JPH06334233A - Piezoelectric element assembly and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a low price piezoelectric element having enhanced dielectric characteristics, moisture resistance, and electromigration resistance. CONSTITUTION:The piezoelectric element assembly comprises a piezoelectric element 1 displaceable upon application of voltage, and a case for holding the piezoelectric element 1 in substantially enclosed state, wherein the case is formed thinner at one end face thereof in the displacing direction of the piezoelectric element as compared with the other end face. The piezoelectric element 1 is inserted from the open end of the case having the other closed end and held in substantially enclosed state by plastic molding simultaneously with assembling thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric element, and more particularly to a piezoelectric element having improved humidity resistance and improved reliability at low cost.

[0002]

2. Description of the Related Art A laminated piezoelectric element, which is a laminated body formed by laminating a plurality of thin plate-shaped or film-shaped piezoelectric materials with internal electrodes interposed therebetween, is known as a piezoelectric element with large displacement and high reliability ( (See JP-A-58-196074). However, this element has a serious defect that electromigration occurs due to the intrusion of water and the insulation resistance sharply decreases, resulting in a short circuit between different electrodes. Therefore, there is known a piezoelectric element assembly in which the piezoelectric element is sealed in a metal can to improve the moisture resistance (see Japanese Patent Laid-Open No. 1-146379). In this piezoelectric element assembly, one end of a cylinder whose both ends are open is covered with a lid member, the piezoelectric element is fixed to the lid member with an adhesive, and the other end is sealed with a terminal member, and the lead of the piezoelectric element is also sealed. It has a structure for drawing out a line.

[0003]

However, even a piezoelectric element assembly sealed in a metal can has severe environmental conditions (for example,
At 85 ° C. and 90% RH), its moisture resistance is not sufficient. It is considered that this is because outgas from the adhesive used inside the tube (gas generated from the organic material of the adhesive by heating) contaminates the electrodes of the piezoelectric element and accelerates electromigration. There is also a problem that the assembling property is poor and the cost is high. This is because the cylinder, the lid member, and the terminal member are separate parts, and therefore a process such as bonding is essential. Further, as a fatal problem of the piezoelectric element assembly, there is a problem that the displacement generated in the piezoelectric element is almost absorbed by the terminal member, and the displacement that can be taken out to the outside is reduced. This is a problem peculiar to a piezoelectric element assembly that is fundamentally different from other hermetically sealed electronic components. Therefore, it is an object of the present invention to provide a piezoelectric element assembly which has a significantly improved moisture resistance at a low cost.

[0004]

According to the present invention, a piezoelectric element is inserted from an open end of a case whose one end is closed and the other end is opened, and at the same time as the piezoelectric element is assembled by plastic working, it is substantially integrated. A method of manufacturing a piezoelectric element assembly, characterized in that the piezoelectric element assembly is held in a sealed state. In the present invention, the case in which one end is closed and the other end is opened can be obtained by cutting, but the cost can be significantly reduced by using plastic working (extrusion, drawing, bulging, rotary forming, etc.). Further, a feature of the present invention is that the piezoelectric element is held in a substantially sealed state at the same time as it is assembled by plastic working. At this time, the air inside the case is discharged to the outside together with plastic working such as extrusion. Alternatively, evacuation is more efficient if the outside is kept in a reduced pressure atmosphere. The material of the case used in the present invention may be any material as long as it can hold the piezoelectric element in a substantially sealed state, such as a metal material and a polymer material. However, particularly when a metal material is used, the piezoelectric element assembly is When it is operated, it has good elastic properties and good plastic workability. As the metal material, any material such as aluminum or its alloy can be used depending on the application, but a good piezoelectric element assembly can be obtained by using a Cu—Cr alloy or the like due to the elastic characteristics and solderability of the piezoelectric element assembly. Further, in the present invention, if plastic working is also used for manufacturing the case, it is easy to process bellows, bellows, etc., so that a piezoelectric element assembly that does not hinder displacement can be obtained at low cost. Furthermore, by performing plastic working such as coining on the operating end face that acts as an actuator of the piezoelectric element assembly, it is possible to keep the operating end face thin while maintaining sufficient mechanical strength. Since the present invention employs a manufacturing method different from the conventional one as described above, it can be easily integrated without the need of using an adhesive, so that there is no adverse effect of outgas from the adhesive even under high temperature and high humidity. The moisture resistance can also be improved. The manufacturing method of the present invention is characterized by adopting plastic working as described above, but when viewed as a piezoelectric element assembly, the manufacturing method is not necessarily limited to the above-described manufacturing method.
That is, the present invention also provides a piezoelectric element assembly including a piezoelectric element that is displaced by application of a voltage and a case that holds the piezoelectric element in a substantially sealed state, and at least one of the cases in the displacement direction of the piezoelectric element. The piezoelectric element assembly is characterized in that the thickness ratio between the end face (operating end face) and the other end face is less than 1. In the present invention, the reason why at least one end face of the case is limited to be less than 1 of the thickness of the other end face is that when the thickness of the other end face is 1 or more, the binding force of the other end face to the operating end face is large and the spring is This is because the property is poor and the displacement characteristics of the piezoelectric element assembly are impaired. In the present invention, at least one end surface (operating end surface) of the case is preferably 0.2 to 0.8 of the thickness of the other end surface, and more preferably 0.3 to 0.7. . The structure of the case is important in the present invention. For example, in the structure shown in FIG. 1, the thickness of the end face 7 that comes into contact with the displaced member is smaller than that of the case 3 as described above to provide spring properties. If a concave circumferential groove is formed in the end part by coining in advance, it will function as a spring there when the piezoelectric element assembly is displaced and can transmit the displacement more efficiently, and also expect a rigid body effect. Therefore, the rigidity can be maintained even if the wall thickness is thin. Therefore, there is no problem that the end surface 7 is deformed by an external force. The case according to the present invention can be easily formed into a shape satisfying a predetermined thickness relationship by deep drawing. In addition, the DI (
Drawing and Ironing) By using drawing, not only the case processing but also the piezoelectric element assembly can be integrally molded. In the case of DI drawing, good airtightness can be easily mass-produced as in the case of DI drawn can beer. Also, without using any adhesive agent, if the laminated piezoelectric element is simply brought into contact with the force transmission plate 4 etc. without using any adhesive agent and subjected to plastic processing such as DI processing, the adhesive agent will be used at all. It is possible to assemble without doing.

