KR20020094329A - Method of fabricating ceramic slurry for multi-layer ceramic capacitor - Google Patents

Abstract

PURPOSE: A preparation method of ceramic slurry for multilayer ceramic condenser is provided, which improves electrical property and sintered density, and prevents segregation of additives by improving mixing and dispersing methods of ceramic raw materials. CONSTITUTION: A preparation method of dielectric ceramic slurry is characterized by dispersing at least two of auxiliary components(<50wt.%) including Y, Cr, Mn, W, Nd, Nb, Co, etc. without agglomeration prior to mixing with main components(>=50wt.%) including one or more of BaTiO3, (Ba, Ca)(Ti, Zr)O3 and (Ba, Ca, Sr )(Ti, Zr)O3. The dielectric ceramic slurry is prepared by the following steps of: (i) grouping auxiliary components by surface area(or particle size, mechanical fracture strength, morphology, etc.); (ii) wet-milling each group with respective solvent and dispersant, differing from kinds and amounts of dispersants, and dispersion condition; (iii) adding a binder to the milled slurry, and wet-milling; (iv) mixing main components, ground and dispersed, with prepared auxiliary components.

Description

METHODS OF FABRICATING CERAMIC SLURRY FOR MULTI-LAYER CERAMIC CAPACITOR}

The present invention relates to a multilayer ceramic capacitor, and more particularly, to a ceramic slurry production method required for manufacturing a multilayer ceramic capacitor.

The present invention provides a method for producing a ceramic slurry in which a high density ceramic can be obtained after sintering without changing the conventional raw materials by improving the method of mixing and dispersing the ceramic raw materials and segregation of additives is suppressed. As a result, the present invention enables the production of high capacity and high reliability multilayer ceramic capacitors by enabling thin and high lamination of dielectrics.

As a dielectric ceramic material for a multilayer ceramic capacitor, the main component is barium titanate (BaTiO ₃ ), (Ba, Ca) (Ti, Zr) O _3, (Ba, Ca, Sr) (Ti, Zr) O _3, etc. The technique which improves reliability by adding various subcomponent additives here, providing reduction resistance, and adjusting temperature characteristics is researched.

As a conventional technique for manufacturing such a multilayer ceramic capacitor, a slurry is prepared by mixing a subsidiary ceramic raw material additive with a dielectric ceramic material containing barium titanate (BaTiO ₃ ) as a main component, and then adding a solvent, a dispersant, and a binder to wet mix. The method of making it is used.

As another conventional technique, some or all of the main raw materials and the additives are mixed, calcined, pulverized and slurryed through a wet mixing process, and then a green sheet is formed of a doctor blade or the like. BACKGROUND ART A technique has been known in which a conductor paste serving as an internal electrode is coated on a surface thereof, laminated, pressed, and fired to produce a multilayer ceramic capacitor.

However, when the dielectric ceramic layer is reduced to 8 μm or less due to the miniaturization and high capacity of the multilayer ceramic capacitor, there is a problem in that a poor current yield occurs due to poor conduction between internal electrodes in the process of manufacturing the multilayer ceramic capacitor according to the prior art. .

Moreover, when the conventional technology is applied, the standard deviation of characteristic values, such as insulation resistance and dielectric breakdown voltage, increases in initial characteristics, and the problems of high temperature load and moisture resistance load are liable to occur in terms of reliability. Problems tend to occur.

That is, the conventional technique of mixing the additives with the above-described dielectric ceramic raw material containing barium titanate as a main component and then adding a solvent, a dispersant, and a binder to perform wet mixing, has various specific surface areas, particle sizes, etc. In the slurry grinding formulation method based on the surface area, particle size, breaking strength, etc., added subcomponents cannot be evenly dispersed and dispersed.

In addition, another conventional technique in which some or all of the main raw materials and the additives are calcined by calcination and then slurried by wet mixing does not form a single phase after calcination, so that the specific surface area and particle size for each phase are different. Not only are the backs different from each other, but the breakdown strengths of the respective phases are different at the time of grinding, so that the specific surface area difference can not be further increased.

As a result, in the prior art based on the slurry blending method mainly on the main component, the high strength subcomponent phase is not easily pulverized, and the subcomponent having a large specific surface area cannot be evenly dispersed due to the dispersant shortage.

