METHOD OF MANUFACTURING ELECTRONIC COMPONENT, AND ELECTRONIC COMPONENT

Abstract

A method of manufacturing an electronic component includes manufacturing a ceramic element including one pair of end surfaces and four side surfaces, forming external electrodes at both end portions of the ceramic element, measuring an initial characteristic value, determining any side surface to be machined among the four side surfaces and then determining, based on stored data, an amount of machining to be performed on the side surface to be machined, and machining, by the determined machining amount, the side surface of the ceramic element, which is determined to be machined, to be flush or substantially flush with the external electrodes.

Claims

1. A method of manufacturing an electronic component, the method comprising: a ceramic element manufacturing process of manufacturing a ceramic element including one pair of end surfaces and four side surfaces each connecting the end surfaces; an external electrode forming process of forming, at both end portions of the ceramic element, one pair of external electrodes each with a cap shape over the corresponding end surface and the four side surfaces continuous with the end surface; an initial characteristic value measuring process of measuring an initial characteristic value between the external electrodes; a machining condition determining process of determining one side surface, two side surfaces, or three side surfaces to be machined from among the four side surfaces and then determining, based on stored data, an amount of machining to be performed on the determined one side surface, two side surfaces, or three side surfaces by comparing the initial characteristic value measured through the initial characteristic value measuring process and a predetermined target characteristic value; and a side surface machining process of machining the determined one side surface, two side surfaces, or three side surfaces to be flush or substantially flush with the external electrodes formed on the side surface by the machining amount determined by the machining condition determining process.

2. The method of manufacturing an electronic component according to claim 1, wherein the characteristic value is a resistance value.

3. The method of manufacturing an electronic component according to claim 1, wherein the external electrode forming process includes a baked external electrode forming process of forming a baked external electrode at each end portion of the ceramic element by applying and baking conductive paste.

4. The method of manufacturing an electronic component according to claim 1, wherein the external electrode forming process includes: a baked external electrode forming process of forming a baked external electrode at each end portion of the ceramic element by applying and baking conductive paste; and a plated external electrode forming process of forming a plated external electrode on the baked external electrode by plating.

5. The method of manufacturing an electronic component according to claim 1, wherein each of the external electrodes is in ohmic contact with the ceramic element.

6. The method of manufacturing an electronic component according to claim 1, wherein the ceramic element is a thermistor element, and the electronic component is a thermistor.

7. The method of manufacturing an electronic component according to claim 1, wherein an internal electrode is formed inside the ceramic element.

8. The method of manufacturing an electronic component according to claim 1, wherein each end surface of the ceramic element is rectangular or substantially rectangular including a first side and a second side orthogonal or substantially orthogonal to each other, and a length of a longer one of the first and second sides is less than or equal to a length of each side surface between the end surfaces.

9. The method of manufacturing an electronic component according to claim 1, wherein each end surface of the ceramic element is rectangular or substantially rectangular including a first side and a second side orthogonal or substantially orthogonal to each other, and a length of a longer one of the first and second sides is longer than a length of each side surface between the end surfaces.

10. The method of manufacturing an electronic component according to claim 8, wherein the length of the first side is different from the length of the second side.

11. The method of manufacturing an electronic component according to claim 1, further comprising a lead terminal joining process of joining a lead terminal with each external electrode.

12. The method of manufacturing an electronic component according to claim 11, further comprising, after the lead terminal joining process, a characteristic value adjusting process of adjusting the characteristic value by machining the ceramic element or machining the ceramic element and the external electrodes.

13. The method of manufacturing an electronic component according to claim 11, further comprising an exterior sealing process of sealing, by an exterior, the ceramic element on which the external electrodes are formed, leaving one end of each lead terminal externally exposed.

14. An electronic component comprising: a ceramic element including one pair of end surfaces and four side surfaces each connecting the end surfaces; and one pair of external electrodes provided on both end surfaces of the ceramic element; wherein each external electrode extends from the corresponding end surface to one side surface, two side surfaces, or three side surfaces of the four side surfaces continuous with the end surface over a side surrounding the end surface; and any of the four side surfaces of the ceramic element, to which no external electrode extends, is machined to be flush or substantially flush.

15. The electronic component according to claim 14, wherein each of the external electrodes only includes a baked external electrode provided on the ceramic element.

16. The electronic component according to claim 14, wherein each of the external electrodes includes a baked external electrode provided on the ceramic element and a plated external electrode provided on the baked external electrode.

17. The electronic component according to claim 14, wherein each external electrode is in ohmic contact with the ceramic element.

18. The electronic component according to claim 14, wherein the ceramic element is a thermistor element and the electronic component is a thermistor.

19. The electronic component according to claim 14, wherein an internal electrode is provided inside the ceramic element.

20. The electronic component according to claim 14, wherein each end surface of the ceramic element is rectangular or substantially rectangular including a first side and a second side orthogonal or substantially orthogonal to each other, and a length of a longer one of the first and second sides is less than or equal to a length of each side surface between the end surfaces.

21. The electronic component according to claim 14, wherein each end surface of the ceramic element is rectangular or substantially rectangular including a first side and a second side orthogonal or substantially orthogonal to each other, and a length of a longer one of the first and second sides is longer than a length of each side surface between the end surfaces.

22. The electronic component according to claim 20, wherein the length of the first side is different from the length of the second side.

23. The electronic component according to claim 14, wherein each of the external electrodes is joined with a lead terminal.

