Laminated Barista

Abstract

To provide a multilayer varistor capable of suppressing the occurrence of migration.SOLUTION: A multilayer varistor 1 includes a sintered body 11, a first internal electrode 12A, a second internal electrode 12B, a first external electrode 14A, a second external electrode 14B, and a high resistance layer 13. The first internal electrode 12A and the second internal electrode 12B are provided inside the sintered body 11. The first external electrode 14A is provided onto the surface of the sintered body 11 and is electrically connected to the first internal electrode 12A. The second external electrode 14B is provided to the surface of the sintered body 11 and is electrically connected to the second internal electrode 12B. The high resistance layer 13 covers at least part of the surface of the sintered body 11, and the high resistance layer 13 has multiple cracks on the surface.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a multilayer varistor. More specifically, it relates to a multilayer varistor having a sintered body with a laminated structure in which a plurality of layers are laminated.

Background Art

[0002] Varistors are used for the purpose of protecting various electronic devices, electronic components, etc. from abnormal voltages caused by lightning surges, static electricity, etc., and preventing malfunction of electronic devices, electronic components, etc. due to noise generated in the circuit.

[0003] Patent Document 1 discloses a chip-type electronic component. The chip-type electronic component has a ceramic element, a glass coat layer covering at least a part of the surface of the ceramic element, and external electrodes provided on both end surfaces of the ceramic element. In Patent Document 1, by setting the thickness of the glass coat layer to a predetermined value or more, deposition of plating on the surface of the ceramic element is suppressed during plating. Patent Document 1 exemplifies PTC thermistors, varistors, etc. as chip-type electronic components.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When a voltage is applied to a varistor in a high-humidity environment, there is a possibility that a phenomenon called migration occurs, in which ionized metal moves between electrodes, resulting in insulation failure.

[0006] An object of the present disclosure is to provide a multilayer varistor capable of suppressing the occurrence of migration.

Means for Solving the Problems

[0007] A multilayer varistor according to one aspect of the present disclosure comprises a sintered body, a first internal electrode, a second internal electrode, a first external electrode, a second external electrode, and a high-resistance layer. The first and second internal electrodes are provided inside the sintered body. The first external electrode is provided on the surface of the sintered body and is electrically connected to the first internal electrode. The second external electrode is provided on the surface of the sintered body and is electrically connected to the second internal electrode. The high-resistance layer covers at least a portion of the surface of the sintered body. The high-resistance layer has a plurality of cracks on its surface. The arithmetic mean of the length of the crack is 10 μm or more and 50 μm or less. The arithmetic mean of the width of the crack is 0.1 μm or more and 2 μm or less. The deepest part of the crack is within the range of the high-resistance layer. [Effects of the Invention]

[0008] According to this disclosure, the occurrence of migration can be suppressed. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic cross-sectional view of a multilayer varistor in one embodiment of the present disclosure. [Figure 2] Figure 2 is a schematic external perspective view of the same multilayer varistor. [Figure 3] Figure 3 shows an example of an image of the surface of the high-resistance layer of the multilayer varistor described above, taken with a scanning electron microscope. [Modes for carrying out the invention]

[0010] (Embodiment) (1) Overview The figures described in the following embodiments are schematic diagrams, and the ratios of the size and thickness of each component in each figure do not necessarily reflect the actual dimensional ratios.

[0011] As shown in Figure 1, the multilayer varistor 1 of this embodiment comprises a sintered body 11, a first internal electrode 12A, a second internal electrode 12B, a first external electrode 14A, a second external electrode 14B, and a high-resistance layer 13.

[0012] The first internal electrode 12A and the second internal electrode 12B are provided inside the sintered body 11.

[0013] The first external electrode 14A is provided on the surface of the sintered body 11 and is electrically connected to the first internal electrode 12A.

[0014] The second external electrode 14B is provided on the surface of the sintered body 11 and is electrically connected to the second internal electrode 12B.

[0015] The high-resistance layer 13 covers at least a portion of the surface of the sintered body 11. The high-resistance layer 13 has multiple cracks 20 on its surface (see Figure 3).

