Thermistor element and method for manufacturing same

Abstract

Provided is a thermistor element which comprises an element body and an external electrode that is positioned at least on an end surface of the element body. The external electrode is provided with: an Ag-containing base layer that is positioned on the element body; and a plating layer that is positioned on the Ag-containing base layer. With respect to the external electrode, there are: a first region which is provided with the Ag-containing base layer that continuously covers the end surface; and a second region which extends along the outer edge of the first region, and in which a plurality of the Ag-containing base layers are intermittently positioned. At least one of the plurality of Ag-containing base layers in the second region includes at least one element that is selected from the group consisting of Cl, Br, and I.

Description

Thermistor element and its manufacturing method

[0001] The present disclosure relates to a thermistor element and a method for manufacturing the same.

[0002] Conventionally, thermistor elements described in Patent Documents 1 to 3 are known. These thermistor elements include an element body made of ceramic, external electrodes covering both end faces of the element body, and internal electrodes provided inside the element body and connected to the external electrodes.

[0003] JP 2023-64513 A JP 2009-283986 A JP 6-61008 A

[0004] Conventional thermistor elements generally use Ag (silver) for the external electrodes. For example, the thermistor elements shown in Patent Documents 1 to 3 include external electrodes in which a layer containing silver is plated with a metal such as Ni (nickel) or Sn (tin). However, silver is known to be an element that is prone to ion migration. In a high-temperature, high-humidity environment, ion migration can occur, potentially causing electrical conduction between the external electrodes covering both end faces of the element, resulting in a short circuit.

[0005] The present disclosure has been made in view of the above-mentioned problems. That is, a main object of the present disclosure is to provide a thermistor element that can suitably suppress ion migration of external electrodes, and a method for manufacturing the same.

[0006] The inventors of the present application attempted to solve the above problems by taking a new approach rather than simply extending the conventional technology, and as a result, they have invented a thermistor element that achieves the above-mentioned main object, as well as a method of manufacturing such a thermistor element.

[0007] A thermistor element according to one embodiment of the present disclosure comprises: an element body; and an external electrode positioned at least on an end surface of the element body; the external electrode comprises an Ag-containing base layer positioned on the element body; and a plating layer positioned on the Ag-containing base layer; the external electrode has a first region comprising the Ag-containing base layer continuously covering at least a portion of the end surface; and a second region extending along the outer edge of the first region and in which a plurality of the Ag-containing base layers are positioned intermittently; and at least one of the plurality of Ag-containing base layers in the second region contains at least one element selected from the group consisting of Cl, Br, and I.

[0008] Furthermore, a method for manufacturing a thermistor element according to an embodiment of the present disclosure includes: a base-forming step of forming an Ag-containing base layer on an element body to obtain a thermistor precursor; and a plating step of forming a plating layer on the Ag-containing base layer, wherein the base-forming step includes forming a first region in which the Ag-containing base layer is continuously present so as to be positioned at least on an end face of the element body, and a second region in which a plurality of the Ag-containing base layers are present intermittently along an outer edge of the first region, and the plating step includes immersing the thermistor precursor in a solution containing at least one ion selected from the group consisting of Cl ions, Br ions, and I ions before forming the plating layer, and wherein a total concentration of Cl ions, Br ions, and I ions in the solution is 1 mol / L or more and 5 mol / L or less.

[0009] In the thermistor element according to the present disclosure, the external electrode includes a first region in which the Ag-containing underlayer is continuous, and a second region extending along the periphery of the first region and in which the Ag-containing underlayer is intermittently arranged. At least a portion of the Ag-containing underlayer in the second region contains at least one element selected from the group consisting of Cl, Br, and I. This allows a thin plating layer to be favorably maintained on the Ag-containing underlayer in the second region. By disposing such a plating layer along the periphery of the first region, ion migration of Ag from the first region can be favorably suppressed.

[0010] FIG. 1 is a schematic perspective view showing the appearance of a thermistor element according to an embodiment of the present disclosure. FIG. 2 is a schematic cross-sectional view showing the internal configuration of a thermistor element according to an embodiment of the present disclosure. FIG. 3 is a schematic cross-sectional view showing an element body of a thermistor element according to an embodiment of the present disclosure, the element body including an Ag-containing base layer. FIG. 4 is a schematic plan view showing an element body of a thermistor element according to an embodiment of the present disclosure, the element body including an Ag-containing base layer. FIG. 5 is a schematic enlarged cross-sectional view showing an Ag-containing base layer on an element body of a thermistor element according to an embodiment of the present disclosure. FIG. 6 is a schematic enlarged cross-sectional view showing a thermistor element according to an embodiment of the present disclosure. FIG. 7 is a schematic cross-sectional view of a thermistor element according to another embodiment of the present disclosure.

[0011] The following describes specific embodiments of the present disclosure. The applicant provides the following description and examples to enable those skilled in the art to fully understand the present disclosure, and it should be noted that these are not intended to limit the subject matter described in the claims. In other words, the present disclosure is not particularly limited to the preferred embodiments described below, and can be implemented with appropriate modifications within the scope of its purpose. For convenience, the present disclosure may be divided into embodiments and examples to facilitate explanation or understanding of the key points. However, partial substitution and / or combination of the configurations shown in different embodiments is possible. In describing such embodiments, redundant explanations of substantially identical features may be omitted, and only differences may be described. In particular, similar effects resulting from similar configurations may not be mentioned in each embodiment.

[0012] Furthermore, references to directions or orientations in the description of this specification are merely for the convenience of explanation and are not intended to limit the scope of the present disclosure unless otherwise explicitly stated. For example, relative terms such as "outside (or outer, external, or outer periphery)" and "inside (or inner, internal, or inner periphery)" and their derivatives should be understood to refer to the directions as described or illustrated. Similarly, "on" an element includes not only contact with the top surface of the element but also non-contact with the top surface of the element. In other words, "on" an element includes not only a position above the element, i.e., a position above the element via another object or a position above the element with a gap, but also a position directly above the element. Furthermore, "on" does not necessarily mean above in the vertical direction. "On" merely indicates the relative position of an element. In other words, unless otherwise explicitly stated, the invention is not limited to a specific direction, orientation, shape, or the like. The same also applies to terms such as "provided," "disposed," "positioned," "connected," and "attached," and their derivatives, and unless otherwise explicitly stated, may not be limited to a direct manner, but may also be a manner in which other elements, such as intervening objects, are involved.

[0013] The various numerical ranges referred to herein are intended to include the lower and upper numerical limits themselves unless otherwise specified, and the term "about" means that there may be a variation or difference of a few percent, e.g., ±10%.

[0014] As used herein, "vertical" and "substantially vertical" do not necessarily mean completely "vertical," but include aspects that are slightly deviated from the completely vertical (for example, a range of ±10° from the completely vertical, e.g., a range of ±5°).

[0015] Furthermore, in this specification, "substantially parallel" does not necessarily mean completely "parallel," but includes a state where the parallelism is slightly deviated from the parallelism (for example, within a range of ±10° from completely parallelism, e.g., within a range of ±5°).

[0016] The terms "plan view" and "plan view shape" used in this specification are based on a sketch of the object viewed along the stacking direction of the ceramic layers. The term "side view" used in this specification is based on the shape of the object viewed from a direction perpendicular to the stacking direction of the ceramic layers.

[0017] The terms "upper and lower directions" and "lower and higher directions" used directly or indirectly in this specification correspond to the upper and lower directions and lower and higher and lower directions in the drawings, respectively. Unless otherwise specified, the same reference numerals or symbols indicate the same components or parts or the same meanings.

[0018] [Basic Configuration of Thermistor Element] Fig. 1 is a perspective view schematically showing a thermistor element according to one embodiment of the present disclosure. Fig. 2 is a schematic cross-sectional view of the thermistor element 100 shown in Fig. 1. As shown in the figure, the thermistor element 100 includes an element body 10, an internal electrode 12 provided inside the element body 10, and an external electrode 20 covering part of the surface of the element body and electrically connected to the internal electrode 12. More specifically, the thermistor element may include a plurality of internal electrodes, namely, first internal electrodes 12A and second internal electrodes 12B, and first external electrodes 20A and second external electrodes 20B electrically connected to the first internal electrodes 12A and second internal electrodes 12B, respectively.

