JP3160855B2 - Multilayer ceramic capacitors - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer ceramic capacitor and a method for manufacturing the same, and more particularly, to a structure in which an external electrode is formed and an external electrode forming step are improved. About things.

[Conventional technology]

In the multilayer ceramic capacitor, a plurality of internal electrodes are arranged in a dielectric ceramic so as to overlap with a ceramic layer interposed therebetween, and the internal electrodes are drawn out to first and second side surfaces of the dielectric ceramic, And the first and second
Has a structure electrically connected to an external electrode formed on the side surface of the.

A general manufacturing method of the multilayer ceramic capacitor is as follows. That is, a ceramic green sheet formed by a molding method such as a doctor blade method is prepared, and a conductive paste for forming an internal electrode is printed and applied on the ceramic green sheet, and a plurality of these are laminated and pressed. A sintered body is obtained by firing. Thereafter, the first and second internal electrodes of the sintered body are drawn out.
An external electrode is formed on the second side surface by applying and baking a conductive paste.

Therefore, in the conventional multilayer ceramic capacitor, it is necessary to perform a firing step for baking the ceramic green sheet laminate into a porcelain and a firing step for firing the external electrodes twice, thereby reducing cost. Was hindered.

Furthermore, dielectric ceramics made into porcelain tend to be deformed, such as warping, by firing, and in the step of applying external electrodes, those that do not require an automatic machine tend to occur. In addition, when the chips are aligned when applying the external electrode material, chipping or cracking may occur due to an automatic machine, and it is difficult to reduce the mass production cost from this point as well.

In recent years, in order to solve the above problem, using an external electrode paste containing a ceramic powder having the same composition as the dielectric ceramic green sheet in a paste mainly composed of a metal powder, a ceramic green sheet laminate is used. A method has been proposed in which porcelain formation and baking of an external electrode are simultaneously achieved by a single baking.

[Technical problem to be solved by the invention]

However, when a ceramic powder having the same composition as the ceramic green sheet for forming the dielectric ceramics is contained in the conductive paste for forming the external electrodes, the lamination is porcelain and the external electrodes are baked once. Although it can be performed in the baking process, the adhesion of the external electrode to the dielectric ceramic varies, the electrode resistance of the external electrode increases, the frequency characteristics deteriorate, and the plating and soldering properties decrease. There was a problem.

That is, the dip method is used for applying the external electrode. However, when the conductive paste for forming the external electrode contains a considerable proportion of ceramic powder, the electrode resistance of the external electrode increases. At the same time, the ceramic powder is present in a portion exposed on the outer surface of the external electrode, so that the wettability with the solder is reduced and the soldering tends to be defective.

On the other hand, when the content of the ceramic powder is small, there are many places where the ceramic powder exists at the joint interface between the side surface of the dielectric ceramic and the external electrode, and the adhesion strength between the dielectric ceramic and the external electrode is increased. Not be able to
The adhesion of the external electrode will be reduced.

Furthermore, even if the content of the ceramic powder is an appropriate amount, sedimentation occurs during storage of the paste due to a difference in specific gravity between the ceramic powder and the metal powder, and it is difficult to uniformly disperse both. As a result, there is a portion where the ceramic powder does not exist at the joining interface between the side surface of the dielectric ceramic and the external electrode, or the ceramic powder exists on the outer surface of the external electrode, and the amount and dispersion state of the ceramic powder vary. In addition, the electrical resistance and solderability varied, and the external electrode adhesion varied.

An object of the present invention is to provide a ceramic laminate having a structure in which porcelain formation and external electrode formation can be performed by firing at a time, the adhesion of the partial electrode to the dielectric ceramic is strong, and the external electrode An object of the present invention is to provide a multilayer ceramic capacitor having sufficiently low electric resistance and having a small specific variation, and a method for manufacturing the same.

[Means for solving technical problems]

According to the present invention, a plurality of internal electrodes are arranged so as to overlap with each other via a ceramic layer in a dielectric ceramic, and the plurality of internal electrodes are alternately arranged in the thickness direction of the dielectric ceramic in the first and second dielectric ceramics. The multilayer ceramic capacitor, which is drawn out to two side surfaces and has first and second external electrodes formed on the first and second side surfaces, is characterized by having the following configuration.