[0016] When a voltage is applied between the first external electrode 14A and the second external electrode 14B in a high-humidity environment, a phenomenon called migration may occur. The metal of the anode-side external electrode of the first external electrode 14A and the second external electrode 14B may ionize and move to the cathode-side external electrode, where it is generated as metal, potentially causing insulation failure between the first external electrode 14A and the second external electrode 14B.

[0017] In contrast, in the multilayer varistor 1 of the present embodiment, a plurality of cracks 20 are provided on the surface of the high-resistance layer 13. Here, the "surface" of the high-resistance layer 13 refers to the surface of the outer surface of the high-resistance layer 13 that is not covered by other layers (for example, the first external electrode 14A, the second external electrode 14B, etc.) and is exposed. Since a plurality of cracks 20 are provided on the surface of the high-resistance layer 13, the creepage distance between the first external electrode 14A and the second external electrode 14B, that is, the distance of the path along the surface of the high-resistance layer 13 between the first external electrode 14A and the second external electrode 14B can be increased. Therefore, when a voltage is applied between the first external electrode 14A and the second external electrode 14B in a high-humidity environment, even if metal ions elute from the external electrode on the anode side, the distance that the metal ions move before reaching the external electrode on the cathode side becomes longer. Thereby, the migration barrier of the metal ions eluted from the external electrode on the anode side can be increased, and the occurrence of migration can be suppressed.

[0018] (2) Details (2.1) Structure of Multilayer Varistor The multilayer varistor 1 in an embodiment of the present disclosure will be described in detail based on FIGS. 1 to 3.

[0019] FIG. 1 is a schematic cross-sectional view of the multilayer varistor 1. FIG. 2 is a schematic external perspective view of the multilayer varistor 1.

[0020] As described above, the multilayer varistor 1 includes a sintered body 11, a first internal electrode 12A, a second internal electrode 12B, a first external electrode 14A, a second external electrode 14B, and a high-resistance layer 13.

[0021] The sintered body 11 is formed in a rectangular parallelepiped shape having a long side in the left-right direction in the orientation shown in FIG. 1. Further, the sintered body 11 has a laminated structure in which a plurality of layers are laminated in the vertical direction in the orientation shown in FIG. 1. The sintered body 11 is composed of a semiconductor ceramic component having non-linear resistance characteristics. The semiconductor ceramic component having non-linear resistance characteristics constituting the sintered body 11 has, for example, ZnO as a main component and Bi2O3, Co2O3, MnO2, Sb2O3, Pr6O as sub-components11 It contains at least one of Co2O3, CaCO3, and Cr2O3. The multiple layers constituting the sintered body 11 are formed, for example, by firing a ceramic sheet containing these components, in which the main component such as ZnO undergoes solid solution sintering with some of the minor components, and the remaining minor components precipitate at the grain boundaries.

[0022] More specifically, the sintered body 11 is produced by stacking multiple ceramic sheets, each mainly composed of ZnO, and then cutting the laminate perpendicular to the stacking surface and firing the individual pieces. The sintered body 11 produced in this way has, for example, a pair of opposing main surfaces, a pair of opposing side surfaces, and a pair of opposing end surfaces. The "main surface" is the stacking surface. Of the two types of cut surfaces, the one with the larger area is the "side surface," and the one with the smaller area 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. For example, in the orientation shown in Figure 1, the top and bottom surfaces are the main surfaces, and the left and right surfaces are the end surfaces.

[0023] The first internal electrode 12A and the second internal electrode 12B are each provided inside the sintered body 11. The first internal electrode 12A and the second internal electrode 12B are arranged inside the sintered body 11 such that at least a portion of the first internal electrode 12A and at least a portion of the second internal electrode 12B overlap in the vertical direction. The first internal electrode 12A and the second internal electrode 12B include, for example, Ag, Pd, PdAg, PtAg, etc. The first internal electrode 12A and the second internal electrode 12B are formed, for example, by laminating ceramic sheets coated with the electrode material and firing them. Note that the first internal electrode 12A and the second internal electrode 12B are sometimes collectively referred to as the internal electrode 12.

