JP2001057282A - Surface mounting-type surge absorbing element and manufacture of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a surface mounting-type surge absorbing element having small electrostatic capacity without requiring complex processes by forming internal electrode layers respectively conducted to external electrodes at both ends with difference in level, inside of an insulating ceramic layer, forming a discharging space as a cavity part in a part between the internal electrode layers, and forming the inside of the discharging space into a hollowed gourd shape. SOLUTION: A pair of internal electrode layers 3 conducted to external electrodes at both ends with difference in level, are formed inside of an insulating ceramic layer 2 having a pair of external electrodes 1 at both ends, a discharging space 4 is partially formed between the internal electrode layers 3, the inside of the discharging space 4 has the shape of a hollowed gourd, and an insulating layer between the internal electrode layers 3 has at least a multilayer structure of at least three layers. By applying this constitution, the discharging is generated by the dielectric breakdown generated in the atmosphere in the discharging space when the excess voltage is applied between the internal electrodes, and the surge voltage is absorbed thereby.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surge absorbing element for protecting electronic circuits and electronic components from surges and a method of manufacturing the same, and more particularly to a surface mount type surge absorbing element which is advantageous for automatic mounting on a printed circuit board. The present invention relates to an element and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as a surge absorbing element for protecting a communication device from a surge, a varistor composed of a high-resistance element having a voltage non-linear characteristic and a discharge type surge absorbing element in which a discharge space is sealed in an airtight container are known. Widely used.

[0003] The conventional varistor has an advantage that it has excellent responsiveness of surge absorption and that it is easy to reduce the size of an element and to adopt a structure corresponding to a surface mount component, but it has an advantage that the capacitance is low. It has the disadvantage of being large and difficult to use in signal-related circuits.

[0004] Further, the conventional discharge-type surge absorbing element is widely used in signal-related circuits because of its small capacitance. However, in order to make the micro gap an airtight structure, the lead wire is drawn out by encapsulating glass.When mounting on a printed circuit board, it is necessary to cut and bend the lead wire to an appropriate length. Become. Thereafter, a lead wire is inserted into a hole in the printed circuit board and soldered. Mounting the discharge type surge absorbing element on such a printed circuit board is a time-consuming method, and many electronic components have been switched to surface-mounted electronic components.

[0005]

However, the above-mentioned conventional surface mount type surge absorbing element has the following disadvantages. In other words, in order to keep the micro gap airtight, evacuation and sealing of the cap, or a step of forming an insulating film on the micro gap so that the cap and the micro gap are not short-circuited, the number of steps is increased and productivity is not reduced. There was a problem.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a surface mount type surge absorbing element having a small capacitance and requiring no complicated manufacturing steps, and a method of manufacturing the same. is there.

[0007]

According to the present invention, there is provided an insulating ceramic layer having a pair of external electrodes at both ends, and an internal electrode layer electrically connected to the external electrodes at both ends so as to be stepped, respectively, inside the insulating ceramic layer. The surface-mounted surge absorbing element has a discharge space formed of a cavity in a part between the internal electrode layers, and the inside of the discharge space has a concave shape.

Further, the present invention is the above-mentioned surface-mounted surge absorbing element, wherein the insulating layer between the internal electrode layers has a multilayer structure of three or more layers.

With this configuration, when an excessive voltage is applied between the internal electrodes, the atmosphere in the discharge space causes dielectric breakdown and discharge occurs, so that the surge voltage can be absorbed.

[0010] In addition, when no depression is formed inside the discharge space of the insulating layer, creeping discharge is likely to occur along the surface of the insulating layer, and the electrode material is sputtered on the surface of the insulating layer. In the structure of the insulating layer according to the present invention, such a short circuit does not easily occur, and the durability against repeated discharge can be improved. Further, the discharge starting voltage can be adjusted by the gap length between the internal electrodes. Since the capacitance of the surge absorbing element according to the present invention is determined by the area of the opposing portion of the internal electrode, it is possible to reduce the capacitance according to the application.