24. A method of manufacturing an electronic component according to claim 23, wherein the ceramic element on which the external electrodes are provided is sealed by an exterior, leaving one end of each lead terminal externally exposed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0066] FIG. 1A is a perspective view showing an NTC thermistor according to a first preferred embodiment of the present invention.

[0067] FIG. 1B is a cross-sectional view taken along line X-X in FIG. 1A.

[0068] FIGS. 2A to 2C are each a cross-sectional view showing a process performed in an exemplary method of manufacturing the NTC thermistor shown in FIG. 1A.

[0069] FIGS. 3D to 3F, which follow FIGS. 2A to 2C, are each a cross-sectional view showing a process performed in the exemplary method of manufacturing the NTC thermistor shown in FIG. 1A.

[0070] FIG. 4A is a correlation diagram showing an exemplary correlation relation between the amount of machining a ceramic element and the increased amount of the resistance value thereof in one-side polishing. FIG. 4B is a correlation diagram showing an exemplary correlation relation between the amount of machining the ceramic element and the increased amount of the resistance value thereof in both-side polishing.

[0071] FIG. 5 is a correlation diagram showing a difference between different external electrodes in a correlation relation between the amount of machining the ceramic element and the increased amount of the resistance value thereof.

[0072] FIG. 6A is a perspective view showing an NTC thermistor according to a second preferred embodiment of the present invention.

[0073] FIG. 6B is a perspective view showing an NTC thermistor according to a third preferred embodiment of the present invention.

[0074] FIG. 7 is a perspective view showing an NTC thermistor according to a fourth preferred embodiment of the present invention.

[0075] FIG. 8A is a perspective view showing an NTC thermistor according to a fifth preferred embodiment of the present invention.

[0076] FIG. 8B is an exploded perspective view of the NTC thermistor shown in FIG. 8A without its exterior.

[0077] FIG. 9 is a perspective view showing an NTC thermistor according to a sixth preferred embodiment of the present invention.

[0078] FIG. 10 is a perspective view showing an NTC thermistor according to a seventh preferred embodiment of the present invention.

[0079] FIG. 11A is a perspective view showing an NTC thermistor according to an eighth preferred embodiment of the present invention. FIG. 11B is a cross-sectional view taken along line X-X in FIG. 11A.

[0080] FIG. 12A is a perspective view showing an NTC thermistor according to a Reference Example. FIGS. 12B-1, 12B-2, and 12B-3 are cross-sectional views of the NTC thermistor shown in FIG. 12A including a protection layer having different thicknesses.

[0081] FIG. 13 is a graph showing a relationship between the thickness of the protection layer of the NTC thermistor shown in FIG. 12A and a resistance change rate through soldering mounting.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Preferred Embodiment

[0082] FIGS. 1A and 1B show an NTC thermistor 100 as an electronic component according to a first preferred embodiment of the present invention. FIG. 1A is a perspective view, and FIG. 1B is a cross-sectional view taken along line X-X in FIG. 1A.

[0083] The NTC thermistor 100 is a chip electronic component that may be, for example, surface-mounted.

[0084] The NTC thermistor 100 includes a ceramic element 1 with a rectangular parallelepiped or a substantially rectangular parallelepiped shape including one pair of end surfaces 1a and 1b and four side surfaces 1c, 1d, 1e, and 1f connecting the end surfaces 1a and 1b.

[0085] In the NTC thermistor 100 according to the present preferred embodiment, the end surfaces 1a and 1b of the ceramic element 1 are each rectangular or substantially rectangular including a first side having a length S and a second side having a length T, which are orthogonal or substantially orthogonal to each other. The length S of the first side is longer than or equal to the length T of the second side. The length S of the first side as the longer side is less than or equal to a length U of each of the side surfaces 1c, 1d, 1e, and 1f between the end surface 1a and the end surface 1b. In FIG. 1A, the lengths S, T, and U each include thicknesses of the external electrodes 3a and 3b, to be described below, which are extremely small.

[0086] Specific dimensions of the lengths S, T, and U are optional, and may be, for example, dimensions of S=about 0.8 mm, about 0.5 mm≦T≦about 0.8 mm, and U=about 1.6 mm.

[0087] The ceramic element 1 includes a composite oxide semiconductor obtained by mixing a plurality of types of fiber metallic oxide, for example, Mn, Co, Ni, Cu, and Fe and sintering the mixture at a high temperature of, for example, about 1200 to about 1500° C., approximately.

[0088] In the present preferred embodiment, internal electrodes 2a, 2b, and 2c are thick rectangular or substantially rectangular films buried inside the ceramic element 1. The internal electrodes 2a, 2b, and 2c each include a primary component, for example, Ag, Pd, Ag—Pd, or Pt, which makes ohmic contact with the ceramic element 1. One side of the internal electrode 2a is externally exposed from the end surface 1a as one end surface of the ceramic element 1. One side of the internal electrode 2b is externally exposed from the end surface 1b as the other end surface of the ceramic element 1. The internal electrode 2c is a floating electrode, and is not externally exposed from the ceramic element 1. A portion of the internal electrode 2c faces portions of the internal electrode 2a and the internal electrode 2b.

[0089] The external electrodes 3a and 3b are provided at both end portions of the ceramic element 1.

[0090] The external electrode 3a is provided on the end surface 1a as one end surface of the ceramic element 1 and extends to the two side surfaces 1c and 1e over two facing sides of four sides surrounding the end surface 1a. The external electrode 3b is provided on the end surface 1b as the other end surface of the ceramic element 1 and extends to the two side surfaces 1c and 1e over two facing sides of four sides surrounding the end surface 1b. In other words, the external electrodes 3a and 3b preferably are C shaped, with depth, at the respective end portions of the ceramic element 1.

