JPH04267301A - Manufacture of ntc thermistor - Google Patents

Abstract

PURPOSE:To decrease the dispersion of initial electric property and the rate of change of resistance by providing an electrode for a thermistor electrode by the method excepting backing, and heat-treating the said substrate in reductive atmosphere or in neutral atmosphere after formation of said electrode. CONSTITUTION:The materials such as Mn, Ni, Co, Cu, etc., are weighed and combined and mixed wetly by a pot mill. Next, the mixed material is dehydrated and dried, and then it is calcined at 800 deg.C to 1000 deg.C, and further it is smashed wetly by a ball mill so as to adjust the material powder. Subsequently, the material is dehydrated and dried again, and then it is pressed and molded in disk shape by adding polyvinyl alcohol. Next, the disclike molded item 11' is heated at approximately 600 deg.C to remove the said polyvinyl alcohol, and then regular baking is performed at 1000 deg.C to 1400 deg.C. Next, Ag film layers 12' and 13' are made at the obverse and the reverse of the disclike molded item 11' each by deposition method. Subsequently, the disclike molded item 11' is heat-treated at 500 deg.C or more in reductive atmosphere.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an NTC thermistor used in temperature sensors and the like.

0002

2. Description of the Related Art A thermistor has the characteristic that its electrical resistance changes significantly when the temperature changes. Therefore, it is used in a wide range of fields as a temperature sensor. This thermistor has a so-called negative temperature coefficient (NTC) whose electrical resistance decreases as its temperature rises.
tive Temperature Coeffi
2. Description of the Related Art A thermistor (hereinafter simply referred to as a thermistor) is known.

FIG. 7 shows the conventional structure of such a thermistor, in which 1 is a transition metal oxide such as Mn, Ni,
A thermistor substrate mainly composed of Co, Cu, etc., 2 and 3 are thick film electrodes provided by baking on the front and back surfaces of this substrate 1, respectively, and 4 and 5 are lead members connected to each electrode 2 and 3. .

The thick film electrodes 2 and 3 are formed by coating the front and back surfaces of the substrate 1 with a heat-resistant conductive paint containing components such as glass frit, for example, a material containing Ag, Pd, Pt, Au, etc., and then exposing it to the atmosphere. It is formed by performing a baking process inside. Moreover, the thick film electrode 2 formed in this way,
Each lead member 4, 5 is also connected to the lead member 3 via a heat-resistant conductive paint. Subsequently, each of these members except the ends of the lead members 4 and 5 are molded with glass or the like to complete the thermistor.

[0005]

However, conventional thermistors equipped with thick film electrodes have the problem of large variations in initial electrical characteristics and a large rate of change in resistance when used at high temperatures.

That is, when baking the heat-resistant conductive paint containing glass frit in the atmosphere to form the thick film electrodes 2 and 3, as shown in FIG. Since a cavity 6 is created between each electrode 2
, 3 and the substrate 1, ohmic characteristics due to good ohmic contact cannot be ensured, resulting in large variations in initial electrical characteristics. In addition, in the manufacturing process of the thermistor, no particular heat treatment is performed after forming the thick film electrodes 2 and 3, so when used at high temperatures exceeding approximately 120°C, the resistance may be affected by the oxygen present on the surface of the substrate 1. The rate of change increases. In particular, in a thermistor containing CuO as the material of the substrate 1, the rate of change in resistance increases significantly at high temperatures exceeding about 80° C., making it impossible to use.

The present invention was made in response to the above-mentioned problems, and it is an object of the present invention to provide a method for manufacturing an NTC thermistor that suppresses variations in initial electrical characteristics and the rate of change in resistance during high-temperature use. That is.

[Configuration of the invention]

[0009]

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a step of preparing an NTC thermistor substrate containing a transition metal oxide as a main component, and a method other than baking at two different locations on this substrate. The present invention is characterized by a method for manufacturing an NTC thermistor, which includes a step of forming electrodes, and a step of heat-treating a substrate on which these electrodes are formed in a reducing atmosphere or a neutral atmosphere.

