JPH04369802A - Positive characteristic thermistor and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a highly reliable positive characteristic thermistor by a method wherein, in the positive characteristic thermistor which is used as the heat-generating body such as a hot-air heater and the like, the problem such as decrease in reliability and migration due to oxidation and corrosion' of an electrode is solved. CONSTITUTION:An aluminum electrode 12 is formed on both main flat surfaces of a positive characteristic thermistor element 11, and after the oxide film on the surface of the aluminum electrode 12 has been removed, a gold electrode 13 is formed, and a positive characteristic thermistor, having excellent reliability and heat-resisting property, can be obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive temperature coefficient thermistor used as a switching element or a heating element, and a method for manufacturing the same.

0002

2. Description of the Related Art In recent years, the use of positive temperature coefficient thermistors has expanded, and they are now being used as personal warm air heaters for home use. Furthermore, there has been a trend towards higher power and higher temperature than before.

A conventional positive temperature coefficient thermistor will be explained below. FIG. 2 shows the structure of a conventional positive temperature coefficient thermistor. In FIG. 2, 1 is a positive temperature coefficient thermistor element;
2 is an aluminum electrode, and positive temperature coefficient thermistor element 1
is applied to both opposing principal planes. Examples of methods for forming this electrode include a method of screen printing and baking aluminum, and a method of thermal spraying aluminum. Also,
The terminals were brought out using pressure welding. Furthermore, a structure in which a copper electrode is provided on an aluminum electrode is also known in order to lead out a terminal by soldering and improve characteristics.

FIG. 3 shows yet another conventional technique. In FIG. 3, 1 is a PTC thermistor element as in FIG. 2, 3 is a nickel electrode formed on both main planes of the PTC thermistor element 1 by electroless plating, and 4 is screen printed on the nickel electrode 3. This is a silver electrode formed by a baking method.

[0005]

[Problems to be Solved by the Invention] However, the conventional configuration as described above has the following problems.

First, when only an aluminum electrode is used as a heating element, there is a problem that an oxide film is formed on the surface of the aluminum electrode, corrosion of the aluminum occurs, and reliability is lowered.

[0007] Furthermore, when a copper electrode is provided on an aluminum electrode, there is no problem in using it as a soldering type switching element. However, when this positive temperature coefficient thermistor is used as a heating element in a hot-air heater or the like, the copper electrode oxidizes in the atmosphere, which poses a problem in terms of reliability.

Furthermore, in the case of a nickel-silver electrode, since a silver electrode is provided when it is used as a heating element, oxidation of the nickel electrode can be suppressed. However, silver can deteriorate due to the formation of compounds due to small amounts of sulfuric gas in the atmosphere, and migration of silver can occur due to electric fields and small amounts of moisture, and in the worst case, there is a risk of short circuiting and destruction. In order to prevent this, it is necessary to reduce the area of the silver electrodes on both opposing surfaces, which poses the problem of being difficult to manufacture and poor in mass production.

The present invention solves the above-mentioned conventional problems, and aims to provide a positive temperature coefficient thermistor that has excellent reliability and heat resistance even when used as a heating element. .

0010

[Means for Solving the Problems] In order to achieve this object, the PTC thermistor of the present invention is provided with aluminum electrodes on both main planes of a PTC thermistor element, and a gold electrode is provided on the aluminum electrodes. It is something.

The present invention also provides a positive temperature coefficient thermistor element characterized in that aluminum electrodes are formed on both main planes of the positive temperature coefficient thermistor element, and after removing an oxide film on the surface of the aluminum electrode, a gold electrode is formed thereon. A method for manufacturing a thermistor is provided.

0012

[Operation] According to this configuration, since the gold electrode is provided on the aluminum electrode, oxidation and corrosion of the aluminum electrode can be prevented. In addition, since no silver electrodes are used, migration deterioration can be prevented, and reliability and
Durability can be improved. Furthermore, by providing a gold electrode after removing the oxide film on the surface of the aluminum electrode, the electrical conduction between the aluminum electrode and the gold electrode can be completed, and reliability can be further improved.

[0013]

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

FIG. 1 is a sectional view showing an embodiment of a positive temperature coefficient thermistor according to the present invention. In FIG. 1, reference numeral 11 denotes a PTC thermistor element, and aluminum electrodes 12 are provided on both opposing main planes of the PTC thermistor element 11, and a gold electrode 13 is provided on the aluminum electrodes 12. It is provided. Further, 14 is a spring terminal.

