JP2897486B2 - 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 element (hereinafter, PTC element) in which electrodes are formed on both main surfaces of a barium titanate-based semiconductor ceramic has been known. For PTC elements, PT
Since the C element is made of semiconductor porcelain, it is necessary to use a conductive material that does not form a barrier between the C element and the semiconductor porcelain. Therefore, Ni is electrolessly plated on the entire surfaces of both main surfaces of the PTC body to form a Ni electrode.
By baking Ag paste on the Ni electrode, A
A structure in which a g electrode is formed has been proposed. However, in a PTC element used at a high temperature, the Ag electrodes on both main surfaces cause thermal migration, and the Ag electrodes on both main surfaces
There is a problem that a short circuit occurs between the electrodes.

A PTC element shown in FIG. 4 has been proposed to prevent the above-mentioned migration between electrodes. In the PTC element 1 shown in FIGS. 4A and 4B, Ni is electrolessly plated on the entire surfaces of both main surfaces of the PTC body 2 made of barium titanate-based semiconductor porcelain, so that the Ni electrode 3a
3b is formed. On these Ni electrodes 3a and 3b,
Ag electrodes 4a and 4b smaller in diameter than the Ni electrodes 3a and 3b are formed around the gap region g. That is, by providing the gap region g, migration via the side surface of the PTC element body 2 between the Ag electrodes 4a and 4b on both main surfaces is less likely to occur.

[0004]

However, as shown in a partially enlarged sectional view of FIG.
Although only the i-electrode 3a exists, Ni has a relatively high specific resistance, so the Ni electrode portion existing in the gap region g functions as a resistive film. As a result, when a voltage was applied to the PTC element 1, the current distribution shown in FIG. 6 (the vertical axis I in the figure showing the current distribution indicates the current intensity) occurred in the PTC element body 2. For this reason, the inside of the PTC body 2 generates heat non-uniformly, and as shown in FIG. 6, a temperature distribution occurs in the PTC body 2 (T on the vertical axis in the figure showing the temperature distribution indicates the temperature). . Therefore, when a pulse voltage is applied to the PTC element several times in a state where the temperature distribution as described above occurs, stress accumulates in the gap region g, and in some cases, the PTC element is broken.

Accordingly, an object of the present invention is to provide a PTC element in which a short circuit between electrodes on both main surfaces due to migration hardly occurs and a PTC element hardly cracks even when a pulse voltage is applied. is there.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and comprises forming a first electrode made of nickel over the entire surface of both main surfaces of a positive temperature coefficient thermistor body, and forming a first electrode made of nickel. PTC formed by forming a second electrode mainly composed of silver on the first electrode while leaving a gap region of a predetermined width
In the device, 48 to 96% by weight of aluminum and 4 to 52% of silicon are formed so as to cover at least the gap region.
A PTC element characterized in that an Al-Si electrode containing 1% by weight is formed on a first electrode. A above
In the composition of the l-Si electrode, the aluminum and silicon contents were limited to the above proportions because the Al content was 48% by weight.
When the content is less than 52% and Si exceeds 52% by weight, the moisture resistance deteriorates. When the content of Al exceeds 96% by weight and the content of Si is less than 4% by weight, the moisture resistance also deteriorates.

[0007] An electrode material containing aluminum and silicon at the above-mentioned specific ratios is disclosed in Japanese Patent Application No. 2-340860 previously filed by the present applicant, and a low melting glass frit and aluminum frit are added to aluminum powder and silicon powder. An organic vehicle is added to form a paste, and the paste is applied and baked to complete the electrode. As aluminum powder, for example, a powder having a particle size of about 5 to 30 μm, and as silicon powder, for example, a particle 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.

[0008]

According to the present invention, the second electrode mainly composed of Ag is formed on the first electrode made of nickel while leaving a gap region around the first electrode, and the specific ratio is set so as to cover the gap region. A containing aluminum and silicon
Since it has a structure in which an l-Si electrode is formed, migration between the electrodes on both main surfaces hardly occurs. Further, in the gap region, since the Al-Si electrode is superimposed on the first electrode made of nickel, the resistance of the electrode film existing in the gap region is reduced. Temperature distribution is unlikely to occur. Therefore, even when used at a high temperature, cracking of the PTC body is unlikely to occur.

[0009]

The present invention will be clarified below by describing non-limiting examples of the present invention. FIG. 1 is a sectional view of a PTC element according to one embodiment of the present invention, and FIG. 2 is a plan view. The PTC element 11 of the present embodiment has a disc-shaped PTC element.
It is configured using the TC element 12. PTC body 12
Is made of a semiconductor porcelain material such as a barium titanate-based material. The entire surface of both main surfaces of the PTC element body 12 is electrolessly plated with nickel to form the first electrode 13.
a, 13b are formed. Then, the first electrode 13
The second electrodes 14a, 14b mainly composed of Ag are formed on the a, 13b by applying and baking an Ag paste while leaving a gap region g of a predetermined width around the periphery. Up to this point, it is the same as the conventional PTC element 1 shown in FIG.