0010

According to the present invention, since the thermistor substrate is provided with an electrode formed by a method other than baking, for example, an electrode made of a thin film layer formed by vapor deposition, the ohmic contact between each electrode and the substrate is improved. Variations in initial electrical characteristics can be suppressed to a small level.

Further, according to the present invention, since the substrate is heat-treated in a reducing atmosphere or a neutral atmosphere after electrode formation, it is not affected by oxygen on the surface of the substrate. The resistance change rate can be kept low.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the method for manufacturing an NTC thermistor according to the present invention, and the steps will be explained below in order.

First, as shown in A, materials such as Mn, Ni, Co, and Cu, which are the main components of the transition metal oxide, are weighed and blended to a predetermined composition ratio, and then wet mixed using a pot mill.

Next, as in step B, the mixed material is dehydrated and dried, then pre-calcined at 800° C. to 1000° C., and further wet-pulverized using a ball mill to prepare material powder.

Next, as shown in C, after the material is dehydrated and dried again, PVA (polyvinyl alcohol) is added as a binder and pressure molded into a disk shape.

Next, as shown in D, after heating the disc-shaped molded body 11' at about 600°C to remove the PVA,
Main firing is performed at 00°C to 1400°C. (FIG. 3) Next, as shown in E, Ag thin film layers 12' and 13' are formed on the front and back surfaces of this disc-shaped molded body 11' by vapor deposition, respectively. A
g The portion of the thin film layer attached to the outer peripheral surface of the disc-shaped molded body is removed by polishing. (Fig. 4) Next, as shown in F, the disc-shaped molded body is heated to 500°C in a reducing atmosphere, for example, N2 atmosphere.
Heat treatment is performed above.

Next, as shown in G, the disc-shaped molded body is diced into sizes that will become individual thermistors. As a result, it is divided into a large number of thermistor substrates 11, and electrodes 12 and 13 made of the Ag thin film layer are provided on the front and back surfaces of each substrate 11. (FIG. 5) Next, as shown in H, each electrode 12, 1
3, lead members 14 and 15 are connected to the lead members 14 and 15 by soldering.

Finally, as shown in I, each thermistor substrate 11 is molded (sealed) with glass except for the ends of the leads 14 and 15, thereby completing the thermistor shown in FIG. In FIG. 2, 11 is a thermistor substrate whose main component is a transition metal oxide such as Mn, Ni, Co, Cu, etc.; 12 and 13 are electrodes made of Ag thin film layers provided on the front and back surfaces of this substrate 11, respectively; , 15 is each electrode 1
This is a lead member connected to 2 and 13. Each of these members, except for the ends of the lead members 14 and 15, is molded with glass or the like.

FIG. 6 shows a partially enlarged view of the thermistor shown in FIG. 2 obtained by this example, and no cavity is formed between each electrode 12 or 13 and the substrate 11. Therefore, the contact between the two is perfect, and each electrode 12 and 13 can ensure good ohmic contact with the substrate 11.

In this embodiment, the components of the thermistor substrate 11 are Mn:Ni:Co in an amount of 66 mol % and 16.5 m, respectively.
Table 1 shows the characteristics of a thermistor manufactured using a thermistor containing 17.5 mol% of mol% in comparison with a conventional example.

[0022]

[Table 1] In Table 1, C. V. indicates the magnitude of variation in resistivity at 25°C, and this C. V is C. V={(standard deviation)/(average value)}×100(%). B indicates the so-called B constant. As is clear from Table 1, conventional R25 C. V. Although it was difficult to suppress the amount to 1% or less, according to this example, it was possible to suppress it to 0.4%. Also, C. of B25/85. V. was also able to reduce the value to half of the conventional value. Thereby, variations in initial electrical characteristics can be suppressed to a small level.

