Thermistor element, temperature sensor including the same, and manufacturing method for thermistor element

Abstract

To provide a thermistor element exhibiting minimal characteristic change over time in high-temperature environments or heat resistance tests, a temperature sensor including the same, and a manufacturing method for the thermistor element.SOLUTION: The thermistor element includes a thermistor body 2 containing an oxide thermistor material having a perovskite crystal structure, and a pair of electrodes 3 formed on the thermistor body. The electrodes include a Pt electrode layer 3a formed on the surface of the thermistor body, and an intermetallic compound layer 3b including Pt, Sn, and M formed outside the Pt electrode layer. M is at least one of Ag, Ni, Co, and Mn, and the thickness of the intermetallic compound layer is 50 nm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thermistor element whose characteristics change little over time even in heat resistance tests or in high-temperature environments, a temperature sensor including the thermistor element, and a method for manufacturing the thermistor element. [Background technology]

[0002] Generally, the resistance value of a thermistor element changes with temperature, and this change is very sensitive to temperature, so it is widely used in applications such as temperature sensors and protection circuits for electronic devices. BACKGROUND ART Conventionally, in order to improve the environmental resistance of the thermistor element, for example, a sensor in which the thermistor element is sealed with resin is known (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3152352 Summary of the Invention [Problem to be solved by the invention]

[0004] The above conventional techniques still have the following problems. In recent years, improvements in motor output, driving range, and high-speed charging of electric vehicles have led to problems with the characteristics of thermistor elements changing over time due to heat resistance tests that assume higher temperatures in the driving environment of the motor, battery, etc. This problem is particularly evident in perovskite-based thermistor elements. In particular, in the case of thermistor elements equipped with electrodes made of Pt, if the electrode thickness is less than 4 μm, there is a problem that the resistance value increases significantly in high-temperature environments or during heat resistance tests. One possible solution to this problem is to thicken the Pt electrodes, but this has the disadvantage of increasing material costs.

[0005] The present invention has been made in view of the above-mentioned problems, and aims to provide a thermistor element whose characteristics change little over time in high-temperature environments and during heat resistance tests, a temperature sensor including the same, and a method for manufacturing the thermistor element. [Means for solving the problem]

[0006] The inventors conducted research into the changes in the characteristics of perovskite thermistor elements over time in high-temperature environments and during heat resistance tests, and discovered that the cause of this change is that when the thermistor element is mounted using solder, oxidation of Sn, the main component of the solder, exposes the thermistor element to a low-oxygen environment, causing oxygen defects in the thermistor material due to reduction. Therefore, the present invention was made based on the above findings, and the following configurations have been adopted to solve the above problems. That is, the thermistor element according to the first aspect of the present invention comprises a thermistor body containing an oxide thermistor material having a perovskite crystal structure, and a pair of electrodes formed on the thermistor body, the electrodes comprising a Pt electrode layer formed on the surface of the thermistor body, and an intermetallic compound layer containing Pt, Sn, and M formed on the outside of the Pt electrode layer, wherein M is at least one of Ag, Ni, Co, and Mn, and the thickness of the intermetallic compound layer is 50 nm or more.

[0007] In this thermistor element, M is at least one of Ag, Ni, Co, and Mn, and the thickness of the intermetallic compound layer is 50 nm or more. Therefore, the thick intermetallic compound layer, which is a conductive material with high heat resistance and low oxygen permeability, functions as an oxygen barrier layer, thereby suppressing the formation of oxygen defects in the thermistor element due to oxidation of Sn, the main component of the solder, even though the Pt electrode layer is thin. The present invention is particularly effective when the Pt electrode layer has a thickness of less than 4 μm.

