JP2014154830A - Thermistor element and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermistor element capable of preventing dispersion of a metal element from a lead wire while maintaining electrical junction and mechanical junction by ensuring direct junction between a conductive adhesive for fixture and an electrode, and a manufacturing method thereof.SOLUTION: The thermistor element comprises: a chip-like or plate-like thermistor element assembly 2; a pair of first electrode films 3 formed on front and rear faces of the thermistor element assembly; a pair of inorganic insulating layers 4 formed on surfaces of the pair of first electrode films while excluding a region on a ridge line of the thermistor element assembly; a pair of second electrode films 5 formed from surfaces of the pair of inorganic insulating layers to the first electrode films exposed in the region on the ridge line of the thermistor element assembly; a pair of lead wires 6 installed in centers on surfaces of the pair of second electrode films; and a conductive adhesive 7 for fixture for fixing the lead wires and the second electrode films.

Description

  The present invention relates to a thermistor element suitable for temperature measurement for high temperature applications and a method for manufacturing the thermistor element.

  In recent years, there is an increasing demand for thermistor elements that can be measured in a wide temperature range from low temperature to high temperature. As a general form of a thermistor element that can be used at such a high temperature, as described in Patent Document 1, a terminal electrode is formed on a thermistor chip and leads to both terminal electrodes via a conductive electrode for fixing. A thermistor element is used in which wires are joined and a thermistor chip is molded with an insulating coating material such as glass.

At present, most lead wires use wires mainly composed of noble metals such as Pt for high temperatures of 500 ° C. or higher, but the proportion of the lead wires occupies the majority of the price of the entire device. For this reason, when the heat-resistant temperature is 500 ° C. or lower, there are increasing cases of considering the use of wires other than noble metals. In such a temperature range, soft glass having a relatively large thermal expansion coefficient is used as the sealing glass in most cases. From the viewpoint of the thermal expansion coefficient and wettability with glass, wires such as dumet wires and Fe / Cr wires are used. However, its use is mainly considered.
For example, as shown in FIGS. 6 and 7, the lead wire 6 of the dumet wire having the cuprous oxide film 6 a formed on the surface thereof is electrically conductive for fixing to the surface electrode 103 formed on the front and back surfaces of the thermistor body 2. A material that is bonded with an adhesive 7 and whose periphery is covered with a molding material 8 that is sealing glass has been studied.

However, when such a wire containing a metal as a main component is used, as shown in FIG. 8, when the process temperature and the use temperature are high, the constituent elements of the lead wire 6 (metal elements such as Fe, Ni, Cu, etc.) ) Diffuses into the fixing conductive adhesive 7, reaches the surface electrode 103 of the thermistor body 2, and further enters the thermistor body 2, depending on the component, the thermistor characteristics may be changed or deteriorated.
In Patent Document 2, the thick film electrode on the thermistor body is used to prevent the metal component in the heat-resistant conductive electrode for fixing from diffusing into the thick film electrode during heating of the glass seal and causing the resistance value to vary. A method of applying another block electrode on top has been proposed.

JP 61-105803 A JP-A-61-105804

The following problems remain in the conventional technology.
As described above, the thermistor characteristics are changed by the metal element (such as Cu) diffused from the lead wire to the thermistor body, so that it is necessary to prevent the diffusion of these metal elements. For example, as in the technique of Patent Document 2, it is conceivable to provide an intermediate layer that suppresses the diffusion of the metal element on the surface electrode. In this case, the intermediate layer is provided between the conductive adhesive for fixing and the intermediate layer. There is a possibility that the electrical junction stability and the mechanical junction stability may be lowered due to the newly formed heterogeneous junction interface between all the surfaces of the thermistor body between the electrode and the thermistor surface electrode.

  The present invention has been made in view of the above-described problems, and ensures the direct bonding between the fixing conductive adhesive and the electrode, thereby maintaining the electrical bonding and the mechanical bonding, and the metal from the lead wire. It is an object of the present invention to provide a thermistor element capable of suppressing element diffusion and a method for manufacturing the thermistor element.

