JPH0851240A - Multilayer piezoelectric element - Google Patents

Abstract

PURPOSE:To provide a multilayer piezoelectric element wherein its internal electrodes are connected surely every two layers with its external electrode, and defective conduction and defective insulation can be prevented. CONSTITUTION:A conductive protrusive part 16 is formed in the end part of an internal electrode 12 exposed every two layers to the side surface of a multilayer piezoelectric element wherein piezoelectric materials and the internal electrodes are superimposed on each other alternately. Further, an insulation layer 18 made of a thermosetting resin or ultraviolet-rays-setting resin is so formed as to be applied to all the piezoelectric materials in the stacking direction of the piezoelectric element. This insulation layer 18 comprises a set part present in the part opposed to the conductive protrusive part 16 and an unhardened part present in the part sandwiched between the conductive protrusive parts 16. Then, a conductive film 13 is thermo-compression-bonded to the insulation layer 18. Thereby, conductive particles 17 included in the conductive film 13 are contacted with a copper foil 15 to be changed into the external electrode of the piezoelectric element. Concurrently, the conductive particles 17 break through the unhardened part, and as a result, the internal electrodes 12 present every two layers are connected electrically with the copper foil 15 via the conductive film 13 and the insulation layer 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated piezoelectric element in which a plurality of thin films of piezoelectric material are laminated and a longitudinal displacement can be obtained by applying a voltage.

[0002]

2. Description of the Related Art Conventionally, when manufacturing a laminated piezoelectric element,
A general method is to print electrodes on the entire surface of the piezoelectric sheet and stack the electrodes. In the case of such a structure, it is necessary to electrically connect every other internal electrode. As an example thereof, a method as shown in FIGS. 8 and 9 is considered.

First, as shown in FIG. 8A, film-shaped piezoelectric materials 71 on which internal electrodes 72 are printed are laminated every other layer so that the end portions of the internal electrodes 72 are exposed, and sintered. The sintered body 70 is formed. Then, temporary external electrodes 73 and 74 are applied to the side surfaces where the end portions of the internal electrodes 72 are exposed every other layer, and electroplating is performed using the temporary external electrodes 73 as a cathode. As shown, the conductive protrusions 75 formed by the electroplating method are formed in alternate layers.

The sintered body 70 will be described below with reference to a vertical sectional view.
As shown in FIG. 9A, the resin component 76 is electrodeposited on the end portions of the conductive protrusions 75 and the internal electrodes 72 by an electrodeposition coating method or the like, and baked at around 150 ° C. As shown, the resin component is melted and then cured to form the insulating layer 77.

On the other hand, as shown in FIG. 9 (c), an anisotropic conductive film 78 which is capable of thermocompression bonding and has conductivity in one direction only in the pressed portion and contains conductive particles 80, A copper foil 79, which will be the external electrode, is prepared and attached, and FIG.
As shown in (d), when thermocompression-bonded, the anisotropic conductive film 78 is formed.
Is only partially pressed with a higher pressure than the other parts, so that the conductive particles 80 in the part pressed with a high pressure are insulated from the insulating layer 77.
Through, and comes into contact with the conductive protrusions 75 and the copper foil 79, and the copper foil 79 serving as an external electrode, the conductive protrusions 75, and the internal electrodes 72 are electrically connected every other layer.

[0006] In the same manner, the sintered body 70 in which the internal electrodes and the copper foil, which are one layer apart, are connected by shifting the layers on the opposite side surface,
Is a finished product after undergoing steps such as lead wire attachment, resin coating, and polarization treatment.

[0007]

However, in the manufacturing process of the laminated piezoelectric element as described above, the conductive convex portion 75 is formed on the end portion of the internal electrode 72 having a width of 5 to 10 μm by the electroplating method. Therefore, due to the nature of the electroplating method, it is formed with a width much wider than the width of the internal electrodes.
As a result, depending on the degree of exposure of the end of the internal electrode 72 and the extent of expansion of the conductive convex portion 75, the conductive convex portion 75 may contact the internal electrodes 72 adjacent on both sides to electrically short-circuit, Alternatively, since the heights of the conductive protrusions 75 are likely to be uneven, there is a problem that electrical connection becomes incomplete during thermocompression bonding of the anisotropic conductive film 78 in a later step.

The present invention has been made in order to solve the above-mentioned problems, and is a laminated type capable of reliably connecting the internal electrodes and the external electrodes every other layer to prevent defective conduction and defective insulation. The purpose is to provide a piezoelectric element.

[0009]

In order to achieve this object, a laminated piezoelectric element of the present invention comprises a layered internal electrode exposed on a side surface of a laminated body in which piezoelectric materials and internal electrodes are alternately laminated. A conductive convex portion formed at an end portion, an insulating layer that covers the entire side surface of the laminated body on which the conductive convex portion is formed, and the conductive layer that is continuously formed on the insulating layer In a laminated piezoelectric element including an internal electrode and a external electrode electrically connected to each other through a convex portion, a portion of the insulating layer corresponding to the conductive convex portion is formed by an uncured portion. A portion of the insulating layer corresponding to a portion between the conductive convex portions is formed by a hardened portion.

