JPH065403A - Positive temperature coefficient thermistor and manufacturing method thereof - Google Patents

Abstract

PURPOSE:To prevent the shortcircuit failure while enhnancing the durability, productivity of an element by adopting printed electrodes mainly comprising aluminum as applicable electrodes. CONSTITUTION:The title positive temperature coefficient thermistor main body 11 mainly comprising barium titanate is formed. The first electrodes 12a, 12b comprising Ni or Cu or Al thin films 0.1-10mum thick are formed on the surface and rear surface of the main body 11 by electron beam evaporation process. Next, the second electrodes 13a, 13b are formed on the first electrodes 12a, 12b by printing, drying and baking an Al paste mainly comprising Al. Through these procedures, the occurrence of migration as well as the shortcircuit failure can be prevented further enhancing the durability due to the lack of cracking or chapping while reducing the with-time fluctuation in the initial resistance value. Furthermore, the resistance value control with high precision as well as the high breakdown voltage against large rushcurrent can be assured.

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 and a manufacturing method thereof, and more particularly to a structure of an electrode thereof and a method of forming the same.

[0002]

2. Description of the Related Art BaTiO ₃ with 0.3 atm of Y, Nd, etc.
Since the oxide semiconductor with% added has a large positive temperature coefficient, it is called a PTC thermistor. This PTC thermistor has an area with a large positive temperature coefficient
Since it can be adjusted by adding r, Pb, etc., it must be used in a wide variety of fields such as temperature measurement and overcurrent prevention, circuit elements for motor start-up, color TV degaussing, low temperature heaters, etc. Has become. An example of such a thermistor is Ba, Ti,
A thermistor body 21 formed by sintering metal oxides such as Nd, carbonates, nitrates, chlorides, etc. into a thin columnar shape, and a Ni plating layer formed on the upper and lower surfaces of the thermistor body 21. One electrode layer 22a, 22b and a second electrode layer 23a, 23b formed on the first electrode layer 22a, 22b containing silver as a main component.
It consists of and. By the way, such a positive temperature coefficient thermistor is usually used by applying a voltage between the second electrode layers 23a and 23b. At this time, silver in the second electrode layer moves in the direction of the electric field. A so-called migration phenomenon occurs, in which precipitation occurs. In particular, when the outer peripheral edge of the second electrode layer is configured to reach the outer peripheral edge of the positive temperature coefficient thermistor body 1, silver moves and precipitates in the direction of the electric field on the outer circumferential surface of the positive temperature coefficient thermistor body 1, Finally, there is a problem that a short circuit occurs. In order to solve this problem, therefore, as shown in FIG. 3, a positive temperature coefficient thermistor is proposed in which the outer diameter (W) of the second electrode layer is smaller than the outer diameter (V) of the first electrode layer. ing. However,
In this structure, since the outer diameter of the second electrode layer is smaller than the outer diameter of the first electrode layer, there is a problem in that it is easily oxidized and the contact resistance gradually increases. In addition, since the migration of silver has a phenomenon of moving along the direction of the electric field, even if only the second electrode layer is provided inside the outer periphery as in the conventional example, the silver in the first electrode layer diffuses, although slightly. Therefore, the problem of short circuit is mitigated but cannot be completely prevented. Further, in the conventional positive temperature coefficient thermistor, the electrodes are formed by using the plating method. Therefore, in this method, the plating solution penetrates into the sintered body when Ni plating is performed in forming the electrodes, and the resistance value decreases. The characteristics of the sintered body may change. This may appear as a property change immediately after formation, or may gradually appear with time. The purpose of the thermistor is
As described above, temperature measurement and control, compensation, gain adjustment, power measurement, overcurrent prevention, motor startup, color TV degaussing, etc. all require high-precision resistance control, and R ± It is necessary to use those within the range of α%. Therefore, the problem of resistance value change due to permeation of the plating solution has become serious. In order to avoid such penetration of the plating solution, a method of forming a low melting point metal such as aluminum by a metal spraying method and using this as an electrode has also been proposed. However, this method also cannot avoid the problem that a crack is generated in the thermistor body or the electrode itself, because the temperature changes rapidly when the electrode is formed. In order to solve the above problem, the present inventor has disclosed in Japanese Patent Application Laid-Open No. 4-118901 that the first electrode 32a and the second electrode 33a are separated from the outer peripheral edge of the thermistor body at the same position as shown in FIG. I have proposed the ones that are overlapped with each other.