The present inventors have conducted research on the diffusion of the metal element from the lead wire, and found that the diffusion of the metal element is significant only in the region immediately below the contact portion between the electrode portion of the thermistor element and the lead wire. I found it.
Therefore, the present invention has been obtained from the above findings, and the following configuration has been adopted in order to solve the above problems. That is, the thermistor element according to the first invention includes a chip-like or plate-like thermistor body, a pair of first electrode films formed on the front and back surfaces of the thermistor body, and a pair of the first electrodes. A pair of inorganic insulating layers formed on the surface of the film excluding the region on the ridge line portion of the thermistor body, and the surface exposed from the surface of the pair of the inorganic insulating layer to the region on the ridge line portion of the thermistor body A pair of second electrode films formed up to the first electrode film, a pair of lead wires installed at the center of the surface of the pair of second electrode films, the lead wire and the second electrode film It has a conductive adhesive for fixing which fixes an electrode film.

Since this thermistor element includes the second electrode film formed from the surface of the inorganic insulating layer to the first electrode film exposed in the region on the ridge line portion of the thermistor body, the lead wire and the first electrode film are provided. The thermistor element is electrically connected to the electrode film through the second electrode film formed in the region on the ridge line portion, and the inorganic insulating layer suppresses the diffusion of the metal element directly below the lead wire. Intrusion into the body can be prevented. In addition, since the junction between the first electrode film and the second electrode film is provided at the farthest position on the installation surface from the lead wire, the diffusion path of the metal element is the longest, and the diffusion by this path is also Can be suppressed. Furthermore, the surface of the second electrode film and the lead wire can be directly and firmly bonded to each other by the fixing conductive adhesive.
In addition, since it is thought that the amount of diffusion decreases as the thickness of the inorganic insulating layer increases, increasing the thickness of the inorganic insulating layer is equivalent to reducing the diffusion characteristics as a result. Is more desirable.

In the thermistor element according to the second invention, in the first invention, the lead wire is made of a material containing Fe, Ni, Cu, and the second electrode film is made of a material containing Ag as a main component. It is characterized by.
Ag is difficult to form a solid solution with the target metal, and it is known that there is almost no solid solution especially at 500 ° C. with respect to Fe and Ni, and the amount of solid solution is less than 5% even with respect to Cu. The diffusion characteristics can be suppressed by using Ag as a main component. On the other hand, by adding Pd or the like to Ag as a further suppression measure, it is possible to alloy and raise the melting point, and to decrease the diffusion rate. That is, in this thermistor element, since the second electrode film is made of a substance containing Ag as a main component, diffusion can be suppressed particularly effectively with respect to Fe, Ni, and Cu contained in the lead wire.

A thermistor element according to a third invention is characterized in that, in the first or second invention, the thermistor element is a metal oxide sintered body containing a perovskite oxide.
That is, in this thermistor element, since the thermistor body is a metal oxide sintered body containing a perovskite type oxide, the influence of metal element diffusion in the perovskite type oxide thermistor body excellent in high temperature stability. Can be suppressed, and the thermistor characteristics can be stably obtained.

A method for manufacturing a thermistor element according to a fourth invention is a method for manufacturing the thermistor element according to any one of the first to third inventions, wherein a pair of first thermistor elements on the front and back surfaces of a chip-like or plate-like thermistor element A step of forming one electrode film, a step of forming a pair of inorganic insulating layers on the surfaces of the pair of first electrode films excluding a region on a ridge line portion of the thermistor body, and a pair of the inorganic insulating layers Forming a pair of second electrode films from the surface of the layer to the first electrode film exposed in the region on the ridge line portion of the thermistor body, and the center of the surface of the pair of second electrode films A step of installing a pair of lead wires in the section and fixing the lead wires and the second electrode film with a conductive adhesive for fixing, and before forming the second electrode film, the thermistor The element body is barrel polished to form a region on the ridge line of the thermistor element body. And removing said inorganic insulating layer which is.
That is, in this method of manufacturing the thermistor element, before forming the second electrode film, the thermistor body is barrel-polished to remove the inorganic insulating layer formed in the region on the ridge line portion of the thermistor body. Only the inorganic insulating layer formed in the region on the ridge line portion of the thermistor body by barrel polishing can be efficiently removed, and high mass productivity can be obtained.

The present invention has the following effects.
That is, the thermistor element according to the present invention includes the second electrode film formed from the surface of the inorganic insulating layer to the first electrode film exposed in the region on the ridge line portion of the thermistor body. In addition, the electrical connection is made through the second electrode film formed up to the region on the ridge line portion, the lead wire is firmly joined, and the inorganic insulating layer further diffuses the metal element directly below the lead wire. Suppressing and entering the thermistor body can be prevented.
Therefore, the thermistor element of the present invention can obtain stable thermistor characteristics with little change in resistance over time due to process conditions and use at high temperatures, for example, high temperature measurement for detecting catalyst temperature and exhaust system temperature around an automobile engine. It is suitable as an industrial sensor.
Further, according to the method for manufacturing a thermistor element according to the present invention, it is possible to efficiently remove only the inorganic insulating layer formed in the region on the ridge line portion of the thermistor body by barrel polishing, thereby obtaining high mass productivity. be able to.