Further, it is desirable that the insulating layer is made of a thermosetting resin which is cured by radiating a high energy ray or an ultraviolet curable resin.

[0011]

In the laminated piezoelectric element of the present invention having the above-mentioned structure, the portion of the insulating layer corresponding to the conductive convex portion is constituted by the uncured portion and corresponds to the portion between the conductive convex portions. Since the portion of the insulating layer is constituted by the hardened portion, it is possible to reliably connect the internal electrode and the external electrode, which are placed in a single layer, and prevent conduction failure and insulation failure.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the laminated piezoelectric element of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of the laminated piezoelectric element of this embodiment. On the side surface of the laminated body in which the film-shaped piezoelectric material 11 and the internal electrode 12 are alternately stacked, the internal electrode 1 having one layer is placed.
A conductive convex portion 16 is formed at the end of No. 2. further,
The insulating layer 18 is formed so as to cover all the piezoelectric materials 11 in the stacking direction of the device, and the conductive film 13 including the conductive particles 17 is thermocompression bonded thereon. The conductive particles 17 penetrate the insulating film 18 and come into contact with the conductive protrusions 16, and the conductive protrusions 16 serve as external electrodes via the conductive film 13 and serve as the copper foil 15.
Electrically connected to.

Next, a method of manufacturing the laminated piezoelectric element shown in FIG. 1 will be described with reference to FIGS.

First, after mixing a piezoelectric material containing PZT (lead zirconate titanate) as a main component to a desired composition, 85
An appropriate amount of binder, a small amount of a plasticizer and a defoaming agent are added to the powder calcined at 0 ° C., and the powder is dispersed in an organic solvent to form a slurry. This slurry is formed into a green sheet by a doctor blade method to a predetermined thickness. A Pd (palladium) paste is screen-printed as the internal electrodes 12 on the green sheet, and a predetermined number of punched products having a predetermined size are stacked and integrated by hot pressing. After degreasing,
Sintering was performed at about 1200 ° C., and as shown in FIG. 2, a sintered body 21 cut at a position where the internal electrodes 12 were exposed at every other layer was used as temporary external electrodes 22 and 23. The paste is applied and baked, and further cut so that another pair of side surfaces 24 and 25 are exposed.

Next, on one side surface 24 of the sintered body 21, the portion other than the area where the conductive protrusion 16 is formed is masked with a tape. That is, a masking tape is applied to the surface on which the temporary external electrodes 22 and 23 are applied, except for the lead wire attachment portion, and further the other side surface 25 is also applied with the masking tape.

Then, when electroplating is performed using the temporary external electrode 22 as a cathode, as shown in the cross-sectional view of FIG. 3, the conductive convex portion 16 is formed on the internal electrode 12 having one layer. Electroplating in this case may be general nickel plating,
Specifically, a nickel sulfamate bath is used as the plating bath, and the current density is 1 to 5 A / with the temporary external electrode 22 as the cathode.
When it is carried out at dm ² for a predetermined time, an electric nickel plating layer to be the conductive convex portion 16 is formed on the internal electrode 12 connected to the temporary external electrode 22.

Next, as shown in FIG. 4, a thermosetting resin or an ultraviolet curable resin is applied as the insulating layer 18, and then the conductive convex portion 16 of the insulating layer 18 is applied as shown in FIG. Then, the photomask 19 is arranged, and the high-energy ray 20 is uniformly irradiated to the entire side surface 24 through the photomask 19. As a result, the insulating layer 18 in the portion where the conductive convex portion 16 is not formed is completely cured by directly receiving the high energy beam 20, and becomes the cured portion 18a of the insulating layer 18, and the insulating layer 18 is also formed. Conductive protrusion 16
The portion corresponding to is not cured because it is shielded by the photomask 19 and becomes the uncured portion 18b of the insulating layer 18.

As the high energy ray 20, it is desirable to use a laser beam such as a carbon dioxide gas laser, a YAG laser or an excimer laser.

Epoxy resin, phenol resin, diallyl phthalate, etc. are used for the thermosetting resin, and acrylic polyester acrylate, epoxy acrylate, urethane acrylate, etc. are used for the ultraviolet curing resin.

Separately from the sintered body 21, an epoxy resin adhesive containing conductive particles 17 made of copper powder or the like having a particle size of about 20 to 50 μm as shown in FIG.
A conductive film 13 which is semi-cured by applying and heating uniformly on a copper foil 15 to be an external electrode with a thickness of about 50 μm is prepared. This is cut into the same size as the side surface 24 of the sintered body 21 on which the conductive convex portion 16 and the insulating layer 18 are formed,
Temporarily fixed on the side surface 24.