[0008] The thermistor element according to the second invention is the thermistor element according to the first invention, characterized in that the thickness of the intermetallic compound layer is 190 nm or more, and the concentration of M in the intermetallic compound layer is 3.0 to 7.6 wt %. That is, in this thermistor element, the thickness of the intermetallic compound layer is 190 nm or more, and the concentration of M in the intermetallic compound layer is 3.0 to 7.6 wt %, so that the rate of change in resistance value in a heat resistance test can be suppressed to 1.6% or less.

[0009] A thermistor element according to a third invention is the thermistor element according to the first or second invention, characterized in that a solder material containing Sn as a main component is joined to at least one of the pair of electrodes. In other words, in this thermistor element, a solder material primarily composed of Sn is joined to at least one of the pair of electrodes, so even if the Sn in the solder material oxidizes when the element is soldered at high temperatures or used in a high-temperature environment, the formation of oxygen defects in the thermistor element can be suppressed, thereby reducing the rate of change in resistance value.

[0010] The thermistor element according to the fourth invention is the third invention, characterized in that the intermetallic compound layer has a high-concentration M region containing more M on the solder material side than on the Pt electrode layer side. That is, in this thermistor element, the intermetallic compound layer has a high-concentration M region containing more M on the solder material side than on the Pt electrode layer side, and the M-rich region enhances the oxygen barrier effect.

[0011] The temperature sensor according to the fifth invention is characterized by comprising the thermistor element of the third invention, a pair of lead wires having one end connected to the pair of electrodes by the solder material, and a resin sealing portion that seals the entire thermistor element, including the one end of the pair of lead wires, with resin. That is, this temperature sensor is provided with a resin sealing portion that seals the entire thermistor element, including one end of the pair of lead wires, with resin, thereby providing a resin-sealed type temperature sensor with a low rate of change in resistance value during heat resistance tests.

[0012] A temperature sensor according to a sixth aspect of the present invention comprises the thermistor element of the third aspect of the present invention and a mounting substrate on which the thermistor element is mounted, the mounting substrate having wiring formed on its surface, and the thermistor element being joined onto the wiring with the solder material. That is, in this temperature sensor, the thermistor element of the above invention is joined to the wiring of the mounting board with solder material, so that even when the thermistor element is mounted on the board, changes in resistance value can be suppressed in high-temperature environments or during heat resistance tests, etc.

[0013] A seventh aspect of the present invention relates to a method for manufacturing a thermistor element, comprising: an electrode forming step of forming a pair of electrodes on a thermistor body containing an oxide thermistor material having a perovskite crystal structure; and a soldering step of joining a solder material containing Sn as a main component to at least one of the pair of electrodes, wherein the electrode forming step comprises a Pt electrode layer step of forming a Pt electrode layer on the surface of the thermistor body; and an intermetallic compound layer forming step of forming an intermetallic compound layer containing Pt, Sn, and M on the outside of the Pt electrode layer, wherein M is at least one of Ag, Ni, Co, and Mn, and the thickness of the intermetallic compound layer is 50 nm or more.

[0014] The eighth invention is a method for manufacturing a thermistor element according to the seventh invention, characterized in that, in the soldering step, when the molten solder material containing M is attached to the Pt electrode layer and then solidified, an intermetallic compound layer forming step is performed to form an intermetallic compound layer containing M and Sn in the solder material and Pt in the Pt electrode layer between the solder material and the Pt electrode layer. In this manufacturing method of thermistor element, when the molten solder material containing M is attached to the Pt electrode layer and then solidified in the soldering step, an intermetallic compound layer formation step is carried out to form an intermetallic compound layer containing M and Sn in the solder material and Pt in the Pt electrode layer between the solder material and the Pt electrode layer, so the intermetallic compound layer formation step can be carried out during the soldering step.