Furthermore, according to the manufacturing method of this embodiment, by performing heat treatment in a reducing atmosphere after electrode formation, it is possible to prevent the influence of oxygen on the surface of the substrate, so that the rate of change in resistance under high temperature use can be reduced. can be kept to a minimum.

Next, Table 2 shows the results obtained when thermistors were manufactured by variously changing the composition of the thermistor substrate 11 and the heat treatment conditions in comparison with the conventional example.

[0025]

[Table 2] In Table 2, the resistance change rate is the resistance value at 25°C,
It shows the rate of change obtained by comparing the resistance value after subjecting the same sample to a heat resistance test at 125° C. for 2000 hours. It means that the smaller this value is, the better it is. As is clear from Table 2, the heat treatment was carried out in a reducing atmosphere (N
According to the manufacturing method of this example, which was carried out in a 2 atmosphere) and at a temperature of approximately 500°C or higher, the rate of change in resistance was suppressed to approximately 1% or less, as indicated by the circle in the judgment column. This shows that excellent effects can be obtained. This allows the resistance change rate to be kept low.

In Table 2, out of 16 samples, only 9 samples obtained in this example showed excellent results. In addition, each electrode 1 provided on the substrate 11
2 and 13 show cases in which the nickel thin film layer was formed by electroless plating.

Each of the electrodes 12 and 13 thus formed on the substrate 11 may be formed as a thin film layer without containing glass frit in the material like a conventional thick film electrode, as long as it is provided as a thin film layer. The formation is not limited to the vapor deposition method shown in , but may be formed by a plating method, a sputtering method, or the like. In short, in the present invention, unlike conventional thick film electrodes, the conductive material does not contain glass frit, and as long as it is provided as a thin film layer that can make good contact with the substrate 11 and ensure ohmic contact, specific means can be used. is not limited.

Furthermore, according to the present invention, the heat treatment atmosphere is not limited to the above-mentioned reducing atmosphere, but even if a neutral atmosphere such as H2 or Ar is selected, the same results as described above can be obtained. Moreover, the electrode material is not limited to Ag or Ni, and Cu, Au, Pd, etc. can be used.

[0029]

[Effects of the Invention] As explained above, according to the present invention, since the electrodes are provided by a method other than baking,
Variations in the initial electrical characteristics can be suppressed to a small level, and since the heat treatment is performed in a reducing atmosphere or a neutral atmosphere after electrode formation, the rate of change in resistance during high-temperature use can be suppressed to a small level.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing an example of a method for manufacturing an NTC thermistor according to the present invention.

FIG. 2 is a sectional view showing an NTC thermistor obtained by the manufacturing method of the present invention.

FIG. 3 is a cross-sectional view showing constituent members in an intermediate step of the manufacturing method of the present invention.

FIG. 4 is a cross-sectional view showing constituent members in an intermediate step of the manufacturing method of the present invention.

FIG. 5 is a cross-sectional view showing constituent members in an intermediate step of the manufacturing method of the present invention.

FIG. 6 is a partially enlarged view showing an NTC thermistor obtained by the manufacturing method of the present invention.

FIG. 7 is a sectional view showing a conventional NTC thermistor.

FIG. 8 is a partially enlarged view showing a conventional NTC thermistor.

[Explanation of symbols]

11 NTC thermistor board 12, 13 Electrode 14, 15 Lead member

Claims (3)

[Claims] [Claim 1] NTC whose main component is a transition metal oxide
The method includes a step of preparing a thermistor substrate, a step of forming electrodes at two different locations on this substrate by a method other than baking, and a step of heat-treating the substrate on which these electrodes are formed in a reducing atmosphere or a neutral atmosphere. NTC characterized by
A method of manufacturing a thermistor. 2. The method for manufacturing an NTC thermistor according to claim 1, wherein the heat treatment step is performed at a temperature of 500° C. or higher. 3. The NTC according to claim 1 or 2, wherein the method other than baking is a plating method or a vapor deposition method.
A method of manufacturing a thermistor.