Multilayer varistor and its manufacturing method

Abstract

To provide a laminated varistor capable of suppressing occurrence of migration on a surface of a high-resistance layer.SOLUTION: A laminated varistor (1) includes: a sintered body (11); an internal electrode (12) provided inside the sintered body (11); a high-resistance layer (13) provided so as to cover at least part of the sintered body (11); and an external electrode (14) provided so as to cover part of the high-resistance layer (13) and electrically connected to the internal electrode (12). An arithmetic mean roughness of a surface of the high-resistance layer (13) is 0.06 μm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a multilayer varistor and a method for manufacturing a multilayer varistor, and more particularly to a multilayer varistor including a sintered body, internal electrodes, and external electrodes, and a method for manufacturing this multilayer varistor. [Background technology]

[0002] Varistors are used to protect various electronic equipment and devices from abnormal voltages caused by lightning surges, static electricity, etc., and to prevent malfunctions of electronic equipment and devices caused by noise generated in circuits.

[0003] Patent Document 1 discloses a chip-type electronic component having a ceramic body, a glass coating layer covering at least a portion of the surface of the ceramic body, and external electrodes on the surfaces of both ends of the ceramic body. Patent Document 1 describes that by making the thickness of the glass coating layer equal to or greater than a predetermined value, plating deposition on the surface of the ceramic body during plating can be suppressed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-151805 Summary of the Invention [Problem to be solved by the invention]

[0005] Similar to the chip-type electronic components, the multilayer varistor generally has a structure including a high resistance layer such as a glass coating layer, and primary electrodes and plated electrodes as external electrodes.

[0006] Therefore, it is possible to suppress plating deposition in multilayer varistors by providing a high-resistance layer. However, particularly in relation to the use of primary electrodes whose main component is Ag, migration may occur on the surface of the high-resistance layer under conditions of applied voltage and humidity.

[0007] An object of the present disclosure is to provide a multilayer varistor capable of suppressing the occurrence of migration on the surface of a high-resistivity layer, and a method for manufacturing a multilayer varistor. [Means for solving the problem]

[0008] A laminated varistor according to one aspect of the present disclosure comprises a sintered body, an internal electrode provided inside the sintered body, a high-resistance layer provided so as to cover at least a part of the sintered body, and an external electrode provided so as to cover a part of the high-resistance layer and electrically connected to the internal electrode, wherein the arithmetic mean roughness of the surface of the high-resistance layer is 0.06 μm or more.

[0009] A laminated varistor according to one aspect of the present disclosure comprises a sintered body having a pair of opposing main surfaces, a pair of opposing side surfaces, and a pair of opposing end surfaces, an internal electrode provided inside the sintered body and facing the main surfaces, a high-resistance layer provided so as to cover at least a portion of the sintered body, and an external electrode provided on the end surfaces so as to cover a portion of the high-resistance layer and electrically connected to the internal electrode, wherein the arithmetic mean roughness of the surface of the high-resistance layer on the side surfaces is greater than the arithmetic mean roughness of the surface of the high-resistance layer on the main surfaces.

[0010] A method for manufacturing a laminated varistor according to one embodiment of the present disclosure includes a first step, a second step, a third step, and a fourth step. In the first step, a sintered body containing ZnO as a main component and having internal electrodes provided therein is prepared. In the second step, a high-resistance layer is formed so as to cover at least a portion of the sintered body. In the third step, a primary electrode paste is applied so as to cover a portion of the high-resistance layer and to contact a portion of the internal electrode. In the fourth step, a plating electrode is formed so as to cover at least a portion of the primary electrode formed from the primary electrode paste. The arithmetic mean roughness of the surface of the high-resistance layer after the second step is 0.06 μm or more and 0.9 μm or less.

[0011] A method for manufacturing a laminated varistor according to one aspect of the present disclosure includes a first step, a second step, a third step, and a fourth step. In the first step, a sintered body containing ZnO as a main component and having internal electrodes provided therein is prepared. In the second step, a high-resistance layer is formed so as to cover at least a portion of the sintered body. In the third step, a primary electrode paste is applied so as to cover a portion of the high-resistance layer and to contact a portion of the internal electrode. In the fourth step, a plating electrode is formed so as to cover at least a portion of the primary electrode formed from the primary electrode paste. The second step includes a step of spraying a solution containing a precursor of the high-resistance layer onto a plurality of the sintered bodies while mixing and stirring the sintered bodies, and a step of heat-treating the sintered body to which the precursor has adhered, thereby forming the high-resistance layer. [Effects of the Invention]

[0012] According to the present disclosure, it is possible to provide a multilayer varistor capable of suppressing the occurrence of migration on the surface of a high-resistivity layer, and a method for manufacturing a multilayer varistor. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic cross-sectional view of a multilayer varistor according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic perspective view of the laminated varistor. DETAILED DESCRIPTION OF THE INVENTION

[0014] 1. Overview Hereinafter, a laminated varistor according to an embodiment of the present disclosure will be described with reference to the drawings. Note that the drawings described in the following embodiments are schematic diagrams, and the ratios of the sizes and thicknesses of the components in the drawings do not necessarily reflect the actual dimensional ratios.

[0015] As shown in Fig. 1, the multilayer varistor 1 of this embodiment comprises a sintered body 11, internal electrodes 12, high-resistance layers 13, and external electrodes 14. The multilayer varistor 1 is characterized in that the arithmetic mean roughness (hereinafter also referred to as Ra) of the surface of the high-resistance layer 13 is 0.06 µm or more. In this specification, the "surface" refers to the exposed area of ​​the surface that is not covered with other layers, etc.

