WO1994000855A1

WO1994000855A1 - Positive characteristic thermistor and method of its manufacture

Info

Publication number: WO1994000855A1
Application number: PCT/JP1993/000808
Authority: WO
Inventors: Hiroshi Inagaki; Hiroshi Sasaki; Takuji Okumura; Masatoshi Tamura; Tadamasa Nishiyama
Original assignee: Kabushiki Kaisha Komatsu Seisakusho
Priority date: 1992-06-23
Filing date: 1993-06-16
Publication date: 1994-01-06
Also published as: JPH065403A

Abstract

A thermistor such that a short circuit failure due to Ag migration is prevented, the resistance can be precisely controlled, and its durability is high. A method of manufacturing highly reliably such a thermistor with a high productivity. This thermistor is provided with a thermistor main body (11) made of a semiconductor having a positive temperature coefficient of resistance, and first electrodes (12a and 12b) or second electrodes (13a and 13b) formed by Al printing using a material containing Al as its main component. Also, on the top face and bottom face of the thermistor main body (11), an Al paste containing Al as its main component is printed, and then, the paste is burned to form the first electrodes (12a and 12b) or the second electrodes (13a and 13b).

Description

Description Positive characteristic thermistor and method of manufacturing the same Technical field

The present invention relates to a positive temperature coefficient thermistor and a method of manufacturing the same, and more particularly, to a structure of the electrode and a method of forming the electrode. Background technology

B a T i 0 ₃ to Y, from the N d 0. 1~ 0. 3 atom% etc. (hereinafter referred to as at%) oxide semiconductor to which added pressure and this has a large positive temperature coefficient, PT C Sa It is called a positive temperature coefficient (Positive Temperature Coefficient Thermistor). The PTC thermistor can adjust the area with a large positive temperature coefficient by adding Sr, Pb, etc. to measure the temperature, prevent overcurrent, start the motor, turn off the color TV. It is indispensable in a wide range of fields such as surface elements for magnets and low-temperature heaters.

As shown in Fig. 3, such a PTC thermistor sinters oxides, carbonates, nitrates, or chlorides of metals such as Ba, Ti, d, etc. to form a thin circle. A pillar-shaped thermistor body 21, first electrode layers 22 a and 22 b composed of Ni-mec layers formed on the upper and lower surfaces thereof, and formed on these upper layers The second electrode layers 23 a and 23 b mainly composed of Ag are provided.

By the way, the PTC thermistor is usually used by applying a voltage between the second electrode layers 23a and 23b. At this time, the Ag in the second electrode layer is moved in the direction of the electric field. So-called migration phenomenon (hereinafter referred to as migration) occurs. In particular, when the outer peripheral edge of the second electrode layers 23a and 23b is configured to reach the outer peripheral end of the thermistor main body 21, the electric field is generated at the outer peripheral end of the thermistor main body 21. There is a problem that Ag precipitates and migrates in the direction, eventually causing a short circuit. this Therefore, as shown in FIG. 3, the outer diameter (W) of the second electrode layers 23a and 23b is formed smaller than the outer diameter (V) of the first electrode layers 22a and 22b. PTC thermistors have been proposed.

However, in this structure, the outer diameter of the second electrode layers 23a and 23b is smaller than the outer diameter of the first electrode layers 22a and 22b. There is a problem that the portions of a and 22b directly exposed to the atmosphere are easily oxidized, and the contact resistance gradually increases. Also, the migration of Ag is a phenomenon that moves along the direction of the electric field, and although a little, Ag diffuses through the first electrode layers 2a and 22b. The problem of short-circuiting is mitigated but cannot be completely prevented. In a conventional PTC thermistor, electrodes are formed by using a Ni plating method. When performing this Ni plating, the plating solution may penetrate into the sintered body and change the characteristics of the sintered body, such as a decrease in the resistance value. This characteristic change may appear immediately after the electrode is formed, or may gradually appear over time. By the way, the applications of PTC thermistors are those that require high-precision resistance value control such as temperature measurement and control, as described above, and R ± or% (where R = 3 to 30, or- 10, 20, 30%). Therefore, the problem of resistance change due to penetration of the plating solution has become more serious.

In order to avoid such penetration of the plating solution, a method has been proposed in which a low-melting-point metal layer such as A1 is formed by a metal spraying method and used as an electrode. However, this method also involves a rapid temperature change at the time of electrode formation, so that the problem that cracks occur in the thermistor body or the electrode itself cannot be avoided.