[0091] The two facing side surfaces 1d and 1f of the ceramic element 1, on which the external electrodes 3a and 3b are not extended, are machined to be flush or substantially flush with each other. This flush or substantially flush machining of the two side surfaces 1d and 1f is performed to adjust the resistance value (as an example of a characteristic value) of the NTC thermistor 100 to be within a desired range of a predetermined target resistance value (as an example of a target characteristic value) as described below.

[0092] Although not shown in the drawings, the external electrodes 3a and 3b each include a baked external electrode directly formed on the ceramic element 1, and a plated external electrode formed on the baked external electrode. The baked external electrode includes a primary component, for example, Ag—Pd, Ag, or Cu. The plated external electrode includes, for example, two layers of a Ni-plated first layer and a Sn-plated second layer.

[0093] In the NTC thermistor 100 according to the present preferred embodiment, the external electrodes 3a and 3b preferably are formed as a baked external electrode and a plated external electrode, but may be both formed as baked external electrodes, for example.

[0094] In the NTC thermistor 100 according to the present preferred embodiment, the side surfaces 1d and 1f of the ceramic element 1 are machined to be flush or substantially flush with the external electrodes 3a and 3b to have an adjusted characteristic value (for example, a resistance value), thus providing an extremely high resistance value accuracy (for example, a characteristic accuracy).

[0095] The following describes an exemplary method of manufacturing the NTC thermistor 100 according to the present preferred embodiment. The method of manufacturing the NTC thermistor 100 according to the present preferred embodiment includes processes described below.

[0096] First, although not shown in the drawings, starting materials, for example, Mn.sub.3O.sub.4 powder, Co.sub.3O.sub.4 powder, and NiO powder, are weighed to provide a predetermined composition and wet-mixed by a ball mill. Subsequently, the mixed materials are calcined at, for example, about 900° C. Subsequently, the calcined materials are crushed again by the ball mill and then mixed together with dispersant and an organic binder to provide slurry.

[0097] Subsequently, the slurry is shaped by a doctor blade method to provide a ceramic green sheet. Subsequently, the ceramic green sheet is cut into rectangles or substantial rectangles each having a relatively large area to form mother sheets for manufacturing a high number of NTC thermistors all at once.

[0098] Subsequently, conductive paste including a primary component, for example, Ag—Pd is printed on the principal surface of each of predetermined mother sheets to form an internal-electrode pattern having a desired shape. However, the internal-electrode pattern is not formed on some of the mother sheets.

[0099] Subsequently, the mother sheets on each of which the internal-electrode pattern is formed are laminated in a predetermined order. Then, the mother sheets on each of which the internal-electrode pattern is not formed are laminated above and below the laminated mother sheets on each of which the internal-electrode pattern is formed, and bonded by pressure to provide a mother laminated body. Subsequently, the mother laminated body is cut at predetermined dimensions to provide a plurality of ceramic bodies to be fired.

[0100] Subsequently, each ceramic element to be fired is heated in air to perform debinder processing. Subsequently, the ceramic element is fired, for example, at about 1100° C. in air to provide the ceramic element 1 as shown in FIG. 2A.

[0101] In the present preferred embodiment, the fired ceramic element 1 preferably has a width of about 0.72 mm, a length of about 1.52 mm, and a height of about 0.72 mm, for example. Barrel polishing may be performed, for example, to trim the profile of the ceramic element 1.

[0102] Subsequently, as shown in FIG. 2B, the external electrodes 3a and 3b are formed at both end portions of the ceramic element 1. Specifically, first, conductive paste including a primary component, for example, Ag—Pd, is applied at both end portions of the ceramic element 1, and baked to form a baked external electrode (not shown in the drawings). Subsequently, a plated external electrode (not shown in the drawings) including a Ni-plated first layer and a solder-plated second layer is formed on the baked external electrode by electrolytic plating.

[0103] Subsequently, an initial resistance value (as an example of an initial characteristic value) between the external electrodes 3a and 3b is measured for each ceramic element 1. Then, the ceramic element 1 is classified into one of a plurality of groups depending on the initial resistance value.

[0104] A correlation diagram between the amount (for example, by percent) of machining the ceramic element 1 and an increased amount (for example by percent) of the resistance value is produced in advance before manufacturing of the NTC thermistor 100. Specifically, a plurality of sample experiments are performed in advance to obtain a correlation relation between a machining amount of the ceramic element 1 and an increase the resistance value by a certain amount.

[0105] FIGS. 4A and 4B each show an exemplary correlation diagram between the machining amount and the increased amount of the resistance value. FIG. 4A shows a case of polishing one side surface of the ceramic element 1. FIG. 4B shows a case of polishing the back side surface of the ceramic element 1, one side surface of which is polished to produce the diagram of FIG. 4A. In FIGS. 4A and 4B, the machining amount does not include the amounts of machining the external electrodes 3a and 3b.

[0106] For example, in the correlation diagram of FIG. 4A, a correlation equation of y=0.2354x+0.7562 holds, where x represents the machining amount, and y represents the increased amount of the resistance value.

[0107] Thus, for example, when one side surface of the ceramic element 1 is machined by about 10%, the resistance value increases by about 3.1%, approximately.

