JP2605743B2 - Manufacturing method of multilayer ceramic capacitor - Google Patents

Description

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

(Prior art) Conventionally, in order to manufacture a multilayer ceramic capacitor, a conductive metal powder paste is printed and applied on a ceramic green sheet, and a plurality of the pastes are laminated and pressed together, and then baked to form a porcelain. There was a method of forming. By such a method, the multilayer ceramic capacitor 1 as shown in FIG. 2 was manufactured. In such a multilayer ceramic capacitor 1, a pair of external electrodes 4, 5 electrically connected to the internal electrodes 2 are formed on both end surfaces of a dielectric sintered body 3 having a plurality of internal electrodes 2. Have been.

In such a multilayer ceramic capacitor 1, the capacitance per unit volume is determined by the dielectric constant of the ceramic dielectric, the total area of the internal electrodes, and the thickness of one dielectric layer. Therefore, in order to obtain a small and large-capacity capacitor, use a ceramic material having a high dielectric constant,
In addition, the thickness of the dielectric layer between the internal electrodes 2 needs to be reduced. Therefore, the thickness of the ceramic green sheet is
It was set to a minimum of about 20 μm.

(Problems to be Solved by the Invention) However, if the ceramic green sheet is further thinned in order to increase the capacity of the capacitor, a minute defect in the ceramic green sheet such as a pinhole causes a short circuit between the electrodes. It may develop into a fatal defect.

Further, the tensile strength of the ceramic green sheet is weakened, and the handleability is deteriorated. For example, it is difficult to automatically perform processes such as peeling of a ceramic green sheet, printing of internal electrodes, and drying of a ceramic green sheet in a continuous sheet state.

Further, the penetration of the solvent for forming the internal electrode deforms the ceramic green sheet, which causes inconvenience in a later step.

SUMMARY OF THE INVENTION Therefore, a main object of the present invention is to provide a method of manufacturing a multilayer ceramic capacitor capable of obtaining a high-strength and large-capacity multilayer ceramic capacitor and having good workability.

(Means for Solving the Problems) The present invention provides a step of preparing a ceramic composition which does not turn into a semiconductor even when fired in a reducing atmosphere, and a step of preparing a base metal powder having a melting point higher than the temperature at which the ceramic composition is fired. A step of preparing a first paste containing a varnish, a step of preparing a second paste containing a base metal powder, a varnish, and a semiconducting agent; and a step of molding a ceramic composition to form a green sheet; A step of applying a first paste to be a first internal electrode on a green sheet, a step of applying a second paste to be a second internal electrode on another green sheet, and a first paste Forming a laminate by alternately laminating green sheets coated with the second paste and green sheets coated with the second paste; and forming the sintered body by firing the laminate in a reducing atmosphere. And a step of forming external electrodes electrically connected respectively to the first internal electrode and the second internal electrode formed by firing on both end surfaces of the sintered body. This is a method for manufacturing a ceramic capacitor.

(Operation) By firing the laminate, the green sheet becomes a dielectric, and the base metal powder contained in the first paste and the second paste becomes an internal electrode. At this time, the semiconductor material contained in the second paste diffuses into the green sheet, so that the dielectric around the internal electrode is converted into a semiconductor. Therefore, only the green sheet portion where the semiconductor agent is not diffused becomes a dielectric. Therefore, in this multilayer ceramic capacitor, a semiconductor layer is formed between the internal electrode formed by firing the second paste and the dielectric.

