WO2020194812A1

WO2020194812A1 - Laminated varistor

Info

Publication number: WO2020194812A1
Application number: PCT/JP2019/040562
Authority: WO
Inventors: 武藤　直樹; 裕司山岸
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2019-03-22
Filing date: 2019-10-16
Publication date: 2020-10-01
Also published as: JPWO2020194812A1

Abstract

This laminated varistor is provided with a sintered body, a pair of external electrodes provided to the sintered body, and a high-resistivity layer provided to the sintered body. The sintered body has: a varistor layer that contains Bi and ZnO as a main component; and a pair of internal electrodes that are embedded in the varistor layer. The sintered body has: a pair of end faces from which the pair of internal electrodes are led out, respectively; and a surface other than the pair of end faces, where the pair of internal electrodes are not exposed. The pair of external electrodes are respectively provided to the pair of end faces of the sintered body, and are electrically connected to the pair of internal electrodes, respectively. The high-resistivity layer is provided to the surface where the pair of internal electrodes are not exposed. The high-resistivity layer has a specific resistance that is four or more times the specific resistance of a portion of the varistor layer located between the pair of internal electrodes. The high-resistivity layer has a thickness of at least 50 μm. This laminated varistor can be made compact while offering excellent anti-surge characteristics, and also enables stable plating of external electrodes.

Description

Laminated varistor

The present invention relates to a laminated varistor used in various electronic devices.

In recent years, miniaturization has progressed in home appliances and in-vehicle materials, and varistor, which is a component thereof, is also required to be miniaturized. At the same time, various element designs and developments are being carried out in order to guarantee surge resistance, and it is required to reduce the size while ensuring surge resistance. Further, in order to improve the mountability, it is required to plate the external electrode. For these purposes, it has been proposed to provide a high resistance layer on the surface of the device. A conventional varistor similar to this varistor is disclosed in Patent Document 1 as an example.

Japanese Unexamined Patent Publication No. 1-295403

The laminated varistor includes a sintered body, a pair of external electrodes provided on the sintered body, and a high resistance layer provided on the sintered body. The sintered body has a varistor layer containing ZnO as a main component and containing Bi, and a pair of internal electrodes embedded in the varistor layer. The sintered body has a pair of end faces from which a pair of internal electrodes are derived, and a surface on which a pair of internal electrodes other than the pair of end faces are not exposed. The pair of external electrodes are provided on each of the pair of end faces of the sintered body and are electrically connected to the pair of internal electrodes. The high resistance layer is provided on the above-mentioned surface where the pair of internal electrodes of the sintered body is not exposed. The high resistance layer has a specific resistance that is four times or more the specific resistance of the portion of the varistor layer sandwiched between the pair of internal electrodes. The thickness of the high resistance layer is 50 μm or more.

This laminated varistor can be miniaturized while ensuring surge resistance, and the external electrodes can be plated stably.

FIG. 1 is a perspective view of a laminated varistor according to an embodiment. FIG. 2 is a cross-sectional view taken along the line II-II of the laminated varistor shown in FIG. FIG. 3 is a cross-sectional view taken along the line III-III of the laminated varistor shown in FIG. FIG. 4 is an enlarged cross-sectional view of the laminated varistor shown in FIG.

FIG. 1 is a perspective view of the laminated varistor 11 in the embodiment. FIG. 2 is a cross-sectional view taken along the line II-II of the laminated varistor 11 shown in FIG. FIG. 3 is a cross-sectional view taken along the line III-III of the laminated varistor 11 shown in FIG. The laminated varistor 11 includes a sintered body 51, a pair of external electrodes 14 provided on each of the pair of end faces 151 of the sintered body 51, and a high resistance layer 15 provided on the surface 251 of the sintered body 51. .. The sintered body 51 has a plurality of varistor layers 12 containing ZnO as a main component, and a plurality of internal electrodes 13 containing Ag as a main component, which are alternately laminated with a plurality of varistor layers 12 in the stacking direction D1. The internal electrode 13 is embedded in the sintered body 51. The plurality of internal electrodes 13 are alternately led out to both end faces on opposite sides of the sintered body 51, and are electrically connected to the pair of external electrodes 14 on both end faces 151. The sintered body 51 of the laminated varistor 11 in the embodiment has a pair of end faces 151 having rectangular shapes on opposite sides, a pair of surfaces 2511 having rectangular shapes on opposite sides, and a rectangular shape on opposite sides. It has a rectangular parallelepiped shape with a pair of faces 2512. The