Then, the copper foil 15 serving as an external electrode is sandwiched from above by a pair of flat pressing jigs (not shown) heated to 150 ° C., and an appropriate load is applied to perform thermocompression bonding. As a result, as shown in FIG. 1, only the portion of the conductive film 13 facing the conductive convex portion 16 is partially pressurized with a higher pressure than the other portions, so that the conductive film 13 is pressurized with the higher pressure. The conductive particles 17 in the open portion break through the insulating layer 18 and the conductive convex portion 1
Contact 6 In particular, since the insulating layer 18, which is a portion corresponding to the conductive convex portion 16, is the uncured portion 18b, the conductive particles 17 and the conductive convex portion 16 can be easily formed with a slight pressure.
And come into contact, and an electrical connection is made. On the contrary, the insulating layer 18
Since the hardened portion 18a is completely hardened, the hardened portion 18a is not destroyed unless an extremely large pressure is applied, and electrical insulation is maintained. Further, by heating during thermocompression bonding, the curing portion 18a is completely cured while being electrically connected.

As a result, the copper foil 15, which is the external electrode, has the conductive convex portion 16 and the internal electrode 12 via the conductive film 13.
And is electrically connected every other layer.

On the other hand, the side surface 2 on which the conductive convex portion 16 is formed
The same process is performed by shifting the layers on the side opposite to 4.

In this way, the sintered body 21 in which the layers of the internal electrodes 12 and the copper foil 15 are electrically connected to each other by shifting the layers on the opposite side surfaces, is cut into a predetermined size, A lead wire for power supply is attached to a part of the copper foil 15, and a resin sheath and polarization treatment are applied to complete the product.

As another method for forming the hardened portion 18a and the uncured portion 18b of the insulating layer 18, as shown in FIG.
The method shown in can be considered.

In this method, a thermosetting resin or an ultraviolet curable resin is applied as the insulating layer 18, and then the beam diameter is 100 to 120 μm in the portion of the insulating layer 18 corresponding to the portion between the conductive convex portions 16. The high-energy ray 20 focused on is irradiated.

As a result, the portion irradiated with the high-energy rays 20 is completely cured and becomes the cured portion 18a. On the other hand, the portion of the insulating layer 18 corresponding to the conductive convex portion 16 is not cured because it is not irradiated with the high energy beam 20, and becomes the uncured portion 18b.

The present invention is not limited to the above-mentioned embodiments, and various modifications can be made without departing from the spirit of the invention. For example, to form the conductive protrusion,
Chromium plating or copper plating may be used instead of nickel plating, and gold, platinum, and
You may use silver etc. Further, various particles such as nickel, carbon, and silver can be used as the conductive particles. Further, if one of the copper foils used as the external electrode is extended as it is, it can be used as a substitute for the lead wire, and the lead wire attaching step can be omitted.

[0030]

As is apparent from the above description,
According to the multilayer piezoelectric element of the present invention, the portion of the insulating layer corresponding to the conductive convex portion is constituted by the uncured portion, and the portion of the insulating layer corresponding to the portion between the conductive convex portions is formed. Since it is composed of the hardened portion, it is possible to reliably connect the internal electrode and the external electrode, which are placed in a single layer, and prevent conduction failure and insulation failure.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a laminated piezoelectric element of this example.

FIG. 2 is a perspective view showing a part of a laminated sintered body.

FIG. 3 is a cross-sectional view showing a state in which conductive protrusions are formed.

FIG. 4 is a cross-sectional view showing a state in which a resin to be an insulating layer is applied on a laminated sintered body on which conductive protrusions are formed.

FIG. 5 is an explanatory diagram of a method of forming an insulating layer including a cured portion and an uncured portion.

FIG. 6 is a diagram showing a state in which a conductive film and a copper foil to be an external electrode are attached.

FIG. 7 is an explanatory diagram of a method of forming an insulating layer including a hardened portion and an uncured portion.

FIG. 8 is a diagram showing a manufacturing process of a conventional laminated piezoelectric element.

FIG. 9 is a diagram showing a manufacturing process of a conventional laminated piezoelectric element.

[Explanation of symbols]

 11 piezoelectric material film 12 internal electrode 13 conductive film 15 copper foil 16 conductive convex portion 18 insulating layer 18a cured portion 18b uncured portion 20 high energy ray

Claims (2)

[Claims] 1. A conductive convex portion formed on an end portion of a one-layer internal electrode exposed on a side surface of a laminated body in which piezoelectric materials and internal electrodes are alternately laminated, and the conductive convex portion are formed. An insulating layer that covers the entire side surface of the stacked body, and an external electrode that is continuously formed on the insulating layer and that is electrically connected to a single-layer internal electrode via the conductive protrusion. In the laminated piezoelectric element including, the portion of the insulating layer corresponding to the conductive convex portion is constituted by an uncured portion, and the portion of the insulating layer corresponding to the portion between the conductive convex portions is a hardened portion. A laminated piezoelectric element characterized by being constituted by: 2. The insulating layer is made of a thermosetting resin or an ultraviolet curable resin which is cured by radiating a high energy ray.
The laminated piezoelectric element according to item 1.