[0015] A ninth aspect of the present invention is a method for manufacturing a thermistor element according to the eighth aspect of the present invention, characterized in that in the soldering step, the solder material is bonded at a bonding temperature of 280° C. or higher. That is, in this manufacturing method of the thermistor element, the solder material is joined at a joining temperature of 280°C or higher in the soldering step, making it possible to suppress the rate of change in resistance value in a heat resistance test to 1.6% or less. In particular, when the solder material is joined at a joining temperature of 380°C or higher, an intermetallic compound layer containing more M on the solder material side than on the Pt electrode layer side is obtained, which further enhances the oxygen barrier effect and reduces the rate of change in resistance value.

[0016] A tenth aspect of the present invention is a method for manufacturing a thermistor element according to the seventh aspect, characterized in that the intermetallic compound layer forming step comprises an M sputtering step of forming an M layer by adhering the M to the surface of the Pt electrode layer by a sputtering method, and an M solid solution step of forming the intermetallic compound layer containing the M in the M layer, the Pt in the Pt electrode layer, and the Sn in the solder material between the solder material and the Pt electrode layer when the solder material melted in the solder joining step is adhered to the M layer and then solidified. That is, in this method for manufacturing a thermistor element, the intermetallic compound layer forming step includes an M sputtering step in which M is deposited on the surface of a Pt electrode layer by sputtering to form an M layer, and an M solidification step in which, when the solder material melted in the solder joining step is deposited on the M layer and then solidified, an intermetallic compound layer containing M in the M layer, Pt in the Pt electrode layer, and Sn in the solder material is formed between the solder material and the Pt electrode layer.Therefore, even if the solder material does not contain M, it is possible to easily obtain an intermetallic compound layer containing a sufficient amount of M by dissolving M in the M layer formed by sputtering. [Effects of the Invention]

[0017] According to the present invention, the following effects are achieved. That is, in the thermistor element, temperature sensor including the same, and method for manufacturing thermistor element according to the present invention, M is at least one of Ag, Ni, Co, and Mn, and the thickness of the intermetallic compound layer is 50 nm or more. Therefore, the thick intermetallic compound layer, which is a conductive material with high heat resistance and low oxygen permeability, functions as an oxygen barrier layer, and therefore it is possible to suppress the formation of oxygen defects in the thermistor element due to oxidation of Sn, the main component of the solder, even if the Pt electrode layer is thin. Therefore, it is possible to suppress the thermistor characteristics from changing over time in a high-temperature environment or during a heat resistance test, and a highly reliable thermistor element and temperature sensor can be obtained. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a conceptual cross-sectional view of a main part of a thermistor element according to one embodiment of the thermistor element, a temperature sensor including the thermistor element, and a method for manufacturing the thermistor element according to the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing a resin-sealed temperature sensor according to the present embodiment. [Figure 3] FIG. 1 is a cross-sectional view showing a temperature sensor including a thermistor element according to the present embodiment. [Figure 4] FIG. 10 is a cross-sectional view showing another example of a temperature sensor including a thermistor element in the present embodiment. [Figure 5] 1A to 1C are schematic cross-sectional views showing a method for manufacturing a thermistor element in the order of manufacturing steps in the present embodiment. [Figure 6] 1A and 1B are composition distribution images of each element (Ni, Sn, Pt) in a cross section of a thermistor element at a bonding temperature of 280°C (a) and at a bonding temperature of 380°C (b) in an embodiment of a thermistor element, a temperature sensor including the thermistor element, and a method for manufacturing a thermistor element according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] An embodiment of a thermistor element, a temperature sensor including the thermistor element, and a method for manufacturing thermistor elements according to the present invention will be described below with reference to Figures 1 to 5. Note that in the drawings used in the following description, the scale has been changed as necessary to make each component recognizable or easily recognizable.