[0019] (Element Body) The element body 10 may be made of ceramic. More specifically, the element body 10 may be made of a plurality of laminated ceramic layers 11. The ceramic layers 11 may include, for example, ceramics having a negative resistance-temperature characteristic. By way of example only, the ceramic layers 11 may be oxides with a spinel structure. More specifically, the ceramic layers 11 may be oxides with a spinel structure containing at least one element selected from the group consisting of Mn (manganese), Ni (nickel), Co (cobalt), Fe (iron), aluminum (Al), copper (Cu), zinc (Zn), zirconium (Zr), and titanium (Ti). A thermistor element including an element body containing such ceramic layers may be an NTC (Negative Temperature Coefficient) thermistor element, the resistance of which decreases with increasing temperature.

[0020] The element body 10 may be formed, for example, in a substantially rectangular parallelepiped shape. The surface of the element body 10 is composed of a first end face 14A, a second end face 14B located opposite the first end face 14A, and a peripheral surface 15 connecting the first end face 14A and the second end face 14B (see FIGS. 1 and 2). The peripheral surface 15 may be composed of two main faces 15A located in the stacking direction of the ceramic layers and two side faces 15B connecting the two main faces 15A. The end face 14, the main faces 15A, and the side faces 15B may extend in directions that intersect with each other.

[0021] Here, the length direction of the thermistor element 100 extending from the first end face 14A to the second end face 14B is defined as the X direction, the width direction of the thermistor element 100 extending across the two side faces is defined as the Z direction, and the thickness direction of the thermistor element extending across the two main faces is defined as the Y direction. The Y direction coincides with the stacking direction of the ceramic layers. The X direction, Y direction, and Z direction may be perpendicular to one another. Specifically, the X direction may be perpendicular to the first end face, the Z direction may be perpendicular to the first side face, and the Y direction may be perpendicular to the first main face.

[0022] The first internal electrodes 12A and the second internal electrodes 12B may be alternately stacked with the ceramic layers 11. The first internal electrodes 12A and the second internal electrodes 12B may contain, for example, at least one element selected from the group consisting of Ag (silver) and Pd (palladium) or a compound thereof. Although not shown, further internal electrodes different from the first internal electrodes 12A and the second internal electrodes 12B may be disposed inside the element body 10.

[0023] The first external electrode 20A may cover at least the first end face 14A. Specifically, the first external electrode 20A may be positioned on the first end face 14A and cover at least a portion of the first end face 14A. More preferably, the first external electrode 20A may cover the entire first end face 14A and the first end face side of the peripheral face 15. For example, the first external electrode 20A may cover the entire first end face 14A and extend from the first end face 14A to a portion of at least one of the main surface and side faces. The first external electrode 20A may be an electrode that extends across five faces, including the entire first end face 14A and portions of the four peripheral faces 15. The first external electrode 20A may cover at least one corner of the element body 10 located on the first end face side. The first external electrode 20A is in contact with and electrically connected to an end of the first internal electrode 12A. More specifically, the first external electrode 20A may be in contact with the end of the first internal electrode 12A that extends to the end face 14 of the element body 10, and the two may be electrically connected to each other.

[0024] The second external electrode 20B may cover at least the second end face 14B. Specifically, the second external electrode 20B may be positioned on the second end face 14B and cover at least a portion of the second end face 14B. More preferably, the second external electrode 20B may cover the entire second end face 14B and the second end face side of the peripheral face 15. For example, the second external electrode 20B may cover the entire second end face 14B and extend from the second end face 14B to a portion of at least one of the main surface and side face. The second external electrode 20B may be an electrode extending across five faces, including the entire second end face 14B and portions of the four peripheral faces 15. The second external electrode 20B may cover at least one corner of the element body 10 located on the second end face side. The second external electrode 20B contacts and is electrically connected to an end of the second internal electrode 12B. More specifically, the second external electrode 20B may be in contact with the end of the second internal electrode 12B that extends to the end face of the element body 10, and the two may be electrically connected to each other.

[0025] The external electrode 20 is composed of multiple electrode layers, the outermost layer of which is a metal plating layer 24. The first external electrode 20A has an innermost base layer 22 that covers the element body 10, and a plating layer 24 positioned on the base layer 22. Similarly, the second external electrode 20B has an innermost base layer 22 that covers the element body 10, and a plating layer 24 positioned on the base layer 22. Hereinafter, the first external electrode 20A will be described simply as the "external electrode 20," but the same applies to the second external electrode 20B.

[0026] For example, the external electrode 20 is composed of a plurality of electrode layers, the outermost layer of which is a metal plating layer 24. When the base layer 22 and the plating layer 24 are laminated, for example, the base layer 22 and the plating layer 24 may be laminated so that they are in contact with each other, or another layer may be interposed between the base layer 22 and the plating layer 24.

[0027] The base layer 22 is a conductive material containing Ag as a main component, and may also be referred to as an "Ag-containing base layer." The base layer 22 may be formed using a sputtering method, a printing method, a dipping method, or the like. For example, the base layer 22 may be a layer formed by printing a paste-like metal material on the base body and sintering it.

[0028] If necessary, an intermediate layer (not shown) can be provided between the underlayer 22 and the plating layer 24. The underlayer 22, the intermediate layer, and the metal plating layer 24 may each be a single layer or multiple layers. The plating layer can be formed using a dry plating method or a wet plating method.

[0029] The plating layer 24 may be a metal plating layer containing a metal as a main component, such as a metal plating layer containing at least one element selected from the group consisting of Ni, Sn (tin), Au (gold), Ag, Cu, and Pd.

[0030] Although the size of the thermistor element is not particularly limited, it is possible to use, for example, a thermistor element of JIS standard 0603 size or a thermistor element of a smaller size, where JIS standard 0603 size is (0.6±0.03) mm (X direction) × (0.3±0.03) mm (Z direction).

[0031] [Features of the Thermistor Element of the Present Disclosure] The thermistor element of the present disclosure has features related to the structure of the external electrodes provided on the thermistor element. The structure of the external electrodes of the thermistor element of the present disclosure will be described below.

[0032] FIG. 3 is a cross-sectional view schematically illustrating the thermistor element 100 of the present disclosure with the plating layer 24 (see FIG. 2) removed. FIG. 4 is a schematic plan view of the thermistor element shown in FIG. 3. FIG. 5 is an enlarged cross-sectional view of the thermistor element shown in FIG. 3. FIG. 6 is an enlarged cross-sectional view of the thermistor element shown in FIG. 2. As shown in FIGS. 3 to 6, the external electrode 20 of the thermistor element of the present disclosure includes a first region I in which the base layer 22 is continuously present and a second region II in which the base layer 22 is intermittently present. In short, in the external electrode, the base layer 22 does not uniformly cover the element body 10; there are portions on the element body where the base layer 22 is present and portions on the element body where the base layer 22 is not present. Specifically, in the external electrode of the thermistor element of the present disclosure, the base layer 22 is disposed so as to continuously cover the surface of the element body in the first region I. On the other hand, in a second region II different from the first region I, a plurality of base layers 22 are randomly scattered or interspersed on the element body. In this manner, the external electrode of the present disclosure includes two regions in which the arrangement of the base layers 22 differs from each other.

[0033] In this specification, the "first region" refers to a region where the underlayer 22 is continuously formed on the element body. Therefore, the "first region" may also be referred to as a "continuous underlayer region." In the first region I, the underlayer 22 may be positioned at least on the end face 14 of the element body 10 and may be continuously provided so as to cover at least a portion of the end face 14. In other words, the underlayer 22 disposed on the end face 14 that requires electrical connection with the internal electrode 12 may extend so as to continuously cover the end face of the element body. That is, the internal electrode 12 may be in contact with the underlayer 22 present in the first region I of the external electrode. Note that "continuously" means that the underlayer 22 is not interrupted macroscopically (e.g., visually) and integrally covers the element body. Such an underlayer 22 may also be referred to as a "first underlayer" or a "continuous underlayer" to distinguish it from the underlayer 22 in the second region II. For example, in the first region I, no portion where the base layer 22 is absent on the element body 10 due to discontinuity of the base layer 22 is visually confirmed. This allows the end of the internal electrode to come into contact with the first region I of the external electrode, and the internal electrode and the external electrode are electrically connected.

