JPH098377A - Production of piezoelectric transformer - Google Patents

Abstract

PURPOSE: To obtain a method for producing a piezoelectric transformer in which mechanical strength of individual piezoelectric ceramic element is enhanced while decreasing the number of production steps. CONSTITUTION: A press die K is filled with ceramic powder (PZT) which then pressed by means of upper and lower punches K1, K2. The press die K is constructed to produce beveled piezoelectric ceramic elements individually. The press molding is fired in the following step at a predetermined temperature for a predetermined time thus producing a sintered ceramic. In order to remove contamination caused at the time of sintering, the sintered piezoelectric ceramic element is subjected to abrasive polishing in a polishing step. Input electrodes are formed on the surface and rear at a drive section defined with respect to the longitudinally central part of the piezoelectric ceramic element and polarization is carried out in the direction of thickness using the surface and rear electrodes. An output electrode is formed on the longitudinal end face at power generating section and polarization is carried out in the longitudinal direction between respective electrodes at the drive section using the output electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer for transforming an AC voltage in electronic equipment and the like.

[0002]

2. Description of the Related Art Piezoelectric transformers have the following advantages.
(2) In response to a short circuit accident on the output side, the input resistance is automatically increased, and there is no danger of burning or the like. (3) The boost ratio can be increased. (4) No electromagnetic induction. And the like, and development for practical use has been advanced in recent years.

As a typical piezoelectric transformer, there is a Rosen type piezoelectric transformer, which uses a rectangular plate-shaped piezoelectric ceramic element, and a pair of input electrodes in the thickness direction is formed on one half of the longitudinal main surface of the element. And an output electrode is formed on the end face of the other half. The former is polarized in the thickness direction, and the latter is polarized in the longitudinal direction. In general, the portion where the input electrode is formed in the thickness direction is called a driving portion, and the other half where the output electrode is formed is called a power generation portion. When an AC voltage is applied to the driving portion of the piezoelectric ceramic element having the electrodes formed through the lead wire, strong mechanical vibration of all wavelength vibration called, for example, λ mode occurs as a whole. A vibration node region appears during excitation, and the support is attached to this vibration node region in order to reduce mechanical vibration damping. The lead wire is also attached to the node area on the input electrode side by a conductive bonding material such as solder. As a result, a high AC voltage can be obtained by the piezoelectric effect at the output electrode of the power generation section, and this is taken out by the lead wire soldered to this output electrode.

When the piezoelectric transformer is driven, strong vibration is excited with a relatively large amplitude as described above. Therefore, a piezoelectric ceramic element having good vibration resistance capable of withstanding this mechanical vibration is required. In order to obtain a piezoelectric ceramic element having good vibration resistance in this way, the edges of the piezoelectric ceramic element are chamfered or rounded so that the surface of the piezoelectric ceramic element can be cracked or chipped as little as possible. Is coming.

Conventionally, such a piezoelectric ceramic element for a piezoelectric transformer has been manufactured in the order shown in FIG. That is, a powder for a piezoelectric ceramic is formed into one large wafer by press molding, baked at a predetermined temperature, the surface is polished, and then cut into individual piezoelectric ceramic element shapes and sizes. Was there. Then, after that, chamfering is performed for each piezoelectric ceramic element to form necessary input / output electrodes to obtain a piezoelectric transformer.

[0006]

In such a manufacturing method, since a plurality of piezoelectric ceramic elements can be obtained from one large wafer, the manufacturing efficiency can be improved in this respect. However, there is a problem in that the number of subsequent processing steps is increased in order to obtain the chamfered individual piezoelectric ceramic elements, and the number of manufacturing steps is increased as a whole. In addition, in each process up to chamfering, there are many opportunities for damage accidents such as cracking or chipping of ridges, and this damage sometimes penetrates deep into the piezoelectric ceramic element as secondary cracks. The damage could not be completely removed even by the chamfering process. Further, since one large wafer is press-molded, the pressure is less likely to be uniformly applied to the press-molded body during press-molding, causing uneven density, voids and pinholes in the sintered body after firing. It was. In such a case, there is a problem that the mechanical strength of each piezoelectric ceramic element decreases.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for manufacturing a piezoelectric transformer that requires a small number of manufacturing steps and enhances the mechanical strength of each piezoelectric ceramic element. To do.