Further, the present invention provides the above surface mount type surge absorbing element, wherein the insulating ceramic layer is formed by a printing method or a green sheet method, the internal electrode layer is formed by a printing method, and the discharge space is formed by shearing. This is a method for manufacturing a surface-mounted surge absorbing element formed, and each sheet is thermocompressed and then integrally sintered.

Such a manufacturing method is excellent in mass productivity, and the external dimensions, the electrode area and the interval, and the number of layers can be appropriately selected according to the desired electric characteristics. As the insulating ceramic layer, ceramic materials having a high specific volume resistivity such as alumina, mullite, steatite, forsteatite, cordierite, glass, titania, and zirconia can be used alone or in combination. You can select it.

For the internal electrode layer, a material having excellent conductivity such as a low resistance metal such as copper, silver, aluminum and nickel, an alloy material such as stainless steel and copearl, and carbon can be used. In addition, SnO ₂ , Nb
₂ O ₅ , MoO ₃ , WO ₃ , TiC, SiC, ZrC,
WC, HfC, VC, TiN, TaN, VN, ZrN,
Conductive ceramic materials such as oxides such as NbN, carbides, and nitrides can also be used. When these conductive ceramics are used, deterioration of the electrodes due to melting and oxidation during gas discharge can be suppressed. These electrode materials may be used alone or in combination of a metal material and a ceramic material, or may be used in combination.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a surface mount type surge absorbing element according to a first embodiment of the present invention. FIG. 1 (a)
As shown in FIG. 1B, a cross section taken along the line AA in FIG. 1A, the surge absorbing element according to the present invention has two ends inside an insulating ceramic layer 2 having a pair of external electrodes 1 at both ends. Has a pair of internal electrode layers 3 electrically connected to each other so as to be different from each other, and a portion between the internal electrode layers 3 is formed of a discharge space 4, and the inside of the discharge space 4 has a concave punch shape. And the insulating layer between the internal electrode layers 3 has a multilayer structure of three or more layers.

As shown in FIGS. 1 (c) and 1 (d), the insulating layer between the internal electrode layers 3 is composed of three or more layers. The discharge space portion diameter 5 of the layer not in contact with the internal electrode layer 3 is made smaller than the discharge space portion diameter 6 of the layer in contact with the internal electrode layer 3, and the layer not in contact with the internal electrode layer 3 is composed of at least one layer. As a result, the discharge space 4 has a punch shape in which the inside is depressed.

FIG. 2 is an explanatory diagram of a method of manufacturing a surface mount type surge absorbing element according to a second embodiment of the present invention.

First, a binder comprising a steatite powder having an average particle size of about 3 μm and a borosilicate glass powder in a ratio shown in Table 1 was prepared.
After mixing with a solvent, a paste for an insulating layer was prepared using a bead mill.

[0019]

[Table 1]

Next, 70 parts by weight of silver-30 parts by weight of palladium alloy powder having an average particle diameter of about 0.3 μm are mixed with a binder and a solvent in the ratio shown in Table 2, and the mixture is mixed with a bead mill to prepare a paste for an internal electrode layer. did.

[0021]

[Table 2]

As shown in FIG. 2A, these are screen-printed on the substrate 8 with the insulating ceramic layer 2,
As shown in FIGS. 2A and 2B, an insulating ceramic sheet provided with the discharge space 4 was formed by punching. In FIG. 2B, the discharge space diameter 6 was 700 μm, and the inner diameter 5 of the discharge space was 300 μm.

After laminating these sheets to form a laminate as shown in FIG. 2D, the laminate was thermocompression-bonded at 110.degree.
Thus, the sample No.
Samples 1 to 3 were integrally sintered in the atmosphere at 1000 ° C. for 5 hours.

Finally, a silver paste containing glass was applied as an external electrode, and sintered at 600 ° C. for 30 minutes to obtain a surge absorbing element capable of surface mounting.