[0016] Although the Ra value of the surface of the sintered body 11 can be controlled by considering the raw materials and firing conditions, the Ra value affects the electrical characteristics, such as the varistor voltage. Therefore, it is difficult to control both the electrical characteristics and Ra to desired values. However, the inventors have discovered that by controlling the Ra value of the surface of the high-resistance layer 13 formed on the surface of the sintered body 11, it is possible to control both the electrical characteristics and Ra to desired values. That is, the Ra of the surface of the high-resistance layer 13 can be changed while maintaining the electrical characteristics. They have also discovered that by setting the Ra of the surface of the high-resistance layer 13 to a specific value or higher, it is possible to suppress the occurrence of migration on the surface of the multilayer varistor 1. The reason why the multilayer varistor 1 having the above-mentioned configuration exhibits the above-mentioned effects is not necessarily clear, but can be inferred, for example, as follows. Migration in the multilayer varistor 1 is thought to occur via the elution and migration of metal ions, such as Ag ions, from the external electrodes 14 and the deposition of metal. In contrast to this, in the multilayer varistor 1, by controlling the Ra of the surface of the high-resistance layer 13 to a specific value or more, the creepage distance between the external electrodes 14, i.e., the distance of the path along the surface of the high-resistance layer 13 between the external electrodes 14, is increased, and the migration distance of ions, etc. required for migration to occur is increased. This makes it possible for the multilayer varistor 1 to increase the migration barrier, and as a result, it is thought that the occurrence of migration on the surface of the high-resistance layer 13 can be suppressed.

[0017] Furthermore, as a result of further investigation into the configuration of the multilayer varistor 1 of this embodiment, the inventors have found that the occurrence of migration on the surface of the high-resistance layer 13 can also be suppressed by controlling the arithmetic mean roughness of each surface of the high-resistance layer 13 to a specific relationship.

[0018] As shown in Fig. 1, the multilayer varistor 1 of this embodiment comprises a sintered body 11, an internal electrode 12, a high-resistance layer 13, and an external electrode 14. The sintered body 11 has a pair of opposing main surfaces (top and bottom surfaces in Fig. 1), a pair of opposing side surfaces, and a pair of opposing end surfaces (right and left surfaces in Fig. 1). The external electrode 14 is provided on the end surfaces so as to cover part of the high-resistance layer 13, and is electrically connected to the internal electrode 12. The multilayer varistor 1 is characterized in that the Ra of the surface of the high-resistance layer on the side surfaces (hereinafter also referred to as side-surface high-resistance layer 13b) is greater than the Ra of the surface of the high-resistance layer on the main surfaces (hereinafter also referred to as main-surface high-resistance layer 13a).

[0019] The inventors have found that when a high-resistance layer is formed on a sintered body 11 produced by firing rectangular parallelepiped pieces obtained by cutting, the Ra of the surface of the side surface high-resistance layer 13b on the cut surface side of the sintered body 11 can be made larger than the Ra of the surface of the main surface high-resistance layer 13a. It is believed that the increase in Ra of the surface of the side surface high-resistance layer 13b enables the multilayer varistor 1 to suppress the occurrence of migration.

[0020] The method for manufacturing the laminated varistor 1 of this embodiment includes a first step, a second step, a third step, and a fourth step. In the first step, a sintered body 11 containing ZnO as a main component and having an internal electrode 12 provided therein is prepared. In the second step, a high-resistance layer 13 is formed so as to cover at least a portion of the sintered body 11. In the third step, a primary electrode paste is applied so as to cover a portion of the high-resistance layer 13 and to contact a portion of the internal electrode 12. In the fourth step, a plating electrode 16 is formed so as to cover at least a portion of the primary electrode 15 formed from the primary electrode paste. The arithmetic mean roughness of the surface of the high-resistance layer 13 after the second step is 0.06 μm or more and 0.9 μm or less.

[0021] According to the method for manufacturing the laminated varistor 1 of the present embodiment, it is possible to set the Ra of the surface of the high-resistance layer 13 within a specific range, and therefore it is possible to manufacture a laminated varistor 1 that can suppress the occurrence of migration on the surface of the high-resistance layer 13.

[0022] The method for manufacturing the laminated varistor 1 of this embodiment also comprises the first to fourth steps described above. The second step comprises spraying a solution containing a precursor of the high-resistance layer 13 onto the sintered bodies 11 while mixing and stirring the plurality of sintered bodies 11, and heat-treating the sintered bodies 11 to which the precursor has adhered, thereby forming the high-resistance layer 13.

[0023] According to such a manufacturing method, it is possible to form a high-resistance layer 13 having a large number of raised portions, thereby increasing the Ra of the surface of the high-resistance layer 13, and as a result, it is possible to manufacture a multilayer varistor 1 that can suppress the occurrence of migration on the surface of the high-resistance layer 13.

[0024] 2.Details <Multilayer varistor> 1 is a cross-sectional view of a multilayer varistor 1 according to an embodiment of the present disclosure. The multilayer varistor 1 comprises a sintered body 11, an internal electrode 12, a high-resistance layer 13, and an external electrode .

[0025] The sintered body 11 is made of a semiconductor ceramic component having non-linear resistance characteristics.

[0026] It is sufficient that the multilayer varistor 1 is provided with at least one pair of external electrodes 14. Here, the pair of external electrodes 14 includes a first external electrode 14A provided on one end face of the sintered body 11 and a second external electrode 14B provided on the other end face of the sintered body 11. When a voltage is applied between the first external electrode 14A and the second external electrode 14B, one of the first external electrode 14A and the second external electrode 14B becomes an electrode on the high potential side, and the other of the first external electrode 14A and the second external electrode 14B becomes an electrode on the low potential side.

[0027] 2, a pair of external electrodes 14 are provided on a pair of opposing end faces. The number and positions of the external electrodes 14 are not limited to this, and for example, a pair may be provided on the side face, or a pair may be provided on each of the end faces and the side face.

[0028] It is sufficient that one or more internal electrodes 12 are electrically connected to each of the external electrodes 14. In the multilayer varistor 1 of Fig. 1, the number of internal electrodes 12 is two. That is, the internal electrodes 12 include a first internal electrode 12A and a second internal electrode 12B, and the first internal electrode 12A is electrically connected to the first external electrode 14A, and the second internal electrode 12B is electrically connected to the second external electrode 14B.