[0007]

In order to solve the above problems, a method of manufacturing a piezoelectric transformer according to a first aspect is a method of manufacturing a plate-shaped piezoelectric transformer having chamfered ridge angles, which is used for a piezoelectric transformer. Using a die corresponding to the chamfered shape of the piezoelectric ceramic element, a step of press-molding the powder for piezoelectric ceramic into a predetermined shape of each piezoelectric ceramic element, and firing the press-molded piezoelectric ceramic element at a predetermined temperature. The firing step, the step of polishing the surface of the fired piezoelectric ceramic element to remove the strain on the surface, and the step of forming predetermined input / output electrodes on the polished piezoelectric ceramic element.

[0008]

According to the present invention, a die corresponding to the chamfered shape of the piezoelectric ceramic element used for the piezoelectric transformer is used to press-mold the piezoelectric ceramic powder into a predetermined shape of the piezoelectric ceramic element, and then fires this. Since the structure is such that polishing is performed and the piezoelectric ceramic elements having chamfered ridge angles are formed into individual shapes before firing, the number of manufacturing steps as a whole is reduced. Further, the ridge angle is not damaged during the manufacturing process. Furthermore, since the piezoelectric ceramic powder is press-molded for each individual piezoelectric ceramic element, the pressing area is reduced, resulting in uneven density, voids, and
Generation of pinholes is reduced.

FIGS. 3 (a) and 3 (b) are S-substituting drawings showing the internal crystal structures of the element after firing of the conventional product and the product of the present invention, respectively.
It is an EM photograph. PZT (lead zirconate titanate) was used as the ceramic material in both the conventional product and the present invention. The conventional product is press-molded into a size of 100 mm × 75 mm in outer diameter and 4 mm in thickness, and the product of the present invention is formed by press-molding in a size of 60 mm × 10 mm in outer diameter and 3 mm in thickness, respectively. The pressing pressure is 1.2 t / cm ₂ . From these photographs, it can be understood that the product of the present invention has significantly reduced voids and pinholes as compared with the conventional product. The thickness of the conventional product is 4 mm with respect to the thickness of the product of the present invention, but this is because the large area of the wafer increases the warpage of the entire fired plate, and in the polishing process in the next step, This is a setting for eliminating such a warped portion by increasing the polishing amount.

The densities of the sintered bodies of the conventional product and the product of the present invention were measured and the results were as follows.

[Table 1] From this table, it can be understood that the product of the present invention has fewer voids and pinholes than the conventional product.

[0011]

Embodiments of the present invention will be described with reference to the drawings. An embodiment according to the present invention will be described by taking a method of manufacturing a Rosen type piezoelectric transformer as an example. 1A and 1B are views showing the manufacturing process of the piezoelectric transformer, in which the left side is a side view and the right side is a plan view. FIG. 2 is a perspective view of a chamfered Rosen type piezoelectric transformer. 3A and 3B are SEM photographs of the conventional product and the product of the present invention, which are microscopically captured cross-sections after firing, and are used as substitutes for the drawings. FIG. 3A shows the conventional product and FIG. 3B shows the product of the present invention. It is a thing.

As shown in FIG. 2, the piezoelectric ceramic element 1 used as a piezoelectric transformer has a rectangular plate shape, and the piezoelectric ceramic element 1 is divided into a drive portion 1A and a power generation portion 1B with a central portion in the longitudinal direction as a boundary. It is divided. The ridges on the front and back surfaces and the side surfaces of this piezoelectric ceramic element are chamfered to form chamfered portions 1a. The drive unit 1A has an input electrode 11 made of silver or silver palladium on the front and back main surfaces,
12 is provided, and polarization processing is performed in the plate thickness direction.
Lead wires L1 and L2 are conductively bonded to the input electrodes on the front and back surfaces at a position corresponding to a node region of vibration in the case of λ mode vibration by a conductive bonding material such as solder. An output electrode 13 is formed on an end face of the power generation unit 1B, and the power generation unit 1B is polarized in the longitudinal direction. The lead wire L3 is conductively bonded to the output electrode 13 by a conductive bonding material.

