JP2841338B2 - 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] In a general manufacturing method of a multilayer ceramic capacitor, a ceramic sheet called a green sheet obtained by a method such as a doctor blade method is used, and a conductive metal powder paste for forming an internal electrode on the sheet is used. Is applied and printed, a plurality of these are alternately laminated and pressed, and the resulting product is baked to form a porcelain and an external electrode is applied. As shown in FIG. 2, in the obtained multilayer ceramic capacitor 1, on both sides of a sintered body 3 made of a dielectric having a plurality of internal electrodes 2, electrically connected to predetermined internal electrodes 2. A pair of external electrodes 4 and 5 are provided. [Problems to be Solved by the Invention] In the multilayer ceramic capacitor, the capacitance per unit volume is determined by the dielectric constant of the ceramic derivative, the total area of the internal electrodes, and the thickness of one dielectric layer. That is, in order to obtain a small and large-capacity capacitor, it is necessary to use a ceramic material having a high dielectric constant and to reduce the thickness of the dielectric layer. However, in the multilayer ceramic capacitor according to the conventional manufacturing method, the thickness of the ceramic green sheet is limited to about 20 μm for the following reasons. That is, if the ceramic green sheet is made thinner than its limit, for example: (1) A minute defect (for example, a pinhole) in the ceramic clean sheet causes a fatal defect such as a short circuit between electrodes. (2) The tensile strength of the ceramic green sheet is weakened, and the handleability is deteriorated. For example, steps such as peeling of the ceramic green sheet, printing of the internal electrode, and drying of the ceramic green sheet cannot be automatically performed in a continuous sheet state. (3) The penetration of the solvent of the internal electrode paste causes deformation of the ceramic green sheet, which causes inconvenience in a later step. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of manufacturing a multilayer ceramic capacitor having a high insulation resistance, a high strength and a large capacity, and a good workability. [Means for Solving the Problems] The method for manufacturing a multilayer ceramic capacitor according to the present invention includes a method of forming a green sheet of a ceramic composition which does not turn into a semiconductor even when fired in a reducing atmosphere, at a temperature lower than the firing temperature of the ceramic. A paste composed of a high melting point base metal powder having a high melting point, a semiconducting agent powder and a varnish is printed so as to form an internal electrode, and the obtained green sheets are laminated to form a laminate, and the laminate is formed. It is characterized in that a semiconductor layer is formed so as to cover each of the internal electrodes by firing in a reducing atmosphere, and external electrodes are provided on both end surfaces of the fired laminate. [Explanation of Means] As the ceramic composition which does not turn into a semiconductor even when fired in a reducing atmosphere, various types are known (for example, Japanese Patent Publication No. 56-46641, Japanese Patent Publication No. 57-37081, and Japanese Patent Publication No.
No. 57-42588 and Japanese Patent Publication No. 57-49515). Examples of such a ceramic composition include the following. In the composition formula _{{(Ba 1-x Ca x} ) O} m · (Ti 1-y Zr y) barium titanate expressed by O ₂ based dielectric ceramic composition, m, x, y is in the range of the following non-reducing derivative ceramic composition: 1.005 ≦ m ≦ 1.03 0.02 ≦ x ≦ 0.22 0 <y ≦ 0.20 compositional formula _{{(Ba 1-xy Ca x} Sr y) O} barium titanate derivative represented by m · TiO ₂ In the ceramic composition, a non-reducing derivative ceramic composition in which m, x, and y are in the following half ranges: 1.005 ≦ m ≦ 1.03 0.02 ≦ x ≦ 0.22 0.05 ≦ y ≦ 0.35 The composition formula ｛(Ba _1-xy Ca _x sr _y) O} m · (in Ti _1-z Zr _z) barium titanate expressed by O ₂ based derivative ceramic composition, m, x, y, z are non-reducing derivative ceramic composition in the range of the following 1.005 ≦ m ≦ 1.03 0.02 ≦ x ≦ 0.22 0.05 ≦ y ≦ 0.35 0.00 <z ≦ 0.20 Consists of (BaCa) ZrO ₃ and MnO ₂ and represented by the general formula (Ba _x Ca _1-x ) _y ZrO ₃ + zMnO ₂ When (Ba _x C
a _1-x ) The x, y of ZrO ₃ is in the following range, and (Ba _x Ca
_1-x ) _y Non-reducing derivative ceramic composition in which MnO ₂ (= z) has the following weight ratio to 1.00 weight of ZrO ₃ : 0.00 <x0.20 0.85 <y <1.30 0.005 <z <0.08 (Weight ratio) These non-reducing dielectric ceramic compositions are
