JP2699716B2 - Positive thermistor element - Google Patents

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 element, and more particularly to a positive temperature coefficient thermistor element having improved electrodes formed on both main surfaces of a positive temperature coefficient thermistor body.

[0002]

2. Description of the Related Art Conventionally, a positive temperature coefficient thermistor (hereinafter referred to as a thermistor) having electrodes formed on both main surfaces of a barium titanate-based semiconductor porcelain.
Elements (abbreviated as PTC) are known. In the PTC element, P
Since the TC element is made of semiconductor porcelain, it is necessary to use a conductive material that does not form a barrier between the TC element and the semiconductor porcelain. The following have been used as electrodes conventionally used in PTC elements. After plating both main surfaces of the PTC body with Ni,
An electrode formed by heat treatment at 500 ° C. After plating both main surfaces of the PTC body with Ni,
An electrode formed by applying and baking an Ag-containing paste on a Ni plating layer. An electrode formed by applying and baking an Ag paste containing an ohmic component such as Ga. An electrode formed by applying and baking an Al paste.

[0003]

However, when the above-mentioned electrodes are formed in a PTC element used in a high-temperature environment, there are various problems as described below. In the case of the Ni-plated electrode, the film resistance of the electrode could not be reduced because of the high specific resistance of the Ni film and the difficulty in increasing the thickness of the electrode. Therefore, the electrode may not be able to withstand a large current when a voltage is applied. In the Ni-Ag electrode of No. 1, when the operating temperature increases, the Ag
In some cases, thermal migration occurred, and a short circuit occurred between electrodes on both main surfaces during use. The ohmic component-containing Ag paste electrode has a short life, and particularly when used in a high-temperature PTC element, has a much shorter life, and thus cannot be used as an actual product. In the electrode using the Al paste, the stability of Al was poor and the life was short. In particular, when a high-temperature PTC element is used in a high-humidity atmosphere, there is a disadvantage that the resistance value is significantly increased.

On the other hand, as a problem of an electrode formed by applying and baking an Ag paste on the other Ni-plated electrode, that is, to prevent thermal migration of Ag, FIG.
Has been proposed. FIG. 4 (a),
In the PTC element 1 shown in (b), Ni electrodes 3a and 3b are formed by plating Ni on both main surfaces of a PTC element body 2 made of a barium titanate-based semiconductor ceramic.
An Ag electrode 4 having a smaller diameter than the Ni electrodes 3a and 3b, leaving a gap region g around the Ni electrodes 3a and 3b.
a, 4b are formed. That is, the gap region g
It has been attempted to prevent thermal migration through the side surface of the PTC element body 2 between the Ag electrodes 4a and 4b on both main surfaces by providing the.

However, as shown in a partially enlarged sectional view of FIG. 5, in the gap region g, only the Ni electrode 3a exists, but since Ni has a relatively high specific resistance, the Ni electrode 3a existing in the gap region g is present. The portion functions as a resistive film. As a result, when a voltage is applied to the PTC element 1,
The current distribution shown in FIG. 6 (the vertical axis I in the diagram showing the current distribution indicates the intensity of the current) occurred in the TC element body 2.
As a result, the inside of the PTC body 2 generates heat unevenly, that is, as shown in FIG. 6, the temperature distribution shown in FIG. 6 in the PTC body 2 (T on the vertical axis of the portion showing the temperature distribution indicates the temperature. ) Had occurred. Therefore, when a pulse voltage is applied to the PTC element 1 several times in a state where the temperature distribution as described above is generated, stress accumulates in the gap region g, and in extreme cases, the PTC element 1 may be broken. .

Accordingly, it is an object of the present invention to provide a PTC device in which a short circuit due to migration is unlikely to occur, has a long service life, and in which a PTC element is unlikely to crack.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and is a positive temperature coefficient thermistor element having electrodes formed on both main surfaces of a positive temperature coefficient thermistor element body, It is characterized by comprising the following electrodes. That is, the invention according to claim 1 is characterized in that the electrode is constituted by an Al—Si electrode containing 48 to 96% by weight of aluminum and 4 to 52% by weight of silicon. According to the second aspect of the present invention, the Ni electrode formed by plating on both main surfaces of the PTC element and the NTC
formed on the i-electrode, and aluminum
Al- containing 96% by weight and 4-52% by weight of silicon
And a Si electrode.

The Al-S according to the first and second aspects of the present invention.
In the composition of the i-electrode, the content of aluminum and silicon is limited to the above range. When Al is less than 48% by weight and Si exceeds 52% by weight, ohmic contact with the PTC element cannot be obtained. This is because the moisture resistance is also deteriorated. Also, when Al exceeds 96% by weight and Si is less than 4% by weight, the moisture resistance is deteriorated. An electrode material containing aluminum and silicon at the above specific ratio is disclosed in Japanese Patent Application No. 2-340860 previously filed by the present applicant, and a low melting point glass frit and an organic vehicle are added to aluminum powder and silicon powder. In addition to paste, apply the paste,
The electrode is completed by baking. As the aluminum powder, for example, a powder having a particle size of about 5 to 30 μm, and as the silicon powder, for example, a powder having a particle size of 0.5 to 1 μm.
A powder of about 0.0 μm is used. The mixing ratio of the low melting point glass frit and the organic vehicle is not particularly limited, but, for example, for example, 10% by weight of the low melting point glass frit and the organic vehicle with respect to 70% by weight of the aluminum powder and silicon powder in total. It can be prepared in a proportion of 20% by weight.