In order to solve such a problem, the present inventors, as shown in FIG.

2a, 32b and the second electrode 33a, 33b are overlapped at the same position inside the outer peripheral end of the thermistor body 31 and at the same position (Japanese Patent Laid-Open No. Hei 4- See 1 189 01).

However, even with the PTC thermistor thus proposed, the second electrode 33a,

3 Because Ag is used as 3b, migration of Ag when an electric field is applied Moves along the direction of the electric field, and although a little, Ag diffuses. Thus, the problem of short circuits is mitigated but cannot be completely prevented. Disclosure of the invention

The present invention focuses on such conventional problems, and can prevent a short-circuit accident due to migration of Ag, and can control high-precision resistance value control with little change with time of the initial resistance value and large inrush power. To provide a positive temperature coefficient thermistor with high durability, since it has a high withstand voltage and no cracks or cracks, and to provide a method of manufacturing with high reliability and high productivity. And for the purpose.

In a thermistor composed of a thermistor main body and an electrode, the first aspect of the present invention is a thermistor main body composed of a semiconductor having a positive characteristic and a first electrode formed by A1 printing mainly composed of A1. Or the second electrode. The second aspect of the present invention is to provide a thermistor body made of a semiconductor having a positive characteristic, and an electron beam evaporation of one of A 1, Ni, Cu, Cr, Ti or an alloy thereof. (Hereinafter, referred to as EB deposition). According to a third aspect of the present invention, there is provided a method for manufacturing a thermistor from a thermistor main body and an electrode, the second electrode being formed by A1 printing containing A1 as a main component in addition to the above-described configuration. A fourth aspect of the present invention is to print an AI paste containing A1 as a main component on the upper and lower surfaces of a thermistor body made of a semiconductor having a positive characteristic, and then sinter the A1 paste to form a second paste. The first electrode or the second electrode is formed. A fifth aspect of the present invention is to provide any one of Al, Ni, Cυ, Cr, Ti or an alloy thereof on the upper and lower surfaces of a thermistor body made of a semiconductor having positive characteristics. The first electrode is formed by EB evaporation. In a sixth aspect of the present invention, in addition to the above method, an A paste containing A 1 as a main component is printed, and after printing, the A paste is baked to form a second electrode.

The present inventors have confirmed that in a PTC thermistor provided with an electrode made of A1, no migration occurs even when a voltage is applied. Therefore, in the present invention, A] is used for the first electrode or the second electrode to prevent a short circuit accident of the positive temperature coefficient thermistor. In addition, since the first electrode or the second electrode uses AI printing or an EB vapor-deposited film, the thermistor body does not crack or crack, so that the durability is improved more than five times. Furthermore, since the initial resistance value does not change with time, high-precision resistance value control is possible. In particular, the electrode structure in which A 1 is printed on the A 1 EB deposited film has a high withstand voltage against a large inrush power. Therefore, by using the first electrode when the applied voltage is low, and further using the second electrode when the applied voltage is high, migration can be completely prevented and a highly durable positive characteristic thermistor can be obtained. You can get a star.

In addition, since the first electrode is formed so as to be located at the same position as the outer periphery of the second electrode, oxidation of the first electrode can be prevented. Further, the first electrode or the second electrode having good adhesion and low contact resistance can be formed by printing A 1 or employing the EB vapor deposition method. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an overall configuration diagram showing an embodiment of a positive temperature coefficient thermistor of the present invention, FIGS. 2A, 2B, and 2A are diagrams showing a manufacturing process of the positive temperature coefficient thermistor of the present invention, and FIG. FIG. 4 is a diagram showing the appearance of a conventional PTC thermistor element, and FIG. 4 is a view showing the appearance of another conventional PTC thermistor element. BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of a positive temperature coefficient thermistor according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is an overall configuration diagram of a positive characteristic thermostat showing an example of a case where the device is used when an applied electric field is high. This positive temperature coefficient thermistor is composed of a first thermistor body 11 mainly composed of barium titanate, and a first body in which Ni, Cu, or A1 is formed on the upper and lower surfaces by EB evaporation. Electrodes 1 2a, 1 2b and A on the first electrode The second electrodes 13 a and 13 b each having 1 as a main component.