[0029] At least one pair of external electrodes 14 is mounted on a printed wiring board on which an electric circuit is formed. The multilayer varistor 1 is connected, for example, to the input side of the electric circuit. When a voltage exceeding a predetermined threshold voltage is applied between the first external electrode 14A and the second external electrode 14B, the electric resistance between the first external electrode 14A and the second external electrode 14B suddenly decreases, allowing a current to flow through the varistor layer, thereby protecting the electric circuit downstream of the multilayer varistor 1.

[0030] [Sintered body] The semiconductor ceramic component having nonlinear resistance characteristics that constitutes the sintered body 11 is, for example, composed of ZnO as the main component and Bi2O3, Co2O3, MnO2, Sb2O3, Pr6O as the secondary components. 11 , Co2O 3、 These components include CaCO3, Cr2O3, etc. The varistor layer that constitutes the sintered body 11 is formed, for example, by firing a ceramic sheet containing these components, in such a way that the main components such as ZnO are dissolved and sintered with some of the secondary components, and the remaining secondary components are precipitated at the grain boundaries.

[0031] More specifically, the sintered body 11 is produced by cutting a laminate of ceramic sheets containing the above-mentioned components perpendicularly to the lamination surface and firing the resulting pieces. The sintered body 11 produced in this manner has a shape having, for example, a pair of opposing main surfaces, a pair of opposing side surfaces, and a pair of opposing end surfaces. The "main surfaces" refer to the lamination surfaces, and of the two cut surfaces, the larger surface is the "side surface" and the smaller surface is the "end surface." The shape of the sintered body 11 is, for example, a rectangular parallelepiped having two of each of these surfaces, for a total of six surfaces.

[0032] [Internal electrode] The internal electrodes 12 are provided inside the sintered body 11. The internal electrodes 12 contain, for example, Ag, Pd, PdAg, PtAg, etc., and are usually formed by stacking ceramic sheets coated with an internal electrode paste and firing them.

[0033] [High resistance layer] The high-resistance layer 13 is provided so as to cover at least a part of the sintered body 11. The surface shape of the high-resistance layer 13, such as Ra, can be controlled by appropriately selecting a method for forming the high-resistance layer 13, a method for producing the sintered body 11, etc., which will be described later.

[0034] The Ra of the surface of the high-resistance layer 13 is 0.06 μm or more. This makes it possible to suppress the occurrence of migration on the surface of the high-resistance layer 13. If the Ra is smaller than this value, the creepage distance between the external electrodes 14 becomes shorter, making migration more likely to occur. The Ra is preferably 0.08 μm or more, more preferably 0.15 μm or more, and even more preferably 0.25 μm or more. The Ra is preferably 0.9 μm or less. In this case, it is believed that the exposed portion of the sintered body 11 is further reduced, and as a result, the occurrence of migration can be further suppressed. If the Ra exceeds the above value, the exposed portion of the sintered body 11 becomes more exposed, making plating deposition more likely to occur, and the occurrence of migration may not be suppressed. Furthermore, solder flux may accumulate on the surface. The Ra is more preferably 0.7 μm or less, and even more preferably 0.4 μm or less. The Ra of the surface of the high-resistivity layer 13 can be measured in accordance with the method specified in, for example, JIS-B0601:(2013), specifically, using a high-precision microprofile measuring instrument, Surfcorder (ET4000A manufactured by Kosaka Laboratory Co., Ltd.) Ra can also be measured using, for example, a scanning probe microscope or a non-contact Leber microscope.

[0035] The Ra of the lamination surface (main surface) of the high-resistance layer 13 formed on the rectangular parallelepiped sintered body 11 produced as described above can be controlled to be in the range of 0.06 μm to 0.85 μm, and the Ra of the cut surfaces (side surfaces and end surfaces) can be controlled to be in the range of 0.11 μm to 0.9 μm. With such a multilayer varistor 1, the Ra of the surface of the side surface high-resistance layer 13b can be made larger than that of the main surface high-resistance layer 13a, thereby further suppressing the occurrence of migration caused by the movement of ions, etc. on the side surfaces. This is particularly effective in suppressing the occurrence of migration in a multilayer varistor 1 that has external electrodes 14 on the side surfaces in addition to the end surfaces, and in which the distance between the external electrodes 14 on the end surfaces and the external electrodes on the side surfaces is smaller than the distance between the pair of external electrodes 14 on the end surfaces.

[0036] The high-resistance layer 13 preferably has a raised portion. The "raised portion" is a region of the high-resistance layer 13 that is more than 1 μm thick. When the high-resistance layer 13 has a raised portion, the creepage distance between the external electrodes 14 becomes longer, and the occurrence of migration can be further suppressed.

[0037] When the high-resistance layer 13 has multiple protrusions, the average major axis of the protrusions is preferably 10 μm or more and 50 μm or less. By setting the average major axis of the protrusions within this range, the creeping distance between the external electrodes 14 can be increased, and as a result, the occurrence of migration can be further suppressed. This average major axis is more preferably 15 μm or more and 45 μm or less, and even more preferably 20 μm or more and 40 μm or less. The "major axis" of a protrusion refers to the longest axis in the planar shape of the protrusion, which is a region of the high-resistance layer 13 with a thickness of more than 1 μm. The "average major axis" refers to the arithmetic mean value of the major axes measured for multiple protrusions (e.g., any 10 points). The average major axis of the protrusions can be measured by observing elemental mapping images using the scanning probe microscope or EPMA.