[0020] As shown in FIG. 1, the thermistor element 1 of this embodiment includes a thermistor body 2 containing an oxide thermistor material having a perovskite crystal structure, and a pair of electrodes 3 on which the thermistor body 2 is formed. The thermistor element 1 of this embodiment has electrodes 3 formed on both the top and bottom surfaces of the flake-shaped thermistor body 2, but FIG. 1 shows only the top surface. The electrode 3 includes a Pt electrode layer 3a formed on the surface of the thermistor body 2, and an intermetallic compound layer 3b containing Pt, Sn, and M formed on the outside of the Pt electrode layer 3a. The above M is at least one of Ag, Ni, Co and Mn, and the thickness of the intermetallic compound layer 3b is 50 nm or more.

[0021] In particular, it is preferable that the thickness of the intermetallic compound layer 3b is 190 nm or more, and the concentration of M in the intermetallic compound layer 3b is 3.0 to 7.6 wt %. At least one of the pair of electrodes 3 is joined with a solder material 4 containing Sn as a main component. The intermetallic compound layer 3b has a high-concentration M region 3c containing a larger amount of M on the solder material 4 side than on the Pt electrode layer 3a side. For example, when the M is Ni, the high-concentration M region 3c becomes a high-concentration Ni region.

[0022] The concentration of M in the intermetallic compound layer 3b (M / (Sn+Pt+M) wt%) is preferably 0.5 to 10 wt% for Ni, 3.0 to 15 wt% for Ag, 0.5 to 10 wt% for Co, and 0.5 to 10 wt% for Mn. The intermetallic compound layer 3b is preferably disposed continuously over the entire surface between the Pt electrode layer 3a and the solder material 4, but may be disposed discontinuously in a plurality of locations. The Pt electrode layer 3a is formed by printing and baking a Pt paste onto the thermistor body 2. The thickness of the Pt electrode layer 3a is, for example, 1 μm. In the present invention, even a thin Pt electrode layer 3a of less than 4 μm can effectively achieve an oxygen barrier effect. The thermistor material of the thermistor element 2 is, for example, 0.5(La 0.8 Ca 0.2 )(Cr 0.45 Mn 0.55 )O3+0.5Y2O3 etc.

[0023] As shown in FIG. 2, the temperature sensor 10A of this embodiment also includes a pair of lead wires 5, one end of which is connected to a pair of electrodes 3 by solder material 4, and a resin sealing portion 6 that seals the entire thermistor element 1, including the one end of the pair of lead wires 5, with resin. The resin sealing portion 6 is made of, for example, epoxy resin. That is, the temperature sensor 10A of this embodiment is a resin-sealed temperature sensor.

[0024] As another example, a temperature sensor 10B according to this embodiment includes a thermistor element 1 and a mounting substrate 8 on which the thermistor element 1 is mounted, as shown in FIG. The mounting substrate 8 has wiring 7 formed on the surface. The thermistor element 1 is bonded onto the wiring 7 with a solder material 4 . The mounting substrate 8 is an insulating substrate such as an FPC made of resin. The wiring 7 is a pattern wiring formed of copper foil or the like on the mounting substrate 8, and at least two wirings are provided in the form of mounting pads. In addition, only the bottom electrode 3 of the thermistor element 1 is joined to one of the wirings 7 of the mounting substrate 8 with solder material 4, and the top electrode 3 and the other wiring 7 are connected with an Au wire 9 by wire bonding.

[0025] As another example, a temperature sensor 10C of this embodiment includes a thermistor element 1C having a Pt electrode layer 3a formed on each end of a cubic thermistor body 2, and a mounting substrate 8 on which the thermistor element 1C is surface-mounted, as shown in FIG. That is, the thermistor element 1C is a chip thermistor. In this temperature sensor 10C, the lower portions of a pair of Pt electrode layers 3a are respectively joined to a pair of wirings 7 on a mounting substrate 8 with solder materials 4. Therefore, an intermetallic compound layer 3b is formed between the lower portions of the Pt electrode layers 3a and the solder materials 4.

