JPH10270145A - Discharge gap element and surge protection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge gap element having small dispersion in discharge start voltage by stacking and sintering an insulator and an internal electrode to be integral and cutting these to use a sectional inter-electrode as a gap. SOLUTION: An insulator sheet (a base insulator 11, an insulator 13 and a cover insulator 15) and internal electrodes 12 and 14 are stacked together, these are cut after being sintered to be made integral, and a sectional inter- electrode is used as a gap to manufacture a discharge gap element 1. Alumina ceramic 7 is used for an insulator sheet, its thickness is set to 7 to 100 μm approx., preferably 10 to 50 μm approx., and for the internal electrodes 12 and 14, conductive ceramics (molybdenum silicide or a mixture of molybdenum silicide and alumina ceramics) is preferred. By incorporating this discharge gap element in a surge protection device, a surge protection device having high durability and no short-circuit breakdown is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surge protection device which absorbs an abnormal voltage which invades electronic equipment and causes destruction or malfunction of the equipment. For more information,
The present invention relates to a structure of a gap element that absorbs an abnormal voltage by discharging in a surge protection device used for an input / output unit connected to the outside such as a power supply circuit, a communication or a signal line.

[0002]

2. Description of the Related Art In recent years, electronic devices have rapidly become intelligent, a large number of semiconductor components have been used, and malfunctions and destructions due to surge voltages have increased. This is because there is little margin for overvoltage of the semiconductor component. In particular, since a lightning surge intrudes from a distribution line of a commercial power supply, a telephone line, or the like with a certain probability, it is increasingly necessary to use a surge protection device to absorb the surge voltage.

[0003] Surge protection devices are roughly classified into three types: a discharge gap element, a silicon semiconductor element, and a zinc oxide varistor, and a composite type combining them.

[0004] Silicon semiconductor devices and zinc oxide varistors have small variations in the discharge starting voltage and are easy to design the protection voltage level of equipment. However, their application range is limited due to their small surge resistance.

On the other hand, the discharge gap element has a small capacitance and a large surge current resistance, but has a drawback that the surge response is poor. A microgap discharge gap element (Japanese Patent Application Laid-Open No.
28283). As shown in FIG. 5, the microgap discharge gap element is formed by uniformly providing narrow stripes using a laser beam on a conductive ceramic film formed on an insulator surface.
The micro-gap discharge starts when electrons are emitted by a high electric field applied between gap electrodes at intervals of several tens of μm. For this reason, the surge can be more stably absorbed at a higher speed as the gap interval is reduced. As a result of this improvement, a surge protection device having excellent surge responsiveness while maintaining the advantages of the related art is obtained.

[0006]

However, as described above, the conventional microgap discharge gap element obtains the microgap by cutting the conductive thin film formed on the insulator surface. Therefore, it was difficult to stabilize the firing voltage. In addition, the variation in the discharge starting voltage has also caused a rise in manufacturing cost.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a discharge gap element having a small variation in a discharge starting voltage and a surge protection device incorporating the same.

[0008]

The above object is achieved by the following (1) to (4).
This is achieved by the present invention of (7).

(1) A discharge gap element in which an insulator and an internal electrode are laminated, and a gap is formed between the electrodes of a section obtained by cutting the insulator and the internal electrode.

(2) The discharge gap element according to (1), wherein the insulator and the internal electrode are laminated and fired integrally.

(3) The discharge gap element according to (1) or (2), wherein the gap interval is in the range of 7 to 100 μm.

(4) The discharge gap element according to (1), wherein the insulator is an alumina ceramic.

(5) The discharge gap element according to (1) or (2), wherein the internal electrode is made of molybdenum silicide or a mixture of molybdenum silicide and alumina ceramic.

(6) A surge protection device including the discharge gap element according to any one of (1) to (5).

(7) The surge protection device according to (6), wherein the discharge gap element is sealed with an inert gas.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A microgap discharge gap element according to the present invention is one in which an insulator and an internal electrode are laminated, and a microgap is formed between the electrodes in a cut cross section. According to this configuration, since the microgap interval is determined by the thickness of the insulator sheet, the accuracy of the electrode interval is significantly improved as compared with the related art. Further, it is possible to obtain a narrow gap which cannot be obtained by the conventional method using thin film cutting.

In the present invention, any structure may be used as long as it has a structure in which an insulator and an internal electrode are laminated, and various methods are employed for its manufacture. For example, it is manufactured by a method in which an insulator such as resin or glass and a metal foil are laminated and bonded, or a method in which a thermosetting resin and a metal paste are laminated and heat-treated to cure the resin. Alternatively, a method of laminating a ceramic insulator and an internal electrode and firing them integrally may be used.
In addition, since an element having excellent durability can be obtained by integral sintering, it is preferable to manufacture by this method. In any case, the electrode is finally cut into a predetermined size, and the terminal electrodes are formed by baking or the like, thereby forming a microgap discharge gap element. By cutting the cross section, an electrode having a stable surface state can be obtained. As a result, a micro-gap discharge gap element having a small variation in the discharge starting voltage can be obtained.

Although a microgap suitable for the purpose can be obtained by changing the thickness of the insulator sheet, the thickness of the insulator sheet is usually 7 to 100 μm. The reason is as follows. This is because when the thickness exceeds 100 μm, the variation in discharge increases, and is preferably 50 μm or less. If it is less than 7μ, the electrode interval becomes too narrow,
Short circuit breakdown is likely to occur. In consideration of workability during lamination, the thickness is preferably 10 μm or more.

As described above, by laminating and integrally firing the ceramic insulator and the internal electrode, a discharge gap element having excellent durability can be obtained. At this time, an alumina-based ceramic is used as the insulator. Either a metal conductor or a conductive ceramic may be used as the internal electrode.