[0034] In this specification, the term "second region" refers to a region of the external electrode where multiple underlayers are provided so as to be scattered on the element body. More specifically, the term "second region" can refer to a region of the element body 10 where the element body 10 is covered with the underlayer 22 and / or plating layer, excluding the first region I described above. The second region II is a region extending along the outer edge of the first region I. That is, the first region I may be positioned in a region toward the center of the external electrode, and the second region II may be positioned in a region toward the edge of the external electrode so as to surround the first region I. In the second region II, the underlayer 22 may be provided intermittently. Therefore, the second region II may also be referred to as a "region with scattered underlayers" or "region with intermittent underlayers." Note that "intermittently" means that multiple underlayers 22 are provided and there are gaps (exposed portions of the element body) between the multiple underlayers 22. That is, in the second region II, the underlayer 22 may be scattered in an island-like pattern on the element body. In this way, the base layer 22b scattered in the second region can also be referred to as a "second base layer," "intermittent base layer," "island-shaped base layer," "scattered base layer," etc., to distinguish it from the base layer 22a formed continuously in the first region I.

[0035] The second region II includes a plurality of second underlayers 22b. At least one of the plurality of second underlayers 22b further contains at least one element selected from the group consisting of Cl, Br, and I. That is, the plurality of second underlayers 22b may include an underlayer having a composition containing Ag and at least one element selected from the group consisting of Cl, Br, and I. Such a second underlayer 22b may contain at least one element selected from the group consisting of AgCl, AgBr, and AgI.

[0036] In the present disclosure, the external electrode includes a second region II on the edge side, and a second underlayer 22b scattered in the second region II has a composition including at least one element selected from the group consisting of Cl, Br, and I. As a result, a plating layer 24 (see FIG. 6 ) formed on the underlayer can be formed in the second region II, starting from the second underlayer 22b. That is, the plating layer 24 can be formed not only in the first region I but also in the second region II extending along the outer edge of the first region I. Furthermore, the at least one element selected from the group consisting of Cl, Br, and I contained in the second underlayer 22b can form sparingly soluble AgCl, AgBr, and / or AgI with the Ag contained in the underlayer 22b. This allows plating nuclei, which serve as starting points for plating layer formation, to be favorably formed on the second underlayer 22b, resulting in favorable formation and retention of the plating layer 24b on the second underlayer 22b.

[0037] In conventional thermistor elements that have only a first region with a continuous base layer, a plating layer is formed to cover the base layer, but there is a concern that Ag ions will migrate to the outside from the interface between the plating layer and the element body at the edge of the first region, causing ion migration.

[0038] In the thermistor element of the present disclosure, the plating layer 24 extends into the second region II around the first region I, resulting in the plating layer 24b in the second region II being present along the outer edge of the base layer 22a in the first region I. In other words, the outer edge of the first base layer 22a in the first region I can be surrounded by the plating layer 24b in the second region II. This allows the plating layer 24b in the second region II, present on the outer edge 17 of the first region I, to effectively suppress the migration of Ag ions from the first base layer 22a. The plating layer 24b in the second region II can effectively function as a protective layer to suppress ion migration of Ag contained in the first base layer 22a. Furthermore, in the thermistor element of the present disclosure, Ag ion migration primarily occurs from the first region I, which contains a large amount of Ag. This is because the second region II has the underlying layer 22b scattered therein, which reduces the Ag content per unit area and makes Ag ion migration less likely to occur compared to the first region I. Therefore, the thermistor element of the present disclosure, having the external electrode provided with the second region II as described above, may be able to effectively suppress Ag ion migration.

[0039] Furthermore, the inventors have found that the configuration of the thermistor element of the present disclosure may be particularly suitable for element bodies with poor acid resistance. After forming the base layer, the element body may be immersed in an acidic plating solution (e.g., nickel electroplating solution such as a Watts bath or a sulfamic acid bath, or tin electroplating solution) to form the plating layer. However, some ceramic materials commonly used for element bodies have poor acid resistance. In other words, depending on the material of the element body, there is a possibility that part of the element body will dissolve during the plating process to form the plating layer.

[0040] The present inventors have newly discovered that when an acidic plating solution is used during plating, the element body in contact with the base layer partially dissolves, which can form a tiny gap between the base layer and the element body, and that this gap can become a cause of Ag ion migration.

[0041] When an element body provided with an underlayer (hereinafter also referred to as a "thermistor precursor") is immersed in a plating solution, the element body may partially dissolve, mainly in exposed portions not covered by the underlayer. If the element body dissolves at the edge of the underlayer, a void (gap) may form between the element body and the edge of the underlayer. When a thermistor element is used in a high-temperature, high-humidity environment, moisture may penetrate through the void, causing Ag in the underlayer to ionize. The migration of Ag ions through the void may cause Ag ion migration. In other words, the void formed between the underlayer and the element body during the plating process serves as a migration path for Ag, potentially causing ion migration.

[0042] In the thermistor element of the present disclosure, at least one element selected from the group consisting of Cl, Br, and I present in the underlayer 22b in the second region II can form poorly soluble AgCl, AgBr, and / or AgI. The present inventors have discovered that the presence of such poorly soluble compounds can suppress dissolution of the element at the edge of the underlayer during plating. This suppresses the formation of gaps at the edge of the underlayer 22, thereby effectively suppressing ion migration through the gaps. The presence of the underlayer 22b in the plated chip component can be confirmed by stripping the plating layer 24b. For example, if the plating layer 24b includes a nickel plating layer and a tin plating layer, it is preferable to strip the tin plating layer using a tin plating stripper and then strip the nickel plating layer using a nickel stripper.

[0043] Furthermore, the presence of Cl, Br, and / or I in the second underlayer 22b can also have the effect of helping to hold the second underlayer 22b on the element body during the plating process. The scattered second underlayers 22b in the second region II have a small area and may fall off the element body 10 as the element body 10 dissolves. Falling off the second underlayer 22b can make it difficult to form and maintain the plating layer 24 originating from the underlayer 22b. On the other hand, the inclusion of Cl, Br, and / or I in the second underlayer 22b suppresses dissolution of the element body 10 at the edge portions of the underlayer 22b, thereby effectively preventing the underlayer 22b from falling off. As a result, the second underlayer 22b is effectively held on the element body during the plating process, and an effective plating layer 24 can be formed originating from the second underlayer 22b. Thus, according to the present disclosure, even when an element having poor acid resistance is used, a thermistor element having excellent resistance to ion migration can be obtained.

[0044] As described above, according to the present disclosure, the presence of the second underlayer 22b containing at least one element selected from the group consisting of Cl, Br, and I allows the plating layer 24b covering the second region II to be suitably formed and maintained. Furthermore, in the manufacturing process of the thermistor element, the second underlayer 22b containing at least one element selected from the group consisting of Cl, Br, and I can suppress dissolution of the element body 10. For this reason, the second underlayer 22b containing at least one element selected from the group consisting of Cl, Br, and I can also be referred to as a "plating-assisting underlayer," "element dissolution suppression layer," etc.

[0045] The multiple second underlayers 22b scattered in the second region II may be spaced apart from one another. That is, between adjacent multiple second underlayers 22b, there may be an area on the element body 10 where no second underlayer 22b is disposed. In such a structure, the plating layer 24b disposed on the second underlayer 22b may be formed continuously across the multiple second underlayers 22b. This may enable the plating layer 24b to be formed over a wide area using less Ag material. In other words, it is possible to reduce the amount of Ag used to form the plating layer 24b in the second region II.