[0009]

According to the first aspect of the present invention, since the Al-Si electrode containing aluminum and silicon in the above specific ratio is used, no migration occurs between the electrodes on both main surfaces. Further, the Al-Si electrode also has excellent life characteristics, as is apparent from the examples described later. According to the second aspect of the present invention, since the Al-Si electrode containing aluminum and silicon in the above-described specific range is formed on the Ni electrode, migration between the electrodes on both main surfaces hardly occurs, and Deterioration of the electrode over time is unlikely to occur. Further, since the Al-Si electrode is formed on the entire surface of the Ni electrode, a temperature distribution hardly occurs in the PTC body, so that even when a pulse voltage is applied, the PTC
The element is hardly cracked.

[0010]

EXAMPLE 1 10 parts by weight of a low-melting glass frit and 20 parts by weight of an organic vehicle based on 70 parts by weight of a metal powder mixed so that the aluminum content is 72% by weight and the silicon content is 28% by weight. Are mixed and kneaded to form an Al-
An Si paste was produced. On the other hand, a 20 × 15 × 4 mm square plate-shaped Pb-containing barium titanate-based PTC element (resistance between both main surfaces was 120Ω) was prepared. This PTC element generates heat at 240 ° C. The Al-Si paste obtained as described above was applied to both main surfaces of the PTC body to a thickness of 10 μm, and baked at a temperature of 600 ° C. for 30 minutes to form the Al-Si electrode into the square plate shape. It was formed on both main surfaces of the PTC body. FIG. 1 shows the PTC element thus obtained. The PTC element 11 is provided on both main surfaces of the square plate PTC element body 12 by the Al-Si electrodes 13.
a and 13b are formed.

Comparative Example 1 The same square plate-shaped PTC element used in Example 1 was prepared, and Ni was electrolessly plated on both principal surfaces.
A heat treatment was performed at a temperature of 500 ° C. to prepare a PTC element in which Ni electrodes were formed on both main surfaces. Comparative Example 2 The same square plate-shaped PTC element used in Example 1 was prepared, Ni was electrolessly plated on both main surfaces, and then Ag was further added.
The containing paste was applied on the entire surface of the Ni electrode and baked to form an Ag electrode, thereby obtaining a PTC element of Comparative Example 2. Comparative Example 3 An ohmic component-containing Ag paste was applied to both main surfaces of the square plate-shaped PTC element body used in Example 1 to a thickness of 5 μm,
An electrode was formed by baking at a temperature of 00 ° C. for 30 minutes to obtain a PTC element of Comparative Example 3. Comparative Example 4 An electrode was formed by applying and baking an Al paste on both main surfaces of the square plate-shaped PTC element used in Example 1 to obtain a PTC element of Comparative Example 4.

Evaluation of PTC Element of Example 1 and Comparative Examples 1-4 In the PTC element of Example 1 and the PTC element of Comparative Example 1, 200 V and a 5-second pulse voltage were applied between the electrodes on both main surfaces, respectively. Times applied. As a result, the PTC of Comparative Example 1
In the device, the Ni electrode burned out.
No abnormalities in appearance were observed in the PTC element of No. Further, the PTC element of Example 1 and the PTC of Comparative Example 2
A voltage of 200 V was applied to the device for 500 hours, and the occurrence of migration was examined. As a result, in the PTC element of Comparative Example 2, four PTC elements per ten PTC elements were used.
The PTC element was destroyed due to migration in the C element, and migration of 2 mm or more occurred in the remaining six PTC elements. On the other hand, in the PTC element of Example 1, the occurrence of migration as described above was not observed at all.

With respect to the PTC element of Example 1 and the PTC elements of Comparative Examples 3 and 4,
After the lapse of 000 hours, the rate of change of the resistance value was measured, thereby comparing the life characteristics. (1) Leaving in humidity: The device was left in a high-temperature and high-humidity environment at 60 ° C. and a relative humidity of 90 to 95%. (2) Humidity interruption continuous load: 60 ° C and relative humidity 90 to 95%
In a high-temperature, high-humidity environment, the operation of applying a voltage of 200 V for 10 minutes and then allowing the voltage to stand for 20 minutes was repeated. (3) High temperature storage: Left in a high temperature bath at a temperature of 150 ° C. (4) Normal temperature continuous load: A voltage of 200 V was continuously applied at normal temperature (25 ° C.) and normal humidity (relative humidity 65 to 75%). Example 1 and Comparative Example 3 under the above four environments
Table 1 below shows the rate of change in resistance of the PTC element No. 4 after 1000 hours.