For these surge absorbing elements, 500
Static electricity of pF-500Ω-10 kV was repeatedly applied, and the discharge starting voltage and its variation were examined. In addition, in the repeated discharge, a point where the variation of the discharge start voltage becomes ± 30% or more of the reference discharge start voltage is defined as the cycle life. Table 3 shows the results.

[0026]

[Table 3]

In each of the devices, the variation of the firing voltage was within ± 22% after 2,000 repeated discharges. The insulation resistance was 10 ¹⁰ Ω or more, and the capacitance was 0.7 pF or less.

From the above results, the gap length of the internal electrode,
By controlling the atmosphere in the discharge space, it has become possible to obtain a surface mount type surge absorbing element having a desired discharge starting voltage and a small capacitance.

Table 4 shows a comparison between the conventionally used surge absorbing element and the present invention.

[0030]

[Table 4]

From Table 4, it can be seen that the surface-mount type surge absorbing element according to the present invention has the same low capacitance as that of the conventional discharge-type surge absorbing element, and has a structure that allows easy surface mounting. It turns out that it is a thing.

It should be noted that the product of the present invention is not limited to the above-described embodiment, and that other insulating ceramic materials or conductive materials can be used as the insulating material and the electrode material. It can be easily analogized.
Similarly, the conditions for producing the paste for printing, applying other methods, and the conditions for producing the laminate, such as the thickness of the printed laminate, the thickness of the electrode layer, and the dimensions of each part, and the sintering conditions are described in this book. The fact that conditions other than the embodiment of the invention may be used can be easily estimated by those skilled in the art.

[0033]

As described above, according to the present invention,
Since a technology with high mass productivity such as a conventional screen printing technology is used, it is possible to provide a surface mount type surge absorbing element which is easy to manufacture, has low capacitance, and has excellent surge absorbing characteristics.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structure of a surface mount type surge absorbing element according to a first embodiment of the present invention. FIG. 1A is a longitudinal sectional view of a surface mount type surge absorbing element. FIG.
FIG. 2 is a cross-sectional view of AA shown in FIG. FIG.
FIG. 3 is a cross-sectional view taken along line BB shown in FIG. FIG.
FIG. 3 is a cross-sectional view taken along the line CC shown in FIG.

FIG. 2 is an explanatory diagram of a method for manufacturing a surface mount type surge absorbing element of the present invention. FIG. 2A is an explanatory diagram of a method for forming an insulating ceramic layer and an internal electrode layer. FIG. 2B is a diagram illustrating a method of forming an insulating ceramic layer inside a discharge space in contact with an internal electrode. FIG. 2C is an explanatory diagram of a method for forming an insulating ceramic layer that is not in contact with an internal electrode. FIG. 2 (d)
Configuration diagram after thermocompression bonding.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 External electrode 2 Insulating ceramic layer 3 Internal electrode layer 4 Discharge space 5 Discharge space part diameter (of the layer not in contact with the internal electrode) 6 Discharge space part diameter (of the layer in contact with the internal electrode) 7 Gap length 8 Substrate

Claims (3)

[Claims] 1. An insulating ceramic layer having a pair of external electrodes at both ends has an internal electrode layer electrically connected to the external electrodes at both ends so as to be different from each other, and further includes a part between the internal electrode layers. Is a surface-mount type surge absorbing element, characterized by having a discharge space consisting of a cavity, wherein the inside of the discharge space is formed in a concave punch shape. 2. The surface mount type surge absorbing element according to claim 1, wherein the insulating layer between the internal electrode layers has a multilayer structure of three or more layers. 3. The surface-mount type surge absorbing element according to claim 1, wherein the insulating ceramic layer is formed by a printing method or a green sheet method, the internal electrode layer is formed by a printing method, and the discharge space is sheared. Formed by
A method for manufacturing a surface mount type surge absorbing element, wherein each sheet is thermally sintered and integrally sintered.