JP2003257781A - Multilayer ceramic capacitor with discharge function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a small multilayer ceramic capacitor with discharge function exhibiting excellent surge absorption properties. <P>SOLUTION: In a multilayer element 2 formed by laying a plurality of ceramic layers, a plurality of inner electrodes 4a and 4b are arranged while sandwiching a ceramic layer. These inner electrodes 4a and 4b are faced each over a specified area so that a desired capacitance is attained. The inner electrodes 4a and 4b are extended up to the opposite side faces of the element 2 and the end parts thereof are conducting, respectively, to outer electrodes 5a and 5b formed on the side faces of the element 2. Between specified inner electrodes 4a and 4b arranged in the element 2 of such a structure, an air gap 6 having an area (w1×w2) smaller than the area (W1×W2) at the overlapping part of the inner electrodes 4a and 4b and a thickness h thinner than the thickness H between the inner electrodes 4a and 4b is provided. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention mainly relates to high breakdown voltage,
The present invention relates to a monolithic ceramic capacitor with a discharge function that is used around a power supply that requires surge absorption.

[0002]

2. Description of the Related Art A capacitor around a power supply is sometimes used in a power supply circuit for converting a relatively high commercial voltage into an arbitrary voltage by a transformer or the like. Such a circuit requires a medium-high voltage type capacitor that can withstand a high applied voltage.

Further, in a circuit around a power supply, generally, a circuit board on which electronic components are directly mounted is used, and a multilayer ceramic capacitor is widely used as a circuit board capacitor. .

A monolithic ceramic capacitor is constructed by providing external electrodes which are alternately connected to a plurality of internal electrodes on opposite side surfaces of an element body in which ceramic layers and internal electrode layers are alternately laminated. In order to reduce the size and increase the capacity of such a monolithic ceramic capacitor, there is a tendency that the thickness of the internal ceramic layer is reduced to form a multilayer.

[0005]

However, the conventional multilayer ceramic capacitors used in circuits around the power supply have the following problems to be solved.

In the circuit around the power supply, not only the voltage conversion from the commercial voltage but also the switching surge voltage generated when the power supply is turned on and off, or the lightning surge voltage generated by lightning strike or the like may be applied. When this surge voltage is applied to the monolithic ceramic capacitor, a surge current is generated between the internal electrodes, the ceramic layer is destroyed, the insulation resistance value is lowered, and the element itself is destroyed.

In particular, the conventional monolithic ceramic capacitor has a lower withstand voltage than a single plate capacitor having a relatively large gap between electrodes, and since it has a multi-layered thin film structure, the withstand voltage tends to be further lowered, resulting in a surge current. There is a high possibility that it will result in destruction.

Therefore, when used in a circuit around a power source, from the viewpoint of protecting the monolithic ceramic capacitor from a surge, a high withstand voltage capacitor is separately used to absorb the surge, or a surge absorber is also used. Was necessary. However, in each case, another element is required, and accordingly, the number of components mounted on the board increases and the component mounting area also increases.
Further, since these elements are connected by a circuit, there is a problem that transmission loss occurs between the connections.

An object of the present invention is to construct a small-sized monolithic ceramic capacitor having a discharge function, which is excellent in surge absorption.

[0010]

The present invention is characterized in that at least one of the ceramic layers between the internal electrodes of the monolithic ceramic capacitor is provided with a void for discharging a surge voltage.

When a surge voltage is received from the circuit to which the monolithic ceramic capacitor is connected, by providing a void that is thinner than the thickness of the ceramic layer and is smaller than the area where the internal electrodes face each other in at least one ceramic layer, It is characterized by discharging in a void.

Further, according to the present invention, by setting the thickness of the void so that the discharge voltage generated in the void becomes lower than the element breakdown voltage of the laminated ceramic capacitor, the breakdown voltage of the laminated ceramic capacitor is reached. It is characterized in that electric discharge is generated in the voids to prevent element destruction.

Further, according to the present invention, by setting the thickness of the air gap so that the discharge voltage generated in the air gap is lower than the creeping leak generation voltage generated in the outer surface of the element body, the creeping surface is formed on the outer surface of the element body. It is characterized by preventing a surge current generated between the internal electrodes via the external electrodes by causing discharge in the air gap at a voltage lower than that at which leakage occurs.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 1 shows the structure of a monolithic ceramic capacitor with a discharge function according to an embodiment of the present invention.
This will be described with reference to FIG. 1A is a plan sectional view of a monolithic ceramic capacitor with a discharge function, FIG. 1B is a side sectional view thereof, and FIG. 1C is an enlarged side sectional view of a void portion provided in a ceramic layer. In FIG. 1, 1 is a monolithic ceramic capacitor, 2 is a monolithic ceramic capacitor 1.
And 4a and 4b are internal electrodes arranged in the element body 2, 5a and 5b are external electrodes provided on opposite side surfaces of the element body 2, and 6 is a ceramic layer of the element body 2. It is a provided void.