[0024] The high-resistance layer 13 is provided so as to cover at least a portion of the sintered body 11. In this embodiment, the high-resistance layer 13 is provided so as to cover almost the entire surface of the sintered body 11 except for the areas where the first internal electrode 12A and the second internal electrode 12B are exposed. However, it may also be provided so as to cover the areas on the surface of the sintered body 11 where the first external electrode 14A and the second external electrode 14B are not provided.

[0025] The main component of the high-resistance layer 13 is, for example, SiO2. By covering the surface of the sintered body 11 with a high-resistance layer 13 whose main component is SiO2, which has high resistivity, it is possible to suppress both plating deposition and migration. The main component of the high-resistance layer is not limited to SiO2. The main component of the high-resistance layer may also be ZnSiO4, which can suppress both plating deposition and migration. Furthermore, the main component of the high-resistance layer may also be borosilicate glass, which can suppress both plating deposition and migration.

[0026] The high-resistance layer 13 is formed, for example, by the following method. That is, the high-resistance layer 13 is formed on the surface of the sintered body 11 by spray coating the surface of the sintered body 11 with a solution containing the components that make up the high-resistance layer 13, and then firing the sintered body 11.

[0027] The average thickness of the high-resistance layer 13 is preferably 0.01 μm or more and 5 μm or less. A higher average thickness of 0.01 μm is preferable, as it suppresses the exposure of the surface of the sintered body 11, which is the base for the high-resistance layer 13, thereby suppressing the occurrence of plating deposition and thus suppressing migration. Furthermore, a lower average thickness of 5 μm is preferable, as it allows for the formation of a high-resistance layer 13 with a stable thickness on the surface of the sintered body 11. The "average thickness" of the high-resistance layer 13 refers to the arithmetic mean of the thicknesses of the high-resistance layer 13 measured at multiple points (for example, any 10 points) on the high-resistance layer 13.

[0028] Here, the solution spray-coated onto the surface of the sintered body 11 shrinks during firing, forming multiple cracks 20 (see Figure 3) on the surface of the high-resistance layer 13. Figure 3 shows, for example, an example image of the surface of the high-resistance layer 13 taken with a scanning electron microscope. The shapes of the multiple cracks 20 vary, but they are generally formed in the shape of elongated grooves. The number and shape of the multiple cracks 20 formed on the surface of the high-resistance layer 13 can be controlled, for example, by adjusting the concentration, temperature, amount of the solution spray-coated onto the surface of the sintered body 11, the heat treatment temperature, the heat treatment time, etc.

[0029] In this case, it is preferable that the deepest part of the crack 20 is within the range of the high-resistance layer 13. That is, the deepest part of the crack 20 does not reach the surface of the sintered body 11, but remains within the range of the high-resistance layer 13. Therefore, since no crack is formed in the sintered body 11, which is the base of the high-resistance layer 13, the strength of the sintered body 11 is not impaired, and the strength of the sintered body 11 can be maintained above a certain level. Therefore, even if mechanical stress such as vibration or shock is applied to the laminated varistor 1, the possibility of the laminated varistor 1 breaking can be reduced.

[0030] The arithmetic mean of the length L1 of the crack 20, which is the longitudinal dimension of the crack 20, is preferably, for example, 10 μm or more and 50 μm or less. The arithmetic mean of the length L1 of the crack 20 can be obtained by observing an image of the surface of the high-resistance layer 13 to determine the length of a predetermined number (for example, any 10) of cracks 20 and calculating the average value. The image of the surface of the high-resistance layer 13 can be, for example, an image taken with a scanning electron microscope or an electron probe microanalyzer (EPMA). The shape of the crack 20 is controlled so that the arithmetic mean of the length L1 of the crack 20 is 10 μm or more and 50 μm or less, thereby reducing the possibility of migration occurring by increasing the creepage distance while reducing the possibility of the surface of the underlying sintered body 11 being exposed.