That is, on the first and second side surfaces of the dielectric ceramic layer,
The ceramic powder comprising at least one of the dielectric compositions constituting the dielectric ceramic layer is fixed to the first and second side surfaces with the firing of the dielectric ceramic in a dispersed state, The present invention is characterized in that first and second external electrodes are formed on the first and second side surfaces, respectively, with a ceramic powder interposed therebetween.

The production method of the present invention includes a step of preparing a laminate formed by laminating a plurality of ceramic green sheets mainly composed of a dielectric material via a conductive paste layer for an internal electrode; No. of paste layer being drawn
1, a step of forming an intermediate layer containing a ceramic powder and a binder comprising at least one of the compositions constituting the dielectric material on the second side surface; and forming a conductive paste for an external electrode on the intermediate layer. Applying, and firing the laminate to simultaneously perform porcelainization of the laminate and baking of the external electrodes, and dispersing the binder to fix the ceramic powder on the side surface in a dispersed state. .

[Action]

The first of dielectric ceramics from which the internal electrodes are drawn
Ceramic powder is dispersed on the second side surface. Since this ceramic powder is a composition composed of at least one kind of a constituent composition of the dielectric ceramic, the ceramic powder is firmly bonded to the dielectric ceramic with the firing of the dielectric ceramic. 1, second
Since the contact area between the side surface of the external electrode and the external electrode is enlarged, the adhesion of the external electrode is effectively increased.

Since the ceramic powder is dispersed on the first and second side surfaces, the internal electrode and the external electrode exposed on the first and second side surfaces even if the ceramic powder is present. The electrical connection with is ensured.

In addition, since the ceramic powder is not uniformly dispersed in the material for forming the external electrode itself, the electrode resistance of the external electrode itself does not increase, and the ceramic powder is exposed on the outer surface of the internal electrode. Therefore, the solderability and the plating property do not decrease.

In addition, in the manufacturing method of the present invention, the sintering of the laminated body and the baking of the external electrodes are simultaneously performed in a single firing step, so that the firing cost is reduced.

[Explanation of Example]

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a multilayer ceramic capacitor according to one embodiment of the present invention. This multilayer ceramic capacitor 1
Then, a plurality of internal electrodes 3 to
6 are arranged so as to overlap with each other via the dielectric ceramic layers 2a to 2c. The internal electrodes 3 to 6 alternately alternate with the first and second side surfaces 2 in the thickness direction of the dielectric ceramic 2.
d, 2e.

This embodiment is characterized in that ceramic powders 7, 8 made of at least one of the dielectric compositions constituting the dielectric ceramics 2 are dispersed on the first and second side surfaces 2d, 2e. These ceramic powders 7, 8 are shown in FIG. 1 as constituting one layer, but are shown in FIG.
As shown representatively of 2d, the ceramic powder 7 is dispersed and arranged on the side surface 2d.

The ceramic powders 7 and 8 are applied to the side surfaces 7 and 8 before firing the dielectric ceramics 2 and are integrated with the dielectric ceramics 2 by firing the dielectric ceramics 2.

Reference numerals 9 and 10 denote first and second external electrodes. The first and second external electrodes 9 and 10 are electrically connected to the internal electrodes 3 to 6 extending to the first and second side surfaces 2d and 2e, respectively.

Next, a method for manufacturing the multilayer ceramic capacitor 1 will be described. First, a powder made of a dielectric ceramic is slurried to form a ceramic green sheet mainly composed of a dielectric material. A plurality of ceramic green sheets are prepared, and a conductive paste for internal electrodes is applied to one main surface and dried to form a conductive paste layer for internal electrodes. The conductive paste layer for internal electrodes is baked in the firing step described below to form the internal electrodes 3 to 6 shown in FIG.
It is completed as

Next, a plurality of ceramic green sheets on which a conductive paste layer is formed are laminated, and a dielectric ceramic green sheet on which the conductive paste for an internal electrode is not applied is laminated on the uppermost and lowermost parts, and pressed in the thickness direction. Thus, a laminate is obtained.

Next, on the first and second side surfaces (side surfaces corresponding to the first and second side surfaces 2d and 2e in FIG. 1) of the laminate, a dielectric ceramic composition used for forming a ceramic green sheet is provided. Is formed into a paste by mixing a binder, for example, to form an intermediate layer. After drying the intermediate layer, a conductive paste for external electrodes for forming the external electrodes 9 and 10 is applied by a dipping method.

