JPH02114800A - Piezoelectric diaphragm - Google Patents

Abstract

PURPOSE:To obtain a piezoelectric diaphragm with high connection reliability and less harmonic wave distortion by forming opposite electrodes between an electrode terminal at the rear face connected by a throughhole to one side and full electrode on the rear side. CONSTITUTION:A full face electrode 13 is formed to a side of a adhering face of a piezoelectric member 11, an electrode takeout terminal 15 of an adhering face surrounded by an electrode non forming part 14 at an open face side opposite to the adhering face and an opposite electrode 16 to the electrode on the adhering face and a throughhole 17 are formed. Then a conventional insulating adhesives is adopted for adhering the piezoelectric member to a support plate thereby forming the diaphragm without no generation of distortion of the diaphragm and with less generation of a harmonic wave in the case of using the diaphragm as a sounding body is obtained. Furthermore, the connection with a lead wire obtained in this way is implemented by soldering or bonding or the like, the reliability of the connection is high and it is possible for the connection by wire bonding even with a small size of 0.5mm or so in the throughhole forming part, then the reliability is not deteriorated.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a piezoelectric diaphragm, and more particularly to a piezoelectric diaphragm that reduces harmonics, which are distortion components of a sounding body, by a diaphragm to which a piezoelectric material and a support plate are attached. This invention relates to an electrode connection method.

(Prior art) A piezoelectric diaphragm obtained by pasting a piezoelectric material on which electrodes are formed on a support plate is made by applying an alternating voltage to the piezoelectric body, which causes the piezoelectric body to expand and contract in the plane direction. Since one surface of the piezoelectric material is fixed, expansion and contraction of the piezoelectric material causes warping in the vertical direction about the bonded surface of the support plate. Therefore, if the outer circumferential portion of the support plate is fixed, the center portion will be displaced up and down due to this warp, resulting in a vibrator that vibrates at the frequency of the applied alternating voltage.

If a signal with a frequency of several kHz is applied to such a diaphragm,
This vibration creates a compressional wave in the air, which becomes a sounding body that produces sound, and has been put into practical use as piezoelectric buzzers and piezoelectric speakers.

This type of piezoelectric diaphragm can be made piezoelectric by applying an electric field between electrodes formed on the piezoelectric material to polarize it (sometimes polarization is done before bonding), and then applying an alternating voltage that does not destroy the polarization. The material expands and contracts, and this results in flexural vibration due to the bonding relationship with the support plate. Therefore, an electrode connection for applying an electric field to a counter electrode formed on the piezoelectric material is necessary in any case.

Conventionally, the electrode connection of the counter electrode formed on this piezoelectric material was
On the non-adhesive side, it is possible to solder the Riet wire as is, but the electrode on the adhesive side cannot be directly connected, so the following two steps are required.
Two methods are used.

First, since the support plate is made of metal, the surface of the support plate is made rough (the surface is roughened by chemical treatment), and a normal insulating adhesive is applied to this. There is a method of crimping a piezoelectric material on which electrodes are formed. In this case, even if the adhesive is an insulating adhesive, the surface of the metal plate is rough, so it breaks through the insulating adhesive layer and connects to the piezoelectric electrode. By connecting the lead wire to the support plate, the adhesive side can be connected.

The second method is to use a conductive adhesive, connect the electrode on the adhesive side of the piezoelectric material to the support plate using the conductivity of this adhesive, and then support the piezoelectric material in the same way as in the first method. Connection on the adhesive side is obtained by connecting lead wires to the plate.

(Problem to be solved by the invention) In this way, in conventional piezoelectric diaphragms, the electrodes on the adhesive side are connected in two ways. The crimping method increases the reliability of this connection when the area of the diaphragm (contact area of the piezoelectric material) is large, but the reliability of the connection becomes high for small diaphragms where the diameter of the piezoelectric material is less than 1.0 mm. performance is greatly reduced.

In addition, in order to lower the frequency of the diaphragm, a piezoelectric material of 1100p was used.
It is necessary to reduce the thickness to below, but in this case there is a high risk of defects due to cracks in the piezoelectric material due to pressure bonding.