A manufacturing method for obtaining such a piezoelectric ceramic element will be described with reference to FIG. Ceramic powder (PZT), which is the base of the piezoelectric ceramic element, is filled in a press die K including a die K3, an upper punch K1 and a lower punch K2,
Press molding is performed with the upper punch K1 and the lower punch K2. The press die K corresponds to the shape of each completed piezoelectric ceramic element, and includes an upper punch K1 and a lower punch K, respectively.
The outer peripheral portion of the piezoelectric ceramic element 2 has a protruding shape so that the ridge angle of the piezoelectric ceramic element 1 is chamfered. In addition, in order to improve the durability as a mold, the protruding portion is not chamfered at its tip to form a sharp protruding portion. Therefore, the shape of each ridge angle portion of the piezoelectric ceramic element is also microscopically a shape corresponding to this mold configuration, and the chamfered portion 1a is followed by the stepped portion 1b. The above-mentioned press-formed body is fired at a predetermined temperature and time in the next firing step to be a ceramic sintered body. The ceramic-sintered piezoelectric ceramic element is subjected to abrasive grain polishing in a polishing step in order to remove dirt and the like during sintering. Input electrodes are formed on the front and back surfaces of the driving portion 1A with the longitudinal central portion of the piezoelectric ceramic element 1 as a boundary, and polarization processing is performed in the thickness direction using the front and back electrodes. At the same time, an output electrode is also formed on the end face in the longitudinal direction of the power generation unit 1B, and this electrode is used to perform polarization treatment in the longitudinal direction between each electrode of the drive unit. As a result, by applying an alternating voltage to each electrode of the drive section, the boosted voltage can be taken out from the output electrode.

The chamfered shape is not limited to the above-described embodiment, but chamfering of other shapes such as rounding may be performed. In this case, a mold corresponding to the chamfered shape may be used.

[0015]

According to the present invention, a die corresponding to the chamfered shape of the piezoelectric ceramic element used for the piezoelectric transformer is used to press-mold the powder for piezoelectric ceramic into a predetermined shape of each piezoelectric ceramic element, and this is pressed. Since the structure is such that firing and polishing are performed, and the piezoelectric ceramic elements having chamfered ridge angles are formed before firing, the number of manufacturing steps as a whole is reduced, and the cost can be reduced.

Further, the ridge angle is not damaged during the manufacturing process, and since the piezoelectric ceramic powder is press-molded for each piezoelectric ceramic element, the pressing area becomes small, and the density of the inside of the element becomes uneven. Generation of voids and pinholes is reduced. Therefore, since the manufacturing yield is improved and the mechanical strength of the piezoelectric ceramic element is improved, the breaking limit during driving the piezoelectric transformer is improved,
It is possible to obtain a highly reliable piezoelectric transformer.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process according to the present invention.

FIG. 2 is a perspective view of a chamfered piezoelectric ceramic element.

FIG. 3 is a drawing-substitute SEM photograph showing the internal crystal structure of the sintered body.

FIG. 4 is a diagram showing a conventional manufacturing process.

[Explanation of symbols]

 1 Piezoelectric Ceramic Element (Piezoelectric Transformer) 11,12 Input Electrode 13 Output Electrode 1a Chamfer 1b Small Step K Mold K1 Upper Punch K2 Lower Punch K3 Dies L1, L2, L3 Lead Wire

Claims (1)

[Claims] 1. A method for manufacturing a plate-shaped piezoelectric transformer having chamfered ridge angles, wherein a die corresponding to a chamfered shape of a piezoelectric ceramic element used for the piezoelectric transformer is used, and a powder for piezoelectric ceramic is made into a predetermined piezoelectric ceramic. A step of press-molding each element into a shape, a step of firing the press-formed piezoelectric ceramic element at a predetermined temperature, and a step of polishing the surface of the fired piezoelectric ceramic element to remove surface strain. A method of manufacturing a piezoelectric transformer, which comprises the steps of: forming a predetermined input / output electrode on the polished piezoelectric ceramic element;