Sintering in a neutral or reducing atmosphere does not result in a decrease in insulation resistance and no increase in dielectric loss. Therefore, even if a base metal such as Ni, Fe, or Co is used as an electrode as described later, firing can be performed in a neutral or reducing atmosphere while preventing oxidation of the base metal and reaction with the ceramic. The high melting point base metal powder, for example, Ni, Fe, Co, Cr,
It is a metal powder selected from base metals such as Cu and Al, or an alloy powder thereof. Further, the semiconducting agent powder is a powder composed of one or more kinds of substances generally called a semiconducting agent, for example, niobium and lanthanum. It is a powder composed of cerium or another rare earth element. More specifically, Nb ₂ O ₅ , Y ₂ O ₃ , CeO ₂ , La ₂ O ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ , Pr ₆ O ₁₁ , Dy ₂ O ₃
And the like, or a compound containing these elements. In order to form the ceramic green sheet from the ceramic composition, for example, a slurry which is a mixture of a ceramic composition powder and an organic binder, a dispersant, and an antifoaming agent is prepared and processed by a doctor blade method. In order to print the paste on the ceramic green sheet, for example, a screen printing method is adopted. The ceramic green sheets on which the paste is printed are stacked so that the paste printed portions serving as internal electrodes face each other, and are integrated by thermocompression bonding. The integrated product is fired in a reducing atmosphere to form an external electrode that is electrically connected to the internal electrode. Thus, a multilayer ceramic capacitor 11 having a structure as schematically shown in FIG. 1 is obtained. In FIG. 1, a ceramic green sheet is fired to form a laminated sintered body made of a dielectric. The internal electrodes 12 arranged to face each other are made of the high melting point base metal. In addition, the semiconducting agent powder thermally diffuses during firing, and penetrates into the laminated sintered body to form the semiconductor layer 13. As a result, the semiconductor layer
The part that did not become 13 is the dielectric layer obtained as a result of firing
It is 14. On the end face 2 of the laminated sintered body, a pair of external electrodes 14 and 15 for taking out a capacitance connected to a predetermined one of the internal electrodes 13 is formed. As is clear from FIG. 1, the overall thickness of the multilayer ceramic capacitor is large, and sufficient strength can be maintained. Moreover, since the semiconductor layer 13 is formed in the laminated sintered body, the thickness of the dielectric layer 14 is reduced, and a large capacitance can be obtained. In addition, since it is not necessary to use a thin green sheet to obtain a large capacity, workability is good. Moreover, the insulation resistance of the obtained multilayer ceramic capacitor can be kept high. The semiconducting agent powder is not limited to the case of an oxide, but may be in another form. [Example] As a ceramic composition which does not turn into a semiconductor even when fired in a reducing atmosphere, for example, a composition disclosed in JP-B-56-46641, that is, a composition formula {(Ba _1-x Ca _x ) O} _m (Ti
_1-y Zr _y) O using represented by composition _2, m, x, y The following ranges; weighed so that 1.005 ≦ m ≦ 1.03 0.02 ≦ x ≦ 0.22 0 <y ≦ 0.20, mixing and temporary It was baked to obtain porcelain raw material powder. 15% by weight of a mixed aqueous solution composed of an organic binder, a dispersant and an antifoaming agent was added thereto, and the mixture was again mixed and pulverized with 50% by weight of water in a ball mill 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, Ni metal powder, Nb ₂ O ₅ , Y ₂ O ₃ , CeO 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 O ₃ , Ho ₂ O ₃ , Er ₂
O ₃ , Tm ₂ O ₃ , and Yb ₂ O ₃ oxide powders were kneaded together with 3 parts by weight of an ethyl cellulose resin and a butyl cellosolve solvent at the mixing ratios shown in Table 1. The kneading method is a method of kneading an ordinary conductive paste, and thus a conductive paste was obtained. The conductive paste was applied on the ceramic green sheet by a screen printing method. After drying a plurality of the sheets, they were stacked so that the electrodes face each other, and integrated by thermocompression bonding. From this laminated block, individual capacitor units were cut out with a blade. After heating the unit thus obtained to 500 ° C. in air to burn the organic binder, the oxygen partial pressure is reduced to 10 ^−9.