[0031] The arithmetic mean of the width L2 of the crack 20, which is the dimension in the shorter direction, is preferably, for example, 0.1 μm or more and 2 μm or less. The arithmetic mean of the width L2 of the crack 20 can be determined by observing images taken with a scanning electron microscope or electron probe microanalyzer, determining the width of a predetermined number (for example, any 10) of cracks 20, and calculating the average value, similar to the length L1. The shape of the crack 20 is controlled so that the arithmetic mean of the width L2 of the crack 20 is 0.1 μm or more and 2 μm or less, thereby reducing the possibility of migration occurring by increasing the creepage distance while reducing the possibility of the surface of the sintered body 11, which is the base material, being exposed.

[0032] Furthermore, it is preferable that the total area of ​​the multiple cracks 20 formed on the surface of the high-resistance layer 13 is 2.5% or more and 3.5% or less of the surface area (exposed area) of the high-resistance layer 13. By making the total area of ​​the multiple cracks 20 2.5% or more of the surface area of ​​the high-resistance layer 13, the creepage distance between the first external electrode 14A and the second external electrode 14B can be increased, thereby reducing the possibility of migration occurring.

[0033] Furthermore, in the multilayer varistor 1 of this embodiment, the arithmetic mean roughness (hereinafter also referred to as Ra) of the surface of the high-resistance layer 13 is adjusted by adjusting the number and shape of a plurality of cracks 20 provided on the surface of the high-resistance layer 13. Here, the arithmetic mean roughness of the surface of the high-resistance layer 13 is preferably 0.06 μm or more and 0.9 μm or less. The Ra of the surface of the high-resistance layer 13 is preferably 0.06 μm or more, which can suppress the occurrence of migration on the surface of the high-resistance layer 13. If the Ra of the surface of the high-resistance layer 13 is less than 0.06 μm, the creepage distance between the external electrodes 14 becomes shorter, and migration is more likely to occur. In addition, the Ra of the surface of the high-resistance layer 13 is preferably 0.9 μm or less, which can reduce the possibility of the underlying sintered body 11 being exposed, suppress the occurrence of plating deposition, and suppress the occurrence of migration. Furthermore, setting the Ra of the surface of the high-resistance layer 13 to 0.9 μm or less has the advantage that solder flux is less likely to accumulate on the surface.

[0034] The Ra of the surface of the high-resistance layer 13 can be measured in accordance with the method specified in, for example, JIS-B0601:(2013), specifically using a high-precision micro-shape measuring instrument, a SurfCorder (ET4000A manufactured by Kosaka Laboratory Co., Ltd.). The Ra of the surface of the high-resistance layer 13 can also be measured using, for example, a scanning probe microscope or a non-contact laser microscope.

[0035] The laminated varistor 1 is provided with a first external electrode 14A and a second external electrode 14B on a pair of end faces. In this embodiment, the first external electrode 14A is provided on the left end face of the sintered body 11, and the second external electrode 14B is provided on the right end face of the sintered body 11. The first external electrode 14A is electrically connected to the first internal electrode 12A, and the second external electrode 14B is electrically connected to the second internal electrode 12B. Here, the first external electrode 14A and the second external electrode 14B are sometimes collectively referred to as the external electrode 14.

[0036] The external electrode 14 includes, for example, a primary electrode 15 and a plated electrode 16. A secondary electrode may also be provided on the primary electrode 15. It is preferable that the secondary electrode is formed to cover the primary electrode 15. Thus, the external electrode 14 (each of the first external electrode 14A and the second external electrode 14B) may have a multilayer structure. In the following, the primary electrode 15 and plated electrode 16 constituting the first external electrode 14A may be referred to as primary electrode 15A and plated electrode 16A, respectively, and the primary electrode 15 and plated electrode 16 constituting the second external electrode 14B may be referred to as primary electrode 15B and plated electrode 16B, respectively.