In order to solve the above problems, Japanese Patent Application Laid-Open No. 5-124857 discloses wet mixing by adding and dispersing subcomponents in advance, pulverizing them to a particle diameter of 0.2 to 1.0 μm, and then adding a main component, a solvent, a dispersant, and a binder. A manufacturing method is disclosed.

However, in the prior art disclosed in Japanese Patent Application Laid-open No. Hei 5-124857, the subcomponents are agglomerated again in the drying step, and the separation phenomenon occurs between the subcomponents, so that the subcomponents are not completely dispersed on the main components, and segregation of several micrometers is performed. (偏析) and abnormal (이상) will cause. For reference, segregation means a phase in which a specific component element forms different aggregates from other main components and is formed non-uniformly with the main part.

In order to solve the above problems, Japanese Patent Application Laid-Open No. 10-255549 discloses mixing and grinding subcomponents by plasma treatment to form mixed and ground subcomponents into ultrafine particles of 0.001 to 0.15 μm and then mixing them with the main component. Disclosed is a manufacturing technique.

In addition, Japanese Patent Application Laid-open No. Hei 10-270284 discloses ultrafine particles having a particle size of 0.001 to 0.15 μm after plasma treatment by mixing the subcomponents, followed by heat treatment and grinding at 600 to 1600 ° C. to produce fine particles having an average particle diameter of 0.05 to 1.0 μm. After forming, a production technique is disclosed in which lyophilization is carried out to form granules and mixed with the main component.

However, in the above-described prior art, as shown in Fig. 1, the subcomponents 21, 22, 23 and 24 are both finely divided and mixed and dispersed with the main component 25 at the same time. , 23, 24) and the amount or type of the dispersant and the binder 30 are not differentiated by the difference in the specific surface area of the main component 25.

Therefore, the prior art does not achieve an optimal dispersion mixing state for each component, especially because of the fact that a large amount of dispersant compared to the main component is required for the subcomponent having a very large specific surface area compared to the main component, Only a very small amount of dispersant is assigned, which causes a problem of hardly performing a dispersing action.

As a result, when the process of reducing the thickness of the dielectric is reduced to 8 μm or less according to the prior art, there is a problem that the process yield decreases due to segregation of subcomponents. On the other hand, there has been proposed a technique for chemically surface-coating the subsidiary raw material on the main raw material, but this method requires an expensive process cost and is likely to be separated precipitation of the sub-components in the evaporation drying process of the chemical solution dissolving the sub-components, There is a problem that the cost is too high to use the chemical surface coating method again in the dispersion of the raw material to be re-added when it is necessary to adjust the minor component content or the mole ratio of Ba and Ti in the future. Moreover, when heat-treating the coated subcomponents, reaggregation of the subcomponents occurs, thereby causing poor dispersion.

On the other hand, in the prior art, in addition to the problem of coagulation segregation of the subcomponents described above, the firing temperature is set relatively high at 1150 to 1300 ° C in firing-resistant dielectric firing, resulting in a problem of reducing reliability by reducing ceramic at high temperatures. . Moreover, the prior art does not allow the subcomponents to be uniformly dispersed, resulting in degradation of the electrical properties.

Accordingly, a first object of the present invention is to provide a method for producing a ceramic slurry which solves a problem of poor dispersion in mixing a main component and a subcomponent of a dielectric ceramic material.

A second object of the present invention is to provide a method for producing a ceramic slurry in addition to the first object, which solves the problem of insulation resistance degradation and dielectric breakdown voltage degradation due to poor dispersion.

It is a third object of the present invention to provide a ceramic slurry production method in which main components and subcomponents of a dielectric ceramic material are mixed, and in admixing the subcomponents, preventing segregation of the subcomponents and improving electrical characteristics, process yield, and reliability. .

1 is a view showing a process for producing a ceramic slurry according to the prior art.

2 is a view illustrating a process of preparing a final ceramic slurry by classifying subcomponents by specific surface area and slurrying them according to an embodiment of the present invention, and then dispersing the subcomponents together with the main component.

3 is a table comparing characteristics of a ceramic capacitor manufactured according to a preferred embodiment of the present invention and a ceramic capacitor manufactured according to the prior art.

