JPH05275273A - Manufacture of multilayer ceramic electronic component - Google Patents

Abstract

PURPOSE:To eliminate occurrence of cracks and make the electric characteristics stable in a manufacture of a multilayer ceramic electronic component such as a multilayer ceramic capacitor which has a varistor function. CONSTITUTION:In a manufacture of a multilayer ceramic electronic component wherein a plurality of green sheets mainly comprised of ceramics and having an internal electrode printed on the surface thereof are laminated and cut to make green chips, a heat treatment is applied under reduced pressure to the chips for removing the binder, and thereafter baking and external electrodes formation are carried out. This prevents the binder from remaining in the center of the green chips to eliminate the occurrence of cracks, and thus uniform sintered chips are obtained, which enables the production of a multilayer ceramic electronic component having less deviation in the electrical characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a laminated ceramic electronic component such as a laminated ceramic capacitor having a varistor function which is used for protecting semiconductors and electronic circuits from abnormal voltage.

[0002]

2. Description of the Related Art In recent years, chip type multi-layer ceramic electronic parts have been widely used with the miniaturization of various electronic devices such as video tape recorders. A typical example of such a monolithic ceramic electronic component is a monolithic ceramic capacitor, and the conventional technique will be described below with reference to this.

FIG. 2 is a partially cutaway perspective view of a conventional multilayer ceramic capacitor, and FIG. 3 is a manufacturing process diagram thereof. Figure 2
In FIG. 1, 1 is a ceramic made of a sintered dielectric, 2 is an internal electrode made of a conductive material such as Ni, which is alternately laminated with the ceramic 1, and the internal electrode 2 is drawn out to different end faces of the ceramic 1 layer by layer. Has been. Three
Is an inner external electrode such as Ni formed on the end surface of the ceramic 1 so as to be connected to the internal electrode 2, and 4 is an outer external electrode such as Ag formed so as to cover the inner external electrode 3.

Next, a method of manufacturing such a multilayer ceramic capacitor will be described with reference to FIG.
First, after weighing various raw materials in predetermined amounts, they are mixed and crushed. This powder is calcined and then crushed, and a binder or the like is added to this to prepare a slurry. Using this slurry, a sheet is formed by a doctor blade method or the like, and cut into a predetermined size to produce a green sheet. And
After printing a conductive material for internal electrodes on this green sheet, a large number of sheets are stacked, and this stacked body is cut into chips to obtain green chips.

Next, the obtained green chip is carried into an electric furnace and heat-treated to remove the binder. The heat treatment for removing the binder is usually carried out under the heat treatment condition of raising the temperature of the binder to a combustion temperature at a slow rate of 5 to 30 ° C./h in the atmosphere. Then, after the green chip after the heat treatment is fired and sintered, the sintered chip is chamfered, and the opposite end faces are coated with a conductive material for the inner external electrode and the outer external electrode and baked. Form external electrodes. In this way, the multilayer ceramic capacitor is manufactured.

[0006]

However, in the conventional multilayer ceramic electronic component, the binder cannot be completely removed by the conventional binder removal by heat treatment in the air depending on the structure or material thereof, and the green chip May remain in the center. When the binder remains, carbon remains due to incomplete combustion, and the carbon promotes reduction of the ceramics and hinders reoxidation, so the sinterability changes and the desired electrical properties are not expressed. .. Further, if the binder remains, the sintered chip after firing becomes non-uniform and cracks occur.

The present invention is intended to solve the above problems, and an object of the present invention is to provide a method for manufacturing a multilayer ceramic electronic component which does not generate cracks and exhibits stable electrical characteristics.

[0008]

In order to achieve this object, the present invention is to carry out a heat treatment for removing a binder from a green chip under reduced pressure in a manufacturing process of a multilayer ceramic electronic component.