To 10 ^-12 MPa of H ₂ -N ₂ - in a reducing atmosphere using the air gas,
It was baked at 1300 ° C. for 2 hours. Apply silver paste for external electrodes to the side wall surface of the obtained dielectric ceramic material,
Baking was performed at 800 ° C. to form external electrodes. Thus, measurement samples as shown in Tables 1 and 2 were obtained. The specifications of the chip-type multilayer capacitor manufactured in this example are as follows. ◎ Appearance dimensions: width = 3.2mm, length = 1.6mm, thickness = 1.2mm ◎ Ceramic element thickness (distance between electrodes): t = 20μm ~ 40μm ◎ Total effective dielectric: N = 19 layers ◎ Counter electrode per layer Area: S = 1.32 mm ^{2 The} capacitance (C) and the dielectric loss tangent (tan δ) were measured at 1 KHz and 1 Vrms by an automatic bridge. Regarding the insulation resistance (R), the value after applying 50 V for 2 minutes with a high insulation meter was measured, and the product of the capacitance and the insulation resistance (CR value) was obtained. The apparent dielectric constant was determined from the following formula based on the capacitance C. ε = C × t / 8.854 × 10 ⁻¹² × S × N = 2.76 × 10 ¹⁴ × C × t The results are shown in Table 2. In Table 1, * indicates a comparative sample outside the scope of the present invention. As is clear from Tables 1 and 2, the present invention in which the Ni powder paste to which the oxide was added was applied as compared with Sample Nos. 1, 8, and 15 in which the Ni powder paste to which the oxide was not added was applied. In all of the samples according to the above, the apparent dielectric constant was twice or more. The capacitance / insulation resistance product (CR product) is 2000Ω
-It was F or more, and it was confirmed that it could be put to practical use. In addition to the non-reducing dielectric porcelain composition mainly composed of titanate shown in FIG. 1, a non-reducing dielectric porcelain composition whose insulation resistance does not deteriorate even when fired in a neutral or reducing atmosphere. The invention can likewise be implemented on objects. In the above embodiment, the firing atmosphere was N ₂ , H ₂
Although a reducing atmosphere consisting of is used, an atmosphere of Ar, H ₂ or CO ₂ , CO or the like may be used. If the resulting oxygen partial pressure is under an oxygen partial pressure at which the electrode (base metal electrode) is not oxidized, exactly the same effect was obtained. [Effects of the Invention] The present invention has found that a general well-known semiconducting agent such as Nb applied to a green sheet can be thermally diffused by firing to form a semiconducting layer in a laminated sintered body, It is an application of that. This makes it possible to realize a thin dielectric layer effective for obtaining a large capacity without reducing the thickness of the green sheet and the laminated sintered body. Therefore, according to the present invention, a significantly higher apparent dielectric constant can be easily obtained than in the case of using the conventional electrode paste to which no semiconducting agent is added. Further, since a large capacity can be obtained without reducing the thickness of the ceramic green sheet, the problem of strength can be solved. For this reason, in the manufacturing process, the handling of the ceramic green sheet is facilitated, and the printing of the internal electrodes, the drying process of the ceramic green sheet, and the like are also easily automated. Furthermore, since the base metal and its alloy are used as electrodes, an inexpensive ceramic capacitor can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a multilayer ceramic capacitor showing one embodiment of the present invention. FIG. 2 is a sectional view of a conventional multilayer ceramic capacitor. 11: multilayer capacitor, 12: internal electrode, 13: semiconductor layer, 14: dielectric layer, 14, 15: external electrode.

   ────────────────────────────────────────────────── ─── Continuation of front page                   (56) References JP-A-63-262815 (JP, A)                 JP-A-62-31108 (JP, A)                 JP-A-61-144813 (JP, A)                 JP-B-56-46641 (JP, B2)                 Tokiko Sho 53-23495 (JP, B2)

Claims (1)

(57) [Claims] A paste consisting of a high melting point base metal powder having a melting point higher than the firing temperature of the ceramic, a semiconducting agent powder, and a varnish, on a plurality of green sheets made of a ceramic composition that does not turn into a semiconductor even when fired in a reducing atmosphere, Printing is performed so as to form an internal electrode, and the obtained green sheets are laminated to form a laminate. The laminate is fired in a reducing atmosphere to form a semiconductor layer so as to cover each of the internal electrodes. A method for manufacturing a multilayer ceramic capacitor, characterized in that external electrodes are provided on both end surfaces of a fired laminate.