<Explanation of symbols for the main parts of the drawings>

21, 22, 23, 24: subcomponents

25: main ingredient

30: binder

In order to achieve the above object, the present invention provides a method of manufacturing a dielectric ceramic comprising a plurality of subcomponent added as a main component and a dielectric ceramic raw material, the method comprising: (a) the plurality of subcomponents according to the criteria selected for each or specific surface area size; Categorizing by group; (b) wet milling the dispersant and the solvent by varying the type of dispersant, the amount of dispersant, or dispersing conditions for each group classified in step (a); (c) adding a binder to the first milled slurry in step (b) and performing secondary wet mixing and dispersing; And (d) wet mixing the slurry classified by each subcomponent or specific surface area with the main component prepared by the same manufacturing method after the second wet mixed dispersion in step (c). do.

In the present invention, for example, BaTiO ₃ , (Ba, Ca) (Ti, Zr) O ₃ , (Ba, Ca, Sr) (Ti, By separately dispersing additives added to Zr) O _3, etc., additives having various particle size distributions and specific surface areas are grouped by specific surface area, and then slurryed through primary and secondary wet grinding and dispersion for each group. This is followed by final mixing and dispersion with a slurry such as a main component.

As a preferred embodiment of the present invention, the grouping method has a specific surface area of 2 to 5 m ² / gr, 5 to 10 m ² / gr, 10 to 20 m ² / gr,. , 50 m ² / gr or more can be classified into a slurry.

Hereinafter, with reference to the accompanying drawings Figures 2 and 3 will be described in detail a preferred embodiment of the method for producing a dielectric ceramic slurry according to the present invention.

According to the present invention, in the production of a dielectric porcelain comprising a dielectric ceramic material such as barium titanate (BaTiO ₃ ) as a main component, and various raw material additives as a subcomponent (less than 50 wt% of the main component), the specific component reaching specific surface area at the completion of grinding Disclosed is a method of manufacturing a dielectric ceramic according to a group, and thereby optimizing and mixing the types, amounts, grinding or dispersing conditions of the dispersant and the binder for each group.

The present invention is wet grinding by adding a solvent and a dispersant, and after adding the binder to the first milled slurry, and the second wet mixed dispersion, the slurry classified by each subcomponent or specific surface area and the main component and the third prepared by the same manufacturing method Wet mixing results in a good structure with no other phases, uniform dispersibility and improved density.

2 is a view illustrating a process of preparing a final ceramic slurry by classifying subcomponents by specific surface area and slurrying them according to an embodiment of the present invention, and then dispersing the subcomponents together with the main component.

Referring to FIG. 2, as a preferred embodiment of the present invention, the subcomponents BaCO ₃ , CaCO ₃ , SiO ₂ , Y ₂ O ₃ , WO ₃ , Nd ₂ O ₃ , Nb ₂ O ₅ , MgCO ₃ , CrO ₃ , ZrO ₂ Group I (1 to 5 m ² / gr), Group II (5 to 10 m ² / gr), Group III (10 to 20 m ² / gr), and IV by the final specific surface area at the end of the dispersion grinding. After dividing into group (20-50 m ² / gr), Group V (50 m ² / gr or more), and using a beads mill to add a solvent and a dispersant of 0.5 to 50 wt% Slurry is prepared by adding a low molecular weight binder and dispersing it again in a bead mill.

Subsequently, the final slurry is prepared by mixing and dispersing the subcomponent slurry, which is classified and grouped into the slurry of the main ingredient raw material including the dispersant and the low-molecular binder.

In addition, a sheet having an average thickness of 5 μm is formed using the prepared final slurry. Subsequently, the inner electrode is printed on the sheet, dried, laminated, compressed, and then cut into several sheets to produce a green chip. In addition, after the produced green chip is calcined, it is calcined in a reducing atmosphere to produce a calcined chip, and then an external electrode can be charted and sintered using a copper face.

3 is a diagram comparing the characteristics of a ceramic capacitor manufactured according to a preferred embodiment of the present invention and a ceramic capacitor manufactured according to the prior art. Referring to FIG. 3, the prior art 1 uses subcomponents BaCO ₃ , CaCO ₃ , SiO ₂ , Y ₂ O ₃ , WO ₃ , Nd ₂ O ₃ , Nb ₂ O ₅ , MgCO ₃ , CrO ₃ , ZrO ₂ and a main ingredient of the raw material. Experimental results of a sample prepared by mixing a solvent, a low-polymer binder, a dispersant, and the like and dispersing the mixture using a beads mill.

Meanwhile, the prior art 2 uses the sub-components BaCO ₃ , CaCO ₃ , SiO ₂ , Y ₂ O ₃ , WO ₃ , Nd ₂ O ₃ , Nb ₂ O ₅ , MgCO ₃ , ZrO ₂ , CrO ₃ and the main component raw materials according to the prior art. After mixing and calcining all of them, they are ground, mixed with a solvent, a low-molecular binder, a dispersant, and the like, and then are dispersed using a bead mill and slurried.

