JP2000340450A - Laminated ceramic capacitor and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a laminated ceramic capacitor whose moisture resistant load characteristics are made excellent for preventing the generation of any crack or delamination, and a method for manufacturing this. SOLUTION: This laminated ceramic capacitor is provided with an inner electrode layer 2 containing nickel between dielectric layers 1 and 1 with reduction resistance in at least two layers, and the inner electrode layer 2 contains 0.05-1 wt.% magnesium, and metallic oxide layers 4 containing 0.05-0.2 μm thick nickel and magnesium are formed on boundary faces between the inner electrode layer 2 and the dielectric layers 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 an improvement in an internal electrode layer of a multilayer ceramic capacitor.

[0002]

2. Description of the Related Art In general, a multilayer ceramic capacitor has a structure in which dielectric layers and internal electrode layers are alternately stacked, each internal electrode layer is sandwiched between dielectric layers, and external layers formed at both ends of the multilayer body. It has a structure in which the electrode layer and each internal electrode layer are electrically connected.

[0003] In recent years, the demand for lighter and smaller electronic components has become more stringent. For capacitors, a dielectric material having a high relative dielectric constant has been used in order to realize a smaller and larger capacity. In addition, the thickness of the dielectric layer and the internal electrode layer is reduced to further increase the number of layers.

[0004] As for the internal electrode layer, conventionally,
A having low resistivity and capable of co-firing with the dielectric layer
Although an internal electrode layer containing a noble metal such as g or Pd as a main component is used, the cost of forming an electrode is significantly increased with an increase in the number of layers, and therefore an inexpensive base metal such as nickel is used as a main component. Multilayer capacitors having internal electrode layers have been put to practical use.

When nickel or the like is used as the internal electrode layer, nickel generally has a low equilibrium oxygen partial pressure, so that when it is fired at high temperature in the air, an oxide is formed, and there is a problem that the conductivity is reduced. Therefore, firing must be performed in a non-oxidizing atmosphere in which the base metal is not oxidized.

In general, such a method of manufacturing a multilayer ceramic capacitor using nickel as an internal electrode layer comprises alternately providing a plurality of non-reducing dielectric sheets having a surface coated with a conductive paste for an internal electrode layer. After sintering in a non-oxidizing atmosphere, external electrode layers are formed on both end surfaces of the sintered body. In such a manufacturing method, it is necessary to select an internal electrode layer paste and a dielectric material having a similar thermal shrinkage behavior in the firing step, otherwise, there is a problem that cracks and delamination occur. Was.

Therefore, for example, Japanese Patent Application Laid-Open No. 6-290985
Japanese Patent Application Laid-Open Publication No. 2002-210, proposes that by using a paste obtained by adding and mixing a magnesium powder to a nickel powder, a sintering temperature can be increased, a difference in thermal shrinkage between a dielectric layer and an internal electrode layer can be reduced, and cracks can be reduced. Also, Japanese Patent Application Laid-Open
In JP-A-172860, by using a paste obtained by adding a glass powder composed of barium, magnesium and silicon oxide to nickel powder as an internal electrode layer, it is possible to reduce the heat shrinkage difference from the dielectric and to improve the moisture resistance load characteristics. It has been proposed to.

[0008]

However, the paste disclosed in JP-A-6-290985 can suppress the generation of cracks and delaminations, but is insufficient to improve the moisture resistance load characteristics. -17
In the paste disclosed in Japanese Patent No. 2860, Ba ₃ Mg as an insulator is used.
Since the Si ₂ O ₈ powder is scattered in the internal electrode layer and the resistance value of the internal electrode layer may increase, it has been difficult to reduce the thickness of the internal electrode layer. Further, when glass is added to the internal electrode layer, there is a problem that the dielectric properties of the capacitor are deteriorated.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to prevent cracks and delaminations from occurring, improve moisture resistance load characteristics, and reduce the thickness of internal electrode layers. It is an object of the present invention to provide a multilayer ceramic capacitor and a method of manufacturing the same.

[0010]

Means for Solving the Problems As a result of repeated studies on the above problems, the present inventors have found that nickel powder coated with magnesium oxide on the surface is used as a conductive paste for forming an internal electrode layer. As a result, the firing start temperature of the internal electrode layer can be increased, the difference in heat shrinkage between the dielectric layer and the internal electrode layer can be reduced, and magnesium can be easily diffused, and nickel is formed at the interface between the internal electrode layer and the dielectric layer. By forming a metal oxide layer containing magnesium and magnesium, the moisture resistance characteristics of the capacitor can be improved, and the thickness of the internal electrode layer is reduced because magnesium diffuses and moves to the end of the internal electrode layer. I learned that I can do it.

That is, in the multilayer ceramic capacitor of the present invention, an internal electrode layer containing nickel is disposed between at least two dielectric layers having reduction resistance, and the internal electrode layer has a weight of 0.05 to 1 wt. % Of magnesium and 0.1% at the interface between the internal electrode layer and the dielectric layer.
It is characterized in that a metal oxide layer containing nickel and magnesium having a thickness of from 0.05 to 0.2 μm is present.

It is preferable that the metal oxide containing nickel and magnesium is MgNiO ₂ .