(Effects of the Invention) According to the present invention, since the semiconductor layer is formed between the dielectric and the internal electrode formed by firing the first paste, the thickness of the ceramic green sheet can be increased. In addition, the dielectric between the internal electrodes can be formed thin. Therefore, a multilayer ceramic capacitor having a large capacitance and a large mechanical strength can be obtained. Further, since it is not necessary to make the ceramic green sheet thin, the handling of the ceramic green sheet is simplified in the manufacturing process, and the printing of the internal electrodes, the drying of the ceramic green sheet, and the like can be automated.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

(Example) FIG. 1 is an illustrative view showing one example of a multilayer ceramic capacitor formed by a manufacturing method of the present invention. This multilayer ceramic capacitor 10 includes a dielectric 12. Dielectric
Inside 12, an internal electrode 14 extending from one end of the dielectric 12 and an internal electrode 16 extending from the other end of the dielectric 12 are formed so as to be alternately opposed to each other. Then, the dielectric 12 around the internal electrode 14 extending from one end of the dielectric 12 is turned into a semiconductor, and a semiconductor layer 18 is formed. Further, an external electrode electrically connected to the internal electrode 14 is provided on one end surface of the dielectric 12.
20 are formed. Similarly, an external electrode 22 that is electrically connected to the internal electrode 16 is formed on the other end surface of the dielectric 12.

Next, a method of manufacturing the multilayer ceramic capacitor 10 will be described.

First, a non-reducing dielectric ceramic composition is prepared as a raw material. The non-reducing dielectric ceramic composition includes ｛(Ba
Using _{1-x Ca x) O}} m (Ti 1-y Zr y) composition represented by O _2, m, x, y are respectively 1.005 ≦ m ≦ 1.03 0.02 ≦ x ≦ 0.22 0 <y ≦ It was weighed to 0.20. The weighed raw materials were mixed and calcined to obtain porcelain raw material powder. 15% by weight of a mixed aqueous solution comprising an organic binder, a dispersant, and an antifoaming agent was added to this porcelain raw material powder, and mixed with a 50% by weight of water in a ball mill and pulverized to prepare a slurry. The slurry was passed through a doctor blade to form a green sheet of 30 μm to 60 μm.

On the other hand, a first paste was prepared by kneading a Ni metal powder as a base metal powder and a semiconducting agent together with a varnish composed of an ethyl cellulose resin and a butyl cellosolve solvent at a mixing ratio shown in the table. Nb ₂ O ₅ , Y ₂ O ₃ , C
eO ₂ , La ₂ O ₃ , Pr ₆ O ₁₁ , Nd ₂ O ₃ , Sm ₂ O ₃ , Eu ₂ O ₃ , Gd ₂ O ₃ , Tb ₂ O ₃ , Dy ₂
A mixture of oxide powders of O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Tm ₂ O ₃ , and Yb ₂ O ₃ was used in a ratio shown in the table.

Further, a Ni metal powder as a base metal powder was kneaded with a varnish comprising an ethyl cellulose resin and a butyl cellosolve solvent to prepare a second paste.

Next, the first paste was applied on the ceramic green sheet by a screen printing method. The second paste was applied on another ceramic green sheet by a screen printing method. The green sheets to which the first paste was applied and the green sheets to which the second paste was applied were alternately stacked so that the respective paste application surfaces faced, and integrated by thermocompression bonding to form a laminate.

The capacitor unit was cut out from the laminate with a blade. This capacitor unit was heated to 500 ° C. in air to burn the organic binder. Thereafter, firing was performed at 1300 ° C. for 2 hours in a reducing atmosphere using H ₂ —N ₂ —air gas having an oxygen partial pressure of 10 ⁻⁹ to 10 ⁻¹² MPa to obtain a dielectric ceramic material. A silver paste for an external electrode was applied to the end surface of the obtained dielectric ceramic material, and baked at 800 ° C. in a neutral atmosphere to form an external electrode. Thus, a sample (chip-type multilayer capacitor) was obtained.

However, the specifications of the chip-type multilayer capacitor prepared in this example are as follows.