[0108] The resistance value tends to have a larger rate of increasing when the baked external electrode has ohmic contact with the ceramic element 1 than when the baked external electrode has no ohmic contact with the ceramic element 1. FIG. 5 shows the correlation diagram when the baked external electrode includes a primary component of Ag—Pd having ohmic contact with the ceramic element 1, and the correlation diagram when the baked external electrode includes a primary component of Cu having no ohmic contact with the ceramic element 1. As shown in FIG. 5, the resistance value has a larger increase rate and the correlation equation has a slightly larger gradient when the primary component is Ag—Pd than when the primary component is Cu. Thus, in the present preferred embodiment, the baked external electrode preferably includes a primary component having ohmic contact with the ceramic element 1, for example, because the resistance value is able to be more greatly increased with a lower machining amount.

[0109] The machining of the ceramic element 1 may be performed on one side surface of the ceramic element 1 or two facing side surfaces thereof. The machining of one side surface involves a lower number of processes, thus providing high productivity. The machining of two side surfaces is able to provide a completed electronic component having a vertically symmetrical or substantially vertically symmetrical shape. The number of machined side surfaces is not limited to one or two, and three continuous side surfaces may be machined.

[0110] However, the above-described correlation equation differs depending on the number of side surfaces of a machined ceramic element and the positions thereof, in some cases. In such a case, the correlation diagram is produced in accordance with the number of side surfaces of the machined ceramic element and the positions thereof.

[0111] When any of the appearance dimensions of width, length, and height of the ceramic element 1 is different from a target dimension, a machined side surface of the ceramic element 1 is preferably determined, for example, to correct the dimension, thus adjusting the resistance value as well as the dimension.

[0112] Any side surface to be machined and the machining amount are determined for each ceramic element 1, which is classified depending on its initial resistance value, based on the produced correlation diagram between the amount of machining the ceramic element 1 and the increased amount of the resistance value. In the NTC thermistor 100 according to the present preferred embodiment, the facing side surfaces 1d and 1f of the ceramic element 1 are determined to be machined by predetermined amounts.

[0113] As shown in FIG. 2C, first, the side surface 1d of the ceramic element 1 is machined by the predetermined amount. The machining is able to be performed by, for example, sandblasting, dicing, wet blasting, or lap polishing. Covering with, for example, a protection film before the machining is not needed over a portion of the ceramic element 1. A plurality of ceramic elements 1 classified into the same group may be fixed to, for example, a jig, and machined all at once. FIG. 3D shows the ceramic element 1 after the side surface 1d is machined.

[0114] Subsequently, as shown in FIG. 3F, the ceramic element 1 is turned over to machine the side surface 1f of the ceramic element 1 by the predetermined amount.

[0115] When the machining of the side surface 1f of the ceramic element 1 is finished, the NTC thermistor 100 according to the present preferred embodiment is completed. The NTC thermistor 100 has a precisely adjusted resistance value within the desired range of the target resistance value.

Second Preferred Embodiment

[0116] FIG. 6A shows a chip NTC thermistor 200 as an electronic component according to a second preferred embodiment of the present invention.

[0117] The NTC thermistor 200 has an adjusted resistance value provided by machining only the one side surface 1d of the ceramic element 1 together with external electrodes 13a and 13b through the side surface machining process. The rest of the configuration of the NTC thermistor 200 and a method of manufacturing the same are the same as or similar to the configuration of the NTC thermistor 100 and the method for manufacturing the same according to the first preferred embodiment described above.

Third Preferred Embodiment

[0118] FIG. 6B shows a chip NTC thermistor 300 as an electronic component according to a third preferred embodiment of the present invention.

[0119] The NTC thermistor 300 has an adjusted resistance value provided by machining the three continuous side surfaces 1c, 1d, and 1e of the ceramic element 1 together with external electrodes 23a and 23b through the side surface machining process. The rest of the configuration of the NTC thermistor 300 and a method of manufacturing the same are the same as or similar to the configuration of the NTC thermistor 100 and the method for manufacturing the same according to the first preferred embodiment described above.

Fourth Preferred Embodiment

[0120] FIG. 7 shows a chip NTC thermistor 400 as an electronic component according to a fourth preferred embodiment of the present invention.

[0121] In the NTC thermistor 400 according to the present preferred embodiment, a ceramic element 11 to be described below has a shape different from the shapes of the NTC thermistors 100 to 300 according to the first to third preferred embodiments described above.

[0122] The NTC thermistor 400 includes the ceramic element 11 with a rectangular parallelepiped or a substantially rectangular parallelepiped shape including one pair of end surfaces 11a and 11b and four side surfaces 11c, 11d, 11e, and 11f connecting the end surfaces 11a and 11b.

[0123] In the NTC thermistor 400, each of the end surfaces 11a and 11b of the ceramic element 11 is rectangular or substantially rectangular including a first side having a length S and a second side having a length T, which are orthogonal or substantially orthogonal to each other. The length S of the first side is longer than or equal to the length T of the second side. The length S of the first side as the longer side is longer than a length U of each of the side surfaces 11c and 11d, 11e, and 11f between the end surfaces 11a and 11b.

[0124] Specific dimensions of the lengths S, T, and U are optional, and may be, for example, dimensions of S=about 1.6 mm, about 0.5 mm≦T≦about 1.6 mm, and U=about 0.8 mm.

[0125] The external electrodes 33a and 33b are formed at both end portions of the ceramic element 11.

[0126] The external electrode 33a is provided on the end surface 11a as one end surface of the ceramic element 11 and extends to the two side surfaces 11c and 11e over two facing sides of four sides surrounding the end surface 11a. The external electrode 33b is provided on the end surface 11b as the other end surface of the ceramic element 11 and extends to the two side surfaces 11c and 11e over two facing sides of four sides surrounding the end surface 11b.