[0026] The manufacturing method of the thermistor element 1 of this embodiment includes an electrode formation process in which a pair of electrodes 3 is formed on a thermistor body 2 containing an oxide thermistor material having a perovskite crystal structure, and a solder joining process in which a solder material 4 containing Sn as a main component is joined to at least one of the pair of electrodes 3. The electrode formation process includes a Pt electrode layer process of forming a Pt electrode layer 3a on the surface of the thermistor body 2, as shown in FIG. 5(a), and an intermetallic compound layer formation process of forming an intermetallic compound layer 3b containing Pt, Sn, and the above-mentioned M on the outside of the Pt electrode layer 3a, as shown in FIG. 5(d). The M is at least one of Ag, Ni, Co and Mn, and the thickness of the intermetallic compound layer 3b is set to 50 nm or more.

[0027] In the soldering step, when the molten solder material 4 containing the M is attached to the Pt electrode layer 3a and then solidified, the intermetallic compound layer forming step may be performed to form an intermetallic compound layer 3b containing the M and Sn in the solder material 4 and the Pt in the Pt electrode layer 3a between the solder material 4 and the Pt electrode layer 3a. In the soldering step, the solder material 4 is preferably bonded at a bonding temperature of 280° C. or higher.

[0028] The intermetallic compound layer forming process may include an M sputtering process in which the above-mentioned M is deposited on the surface of the Pt electrode layer 3a by sputtering to form an M layer 3d, as shown in FIG. 5(b), and an M solid solution process in which, when the solder material 4 melted in the solder joining process is deposited on the M layer 3d and then solidified, an intermetallic compound layer 3b containing the above-mentioned M in the M layer 3d, the Pt in the Pt electrode layer 3a, and the Sn in the solder material 4 is formed between the solder material 4 and the Pt electrode layer 3a, as shown in FIG. 5(d). For example, when Ni is used as the M, Ni is attached to the Pt electrode layer 3a by sputtering to form an M layer 3d of Ni, and when a solder material 4 that has been heated and melted is attached to this M layer 3d and solidified, an intermetallic compound layer 3b containing Ni in the M layer 3d, Pt in the Pt electrode layer 3a, and Sn in the solder material 4 is formed between the solder material 4 and the Pt electrode layer 3a.

[0029] As described above, in the thermistor element 1 of this embodiment, the M is at least one of Ag, Ni, Co, and Mn, and the thickness of the intermetallic compound layer 3b is 50 nm or more. Therefore, the thick intermetallic compound layer 3b, which is made of a conductive material with high heat resistance and low oxygen permeability, functions as an oxygen barrier layer, and therefore, even if the Pt electrode layer 3a is thin, it is possible to suppress the formation of oxygen defects in the thermistor body 2 due to oxidation of Sn, which is the main component of the solder. Furthermore, when the thickness of the intermetallic compound layer 3b is 190 nm or more and the concentration of M in the intermetallic compound layer 3b is 3.0 to 7.6 wt%, it becomes possible to suppress the rate of change in resistance value in a heat resistance test to 1.6% or less.

[0030] Furthermore, since the solder material 4, which is primarily composed of Sn, is joined to at least one of the pair of electrodes 3, even if the Sn in the solder material 4 oxidizes when soldered at high temperatures or when used in a high-temperature environment, the formation of oxygen defects in the thermistor body 2 can be suppressed, thereby reducing the rate of change in resistance value. Furthermore, the intermetallic compound layer 3b has a high-concentration M region 3c containing more M on the solder material 4 side than on the Pt electrode layer 3a side, and the region with a high M content provides a stronger oxygen barrier effect.

[0031] The temperature sensor 10A of this embodiment is provided with a resin sealing portion 6 that seals the entire thermistor element 1 with resin, including one end of a pair of lead wires 5, thereby providing a resin-sealed type temperature sensor with a low rate of change in resistance value during heat resistance testing. Furthermore, in the temperature sensors 10B and 10C of this embodiment, the thermistor element 1 is joined to the wiring 7 of the mounting substrate 8 with a solder material, so that even when the thermistor element 1 is mounted on the substrate, changes in resistance value can be suppressed in high-temperature environments or during heat resistance tests, etc.