[0046] Furthermore, at least some of the second underlayers 22b may be disposed close to one another. In one embodiment, adjacent second underlayers 22b may be in contact with one another at least at their outer edges. In short, at least some of the second underlayers 22b may be disposed so as to be connected to one another. In such a structure, grooves 221 may be present between the second underlayers 22b disposed so as to be connected to one another. Such grooves 221 may be interpreted as grooves forming boundaries extending between adjacent second underlayers 22b, and may also be simply referred to as "boundary portions," "boundary grooves," or the like. Such grooves 221 may also be interpreted as extending to divide the second underlayer 22b into multiple pieces. The grooves 221 may extend to completely divide the second underlayer 22b, or may extend to partially divide it.

[0047] In a plan view, the width dimension of the groove 221 (i.e., the distance between adjacent second underlayers 22b) may be 0.01 μm or more and 0.1 μm or less, or 0.02 μm or more and 0.08 μm or less. Such groove 221 may be formed by the absence of the second underlayer 22b on the element body 10 or by the second underlayer 22b having a locally small thickness. In a structure including such a groove 221, the plating layer 24b formed in the second region II may be disposed so as to penetrate into the groove 221. This provides an anchor effect to the plating layer 24b, allowing the plating layer 24b to be more suitably held on the element body 10 in the second region II.

[0048] FIG. 5 is a partially enlarged view of the thermistor element shown in FIG. 3 , excluding the plating layer 24. In a preferred embodiment, at least one element selected from the group consisting of AgCl, AgBr, and AgI may be located on at least the outer surface of the second underlayer 22b. That is, at least one element selected from the group consisting of AgCl, AgBr, and AgI may be present at least in the surface region of the second underlayer 22b. More preferably, at least one element selected from the group consisting of AgCl, AgBr, and AgI may be present so as to form the outer layer 23 of the second underlayer 22b. That is, at least one element selected from the group consisting of AgCl, AgBr, and AgI may be disposed so as to cover the second underlayer 22b. This structure can also be interpreted as a barrier layer 23 containing at least one element selected from the group consisting of AgCl, AgBr, and AgI being provided on the outer surface of the underlayer 22b. It is more preferable that the barrier layer 23 continuously covers the entire outer surface of the second underlayer 22b. On the other hand, the barrier layer 23 does not have to continuously cover the second underlayer 22b, and may, for example, cover only a portion of the second underlayer 22b. In particular, it is more preferable that the barrier layer 23 cover at least the edge portion of the second underlayer 22b.

[0049] In one embodiment, the first underlayer 22a in the first region I may also contain at least one element selected from the group consisting of Cl, Br, and I. For example, a barrier layer 23 containing at least one element selected from the group consisting of AgCl, AgBr, and AgI may be formed on the outer surface of the first underlayer 22a. It is more preferable that the barrier layer 23 be provided at least on the edge portion of the first underlayer 22a. This can suppress dissolution of the element body 10 at the edge portion of the first underlayer 22a, thereby preferably suppressing the formation of voids between the first underlayer 22a and the element body 10.

[0050] As described above, the second region II is provided along the outer edge 17 of the first region I (see FIGS. 1 and 3 ). The outer edge 17 of the first region I may be surrounded by the second region II. In other words, the second region II may extend to surround the outer edge 17 of the first region I. More specifically, the outer edge 17 of the first region I may be in contact with the second region II. This structure can also be interpreted as the second region II being provided in a band shape along the outer edge 17 of the first region I. As described above, ion migration from the first underlayer 22a may occur primarily due to the migration of Ag ions from the edge of the first underlayer 22a. According to the above structure, the presence of the plating layer 24b originating from the second underlayer 22b in the second region II along the edge 25 of the first region I may prevent the migration of Ag ions from the edge 25 of the first region I. As a result, ion migration from the first region I can be more effectively suppressed.

[0051] The planar shape of the second underlayer 22b is not particularly limited and may be circular, elliptical, polygonal, or irregular. The second underlayers 22b may have the same planar shape or different planar shapes.

[0052] 6 is a schematic enlarged cross-sectional view of a thermistor element including a plating layer 24b. As shown in the figure, the plating layer 24b may extend continuously throughout the entire second region II. That is, the plating layer 24b may be integrally formed so as to entirely cover the second region II including the second underlayer 22b scattered on the element body. In such a structure, the plating layer 24b may extend over both the second underlayer 22b and the element body 10 that does not include the second underlayer 22b. In short, the plating layer 24b may cover not only the underlayer 22b but also the exposed portion of the element body 10 in the second region II. More specifically, the second region II may include a covered portion where the second underlayer 22b is located on the element body 10 and an uncovered portion where the second underlayer is not present on the element body, and the plating layer 24b in the second region II may extend to cover both the covered portion and the uncovered portion.

[0053] According to this configuration, the plating layer 24b is provided not only on the second underlayer 22b scattered on the element body 10 but also so as to extend beyond the second underlayer 22b, so that the underlayer 22 is more suitably covered by the plating layer 24. This makes it possible for the plating layer 24 to more suitably isolate the underlayer 22 from the external environment, resulting in a thermistor element with superior ion migration resistance.

[0054] Furthermore, the plating layer 24 may extend continuously from the first region I to the second region II. That is, the plating layer 24 may integrally cover both the first underlayer 22a and the second underlayer 22b in the first region I. This structure can also be interpreted as the plating layer 24a provided in the first region I and the plating layer 24b provided in the second region II being continuous with each other. Alternatively, the plating layer 24a provided in the first region I can be interpreted as extending into the second region II and covering the second region II. With this structure, the edge of the first region I is more effectively covered by the plating layer 24, thereby preventing the migration of Ag ions out of the plating layer 24 and suppressing the occurrence of migration.

[0055] As described above, in the second region II, there are covered portions where the second underlayer 22b is present on the element body 10, and uncovered portions where the second underlayer 22b is not present. The area ratio of the second underlayer 22b in the second region II can be, for example, 1% to 50%, 5% to 30%, or 10% to 20%. When the area ratio is within the above range, the second underlayer 22b can function favorably as a starting point for the plating layer 24b to be formed in the second region II.

[0056] This area ratio can be measured, for example, by the following procedure. A secondary electron image of the second region II or a mapping image obtained by EDX analysis is binarized using image analysis software. A predetermined measurement area (e.g., an area of ​​50 μm × 50 μm) may be set in the binarized image, and the area ratio of the region where the underlayer 22 b is present within the measurement area may be calculated. Known commercially available analysis software may be used as the image analysis software. For example, A-Zou-kun (registered trademark), Winroof, or ImageJ manufactured by Asahi Kasei Engineering Co., Ltd. may be used as the image analysis software.

[0057] The area ratio of the second underlayer 22b in the second region II may be uniform throughout the second region II. The uniform area ratio allows the plating layer 24b in the second region II to be formed more uniformly.

[0058] Alternatively, the area ratio of the second underlayer 22b in the second region II may not be uniform throughout the second region II. For example, the area ratio of the second underlayer 22b on the side relatively closer to the first region I may be greater than the area ratio of the second underlayer 22b on the side relatively more distal to the first region I. In other words, the area ratio of the second underlayer 22b on the side relatively more distal to the first region I may be smaller than the area ratio of the second underlayer 22b on the side relatively closer to the first region I. For example, the area ratio of the second underlayer 22b may gradually change so as to increase closer to the first region I. In other words, the area ratio of the second underlayer 22b may gradually decrease farther from the first region I. This allows more plating starting points to be provided in the second region II closer to the first region I, and the plating layer 24b can be suitably formed and maintained. Therefore, the first base layer 22a in the first region I can be more suitably covered with the plating layer 24, and excellent migration resistance can be obtained.

[0059] A plurality of second underlayers 22b are present in the second region II. The plurality of second underlayers 22b may be uniformly distributed throughout the entire second region II. In other words, the number of second underlayers 22b scattered on the element body 10 may be uniform throughout the entire second region II. The uniform distribution of the number of second underlayers 22b enables the plating layer 24b in the second region II to be formed more uniformly.