[0127] The external electrodes 33a and 33b preferably have cap shapes at the respective end portions of the ceramic element 11 in advance, and then formed in the above-described shape by machining the side surfaces 11d and 11f of the ceramic element 11 to be flush or substantially flush with each other to adjust the resistance value.

[0128] In the NTC thermistor 400 according to the fourth preferred embodiment, the side surfaces 11d and 11f of the ceramic element 11 are machined to adjust the resistance value. However, as a modification, any one of the four side surfaces 11c to 11f of the ceramic element 11 may be machined to be flush or substantially flush with the external electrodes 33a and 33b. Alternatively, as another modification, three continuous side surfaces of the four side surfaces 11c to 11f of the ceramic element 11 may be machined to be flush or substantially flush with the external electrodes 33a and 33b.

[0129] The NTC thermistor 400 according to the fourth preferred embodiment is able to be manufactured through processes the same as or similar to the processes included in the method for manufacturing the NTC thermistor 100 according to the first preferred embodiment described above. Specifically, the NTC thermistor 400 is able to be manufactured by a manufacturing method including ceramic element manufacturing process, external electrode forming process, initial characteristic value measuring process, machining condition determining process, and the side surface machining process.

Fifth Preferred Embodiment

[0130] FIGS. 8A and 8B show an NTC thermistor 500 as an electronic component according to a fifth preferred embodiment of the present invention. FIG. 8A is a perspective view of the NTC thermistor 500. FIG. 8B is an exploded perspective view of the NTC thermistor 500 without an exterior 60 to be described below.

[0131] The NTC thermistor 500 is a lead-terminal NTC thermistor provided by joining one pair of lead terminals 50a and 50b to be described below with the chip NTC thermistor 400 according to the fourth preferred embodiment shown in FIG. 7.

[0132] As shown in FIG. 8B, the NTC thermistor 500 includes the NTC thermistor 400.

[0133] The NTC thermistor 400 includes the ceramic element 11 including one pair of the end surfaces 11a and 11b and the four side surfaces 11c, 11d, 11e, and 11f. Each of the end surfaces 11a and 11b is rectangular or substantially rectangular including a first side having a length S and a second side having a length T, which are orthogonal or substantially orthogonal to each other. The length S of the first side is longer than the length T of the second side and longer than a length U of each of the side surfaces 11c and 11d, 11e, and 11f between the end surfaces 11a and 11b.

[0134] The external electrodes 33a and 33b are provided on the ceramic element 11. The external electrode 33a is provided on the end surface 11a as one end surface of the ceramic element 11 and extends to the two side surfaces 11c and 11e over two facing sides of four sides surrounding the end surface 11a. The external electrode 33b is provided on the end surface 11b as the other end surface of the ceramic element 11 and extends to the two side surfaces 11c and 11e over two facing sides of four sides surrounding the end surface 11b.

[0135] The external electrodes 33a and 33b are joined with lead terminals 50a and 50b, respectively, by a joining material 40. The joining material 40 is, for example, solder or conductive adhesive agent. The lead terminals 50a and 50b preferably include an alloy containing Fe as a primary component or an alloy containing Cu as a primary component, for example.

[0136] In the NTC thermistor 500 according to the present preferred embodiment, the lead terminals 50a and 50b are joined in parallel or substantially in parallel to the first side having the length S of each of the end surfaces 11a and 11b of the ceramic element 11. The first side having the length S is a side of the ceramic element 1 having a greatest length and is longer than the lengths T and U as shown in FIG. 8B.

[0137] In the NTC thermistor 500 with the configuration described above, the lead terminals 50a and 50b are in contact with the external electrodes 33a and 33b, respectively, over longer lengths. In addition, the lead terminals 50a and 50b are able to be joined with the external electrodes 33a and 33b, respectively, through a sufficient amount of the joining material 40. Accordingly, in the NTC thermistor 500, the lead terminals 50a and 50b are solidly joined with the external electrodes 33a and 33b, respectively.

[0138] The exterior 60 is provided as shown in FIG. 8A, leaving one end of each of the lead terminals 50a and 50b externally exposed. The exterior 60 includes, for example, resin such as epoxy resin or glass. The exterior 60 protects a body portion of the NTC thermistor 500.

[0139] The NTC thermistor 500 according to the present preferred embodiment, which has the above-described structure, is able to be manufactured by, for example, the following method.

[0140] First, the NTC thermistor 400 according to the fourth preferred embodiment is prepared. The NTC thermistor 400 is manufactured at least through the ceramic element manufacturing process, the external electrode forming process, the initial characteristic value measuring process, the machining condition determining process, and the side surface machining process. The NTC thermistor 400 has a high characteristic accuracy when manufactured through the initial characteristic value measuring process, the machining condition determining process, and the side surface machining process.

[0141] Subsequently, as a lead terminal joining process, the external electrodes 33a and 33b of the NTC thermistor 400 are joined with the lead terminals 50a and 50b, respectively, by the joining material 40.

[0142] Thereafter, a characteristic value adjusting process may be performed as an optional process. The characteristic value adjusting process is performed to adjust, again into a desired range, a characteristic value shifted due to, for example, the joining of the lead terminals 50a and 50b. The characteristic value adjusting process may include, for example, a characteristic value measuring process, a machining condition determining process, and a side surface machining process.

[0143] Similarly to the machining condition determining process in the method of manufacturing the NTC thermistor 100 according to the first preferred embodiment described above, the machining condition determining process may be performed or is preferably performed, for example, by using a previously produced correlation diagram between the machining amount and change of the characteristic value. The machining condition determining process is preferably performed, for example, in consideration of the change of the characteristic value through an exterior forming process performed next.