It is sectional drawing (a) along the lead wire which shows one Embodiment of the thermistor element which concerns on this invention, and sectional drawing (b) orthogonal to the lead wire. In this embodiment, it is a perspective view which shows the manufacturing method of the thermistor element in order of a process to a dicing process. In this embodiment, it is sectional drawing which shows the manufacturing method of the thermistor element in order of process from formation of an inorganic insulating layer to formation of a 2nd electrode film. In this embodiment, it is sectional drawing orthogonal to the lead wire in one surface which shows the thermistor element before glass sealing. It is a graph which shows the resistance value change rate by a heat test in the conventional example and Example of the thermistor element which concerns on this invention. It is a perspective view which shows the prior art example of the thermistor element which concerns on this invention. In the conventional example of the thermistor element concerning this invention, it is sectional drawing orthogonal to the lead wire. It is explanatory drawing which shows spreading | diffusion of Cu etc. in the prior art example of the thermistor element which concerns on this invention.

  Hereinafter, an embodiment of a thermistor element and a manufacturing method thereof according to the present invention will be described with reference to FIGS. In each drawing used for the following description, the scale is appropriately changed in order to make each member recognizable or easily recognizable.

  As shown in FIGS. 1 and 2, the thermistor element 1 of the present embodiment includes a chip-like or plate-like thermistor element body 2 and a pair of first electrode films formed on the front and back surfaces of the thermistor element body 2. 3, a pair of inorganic insulating layers 4 formed on the surface of the pair of first electrode films 3 excluding the region on the ridge line portion of the thermistor body 2, and the thermistor body from the surface of the pair of inorganic insulating layers 4 A pair of second electrode films 5 formed up to the first electrode film 3 exposed in the region on the two ridge lines, and a pair of central electrodes on the surface of the pair of second electrode films 5 Mold of insulating material for sealing the entire thermistor body 2 including the lead wire 6, the fixing conductive adhesive 7 for fixing the lead wire 6 and the second electrode film 5, and the joint portion of the lead wire 6. Material 8 is provided.

The thermistor body 2 is a metal oxide sintered body containing a perovskite oxide, for example, a general formula: La _1-y Ca _y (Cr _1-x Mn _x ) O ₃ (0.0 ≦ x ≦ 1.0, 0.0 <y ≦ 0.7). For example, Y ₂ O ₃ , ZrO ₂ , MgO, Al ₂ O ₃ , or CeO ₂ may be added to the sintered body as an insulator material.
The thermistor body 2 is formed in a chip shape or flake shape, and the first electrode film 3, the inorganic insulating layer 4, and the second electrode film 5 are formed on the upper and lower surfaces thereof.

The first electrode film 3 is a metal film containing at least one of Pt, Au, and Ag, for example.
The lead wire 6 is a so-called dumet wire and contains a metal element such as Fe, Ni, Cu or the like as a constituent component, and a cuprous oxide film 6a is formed on the surface.
The inorganic insulating layer 4 is made of an inorganic insulating material (glass) for the purpose of blocking the diffusion of the metal component of the lead wire 6.
The second electrode film 5 is formed of a material that has a lower diffusion characteristic of the metal element contained in the lead wire 6 than the first electrode film 3. For example, the second electrode film 5 is formed of a metal film containing at least one of Ag and Pd.

The material constituting the second electrode film 5 is not limited to the metal as described above, but may be another conductive material, but the material has a lower diffusion characteristic than that of the first electrode film 3. Is preferred. In addition, as a material which comprises the 2nd electrode film 5, it is more preferable to consist of a substance which has Ag as a main component.
For example, an Au paste is used as the fixing conductive adhesive 7. Further, for example, a glass material is employed as the mold material 8.

  Next, an example of a method for manufacturing the thermistor element 1 of the present embodiment will be described with reference to FIGS.