[0037] 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, for example, 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 mainly composed of metal, and more preferably mainly composed of silver. When the primary electrode 15 is mainly composed of silver, migration is more likely to occur, but in the multilayer varistor 1 of this embodiment, the occurrence of migration is suppressed by providing a plurality of cracks 20 on the surface of the high-resistance layer 13. The primary electrode 15 is usually formed by applying a paste-like metal material to a portion of the high-resistance layer 13 to form the primary electrode 15.

[0038] 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 15 or a secondary electrode provided on the primary electrode 15, and a Sn electrode provided so as to cover at least a portion of the Ni electrode.

[0039] The multilayer varistor 1 is mounted, for example, on a printed circuit board on which an electrical circuit is formed. The multilayer varistor 1 is connected, for example, to the input side of an electrical circuit. 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 the high-potential side (anode side) electrode, and the other of the first external electrode 14A and the second external electrode 14B becomes the low-potential side (cathode side) electrode. When a voltage exceeding a predetermined threshold voltage is applied between the first external electrode 14A and the second external electrode 14B, the electrical resistance between the first external electrode 14A and the second external electrode 14B decreases sharply, and current flows through the semiconductor ceramic component layer present between the first external electrode 14A and the second external electrode 14B, thereby protecting the electrical circuit downstream of the multilayer varistor 1.

[0040] (2.2) Method for manufacturing a multilayer varistor An example of a manufacturing method for the multilayer varistor 1 of this embodiment is described below. Note that the manufacturing method for the multilayer varistor 1 is not limited to the method described below and can be modified as appropriate.

[0041] The manufacturing method for the multilayer varistor 1 comprises, for example, a first step, a second step, a third step, and a fourth step. Each step will be described below.

[0042] [1st step] In the first step, a sintered body 11 is prepared, which contains ZnO as the main component and has an internal electrode 12 arranged inside.

[0043] Multiple ceramic sheets are prepared using a slurry containing ZnO. An internal electrode paste, which will become the first internal electrode 12A, and an internal electrode paste, which will become the second internal electrode 12B, are applied to the surfaces of two of the multiple ceramic sheets. Then, the multiple ceramic sheets are stacked, pressed, and cut, followed by debinding and firing to create a sintered body 11.

[0044] The slurry used to create the ceramic sheet is, for example, made from ZnO as the main raw material and Bi2O3, Co2O3, MnO2, Sb2O3, and Pr6O as secondary raw materials. 11 It can be prepared by mixing at least one of Co2O3, CaCO3, and Cr2O3 with a binder.

[0045] For the internal electrode paste, for example, Ag paste, Pd paste, Pt paste, PdAg paste, PtAg paste, etc., can be used.

[0046] The temperature at which the binder is removed is, for example, 300°C to 500°C. The temperature at which the firing is performed can be appropriately adjusted depending on the structure and composition of the resulting sintered body 11, for example, 800°C to 1300°C.

[0047] The first step includes, for example, a coating step, an electrocoating step, a lamination step, a cutting step, and a firing step. In the coating step, a ceramic sheet containing ZnO as the main component is produced. In the electrocoating step, an internal electrode paste is applied to the surface of the ceramic sheet. Examples of application methods in the electrocoating step include printing. In the lamination step, a ceramic sheet coated with the internal electrode paste and a ceramic sheet without the internal electrode paste are laminated to obtain a laminate. In the cutting step, the laminate is cut to obtain a laminate having a laminated surface and a cut surface. In the firing step, the laminate is fired to obtain a sintered body having a laminated surface (main surface) and cut surfaces (side and end surfaces).

[0048] By this method, a sintered body 11 having a pair of opposing main surfaces, a pair of opposing side surfaces, and a pair of opposing end surfaces can be manufactured.

[0049] [Second process] In the second step, a high-resistance layer 13 is formed so as to cover at least a portion of the sintered body 11 after the first step.

[0050] 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 a sintered body 11 mainly composed of ZnO, and (iii) thermally diffusing alkali metals into the sintered body 11.