A feature of the PTC element 11 of this embodiment is that the first electrode 1 made of Ni is formed on the gap region g.
Al-Si electrodes 15a, 1b are provided so as to cover 3a, 13b.
5b is formed. The Al-Si electrode is
The paste is formed by applying and baking a paste containing 48 to 96% by weight of aluminum and 4 to 52% by weight of silicon in this ratio. In the PTC element 11 of this embodiment, the gap region g is formed around the second electrodes 14a and 14b made of Ag, and the Al-Si electrode is formed on the gap region g. A
Migration between the second electrodes 14a and 14b mainly composed of g is reliably prevented.

Incidentally, as is apparent from FIGS. 1 and 2,
In the present embodiment, the Al-Si electrodes 15a and 15b are formed such that the inner edges thereof reach the second electrodes 14a and 14b.
Si electrodes 15a and 15b are formed, and the outer edges of the second electrodes 14a and 14b mainly composed of Ag are hidden. Therefore, the occurrence of migration between the second electrodes 14a and 14b is more reliably prevented, but the inner edges of the Al-Si electrodes 15a and 15b are connected to the second electrodes 14a and 1b.
4b may be in contact with the outer peripheral edge. As well,
In the gap region g, the first electrode 1 made of Ni
Since the Al-Si electrodes 15a and 15b exist on 3a and 13b, the electrode resistance in the gap region g is reduced. Accordingly, in the use state, as shown in FIG. 3, the current distribution becomes uniform over the entire area of the PTC body 12, and the temperature distribution in the PTC body 12 is also different from that of the conventional example shown in FIG. It can be seen that there is no bias.
Therefore, even if a pulse voltage is applied when used at a high temperature, cracking of the PTC element body 12 hardly occurs.

Next, specific experimental results will be described.
The PTC element 11 of the embodiment is made of a barium titanate-based semiconductor porcelain having a diameter of 14 mm and a thickness of 2.3 mm.
A TC body 12 was prepared. The resistance between the two main surfaces of the PTC body 12 was 15Ω. Next, the PTC body 12
The first electrodes 13a and 13 having a thickness of 1.5 μm
b was formed by electroless plating Ni. Further, a conductive paste containing Ag powder is screen-printed on the first electrodes 13a and 13b, and the width of the conductive paste is 1.5
The second electrodes 14a and 14b having a film thickness of 4 μm were formed while leaving a gap region g of mm. Further, on the first electrodes 13a and 13b made of Ni on the gap region g,
Al and S at a ratio of 72% by weight of Al and 28% by weight of Si
A conductive paste containing metal powder containing i is applied and baked to form an Al-Si electrode 15 having a film thickness of 10 μm.
a, 15b were formed, and a PTC element 11 was obtained.

For comparison, a PTC element without the Al-Si electrode was prepared (the conventional example shown in FIG. 4). 200V is applied to the PTC element of the above embodiment and the conventional example.
And when a pulse voltage of 5 seconds is applied 100 times, the PTC element of the conventional example has 15 PTC elements per 20 elements.
The element cracked. In contrast, the PTC of the present embodiment
No abnormalities in appearance were observed in the device. In addition, in the PTC element of this example, when the presence or absence of migration when applying the pulse voltage was visually examined, no occurrence of migration between electrodes was observed. In the illustrated embodiment, the PTC element 11 is configured using the disc-shaped PTC element body 12, but the PTC element 11 using the PTC element body having another shape such as a rectangular plate shape is used.
The present invention can be applied to a TC element.

[0014]

As described above, according to the present invention, the second electrode mainly composed of Ag is formed on the first electrode made of Ni while leaving the gap region around the first electrode. Since the Al-Si electrode is formed so as to cover the first electrode, migration between the second electrodes mainly composed of Ag on both main surfaces hardly occurs. Therefore, a short circuit due to the migration of the Ag electrode hardly occurs. In addition, in the gap region, the Al-Si electrode is formed so as to cover the first electrode made of Ni, so that the electrode resistance in the gap region is reduced. Therefore, even when used at a high temperature, the temperature is made uniform over substantially the entire PTC body, so that even if a pulse voltage is applied, the PTC body is unlikely to crack. Therefore, according to the present invention, it is possible to provide a highly reliable PTC element in which a short circuit accident due to migration between electrodes is less likely to occur, a PTC element is less likely to crack, and the reliability is excellent.

[Brief description of the drawings]

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

FIG. 2 is a plan view of the PTC element of the embodiment.

FIG. 3 is a diagram for explaining current distribution and temperature distribution in the PTC element of the example.

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 body 13a, 13b First electrode 14a, 14b Second electrode 15a, 15b Al-Si electrode

Claims (1)

(57) [Claims] 1. A first electrode made of nickel is formed on the entire surface of both main surfaces of a positive temperature coefficient thermistor body, and silver is mainly formed on the first electrode while leaving a gap region of a predetermined width around the first electrode. In a positive temperature coefficient thermistor element formed with a second electrode, an Al-Si electrode containing 48 to 96% by weight of aluminum and 4 to 52% by weight of silicon is formed on the first electrode so as to cover at least the gap region. A positive temperature coefficient thermistor element, characterized in that the element is formed as follows.