[0003]

However, even in the positive temperature coefficient thermistor according to Japanese Patent Laid-Open No. 4-118901 proposed by the present inventors, silver is used for the second electrode layer, and therefore, when an electric field is applied, silver is applied. However, since the migration of Al2 is small along with the direction of the electric field, silver diffuses, so that the problem of short-circuiting is mitigated but cannot be completely prevented.

The present invention focuses on the above-mentioned conventional problems, and relates to a positive temperature coefficient thermistor and its manufacturing method, and more particularly to improvement of its electrode structure and its forming method.

[0005]

In order to achieve the above object, in the first invention of the positive temperature coefficient thermistor and the manufacturing method thereof according to the present invention, the thermistor including the thermistor element body and the electrode is made of a semiconductor having a positive temperature coefficient. It comprises a thermistor element body and at least a first electrode or a second electrode made of an aluminum (Al) printed electrode containing aluminum (Al) as a main component. In the second invention, an aluminum (Al) paste containing Al as a main component is printed on the thermistor element body made of a semiconductor having a positive characteristic or the first electrode, and the Al paste is fired after printing to print the first electrode or the second electrode. Configure electrodes.

In the third invention, the thermistor element body made of a semiconductor having a positive characteristic and Al or Al and Ni, C.
Electron beam of any alloy of r, Ti, Cu (E
B) a first electrode formed by a vapor-deposited thin film. Also, the fourth
According to the present invention, Al or Al and Ni, Cr, Ti, Cu,
One of the alloys is formed by the EB vapor deposition method.

In the fifth invention, the thermistor element body made of a semiconductor having a positive characteristic and Ni, Cr, Ti, Cu, A.
1 or an EB vapor-deposited thin film of an alloy of any one of Ni, Cr, Ti, Cu and Al, and a second electrode of an Al printed electrode containing Al as a main component.

According to the sixth aspect of the invention, the thermistor element body made of a semiconductor having positive characteristics is provided with Ni, Cr, Ti, Cu, A.
1 or an alloy of any one of Ni, Cr, Ti, Cu, Al is used to form the first electrode by the EB vapor deposition method, and an Al paste containing Al as a main component is printed on the first electrode.
The 1 paste is fired to form the second electrode.

[0009]

The present inventor has confirmed that aluminum does not cause migration. From this result, according to the above configuration, since aluminum is used for the first electrode or the second electrode, migration is completely prevented, and a short circuit accident of the element can be prevented. Further, since AI printing or vapor deposition film is used for the electrodes, the element body is not cracked or cracked. Therefore, the durability is about 5 times or more, and the initial resistance value changes little with time. In addition, the highly accurate resistance value control described above, R ± α%
Within the range, it can be made almost equal to the case of using Ni and silver, and the structure in which the printed electrode is formed on the vapor deposition film has a high withstand voltage against a large rush power. Therefore, by using the first electrode when the applied electric field is low and by using the second electrode when the applied electric field is high, it is possible to completely prevent migration and obtain a positive temperature coefficient thermistor having excellent durability. it can. Moreover, since the first electrode can be formed to the end face, it is possible to prevent the first electrode from being oxidized. Furthermore, an electrode having high adhesion and low contact resistance can be formed by printing aluminum or by vapor deposition.

[0010]

Embodiments of the PTC thermistor according to the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an embodiment of a positive temperature coefficient thermistor of the present invention, and is an overall configuration diagram showing an example of use when a high electric field is applied. In FIG. 1, the positive temperature coefficient thermistor includes a thermistor body 11 containing barium titanate as a main component, and first and second electrodes 12a and 12b composed of Ni, Cu, or Al on the upper and lower surfaces thereof by an EB vapor deposition method. First
A second electrode 13a containing Al as a main component on the upper layer of the electrode
And 13b.

Next, the manufacturing process of the PTC thermistor will be described. 2A to 2C are process diagrams showing the manufacturing process of the thermistor according to the embodiment of the present invention. First, as shown in FIG. 2A, TiO ₂ , BaCO ₃ , Nd ₂
O ₃ powder was mixed at a predetermined ratio, pressure-molded into a disk shape by a cooling press method, and then sintered at 1300 ° C. to obtain a disk-shaped thermistor body 11 having a diameter of 4.47 mm.
To form. Then, the surface roughness of the end surface (electrode forming surface) of the thermistor body 1 is measured using a surface roughness meter.
When the surface roughness is 6.3 to 1.6 s (JIS standard triangle symbol ▽▽▽), the surface roughness is 0.8 s.
(JIS standard triangle symbol ▽▽▽▽) or more.