[0014]

[Table 1]

As is clear from Table 1, the PTC element of Example 1 has a very small change in resistance value in all environments as compared with Comparative Examples 3 and 4.

Embodiment 2 Embodiment 2 corresponds to the embodiment according to the second aspect of the present invention. A disc-shaped barium titanate-based PTC element having a diameter of 14 mm and a thickness of 2.3 mm (the resistance value between both principal surfaces is 15
Ω), and Ni was electrolessly plated on both main surfaces to form a 1.5 μm thick Ni electrode. Next, the same Al-Si paste as used in Example 1 was applied on the Ni electrode and baked at a temperature of 600 ° C. for 30 minutes to form an Al-Si electrode. FIG. 2 shows the structure of the PTC element of Example 1 thus obtained. PTC
In the element 21, Ni electrodes 23 a and 23 b are formed on the entire surfaces of both main surfaces of the PTC element body 22.
The Al-Si electrodes 24a, 24a
4b is formed. Example 2 obtained as described above
A voltage was applied to both main surfaces of the PTC element 21, and the current density distribution and the temperature distribution in the PTC element 22 were measured. The results are shown in FIG. As is clear from FIG.
Since the Al-Si electrodes 24a and 24b are formed on the entire surface of the PTC elements a and 23b, it can be seen that the current distribution is uniform over the entire area of the PTC body 22. PTC body 2
It can be seen that the temperature distribution is not so biased within 2.

For comparison, the same PTC body used in Example 2 was electrolessly plated with Ni on both main surfaces, and further contained Ag powder except for a gap region having a width of 1.5 mm. Ag paste is screen-printed to a thickness of 4 μm
A PTC element having electrodes formed by printing and baking at a temperature of 600 ° C. for 30 minutes was prepared as Comparative Example 5. When a pulse of 200 V and 5 seconds was applied 100 times to each of the PTC elements of Example 2 and Comparative Example 5, cracks occurred in 15 out of 20 PTC elements of Comparative Example 5. On the other hand, in the PTC element of Example 2, no more than the appearance was recognized. After the application of the pulse, the presence or absence of migration between the electrodes was visually examined. As a result, no migration was observed in the PTC element of Example 2.

[0018]

The PTC element according to the first aspect of the present invention has a structure in which Al-Si electrodes containing aluminum and silicon in the above specific range are formed on both main surfaces of the PTC element body. It is possible to prevent a short circuit accident due to the migration and prevent deterioration of the characteristics of the PTC element over time. Therefore, long life P
A TC device is provided. Similarly, in the invention described in claim 2, the Ni electrode is formed on the entire surface of both main surfaces of the PTC element body, and the Al-Si electrode containing aluminum and silicon in the above specific range is formed on the entire surface of the Ni electrode. Formed, it is possible to prevent a short circuit accident due to migration, to prevent deterioration of the characteristics of the PTC element over time, and to use the PTC element due to a pulse voltage or the like even when used in a high temperature environment. It is possible to provide a highly reliable PTC element which is less likely to break the body.

[Brief description of the drawings]

FIG. 1 is a side view showing a PTC element according to one embodiment of the present invention.

FIG. 2 is a side view showing a PTC element according to another embodiment of the present invention.

FIG. 3 is a diagram for explaining current distribution and temperature distribution in a PTC element according to another embodiment of the present invention.

FIGS. 4A and 4B are a perspective view and a side view for explaining a conventional PTC element.

FIG. 5 is a partially enlarged sectional view for explaining a problem of the conventional PTC element.

FIG. 6 is a diagram for explaining current distribution and temperature distribution in a PTC element body of a conventional PTC element.

[Explanation of symbols]

 11: PTC element 12: PTC element 13a, 13b: Al-Si electrode

Continuation of front page (56) References JP-A-56-124201 (JP, A) JP-A-2-216806 (JP, A) JP-A-2-305404 (JP, A) JP-A-49-32182 (JP, A) , A)

Claims (2)

(57) [Claims] 1. A positive temperature coefficient thermistor element comprising electrodes formed on both main surfaces of a positive temperature coefficient thermistor element, wherein said electrode is made of Al-Si containing 48 to 96% by weight of aluminum and 4 to 52% by weight of silicon. A positive temperature coefficient thermistor element comprising an electrode. 2. A positive temperature coefficient thermistor element comprising electrodes formed on both main surfaces of a positive temperature coefficient thermistor body, wherein said electrodes are formed on both main surfaces of said positive temperature coefficient thermistor body by Ni.
A Ni electrode formed by plating
formed on the entire surface of the i-electrode and made of aluminum 48
Al containing ~ 96% by weight and 4-52% by weight of silicon
A positive temperature coefficient thermistor element comprising a Si electrode;