[0032] In the manufacturing method of the thermistor element of this embodiment, when the molten solder material 4 containing the above M is attached to the Pt electrode layer 3a and then solidified in the soldering step, an intermetallic compound layer forming step is performed to form an intermetallic compound layer 3b containing the above M and Sn in the solder material 4 and Pt in the Pt electrode layer 3a between the solder material 4 and the Pt electrode layer 3a, so the intermetallic compound layer forming step can be performed during the soldering step.

[0033] Furthermore, by joining the solder material 4 at a joining temperature of 280°C or higher during the solder joining process, it is possible to suppress the rate of change in resistance value during the heat resistance test to 1.6% or less, and by joining the solder material 4 at a joining temperature of 320°C or higher, it is possible to suppress the rate of change in resistance value during the heat resistance test to 0.8% or less. In particular, when the solder material 4 is bonded at a bonding temperature of 380°C or higher, an intermetallic compound layer 3b containing more of the above M on the solder material 4 side than on the Pt electrode layer 3a side is obtained, which further enhances the oxygen barrier effect and reduces the rate of change in resistance value.

[0034] Furthermore, the intermetallic compound layer forming process includes an M sputtering process in which the M is deposited on the surface of the Pt electrode layer 3a by sputtering to form an M layer 3d, and an M solid solution process in which, when the solder material 4 melted in the solder joining process is deposited on the M layer 3d and then solidified, an intermetallic compound layer 3b containing the M in the M layer 3d, the Pt in the Pt electrode layer 3a, and the Sn in the solder material 4 is formed between the solder material 4 and the Pt electrode layer 3a.This makes it possible to easily obtain an intermetallic compound layer 3b containing a sufficient amount of M by dissolving the M in the M layer 3d formed by sputtering, even if the solder material 4 does not contain M. [Example]

[0035] Example 1 First, a Pt paste was printed on a 0.35 mm thick thermistor wafer, which served as the thermistor element, and then baked to form a Pt electrode layer.Then, the wafer was cut into 0.5 mm square pieces to produce flake-shaped thermistor chips. A 20 nm thick M layer was formed on the surface of the Pt electrode layer of this flake thermistor chip by Ni sputtering, and then lead wires were joined with solder in a solder bath at 230°C. The solder material used was PF04 (Sn / Cu0.7) manufactured by Nihon Handa. Thereafter, the substrate was dipped in Epiform (registered trademark: manufactured by Somar Co., Ltd.) and cured at 120°C for 60 minutes, thereby forming an intermetallic compound layer composed of Sn, Pt, and Ni (M above) between the Pt electrode layer and the solder material, and a thermistor element and temperature sensor with lead wires connected was produced as Example 1 of the present invention.

[0036] <Example 2> Flake-shaped thermistor chips were prepared in the same manner as in Example 1, and then soldered at 280°C using a solder material containing Ni (SN100C: manufactured by Nippon Superior, Sn / 0.7Cu / 0.05Ni / Ge) to form an intermetallic compound layer composed of Sn, Pt, and Ni (M above) at the interface between the Pt electrode layer and the solder material.Otherwise, the chip was prepared in the same manner as in Example 1.This was designated Example 2 of the present invention.

[0037] Example 3 Example 3 of the present invention was prepared in the same manner as in Example 1, except that the soldering temperature in Example 2 was changed to 380° C., thereby varying the Ni content in the intermetallic compound layer. Example 4 Example 4 of the present invention was prepared in the same manner as Example 1 except that M731 (manufactured by Senju Metal Co., Ltd., Sn / 3.9Ag / 0.6Cu / 3.0Sb) was used as the solder material and soldering was performed at 380°C to form an intermetallic compound layer composed of Sn, Pt, and Ag (M above).