surfaces

2511 and 2512 are connected to the end surface 151. The end faces 151 are arranged in the direction D2 perpendicular to the stacking direction D1. The surfaces 2511 are arranged in the stacking direction D1. The surfaces 2512 are arranged in the direction D3 perpendicular to the stacking direction D1 and the direction D2. The internal electrode 13 is derived from the end face 151. The plurality of internal electrodes 13 are arranged in the stacking direction D1. A pair of internal electrodes 131 located at the outermost edges of the plurality of internal electrodes 13 arranged in the stacking direction D1 are led out to a pair of end faces 151. That is, the sintered body 51 has a pair of end faces 151 from which the pair of internal electrodes 131 (13) are derived, and a surface 251 on which the pair of internal electrodes 131 (13) excluding the pair of end faces 151 are not exposed. And have. Surface 251 includes

surfaces

2511 and 2512. The sintered body 51 (laminated varistor 11) has an effective portion 111 sandwiched between a pair of internal electrodes 131 and an invalid portion 211 surrounding the effective portion 111. The effective portion 111 functions as a varistor, and the invalid portion 211 does not function as a varistor. A high resistivity layer 15 having a specific resistance four times or more the specific resistance of the sintered body 51 between the internal electrodes 13, that is, the effective portion 111 of the laminated varistor 11, is provided on the surface 251 (2511, 2512). The thickness of the high resistance layer 15 is about 100 μm. The invalid portion 211 of the sintered body 51 and the high resistance layer 15 form an invalid portion 311 surrounding the effective portion 111 of the laminated varistor 11. The invalid part 311 does not function as a varistor.

FIG. 4 is an enlarged cross-sectional view of the laminated varistor 11. A plating layer 141 made of Sn and Ni is formed on the outer surface of the external electrode 14.

The varistor layer 12 laminated between the internal electrodes 13 and the outer side thereof contains ZnO as a main component, and further contains subcomponents such as Bi ₂ O ₃ , Co ₂ O ₃ , MnO ₂ , or Sb ₂ O ₃ . .. In the embodiment, the composition contains only 1.0 mol% of Bi ₂ O ₃ and 2.0 mol% of other subcomponents such as Co ₂ O ₃ , Mn O ₂ and Sb ₂ O ₃ , and ZnO. Is contained only in the remaining 97 mol%.

The high resistance layer 15 has an inner surface 115 facing the sintered body 51 and an outer surface 215 on the opposite side of the inner surface 115. The surface layer portion 2151 of the high resistance layer 15 near the outer surface including the outer surface 215 contains Zn, Si, and Bi, and in the embodiment, contains Zn ₂ SiO ₄ as a main component. With this configuration, the high resistivity layer 15 has a resistivity much higher than the resistivity of the effective portion 111 between the internal electrodes 13 of the sintered body 51. As the composition of the high resistance layer 15, only 58.2 mol% of Zn is contained, only 38.8 mol% of Si is contained, and only 3.0 mol% of Bi is contained.

Glass is coated to form a high resistance layer on the surface. In this case, it is difficult to secure a sufficient thickness, and it is difficult to stably plate the external electrode due to the variation in thickness. On the other hand, in the laminated varistor 11 in the embodiment, the specific resistance of the sintered body 11 between the internal electrodes 13 is four times as large as the surface 251 excluding the end surface 151 from which the internal electrode 13 is derived, that is, the four

surfaces

2511 and 2512. The high resistance layer 15 having the above specific resistance is provided with a thickness of 50 μm or more. As a result, sufficient insulation can be achieved, and the external electrode 14 can be stably plated to form the plating layer 141.

The space between the internal electrode 131 (13) and the high resistance layer 15 is composed of a varistor layer having the same composition as the sintered body 51 (varistor layer 12) of the effective portion 111 sandwiched between the internal electrodes 13. If the Si of the high resistance layer 15 diffuses into the varistor layer 12 of the effective portion 111 sandwiched between the internal electrodes 13, the resistance value increases. The ineffective portion 211 between the effective portion 111 and the high resistance layer 15 prevents the Si of the high resistance layer 15 from diffusing into the effective portion 111, and prevents the effective portion 111, that is, the resistance value of the laminated varistor 11 from increasing. In the present embodiment, the thickness of the invalid portion 211 is about 300 μm.

In the stacking direction D1, the thickness T of the invalid portion 311 of the outer surface 215 and the thickness Tx of the high resistance layer 15 are 0.1 ≦ (Tx / T) ≦ 0.8 with respect to the internal electrode 131 (13). It is desirable to satisfy the relationship. If the value of (Tx / T) is smaller than 0.1, it becomes difficult to secure sufficient insulation, and conversely, if it is larger than 0.8, the characteristics may be affected by diffusion. is there.