[0060] Alternatively, the distribution of the plurality of second underlayers 22 b may not be uniform throughout the second region II. For example, the number of second underlayers 22 b relatively closer to the first region I may be greater than the number of second underlayers 22 b relatively farther from the first region I. In other words, the number of second underlayers 22 b in the second region II relatively farther from the first region I may be less than the number of second underlayers 22 b in the second region II relatively closer to the first region I. For example, the number of second underlayers 22 b may gradually increase closer to the first region I. In other words, the number of second underlayers 22 b may gradually decrease farther from the first region I. This allows more plating starting points to be provided in the second region II near the first region I, thereby enabling the plating layer to be formed and maintained favorably. Therefore, the first underlayer 22a in the first region I can be more suitably covered with the plating layer, and excellent migration resistance can be obtained.

[0061] Furthermore, the average area of ​​each of the plurality of second underlayers 22b present in the second region II may be uniform throughout the second region II. This means that the size of each of the plurality of second underlayers 22b is uniform throughout the second region II. The average area of ​​the second underlayers 22b can be measured, for example, by image processing such as binarization from a secondary electron image of the second region II or a mapping image obtained by EDX analysis. The average area is defined as the average value of the areas of any 20 second underlayers 22b. The uniform area of ​​the second underlayers 22b enables the plating layer in the second region II to be formed more uniformly.

[0062] Alternatively, the area of ​​each of the plurality of second underlayers 22 b may not be uniform throughout the second region II. For example, the average area of ​​the second underlayers 22 b located in the second region II on the side relatively closer to the first region I may be larger than the average area of ​​the second underlayers 22 b located on the side relatively more distal to the first region I. In other words, the average area of ​​the second underlayers 22 b located in the second region II on the side relatively more distal to the first region I may be smaller than the average area of ​​the second underlayers 22 b located on the side relatively closer to the first region I. In other words, the second underlayers 22 b located in the second region II on the side near the first region I may be larger in size than the side distal to the first region I. For example, the average area of ​​the plurality of second underlayers 22 b may gradually increase as they approach the first region I. In other words, the average area value of the plurality of second underlayers 22b may gradually decrease as it becomes more distant from the first region I. This allows more plating starting points to be provided in the second region II closer to the first region I, and the plating layer can be suitably formed and maintained. Therefore, the first underlayers 22a in the first region I can be more suitably covered with the plating layer, and excellent migration resistance can be obtained.

[0063] The average area and number of the second underlayers 22 b present in the second region II may be uniform throughout the second region II. The uniform average area and number of the second underlayers 22 b of the second underlayers 22 b allows the plating layer in the second region II to be formed more uniformly.

[0064] Alternatively, the average area and number of the second underlayers 22b may not be uniform throughout the second region II. For example, in the second region II located closer to the first region I, more second underlayers 22b having a larger average area may be positioned than second underlayers 22b located closer to the first region I. In other words, in the second region II located closer to the first region I, second underlayers 22b having a smaller average area may be positioned than second underlayers 22b located closer to the first region I, and the number of second underlayers 22b may be fewer than that of the second region II located closer to the first region I. For example, the average area and number of the second underlayers 22b may gradually increase closer to the first region I. In other words, the average area and number of the second underlayers 22b may gradually decrease farther from the first region I. This allows more plating starting points to be provided on the side closer to the first region I, and the plating layer can be suitably formed and maintained. Therefore, the first base layer 22 a in the first region I can be more suitably covered with the plating layer, and excellent migration resistance can be obtained.

[0065] As described above, in the thermistor element of the present disclosure, at least some of the second underlayers 22b present in the second region II contain at least one element selected from the group consisting of Cl, Br, and I. Preferably, all of the second underlayers 22b present in the second region II contain at least one element selected from the group consisting of Cl, Br, and I. For example, at least 10%, at least 30%, or at least 50% of the second underlayers 22b present in the second region II may contain at least one element selected from the group consisting of Cl, Br, and I. When the proportion of second underlayers 22b containing at least one element selected from the group consisting of Cl, Br, and I in the second region II is as described above, the plating layer 24b in the second region II can be more effectively formed and maintained. The above-mentioned ratio can be measured by analyzing a predetermined area (50 μm×50 μm area) in the second region using EDX, DWX, XPS, or the like.

[0066] In the thermistor element of the present disclosure, the presence of the second region II allows the plating layer 24 to extend beyond the first region I. Hereinafter, the plating layer 24 present in the first region I will be referred to as the first portion 24a, and the plating layer 24 present in the second region II will be referred to as the second portion 24b. The plating layer thickness of the first portion 24a may be greater than that of the second portion 24b. In other words, the plating layer thickness of the second portion 24b may be smaller than that of the first portion 24a. Herein, the "thickness of the plating layer" refers to the shortest distance from the outer surface of the base layer 22 to the outer surface of the plating layer 24. When the plating layer 24 comprises multiple plating films, the "thickness of the plating layer" may be the sum of the thicknesses of the multiple plating films. For example, the thickness of the plating layer of the first portion 24a may be 80% to 150%, 90% to 130%, or 100% to 120% of the thickness of the plating layer of the second portion 24b. This allows the first region I, which includes the first underlayer 22a, to be more reliably covered with the underlayer 22a. On the other hand, in the second region II surrounding the first region I, the thickness is thinner, which reduces the stress acting on the plating layer 24b and favorably reduces the occurrence of cracks in the plating layer 24b. This makes it possible to favorably cover the first underlayer 22a in the first region I while suppressing the occurrence of cracks in the plating layer 24 near the edge of the first region I, resulting in a thermistor element with better migration resistance.

[0067] The thickness of the plating layer may be based on an electron microscope image. For example, the thickness of the plating layer may be based on an image obtained by polishing a cross section of a resin-embedded electronic component and using a scanning electron microscope (e.g., Hitachi High-Tech Corporation, Model No. SU-8040). In other words, the thickness in this specification may refer to a value calculated from dimensions measured from an image obtained by such a method. Measurements may be taken at any five points, and the average value may be used as the thickness. Alternatively, the thickness of the plating layer may be a value measured using a fluorescent X-ray film thickness meter (e.g., Hitachi High-Tech Corporation, Model No. FT160h). In such a method, measurements may be taken at any five points, and the average value may be used as the thickness.

[0068] Furthermore, the plating layer 24b in the second region II preferably extends to a position farther away from the first region I. This means that the average plating width of the plating layer 24b in the second region II is preferably larger. In other words, the average plating width of the plating layer 24b in the second region II corresponds to the average distance from the outer edge 17 of the first region I to the outer edge of the second region II located opposite the outer edge 17. The average plating width may be an average value measured at any five points. Alternatively, the average plating width can be calculated from the area of ​​the plating layer 24b in the second region II and the dimension of the second region II in the width direction Z. Specifically, the average plating width can be calculated by taking a planar view (Z-X plane) image of the thermistor element using a microscope, binarizing the image to determine the area of ​​the plating layer 24b in the second region II, and dividing the obtained area value by the dimension of the second region II in the width direction Z. In one embodiment, the dimension of the second region II in the width direction Z corresponds to the dimension of the element in the width direction Z. The larger the average plating width of the second region II, the more the plating layer 24b can cover the base layer 22 so that it reaches the surface of the element body surrounding the base layer 22, thereby effectively suppressing ion migration. Although not particularly limited, the average plating width of the plating layer 24b in the second region II (i.e., the second portion) may be, for example, 10 μm to 100 μm, 20 μm to 80 μm, or 30 μm to 70 μm.

[0069] To emphasize the ability to cover a wider area of ​​the base layer 22 while preventing cracking, the plating layer 24 in the second region II preferably has a thinner film thickness and a wider plating width. In this regard, the ratio of the average plating width to the thickness of the plating layer in the second region II (i.e., the lateral elongation of the plating layer in the second region) can be 3.5 to 120, 5 to 100, 10 to 60, or 20 to 40. A plating layer with a larger lateral elongation indicates a thinner film thickness and a wider area, which may be more advantageous in terms of suppressing cracking and ion migration. When the lateral elongation of the plating layer in the second region II is within the above-described range, a thermistor element can be obtained that includes a plating layer that can effectively cover the base layer while suppressing cracking.