Next, one embodiment of the manufacturing method will be described. First, conductive aluminum paste is screen printed on both opposing main planes of the PTC thermistor element 11 and baked to form the aluminum electrodes 12. Thereafter, the oxide film on the surface of the aluminum electrode 12 is removed by buffing. Next, a gold electrode 13 is formed on the aluminum electrode 12 using a DC sputtering device. In this way, a positive temperature coefficient thermistor is manufactured.

Now, when the positive temperature coefficient thermistor of the present invention is used in a hot air heater, the switching temperature is around 300°C, so the temperature of the positive temperature coefficient thermistor is 300°C, and heat resistance becomes important. Therefore, as a comparison between the example of the present invention and the conventional example, the initial characteristics and the rate of change in resistance value of the positive temperature coefficient thermistor after 50 hours of heat resistance test at 300° C. are shown in Table 1 below.

Here, the positive temperature coefficient thermistor element has (B
a0.65Pb0.35) TiO3+0.0003Nb
A disk-shaped element having a composition of 2O5+0.001MnO2+0.02SiO2 and having a diameter of 14 mm and a thickness of 3.0 mm was made. In this example, an aluminum electrode was formed with a thickness of 20 μm by screen printing and baking, and after removing the oxide film on the surface, a gold electrode with a thickness of 1.0 μm was formed thereon using a DC sputtering device. On the other hand, in Conventional Example I, the aluminum electrode has a thickness of 20 μm.
In Conventional Example II, the thickness of the nickel electrode was 2 μm, and the thickness of the silver electrode formed thereon was 30 μm. At this time,
Both Conventional Examples I and II use a positive temperature coefficient thermistor element having the same composition and shape as the present example, and the switching temperature is 300°C.

[0018]

[Table 1]

As shown in Table 1 above, the conventional example I, which only uses aluminum electrodes, has a large rate of change in resistance value. This is considered to be due to the fact that surface oxidation is promoted because the aluminum electrode is in contact with the atmosphere. In contrast, in this example, the aluminum electrode is protected by the gold electrode, and gold is less likely to be oxidized than aluminum, so the rate of change in resistance value is half that of Conventional Example I. In addition, conventional example I in which a silver electrode was provided on a nickel electrode
I has a smaller resistance change rate than conventional example I, but
As mentioned above, this method has another problem in that migration is likely to occur.

Therefore, the device of this example has initial characteristics on the same level as the conventional example, has improved heat resistance, and is highly reliable. In addition, in this example,
By forming the gold electrode after removing the oxide film on the surface of the aluminum electrode, the electrical conduction between the aluminum electrode and the gold electrode is made complete, further increasing reliability.

In this embodiment, the aluminum electrode may be formed by thermal spraying or sputtering, and the gold electrode may be formed by plating.

[0022]

As described above, according to the present invention, by forming a two-layer structure of an aluminum electrode and a gold electrode provided thereon, oxidation of aluminum can be prevented and a positive electrode with excellent heat resistance can be obtained. A characteristic thermistor is obtained. Furthermore, since the structure does not use silver electrodes, there is no risk of short circuit or destruction due to migration. Then, by forming a gold electrode after removing the oxide film on the surface of the aluminum electrode, conduction between the aluminum electrode and the gold electrode can be made more complete, and reliability can be further improved. Therefore, according to the present invention, it is possible to provide a highly reliable positive temperature coefficient thermistor even when used as a heating element.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a positive temperature coefficient thermistor according to an embodiment of the present invention.

[Figure 2] Cross-sectional view showing a conventional positive temperature coefficient thermistor

[Figure 3]
Cross-sectional diagram showing other conventional positive temperature coefficient thermistors

[Explanation of symbols]

11 Positive temperature coefficient thermistor element 12 Aluminum electrode 13 Gold electrode

Claims (2)

[Claims] 1. A positive temperature coefficient thermistor comprising aluminum electrodes provided on both main planes of a positive temperature coefficient thermistor element, and a gold electrode provided on the aluminum electrodes. 2. Manufacture of a positive temperature coefficient thermistor, characterized in that aluminum electrodes are formed on both main planes of a positive temperature coefficient thermistor element, and after removing an oxide film on the surface of the aluminum electrode, a gold electrode is formed thereon. Method.