As shown in FIG. 1, inside the element body 2 formed by laminating a plurality of ceramic layers, a plurality of internal electrodes 4a,
4b are arranged alternately with the ceramic layer sandwiched therebetween,
In order to obtain the desired capacitance, a predetermined area (W1 ×
W2) faces each other. The internal electrodes 4a and 4b are
The two sides of the element body 2 are formed, and the ends thereof are electrically connected to the external electrodes 5a and 5b formed on the side surfaces of the element body 2, respectively.

Predetermined internal electrodes 4a of such an element body 2,
4b, the area of the overlapping portion of the internal electrodes 4a and 4b (W1 ×
The internal electrode 4 has an area (w1 × w2) smaller than W2).
The thickness h is thinner than the thickness H of the ceramic layer between a and 4b.
The void 6 is provided.

With such a structure, the monolithic ceramic capacitor 1 having the void 6 at a predetermined position is formed.

Next, the operation of this laminated ceramic capacitor will be described.

The discharge voltage is proportional to the distance between the discharge electrodes according to Paschen's law. That is, the narrower the space between the electrodes, the lower the discharge voltage.

In the monolithic ceramic capacitor, internal electrodes 4a and 4b, which are electrically connected to the external electrodes 5a and 5b different from each other, are arranged inside each other so as to face each other at a very short distance. By providing the void 6 in the ceramic layer between the internal electrodes 4a and 4b, the discharge start voltage between the internal electrodes is lowered, and the internal electrodes 4a and 4b sandwiching the void 6 are used as discharge electrodes.
When a predetermined threshold voltage is applied, electric discharge occurs in the void portion 6. In this way, the function of the discharge element can be obtained.

On the other hand, since the voids 6 are not provided in all the facing areas between the internal electrodes 4a and 4b, but the voids 6 having a predetermined thickness are provided in a part of the area, the internal electrodes 4
There is a portion made of a ceramic layer between a and 4b, and the function as a capacitor can be obtained.

As described above, with a normal applied voltage, it functions as a monolithic ceramic capacitor, and when a surge voltage equal to or higher than a predetermined threshold voltage is applied, discharge is generated in the void portion and it functions as a discharge element. This makes it possible to construct a monolithic ceramic capacitor that is not destroyed even when a surge voltage such as a switching surge or a lightning surge is applied.

By controlling the thickness of the voids,
The discharge voltage (threshold voltage) can be adjusted. Also,
Design the thickness of the air gap and other ceramic layers to ensure discharge before the capacitor is destroyed by the surge. Preferably, the thicknesses (element thicknesses) of all the ceramic layers are made substantially equal. Further, the thickness of the air gap is designed in consideration of the external dimensions of the monolithic ceramic capacitor so that the electric discharge due to the air gap has a lower voltage than the electric discharge generated outside the monolithic ceramic capacitor.

Next, a method of manufacturing such a monolithic ceramic capacitor with a discharge function will be described with reference to FIG. FIG. 2 is an exploded perspective view of an element body forming the monolithic ceramic capacitor. In FIG. 2, 2 is an element body of a monolithic ceramic capacitor, 3, 3a, 3b and 3c are ceramic green sheets, 40a and 40b are internal electrode pastes, and 60 is a carbon paste.

Dielectric constant 30 whose main component is BaTiO ₃
At 00, a solvent, an organic binder, a dispersant, and a plasticizer are added to the B characteristic ceramic material powder to prepare a ceramic slurry, which is molded by a predetermined method to form ceramic green sheets 3, 3a, 3b, 3c. . Ag-Pd is formed on the surface of each of the ceramic green sheets 3a and 3b.
And Ni for the internal electrode paste 40a, 40
b is applied in a predetermined shape. Further, the carbon paste 60 is applied to a predetermined ceramic green sheet 3c in an area smaller than that of the internal electrode pastes 40a and 40b.

In this embodiment, the ceramic green sheet and the internal electrode paste are formed of the above-mentioned materials, but other materials may be used depending on the desired characteristics.

Next, the ceramic green sheets 3, 3
As shown in FIG. 2, pastes a and 3b for internal electrode paste 4
0a ceramic green sheet 3a formed on the surface
And the ceramic green sheet 3b having the internal electrode paste 40b formed on the surface thereof are laminated so as to sandwich the ceramic green sheet 3 having no surface formed thereon. Here, the predetermined ceramic green sheet 3
A ceramic green sheet 3c having a carbon paste 60 formed on its surface is sandwiched between a and the ceramic green sheet 3b.