[0038] Furthermore, when there are multiple raised portions, the total area of ​​the multiple raised portions is preferably 5% to 30% of the total surface area of ​​the high-resistivity layer 13. By setting the total area of ​​the raised portions within this range, it is possible to form a roughened surface that cannot be controlled simply by producing the sintered body 11, and as a result, the occurrence of migration can be further suppressed. This total area is more preferably 7% to 27%, and even more preferably 10% to 25%. The "total surface area" of the high-resistivity layer 13 refers to the sum of the areas of the exposed portions of the high-resistivity layer 13 that are not covered by the external electrodes 14, etc. The total area of ​​the raised portions can be measured from the observed image of elemental mapping by the EPMA.

[0039] In order to form more protrusions, it is preferable to use a method of forming the high resistance layer 13 by spraying a solution containing a precursor of the high resistance layer 13, which will be described later.

[0040] The average thickness of the high-resistance layer 13 is preferably 0.01 μm or more. In this case, it is believed that the exposed portion of the sintered body 11 is further reduced, and as a result, the occurrence of migration can be further suppressed. This average thickness is more preferably 0.05 μm or more, and even more preferably 0.1 μm or more. The average thickness of the high-resistance layer 13 is preferably 5 μm or less. In this case, it is believed that the movement of ions and the like by the high-resistance layer 13 is further suppressed, and as a result, the occurrence of migration can be further suppressed. This average thickness is more preferably 3 μm or less, and even more preferably 1 μm or less. The "average thickness" refers to the arithmetic mean value of the thickness of the high-resistance layer 13 measured at multiple points (for example, any 10 points) on the high-resistance layer 13.

[0041] [External electrode] The external electrode 14 is provided so as to cover a part of the high resistance layer 13. The external electrode 14 is electrically connected to the internal electrode 12.

[0042] The external electrode 14 includes, for example, a primary electrode 15 and a plating electrode 16. A secondary electrode may also be provided on the primary electrode 15. The secondary electrode is preferably formed so as to cover the primary electrode 15. In this way, the external electrode 14 (each of the first external electrode 14A and the second external electrode 14B) may have a multi-layer structure.

[0043] (Primary electrode) The primary electrode 15 is provided so as to cover a portion of the high-resistance layer 13 and to be electrically connected to the internal electrode 12. The primary electrode 15 contains a metal component, such as Ag, AgPd, or AgPt, and a glass component, such as Bi2O3, SiO2, or B2O5. The primary electrode 15 is preferably primarily composed of a metal, and more preferably primarily composed of silver. When the primary electrode 15 is primarily composed of silver, migration is likely to occur in the multilayer varistor. However, the present disclosure can suppress the occurrence of migration, providing significant benefits. The primary electrode 15 is usually formed by applying a primary electrode paste to a portion of the high-resistance layer 13.

[0044] (plating electrode) The plating electrode 16 is provided so as to cover at least a portion of the primary electrode 15. The plating electrode 16 includes, for example, a Ni electrode provided so as to cover at least a portion of the primary electrode or the secondary electrode, and a Sn electrode provided so as to cover at least a portion of the Ni electrode.

[0045] <Manufacturing method of multilayer varistor> The method for manufacturing a laminated varistor according to this embodiment comprises steps 1, 2, 3, and 4. Each step will be explained below.

[0046] [1st step] In the first step, a sintered body 11 containing ZnO as a main component and having an internal electrode 12 disposed therein is prepared.

[0047] The sintered body 11 can be produced by applying an internal electrode paste to ceramic sheets prepared using a slurry containing ZnO, laminating the ceramic sheets, pressing, cutting, and then removing the binder and firing. The slurry may contain, for example, ZnO as the main raw material and Bi2O3, Co2O3, MnO2, Sb2O3, and Pr6O as auxiliary raw materials. 11 , Co2O 3、 It can be prepared by mixing CaCO3, Cr2O3, etc. with a binder.

[0048] As the internal electrode paste, for example, Ag paste, Pd paste, Pt paste, PdAg paste, PtAg paste, etc. can be used.

[0049] The temperature for removing the binder is, for example, 300° C. or higher and 500° C. or lower. The temperature for firing can be appropriately adjusted depending on the structure, composition, etc. of the sintered body 11 to be obtained, and is, for example, 800° C. or higher and 1300° C. or lower.

[0050] The first step includes, for example, a coating step, an internal electrode coating step, a lamination step, a cutting step, and a firing step. In the coating step, a ceramic sheet containing ZnO as a main component is prepared. In the internal electrode coating step, an internal electrode paste is applied to the surface of the ceramic sheet. An example of an application method in the internal electrode coating step is a printing method. In the lamination step, a ceramic sheet coated with the internal electrode paste and a ceramic sheet not coated with the internal electrode paste are laminated to obtain a laminate. In the cutting step, the laminate is cut to obtain a laminate having a laminate surface and a cut surface. In the firing step, the laminate is fired to obtain a sintered body having a laminate surface and a cut surface.

[0051] By this method, it is possible to produce a sintered body 11 having a pair of opposing main surfaces, a pair of opposing side surfaces, and a pair of opposing end surfaces. The sintered body 11 produced in this manner can have a larger Ra at the cut surface than at the stacked surface.

[0052] [Second process] In the second step, the high resistance layer 13 is formed so as to cover at least a part of the sintered body 11 after the first step.

[0053] Methods for forming the high resistance layer 13 include, for example, (i) applying a solution containing a precursor of the high resistance layer 13 to the sintered body 11, (ii) reacting SiO2 with the sintered body 11 whose main component is ZnO, and (iii) thermally diffusing an alkali metal into the sintered body 11.

[0054] In method (i), for example, a solution containing a precursor of the high-resistance layer 13 is applied to the sintered body 11, followed by dehydration and curing, thereby forming the high-resistance layer 13 on the surface of the sintered body 11. Examples of precursors of the high-resistance layer 13 include glass components having Si in the main chain, such as polysilazane. By using a glass component having Si in the main chain, such as polysilazane, as the precursor of the high-resistance layer 13, a continuous high-resistance layer 13 mainly composed of SiO2 can be formed. It is believed that such a high-resistance layer 13 can further reduce the exposed portion of the sintered body 11, and as a result, a multilayer varistor 1 can be manufactured that can further suppress the occurrence of migration on the surface of the high-resistance layer 13.