[0051] For example, a high-resistance layer 13 can be formed on the surface of the sintered body 11 by applying a solution containing a precursor for the high-resistance layer 13 to the sintered body 11, followed by dehydration and curing. Examples of precursors for 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 a precursor for 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 area where the sintered body 11 is exposed, and as a result, a laminated varistor 1 can be manufactured that can further suppress the occurrence of migration on the surface of the high-resistance layer 13.

[0052] Examples of coating methods include spraying, dipping, and printing. Furthermore, spraying is preferably performed on multiple sintered bodies 11 that have been stirred and mixed.

[0053] In method (ii), a high-resistance layer 13 can be formed by reacting a sintered body 11 mainly composed of ZnO with SiO2, thereby converting the surface region of the sintered body 11 into a high-resistance layer 13 mainly composed of Zn2SiO4. Specifically, this method can be carried out, for example, by attaching a powder or liquid containing SiO2 to a sintered body 11 mainly composed of ZnO, and then performing a heat treatment.

[0054] In method (iii), the surface region of the sintered body 11 can be converted into a high-resistance layer 13 by thermal diffusion of alkali metal into the sintered body 11, thereby forming a high-resistance layer 13. Specifically, this method can be carried out, for example, by mixing the sintered body 11 with a liquid mainly composed of alkali metal powder or alkali metal salt, and then performing heat firing.

[0055] 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 for the high-resistance layer 13 is sprayed onto the sintered bodies 11 while mixing and stirring the sintered bodies 11. In the heat treatment step, the high-resistance layer 13 is formed by heat-treating the sintered bodies 11 to which the precursor has adhered. According to this method, a high-resistance layer 13 having multiple cracks 20 on its surface can be formed during the heat treatment process of the sintered bodies 11 to which the precursor has adhered, and as a result, the occurrence of migration can be suppressed.

[0056] The Ra of the surface of the high-resistance layer 13 after the second step is preferably greater 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, the Ra of the surface of the high-resistance layer 13 can be increased, and as a result, the occurrence of migration can be further suppressed.

[0057] The average thickness of the high-resistance layer 13 after the second step is preferably greater than the Ra of the surface of the sintered body 11 after the first step. In this case, the exposed portion of the sintered body 11 is thought to be reduced, and as a result, the occurrence of migration can be further suppressed. If the average thickness of the high-resistance layer 13 is less than the Ra of the surface of the sintered body 11, a part of the sintered body 11 will be exposed in the multilayer varistor 1, making it easier for plating deposition and migration 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.

[0058] Furthermore, the Ra of the surface of the high-resistance layer 13 after the second process can be controlled by methods such as surface polishing using a rotating pot containing abrasive powder, or by using blasting. The Ra of the surface of the sintered body 11 after the first process can be controlled by methods such as surface dissolution treatment of the sintered body 11 by acid treatment. This dissolution treatment causes some of the particles of the sintered body 11 to dissolve and grain boundaries to be formed, thereby increasing the Ra of the surface of the sintered body 11. By using this sintered body 11, the Ra of the surface of the high-resistance layer 13 after the second process can be increased.

[0059] [3rd step] In the third step, a primary electrode paste is applied so as to cover a portion of the high-resistance layer 13 and come into contact with a portion of the internal electrode 12.

[0060] The primary electrode paste can be prepared by mixing a metal component, such as Ag powder, AgPd powder, or AgPt powder, with a glass component, such as Bi2O3, SiO2, or B2O5, and a solvent. Alternatively, a primary electrode paste with Ag as the main component and containing a resin component can also be used. After applying the primary electrode paste, baking at 700°C to 800°C promotes alloying with the internal electrode 12, resulting in a primary electrode 15 with improved adhesion.

[0061] [4th step] In the fourth step, a plated electrode 16 is formed so as to cover at least a portion of the primary electrode 15 formed from the primary electrode paste. Methods for forming the plated electrode 16 include, for example, electroplating, where Ni plating and then Sn plating are performed sequentially.

[0062] (Examples) The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to the examples.

[0063] A multilayer varistor 1 was manufactured using the following procedure.

