JPH0992567A - Manufacture of laminated ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a laminated ceramic capacitor of high reliability to be manufactured high in yield keeping it free from delamination. SOLUTION: A first process where ceramic slurry is introduced into a vessel 1 possessed of side walls and dried up for the formation of a green ceramic sheet 2, a second process where an inner electrode is formed on the green ceramic sheet 2, a third process where ceramic slurry is introduced onto the first green ceramic sheet 2 where the inner electrode layer is formed and dried up for the formation of a second green ceramic sheet 4, a fourth process where an inner electrode layer 3 is formed, and a fifth process where a second green ceramic sheet 4 is formed are provided, and these processes are atternately repeatedly carried out a few times for the formation of a laminated ceramic capacitor.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for manufacturing a multilayer ceramic capacitor.

[0002]

2. Description of the Related Art Multilayer ceramic capacitors (MLC)
Has a small size, high capacity, excellent frequency characteristics and heat resistance, and high reliability, and is widely used in a wide range of fields. As shown in FIG. 8, the MLC includes a plurality of dielectric layers 31 made of ceramics and the dielectric layers 31.
A plurality of internal electrodes 32, which are arranged between the inner electrodes and are alternately exposed at the opposite side surfaces, a cover sheet 33 made of ceramics not sandwiched between the internal electrodes, and a pair of internal electrodes 32 provided on the opposite side surfaces, respectively. It is composed of an external electrode 34. The multilayer ceramic capacitor of FIG.
In addition to the chip type, a dip type in which a lead wire is attached as an external electrode and resin is applied is also known.

In recent years, in such MLC, due to the demand for miniaturization and large capacity, it was previously 20 μm after sintering per layer.
It is necessary to reduce the thickness of the above-mentioned dielectric.

The MLC is conventionally manufactured by the following method. First, as shown in FIG. 9, a dielectric green sheet 41 made of a dielectric powder and an organic binder is formed on a support film 44, and the dielectric green sheet 4 is formed.
An internal electrode pattern 42 is printed on 1 to produce a sheet 43.

Next, the sheet 43 is peeled off from the support film 44, and the sheet 43 is removed as shown in FIG.
Are stacked between the two cover sheets 45 and 46, heated and pressed to be integrated, and then cut into individual chips by cutting in the thickness direction as shown by the dashed line in FIG. . Then, it is baked and barrel-polished to give the corners roundness. Next, an MLC is manufactured by baking a pair of external electrodes.

However, the conventional manufacturing method described above has the following problems. The first problem is caused by the step between the internal electrode forming portion and the portion where the internal electrode is not formed in the dielectric green sheet 41. That is, in the process shown in FIG.
When a plurality of 3 are laminated and the dielectric sheet is thick, the internal electrode 42 is buried in the dielectric green sheet 41, and the step is absorbed by the dielectric green sheet 41.
When the dielectric green sheet 41 is thin, particularly when the thickness after sintering is 20 μm or less, the step cannot be absorbed by the dielectric green sheet 41, and delamination occurs in the side margin portion of the MLC. This occurs, causing poor capacity, poor insulation, etc., and lowering the yield.

As a method for solving such a problem, many methods for eliminating the step between the internal electrode portion and the portion where the internal electrode is not formed have been proposed. For example, in Japanese Unexamined Patent Publication No. 56-105619, an internal electrode is printed on a supporting film, and a dielectric green sheet is formed on the internal film, so that the dielectric enters a portion where the internal electrode is not formed, resulting in a step Disclosed is a method of producing an MLC by laminating the composite sheets thus obtained.

In Japanese Patent Laid-Open No. 60-193318, an internal electrode is formed on a dielectric green sheet formed on a support film, and a dielectric green sheet is further formed on the internal electrode. A method is disclosed in which a dielectric material enters a portion where no electrode is formed to eliminate a step, and the MLC is manufactured by laminating the composite sheets thus obtained.

Further, Japanese Patent Application Laid-Open No. 1-215095 discloses a method of eliminating a step by printing an electrode on a green sheet and printing a ceramic paste having substantially the same composition as that of the green sheet except the printed portion. ing.

However, in any of the above-mentioned methods, the steps are alleviated but not completely eliminated, and as the number of stacked dielectric green sheets increases, the steps become non-negligible and degreasing is performed. And it was a cause of delamination during firing. As a result, there is a problem in that the defective capacity and the insulation resistance value are reduced in the MLC after firing, and the yield is reduced.

Particularly, in the case of a thin green sheet in which the thickness of the dielectric after firing is 10 μm or less, the above-mentioned step becomes fatal, and after firing, delamination occurs in most of the MLCs, causing a short circuit. Mode failure, ML
It becomes impossible to configure C.