In FIG. 3, multilayer ceramic capacitors were made and used in composition A and B under the same conditions, and the results are shown in a diagram. In Fig. 3, the failure of the breakdown voltage was determined to be a failure of an insulation resistance of 100 kPa after applying a direct current 25V, and the high-speed accelerated life test was a result of continuously applying a DC voltage of 25V at an ambient temperature of 200 deg. Referring to FIG. 2, it can be seen that the multilayer ceramic capacitor manufactured according to the present invention has an excellent breakdown voltage rate of 100 times or more, and a 700-fold improvement in high-speed acceleration life time.

According to the present invention, a method for preparing a slurry of subcomponents by classification according to specific surface area may be grouped by using physicochemical properties such as particle size, mechanical fracture strength or shape morphology in addition to specific surface area as a grouping classification criterion.

The foregoing has outlined rather broadly the features and technical advantages of the present invention to better understand the claims of the invention which will be described later. Additional features and advantages that make up the claims of the present invention will be described below. It should be appreciated by those skilled in the art that the conception and specific embodiments of the invention disclosed may be readily used as a basis for designing or modifying other structures for carrying out similar purposes to the invention.

In addition, the inventive concepts and embodiments disclosed herein may be used by those skilled in the art as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. In addition, such modifications or altered equivalent structures by those skilled in the art may be variously changed, substituted, and changed without departing from the spirit or scope of the invention described in the claims.

As described above, in the present invention, in the ceramic slurry manufacturing process, the sub-components are uniformly dispersed without aggregation, thereby obtaining a dense sintered structure, and as a result, a highly laminated ceramic capacitor can be manufactured without problems such as deterioration of reliability. .

Moreover, this invention has the effect of suppressing the phenomenon that a raw material is reduced by the strong reducing atmosphere at high temperature by making baking temperature maintain at 5-100 degreeC or less than the prior art. In addition, the present invention is to facilitate the control of the electrical properties by allowing the even components to be evenly distributed to improve the dielectric constant up to about 50%.

Claims (8)

In the dielectric ceramic manufacturing method comprising a plurality of subcomponent added as a main component of the dielectric ceramic raw material, (a) classifying the plurality of subcomponents into groups according to a criterion selected for each or specific surface area size; (b) wet milling the dispersant and the solvent by varying the type of dispersant, the amount of dispersant, or dispersing conditions for each group classified in step (a); (c) adding a binder to the first milled slurry in step (b) and performing secondary wet mixing and dispersing; And (d) after the second wet mixed dispersion in step (c), wet mixing the slurry classified by each subcomponent or specific surface area with the main component prepared by the same production method. Dielectric ceramic slurry manufacturing method comprising a. The main component of the dielectric ceramic raw material is any one of BaTiO ₃ , (Ba, Ca) (Ti, Zr) O ₃ , (Ba, Ca, Sr) (Ti, Zr) O ₃ , A method for producing a dielectric ceramic slurry, characterized in that the component ratio constitutes 50% or more of the total. The method of claim 1, wherein the secondary component of the dielectric ceramic comprises any one or a combination of Y, Cr, Mn, W, Nd, Nb, Co, Si, Mg, Zr, Ba, Ti, Ca, Sr, A method for producing a dielectric ceramic slurry, characterized in that the component ratio constitutes less than 50% of the total. In the dielectric ceramic manufacturing method comprising a plurality of subcomponent added as a main component of the dielectric ceramic raw material, (a) simultaneously mixing and grinding all of the plurality of subcomponents to form a slurry; (b) adding the first slurry slurry ground in step (a) to disperse the second wet mixing; And (c) after the second wet mixed dispersion in step (b), wet mixing with the main component prepared in the same manufacturing method Dielectric ceramic slurry manufacturing method comprising a. The method of claim 1, wherein the classification criteria for each group of step (a) are classified according to physicochemical classification criteria including particle size, mechanical fracture strength, morphology, etc. instead of the specific surface area. Way. The method of claim 1, wherein step (c) is omitted. The method of claim 1, wherein step (c) further comprises adding a dispersing aid. The method of manufacturing a dielectric ceramic according to claim 1, wherein when classifying by group in step (a), some or all of the main components may be included.