[0064] (Preparation of slurry) The main component is ZnO, and the minor component is Pr6O 11 A slurry was prepared by mixing Co2O3, CaCO3, Cr2O3, etc., with a binder.

[0065] (Fabrication of ceramic sheets) Using the prepared slurry, a ceramic sheet was fabricated by molding it to a predetermined thickness of 20 μm to 50 μm.

[0066] (Fabrication of laminates) Pd paste was used as the internal electrode paste, and the internal electrode paste was printed onto the prepared ceramic sheet in a predetermined shape. The ceramic sheet with the printed internal electrode paste and the ceramic sheet without the printed internal electrode paste were then laminated to form a predetermined electrode structure. The resulting laminate was pressed to a predetermined thickness, then cut to a length of 1.0 mm, a width of 0.5 mm, and a height of 0.5 mm to produce a laminate.

[0067] (Fabrication of sintered bodies) The prepared laminate was debindered 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.

[0068] (Formation of a high-resistance layer) A coating solution containing polysilazane was sprayed onto the prepared sintered body using a sprayer, and then a high-resistance layer was formed by curing the precursor attached to the sintered body at a temperature of 400°C to 600°C.

[0069] (Formation of the primary electrode) A primary electrode paste was prepared by mixing Ag powder, glass frit, and a solvent. This primary electrode paste was applied to the end face of the sintered body on which the high-resistance layer was formed, and then baked at 800°C to form the primary electrode.

[0070] (Formation of plated electrodes) On the primary electrode formed as described above, a Ni-plated electrode of a predetermined thickness was formed by electroplating, and then a Sn-plated electrode was formed on top of that.

[0071] A laminated varistor 1 was fabricated by selecting conditions such as the concentration and spraying speed of the coating solution during the formation of the high-resistance layer.

[0072] (3) Variant The above embodiments are merely one of many embodiments of this disclosure. The above embodiments can be modified in various ways depending on the design, etc., as long as they achieve the objectives of this disclosure.

[0073] Modifications of the above embodiment will be described below.

[0074] In the stacked varistor 1 of the above embodiment, a pair of external electrodes 14 are provided on a pair of opposing end faces, but the number and position of the external electrodes 14 are not limited thereto. For example, a pair of external electrodes may be provided on a pair of opposing side faces, or one pair of external electrodes may be provided on a pair of end faces and a pair of side faces, respectively.

[0075] Furthermore, the sintered body 11 contains one first internal electrode 12A electrically connected to the first external electrode 14A and one second internal electrode 12B electrically connected to the second external electrode 14B, but the number of first internal electrodes 12A and second internal electrodes 12B is not limited to one. The sintered body 11 may contain multiple first internal electrodes 12A electrically connected to the first external electrode 14A, or multiple second internal electrodes 12B electrically connected to the second external electrode 14B.

[0076] (summary) As described above, the multilayer varistor (1) of the first embodiment comprises a sintered body (11), a first internal electrode (12A), a second internal electrode (12B), a first external electrode (14A), a second external electrode (14B), and a high-resistance layer (13). The first internal electrode (12A) and the second internal electrode (12B) are provided inside the sintered body (11). The first external electrode (14A) is provided on the surface of the sintered body (11) and is electrically connected to the first internal electrode (12A). The second external electrode (14B) is provided on the surface of the sintered body (11) and is electrically connected to the second internal electrode (12B). The high-resistance layer (13) covers at least a portion of the surface of the sintered body (11). The high-resistance layer (13) has a plurality of cracks (20) on its surface.

[0077] According to this embodiment, by providing multiple cracks (20) on the surface of the high-resistance layer (13), the creepage distance between the first external electrode (14A) and the second external electrode (14B) can be increased. Therefore, even if metal ions are eluted from the anode-side external electrode when a voltage is applied between the first external electrode (14A) and the second external electrode (14B) in a high-humidity environment, the distance the metal ions have to travel to reach the cathode-side external electrode becomes longer. This increases the migration barrier for metal ions eluted from the anode-side external electrode, thereby suppressing the occurrence of migration.