[0144] Lastly, as an exterior sealing process, the ceramic element 11 is sealed by the exterior 60, leaving one end of each of the lead terminals 50a and 50b externally exposed. This completes the NTC thermistor 500 according to the present preferred embodiment.

Sixth Preferred Embodiment

[0145] FIG. 9 shows a chip NTC thermistor 600 as an electronic component according to a sixth preferred embodiment of the present invention.

[0146] The NTC thermistor 600 according to the present preferred embodiment is provided by changing the NTC thermistor 100 according to the first preferred embodiment shown in FIGS. 1A and 1B. Specifically, the ceramic element 1 of the NTC thermistor 100 is replaced by a ceramic element 21 having a different shape.

[0147] The NTC thermistor 600 includes the ceramic element 21 with a rectangular parallelepiped or a substantially rectangular parallelepiped shape including one pair of end surfaces 21a and 21b and four side surfaces 21c, 21d, 21e, and 21f connecting the end surfaces 21a and 21b.

[0148] In the NTC thermistor 600, each of the end surfaces 21a and 21b of the ceramic element 21 is rectangular or substantially rectangular including a first side having a length S and a second side having a length T, which are orthogonal or substantially orthogonal to each other. The length T of the second side is longer than the length S of the first side. The length T of the second side as the longer side is less than or equal to a length U of each of the side surfaces 21c, 21d, 21e, and 21f between the end surfaces 21a and 21b.

[0149] Specific dimensions of the lengths S, T, and U are optional, and may be, for example, dimensions of S=about 0.8 mm, about 0.8 mm<T≦about 1.6 mm, and U=about 1.6 mm.

[0150] External electrodes 43a and 43b are provided at both end portions of the ceramic element 21.

[0151] The external electrode 43a is provided on the end surface 21a as one end surface of the ceramic element 21 and extends to two side surfaces 21c and 21e over two facing sides of four sides surrounding the end surface 21a. The external electrode 43b is provided on the end surface 21b as the other end surface of the ceramic element 21 and extends to two side surfaces 21c and 21e over two facing sides of four sides surrounding the end surface 21b.

[0152] The external electrodes 43a and 43b are provided in cap shapes at both end portions of the ceramic element 21 in advance, and then formed in the above-described shape by machining the side surfaces 21d and 21f of the ceramic element 21 to be flush or substantially flush with each other to adjust the resistance value.

[0153] In the NTC thermistor 600 according to the sixth preferred embodiment, a length T of a second side of each of the end surfaces 21a and 21b is longer than the length T of the second side of each of the end surfaces 1a and 1b of the NTC thermistor 100 according to the first preferred embodiment, and thus the side surfaces 21d and 21f of the ceramic element 21 are able to be greatly machined to adjust the resistance value. The shape of the NTC thermistor 600 is desirable when the characteristic value is significantly adjusted.

[0154] In the NTC thermistor 600 according to the sixth preferred embodiment, the side surfaces 21d and 21f of the ceramic element 21 are machined to adjust the resistance value. Instead, as a modification, any one of the four side surfaces 21c to 21f of the ceramic element 21 may be machined to be flush or substantially flush with the external electrodes 43a and 43b. Alternatively, as another modification, three continuous side surfaces of the four side surfaces 21c to 21f of the ceramic element 21 may be machined to be flush or substantially flush with the external electrodes 43a and 43b.

Seventh Preferred Embodiment

[0155] FIG. 10 shows a chip NTC thermistor 700 as an electronic component according to a seventh preferred embodiment of the present invention.

[0156] The NTC thermistor 700 according to the present preferred embodiment is provided by changing the NTC thermistor 400 according to the fourth preferred embodiment shown in FIG. 7. Specifically, the ceramic element 11 of the NTC thermistor 400 is replaced by a ceramic element 31 having a different shape.

[0157] The NTC thermistor 700 includes the ceramic element 31 with a rectangular parallelepiped or a substantially rectangular parallelepiped shape including one pair of end surfaces 31a and 31b and four side surfaces 31c, 31d, 31e, and 31f connecting the end surfaces 31a and 31b.

[0158] In the NTC thermistor 700, each of the end surfaces 31a and 31b of the ceramic element 31 is rectangular or substantially rectangular including a first side having a length S and a second side having a length T, which are orthogonal or substantially orthogonal to each other. The length T of the second side is longer than or equal to the length S of the first side. The length T of the second side as the longer side is longer than a length U of each of the side surfaces 31c, 31d, 31e, and 31f between the end surfaces 31a and 31b.

[0159] Specific dimensions of the lengths S, T, and U are optional, and may be, for example, dimensions of S=about 1.2 mm, about 1.2 mm≦T≦about 1.6 mm, and U=about 0.8 mm.

[0160] External electrodes 53a and 53b are provided at both end portions of the ceramic element 31.

[0161] The external electrode 53a is provided on the end surface 31a as one end surface of the ceramic element 31 and extends to two side surfaces 31c and 31e over two facing sides of four sides surrounding the end surface 31a. The external electrode 53b is provided on the end surface 31b as the other end surface of the ceramic element 31 and extends to two side surfaces 31c and 31e over two facing sides of four sides surrounding the end surface 31b.

[0162] The external electrodes 53a and 53b are preferably provided in cap shapes at both end portions of the ceramic element 31 in advance, and then formed in the above-described shape by machining the side surfaces 31d and 31f of the ceramic element 31 to be flush or substantially flush with each other to adjust the resistance value.

