectively. Has been done.

Next, the operation and action of the acceleration sensor 1 described above will be described. When the piezoelectric element 2 bends upward as shown in FIG. 3 due to the action of the acceleration G, the outer main surface of the central portion 5a of the piezoelectric ceramic plate 5 located outside the bending direction of the piezoelectric element 2 is polarized. Direction A
And the tensile stress Pt, positive (+) charges are generated, and also on the outer main surface of the end portion 5b, positive charges are generated due to the relationship between the polarization direction B and the compressive stress Pc.

Therefore, the positive charges generated on the outer main surfaces of the central portion 5a and the end portion 5b of the piezoelectric ceramic plate 5 are transmitted to the external extraction electrode 4 from the signal extraction electrode 6 while strengthening each other. . Further, at this time, a negative (-) charge is generated on the outer main surface of the central portion 5a of the piezoelectric ceramic plate 5 located on the inner side in the bending direction of the piezoelectric element 2 due to the relationship between the polarization direction C and the compressive stress Pc. Further, negative charges are also generated on the outer main surface at the end portion 5b due to the relationship between the polarization direction D and the tensile stress Pt, and these negative charges are transferred from the signal extraction electrode 6 to the external extraction electrode 4. Will be transmitted.

The piezoelectric element 2 is driven by the action of the acceleration G.
The reason why the stress generated in each of the piezoelectric ceramic plates 5 and 5 constituting the above is divided into "pull" and "compression" will be described.
First, when the acceleration G acts on the entire acceleration sensor 1, the acceleration G directly acts on the package 3 that fixes and supports the piezoelectric element 2. Try to move along the direction of action. However, even at this time, since the acceleration G does not act directly on the piezoelectric element 2, the piezoelectric element 2 tries to maintain the state before the acceleration G acts as it is. Acceleration G
The inertial force generated by the action of is applied.
Therefore, each piezoelectric ceramic plate 5, which constitutes the piezoelectric element 2,
Each of the end portions 5b and 5b of 5 tries to move together with the package 3, while each of the central portions 5a tries to remain in the initial position. As a result, the piezoelectric element 2 bends toward the acting side of the acceleration G. It is deformed to have a curved shape (upward convex shape in the figure). Therefore, as shown in FIG. 3, the tensile stress P is applied to the central portion 5a of the piezoelectric ceramic plate 5 located on the outer side in the bending direction (the upper side in the figure).
The compressive stress Pc appears at the end portion 5b of the piezoelectric ceramic plate 5, and the compressive stress Pc appears at the central portion 5a of the piezoelectric ceramic plate 5 located on the inner side (lower side in the drawing) of the bending direction.
In addition, the tensile stress Pt appears at c and at the end portion 5b.

The acceleration sensor 1 described in detail above is
As shown in FIGS. 4A and 4B, it is mounted on the printed circuit board 12 in a posture in which a required surface out of the four surfaces faces upward depending on the direction of the sensitivity axis required by design. . The orientation of the piezoelectric sensor 1 specifies the direction of the sensitivity axis. Even if the mounting is performed with any of the surfaces facing upward, there is no problem that the acceleration sensor 1 falls over in the process of soldering and the attitude changes. In addition,
In FIG. 4, 1a indicates the upper surface, 1b indicates the lower surface, 1c indicates the right side surface, 1d indicates the left side surface, and the direction of the sensitivity axis is as shown in FIG.
In the case of (a), they are arranged in a direction parallel to the printed circuit board 12 as indicated by an arrow, and in the case of FIG. 4 (b), they are arranged in a vertical direction.

In the mounting process of such an acceleration sensor 1, for example, a tape carrier 20 as shown in FIG. 5 is used. That is, the tape carrier 20 accommodates a plurality of the acceleration sensors 1 individually, and has an embossed tape 21 having substantially square recesses 23 that approximate the outer shape of the acceleration sensor 1 at predetermined intervals in the longitudinal direction. The embossed tape 21 is attached to the upper surface of the recess 23 and
And an upper tape 22 for closing the Then, all the acceleration sensors 1 are housed in the respective recesses 23 in a state in which the directions of their sensitivity axes are aligned in a certain direction as indicated by the arrows in the figure. That is, depending on the direction of the sensitivity axis of the acceleration sensor 1 when mounted on a printed circuit board or the like, for example, the left side surface 1d of the acceleration sensor 1 is attached to the tape carrier 20.
The accommodating attitude of the acceleration sensor 1 with respect to the recess 23 of the tape carrier 20 may be determined by, for example, positioning it in the opening of the recess 23.