2A to 2C are process diagrams showing the steps of manufacturing the thermistor according to the embodiment of the present invention. First, as shown in FIG. 2 A, and mixed _{T i 0 2, B a C} 0 3, N d ζ 0 3, the powder at the rate of Jo Tokoro was pressed into disks shape by cooling press method Thereafter, sintering is performed at 130 tons to form a disk-shaped thermistor body 11 having a diameter of .47 mm.

Then, the surface roughness of the upper surface and lower surface (electrode formation surface) of the thermistor body 11 is measured using a surface roughness meter. When the surface roughness is 6.3 to 1.6 s (JIS standard triangle symbol ▽▽▽) and when the surface roughness is 0.8 s (JIS standard triangle symbol ▽▽▽▽) It is divided into the above cases.

Next, as shown in FIG. 2B, a first electrode 12 a composed of a thin film of Ni, Cu, or A] having a thickness of 0.1 to 10 m is formed on the upper and lower surfaces by EB vapor deposition. , Forming 1 2b. In this embodiment, the film formation conditions: 1 5 0 'C, vacuum ^{degree: 5 x 1 0- 4 t 0} rr, film thickness: was carried out at 5 0 0 0 A.

At this time, vapor deposition is performed through a metal mask so that Ni, Cu, or A1 is not formed on the end face 11a of the main body 11. Here, the film forming conditions may be as follows.

'' When the surface roughness is 6.3 to 1.6 s:

^{_{Vacuum: 1 X 1 0 4 t 0}} rr~ 1 X 1 0 6 t 0 rr

Film formation conditions: room temperature to 250 ° C

-When the surface roughness is 0.8 s or more:

Degree of ^{vacuum: 5> 1 0 - 4 torr~l} X l O- 6 torr

Film formation conditions: 100 to 250'C

Next, as shown in FIG. 2C, a second electrode 13a containing A1 as a main component (A1 contains about 50% by volume ratio) is formed on the upper layer of the first electrodes 12a and 12b. > 1 3b. For this purpose, an A1 paste mainly composed of A1 is printed. Then, drying and baking were performed after printing _{c. In} this example, the film thickness was 10 m, and the drying was baking at 12 O'C for 5 minutes. Formation temperature: The temperature was raised to 640 in 30 minutes, kept at 640 ° C for 5 minutes, and then carried out by natural cooling. In this step, the following should be performed.

• Printing thickness of A1 paste: 0. lum to 10 / m

• Firing temperature: 600 to 75 ° C. Next, the results of comparative tests between the present embodiment and the conventional example will be described.

(1) Comparison test result 1

In the manufacturing method, Ni, or Cu, or a first electrode 12 a, 12 b formed of a thin film made of A 1 and second electrodes 13 a, 13 mainly composed of A 1 1 (N0.1-3) and the combination of the first electrodes 22a, 22b of the conventional Ni and the second electrodes 23a, 23a of Ag Seven types (N 0.4) shall be created for each. First, the resistance (Ω cm) of the thin film after EB deposition was measured for each of seven positive characteristic thermistors of No. 1 to 4. Table 1 shows the obtained results. table 1

N 0 electrode E B Resistance after deposition

! —— i i

E B evaporation (Ω cm)

(First)

1 A 1 18.6 16.4 16.3 18.5 17. 8 16.8 16.6!

2 Ni 18.5 17.8 15.6 18.0 17.4 16.9 18.3

3 Cu 17.6 17.8 14.2 19.8 17.6 17.5 16.5

4 16.9 18.7 17.7 17.4 17. 2 17. 9 17.0

The resistance values after the EB deposition were all the same as the conventional No. 4. (2) Comparison test result 2

The resistance value (Ωcm) after firing the paste was measured for each of seven positive characteristic thermistors with No. 1 to 4. Table 2 shows the obtained results. Table 2

Except for the resistance value of the paste after firing, the positive temperature coefficient thermistors No. 1 and No. 2 showed good results equivalent to the conventional N 0.

(3) Comparison test result 3

Inrush current value (A pp) Ampere peak for each of 7 positive characteristic thermistors N 0.1 to 4 by the measurement circuit (voltage: 220 V rms, frequency: 50 Hz, resistance: 12 Ω) The to peak was measured and was as follows.

In the case of A 1 — A 1 of No. 1, the minimum value is 22.3 to the maximum value of 24.8, and in the case of Ni of A No. 2 — A 1, the minimum value is 2. 0 to the maximum value 23.7, and the Cu of No. 3 is the minimum value for AI 18.5 to the maximum value 20.8, and the Ni of the No. 4 is Ni—Ag In the case, the minimum value was 22.1 to the maximum value 23.0. From this result, it can be seen that a high inrush current value was obtained in the case of A 1 —A I of No. 1.