Then, as shown in FIG. 2B, a film thickness of 0.1 to 0.1 is formed on the upper and lower surfaces by electron beam evaporation.
The second electrodes 12a and 12b (hereinafter, represented by one side as 12a) made of a thin film of Ni, Cu, or Al having a thickness of 10 μm are formed. In this embodiment, the film forming condition: 1
50 ° C., vacuum degree: 5 × 10 ⁻⁴ torr, film thickness: 500
It was carried out with 0Å. At this time, vapor deposition is performed through a metal mask so that Ni, Cu, and Al are not formed on the end surface 11a of the main body. Here, when the surface roughness is 6.3 to 1.6 s, the film forming conditions are: vacuum degree: 1 × 10 ⁻⁴ torr to 1 × 10 ⁻⁶ torr Film forming condition: room temperature to 250 ° C. When the surface roughness is 0.8 s or more, the degree of vacuum: 5 × 10 ⁻⁴ torr to 1 × 10 ⁻⁶ torr Film forming condition: 100 ° C. to 250 ° C.

After this, as shown in FIG. 2 (c), the first
Al as the main component on the upper layer of the electrode (Al is approximately 50% in volume ratio)
The second electrode 13a having the composition For this purpose, an Al paste containing Al as a main component is printed. After printing, drying and baking were performed. In this embodiment, the film thickness: 1
0 μm, drying: 120 ° C. for 5 minutes, baking temperature: 30 minutes, the temperature was raised to 640 ° C., the temperature was maintained at 640 ° C. for 5 minutes, and then natural cooling was performed. In this step, the printing of the Al paste is 0.1 μm to 10 μm, and the firing temperature is about 600 μm.
It is preferable to sinter at 750 to 750 ° C.

(1) Regarding the comparison test result 1,

[Table 1] In the above manufacturing method, three types of the first electrode 12a composed of a thin film made of Ni, Cu, or Al, and the second electrode 13a containing Al as a main component, and the first type made of Ni having the conventional structure are used. Seven positive-characteristic thermistors each of which is a combination of the electrode 22a and the second electrode 23a made of Ag are prepared,
The resistance value (Ωcm) after thin film deposition was measured.

(2) Regarding the comparison test result 2,

[Table 2] The resistance value (Ωcm) of each of the above positive temperature coefficient thermistors after seven pastes were fired was measured. As a result, the same results as those of the conventional method (NO4) were obtained except after burning NO3 paste. In particular, good results were obtained with the combination of the first electrode 12a composed of a thin film of NO1 Al and the second electrode 13a containing Al as a main component.

(3) With respect to the comparison test result 3, the inrush current value (App) is measured by the measuring circuit (voltage: 220 Vrms,
It was as follows when measured at 50 Hz and resistance: 12 Ω. First electrode 12 composed of a thin film of Al
a and a second electrode 13a containing Al as a main component (hereinafter, A
It is described as 1-Al. ), The minimum value is 22.3 to the maximum value 2
4.8, the minimum value 22.0 to the maximum value 23.7 in the case of Ni-Al, and the minimum value 18.2 in the case of Cu-Al.
5 to the maximum value 20.8, and in the case of Ni-Ag, the minimum value 22.1 to the maximum value 23.0. From this result,
A high inrush current value is obtained in the case of Al-Al.

(4) Regarding the comparison test result 4,

[Table 3] The voltage value (V) was changed in the above four types of positive temperature coefficient thermistors, and the change in the current value (mA) was measured. From this result, a current displacement point was obtained at 450 V to 500 V, and almost the same performance was obtained.

(5) Comparative Test Results 5 were compared in intensity with respect to current. In this result, the current value of 20 A to 3 is obtained in the case where Al is thin-film deposited on the first electrode 12a.
Although the thermistor body was cracked at 0 A, the thermistor body was cracked at a current value of 10 A in the case where a thin film of Ni was vapor-deposited on the first electrode 22a. From these results, it was found that the strength of Al thin film deposition was high.