[0070] The plating layer 24 may be a single layer, or may have a multi-layer structure of two or more layers as shown in Figure 7. In a preferred embodiment, the plating layer 24 includes a plurality of plating films 241, 242, which are laminated on the base layer 22. In other words, the plating layer may be a composite plating film having a multi-layer structure of two or more layers. By providing such a plurality of plating films on the base layer 22, the base layer 22 is more effectively covered, resulting in a thermistor element with excellent ion migration resistance.

[0071] The multiple plating films may be different types of metal plating films. For example, the plating layer 24 may be a multilayer film in which a plating film 241 containing Ni as a primary component and a plating film 242 containing Sn as a primary component are stacked in this order on the base layer 22. With this configuration, the plating film 242 containing Sn as a primary component is disposed on the outer side, thereby improving the solder wettability of the thermistor element. The inner plating film 241 containing Ni can function as a barrier film that can suppress the diffusion of Sn from the outer plating film 242 into the base layer and / or the erosion of the base layer by solder when mounting the thermistor element.

[0072] The thickness of the plating film is not particularly limited, but may be, for example, in the range of 0.5 μm to 50 μm, 1 μm to 20 μm, or 2 μm to 10 μm. When the plating layer includes multiple plating films, the thicknesses of the multiple plating films may be the same or different from each other.

[0073] [Method for Manufacturing Thermistor Element] Next, a method for manufacturing the thermistor element of the present disclosure will be described.

[0074] The method for manufacturing a thermistor element mainly includes an element body fabrication step of fabricating an element body, and an external electrode fabrication step of fabricating external electrodes on the element body.

[0075] (Element body fabrication process) In the element body fabrication process, ceramic materials may first be mixed and pulverized to produce a mixed powder, and the mixed powder may be subjected to a calcination process to produce a calcined powder. The calcined powder is then formed into a sheet shape to produce a sheet body, and the sheet body and the material of the internal electrodes are alternately stacked to produce a laminate. The laminate is then fired in a reducing atmosphere to produce an element body with internal electrodes provided therein. If necessary, chamfering such as barrel processing may be performed to chamfer the corners and ridges of the element body.

[0076] (External electrode fabrication process) The external electrode fabrication process includes a base formation process in which a base layer is formed on the element body to obtain a thermistor precursor having the base layer, and a plating process in which the thermistor precursor is plated to form a plating layer on the base layer. A thermistor element can be obtained through these processes. The present disclosure is characterized by this external electrode fabrication process.

[0077] (Underlayer Forming Step) The underlayer can be formed by, for example, sputtering, vapor deposition, printing, or immersion. Given the need for work efficiency, immersion is preferred. The underlayer forming step includes forming a first region and a second region II. That is, the first region I including the first underlayer 22a may be formed by continuously forming the underlayer 22 so as to cover at least a portion of the end face 14 of the element body, and the second region II may be formed by forming multiple second underlayers 22b along the outer edge 17 of the first region (see FIGS. 3 and 4 ). More specifically, in the underlayer forming step, the first region I may be formed by forming the underlayer 22a positioned at least on the end face 14 and continuously covering at least a portion of the end face 14. Furthermore, the second region II may be formed by forming multiple underlayers 22b intermittently along the outer edge 17 of the first region I. In forming the second region II, the underlayer may be formed by patterning the second underlayer 22b so that it is dotted, or alternatively, the underlayer may be formed after masking the areas where the element body 10 is to be exposed (i.e., areas where no underlayer is to be disposed). By forming the underlayer on the element body in this manner, the thermistor precursor 50 can be obtained.

[0078] (Plating Step) After obtaining the thermistor precursor 50 through the underlayer forming step, a plating layer is formed on the underlayer of the thermistor precursor 50 in the plating step. In the present disclosure, the step of forming the plating layer includes immersing the thermistor precursor in a solution containing at least one ion selected from the group consisting of Cl ions, Br ions, and I ions before forming the plating layer. This allows for the production of a thermistor precursor having an underlayer containing at least one ion selected from the group consisting of Cl, Br, and I. The solution in which the thermistor precursor is immersed may contain at least one ion selected from the group consisting of Cl ions, Br ions, and I ions in a total concentration of 1 mol / L to 5 mol / L, 1.25 mol / L to 3 mol / L, or 1.5 mol / L to 2 mol / L. By setting the concentration of at least one ion selected from the group consisting of Cl ions, Br ions, and I ions contained in the solution within the above-mentioned range, at least one ion selected from the group consisting of AgCl, AgBr, and AgI is suitably produced in the underlayer, and an underlayer containing at least one ion selected from the group consisting of Cl, Br, and I can be obtained (see FIG. 5 ).

[0079] The resulting thermistor precursor may then be plated to form a plating layer 24 (see FIG. 6). The plating may be performed by, for example, dry plating or wet plating. When emphasis is placed on processing efficiency, wet plating is preferred, and among wet plating, electroplating is more preferred. While the plating method is not particularly limited, when emphasis is placed on processing efficiency, barrel plating is preferred.

[0080] When the thermistor precursor includes the second region II and the underlayer 22 includes at least one element selected from the group consisting of Cl, Br, and I, plating can form a thin plating layer 24b that extends over a wider area in the second region II. This may be because plating nuclei are preferably formed in the second underlayer 22b, which includes at least one element selected from the group consisting of Cl, Br, and I, and the plating layer 24b is formed widely from these plating nuclei. Furthermore, the plating layer 24b is formed so as to connect the discontinuously scattered plating nuclei on the underlayer 22b, allowing the plating layer 24b to be formed thinly and widely. Furthermore, the presence of multiple plating starting points allows the plating layer to be preferably held on the element body.

[0081] The solution in which the thermistor precursor 50 is immersed may be a plating solution for forming a plating layer. That is, a plating solution containing at least one selected from the group consisting of Cl ions, Br ions, and I ions may be used in the plating process. For example, the thermistor precursor may be immersed in an electrolytic nickel plating solution containing at least one selected from the group consisting of nickel chloride, nickel bromide, and nickel iodide. Preferably, the thermistor precursor may be immersed in a plating solution of a Watts bath or sulfamic acid bath containing nickel chloride. In this embodiment, the plating solution may contain nickel chloride, nickel bromide, and / or nickel iodide having a molar concentration higher than the molar concentration of nickel sulfate or nickel sulfamate contained in the plating solution. For example, the total molar concentration of nickel chloride, nickel bromide, and nickel iodide may be 80% to 300%, 100% to 200%, or 110% to 150% of the molar concentration of nickel sulfate. For example, the total molar concentration of nickel chloride, nickel bromide, and nickel iodide may be 80% or more and 300% or less, 100% or more and 200% or less, or 110% or more and 150% or less of the molar concentration of nickel sulfamate.

[0082] Generally, in Watts baths and sulfamic acid baths, nickel chloride, nickel bromide, and nickel iodide can supply chloride ions, bromide ions, and iodide ions to the solution, respectively. This prevents passivation of the nickel anode and promotes nickel deposition. On the other hand, excessively high concentrations of nickel chloride, nickel bromide, and nickel iodide (i.e., chloride, bromide, and iodide ion concentrations) are known to increase the internal stress of the resulting plating film. When a plating film is used to prevent ion migration from a base layer, such as the external electrode of a thermistor element, it is preferable for the plating film to cover the base and prevent cracking in the plating film. From the perspective of suppressing cracking, reducing the internal stress of the plating film is considered, so generally, low concentrations of nickel chloride, nickel bromide, and nickel iodide in the plating solution are desirable. On the other hand, in the present disclosure, it is possible to form a thin plating film over a wide area by providing a second region having an underlayer containing Cl, Br, and / or I. Therefore, even when using a plating solution with high concentrations of nickel chloride, nickel bromide, and nickel iodide, it is possible to obtain a suitable plating layer in which the occurrence of cracks is suppressed.

[0083] Furthermore, various additives may be further added to the plating solution as needed. While merely illustrative, plating solutions containing known additives such as leveling agents, dispersants, stress relief agents, and surfactants may be used. More specifically, plating solutions containing at least one additive selected from the group consisting of saccharin and saccharin compounds, sodium naphthalenesulfonate, butynediol, propargyl alcohol, coumarin, thiourea, and zinc may be used.