[0055] Examples of application methods include spraying, dipping, printing, etc. Among these, the spraying method is desirable because it allows the formation of a high-resistance layer 13 having more protrusions with a thickness exceeding 1 μm, thereby increasing the Ra of the surface of the high-resistance layer 13. In addition, this spraying is preferably performed on a plurality of sintered bodies 11 that have been stirred and mixed.

[0056] In the method (ii), the sintered body 11 containing ZnO as the main component is reacted with SiO2 to convert the surface region of the sintered body 11 into a high-resistance layer 13 containing Zn2SiO4 as the main component, thereby forming the high-resistance layer 13. Specifically, this method can be carried out by, for example, adhering a powder or liquid containing SiO2 to the sintered body 11 containing ZnO as the main component, followed by heat treatment.

[0057] In the method (iii), the high-resistance layer 13 can be formed by thermally diffusing an alkali metal into the sintered body 11 to convert the surface region of the sintered body 11 into the high-resistance layer 13. Specifically, this method can be carried out by, for example, mixing the sintered body 11 with a liquid containing an alkali metal powder or an alkali metal salt as a main component, and then thermally firing the mixture.

[0058] The second step preferably includes a spraying step and a heat treatment step, as in method (i). In the spraying step, a solution containing a precursor of the high-resistance layer 13 is sprayed onto the sintered compacts 11 while mixing and stirring the sintered compacts 11. In the heat treatment step, the sintered compacts 11 to which the precursor has adhered are heat-treated to form the high-resistance layer 13. This method makes it possible to form a high-resistance layer 13 having many raised portions, and as a result, it is possible to manufacture a multilayer varistor 1 that can suppress the occurrence of migration.

[0059] The Ra of the surface of the high-resistance layer 13 after the second step is preferably larger than the Ra of the surface of the sintered body 11 after the first step. By appropriately selecting the method for forming the high-resistance layer 13, it is possible to increase the Ra of the surface of the high-resistance layer 13, and as a result, it is possible to manufacture a multilayer varistor 1 that can further suppress the occurrence of migration.

[0060] The average thickness of the high-resistance layer 13 after the second step is preferably larger than the Ra of the surface of the sintered body 11 after the first step. In this case, it is believed that the exposed portion of the sintered body 11 is further reduced, and as a result, the occurrence of migration can be further suppressed. If the average thickness of the high-resistance layer 13 is smaller than the Ra of the sintered body 11, part of the sintered body 11 will be exposed in the multilayer varistor 1, making plating deposition and migration more likely to occur. Furthermore, the Ra of the surface of the high-resistance layer 13 after the second step is preferably 0.06 μm or more and 0.9 μm or less.

[0061] Furthermore, the Ra of the surface of the high-resistance layer 13 after the second step can be controlled by, for example, a method of polishing the surface using a rotary pot containing polishing powder, a method using blasting, etc. The Ra of the surface of the sintered body 11 after the first step can be controlled by, for example, a method of dissolving the surface of the sintered body 11 by acid treatment. This dissolution treatment dissolves some of the particles of the sintered body 11, forming grain boundaries, thereby increasing the Ra of the surface of the sintered body 11, and by using this sintered body 11, the Ra of the surface of the high-resistance layer 13 after the second step can be increased.

[0062] [3rd step] In the third step, a primary electrode paste is applied so as to cover a part of the high resistance layer 13 and to come into contact with a part of the internal electrode 12 .

[0063] The primary electrode paste can be prepared by mixing a metal component including, for example, Ag powder, AgPd powder, or AgPt powder, a glass component including, for example, Bi2O3, SiO2, or B2O5, and a solvent. Alternatively, a primary electrode paste containing Ag as the main component and a resin component can also be used. After applying the primary electrode paste, baking at a temperature of 700°C to 800°C can promote alloying with the internal electrode 12, resulting in the formation of a primary electrode 15 with improved adhesion.

[0064] [4th step] In the fourth step, a plating electrode is formed so as to cover at least a part of the primary electrode 15 formed from the primary electrode paste. The plating electrode may be formed, for example, by electroplating, in which Ni plating and Sn plating are carried out in that order. [Example]

[0065] Hereinafter, the present disclosure will be described more specifically with reference to examples, but the present disclosure is not limited to only these examples.

[0066] <Manufacturing of multilayer varistors> The multilayer varistors of Examples 1 and 2 and Comparative Example 1 were manufactured according to the following procedure.

[0067] (Preparation of Slurry) The main component is ZnO and the secondary component is PrO 11 , Co2O 3、 CaCO3, Cr2O3, etc. were mixed with a binder to prepare a slurry.

[0068] (Ceramic sheet fabrication) The prepared slurry was molded into a ceramic sheet having a predetermined thickness of 20 μm or more and 50 μm or less.

[0069] (Preparation of laminate) A Pd paste was used as the internal electrode paste, and the internal electrode paste was printed in a predetermined shape on the prepared ceramic sheet. The ceramic sheet on which the internal electrode paste was printed and the ceramic sheet on which the internal electrode paste was not printed were laminated to form a predetermined electrode structure. The obtained laminate was pressed to a predetermined thickness, and then cut to a length of 1.0 mm, a width of 0.5 mm, and a height of 0.5 mm to prepare a laminate.

[0070] (Production of sintered body) The produced laminate was subjected to binder removal at a temperature of 300° C. to 500° C., and then fired at a temperature of 800° C. to 1300° C. to produce a sintered body.

[0071] (Formation of high resistance layer) A coating liquid containing polysilazane was sprayed onto the prepared sintered body using a sprayer, and then the precursor attached to the sintered body was cured at a temperature of 400°C or higher and 600°C or lower, thereby forming a high-resistance layer.