Then, the ceramic green sheet 3 serving as an exterior is laminated so as to sandwich the plurality of ceramic green sheets 3, 3a, 3b, 3c laminated as described above.

These ceramic green sheets 3, 3
The element body 2 is formed by press-pressing the laminated body including a, 3b, and 3c to form a press-molded body, degreasing, and then firing.

The carbon paste 6 formed on the surface of the ceramic green sheet 3c by firing
0 burns and scatters to form voids in the carbon paste portion. By doing so, the thickness of the ceramic layer (element thickness) between the internal electrodes can be made substantially the same,
The discharge voltage can be reliably discharged in the voids without being undesirably discharged in the ceramic layer in which voids are not formed.

An external electrode is formed by applying an external electrode paste on the side surface of the element body in which the void is provided and exposing the internal electrode, baking it, and plating the surface.

In this way, a monolithic ceramic capacitor having a void inside can be formed.

Here, the area and thickness of the void are controlled by the amount and shape of the carbon paste formed on the ceramic green sheet.

As described above, it is possible to form a small-sized monolithic ceramic capacitor having a discharge function having a desired discharge characteristic and an excellent surge absorption characteristic.

According to this embodiment, since the periphery of the void formed in the ceramic layer is entirely surrounded by the ceramic, the space due to the void becomes constant and the discharge characteristics can be stabilized.

In this embodiment, the monolithic ceramic capacitor provided with one void inside is shown, but in order to obtain the effect of the present invention, at least one is required. As shown in FIG. A plurality of voids may be provided.

In the above embodiment, the ceramic layers between the internal electrodes have the same thickness, but they may have different thicknesses.

[0038]

According to the present invention, at least one ceramic layer is provided with a void smaller than the thickness of the ceramic layer and smaller than the area where the internal electrodes face each other. It is possible to discharge the received surge voltage in the air gap, and it is possible to form a small monolithic ceramic capacitor with a discharge function that is excellent in surge absorption characteristics.

Further, according to the present invention, by setting the thickness of the void so that the discharge voltage generated in the void becomes lower than the element breakdown voltage of the multilayer ceramic capacitor, the breakdown voltage of the multilayer ceramic capacitor is reached. In addition, it is possible to prevent the element from being destroyed by generating a discharge in the void.

Further, according to the present invention, by setting the thickness of the void so that the discharge voltage generated in the void is lower than the creeping leak occurrence voltage generated in the outer face of the element, It is possible to prevent a surge current generated between the internal electrodes via the external electrodes due to discharge occurring in the air gap at a voltage lower than the creeping leak.

Further, according to the present invention, by making the thicknesses of the respective ceramic layers between the internal electrodes substantially the same, the surge voltage can be surely discharged in the air gap.

[Brief description of drawings]

FIG. 1 is a plan sectional view, a side sectional view, and an enlarged side sectional view of a void portion provided in a ceramic layer of a monolithic ceramic capacitor with a discharge function.

FIG. 2 is an exploded perspective view of an element body forming a monolithic ceramic capacitor.

FIG. 3 is a plan sectional view of another structure of a laminated ceramic capacitor with a discharge function.

[Explanation of symbols]

1-multilayer ceramic capacitor 2-element 3, 3a, 3b, 3c-ceramic green sheet 4a, 4b-internal electrodes 5a, 5b-external electrodes 6-void 40a, 40b-Patterns for internal electrodes 60-carbon paste

Claims (5)

[Claims] 1. An element body is formed by alternately stacking a plurality of ceramic layers and internal electrodes, and external electrodes that are electrically connected to the plurality of internal electrodes are provided on opposite side surfaces of the element body. In the multilayer ceramic capacitor consisting of, the gap for discharging the surge voltage received between the internal electrodes,
A monolithic ceramic capacitor with a discharge function, which is provided in at least one of the ceramic layers between internal electrodes. 2. The laminated ceramic with a discharge function according to claim 1, wherein the void is formed to be thinner than a thickness of the ceramic layer and smaller than an area where the internal electrodes face each other. Capacitors. 3. The monolithic ceramic capacitor with a discharge function according to claim 1, wherein the thickness of the air gap is formed so that the discharge voltage generated in the air gap is lower than the element breakdown voltage of the monolithic ceramic capacitor. . 4. The discharge function according to claim 1, wherein the thickness of the gap is formed so that the discharge voltage generated in the gap is lower than the creeping leak generation voltage generated on the outer surface of the element body. Monolithic ceramic capacitor with. 5. The multilayer ceramic capacitor with a discharge function according to claim 1, wherein the ceramic layers between the internal electrodes have the same thickness.