[0009]

By using the above heat treatment, the low-molecular particles generated by the decomposition of the binder due to the reduced pressure are sucked out from the inside of the green chip, and the binder does not remain.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a multilayer ceramic capacitor having a varistor function according to an embodiment of the present invention will be described below with reference to the manufacturing process chart of FIG.

First, SrTiO ₃ which is a main component is added to Nb ₂ O ₅ , Ta ₂ O ₅ which is a semiconducting substance, a sintering aid MnO ₂ ,
Add SiO ₂ and oxidation promoter Na ₂ SiO ₃ , respectively,
After mixed and pulverized, it is calcined at 1000 to 1200 ° C. and pulverized again. The powder thus obtained is mixed with an organic solvent composed of butyl acetate and trichloroethane, a binder composed of butyral resin and a plasticizer, and a dispersant to prepare a slurry. A sheet is formed by a doctor blade method using this slurry to produce a green sheet, which is cut into a predetermined size. N on the surface of the cut green sheet
The internal electrode material made of iO is printed, and a predetermined number of layers are stacked. Then, the laminate is cut into chips to produce green chips.

Next, a heat treatment for removing the binder is performed. In this heat treatment step, green chips are put into a vacuum furnace capable of maintaining airtightness, oxygen in the furnace is removed by a suction pump, and the furnace pressure is kept at 10 ^-2 Torr or less. When the pressure in the furnace falls below 10 ^-2 Torr, continue to draw at room temperature for 1 hour to remove the low boiling point solvent. After that, the heat treatment temperature is set and raised according to the decomposition temperature of the binder used. Gas is generated during the decomposition of the binder, and the maximum pressure in the vacuum furnace at that time is preferably 50 Torr or less. The set temperature is 700 ° C., which has the highest decomposition temperature in the binder, so the temperature was raised to 700 ° C. at a predetermined heating rate, and the temperature was maintained for a predetermined time. Although this condition varies depending on the number of layers and the shape, if the binder is difficult to remove, the temperature rising rate may be slowed down or the temperature may be maintained at another decomposition temperature of the binder for 1 to 2 hours.

The green chip subjected to the heat treatment for removing the binder is non-uniformly reduced by the heat treatment under reduced pressure. Therefore, if reduction firing is performed as it is, reduction is not performed uniformly, and variations in electrical characteristics after reoxidation are likely to occur. Therefore, after heat treatment,
It is desirable to oxidize the green chip by performing an oxidation treatment at 00 to 1200 ° C. In addition, the oxidation treatment also helps to give the green chip strength. This oxidation treatment may be carried out by introducing air into the vacuum furnace to further raise the temperature after the above heat treatment, but depending on the structure of the furnace, even if it is cooled once and then subjected to oxidation treatment in air, the electrical characteristics will change. There is no. In this case, for comparison, the binder was removed under various heat treatment conditions, followed by once cooling and then oxidizing treatment.

Next, chamfering of the green chip after the oxidation treatment
And form the inner and outer electrodes with the same paste as the inner electrodes.
Then, reduction firing is performed. Reduction firing is 1100 to 1300 ° C
And N ₂And H₂Firing is performed in the mixed gas of. At this time the internal power
NiO of the electrode and the inner external electrode is reduced to Ni.
And becomes conductive. Then 800 in the air
Re-oxidize at ~ 1000 ℃, Ag external electrode inside outside
After applying on the electrode, baking is performed.

Regarding the sample of the multilayer ceramic capacitor having the varistor function obtained as described above,
Varistor voltage (V _0.1mA ) at _0.1mA and 1kHz
The electrostatic capacitance (C _1kHz ) was measured. The measurement results are shown in (Table 1) and (Table 2).

[0016]

[Table 1]

[0017]

[Table 2]

However, (Table 1) shows the electrical characteristics of the samples obtained by heat-treating the green chips having the number of laminated green sheets of 30 layers and 50 layers under various heat treatment conditions. Also,
Table 2 shows the electrical characteristics of samples in which the number of stacked green chips was changed at various processing temperatures in the oxidation process, and also the crack occurrence rate evaluated by observing the inside of the sample.