First, predetermined amounts of powdered La ₂ O ₃ , MnCO ₃ , Cr ₂ O ₃ , and CaCO ₃ as starting materials are weighed and mixed, dried, and then calcined at 1300 ° C. for 10 hours. The raw material powder weighed here is wet-mixed by a ball mill. The calcined powder is pulverized for 24 hours by a ball mill. Furthermore, a binder such as PVA is added to the pulverized powder to obtain a granulated powder.

  Next, the granulated powder is formed into a round block having a diameter of 42 mm and a thickness of 10 mm by a press molding machine, and degreased at 500 ° C. The degreased block is fired at 1550 to 1650 ° C. for 5 to 15 hours to produce a sintered body block 11 as shown in FIG. Next, the sintered body block 11 is sliced and lapped to a thickness of about 0.3 mm to form a thermistor wafer 12 as shown in FIG.

  After that, the first electrode film 3 which is a Pt film is formed on both the surfaces of the thermistor wafer by 300 nm using a sputtering method, and the thermistor wafer 13 with the electrode film is obtained as shown in FIG.

Further, the thermistor wafer 13 is cut into a 0.3 to 0.4 mm square chip shape by a dicing machine, and as shown in FIG. 2D, the chip shape or flakes on which the first electrode film 3 is formed. A thermistor element body 2 is formed.
Next, an inorganic insulating layer 4 is formed by applying and baking glass on the first electrode film 3 formed on the upper and lower surfaces of the thermistor body 2. If this formation method (dipping method) is described in detail, a glass paste is thinly stretched on a flat plate to 20 to 100 μm (for example, about 30 μm), and the chip-like thermistor body 2 is immersed (dip) in the glass paste, A glass paste is applied to one surface of the upper and lower surfaces.

The glass material of the glass paste is preferably SiO ₂ / B ₂ O ₃ / ZnO / Al ₂ O ₃ / MgO / ZrO ₂ , for example, PLS-3170 (thermal expansion coefficient: 76 × 10 ⁷ / manufactured by Nippon Electric Glass). ° C) can be used.
Next, after drying the applied glass paste at 150 ° C. for 5 minutes, the opposite surface is similarly applied and dried, and baked in a belt furnace at 850 ° C. The inorganic insulating layer 4 is formed so as to partially cover the side surface of the thermistor body 2 and cover the region on the ridge line portion of the thermistor body 2. At this time, the inorganic insulating layer 4 may cover the entire side surface of the thermistor body 2. The film thickness of the inorganic insulating layer 4 after firing is desirably about 10 to 50 μm.

  Next, the thermistor body 2 on which the inorganic insulating layer 4 is formed is subjected to barrel polishing, and the ridgeline is removed by removing the inorganic insulating layer 4 covering the region on the ridgeline portion as shown in FIG. The first electrode film 3 is exposed. That is, the ridge line portion of the many chip-like thermistor bodies 2 put together with the abrasive in the barrel of the barrel polishing machine is polished in the rotating barrel, and the inorganic insulating layer 4 in the ridge line portion is partially cut.

  If the inorganic insulating layer 4 covering the region on the ridge line portion is thin and the first electrode film 3 is exposed at a part of the ridge line portion, the barrel polishing can be omitted. In order to expose the first electrode film 3, it is preferable to perform barrel polishing.

  Next, in the same manner as the above dipping method using Ag paste, as shown in FIG. 3C, a second electrode film that is an Ag electrode is formed on the inorganic insulating layers 4 on the upper and lower surfaces of the thermistor body 2. 5 is formed. In addition, the baking temperature of Ag paste is 800 degreeC. The film thickness of the second electrode film 5 is set to 5 to 10 μm. At this time, the second electrode film 5 is also formed on the first electrode film 3 exposed on the ridge line portion of the thermistor body 2, and the first electrode film 3 and the second electrode film 5 are connected to each other. It joins in the junction part 5a on a ridgeline part. In addition to the dipping method, the second electrode film 5 may be formed by a screen printing method, for example.

  Next, an Au paste serving as the fixing conductive adhesive 7 is applied to the tip of the lead wire 6 that is two 0.2 mm diameter dumet wires (Fe—Ni—Cu), and FIGS. As shown in FIG. 4, the upper and lower surfaces are brought into contact with the central portion of the second electrode film 5 and dried at 80 ° C. for temporary fixing. Thereafter, a thermistor element 1 shown in FIG. 1 is manufactured by covering the glass tube and performing heat treatment at 750 ° C. in a belt furnace and applying a glass mold as the molding material 8.