[0038] <Example 5> Example 5 of the present invention was prepared in the same manner as Example 1, except that an intermetallic compound layer consisting of Sn, Pt, and Co (M) was formed by soldering Sn992 (manufactured by Tomoe Engineering, 99.2Sn / 0.5Cu+Bi+Co) at 400°C using the solder material. Example 6 Example 6 of the present invention was fabricated in the same manner as in Example 1, except that the soldering temperature was changed to 400°C.

[0039] Example 7 Example 7 of the present invention was prepared in the same manner as Example 1, except that an intermetallic compound layer consisting of Sn, Pt, Ag (M mentioned above) and Mn (M mentioned above) was formed by soldering at 400°C using SACm (manufactured by Tomoe Engineering Co., Ltd.) as the solder material. Example 8 Example 8 of the present invention was prepared in the same manner as in Example 1, except that the soldering temperature in Example 2 was changed to 320° C. to vary the Ni content in the intermetallic compound layer. Example 9 Example 9 of the present invention was prepared in the same manner as Example 1, except that the soldering temperature in Example 2 was changed to 350° C. to vary the Ni proportion in the intermetallic compound layer.

[0040] <Comparative Example 1> Comparative Example 1 of the present invention was prepared in the same manner as in Example 1, except that the step of forming the M layer (Ni) by sputtering in Example 1 was omitted, and the intermetallic compound layer containing M was not formed. <Comparative Example 2> Comparative Example 2 of the present invention was prepared in the same manner as in Example 1, except that the M layer in Example 1 was changed to a thickness of 2 nm and the intermetallic compound layer was changed to a thickness of 4 nm.

[0041] Table 1 shows the M solid solution rate (M / (Sn+Pt+M) wt%) and thickness of the intermetallic compound layer composed of Sn, Pt, and the above M for these examples and comparative examples of the present invention. Furthermore, for these examples and comparative examples of the present invention, the initial resistance value at 25°C was measured, and then a heat resistance test was carried out at 150°C for 1000 hours, and the resistance value at that time was measured. The rate of change in resistance value between the initial state and after the heat resistance test was taken as ΔR and is shown in Table 1.

[0042] [Table 1]

[0043] As can be seen from these results, in Comparative Example 1, the intermetallic compound layer containing M was not formed, and therefore there was no oxygen barrier effect, and the rate of change in resistance value after the heat resistance test was large at 6.6%, whereas in each of the Examples of the present invention in which the intermetallic compound layer containing M was formed, the rate of change in resistance value after the heat resistance test was small at 1.6% or less. In Comparative Example 2, although an intermetallic compound layer was formed, its thickness was as thin as 40 nm, so that a sufficient oxygen barrier effect was not obtained, and the rate of change in resistance value was large at 5.7%. In each of the Examples of the present invention, however, the thickness of the intermetallic compound layer was as thick as 190 nm or more, so that, as described above, the rate of change in resistance value was significantly reduced to 1.6% or less. In particular, when the solder material is bonded at a bonding temperature of 320°C or higher, the intermetallic compound layer becomes even thicker, and the rate of change in resistance is suppressed to 0.8% or less.

[0044] Next, for Example 2 where the soldering temperature was 280° C. and Example 3 where the soldering temperature was 380° C., composition distribution images of each element (Ni, Sn, Pt) in the cross section of the thermistor element are shown in FIG. In Example 2, where the soldering temperature was 280°C, as shown in Figure 6(a), it can be seen that an intermetallic compound layer consisting of Sn, Pt, and Ni was formed between the Sn of the solder material and the Pt of the Pt electrode layer. In Example 3, where the soldering temperature was 380°C, an intermetallic compound layer consisting of Sn, Pt, and Ni was formed between the Sn of the solder material and the Pt of the Pt electrode layer, as shown in Figure 6(b), and a region where Ni, the M, was concentrated (high-concentration M region) was formed on the solder material side of the intermetallic compound layer. As such, as the intermetallic compound layer became thicker, the region where M (Ni) was concentrated was formed, and as shown in Table 1, it was found that the rate of change in resistance value was quite small at 0.4%. In Figure 6, it appears that Ni is distributed within the Pt electrode layer, but this is merely the tail of the detected Pt spectrum and is not actually a reaction of Ni.