As is clear from this (Table 1), when the maximum pressure during binder removal is greater than 50 Torr,
The binder remains and the inside remains as a semiconductor, and the characteristics do not appear. However, when the maximum pressure was set to 50 Torr or less, the binder could be completely removed, and the target electric characteristics could be obtained. When the pressure is further reduced, the electric characteristics become larger, and the effect becomes remarkable. Further, by increasing the number of laminated layers, it becomes possible to remove the binder even if the binder is hard to come off by lowering the heating rate. Organic substances such as binders decompose and burn in the air, but when sufficient oxygen for combustion cannot be supplied as in the inside of the green chips, they remain as carbon and adversely affect the characteristics. However, when the binder is removed under reduced pressure, it is considered that the decomposed low molecular weight compounds are sucked from the inside of the green chip and sublimate.

As is clear from (Table 2), after the heat treatment for removing the binder, direct reduction firing is performed, or
When the reduction firing is performed after the oxidation treatment at a temperature lower than 00 ° C., the sintered body is cracked or the varistor voltage varies greatly. However, when the oxidation treatment is performed at 1100 to 1200 ° C., the strength of the sintered body is increased, cracks are eliminated, and variations in varistor voltage are reduced. But 1200
When the temperature exceeds ℃, the internal electrode reacts with the green chip, and the capacitance is remarkably reduced.

In this embodiment, SrT is used as the ceramic material.
An example of a material containing iO ₃ as a main component is shown, but SrTiO ₃
Even if a part of Sr in (1) is replaced with Ca or Ba or both, the same effect as in the present embodiment can be obtained. Further, in this embodiment, Ni is used for the inner electrode and the inner outer electrode.
Although an example in which Ag is used for the outer external electrode has been shown, examples of these electrode materials include Ag, Pd, Ni, Cu and Zn.
Among these, one or more elemental metals or alloys containing these as the main components may be used, or alloys containing one or more of Na, K and Li as their main components may be used.

Further, in the present embodiment, an example of a method of manufacturing a laminated ceramic capacitor having a varistor function is shown. However, the manufacturing method of heat treatment under reduced pressure may be another laminated ceramic capacitor such as a laminated ceramic capacitor using dielectric ceramics. It is also applicable to type ceramic electronic parts.

[0023]

As is apparent from the above description, in the method for manufacturing a multilayer ceramic electronic component of the present invention, the heat treatment for removing the binder is performed under reduced pressure, so that the binder does not remain in the central portion of the green chip. It is possible to obtain stable electric characteristics without the occurrence of cracks.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram of a multilayer ceramic capacitor having a varistor function according to an embodiment of the present invention.

FIG. 2 is a partially cutaway perspective view of a conventional multilayer ceramic capacitor.

FIG. 3 is a manufacturing process diagram of a conventional multilayer ceramic capacitor

[Explanation of symbols]

 1 Ceramics 2 Internal Electrode 3 Inner External Electrode 4 Outer External Electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuo Wakabata 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Iwa Ueno, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A step of laminating a plurality of green sheets containing ceramics as a main component and having internal electrodes formed on the surface thereof,
This laminate is provided with a step of cutting the laminated body to produce a green chip, a step of heat-treating the green chip to remove the binder, and a step of performing firing and external electrode formation after the heat treatment, wherein the heat treatment is performed under reduced pressure. A method of manufacturing a laminated ceramic electronic component. 2. The method for producing a multilayer ceramic electronic component according to claim 1, wherein the heat treatment is performed under a reduced pressure of 50 Torr or less. 3. After heat treatment, 1100 to 1200 are continued.
The method for manufacturing a multilayer ceramic electronic component according to claim 1, wherein the oxidation treatment is performed in the atmosphere of ° C.