The structure and operation of the piezoelectric element assembly according to the present invention will be described with reference to FIG. From the piezoelectric laminate 1 + and-
Lead wires (5a and 5b, respectively) of the above-mentioned penetrate through the piezoelectric element mounting base 2 and are drawn out. The piezoelectric element 1 is displaced by applying a voltage between the two lead wires. At this time,
Then, in the piezoelectric vertical effect element using the piezoelectric coefficient D ₃₃ , the operating end surface is parallel to the stacking direction, but when the piezoelectric lateral effect element using the piezoelectric coefficient D ₃₁ is used, the operating end surface is in the stacking direction. Cross at right angles. The displacement of the piezoelectric element 1 may be brought into direct contact with the operating end surface of the case 3, or may be via the force transmission plate 4.
In FIG. 1, the ring-shaped groove 6 and the flat portion 7 are formed by coining on the working end surface of the case. The former has a function of improving the mechanical strength of the working end surface of the case 3, and the latter has a piezoelectric element. This is to have a function of making surface contact with the corresponding pressure receiving surface of the assembly that receives the displacement. In FIG. 1, an adhesive is not used between the end face 7 and the force transmitting plate 4 that is brought into contact with the piezoelectric element, and the end face 7 is simply brought into contact with the end face 7 or the circumference of the end portion 7 provided near the center in the circumferential direction. If a circumferential groove corresponding to the force transmitting plate 4 is provided in accordance with the groove 6 in the shape, it is possible to assemble without using an adhesive at all for positioning. Force transmission plate 4 in FIG.
Although the cut-out member is shown as, the metal member can be hollow and lightweight. In the present invention, the adhesive is not used at all, the so-called integral firing type is also used as the laminated piezoelectric element, and the piezoelectric element 1 is mounted on the piezoelectric element mounting base 2 having the through hole for taking out the lead wire. After the force transmission member 4 is placed, the case 3 is covered and the open end is caulked in the recess provided in the piezoelectric element mounting base to seal the piezoelectric element 1. At this time, the air remaining inside the piezoelectric element 1 and the case 3 is exhausted from the lead wire take-out hole of the piezoelectric element mounting base 2, so that the compression force of the residual air in the caulking hinders the caulking process. Nor. After that, the lead wire take-out hole is closed by brazing or the like. Alternatively, instead of caulking, the opening end of the case 3 may be fitted in a circumferential groove provided in the mounting base 2 in advance by the spring force of the case 3 itself. In this case, since there is no need for caulking, there is an advantage that no special machine is required. As mentioned above, D
If the I drawing process is used, not only the case can be formed but also the caulking process can be performed at the same time, resulting in excellent mass productivity. Case 3 in Figure 1
Shows the case of a single layer, but of course, a double structure can be used if necessary. In this case, the humidity resistance of the piezoelectric element is significantly improved. Further, dry air or an inert gas may be enclosed in the case 3. Also, these gases may be pressurized and sealed. Alternatively, by enclosing a desiccant or incorporating a PTC heater or the like, the moisture resistance can be secured even if dew condensation should occur. In the present invention, the case 3 can be used not only with metal such as aluminum, stainless steel, and Kovar, but also with plastic or paper. Alternatively, a composite material in which plastic is lined inside and outside of metal may be used. It can be easily formed by using plastic working, and bellows and bellows shapes can be easily produced. Furthermore, if plastic working is used in the assembly process, a piezoelectric element assembly with excellent productivity can be obtained.