[0078] In the second embodiment of the laminated varistor (1), the arithmetic mean of the length of the crack (20) is 10 μm or more and 50 μm or less, as in the first embodiment.

[0079] According to this embodiment, it is possible to suppress the exposure of the sintered body (11), which is the base of the high-resistance layer (13), while suppressing the occurrence of migration.

[0080] In the third embodiment of the stacked varistor (1), in the first or second embodiment, the arithmetic mean of the width of the crack (20) is 0.1 μm or more and 2 μm or less.

[0081] According to this embodiment, it is possible to suppress the exposure of the sintered body (11), which is the base of the high-resistance layer (13), while suppressing the occurrence of migration.

[0082] In the fourth embodiment of the multilayer varistor (1), in any of the first to third embodiments, the average thickness of the high-resistance layer (13) is 0.01 μm or more and 5 μm or less.

[0083] According to this embodiment, it is possible to suppress the exposure of the sintered body (11), which is the base of the high-resistance layer (13), while suppressing the occurrence of migration.

[0084] In the fifth embodiment of the multilayer varistor (1), in any of the first to fourth embodiments, the deepest part of the crack (20) is located within the high-resistance layer (13).

[0085] According to this embodiment, it is possible to suppress the occurrence of cracks in the sintered body (11) and to suppress a decrease in the strength of the sintered body (11).

[0086] In the sixth embodiment of the multilayer varistor (1), the main component of the high-resistance layer (13) is SiO2, in any of the first to fifth embodiments.

[0087] According to this embodiment, by using SiO2, which has a higher resistivity than the sintered body (11), as the main component of the high-resistivity layer (13), it is possible to suppress the occurrence of migration while suppressing plating deposition.

[0088] In the seventh embodiment of the multilayer varistor (1), the main component of the high-resistance layer (13) is ZnSiO4, in any of the first to fifth embodiments.

[0089] According to this embodiment, by using ZnSiO4, which has a higher resistivity than the sintered body (11), as the main component of the high-resistivity layer (13), it is possible to suppress the occurrence of migration while suppressing plating deposition.

[0090] In the eighth embodiment of the multilayer varistor (1), in any of the first to seventh embodiments, 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.

[0091] According to this embodiment, the creepage distance between the first external electrode (14A) and the second external electrode (14B) can be increased. Therefore, even if metal ions are eluted from the anode-side external electrode when a voltage is applied between the first external electrode (14A) and the second external electrode (14B) in a high-humidity environment, the distance the metal ions have to travel to reach the cathode-side external electrode becomes longer. This increases the migration barrier for metal ions eluted from the anode-side external electrode, thereby suppressing the occurrence of migration.

[0092] The configurations relating to the second to eighth aspects are not essential to the stacked varistor (1) and can be omitted as appropriate. [Explanation of symbols]

[0093] 1. Stacked varistor 11 Sintered body 12A 1st internal electrode 12B 2nd internal electrode 13 High resistance layer 14A 1st external electrode 14B 2nd external electrode 20 cracks

Claims

1. Sintered body and, The first internal electrode and the second internal electrode are provided inside the sintered body, A first external electrode is provided on the surface of the sintered body and is electrically connected to the first internal electrode, A second external electrode is provided on the surface of the sintered body and is electrically connected to the second internal electrode, The sintered body comprises a high-resistance layer covering at least a portion of its surface, The aforementioned high-resistance layer has multiple cracks on its surface. The arithmetic mean of the length of the crack is 10 μm or more and 50 μm or less. The arithmetic mean of the width of the crack is 0.1 μm or more and 2 μm or less. The deepest part of the crack is within the range of the high-resistance layer. Stacked barista.

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

3. The main component of the high-resistance layer is SiO₂, A multilayer varistor according to claim 1 or 2.

4. The main component of the high-resistance layer is ZnSiO4, A multilayer varistor according to claim 1 or 2.

5. The arithmetic mean roughness of the surface of the high-resistance layer is 0.06 μm or more and 0.9 μm or less. A multilayer varistor according to any one of claims 1 to 4.

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