The second problem is that it is extremely difficult to make the thickness uniform when manufacturing a thin dielectric green sheet. As a method for producing a thin dielectric sheet, sheet molding by so-called tape casting using gravure printing or a doctor blade is widely known, but in any method, scratches on the gravure roll or the doctor blade can be completely removed. It is almost impossible to remove it and keep the roll or doctor blade level. Therefore, the manufactured sheet inevitably has unevenness in thickness and unevenness.

When the thickness of the dielectric sheet becomes 10 μm or less, the voltage tends to concentrate on the thin portion,
Dielectric breakdown occurs, dielectric loss increases,
The characteristics become very bad. Furthermore, since the dielectric sheet has a shape in which the central portion is raised due to the surface tension, the edge portion is difficult to be pressure-bonded, which causes delamination.

[0014]

As described above, according to the conventional manufacturing method, when the dielectric layer is as thin as 10 μm or less, the delamination only occurs due to the step between the internal electrode and the dielectric sheet. Not only that, variations in thickness also occur in each dielectric layer, which deteriorates the characteristics of the multilayer ceramic capacitor and extremely reduces the yield.

The present invention provides a method for manufacturing a laminated ceramic capacitor which solves the above problems and enables a highly reliable laminated ceramic capacitor to be manufactured with high yield without causing delamination. The purpose is to do.

[0016]

In order to solve the above problems, the present invention (Claim 1) introduces a ceramics slurry into a container having a side wall and dries it to form a first green ceramics sheet. Step, step of forming internal electrode layer on first green ceramic sheet, ceramic slurry is introduced onto the first green ceramic sheet having the internal electrode layer formed on the surface, dried, second green ceramic And a step of forming the internal electrode layer and a step of molding the second green ceramics sheet, which are alternately repeated a plurality of times. provide.

The method of manufacturing the laminated ceramic capacitor of the present invention will be described in more detail below. In the method of the present invention, first, a certain amount of ceramics slurry is poured into a container having a side wall and dried. As a result, due to the surface tension, as shown in FIG. 1, it is possible to mold a green ceramics sheet having a uniform surface and thick edges. When a multilayer ceramic capacitor is laminated using the green ceramic sheet obtained in this way, not only is it easy to peel off due to its thick edge, but it also prevents deformation during handling after peeling. You can

Further, since it is possible to use a ceramic slurry having a low viscosity which is difficult to use by the conventional method, it is possible to reduce the amount of the binder in the ceramic slurry, thereby reducing the manufacturing cost. It is possible to plan.

Further, even when pressure-bonded by a press, this portion is strongly pressure-bonded, so that delamination hardly occurs in the manufacturing process. Moreover, the thickness of such a sheet can be accurately controlled by the injection amount of the slurry. Further, when combined with the mold release treatment applied to the inner surface of the container, the thin sheet can be peeled off more easily.

By repeating the above steps, it is possible to manufacture a laminated ceramic capacitor having a uniform dielectric layer thickness. As described above, since the surface smoothness and the film thickness uniformity of the dielectric layer are excellent, the breakdown voltage failure due to the concentration of the electric field does not occur. Further, the defect rate of electrostatic capacitance such as delamination, cracks, or lack of desired electrostatic capacitance is significantly reduced.

Further, the manufacturing process is extremely simplified as compared with the conventional one, and not only the time required for the manufacturing is drastically shortened, but also due to the high speed manufacturing, defects such as dust adhesion in each process are caused. It is possible to hold it to the limit. further,
It is possible to extremely reduce the variation in the quality of the sheet due to the change with time of the slurry.

Further, in the conventional method by tape casting, the thinner the dielectric sheet, the more the amount of the supporting film increases, which not only raises the manufacturing cost but also causes the environmental damage. Since the method of the invention does not use a supporting film at all, it has advantages that the manufacturing cost is reduced and unnecessary industrial waste is not generated at all.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a manufacturing process of a multilayer ceramic capacitor according to the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a container 1 having a side wall used in the method of the present invention. The material of the container 1 is not particularly limited, but examples thereof include metals and organic materials such as paper and plastic. The container is preferably circular, but the shape is not particularly limited. 2 (a) to (c)
Examples of various cross-sectional shapes of containers having side walls are shown in FIG. When the container has a circular shape, the uniformity can be improved by rotating the container at a low speed.

First, as shown in FIG. 3, a ceramic slurry is poured into a container 1 and dried to mold a green ceramic sheet 2. The slurry used preferably has a lower viscosity than that used in the tape casting method. In addition, as shown in FIG.
The surface of the green ceramics sheet 2 is horizontal even if it is slightly inclined. At this time, the thickness of the central portion of the ceramic sheet 2 was 100 μm.