Next, by firing the laminate at a predetermined temperature, the laminate is porcelain and the external electrodes 9 and 10 are simultaneously baked, and the chip-type multilayer ceramic capacitor 1 is obtained. During this firing, the ceramic powders 7 and 8 of the above-mentioned intermediate layer are baked so as to be integrated with the dielectric ceramics 2. Therefore, the ceramic powders 7, 8
The dielectric ceramics 2 is firmly joined to the first and second side surfaces 2d and 2e in a dispersed state.

Since the ceramic powders 7 and 8 are dispersed on the first and second side surfaces 2d and 2e, the first and second external electrodes 9 and 10 and the first and second side surfaces 2d and 2d of the dielectric ceramic 2 are formed. , 2e, the adhesion of the external electrodes 9, 10 is effectively increased.

Since the ceramic powders 7 and 8 are distributed on the first and second side surfaces 2d and 2e as shown in FIG.
The electrical connection with the internal electrodes 3 to 6 exposed on the first and second side surfaces 2d and 2e is sufficiently ensured.

Moreover, since the external electrodes 9 and 10 themselves are made of a normal conductive paste, the ceramic powder is not mixed into the paste to form the external electrodes as in the conventional example described above. Also, there is no possibility that the electrode resistance becomes high. In addition, since the ceramic powder is not exposed on the outer surface side of the external electrodes 9 and 10, the solderability at the time of joining with the outside is not reduced.

 Hereinafter, specific examples of the present invention will be described.

Example 1 First, as a material constituting a dielectric ceramic, BaCO ₃ , CaCO ₃ , ZrO ₂ and TiO ₂ having a purity of 99% or more were prepared by a composition formula {(Ba _0.90 Ca _0.10 O} _1.01 (Ti _0.80 Zr _0.20 ) O Weighed to ₂

The weighed powder was mixed and calcined to obtain a raw material powder for a dielectric ceramic.

15% by weight of a mixed aqueous solution composed of an organic binder, a dispersant and an antifoaming agent was added to the raw material powder, and the mixture was mixed and pulverized with 50% by weight of water by a ball mill to prepare a slurry.

Next, the slurry was formed into a sheet by a doctor blade method to obtain a ceramic green sheet having a thickness of 35 μm. On this ceramic green sheet, a conductive paste for an internal electrode mainly composed of nickel powder was printed to form a conductive paste layer for an internal electrode for forming the internal electrode.

A plurality of ceramic green sheets on which the conductive paste layers for internal electrodes were formed were laminated such that the side from which the conductive paste layers for internal electrodes were drawn out staggered, to obtain a laminate.

Next, the ceramic powders shown in Table 1 below were pulverized, and an organic binder composed of an ethyl cellulose resin and a butyl cellosolve solvent was added and kneaded to obtain a ceramic powder paste. This paste is applied to the first and second side surfaces of the laminate where the internal electrodes are exposed, and dried to form an intermediate layer. A conductive paste was applied and dried.

The laminate obtained as described above was heated to a temperature of 500 ° C. in an N ₂ atmosphere, and after firing and scattering the organic binder, H ₂ − having an oxygen partial pressure of 10 ⁻¹ to 10 ⁻¹² MPa was used. N ₂ and H ₂ O
In a reducing atmosphere using a mixed gas, the laminate was fired at a temperature of 1300 ° C. for 2 hours, and the laminate was porcelain and the external electrodes were baked simultaneously. In this way, a multilayer ceramic capacitor in which the above-mentioned ceramic powder was dispersed and interposed between the first and second side surfaces on which the internal electrodes of the dielectric ceramic were exposed and the external electrodes was obtained.

The specifications of the multilayer ceramic capacitor obtained as described above are shown below.

The external dimensions are width: 3.2 mm, length; 1.6 mm, thickness; 1.2 mm, the thickness of the ceramic layer between the internal electrodes is 20 μm,
The number of effective dielectric layers is 19, and the counter electrode area per layer is 1.3 mm ² .