[0072] (Formation of primary electrode) A primary electrode paste was prepared by mixing Ag powder, glass frit, and a solvent, and the primary electrode paste was applied to the end surface of the sintered body on which the high-resistance layer was formed, followed by baking at 800°C to form a primary electrode.

[0073] (Formation of plating electrodes) On the primary electrode thus formed, a Ni-plated electrode having a predetermined thickness was formed by electrolytic plating, and then a Sn-plated electrode was formed thereon.

[0074] By selecting conditions such as the concentration of the coating liquid and the spray rate when forming the high-resistance layer, the multilayer varistor of Example 1 having an arithmetic mean roughness Ra of the surface of the high-resistance layer of 0.3 μm and the multilayer varistor of Example 2 having Ra of 0.09 μm were produced. In addition, the multilayer varistor of Comparative Example 1 having Ra of 0.03 μm was produced by immersing the sintered body in the coating liquid and then curing it.

[0075] <Evaluation> The produced laminated varistors were subjected to a humidity load test under the following conditions to evaluate the occurrence of migration.

[0076] (conditions) Temperature: 85°C, Relative humidity: 85%RH, Load voltage: 18V, Test time: 1000h (Migration evaluation) After the humidity and ambient load test, the appearance was observed and elemental analysis was carried out to check whether Ag had precipitated on the surface of the high-resistivity layer, i.e., whether migration had occurred.

[0077] [Table 1]

[0078] The results in Table 1 show that the arithmetic mean roughness Ra of the high-resistance layer surface of the multilayer varistors of Examples 1 and 2 was 0.3 μm and 0.09 μm, respectively, which is within the range of the present disclosure, and migration was suppressed. Also, the multilayer varistor of Comparative Example 1 had a high-resistance layer surface Ra of 0.03 μm, which is outside the range of the present disclosure, and migration occurred.

[0079] (summary) As is clear from the above-described embodiments and examples, the laminated varistor (1) of the first aspect comprises a sintered body (11), an internal electrode (12) provided inside the sintered body (11), a high-resistance layer (13) provided so as to cover at least a part of the sintered body (11), and an external electrode (14) provided so as to cover a part of the high-resistance layer (13) and electrically connected to the internal electrode (12). The arithmetic mean roughness of the surface of the high-resistance layer (13) is 0.06 μm or more.

[0080] According to the first aspect, by increasing the creepage distance between the external electrodes (14) and increasing the distance that ions and the like must travel before migration occurs, the migration barrier can be increased, and as a result, the occurrence of migration on the surface of the high-resistance layer (13) can be suppressed.

[0081] In the multilayer varistor (1) of the second embodiment, in the first embodiment, the arithmetic mean roughness of the surface of the high resistance layer (13) is 0.9 μm or less.

[0082] According to the second embodiment, it is believed that the exposed portion of the sintered body (11) is further reduced, and as a result, the occurrence of migration can be further suppressed.

[0083] In the multilayer varistor (1) of the third aspect, in the first or second aspect, the average thickness of the high resistance layer (13) is 0.01 μm or more and 5 μm or less.

[0084] According to the third aspect, it is believed that the exposed portion of the sintered body (11) is further reduced and the movement of ions and the like is further suppressed by the high resistance layer (13), thereby making it possible to further suppress the occurrence of migration.

[0085] In the laminated varistor (1) of the fourth aspect, in any one of the first to third aspects, the high resistance layer (13) has a plurality of raised portions which are parts of an area having a thickness of more than 1 μm, and the average major axis of the raised portions is 10 μm or more and 50 μm or less.

[0086] According to the fourth aspect, by setting the average major axis of the protrusions within a specific range, the creeping distance between the external electrodes (14) can be increased, and as a result, the occurrence of migration can be further suppressed.

[0087] In the laminated varistor (1) of the fifth aspect, in the fourth aspect, the total area of ​​the plurality of protrusions is 5% or more and 30% or less of the total area of ​​the surface of the high resistance layer (13).

[0088] According to the fifth aspect, by setting the total area of ​​the protrusions within a specific range, it becomes possible to form a roughened surface that cannot be controlled only by producing the sintered body (11), and as a result, the occurrence of migration can be further suppressed.

[0089] In the laminated varistor (1) of the sixth aspect, in any one of the first to fifth aspects, the external electrode (14) includes a primary electrode (15) provided so as to cover a part of the high-resistance layer (13), and a plated electrode (16) provided so as to cover at least a part of the primary electrode (15). The primary electrode (15) is mainly composed of silver.

[0090] According to the sixth aspect, when the primary electrode (15) is mainly composed of silver, migration is likely to occur in the laminated varistor, but the present disclosure can suppress the occurrence of migration, so the benefits of the present disclosure are great.

[0091] In the laminated varistor (1) of the seventh aspect, in any one of the first to sixth aspects, the sintered body (11) has a pair of opposing main surfaces, a pair of opposing side surfaces, and a pair of opposing end surfaces. Internal electrodes (12) face the main surfaces. External electrodes (14) cover the end surfaces. The arithmetic mean roughness of the surface of the high-resistance layer (13) on the side surfaces is greater than the arithmetic mean roughness of the surface of the high-resistance layer (13) on the main surfaces.

[0092] According to the seventh aspect, it is possible to further suppress the occurrence of migration caused by the movement of ions and the like on the side surfaces, and it is particularly effective in suppressing the occurrence of migration in a multilayer varistor (1) having external electrodes (14) on the end faces and side surfaces, in which the spacing between the external electrodes (14) is smaller.

[0093] In the laminated varistor (1) of the eighth aspect, in any one of the first to seventh aspects, the high resistance layer (13) contains SiO2 as a main component.

[0094] According to the eighth aspect, the high resistance layer (13) is mainly composed of SiO2, and thus can be made into a continuous high resistance layer (13). It is believed that such a high resistance layer (13) can further reduce the exposed portion of the sintered body (11), and as a result, the occurrence of migration can be further suppressed.