[0163] In the NTC thermistor 700 according to the seventh preferred embodiment, the length T of the second side of each of the end surfaces 31a and 31b is longer than the length T of the second side of each of the end surfaces 11a and 11b of the NTC thermistor 400 according to the fourth preferred embodiment, and thus the side surfaces 31d and 31f of the ceramic element 31 are able to be greatly machined to adjust the resistance value. The shape of the NTC thermistor 700 is desirable when the characteristic value is significantly adjusted.

[0164] To provide a lead-terminal NTC thermistor by joining one pair of lead terminals (not shown in the drawings) with the NTC thermistor 700, the lead terminals are preferably disposed, for example, in parallel or substantially in parallel to the second sides, each having the length T, of the end surfaces 31a and 31b of the ceramic element 31 and joined with the external electrodes 53a and 53b. In this case, the lead terminals are in contact with the external electrodes 53a and 53b over longer lengths. In addition, the lead terminals are able to be joined with the external electrodes 53a and 53b through a sufficient amount of the joining material. Accordingly, the lead terminals are able to be solidly joined with the external electrodes 53a and 53b.

[0165] In the NTC thermistor 700 according to the seventh preferred embodiment, the side surfaces 31d and 31f of the ceramic element 31 are machined to adjust the resistance value. Instead, as a modification, any one of the four side surfaces 31c to 31f of the ceramic element 31 may be machined to be flush or substantially flush with the external electrodes 53a and 53b. Alternatively, as another modification, three continuous side surfaces of the four side surfaces 31c to 31f of the ceramic element 31 may be machined to be flush or substantially flush with the external electrodes 53a and 53b.

Eighth Preferred Embodiment

[0166] FIGS. 11A and 11B show a chip NTC thermistor 800 as an electronic component according to an eighth preferred embodiment of the present invention. FIG. 11A is a perspective view, and FIG. 11B is a cross-sectional view taken along line Y-Y in FIG. 11A.

[0167] The NTC thermistor 800 includes a ceramic element 41 with a rectangular parallelepiped or a substantially rectangular parallelepiped shape including one pair of end surfaces 41a and 41b and four side surfaces 41c, 41d, 41e, and 41f connecting the end surfaces 41a and 41b.

[0168] In the NTC thermistor 800, each of end surfaces 41a and 41b of the ceramic element 41 is rectangular or substantially rectangular including a first side having a length S and a second side having a length T, which are orthogonal or substantially orthogonal to each other. A length U is the distance between the end surfaces 41a and 41b.

[0169] In the present preferred embodiment, specific dimensions of the lengths S, T, and U of the NTC thermistor 800 preferably are S=about 1.6 mm, T=about 1.0 mm, and U=about 0.8 mm, for example. However, each dimension may be changed as desired.

[0170] External electrodes 63a and 63b are provided at both end portions of the ceramic element 41.

[0171] The external electrode 63a is provided on the end surface 41a as one end surface of the ceramic element 41 and extends to the three side surfaces 41c, 41e, and 41f over three sides of four sides surrounding the end surface 41a. The external electrode 63b is provided on the end surface 41b as the other end surface of the ceramic element 41 and extends to the three side surfaces 41c, 41e, and 41f over three sides of four sides surrounding the end surface 41b. In other words, neither of the external electrodes 63a and 63b are extended to the side surface 41d of the ceramic element 41.

[0172] The external electrodes 63a and 63b are preferably provided in cap shapes at both end portions of the ceramic element 41 in advance, and then formed in the above-described shape by machining the side surface 41d of the ceramic element 41 to be flush or substantially flush to adjust the resistance value.

[0173] As shown in FIG. 11B, an internal electrode 12a connected with the external electrode 63a, and an internal electrode 12b connected with the external electrode 63b are provided inside the ceramic element 41. The internal electrodes 12a and 12b have widths of about 20 μm, approximately.

[0174] In the NTC thermistor 800 according to the present preferred embodiment, a distance D from the external electrode 63b on the side surface 41f of the ceramic element 41 to the nearest internal electrode 12a is set to be longer than about 225 μm. The distance D, which is the distance from the side surface 41f of the ceramic element 41 to the nearest internal electrode 12a, is the thickness of a protection layer.

[0175] In the NTC thermistor 800, the distance D is set to be longer than about 225 μm to reduce change of the resistance of the NTC thermistor 800 due to heat when the NTC thermistor 800 is mounted by soldering. In other words, change of the resistance due to heat when the NTC thermistor 800 is mounted by soldering is able to be reduced when the distance D is set to be longer than about 225 μm, for example. This finding was acquired through the following experiment performed by the inventors of the present invention.

[0176] FIG. 12A shows an NTC thermistor 1000 according to a Reference Example. The NTC thermistor 1000 includes a ceramic element 101 having dimensions of S=about 1.6 mm, T=about 1.0 mm, and U=about 0.8 mm. External electrodes 103a and 103b in cap shapes are formed at both end portions of the ceramic element 101. Unlike the present invention, side surfaces of the ceramic element 101 are not machined.

[0177] In the NTC thermistor 1000 according to the Reference Example, an internal electrode 102a connected with the external electrode 103a, and an internal electrode 102b connected with the external electrode 103b are provided inside the ceramic element 101 as shown in FIGS. 12B-1 to 12B-3. FIGS. 12B-1 to 12B-3 show thermistors different from each other, between which the distance from the external electrode 103b on the bottom surface of the ceramic element 101 to the internal electrode 102a differs. Specifically, FIG. 12B-1 shows an example in which the distance from the external electrode 103b to the internal electrode 102a is about 43 μm. FIG. 12B-2 shows an example in which the distance from the external electrode 103b to the internal electrode 102a is about 225 μm. FIG. 12B-3 shows an example in which the distance from the external electrode 103b to the internal electrode 102a is about 432 μm.