On the other hand, in the latter method using a conductive adhesive, the type of adhesive is limited. Additionally, depending on the curing conditions of the adhesive, the temperature must be raised, and as a result, due to the difference in thermal expansion coefficients between the piezoelectric ceramic and the support plate, distortion may occur in the support plate when the temperature is returned to room temperature after curing. Put it away. In this way, when the counter electrode formed on the piezoelectric material is taken out, there is a problem in the connection on the adhesive surface side.

(Means for solving the problem) That is, in a piezoelectric diaphragm obtained by pasting a piezoelectric material on a support plate, the electrode of the piezoelectric material is a full-surface electrode on the adhesive surface side,
The side opposite to the adhesive side is divided into two partial electrodes, a center part and a peripheral part, and the partial electrode in the center part and the adhesive side electrode are connected through holes, and electrodes are formed on both sides. In a piezoelectric diaphragm with a structure in which a piezoelectric material is attached to a support plate, a through hole is formed in the support plate.
The structure is such that a conductive material is embedded in the through hole so as to be connected to the electrode on the support plate side among the electrodes.

(Function) In the present invention, electrode paste is printed on the green sheet before sintering to form electrodes of the piezoelectric material to be attached to the support plate. A hole for through-hole connection is drilled in the central position of the green sheet, and there is a partial electrode surrounded by a non-electrode part in the hole part of the green sheet, and the outside of this non-electrode part is the back side. By making the back surface a full electrode, the electrode paste is filled into the hole of the through hole, and the through hole connection is completed. The green sheet obtained in this way is processed into a desired external shape and fired to form an electrode terminal on the back side connected to one side with a through hole.
The piezoelectric material is formed with an electrode facing the entire surface electrode on the back surface, and electrode connection is possible on only one surface. Therefore, it is possible to use an adhesive that can be cured at room temperature for adhesion to the support plate, resulting in a piezoelectric diaphragm with high connection reliability and low harmonic distortion.

In addition, by forming a small hole in the surface of the support plate to which the piezoelectric material is attached, and after adhering the piezoelectric material on which the electrode is formed to the support plate, filling the small hole with conductive paste, A portion of the electrode formed on the piezoelectric material can be connected to the support plate.

In this way, in the first structure, electrode connections can be made only on the open surface of the piezoelectric material pasted on the support plate, and in the second structure, a small hole is made in the support plate and the bonding is done through this small hole. The feature is that a part of the electrode of the piezoelectric material is connected.

(Example) Hereinafter, the piezoelectric diaphragm of the present invention will be explained with reference to the illustrated example.

FIG. 1 shows the structure of a piezoelectric diaphragm showing an embodiment of the present invention, in which a piezoelectric material 11 is bonded to a support plate 12.
At this time, the entire surface electrode 13 is formed on the adhesive surface side of the piezoelectric material 11, and on the open surface side opposite to the adhesive surface,
There is an electrode extraction terminal 15 on the adhesive surface surrounded by the electrode-free portion 14, and furthermore, an electrode 16 facing the electrode on the adhesive surface is formed around the electrode-free portion 14. Further, an electrode terminal 15 on the adhesive surface of the piezoelectric material 11
A through hole 17 is formed in the portion.

With this configuration, electrode leads added for polarization and drive can be connected only through the open surface of the diaphragm. As a result, when bonding the piezoelectric material to the support plate, it is possible to use a normal insulating adhesive, and it is also possible to use an anaerobic adhesive that can be cured at room temperature. Therefore, there is no distortion of the diaphragm caused by this, and the diaphragm can generate less harmonics even when used as a sounding body.

Furthermore, the connection with the lead wires obtained at this time is made by soldering or bonding, so the connection reliability is high, and even if the diameter of the diaphragm is small, the through-hole forming part is 0. Since connection by wire bonding is possible even with a thickness of about .5 mm, reliability does not deteriorate.