With this configuration, the tape carrier 2
When the acceleration sensor 1 is mounted on a printed circuit board or the like using 0, the upper tape 22 of the tape carrier 20
It suffices to peel off, pick up the surface of the acceleration sensor 1 located in this opening from the opening of the recess 23 by a suction jig (not shown), take it out, and mount it on the required position of the printed circuit board.

It should be noted that the present invention is not limited to only the above embodiment, and various applications and modifications are conceivable.

(1) The present invention also has a cantilever structure in which the piezoelectric element 2 has a so-called unimorph type structure, and the piezoelectric element 2 is clamped and supported by the clamping components 8 and 9 only at one end, not at both ends in the longitudinal direction. Included in.

(2) In the above embodiment, the acceleration sensor is taken as an example, but a vibration sensor may be used.

(3) In the above embodiment, the external extraction electrode 4
Are formed on the end surface of the package 3 and the peripheral surfaces of both ends of the package 3 in the longitudinal direction, but those formed only on the end surface of the package 3 are also included in the present invention.

(4) As the piezoelectric element 2, the polarization direction A in each of the central portions 5a of the piezoelectric ceramic plate 5
The present invention also includes a configuration in which C and C are outwardly directed away from each other and polarization directions B and D at the end portions 5b and 5b are outwardly directed away from each other.

[0027]

According to the piezoelectric sensor of the present invention, even if the posture at the time of mounting on the printed circuit board is changed, the sensor is designed so that the user can always sit comfortably and stabilize, so that the printing can be performed according to the required direction of the sensitivity axis. The structure can be changed to various sensitivity axes simply by changing the attitude when mounting it on a substrate, so that it can be used as a plurality of types with different sensitivity axes even though it has a single structure. By increasing the versatility in this way, it is possible to significantly reduce the manufacturing cost and management cost of the piezoelectric sensor compared to the past,
Price reduction can be realized.

[Brief description of drawings]

FIG. 1 is a perspective view showing an acceleration sensor according to an embodiment of the present invention with a part thereof cut away.

FIG. 2 is an exploded perspective view of the acceleration sensor shown in FIG.

FIG. 3 is an explanatory view schematically showing a deformed state of a piezoelectric element when an acceleration acts.

FIG. 4 is an explanatory view showing a posture of the acceleration sensor of FIG. 1 when mounted on a printed circuit board.

5 is an explanatory diagram showing a tape carrier for the acceleration sensor of FIG. 1. FIG.

[Explanation of symbols]

 1 Acceleration Sensor 2 Piezoelectric Element 3 Package 4 External Extraction Electrode 5 Piezoelectric Ceramic Plate Constituting Piezoelectric Element 6 Signal Extraction Electrode of Piezoelectric Element 7 Intermediate Electrode of Piezoelectric Element 8,9 Clamping Components Comprising Package 10,11 Package Lid parts

Claims (2)

[Claims] 1. A piezoelectric sensor having a structure in which a piezoelectric element having a specific sensitivity axis is surrounded by a package, wherein the outer shape of the package is formed in a rectangular parallelepiped shape, and the longitudinal and lateral dimensional ratios of its end faces are substantially the same. The piezoelectric sensor is set to 1: 1 and an external lead electrode of the piezoelectric element is formed on at least the end face. 2. A piezoelectric sensor having a structure in which a piezoelectric element having a specific sensitivity axis is surrounded by a package, wherein the piezoelectric element is composed of a pair of strip-shaped piezoelectric ceramic plates bonded to each other vertically. However, two sandwiching parts for sandwiching at least one end portion along the longitudinal direction of the piezoelectric element from above and below to support the piezoelectric element in a bridge shape, and both left and right side surfaces of the piezoelectric element attached to both sides of the sandwiching part. The package is composed of two cover parts, and the package has an outer shape of a rectangular parallelepiped, and the end face has a vertical / horizontal dimension ratio of approximately 1: 1.
And the external lead electrode of the piezoelectric element is formed on at least the end face.