(6) A comparison test result 6 was subjected to a confirmation test by a migration intermittent current test. The test method was performed by repeatedly applying a voltage of 220 V for 1 minute and then spraying water for 5 minutes, and the cycle in which migration occurred was confirmed. In this result, no abnormality occurred in the case of the Al electrode after 10,000 cycles. In the case of Ag electrode, 1000 to 20
A short circuit occurred at 00 cycles.

In the above structure, the first electrodes 12a, 1
2b or the second electrodes 13a and 13b cover up to the end surface of the thermistor body, but as in Japanese Patent Laid-Open No. 4-118901 proposed by the present inventor, the end surface is the same inside the outer peripheral edge of the thermistor body, or You may make it shift | deviate and it may be covered.

[0021]

As described above, according to the present invention,
Since aluminum is used for the electrodes, migration is completely prevented, and short-circuit accidents of the element can be prevented. Also, since AI printing or a vapor deposition film is used for the electrodes, the element body is not cracked or cracked. Therefore, the durability is almost 5 times or more, and the initial resistance value changes little with time. In addition, highly accurate resistance value control and high withstand voltage for large inrush power can be obtained. Moreover, since the first electrode can be formed to the end face, it is possible to prevent the first electrode from being oxidized. Further, it is possible to form an electrode having a high adhesion and a low contact resistance by printing or vapor deposition of aluminum, and it is possible to obtain an excellent effect that the productivity is high because the AI printing or the vapor deposition film is used.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of a positive temperature coefficient thermistor of the present invention,

FIG. 2 is a diagram showing a manufacturing process of the positive temperature coefficient thermistor of the present invention;

FIG. 3 is a diagram showing an external shape of a conventional thermistor element,

FIG. 4 is a diagram showing an external shape of a conventional thermistor element,

[Explanation of symbols]

1 Positive Characteristic Thermistor 11 Thermistor body 12 First electrode 13 composed of Ni, Cu, or Al by EB evaporation method Second electrode containing Al as a main component

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masatoshi Tamura 1200 Manda, Hiratsuka, Kanagawa Pref., Komatsu Seisakusho Co., Ltd. (72) Inventor Tadamasa Nishiyama 1200, Hiratsuka, Kanagawa Komatsu Seisakusho Co., Ltd.

Claims (6)

[Claims] 1. A thermistor comprising a thermistor element body and an electrode, wherein the thermistor element body is made of a semiconductor having a positive characteristic and an aluminum (Al) printed electrode containing aluminum (Al) as a main component. A positive temperature coefficient thermistor comprising an electrode and. 2. A thermistor including a thermistor element body and an electrode, wherein an aluminum (Al) paste containing Al as a main component is printed on the thermistor element body or a first electrode made of a semiconductor having a positive characteristic, and the Al paste is printed after printing. Is fired to form the first electrode or the second electrode. 3. A thermistor comprising a thermistor element body and an electrode, the thermistor element body comprising a semiconductor having a positive characteristic, and Al or Al and Ni, Cr, Ti,
A positive temperature coefficient thermistor, comprising: a first electrode made of an electron beam (EB) vapor-deposited thin film of an alloy of Cu. 4. A thermistor comprising a thermistor element body and electrodes, wherein Al or Al and Ni, Cr, Ti, and
A method for producing a positive temperature coefficient thermistor, characterized in that an alloy of Cu or Cu is formed by an EB vapor deposition method. 5. A thermistor comprising a thermistor element body and an electrode, the thermistor element body comprising a semiconductor having a positive characteristic, and Ni, Cr, Ti, Cu, Al or Ni, Cr, Ti, Cu, Al. Alloy EB
A positive temperature coefficient thermistor comprising a first electrode formed of a vapor-deposited thin film and a second electrode formed of an Al printed electrode containing Al as a main component. 6. A thermistor comprising a thermistor element body and an electrode, wherein the thermistor element body comprising a semiconductor having a positive characteristic is Ni, Cr, Ti, Cu, Al or Ni, Cr, Ti, Cu, Al. EB alloy
Manufacture of a positive temperature coefficient thermistor characterized in that a first electrode is formed by a vapor deposition method, an Al paste containing Al as a main component is printed on the first electrode, and the Al paste is baked after printing to form a second electrode. Method.