However, when a metal conductor is used as an internal electrode, migration of a metal may occur during the use of the element, and short-circuit breakdown may occur. Therefore, it is preferable to use a conductive ceramic. As the conductive ceramic, molybdenum silicide or a mixture of molybdenum silicide and alumina-based ceramic is used.
By using such a conductive ceramic internal electrode, a surge protection device having high durability and not causing short-circuit breakdown can be obtained. Further, it is easy to use an electrode having a larger thickness than a conductive thin film on the surface of an insulator constituting a conventional microgap discharge gap element, and it is possible to further improve the durability.

Further, by laminating a plurality of ceramic insulating layers and internal electrode layers, the effective electrode length can be increased, and the durability can be further improved.

The microgap element of the present invention is made into a surge protection device by glass sealing in a ceramic package. At this time, the discharge starting voltage can be reduced by sealing with an inert gas such as Ar, Ne, or N2.

[0023]

Embodiments will be described below.

Alumina is used as an insulator, and a mixture of molybdenum silicide and alumina is used as an internal electrode (volume ratio: Mo).
(Si ₂ / Ai ₂ O ₃ = 80/20) was used. For each, a methacrylic binder was added as a binder, and toluene was added as a solvent, and mixed with a ball mill for 24 hours to prepare a slurry. Using these, a sheet was prepared by a doctor blade method and laminated in a mold so as to have a layer structure shown in FIG. The thickness of the sheet was 200 μm for the base insulator 11 (about 170 μm after firing),
2:40 μm (about 35 μm after firing), insulator 13:40
μm (about 35 μm after firing), internal electrode 14: 40 μm
(Approximately 35 μm after firing), cover insulator 15: 200 μm
(About 170 μm after firing).

The molded body thus obtained is heated to 350 ° C. at a rate of 1 ° C./min in a nitrogen gas atmosphere.
Hold at this temperature for 5 hours, and then at a heating rate of 5 ° C./min.
After the temperature was raised to 00 ° C and kept at this temperature for 2 hours, 5 ° C
Per minute, and a binder removal treatment was performed. The molded body subjected to the binder removal treatment is subjected to heating at a rate of 5 ° C./min.
Raise the temperature to 50 ° C., hold at this temperature for 1 hour, and then
Baking was performed by cooling at a rate of 00 ° C./min. However, 8
Natural furnace cooling was performed at a temperature below 00 ° C. After firing, cutting was performed to obtain a gap formed between the internal electrodes. FIG. 2 shows a perspective view thereof. The dimensions after cutting were 10 mm in length and 1 mm in width. Note that a gap can be obtained by breaking instead of cutting. After cutting, the terminal electrode was coated with silver paste and baked at 800 ° C. to obtain a discharge gap element.

Further, a sample was obtained by sealing the discharge gap element obtained as described above with a glass in a ceramic package with dry air.

Next, a discharge gap element having a conventional structure was manufactured as a comparative example (FIG. 3). As the insulator 21, an alumina cylinder having a length of 10 mm and a diameter of 2 mm was used. As the conductive film 22, tin oxide was formed to a thickness of 2 μm by sputtering. This is cut with a laser and 25μm
The gap 23 of the degree was formed. Finally, cap electrode 2
4 and the lead wire 25 were attached to obtain a discharge gap element.

To measure the discharge starting voltage, a programmable power supply is connected to the measurement sample, and the output voltage is changed from 0V to 100V.
The discharge was started at a rising speed of / sec, the discharge started, and the voltage at the time when the current began to flow was read. FIG. 4 shows the variation of the firing voltage of the discharge gap elements of the present invention and the comparative example.

The durability was evaluated by 8/20 μsec.
c. The impulse current waveform was applied to the measurement sample, and the change in the firing voltage before and after the application was evaluated. FIG. 5 shows the durability of the discharge gap elements of the present invention and the comparative example.

FIGS. 4 and 5 show that the discharge gap element of the present invention has a small variation in the firing voltage and has improved durability.

[0031]

The microgap discharge gap element and the surge protection device of the present invention can improve the disadvantage that the variation of the firing voltage is large without losing the advantages of the conventional microgap discharge gap element. . Further, a highly durable element can be obtained.

[Brief description of the drawings]

FIG. 1 is a side view showing an example of a discharge gap element of the present invention.

FIG. 2 is a perspective view showing one example of a discharge gap element of the present invention.

FIG. 3 is a view showing a conventional discharge gap element.

FIG. 4 is a diagram showing a variation in a discharge starting voltage of the discharge gap elements of the present invention and a comparative example.

FIG. 5 is a diagram showing the durability of the discharge gap elements of the present invention and a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Discharge gap element 11 Base insulator 12, 14 Internal electrode 13 Insulator 15 Cover insulator 16 Terminal electrode

Claims (7)

[Claims] 1. A discharge gap element in which an insulator and an internal electrode are laminated, and a gap is formed between electrodes of a cross section obtained by cutting the laminated body. 2. The discharge gap element according to claim 1, wherein an insulator and an internal electrode are laminated and integrally fired. 3. The discharge gap element according to claim 1, wherein a gap interval is in a range of 7 to 100 μm. 4. The discharge gap element according to claim 1, wherein the insulator is an alumina-based ceramic. 5. The discharge gap element according to claim 1, wherein the internal electrode is made of molybdenum silicide or a mixture of molybdenum silicide and alumina-based ceramic. 6. A surge protection device incorporating the discharge gap element according to claim 1. 7. The surge protection device according to claim 6, wherein the discharge gap element is sealed with an inert gas.