Then, as shown in FIG. 4, an internal electrode 3 is formed by applying an electrode paste in a predetermined pattern on the surface of the green ceramic sheet 2. Internal electrode 3
The method for forming is not particularly limited, but examples thereof include screen printing, gravure printing, thermal transfer printing, and stamp printing. In this embodiment, the stamp type is used. The solvent for the electrode paste and the ceramics slurry is preferably incompatible with each other.

Next, as shown in FIG. 5, a predetermined amount of raw ceramics slurry is further accurately poured onto the raw ceramics sheet 2 having the internal electrodes 3 formed on its surface, and dried. As a result, the dielectric layer 4 is formed so as to cover the internal electrodes 3. The surface of this dielectric layer 4 is uniform and has no unevenness,
The thickness was also uniform. The thickness of the dielectric layer 4 is as shown in FIG.
Stipulated as shown in. At this time, the thickness of the dielectric layer 4 was 5 μm.

By repeating the above steps, a laminated ceramic capacitor was obtained as shown in FIG.
The composition of the above-mentioned dielectric slurry and electrode paste is not particularly limited, but generally either an aqueous system or an organic solvent system is used.

Dielectric materials usable in the present invention include:
Various materials such as barium titanate-based materials and lead-based dielectric materials called relaxers, which are generally used as high-dielectric constant materials, can be mentioned.

When the container having the side wall is made of a binder-based material such as paper or PVA, if the container is laminated, the chips are diced and then the container is baked. Since the container burns out, it is possible to prevent defects that occur when taking out the unbaked bar from the container and to simplify the manufacturing process.

When the container is made of a refractory material (for example, MgO), even if the container is fired, the container remains unburned and the capacitor shrinks due to firing.
After firing, it can be easily taken out from the container, and not only can defects that occur when taking out an unfired bar from the container be prevented, but it can also be used as a sheath used during firing. Therefore, the manufacturing process can be simplified.

Further, when the container is made of a hygroscopic material such as filter paper, the solvent or water in the slurry can be absorbed, and therefore the drying time of the slurry can be greatly shortened. . Further, by using a mechanism for sucking the solvent or water outside the container, the slurry can be efficiently dried.

Further, by making the shape of the container circular and rotating the center of the circle as an axis, the slurry can be uniformly molded, and a dielectric green sheet having excellent smoothness can be manufactured. Can be done.

Furthermore, as shown in FIG. 3, even if the container is tilted, the surface of the sheet is horizontal, and a dielectric layer having a uniform thickness can be formed from the second layer, which is large. There is no problem, but if it is necessary to make the thickness of the first layer uniform, by floating the container on a fluid such as water, it is possible to easily obtain a horizontal surface and make the thickness of all dielectric layers uniform. Can be formed.

The characteristics of the multilayer ceramic capacitor manufactured by the above method and those manufactured by other methods were determined and compared. Example 1 As the dielectric ceramics, (Pb _0.875 Ba _0.125 )
[Mg _1/3 Nb _2/3 ) _0.5 (Zn _1/3 Nb _2/3 ) _0.3 T
Using a dielectric powder having a composition of i _0.2 ] O ₃ , a 240-layer laminated ceramic capacitor was manufactured by the above manufacturing process. The appearance of the obtained multilayer ceramic capacitor was good without unevenness in thickness. The thickness of the dielectric layer was 5 μm before firing and 4 μm after firing. The capacitance was 8.6 μF and the dielectric loss was 0.7%. The capacitance-insulation resistance product was 20,000 ΩF at room temperature (20 ° C.) and 10,000 ΩF at high temperature (125 ° C.). Breakdown voltage is 5
It was 00 V, and the yield was 90%, which was good.

Comparative Example 1 As a dielectric ceramics, (Pb _0.875 Ba
_0.125 ) [Mg _1/3 Nb _2/3 ) _0.5 (Zn _1/3 Nb
_A comparative experiment was conducted by a conventional tape casting method using a dielectric powder having a composition of _2/3 ) _0.3 Ti _0.2 ] O ₃ .

First, a dielectric sheet was produced with a lip coater, but the thickness was uneven, and the obtained sheet had a thickness of 5 μm-
It had a thickness of 6 μm. When 240 layers of this dielectric sheet were laminated, uneven thickness occurred. When this laminate was fired, a large amount of delamination occurred.
The thickness of the laminated body after firing was 4 μm to 5 μm.

The capacitance of the obtained multilayer ceramic capacitor was 8.4 μF and the dielectric loss was 1.5%. The capacitance-insulation resistance product is 1000ΩF at room temperature (20 ° C) and high temperature (12
It was 100ΩF at 5 ° C. The breakdown voltage was 15 V and the yield was 0%.