[0178] In addition to the three examples described above and shown in FIGS. 12B-1 to 12B-3, the NTC thermistor 1000 was manufactured as a plurality of specimens with different distances from the external electrode 103b on the bottom surface of the ceramic element 101 to the internal electrode 102a. Then, all specimens were each mounted on a substrate by reflow soldering to measure a resistance change rate through the mounting.

[0179] FIG. 13 shows a relationship between the distance from the external electrode 103b on the bottom surface of the ceramic element 101 to the internal electrode 102a (for example, the thickness of the protection layer) and the resistance change rate through the mounting by soldering.

[0180] As shown FIG. 13, when the thickness of the protection layer is not greater than about 225 μm, the resistance change rate proportionally decreases as the thickness increases. However, when the thickness of the protection layer is greater than about 225 μm, the resistance change rate does not significantly decrease further.

[0181] The resistance of the NTC thermistor 1000 receives largest contribution from a resistance component between the internal electrodes 102a and 102b, but also receives contributions from a resistance component between the internal electrode 102a and the external electrode 103b at different potentials, and from a resistance component between the internal electrode 102b and the external electrode 103a at different potentials.

[0182] When the NTC thermistor 1000 is mounted on a substrate by soldering, an oxygen reaction occurs, and the ceramic is oxidized at a portion near the surface of the ceramic element 101 due to heat of the mounting, thus increasing the resistance value of the portion. The increase in the resistance value at the portion near the surface of the ceramic element 101 increases the resistance between the internal electrode 102a and the external electrode 103b and the resistance between the internal electrode 102b and the external electrode 103a. Accordingly, the resistance of the NTC thermistor 1000, that is, the resistance between the external electrodes 103a and 103b, increases. This increase in resistance can be a primary cause of variation in the resistance when the NTC thermistor 1000 is mounted on the substrate by soldering.

[0183] However, as shown in FIG. 13, when the thickness of the protection layer is greater than about 225 μm and the internal electrode 102a and the internal electrode 102b are disposed more inside in the direction of the length T of the ceramic element 101, a change of the resistance between the internal electrode 102a and the external electrode 103b and a change of the resistance between the internal electrode 102b and the external electrode 103a, which are caused by heat of the mounting by soldering, are able to be reduced.

[0184] Accordingly, in the NTC thermistor 800 according to the eighth preferred embodiment, the distance D from the external electrode 63b on the side surface 41f of the ceramic element 41 to the nearest internal electrode 12a was set to be longer than about 225 μm based on the above-described finding. The NTC thermistor 800 undergoes a reduced change of the resistance due to heat when mounted by soldering.

[0185] It was discovered that the technology of reducing change of the resistance due to heat at the soldering mounting, in which the distance (for example, the thickness of the protection layer) from an external electrode on the bottom surface or the top surface to a nearest internal electrode is set to be longer than about 225 μm, provides a greater effect on an NTC thermistor including a ceramic element having dimensions longer than a width of about 0.5 mm, a thickness of about 0.5 mm, and a length of about 1.0 mm, for example.

[0186] The above description is provided with respect to the exemplary structures of the NTC thermistors 100 to 800 according to the first to eighth preferred embodiments of the present invention, and the exemplary methods of manufacturing the same. However, the present invention is not limited to the above-described configurations, and various modifications are possible without departing from the scope of the present invention.

[0187] For example, an NTC thermistor is described as an electronic component in each above-described preferred embodiment. However, electronic components according to preferred embodiments of the present invention is not limited to an NTC thermistor, but may be, for example, a coil, a capacitor, or a resistance. Alternatively, the electronic component may be a PTC thermistor in place of an NTC thermistor, for example.

[0188] An adjusted characteristic value is not limited to the resistance value, but may be, for example, the inductance value or the capacitance value.

[0189] The appearance of a ceramic element may have various kinds of shapes and dimensions. For example, the ceramic element may be cube or substantially cube shaped, all sides of which have equal or substantially equal lengths.

[0190] It was discovered that preferred embodiments of the present invention are effective at least for the electronic component 100 according to the first preferred embodiment shown in FIGS. 1A and 1B, which includes the ceramic element 1 having a shape with dimensions of S=about 0.8 mm, about 0.5 mm≦T≦about 0.8 mm, and U=about 1.6 mm, for example.

[0191] It was also discovered that the present invention is effective for the electronic component 400 according to the fourth preferred embodiment shown in FIG. 7, which includes the ceramic element 11 having a shape with dimensions of S=about 1.6 mm, about 0.5 mm≦T≦about 1.6 mm, and U=about 0.8 mm, for example.

[0192] It was also discovered that preferred embodiments of the present invention are effective for electronic component 600 according to the sixth preferred embodiment shown in FIG. 9, which includes the ceramic element 21 having a shape with dimensions of S=about 0.8 mm, about 0.8 mm<T≦about 1.6 mm, and U=about 1.6 mm, for example.

[0193] It was also discovered that preferred embodiments of the present invention is effective for the electronic component 700 according to the seventh preferred embodiment shown in FIG. 10, which includes the ceramic element 31 having a shape with dimensions of S=about 1.2 mm, about 1.2 mm≦T≦about 1.6 mm, and U=about 0.8 mm, for example.

[0194] The number of side surfaces of a ceramic element, which are machined to be flush or substantially flush with each other, may be optionally selected from among one to three.

[0195] While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.