A voltage of 1 KHz and 1 V _rms was applied to each of the multilayer ceramic capacitors of Sample Nos. 1 to 5 to which each of the ceramic powder pastes in Table 1 was applied using an automatic bridge type measuring instrument, and the capacitance C and the dielectric loss tnaδ were applied. Was measured. Also,
The insulation resistance R was measured by applying a DC voltage of 50 V for 2 minutes using an insulation meter.

Furthermore, in order to evaluate the wettability of the solder to the external electrode, the solder was immersed in a solder at 230 ° C. for 2 seconds to perform a soldering test. In the evaluation of the soldering test, the case where the solder is continuously attached to the external electrode surface more than 3/4 without break is indicated as good. In Table 2 below, it is indicated by a circle, and when it is not, it is indicated in Table 2 below. Indicated by X.

Further, the laminated ceramic capacitors of each of the above samples were soldered to a glass epoxy substrate on which silver-palladium was wired, the back side of the substrate was pressed, and the strength at the time of breakage (that is, the external electrode fixing force) was measured.

 The results of the above measurements are also shown in Table 2 below.

As is clear from Table 2, when the ceramic powders of Sample Nos. 1 to 3 which fall within the scope of the present invention are applied, the properties such as capacity, dielectric loss and insulation resistance do not decrease or the solderability is deteriorated. It can be seen that they are excellent and the external electrode fixing force is enhanced.

On the other hand, sample number 4 using a glass frit
It can be seen that all the characteristics of the multilayer ceramic capacitor significantly deteriorate. In addition, in the case of a normal multilayer ceramic capacitor (corresponding to sample number 5) in which ceramic powder is not applied to the side surface of the dielectric ceramic, the capacitance,
Dielectric loss and insulation resistance are reduced compared to the present invention,
It can be seen that although the solderability is good, the external electrode fixing force is not sufficient.

Example 2 As a composition material constituting dielectric ceramics, 8
2.5 Pb (Mg _1/3 Nb _2/3 ) O ₃ +5.0 PbTiO ₃ +12.5 Pb (Mo _1/2 W
The _1/2) O ₃ with respect to 100 wt%, Pb a _{(Mn 2/3 W 1/3) O 3} 0.5
A mixed powder added at a ratio of% by weight was used. In addition,
In the above composition, the numbers indicate mol%.

A slurry was obtained by adding a polyvinyl butyral-based binder and an organic solvent such as ethanol to the raw material powder.
The slurry was formed into a sheet by a doctor blade method to form a ceramic green sheet having a thickness of 35 μm.

On the ceramic green sheet, a conductive paste for internal electrodes mainly composed of 70Ag-30Pd (the number is% by weight) was printed to form a conductive paste layer for internal electrodes. Next, through the same steps as in Example 1, a laminate was obtained in which the conductive paste layers for internal electrodes were exposed on the first and second side surfaces.

On the other hand, an organic binder composed of an ethylcellulose resin and an α-terpineol solvent was added to each of the pulverized ceramic powders having the composition shown in Table 3 below and kneaded to obtain a ceramic powder paste. This ceramic powder paste is applied to the first and second exposed inner electrodes of the laminate.
And dried to form an intermediate layer. Thereafter, a conductive paste for external electrodes mainly composed of 70Ag-30Pd (the number is% by weight) was applied on the ceramic powder paste, and dried.

The obtained laminate is heated in air at 1000 ° C. for 2 hours.
The ceramic powder is dispersed between the first and second side surfaces where the internal electrodes of the dielectric ceramic are exposed and the external electrodes, while firing for a period of time to simultaneously produce the laminated body and bake the external electrodes. To obtain a multilayer ceramic capacitor interposed.

The external dimensions and other specifications of the multilayer ceramic capacitor formed as described above are the same as those in the first embodiment.

Further, in order to examine the electrical characteristics, the same various measurement tests were performed under the same conditions as in Example 1. The measurement results are shown in Table 4 below.

As is clear from Table 4, in the multilayer ceramic capacitor of Example 2 in which the ceramic powder pastes of Sample Nos. 6 to 8 which are within the scope of the present invention were applied, all of the capacitance C, the dielectric loss tan δ, and the insulation resistance R were all different. It is clear that the solderability and the external electrode fixing force are also excellent.
On the other hand, the glass frit of sample number 9 was
The multilayer ceramic capacitor interposed on the side surface of (1) had a low capacitance, a large dielectric loss, and a low insulation resistance.
In addition, the solderability was not sufficient, and the external electrode fixing force was poor. Similarly, in the sample No. 10, that is, in the conventional product to which the ceramic powder paste was not applied, the electrical characteristics were inferior to those of the multilayer ceramic capacitor of the example, and the solderability was excellent, but the external electrode fixing force was excellent. Is also not enough.