[0006]

EXAMPLE 1 An example of the present invention will be described in detail below with reference to FIG. First, the manufacturing method of the piezoelectric element 1 will be outlined. That is, Pb (Zr, Ti)
A small amount of an organic binder is added to a pre-calcined powder of a piezoelectric material containing O ₃ as a main component, and a slurry is prepared by dispersing this in an organic solvent, and the slurry is prepared to have a predetermined thickness (for example, 100 μm) by a doctor blade method. To form a piezoelectric body. An internal electrode is formed by screen-printing Pd paste on the entire surface of the piezoelectric body. A predetermined number (for example, 100) of piezoelectric bodies on which the internal electrodes are formed are laminated, integrated by hot pressing, and then sintered at about 1250 ° C. to obtain a piezoelectric laminate including the piezoelectric bodies and the internal electrodes. To be This piezoelectric body is cut into a required size (5 mm × 5 mm), an insulating material layer is formed on the two side surfaces over the entire area in the stacking direction, and then a part of the insulating material layer on one side surface is alternated. The internal electrodes are exposed by cutting with a dicing saw. Next, a part of the insulating material layer on the other side surface is exposed in every other layer by cutting with a dicing saw to expose the internal electrodes which have not been exposed previously. Next, a silver paste is applied so as to reach the ends of the internal electrodes exposed on both sides and to be electrically connected to form a conductive material layer to form external electrodes. As a result, the external electrodes are connected to the internal electrodes every other layer. Next, the outer electrode has an outer diameter of 0.
Solder the 4 mm lead wires 5a and 5b and pull them out. The piezoelectric element 1 thus obtained is placed on the piezoelectric element mount 2 made of Kovar. At this time, the piezoelectric element mounting base 2 has two holes for taking out lead wires and an outer diameter of 0.
Form and set to 5 mm. On the other hand, the lead wires 5a and 5b are coated with Teflon. Piezoelectric element 1 to piezoelectric element mounting base 2
Then, the force transmitting member 4 is placed, and then the case 3 is covered and the open end is caulked by the recess provided in the piezoelectric element mounting base, whereby the piezoelectric element 1 is sealed. At this time, since the air remaining inside the piezoelectric element 1 and the case 3 is exhausted from the lead wire take-out hole of the piezoelectric element mounting base 2, the caulking work may be hindered by the compressive force of the residual air in the caulking. Absent. After that, sealing glass 8
A and 8b are partially melted by a laser and sealed. At this time, it is more preferable to depressurize the working atmosphere with an inert gas. (Comparative Example) As a comparative example, the same component as that used in Example 1 was prepared and bonded with an epoxy resin as conventionally done. Fifty piezoelectric element assemblies prepared as described above were prepared at 85 ° C, 90%
A durability test was conducted by applying a DC voltage of 150 V in an RH atmosphere. Table 1 shows the relationship between the test time and the cumulative defective rate.

[Table 1]

(Embodiment 2) As shown in FIG. 2, the piezoelectric element 1 was placed on the piezoelectric body mounting base 2 without forming a hole, and a sphere was used as the force transmitting member 4. Accordingly, even if the displacement direction of the piezoelectric element 1 is not orthogonal to the operating end face of the case and is slightly displaced due to the assembly accuracy, the component force orthogonal to the sphere is effectively transmitted to the operating end face of the case. In addition,
A hemisphere may be used instead of a sphere. Further, in this embodiment, since the bellows is provided on the side surface orthogonal to the operation end surface as the case by the rotary swaging process, the displacement of the piezoelectric element 1 can be largely prevented from being displaced by the case, and a large displacement can be taken out. Can be done. The lead wires 5a and 5b were taken out in a direction orthogonal to the operating direction of the piezoelectric element assembly. As a result, a piezoelectric element assembly that is thin in the operating direction can be obtained. In addition, the lead wire 5
It is preferable to provide some stress relief inside the case 3 so that the solder does not peel off due to the displacement of the piezoelectric element 1 on a and 5b. Also, in this embodiment, case 3
Since a part 7 of the above is provided in a hemispherical shape, if the driven side is formed into a pair of hemispherical concave portions, the direction deviation of force transmission due to some mounting error can be absorbed. As shown in FIG. 2, a plate member 10 having a recess corresponding to the hemispherical protrusion 7 may be provided on the driven side. In that case, the driving force is transmitted more smoothly.

[0008]

As described above, according to the present invention, it is possible to obtain a piezoelectric element having improved insulation characteristics and improved moisture resistance and electromigration resistance.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a piezoelectric element according to the present invention.

FIG. 2 is a diagram showing another embodiment of the piezoelectric element according to the present invention.

[Explanation of symbols]

 1 Piezoelectric element 3 Case

Claims (3)

[Claims] 1. A piezoelectric element which is displaced by application of a voltage,
In a piezoelectric element assembly including a case that holds the piezoelectric element in a substantially sealed state, at least one end surface of the case in the displacement direction of the piezoelectric element extends integrally and is thinner than the other surface plate thickness and has a large elastic coefficient. A piezoelectric element assembly characterized by: 2. A piezoelectric element, characterized in that a piezoelectric element is inserted from an open end of a case whose one end is closed and the other end is opened, and the piezoelectric element is held in a substantially sealed state at the same time as it is assembled by plastic working. Manufacturing method of element assembly. 3. The method for manufacturing a piezoelectric element assembly according to claim 2, wherein the plastic working is any one of deep drawing, bulging, drawing and extruding.