  Thus, in the thermistor element 1 of the present embodiment, the second electrode film 5 formed from the surface of the inorganic insulating layer 4 to the first electrode film 3 exposed in the region on the ridge line portion of the thermistor body 2 is formed. The electrical connection between the lead wire 6 and the first electrode film 3 is performed through the second electrode film 5 (joint part 5a) formed up to the region on the ridge line part, and the inorganic It is possible to prevent the insulating layer 4 from entering the thermistor element body 2 by suppressing the diffusion of the metal element directly from the lead wire 6. In addition, since the joint 5a between the first electrode film 3 and the second electrode film 5 is provided at the farthest position on the installation surface from the lead wire 6, the diffusion path of the metal element becomes the longest, and this Diffusion due to the route can also be suppressed. In particular, it is most effective when the joint portion 5a is provided at the corners of the four corners among the ridge line portions (edge portions) of the four sides. Further, the surface of the second electrode film 5 and the lead wire 6 can be directly and strongly bonded by the fixing conductive adhesive 7.

Further, since the second electrode film 5 is made of a substance containing Ag as a main component, diffusion can be suppressed particularly effectively with respect to Fe, Ni, and Cu contained in the lead wire 6.
Furthermore, since the thermistor body 2 is a metal oxide sintered body containing a perovskite oxide, the influence of metal element diffusion in the perovskite oxide-based thermistor body 2 excellent in high-temperature stability can be suppressed. The thermistor characteristics can be obtained stably.

  In the method for manufacturing the thermistor element 1, the inorganic insulating layer formed in the region on the ridge line portion of the thermistor element body 2 by barrel polishing the thermistor element body 2 before forming the second electrode film 5. Since 4 is removed, only the inorganic insulating layer 4 formed in the region on the ridge line portion of the thermistor body 2 by barrel polishing can be efficiently removed, and high mass productivity can be obtained.

About the thermistor element produced according to the said embodiment, it applied to the heat test of 300 degreeC, and evaluated the characteristic change rate (resistance value change rate) after progress for 1000 hours. The evaluation results are shown in FIG. For comparison, the conventional example shown in FIG. 7 was also evaluated in the same manner.
As a result, in the Example of this invention, it was confirmed that resistance value change rate is as favorable as 0.2% or less. On the other hand, in the conventional example evaluated as a comparison, the characteristic change rate by the heat resistance test was as large as about 1%. Therefore, in the structure of the present invention, it is understood that the diffusion of Cu is suppressed, the heat resistance reliability is improved, and the temperature sensor element that can measure with high accuracy with little characteristic deterioration even at high temperature is obtained.

  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.

  DESCRIPTION OF SYMBOLS 1 ... Thermistor element, 2 ... Thermistor body, 3 ... 1st electrode film, 4 ... Inorganic insulating layer, 5 ... 2nd electrode film, 6 ... Lead wire, 7 ... Conductive adhesive for fixation, 8 ... Mold Material

Claims (4)

A chip-like or plate-like thermistor body;
A pair of first electrode films formed on the front and back surfaces of the thermistor body;
A pair of inorganic insulating layers formed on the surfaces of the pair of first electrode films excluding the region on the ridge line portion of the thermistor body;
A pair of second electrode films formed from the surface of the pair of inorganic insulating layers to the first electrode film exposed in a region on the ridge line portion of the thermistor body;
A pair of lead wires installed at the center of the surface of the pair of second electrode films;
A thermistor element, comprising: a conductive adhesive for fixing the lead wire and the second electrode film. The thermistor element according to claim 1,
The lead wire is made of a material containing Fe, Ni, Cu,
The thermistor element, wherein the second electrode film is made of a substance containing Ag as a main component. The thermistor element according to claim 1 or 2,
The thermistor element is a metal oxide sintered body containing a perovskite oxide. A method for producing the thermistor element according to any one of claims 1 to 3,
Forming a pair of first electrode films on the front and back surfaces of a chip-like or plate-like thermistor body;
Forming a pair of inorganic insulating layers on the surface of the pair of first electrode films, excluding a region on the ridge line portion of the thermistor body;
Forming a pair of second electrode films from the surface of the pair of inorganic insulating layers to the first electrode film exposed in the region on the ridge line portion of the thermistor body;
A step of installing a pair of lead wires in the center of the surface of the pair of second electrode films and fixing the lead wires and the second electrode film with a conductive adhesive for fixing;
Before forming the second electrode film, the thermistor body is barrel-polished to remove the inorganic insulating layer formed in the region on the ridge line portion of the thermistor body. Production method.