[0084] By immersing the thermistor precursor 50 in such a plating solution and performing nickel electroplating in the plating solution, AgCl, AgBr, and / or AgI are formed on the underlayer, and then a nickel plating layer can be formed. This eliminates the need to prepare a solution separate from the plating solution to form the underlayer containing Cl, Br, and / or I. This makes it possible to more efficiently form a thermistor element with excellent ion migration resistance.

[0085] When electroplating using an acidic plating solution is performed in the plating step, it is more preferable to perform plating at a substantially uniform current density after immersing the thermistor precursor in the plating solution. In other words, it is preferable to perform plating in which current is continuously applied rather than pulse plating using an intermittent current profile. If an intermittent current profile results in current being applied at a current density insufficient to form a plating layer, or if there are periods when no current is applied, dissolution of the element body in the areas where no underlayer is provided may progress. Therefore, performing plating at a substantially uniform current density can prevent dissolution of exposed portions of the element body in the plating solution.

[0086] Furthermore, in the plating process by barrel plating, plating is preferably performed at a lower stirring speed. Gentle stirring makes it easier to form a plating layer that connects the second underlayer in the second region, allowing for the formation of a plating layer over a wider area.

[0087] In the plating step, multiple plating processes may be performed to form a multi-layer plating film. For example, the thermistor precursor may be subjected to the above-mentioned nickel electroplating, followed by tin plating, and then tin plating may be formed on the nickel plating film.

[0088] Although the embodiments of the present disclosure have been described above, they are merely typical examples. Those skilled in the art will readily understand that the present disclosure is not limited thereto, and that various modifications are possible within the scope of the present disclosure.

[0089] For example, in the above-described embodiment, the thermistor element is an NTC thermistor, but it may be a PTC (Positive Temperature Coefficient) thermistor. Also, in the above-described embodiment, the cross section of the peripheral surface of the element body is rectangular, but it may be triangular, pentagonal or more polygonal, or may be circular, elliptical or oblong.

[0090] Note that one embodiment of the present disclosure as described above includes the following preferred aspects: <1> A thermistor element comprising: an element body; and external electrodes positioned at least on end faces of the element body, wherein the external electrodes comprise an Ag-containing underlayer positioned on the element body; and a plating layer positioned on the Ag-containing underlayer, wherein the external electrodes have a first region including the Ag-containing underlayer continuously covering at least a portion of the end faces; and a second region extending along an outer edge of the first region and in which a plurality of the Ag-containing underlayers are positioned intermittently, wherein at least one of the plurality of Ag-containing underlayers in the second region contains at least one element selected from the group consisting of Cl, Br, and I. <2> A thermistor element according to <1>, wherein the external electrodes cover the entire surfaces of the end faces. <3> The thermistor element according to <1> or <2>, wherein the plating layer has a first portion located in the first region and a second portion located in the second region, and the second portion continuously covers the second region. <4> The thermistor element according to any one of <1> to <2>, wherein the element body has a peripheral surface continuous from the end face, the first region covers the end face and extends to a portion of the peripheral surface, and the second region covers a portion of the peripheral surface along the outer edge of the first region. <5> The thermistor element according to any one of <1> to <4>, wherein the plating layer continuously covers the Ag-containing underlayer from the first region to the second region. <6> The thermistor element according to any one of <1> to <5>, wherein the second region includes an exposed portion on the element body where the Ag-containing underlayer is not present, and the plating layer covers both the Ag-containing underlayer and the exposed portion in the second region. <7> The thermistor element according to any one of <1> to <6>, wherein at least one of the plurality of Ag-containing underlayers present in the second region contains at least one compound selected from the group consisting of AgCl, AgBr, and AgI, and the compound is located on at least an outer surface of the Ag-containing underlayer.<8> The thermistor element according to any one of <1> to <7>, wherein at least one of the plurality of Ag-containing underlayers present in the second region has an outer layer containing at least one selected from the group consisting of AgCl, AgBr, and AgI on the outer surface of the Ag-containing underlayer. <9> The thermistor element according to any one of <1> to <8>, wherein, in a plan view, an area ratio of the Ag-containing underlayer in the second region is 1% to 50%. <10> The thermistor element according to any one of <1> to <9>, wherein, in a plan view, an area ratio of the Ag-containing underlayer in the second region increases with increasing proximity to the first region. <11> The thermistor element according to any one of <1> to <10>, wherein the second region comprises a plurality of the Ag-containing underlayers scattered on the element body, and the number of the plurality of Ag-containing underlayers increases with increasing proximity to the first region. <12> The thermistor element according to any one of <1> to <11>, wherein the second region comprises a plurality of the Ag-containing underlayers scattered on the element body, and the area of ​​each of the plurality of Ag-containing underlayers increases toward the first region in a plan view. <13> The thermistor element according to any one of <1> to <12>, wherein a ratio of a total area of ​​second Ag-containing underlayers containing at least one element selected from the group consisting of Cl, Br, and I to a total area of ​​the Ag-containing underlayers present in the second region is at least 10%. <14> The thermistor element according to any one of <1> to <13>, wherein the plating layer is a nickel plating layer containing nickel as a main component. <15> The thermistor element according to any one of <1> to <14>, wherein the plating layer comprises a first portion located on the first region and a second portion located on the second region, and wherein a ratio of an average plating width of the second portion to a film thickness of the second portion is equal to or greater than 5 and equal to or less than 100. <16> The thermistor element according to any one of <1> to <15>, wherein the second region comprises a plurality of the Ag-containing underlayers scattered on the element body, and at least some of the Ag-containing underlayers among the plurality of Ag-containing underlayers are connected to each other via grooves extending between the Ag-containing underlayers.<17> A method for manufacturing a thermistor element, comprising: a base-forming step of forming an Ag-containing base layer on an element body to obtain a thermistor precursor; and a plating step of forming a plating layer on the Ag-containing base layer, wherein the base-forming step includes forming a first region in which the Ag-containing base layer is positioned at least on an end face of the element body and exists continuously so as to cover at least a part of the end face; and a second region in which a plurality of the Ag-containing base layers exist intermittently along an outer edge of the first region, and the plating step includes immersing the thermistor precursor in a solution containing at least one ion selected from the group consisting of Cl ions, Br ions, and I ions before forming the plating layer, and wherein a total concentration of Cl ions, Br ions, and I ions in the solution is 1 mol / L or more and 5 mol / L or less. <18> The manufacturing method according to claim <17>, wherein the plating layer includes a nickel plating film, and the solution is a nickel plating solution containing nickel chloride and nickel sulfate or nickel sulfamate, and the molar concentration of the nickel chloride is higher than the molar concentration of the nickel sulfate or the nickel sulfamate.

[0091] The above effects are merely exemplary, and the present disclosure is not limited to the above, and additional effects may also be provided.

[0092] A demonstration test was carried out in accordance with the present disclosure. The thermistor element had the structure shown in FIG.

[0093] The element body was made of a Co-Mn-Fe-Al oxide. The dimensions of the element body were 0.6 mm x 0.3 mm x 0.3 mm. An Ag-based conductive paste was applied to the element body in a predetermined pattern and baked to form an underlayer including a first region and a second region. The thermistor precursor was then plated using electrolytic nickel plating solutions in Watts baths with different chloride ion concentrations to obtain thermistor elements. The nickel sulfate concentration in each plating solution was 0.75 mol / L. Plating was performed by barrel plating. The resulting thermistor elements were measured for the silver chloride ratio of the second underlayer, the area ratio of the second underlayer, and the lateral elongation ratio (average plating width / layer thickness) of the plating layer present in the second region.

[0094] (Area Ratio of Second Underlayer) The area ratio of the second underlayer was measured using EDX. Element mapping was performed on a 50 μm × 50 μm second region that barely included the first region, and the resulting mapping image was binarized to determine the area ratio of the total area of ​​the second underlayer to the measurement region. The total area of ​​the second underlayer was determined by regarding the region in the measurement region where chlorine and / or silver were present as the second underlayer. A Hitachi High-Technologies Corporation model SU-8040 was used for the measurement.