FIG. 2 shows the configuration of a piezoelectric diaphragm according to another invention.
The piezoelectric material 21 is adhered to the support plate 22, but at this time, a small hole 23 is formed in the adhesive surface of the support plate 22, and a conductive paste 24 is embedded in this hole. There is. With this configuration, the electrode 25 on the adhesive side is transmitted to the support plate 22 via the conductive paste 24, so the electrode 25 on the adhesive side can be connected by soldering the lead wire 26 to the support plate 22. The electrode 27 on the open surface side is obtained by directly soldering the lead wire 28. In this case as well, the piezoelectric material 21 can be bonded to the support plate 22 using an ordinary insulating adhesive, and an anaerobic adhesive that can be cured at room temperature can be used, so the thermal expansion coefficient There is no distortion of the diaphragm due to differences in the diaphragm, and the diaphragm can generate less harmonics even when used as a sounding body. In addition, in this method, even if the diameter of the piezoelectric material becomes smaller due to the smaller diameter of the diaphragm, the electrodes 25 and 27 formed on the piezoelectric material can be made of full-surface electrodes on either side. The area where the piezoelectric material is formed becomes maximum, and the displacement (expansion and contraction in the plane direction) of the piezoelectric material becomes maximum. As a result, the sound pressure level can also become high.

FIG. 3 shows the configuration of a piezoelectric diaphragm showing yet another embodiment, in which a piezoelectric material 31 is bonded to a support plate 32.
At this time, the support plate 32 is an insulating substrate on which lead-out electrode patterns 33 and 34 are formed, and small holes 35 are formed in the plane of this adhesive surface and in accordance with the positions of the electrode patterns 33 and 34. A conductive paste 36 is embedded in the hole. On the other hand, the piezoelectric material has a full-surface electrode 37 formed on the open surface side,
On the adhesive surface side, there is an electrode connection terminal 39 on the open surface side surrounded by a non-electrode portion 38, and an electrode 40 opposite to the electrode on the open surface side is formed around the non-electrode portion 38. . Furthermore, a through hole 41 is formed in the portion of the electrode connection terminal 39 on the open surface side.

With this configuration, the electrode leads 42 added for polarization and driving can be soldered to the lead-out electrode patterns 33 and 34 formed on the support plate 32. As a result, it is the electrical material 31 that adheres the piezoelectric material to the support plate.
For adhesion, ordinary insulating adhesive can be used,
Since it is possible to use an anaerobic adhesive that can be cured at room temperature, there is no distortion of the diaphragm due to differences in thermal expansion coefficients, and the diaphragm can generate less harmonics when used as a sounding body. . In addition, in this method, if the lead-out electrode patterns 33 and 34 formed on the support plate are formed up to the peripheral fixed part, there is no need to connect thin lead wires and relay connections with the outside using the fixed body. The number of components for the diaphragm is reduced. As a result, the reliability of the diaphragm is greatly improved.

The piezoelectric material attached to the groove-formed support plate used here is magnesium lead niobate Pb (Mgl/3 Nb
2/3) Powder of an electrostrictive material containing 03 as a main component is dispersed in a solvent together with an organic binder to form a slanow shape. This is made into a piezoelectric material green sheet having a uniform thickness of about 40 to 1100 p by a slip casting method using a doctor blade. Next, this piezoelectric material green sheet is punched out to a specified size, and holes for through-hole connections for pulling up the electrodes on the adhesive side to the front side are formed using a punch and a die. Next, electrode paste is printed on both sides of the piezoelectric green sheet with holes made using a screen printer. At this time, the side that will be bonded has a full electrode, and the opposite side, the front side, has a through-hole electrode paste. The electrode pattern has a part of the terminal pattern connected to the hole part. Furthermore, the piezoelectric material green sheet on which this electrode pattern is printed is set in a press mold, heated at a temperature of around 1008 C, and a pressure of approximately 250 kg/cm is applied to obtain a piezoelectric material green sheet with increased density.

Next, after cutting the pressed piezoelectric green sheet into predetermined dimensions, the organic matter present in the ceramic green sheet is slowly heated in an oxidizing atmosphere in a binder removal step to decompose and eliminate it. Normally, these organic substances are completely decomposed and oxidized by 500°C to 600°C, but if the temperature is suddenly raised to the decomposition temperature, the piezoelectric material will be damaged, so the temperature should be increased for 25°C or more slowly. Raise the temperature at a heating rate of 500°C to 600°
By holding the sample in C for a sufficiently long time, the organic matter will completely disappear. Thereafter, by firing at a temperature of 900° C. to 1200° C., a piezoelectric material flat plate to be attached to the support plate described in the above explanation is obtained.