() Comparison test result 4

For the positive temperature coefficient thermistor, the voltage value (V) was varied and the current value (ιηΑ) was measured. Table 3 shows the obtained results. Table 3

No. 1 to 3 can obtain the current displacement point (3.30 mA, 3.32 mA, 3.44 mA) at a voltage of 450 V to 500 V, and all of them have the same values as the conventional No. 4 (3.15 mA). It can be seen that almost the same performance was obtained.

(5) Comparison test result 5

The intensity was compared with the current. As a result, in the case of A 1 —A 1 of No. 1, the current value became 20 A to 3 O A, and the thermistor body 11 was broken. On the other hand, in the case of Ni-Ag of No. 4, the thermistor body 22 was broken at a current value of 10 A. From this result, it can be seen that the positive characteristic thermistor strength of Al — A 1 of No, 1 is high.

(6) Comparison test result 6

A confirmation test was performed by an intermittent energization test of the migration. As a test method, an operation of applying a voltage of 220 V for one minute and then spraying water for five minutes was defined as one cycle, and this operation was repeated to confirm the number of cycles at which migration occurred. As a result, in the case of A 1 —A 1 of No, 1, no short circuit occurred even in 1000 cycles. On the other hand, in the case of Ni, Ag of No, 4, a short circuit occurred in 100000 to 2000 cycles. From these results, it can be seen that the positive characteristic thermistor of A 1 —A 1 of N 0,1 can prevent short circuit accident. In the present embodiment, the first electrodes 12a, 12b or the second electrodes 13a, 13b are fully covered up to the end surface of the thermistor body 11, but the first electrodes 12a, The 12b or the second electrodes 13a and 13b may be located inside the outer peripheral end of the thermistor body 11 and the outer circumferences thereof may be aligned and coated at the same position. In addition, the first electrodes 12a and 12b or the second electrodes 13a and 13b may be coated inside the outer peripheral end of the thermistor body 11 and by shifting their outer peripheral edges. it can. In addition, although the examples of Al, Ni, Cu, as the first electrodes 12a, 12b are shown, Cr, Ti, which can be EB deposited and have good compatibility with A1, are shown. Can also be used.

Industrial applicability

The present invention can prevent short-circuit accidents due to migration of Ag, minimize changes in the initial resistance with time, and achieve high-precision resistance control and high withstand voltage against large inrush power. In addition, it is useful as a highly durable positive temperature coefficient thermistor. In addition, an electrode having high adhesion and low contact resistance can be formed, which is useful as a method for manufacturing a PTC thermistor with high productivity. '

Claims

The scope of the claims

1. A thermistor consisting of a thermistor body and electrodes; a thermistor body made of a semiconductor having positive characteristics; and a first electrode or a first electrode formed by A1 printing mainly composed of A1. Positive characteristic thermistor characterized by comprising two electrodes.

2. In the thermistor consisting of the thermistor body and the electrodes, the thermistor body consisting of a semiconductor having positive characteristics and the electron of one of A, i, Cu, Cr, Ti or an alloy of these. A positive characteristic thermistor comprising a first electrode formed by a beam-deposited thin film.

3. The positive temperature coefficient thermistor comprises the thermistor main body, the first electrode, and a second electrode formed by A1 printing with A1 as a main component. PTC thermistor according to range 2.

4. In the method of manufacturing a thermistor from a thermistor body and electrodes, an A A paste containing A 1 as a main component is printed on the upper and lower surfaces of a thermistor body made of a semiconductor having positive characteristics. Thereafter, the A1 paste is fired to form the first electrode or the second electrode, and a method for manufacturing a positive temperature coefficient thermistor.

5. In the method of manufacturing a thermistor from the thermistor body and the electrode, any one of A 1, Ni, Cu, Cr, and Ti is placed on the upper and lower surfaces of the thermistor body made of a semiconductor having positive characteristics. A method for manufacturing a positive characteristic thermistor, comprising forming one or more of these alloys by electron beam evaporation to form a first electrode.

6. The method of manufacturing the positive temperature coefficient thermistor includes printing an A1 paste containing A1 as a main component on the upper and lower surfaces of the first electrode formed on the thermistor body, and printing the A1 paste after the printing. 6. The method for manufacturing a positive temperature coefficient thermistor according to claim 5, wherein the paste is baked to form the second electrode.