[0095] The laminated varistor (1) of the ninth aspect comprises a sintered body (11) having a pair of opposing main surfaces, a pair of opposing side surfaces, and a pair of opposing end surfaces, an internal electrode provided inside the sintered body (11) and facing the main surfaces, a high-resistance layer (13) provided so as to cover at least a part of the sintered body (11), and an external electrode (14) provided at the end surfaces so as to cover a part of the high-resistance layer (13) and electrically connected to the internal electrode (12). The arithmetic mean roughness of the surface of the high-resistance layer (13) on the side surfaces is greater than the arithmetic mean roughness of the surface of the high-resistance layer (13) on the main surfaces.

[0096] According to the ninth aspect, the surface Ra of the side surface high resistance layer (13b) can be made larger than that of the main surface high resistance layer (13a), and it is considered that the larger surface Ra of the side surface high resistance layer (13b) enables the laminated varistor (1) to suppress the occurrence of migration.

[0097] A tenth aspect of the method for manufacturing a laminated varistor (1) includes a first step, a second step, a third step, and a fourth step. In the first step, a sintered body (11) containing ZnO as a main component and having an internal electrode (12) provided therein is prepared. In the second step, a high-resistance layer (13) is formed so as to cover at least a portion of the sintered body (11). In the third step, a primary electrode paste is applied so as to cover a portion of the high-resistance layer (13) and to contact a portion of the internal electrode (12). In the fourth step, a plating electrode (16) is formed so as to cover at least a portion of the primary electrode (15) formed from the primary electrode paste. After the second step, the arithmetic mean roughness of the surface of the high-resistance layer (13) is 0.06 μm or more and 0.9 μm or less.

[0098] According to the tenth aspect, the arithmetic mean roughness of the surface of the high resistance layer (13) can be set within a predetermined range, and as a result, a multilayer varistor (1) can be manufactured that can suppress the occurrence of migration.

[0099] In the method for producing a laminated varistor (1) of the eleventh aspect, the arithmetic mean roughness of the surface of the high resistance layer (13) after the second step is greater than the arithmetic mean roughness of the surface of the sintered body (11) after the first step in the tenth aspect.

[0100] According to the eleventh aspect, by appropriately selecting a method for forming the high resistance layer (13), it is possible to increase the Ra of the surface of the high resistance layer (13), and as a result, it is possible to manufacture a laminated varistor (1) that can further suppress the occurrence of migration.

[0101] In the method for producing the laminated varistor (1) of the twelfth aspect, in the tenth or eleventh aspect, the second step comprises the steps of spraying a solution containing a precursor of the high resistance layer (13) onto the sintered bodies (11) while mixing and stirring the plurality of sintered bodies (11), and heat-treating the sintered bodies (11) to which the precursor has adhered, thereby forming the high resistance layer (13).

[0102] According to the twelfth aspect, the high resistance layer (13) formed by such a method can have more raised portions, and therefore the arithmetic mean roughness of the surface of the high resistance layer (13) can be made larger, and as a result, a laminated varistor (1) can be manufactured that can further suppress the occurrence of migration.

[0103] In the method for producing the laminated varistor (1) of the thirteenth aspect, in the twelfth aspect, the precursor solution contains polysilazane.

[0104] According to the thirteenth aspect, by using polysilazane, which is a glass component having Si in the main chain, as a precursor of the high resistance layer (13), it is possible to form a continuous high resistance layer (13) mainly composed of SiO2, and it is thought that such a high resistance layer (13) can further reduce the exposed portion of the sintered body (11), and as a result, it is possible to manufacture a laminated varistor (1) that can further suppress the occurrence of migration.

[0105] In a fourteenth aspect of the method for producing a laminated varistor (1), in any one of the tenth to thirteenth aspects, the first step includes a coating step, an internal electrode coating step, a lamination step, a cutting step, and a firing step. In the coating step, a ceramic sheet containing ZnO as a main component is produced. In the internal electrode coating step, an internal electrode paste is applied to the ceramic sheet. In the lamination step, a ceramic sheet coated with the internal electrode paste and a ceramic sheet not coated with the internal electrode paste are laminated to obtain a laminate. In the cutting step, the laminate is cut to obtain a laminate having a lamination surface and a cut surface. In the firing step, the laminate is fired to obtain a sintered body (11) having a lamination surface and a cut surface. The arithmetic mean roughness of the cut surface of the sintered body (11) is greater than the arithmetic mean roughness of the lamination surface of the sintered body (11).

[0106] According to the fourteenth aspect, it is possible to produce a sintered body (11) having a pair of main surfaces opposing each other, a pair of side surfaces opposing each other, and a pair of end surfaces opposing each other. This sintered body (11) can have a cut surface with a larger Ra than the laminated surface. Therefore, by forming a high resistance layer (13) on the sintered body (11) and producing a multilayer varistor (1), it is possible to make the surface Ra of the side surface high resistance layer (13b) larger than that of the main surface high resistance layer (13a). As a result, it is possible to further suppress the occurrence of migration caused by the movement of ions, etc. on the side surfaces.

[0107] A method for manufacturing a laminated varistor (1) according to a fifteenth aspect includes a first step, a second step, a third step, and a fourth step. In the first step, a sintered body (11) containing ZnO as a main component and having an internal electrode (12) provided therein is prepared. In the second step, a high-resistance layer (13) is formed so as to cover at least a portion of the sintered body (11). In the third step, a primary electrode paste is applied so as to cover a portion of the high-resistance layer (13) and to be in contact with a portion of the internal electrode (12). In the fourth step, a plating electrode (16) is formed so as to cover at least a portion of the primary electrode (15) formed from the primary electrode paste. The second step includes a step of spraying a solution containing a precursor of the high-resistance layer (13) onto the sintered bodies (11) while mixing and stirring the sintered bodies (11) and a step of heat-treating the sintered bodies (11) to which the precursor has been attached, thereby forming the high-resistance layer (13).