[0095] (Measurement of Silver Chloride Ratio) The silver chloride ratio was measured using EDX. Elemental mapping was performed on a 50 μm × 50 μm second region that barely contained the first region, and each element was quantified by quantitative analysis. The ratio of the chlorine element concentration to the silver element concentration was defined as the silver chloride ratio. The measurement was performed using a Hitachi High-Technologies Corporation model number SU-8040.

[0096] (Measurement of Transverse Elongation Ratio) The plating film thickness in the second region was measured using a fluorescent X-ray film thickness meter (FT160h, manufactured by Hitachi High-Technologies Corporation). The average plating width was calculated by taking an image of the Z-X plane (plan view) of the thermistor element using a microscope (VHX-5000, manufactured by Keyence Corporation), calculating the plating area of ​​the second region from the image, and dividing this value by the length in the width direction (Z) of the element body.

[0097] Based on the measurement results of the silver chloride ratio and lateral extension ratio of the thermistor, the thermistor elements were rated as follows: A: Silver chloride ratio of 30% or more and lateral extension ratio of 10 or more; B: Silver chloride ratio of 10% or more and lateral extension ratio of 3.5 or more; C: Silver chloride ratio less than 10% or lateral extension ratio less than 3.5 Thermistor elements rated C have insufficient silver chloride ratio and / or lateral extension ratio of the plating layer, and therefore do not achieve a sufficient migration suppression effect. On the other hand, thermistor elements rated B have high silver chloride ratio and lateral extension ratio, and therefore the external electrodes are suitably covered by the plating layer, and can achieve an excellent migration suppression effect. Thermistor elements rated A have higher silver chloride ratio and lateral extension ratio, and achieve an even greater migration suppression effect.

[0098] The measurement results of the obtained thermistor element are shown in Table 1 below.

[0099]

[0100] As can be seen from the above results, the thermistor elements of Examples 1 to 3, which included a second underlayer containing silver chloride (i.e., Cl), exhibited improved lateral extension ratios of the plating in the second region. On the other hand, the thermistor elements of the comparative example, which included a second underlayer but did not include a second underlayer containing silver chloride, exhibited only a small lateral extension ratio. Furthermore, because the second underlayer did not include silver chloride, the thermistor elements exhibited poor adhesion of the plating formed on the second underlayer. These results demonstrate that the thermistor elements of Examples 1 to 3 according to the present disclosure form a plating layer that more effectively covers the external electrodes. This effectively protects the external electrodes with the plating layer, improving the migration resistance of the thermistor element. In particular, the thermistor element of Example 2, which had a high area ratio and silver chloride ratio of the second underlayer, exhibited a high lateral extension ratio and formed a plating layer that extended widely from the first region to the second region, resulting in a thermistor element with particularly high migration resistance.

[0101] Furthermore, the thermistor element of Example 3 exhibited a superior lateral elongation rate to the comparative example, despite the lower area ratio of the second underlayer compared to the comparative example. This indicates that the thermistor element of the present disclosure, including the second underlayer containing Cl, can effectively suppress ion migration of the external electrodes because the external electrodes are covered over a wider area with the plating layer. Therefore, even when the second underlayer contains Br and / or I, which have properties similar to Cl, instead of or in addition to Cl, it can effectively suppress ion migration of the external electrodes, similar to when Cl is included.

[0102] REFERENCE SIGNS LIST 100 Thermistor element 50 Thermistor precursor 10 Body 11 Ceramic layer 12 Internal electrode 14 End face 15 Peripheral surface 15A Main surface 15B Side surface 20 External electrode 22 Underlayer 22a First underlayer 22b Second underlayer 23 Barrier layer 24 Plating layer 241, 242 Plating film I First region II Second region

Claims

1. A thermistor element comprising a base body and an external electrode positioned at least on an end face of the base body, the external electrode comprising an Ag-containing base layer positioned on the base body and a plating layer positioned on the Ag-containing base layer, in the external electrode, there being a first region including the Ag-containing base layer that continuously covers at least a part of the end face, and a second region extending along an outer edge of the first region and having a plurality of the Ag-containing base layers intermittently positioned therein, and at least one of the plurality of the Ag-containing base layers in the second region containing at least one selected from the group consisting of Cl, Br, and I.

2. The thermistor element according to claim 1, wherein the external electrode covers the entire end face.

3. The thermistor element according to claim 1 or 2, wherein the plating layer comprises a first part positioned in the first region and a second part positioned in the second region, and the second part continuously covers the second region.

4. The thermistor element according to any one of claims 1 to 3, wherein the base body comprises a peripheral surface continuous from the end face, the first region covers the end face and extends to a part of the peripheral surface, and the second region covers a part of the peripheral surface along the outer edge of the first region.

5. The thermistor element according to any one of claims 1 to 4, wherein the plating layer continuously covers the Ag-containing base layer from the first region to the second region.

6. The thermistor element according to any one of claims 1 to 5, wherein the second region includes an exposed portion where the Ag-containing base layer does not exist on the base body, and the plating layer covers both the Ag-containing base layer and the exposed portion in the second region.

7. The thermistor element according to any one of claims 1 to 6, wherein at least one of the plurality of the Ag-containing base layers in the second region contains at least one compound selected from the group consisting of AgCl, AgBr, and AgI, and the compound is positioned at least on an outer surface of the Ag-containing base layer.

8. The thermistor element according to any one of claims 1 to 7, wherein at least one of the plurality of the Ag-containing base layers in the second region comprises an outer layer containing at least one selected from the group consisting of AgCl, AgBr, and AgI on an outer surface of the Ag-containing base layer.

9. The thermistor element according to any one of claims 1 to 8, wherein in plan view, the area ratio of the Ag-containing underlayer in the second region is 1% or more and 50% or less.

10. The thermistor element according to any one of claims 1 to 9, wherein in plan view, the area ratio of the Ag-containing underlayer in the second region increases as it approaches the first region.

11. The thermistor element according to any one of claims 1 to 10, wherein the second region includes a plurality of the Ag-containing underlayers scattered on the element body, and the number of the plurality of Ag-containing underlayers increases as it approaches the first region.

12. The thermistor element according to any one of claims 1 to 11, wherein the second region includes a plurality of the Ag-containing underlayers scattered on the element body, and in plan view, the area of each of the plurality of Ag-containing underlayers increases as it approaches the first region.

13. The thermistor element according to any one of claims 1 to 12, wherein the ratio of the total area of the second Ag-containing underlayers containing at least one selected from the group consisting of Cl, Br, and I in the total area of the Ag-containing underlayers present in the second region is at least 10%.

14. The thermistor element according to any one of claims 1 to 13, wherein the plating layer is a nickel plating layer containing nickel as a main component.

15. The thermistor element according to any one of claims 1 to 14, wherein the plating layer includes a first portion located on the first region and a second portion located on the second region, and the ratio of the average plating width of the second portion to the film thickness of the second portion is 5 or more and 100 or less.

16. The thermistor element according to any one of claims 1 to 15, wherein the second region includes a plurality of the Ag-containing underlayers scattered on the element body, and at least some of the plurality of Ag-containing underlayers are connected to each other via groove portions extending between the Ag-containing underlayers.

17. A method for manufacturing a thermistor element, comprising: a base formation step of forming an Ag-containing base layer on a substrate to obtain a thermistor precursor; and a plating step of forming a plating layer on the Ag-containing base layer, wherein the base formation step includes forming a first region in which the Ag-containing base layer is at least positioned on an end face of the substrate and continuously exists so as to cover at least a part of the end face, and a second region in which a plurality of the Ag-containing base layers intermittently exist along an outer edge of the first region, and the plating step includes immersing the thermistor precursor in a solution containing at least one selected from the group consisting of Cl ions, Br ions, and I ions before forming the plating layer, and a total concentration of Cl ions, Br ions, and I ions in the solution is 1 mol / L or more and 5 mol / L or less.

18. The manufacturing method according to claim 17, wherein the plating layer includes a nickel plating film, the solution is a nickel plating solution containing nickel chloride and nickel sulfate or nickel sulfamate, and a molar concentration of the nickel chloride is higher than a molar concentration of the nickel sulfate or the nickel sulfamate.

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