The above is the same for the high resistance layer 15 on the side surface side. As shown in FIG. 3, the distance W from the end of the internal electrode 13 to the outer surface 215 of the high resistance layer 15 and the thickness Wx of the high resistance layer 15 are 0.1 ≦ (Wx / W) ≦ 0. It is desirable to satisfy the relationship of 8.

The surface layer portion 2151 of the high resistance layer 15 contains at least Zn, Bi, and Si. The Bi content of the surface layer portion 2151 is twice or more and five times or less the Bi content of the varistor layer 12. It is desirable that the atomic ratio Ra of Zn to Si satisfies 1.0 ≦ Ra ≦ 2.0. When Zn and Si react to form Zn ₂ SiO ₄ , Bi ₂ O ₃ acts as a reaction accelerator to promote this reaction. If the Bi content of the high resistance layer 15 is less than twice the Bi content of the varistor layer 12, Bi may move from the varistor layer 12 and the non-linearity of the varistor may deteriorate. On the other hand, when the Bi content of the high resistance layer 15 is more than 5 times the Bi content of the varistor layer 12, the difference in shrinkage between the high resistance layer 15 and the varistor layer 12 becomes large, and the varistor layer 12 and the varistor layer 12 are high. Peeling, cracks, etc. may occur between the resistance layers 15. Further, when the atomic ratio Ra becomes larger than 2.0, the insulation resistance of the high resistance layer 15 deteriorates due to the excess ZnO. On the contrary, when the atomic ratio Ra is smaller than 1.0, there is a possibility that problems such as fusion of elements during firing may occur due to the surplus SiO ₂ .

In the embodiment, the high resistance layer 15 contains Si. The high resistance layer 15 may contain Sb instead of Si. In this case, the surface layer portion 2151 of the high resistance layer 15 contains at least Zn, Bi, and Sb, and the Bi content of the surface layer portion 2151 of the high resistance layer 15 is twice or more and five times the Bi content of the varistor layer 12. It is as follows. It is desirable that the atomic ratio Rb of Zn to Sb satisfies 3.5 ≦ Rb ≦ 7.0. In this case as well, as with Si, when Zn and Sb react to form Zn ₇ Sb ₂ O ₁₂ , Bi ₂ O ₃ acts as a reaction accelerator to promote this reaction. When the Bi content of the surface layer portion 2151 of the high resistance layer 15 is less than twice the Bi content of the varistor layer 12, Bi moves from the varistor layer 12 and the electrical characteristics of the varistor layer 12 (sintered body 51). May deteriorate. On the other hand, when the Bi content of the surface layer portion 2151 of the high resistance layer 15 is more than 5 times the Bi content of the varistor layer 12, the difference in shrinkage between the high resistance layer 15 and the varistor layer 12 becomes large, and the varistor There is a possibility that peeling, cracks, etc. may occur between the layer 12 and the high resistance layer 15. Further, when the atomic ratio Rb becomes larger than 2.0, the resistance value of the sintered body 51 becomes large due to the surplus ZnO and deteriorates. On the other hand, if the atomic ratio Rb is smaller than 1.0, problems such as fusion of elements during firing may occur due to excess Sb ₂ O ₃ .

Next, the manufacturing method of the laminated varistor 11 in the embodiment will be described.

First, a slurry of a high resistance material, which is a material of the high resistance layer 15, is prepared. The blending ratio of this slurry is that the ZnO content is 58.2 mol%, the SiO ₂ content is 38.8 mol%, and the Bi ₂ O ₃ content is 3.0 mol%.

Similarly, a slurry of the varistor material which is the material of the varistor layer 12 is prepared. The blending ratio of this slurry is that the content of Bi ₂ O ₃ is 1.0 mol%, and the content of auxiliary components containing Co ₂ O ₃ , MnO ₂ , Sb ₂ O _3, etc. is 2.0 mol%. , ZnO content is the remaining 97 mol%.

A slurry of high resistance material is applied and dried on a carrier film and transferred onto a carrier plate to form a high resistance green sheet having a thickness of about 100 μm.

A high resistance material formed in a pattern having a width of about 200 μm is laminated on the high resistance green sheet so as to be a portion of the high resistance layer 15 located on the surface 2512 of the sintered body 51 so as to have a height of about 300 μm. To do. By being divided at the center of this pattern, the width of the high resistance layer 15 on the surface 2512 of the sintered body 51 becomes about 100 μm.

Next, the varistor material is laminated between the pattern-formed high resistance materials.

A high resistance material with a pattern formed on it and a varistor material with an internal electrode material printed between them are laminated.

Further, a pattern-formed high resistance material and a varistor material are laminated between them, and a high resistance material is laminated on the high resistance material to form a laminate.