In the above Examples 1 and 2, the ceramic powder was dispersed on the first and second side surfaces by applying the ceramic powder paste. However, the present invention is not limited to this.
Similar effects can be obtained by forming a paste containing ceramic powder on a sheet and pressing the paste on the first and second side surfaces of the laminate, or forming a layer containing ceramic powder by vapor deposition or the like.

In addition to the method of forming an external electrode, in addition to the method of applying a conductive paste, after forming a conductive powder layer on a resin film, this is applied to a laminate by thermal transfer, or formed by vapor deposition or sputtering. The external electrodes may be formed by a method.

Further, a conductive film may be laminated and formed in advance on the ceramic powder paste layer formed into a sheet, and this may be bonded to the first and second side surfaces of the laminate.

〔The invention's effect〕

As described above, according to the present invention, at least one of the compositions constituting the dielectric ceramic between the first and second side surfaces of the dielectric ceramic where the internal electrode is exposed and the external electrode is provided. Since the ceramic powder is interposed in a dispersed state and the ceramic powder is firmly integrated with the dielectric ceramic, the adhesion strength between the dielectric ceramic and the external electrode is increased. In addition, since the ceramic powder is dispersed on the first and second side surfaces, electrical connection between the internal electrode and the external electrode is also ensured.

Also, since ceramic powder is not kneaded in the external electrode material itself, the electrode resistance of the external electrode does not increase and the solderability of the external electrode does not deteriorate.

Further, in the manufacturing method of the present invention, the ceramic powder composed of at least one of the compositions constituting the dielectric ceramic is disposed on the first and second side surfaces, and the baking of the external electrodes is performed by firing the dielectric ceramic In order to perform simultaneously, that is, to apply an external electrode material before porcelain formation, not only can the firing cost be reduced, but also to effectively prevent the deformation, chipping and cracking of the chip when applied to an automatic machine. Can be. Therefore, it is possible to greatly improve the product yield.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a multilayer ceramic capacitor according to one embodiment of the present invention, and FIG. 2 is a schematic side view for explaining ceramic powder dispersed and fixed on a side surface of a dielectric ceramic in the embodiment of FIG. It is. In the figure, 1 is a multilayer ceramic capacitor, 2 is a dielectric ceramic, 2a to 2c are ceramic layers, 2d and 2e are first and second ceramic capacitors.
The second side, 3 to 6 denote internal electrodes, 7, 8 denote ceramic powder, and 9, 10 denote external electrodes.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-86414 (JP, A) JP-B-62-40843 (JP, B2)

Claims (2)

(57) [Claims] 1. A dielectric ceramic, wherein the dielectric ceramic is disposed so as to overlap with a ceramic layer therebetween via a ceramic layer, and is alternately drawn to first and second side surfaces of the ceramic in a thickness direction of the ceramic. A multilayer ceramic capacitor comprising a plurality of internal electrodes and first and second external electrodes formed on first and second side surfaces of the dielectric ceramic, wherein the first and second side surfaces of the dielectric ceramic are provided. A ceramic powder composed of at least one of the dielectric compositions constituting the dielectric ceramic is dispersed and fixed to the first and second side surfaces by firing the dielectric ceramic; With the powder interposed,
1. A multilayer ceramic capacitor wherein the first and second external electrodes are formed on a second side surface. 2. A step of preparing a laminate formed by laminating a plurality of ceramic green sheets mainly composed of a dielectric material via a conductive paste layer for an internal electrode; and a conductive paste layer for an internal electrode of the laminate. Forming, on the first and second side surfaces, a middle layer containing a ceramic powder and a binder comprising at least one of the compositions constituting the dielectric material; and A step of applying a conductive paste for an external electrode, and baking the laminate to simultaneously perform porcelainization of the laminate and baking of the external electrode, and simultaneously scatter the binder to disperse the ceramic powder on the side surface. Fixing the multilayer ceramic capacitor.