Note that the piezoelectric diaphragm shown in the examples is the same as the piezoelectric diaphragm shown in the first example of the unimorph structure formed on one side of the support plate.
In this embodiment, a bimorph structure in which piezoelectric materials with electrodes formed on both sides of a support plate are bonded can be easily constructed, and in the second or third embodiment, a plurality of piezoelectric materials can be bonded on one support plate. It is also effective when forming a composite piezoelectric diaphragm. In particular, in the third embodiment, the pattern of the support plate allows electrode connections between multiple piezoelectric materials, and the configuration of vibrators with different characteristics allows a composite piezoelectric diaphragm to be formed. easily obtained. Furthermore, although the support plates shown in these examples are simply shown as flat plates, Japanese Patent Applications No. 62-188194 and No.
It is clear that it is also effective as an electrode connection for a piezoelectric sounding body with a wide band, low distortion, and high sound pressure by supporting the grooves in the peripheral part and forming grooves in the adhesive part as shown in FIG. Furthermore, although the piezoelectric material shown was obtained using a green sheet method, we also created a composite piezoelectric material in which powdered piezoelectric ceramics were mixed with epoxy resin, etc., and electrodes were formed by exposing both end faces of the piezoelectric material. It can also be used to connect electrodes, and is not limited to the shape and type of piezoelectric material. In addition, in the third embodiment, electrode connections are made by forming a lead-out electrode pattern on the support plate, but this lead-out electrode pattern is formed in a manner that is equal to the external shape of the diaphragm, so that vibration can be improved. It is well known from the design of diaphragms that the distortion of the plate is reduced. Furthermore, bimorphs made of two or more laminated layers also have through holes formed in the laminated body, making it possible to draw out these electrodes to the open surface or support plate side.

(Effects of the Invention) As is clear from the above explanation, according to the piezoelectric diaphragm of the present invention, an insulating adhesive can be used to bond the piezoelectric material to the support plate, and an anaerobic adhesive that can be cured at room temperature can be used. Since it is possible to use a diaphragm adhesive, distortion of the diaphragm does not occur due to differences in thermal expansion coefficients, and even when used as a sounding body, the diaphragm can generate less harmonics. In addition, since the electrodes formed on the piezoelectric material and the external lead wires are securely connected by soldering or wire bonding, the reliability of the connection will not deteriorate even when the diameter of the diaphragm becomes smaller. do not have.

[Brief explanation of drawings]

1, 2, and 3 are cross-sectional structural views showing a method of connecting electrodes of a piezoelectric diaphragm according to an embodiment of the present invention. In the figure, 11... Piezoelectric material, 12... Support plate, 13... Electrode on adhesive surface side, 14... Portion where electrode is not formed, 15... Electrode connection terminal on adhesive surface side, 16.・・Counter electrode to adhesive side, 17・Through hole, 21・Piezoelectric material, 22・・
・Support plate, 23...hole, 24...conductive paste 25
...Adhesive surface side electrode, 2610, electrode lead, 27.
... Opposite electrode to adhesive side, 28 ... Electrode lead, 3
1... Piezoelectric material, 31... Insulating support plate, 33...
・Takeout electrode pattern, 34... Takeout electrode pattern, 35... Through hole, 36... Conductive paste, 3
7... Electrode on the open surface side, 38... Portion where no electrode is formed,
39... Electrode connection terminal on the open surface side, 40... Opposite electrode to the open surface side, 41... Through hole, 42... Electrode lead.

Claims (2)

[Claims] 1. In a piezoelectric diaphragm that has a structure in which a piezoelectric material with electrodes formed on both sides is attached to a support plate, the electrode of the piezoelectric material is a full-surface electrode on the adhesive side, and the electrode on the opposite side to the adhesive side is a central part and the surrounding area. A piezoelectric diaphragm characterized in that it is divided into two partial electrodes, and the central partial electrode and the adhesive surface side electrode are connected through holes. 2. In a piezoelectric diaphragm having a structure in which a piezoelectric material with electrodes formed on both sides is attached to a support plate, a through hole is formed in the support plate, and the electrode on the support plate side of the electrodes and the through hole are formed in the support plate. A piezoelectric diaphragm characterized by having a conductive material embedded therein for connection.