However, in both Example 1 and Comparative Example 1, the capacitance was 8.0 μF or more, the dielectric loss was less than 2.5%, and the capacitance
The insulation resistance product was 2,000 F or higher at both room temperature and high temperature, and the yield was determined to be good. The number of manufactured chips is 100
It was an individual.

Example 2 A BaTiO ₃ type dielectric powder was used as the dielectric ceramic, and a 240-layer laminated ceramic capacitor was manufactured by the above manufacturing process. The appearance of the obtained multilayer ceramic capacitor was good without unevenness in thickness. The thickness of the dielectric layer is 9 μm before firing and 7 μm after firing.
Met. The capacitance was 3.8 μF and the dielectric loss was 2.5%. The capacity-insulation resistance product is 60 at room temperature (20 ° C).
It was 00 ΩF and 1500 ΩF at high temperature (125 ° C.).
The breakdown voltage was 500 V and the yield was good at 98%.

Comparative Example 2 A comparative experiment was conducted by a conventional tape casting method using BaTiO ₃ type dielectric powder as the dielectric ceramics.

First, a dielectric sheet was produced by a lip coater, but the thickness was uneven, and the obtained sheet had a thickness of 9 μm-
It had a thickness of 10 μm. When 240 layers of this dielectric sheet were laminated, uneven thickness occurred. When this laminate was fired, a large amount of delamination occurred. The thickness of the laminated body after firing was 7 μm to 8 μm.

The capacitance of the obtained multilayer ceramic capacitor was 3.5 μF and the dielectric loss was 2.8%. The capacitance-insulation resistance product is 1000ΩF at room temperature (20 ° C) and high temperature (12
It was 100ΩF at 5 ° C. The breakdown voltage was 15 V and the yield was 0%.

However, in both Example 2 and Comparative Example 2, the capacitance was 3.4 μF or more, the dielectric loss was less than 2.5%, and the capacitance
The insulation resistance product was 1000 ΩF or higher at both room temperature and high temperature, and the yield was determined as good. The number of manufactured chips is 100
It was an individual. From the above results, it is understood that according to this example, it is possible to manufacture a laminated ceramic capacitor having a uniform dielectric layer with a high yield.

[0044]

As described above, according to the present invention,
As compared with the conventional method, the withstand voltage failure rate is reduced and the reliability can be improved. Further, since delamination and cracks can be reduced, there is an effect that the capacity defect rate can be significantly improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a container used in the method of the present invention.

FIG. 2 is a cross-sectional view showing various examples of containers used in the method of the present invention.

FIG. 3 is a cross-sectional view of a raw ceramic sheet molded in a container according to the method of the present invention.

FIG. 4 is a cross-sectional view of a raw ceramic sheet having internal electrodes formed by the method of the present invention.

FIG. 5 is a cross-sectional view showing a state in which an internal electrode is further formed on the green ceramic sheet on which the internal electrode is formed in the method of the present invention.

FIG. 6 is a diagram that defines the thickness of a dielectric layer.

FIG. 7 is a sectional view showing the structure of a laminated ceramic capacitor manufactured by the method of the present invention.

FIG. 8 is a sectional view showing the structure of a general laminated ceramic capacitor.

FIG. 9 is a cross-sectional view showing a state in which a dielectric layer and internal electrodes are formed on a support film.

FIG. 10 is a cross-sectional view showing a state in which dielectric sheets are laminated.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container 2 ... 1st raw ceramic sheet 3 ... Internal electrode 4 ... 2nd raw ceramic sheet

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yohachi Yamashita 70 Yanagimachi, Saiwai-ku, Kawasaki-shi, Kanagawa Toshiba Yanagimachi Factory

Claims (4)

[Claims] 1. A step of introducing a ceramics slurry into a container having a side wall and drying it to form a first green ceramics sheet, a step of forming an internal electrode layer on the first green ceramics sheet, and a surface thereof. A step of introducing a ceramics slurry onto the first green ceramics sheet on which the internal electrode layers are formed, and drying it to form a second green ceramics sheet; and a step of forming the internal electrode layers and a second step A method for manufacturing a laminated ceramic capacitor, comprising a step of alternately repeating a step of molding a raw ceramics sheet a plurality of times. 2. The method for manufacturing a laminated ceramic capacitor according to claim 1, wherein the container has a circular bottom surface, and the container is rotated after the ceramic slurry is introduced. 3. The laminated ceramics according to claim 1, wherein a component contained in the internal electrode paste for forming the internal electrode layer and a component contained in the ceramics slurry are incompatible with each other. Capacitor manufacturing method. 4. The method for manufacturing a laminated ceramic capacitor according to claim 1, wherein the inner surface of the container is subjected to a mold release treatment.