[0108] According to the fifteenth aspect, a high resistance layer (13) having a large number of protrusions can be formed, so that the Ra of the surface of the high resistance layer (13) can be increased, and as a result, a laminated varistor (1) capable of suppressing the occurrence of migration can be manufactured.

[0109] In the method for producing the laminated varistor (1) of the sixteenth aspect, in the fifteenth aspect, the precursor solution contains polysilazane.

[0110] According to the sixteenth aspect, by using polysilazane, which is a glass component having Si in the main chain, as a precursor of the high resistance layer (13), it is possible to form a continuous high resistance layer (13) mainly composed of SiO2, and it is thought that such a high resistance layer (13) can further reduce the exposed portion of the sintered body (11), and as a result, it is possible to manufacture a laminated varistor (1) that can further suppress the occurrence of migration. [Explanation of symbols]

[0111] 1 Multilayer varistor 11 Sintered body 12 Internal electrode 13 High resistance layer 13a Main surface high resistance layer 13b Side high resistance layer 14 External electrode 15 Primary electrode 16 Plating electrode

Claims

1. a sintered body; an internal electrode provided inside the sintered body; a high resistance layer provided so as to cover at least a portion of the sintered body; an external electrode provided so as to cover a part of the high resistance layer and electrically connected to the internal electrode; A laminated varistor in which the arithmetic mean roughness of the surface of the high resistance layer is 0.06 μm or more and 0.9 μm or less.

2. 2. The multilayer varistor according to claim 1, wherein the average thickness of said high resistance layer is 0.01 μm or more and 5 μm or less.

3. 3. The laminated varistor according to claim 1, wherein the high resistance layer has a plurality of raised portions which are portions of an area having a thickness of more than 1 μm, and the average major axis of the raised portions is 10 μm or more and 50 μm or less.

4. 4. The multilayer varistor according to claim 3, wherein the total area of ​​said plurality of protrusions is 5% or more and 30% or less of the total area of ​​the surface of said high resistance layer.

5. 5. The multilayer varistor according to claim 1, wherein the external electrodes include a primary electrode provided so as to cover a portion of the high-resistivity layer, and a plated electrode provided so as to cover at least a portion of the primary electrode, and the primary electrode is mainly composed of silver.

6. the sintered body has a pair of main surfaces facing each other, a pair of side surfaces facing each other, and a pair of end surfaces facing each other, the internal electrode faces the main surface, the external electrode covers the end surface, 6. The multilayer varistor according to claim 1, wherein the arithmetic mean roughness of the surface of said high resistance layer on said side surfaces is greater than the arithmetic mean roughness of the surface of said high resistance layer on said main surfaces.

7. The high resistance layer is made of SiO ２ 7. The multilayer varistor according to claim 1, wherein the main component is

8. a sintered body having a pair of opposing main surfaces, a pair of opposing side surfaces, and a pair of opposing end surfaces; an internal electrode provided inside the sintered body and facing the main surface; a high resistance layer provided so as to cover at least a portion of the sintered body; an external electrode provided on the end surface so as to cover a part of the high resistance layer and electrically connected to the internal electrode; A multilayer varistor in which the arithmetic mean roughness of the surface of the high resistance layer on the side surfaces is greater than the arithmetic mean roughness of the surface of the high resistance layer on the main surfaces.

9. A first step of preparing a sintered body containing ZnO as a main component and having an internal electrode provided therein; a second step of forming a high resistance layer so as to cover at least a portion of the sintered body; a third step of applying a primary electrode paste so as to cover a portion of the high-resistance layer and to contact a portion of the internal electrode; a fourth step of forming a plating electrode so as to cover at least a part of the primary electrode formed from the primary electrode paste, The method for manufacturing a multilayer varistor, wherein the arithmetic mean roughness of the surface of the high resistance layer after the second step is 0.06 μm or more and 0.9 μm or less.

10. 10. The method for producing a multilayer varistor according to claim 9, wherein the arithmetic mean roughness of the surface of the high-resistance layer after the second step is greater than the arithmetic mean roughness of the surface of the sintered body after the first step.

11. The second step is a step of spraying a solution containing a precursor of the high-resistance layer onto a plurality of the sintered bodies while mixing and stirring the sintered bodies; 11. The method for producing a multilayer varistor according to claim 9, further comprising the step of forming the high resistance layer by heat treating the sintered body to which the precursor has been attached.

12. The method for producing a laminated varistor according to claim 11, wherein the precursor solution contains polysilazane.

13. The first step A step of preparing a ceramic sheet containing ZnO as a main component; applying an internal electrode paste to the ceramic sheet; a step of laminating the ceramic sheet coated with the internal electrode paste and the ceramic sheet not coated with the internal electrode paste to obtain a laminate; cutting the laminate to obtain a laminate having a laminated surface and a cut surface; and firing the laminate to obtain a sintered body having a laminated surface and a cut surface, 13. The method for producing a multilayer varistor according to claim 9, wherein the arithmetic mean roughness of the cut surface of the sintered body is greater than the arithmetic mean roughness of the lamination surface of the sintered body.

14. A first step of preparing a sintered body containing ZnO as a main component and having an internal electrode provided therein; a second step of forming a high resistance layer so as to cover at least a portion of the sintered body; a third step of applying a primary electrode paste so as to cover a portion of the high-resistance layer and to contact a portion of the internal electrode; a fourth step of forming a plating electrode so as to cover at least a part of the primary electrode formed from the primary electrode paste, The second step is a step of spraying a solution containing a precursor of the high-resistance layer onto a plurality of the sintered bodies while mixing and stirring the sintered bodies; and forming the high-resistance layer by heat-treating the sintered body to which the precursor has been attached.

15. The method for producing a laminated varistor according to claim 14, wherein the precursor solution contains polysilazane.

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