External dimensions: width 3.2 mm, length 1.6 mm, thickness 1.2 mm Ceramic element thickness (distance between electrodes): t = 20 μm to 40 μm Total number of effective dielectrics: N = 19 layers Counter electrode area per layer: S = 1.32 mm ² For these samples, the capacitance (C), the dielectric loss (tan δ), and the insulation resistance (R) were measured, and the product of the capacitance and the insulation resistance (CR product) was obtained. The capacitance (C) and dielectric loss (tan δ) were measured at 1 kHz and 1 V using an automatic bridge.
Measured in _rms . The insulation resistance (R) was measured using a high insulation meter after applying 50 V for 2 minutes. Further, the apparent dielectric constant (ε) was determined from the following equation based on the capacitance (C).

ε = C × t / 8.854 × 10 ⁻¹² × S × N = 4.50 × 10 ¹⁵ × C × t As can be seen from the table, a sample obtained by laminating only green sheets coated with a paste containing no semiconducting agent. number
The apparent dielectric constant of the sample of this example, that is, sample numbers 2 to 7, 9 to 14, 16 to 22 was twice or more as compared with the comparative samples of 1, 8, and 15. Further, the CR product was 2000ΩF or more, and it was confirmed that the product was practically used.

The non-reducing dielectric porcelain composition may be, for example, _もの (Ba _1-xy Ca _{x
Sr y) 0} m · TiO} 2 ( provided that, 1.005 ≦ m ≦ 1.03,0.02 ≦
x ≦ 0.22,0.05 ≦ y ≦ 0.35) , {(Ba 1-xy Ca x Sr y)
O｝ _m · (Ti _1-z Zr _z ) O ₂ (However, 1.005 ≦ m ≦ 1.03,
0.02 ≦ x ≦ 0.22, 0.05 ≦ y ≦ 0.35, 0.00 <z ≦ 0.20) and (Ba _x Ca _1-x ) _y ZrO ₃ + zMnO ₂ (where 0.00 <x <0.
20, 0.85 <y <1.30, 0.005 <z <0.08 (z is (Ba _x Ca
Other non-reducing dielectric ceramic compositions represented by general formulas such as _1-x ) _y ZrO ₃ weight ratio to weight 1.00)) may be used. Further, in addition to the above non-reducing dielectric ceramic composition mainly composed of titanate, non-reducing dielectric ceramics which do not decrease in specific resistance and do not increase in dielectric loss even when fired in a neutral or reducing atmosphere. It is also possible to use body porcelain compositions.

Further, as the base metal powder used for the first paste and the second paste, other than Ni, Fe, Co, Cr, Cu, Al
Etc. can be used.

In the above-described embodiment, a reducing atmosphere made of N ₂ and H ₂ is used as the firing atmosphere, but an atmosphere made of Ar, H ₂ or CO ₂ or CO may be used. The same effect can be obtained if the resulting oxygen partial pressure is under an oxygen partial pressure that does not oxidize the electrode (base metal electrode).

[Brief description of the drawings]

FIG. 1 is an illustrative view showing one embodiment of the present invention. FIG. 2 is an illustrative view showing a conventional multilayer ceramic capacitor as a background of the present invention. In the figure, 10 is a multilayer ceramic capacitor, 12 is a dielectric, 14 and 16 are internal electrodes, 18 is a semiconductor layer, 20 and 22
Indicates an external electrode.

Claims (1)

(57) [Claims] A step of preparing a ceramic composition which does not turn into a semiconductor even when fired in a reducing atmosphere; and a step of preparing a first paste containing a base metal powder having a melting point higher than a temperature at which the ceramic composition is fired and a varnish. Providing a second step including the base metal powder, the varnish, and the semiconducting agent;
Preparing a paste, forming a green sheet by molding the ceramic composition, applying the first paste to be a first internal electrode on the green sheet, and applying another green sheet. A step of applying the second paste to be a second internal electrode thereon, a green sheet to which the first paste is applied and a green sheet to which the second paste is applied are alternately stacked to form a laminate Forming the sintered body in a reducing atmosphere to form a sintered body; and forming the first internal electrode formed by firing on both end surfaces of the sintered body; A method for manufacturing a multilayer ceramic capacitor, comprising a step of forming external electrodes each electrically connected to a second internal electrode.