[0045] The technical scope of the present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the spirit of the present invention. [Explanation of symbols]

[0046] 1, 1C... thermistor element, 2... thermistor element, 3... electrode, 3a... Pt electrode layer, 3b... intermetallic compound layer, 3d... M layer, 4... solder material, 5... lead wire, 6... resin sealing portion, 7... wiring, 8... mounting board drawing number change, 10A, 10B, 10C... temperature sensor

Claims

1. a thermistor element including an oxide thermistor material having a perovskite crystal structure; a pair of electrodes on which the thermistor element is formed, The electrode comprises a Pt electrode layer formed on the surface of the thermistor body; an intermetallic compound layer containing Pt, Sn, and M formed on the outer side of the Pt electrode layer, M is at least one of Ag, Ni, Co, and Mn, A thermistor element characterized in that the thickness of the intermetallic compound layer is 50 nm or more.

2. 2. The thermistor element according to claim 1, the thickness of the intermetallic compound layer is 190 nm or more, A thermistor element characterized in that the concentration of M in the intermetallic compound layer is 3.0 to 7.6 wt %.

3. 3. The thermistor element according to claim 1, A thermistor element characterized in that a solder material containing Sn as a main component is joined to at least one of the pair of electrodes.

4. 4. The thermistor element according to claim 3, A thermistor element characterized in that the intermetallic compound layer has a high-concentration M region containing a larger amount of M on the solder material side than on the Pt electrode layer side.

5. The thermistor element according to claim 3; a pair of lead wires, one ends of which are connected to the pair of electrodes by the solder material; A temperature sensor comprising a resin sealing portion that seals the entire thermistor element with resin, including one end of the pair of lead wires.

6. The thermistor element according to claim 3; a mounting substrate on which the thermistor element is mounted, the mounting substrate has wiring formed on its surface, A temperature sensor characterized in that the thermistor element is joined onto the wiring with the solder material.

7. an electrode forming step of forming a pair of electrodes on a thermistor element including an oxide thermistor material having a perovskite crystal structure; a soldering step of joining a solder material containing Sn as a main component to at least one of the pair of electrodes, the electrode forming step includes a Pt electrode layer step of forming a Pt electrode layer on the surface of the thermistor body; and forming an intermetallic compound layer on the outer side of the Pt electrode layer, the intermetallic compound layer including Pt, Sn, and M; M is at least one of Ag, Ni, Co, and Mn, A method for manufacturing a thermistor element, characterized in that the thickness of the intermetallic compound layer is 50 nm or more.

8. 8. The method for manufacturing a thermistor element according to claim 7, a step of forming an intermetallic compound layer between the solder material and the Pt electrode layer, the step of forming an intermetallic compound layer containing M and Sn in the solder material and Pt in the Pt electrode layer, when the molten solder material containing M is attached to the Pt electrode layer and then solidified in the solder joining step;

9. 9. The method for manufacturing a thermistor element according to claim 8, A method for manufacturing a thermistor element, wherein the soldering step is performed by bonding the solder material at a bonding temperature of 280° C. or higher.

10. 8. The method for manufacturing a thermistor element according to claim 7, the intermetallic compound layer forming step is an M sputtering step of depositing the M on the surface of the Pt electrode layer by a sputtering method to form an M layer; a M solid solution step of forming an intermetallic compound layer containing the M in the M layer, the Pt in the Pt electrode layer, and the Sn in the solder material between the solder material and the Pt electrode layer when the solder material melted in the solder joining step is attached to the M layer and then solidified.

Images