The laminate is pressed to cut it into pieces, and then fired. The end face 151 of the sintered body 51 with the internal electrode 13 exposed is coated with a paste containing Ag as a main component and baked, and the external electrode 14 (lower) It forms a stratum 142). After that, the plating layer 141 is formed by plating Sn and Ni on the external electrode 14 (base layer 142) to obtain the laminated varistor 11.

In the state before plating the external electrode 14, the portion of the sintered body 11 other than the portion where the external electrode 14 is provided is entirely covered with the high resistance layer 15 having a thickness of 50 μm or more. That is, the sintered body 51 is entirely covered with the external electrode 14 and the high resistance layer 15 so as not to be exposed to the outside of the laminated varistor 11. Therefore, the external electrode 14 can be stably plated.

The high resistance layer can be formed by applying a high resistance paste to the surface of the varistor element and baking it, but it takes a lot of man-hours and the varistor becomes expensive. In addition, the thickness of the high resistance layer tends to vary, which tends to cause plating defects in the external electrodes. Further, since the high resistance paste is applied and baked on the six surfaces of the varistor element, a part of the components of the high resistance paste is diffused inside the varistor element from the surface from which the internal electrode is derived, and the specific resistance of the varistor layer is increased. The surge resistance may be reduced.

As described above, the laminated varistor 11 does not require a special step of forming the high resistance layer 15 such as a glass coating, and since the sheet-like materials are laminated to form the high resistance layer 15, the thickness and the thickness and the thickness of the laminated varistor 11 are increased. The width can be formed with high accuracy. Further, since it is possible to prevent the diffusion of the components of the high resistance layer from the end face from which the internal electrode 13 is led out, it is possible to obtain a laminated varistor 11 which is inexpensive, has excellent surge resistance, and can apply stable plating to the external electrode 14. Can be done.

11 Laminated varistor 12 Varistor layer 13 Internal electrode 14 External electrode 15 High resistance layer 51 Sintered body

Claims

A varistor layer containing ZnO as the main component and Bi,
A pair of internal electrodes embedded in the varistor layer,
A sintered body having a pair of end faces from which the pair of internal electrodes have been derived, and a surface on which the pair of internal electrodes other than the pair of end faces are not exposed.
A pair of external electrodes provided on the pair of end faces of the sintered body and electrically connected to the pair of internal electrodes, respectively.
A high resistance layer provided on the surface of the sintered body where the pair of internal electrodes are not exposed,
With
The high resistance layer has a specific resistance of four times or more the specific resistance of the portion of the varistor layer sandwiched between the pair of internal electrodes.
A laminated varistor having a high resistance layer having a thickness of 50 μm or more.
The portion of the varistor layer that is not sandwiched between the pair of internal electrodes and the high resistance layer form an invalid layer that surrounds the portion of the varistor layer that is sandwiched between the pair of internal electrodes.
In the cross section passing through the sintered body and the high resistance layer, the thickness T of the ineffective layer and the thickness Tx of the high resistance layer satisfy the relationship of 0.1 ≦ (Tx / T) ≦ 0.8. The laminated varistor according to claim 1.
The high resistance layer has an inner surface that comes into contact with the sintered body and an outer surface that is opposite to the inner surface.
The surface layer portion of the high resistance layer including the outer surface contains at least Zn, Bi, and Si, and contains at least Zn, Bi, and Si.
The Bi content of the surface layer portion of the high resistance layer is twice or more and five times or less the Bi content of the varistor layer.
The laminated varistor according to claim 1, wherein the atomic ratio Ra of Zn in the surface layer portion of the high resistance layer to Si satisfies the relationship of 1.0 ≦ Ra ≦ 2.0.
The high resistance layer has an inner surface that comes into contact with the sintered body and an outer surface that is opposite to the inner surface.
The surface layer portion of the high resistance layer including the outer surface contains at least Zn, Bi, and Sb.
The Bi content of the surface layer portion of the high resistance layer is twice or more and five times or less the Bi content of the varistor layer.
The laminated varistor according to claim 1, wherein the atomic ratio Rb of Zn in the surface layer portion of the high resistance layer to Si satisfies the relationship of 3.5 ≦ Rb ≦ 7.0.
The laminated varistor according to any one of claims 1 to 4, wherein the sintered body is entirely covered with the pair of external electrodes and the high resistance layer so as not to be exposed to the outside of the laminated varistor. ..
The sintered body has a rectangular parallelepiped shape having a pair of faces opposite to each other, which are the pair of end faces, and four faces connected to the pair of faces.
The laminated varistor according to any one of claims 1 to 5, wherein the surface of the sintered body where the pair of internal electrodes is not exposed includes the four surfaces of the rectangular parallelepiped shape.