The method of manufacturing a multilayer ceramic capacitor according to the present invention is characterized in that the surface of the nickel particles has a metal equivalent of 0.05%.
A step of preparing a conductive paste containing a metal powder coated with マ グ ネ シ ウ ム 1% by weight of magnesium oxide; and a step of applying the conductive paste to a surface of a dielectric sheet made of a dielectric material having reduction resistance. And a step of laminating a plurality of the dielectric sheets, a step of firing the laminate in a reducing atmosphere, and a step of forming external electrode layers on both end surfaces of the sintered body. Things.

Preferably, the coating thickness of the magnesium oxide is 10 to 100 nm.

[0015]

According to the present invention, by using a metal powder whose surface is coated with magnesium oxide as the main metal powder of the conductive paste forming the internal electrode layer, the nickel particles do not come into direct contact with each other. In addition, the reaction between nickel and magnesium can increase the sintering start temperature between nickel particles.

Further, since the dispersibility of magnesium in the paste is high, it can be easily diffused and moved to the end of the internal electrode layer, and contains nickel and magnesium of a specific thickness at the interface with the dielectric layer. A metal oxide layer can be formed. This composite oxide layer can prevent moisture from entering the inside of the internal electrode layer, improve the moisture resistance load characteristics, and make it difficult for the internal electrode layer to be oxidized even when the capacitor after firing is reoxidized. The resistance value of the internal electrode layer does not increase.

Further, since magnesium moves to the surface side of the internal electrode layer, the substantial thickness of the internal electrode layer can be reduced, and the internal electrode layer can be thinned. The metal oxide layer containing nickel and magnesium functions to increase the insulation resistance of the dielectric layer.

[0018]

FIG. 1 is a schematic perspective view of a multilayer ceramic capacitor according to the present invention. According to FIG. 1, dielectric layers 1 and internal electrode layers 2 are alternately laminated, and external electrode layers 3 are formed on both left and right end surfaces of the laminated body. And
The internal electrode layer 2 has a structure in which every other layer is electrically connected to the left and right external electrode layers 3.

According to the present invention, as shown in the enlarged view of the main part of FIG. 2, magnesium oxide in the nickel particles constituting the internal electrode layer is fired at the interface of the internal electrode layer 2 with the dielectric layer 1. It is a great feature that the metal oxide layer 4 containing nickel and magnesium formed by diffusing and moving to the end side of the internal electrode layer exists.

As the metal oxide layer 4, specifically, MgNiO ₂ , Mg _0.4 Ni _0.6 O, Mg ₄ NiO
(OH) _{9 and the} like.
Desirably, it is NiO ₂ .

The presence of the metal oxide layer 4 can prevent the intrusion of moisture into the internal electrode layers, improve the moisture resistance load characteristics, and re-oxidize the fired multilayer ceramic capacitor. Even in such a case, since the internal electrode layer is not easily oxidized, the resistivity of the internal electrode layer does not increase.

The thickness of the composite oxide layer 4 is set at 0.1.
It is important that the thickness is from 0.5 to 0.2 μm. That is,
If the thickness of the composite oxide layer 4 is less than 0.05 μm, penetration of moisture cannot be prevented, the effect of improving the moisture load resistance is low, and the effect of preventing oxidation of the internal electrode layer is insufficient. On the contrary, if the thickness of the oxide layer 4 is larger than 0.2 μm, the resistance value of the internal electrode layer increases and the internal electrode layer cannot be made thin. In particular, the thickness of the composite oxide layer 4 is 0.1 to 0.15 μm from the viewpoint of improving the moisture resistance and oxidation resistance and reducing the thickness of the internal electrode layer.
Is desirable.

The shape of these nickel particles is spherical,
There are a flake shape, a protrusion shape and an irregular shape, and the shape is not particularly limited. However, a spherical shape is desirable from the viewpoint of enhancing the filling property of the internal electrode layer. The average particle diameter of the nickel particles is 0.0 as a value (BET value) determined as a specific surface area diameter because the thickness of the internal electrode layer is reduced and the thickness variation is reduced.
Desirably, it is 5 to 0.8 μm.

In addition, magnesium remaining in a trace amount inside the internal electrode layer may be alloyed with nickel, or may be Mg _x Ni _2-x
O ₂ (0.1 ≦ x ≦ 1) exists in the form of a complex oxide or MgO.

Next, a method for manufacturing the multilayer ceramic capacitor of the present invention will be described. First, using a dielectric powder made of a dielectric material having reduction resistance, a pulling method,
A dielectric sheet is prepared by a well-known forming method such as a doctor blade method, a reverse roll coater method, a gravure coater method, a screen printing method, and a gravure printing method.

As the dielectric material having reduction resistance, specifically, BaTiO ₃ —CaZrO ₃ —MnO—Y ₂
O ₃ or the like can be used. In addition, the thickness of the dielectric sheet is 0.5 to 50 μm for reasons of small size and large capacity.
It is desirable that

On the other hand, as for the method of preparing the conductive paste, first, nickel particles are placed in a non-oxidizing atmosphere at 500 to 8%.
After heat treatment at 00 ° C to reduce the oxide layer on the particle surface,
By introducing into a vacuum chamber and depositing magnesium oxide, a metal powder in which the surface of base metal particles is coated with magnesium oxide of a desired thickness can be produced. As another method, a magnesium-containing organic compound such as magnesium acetate is applied to the surface of nickel particles, and then heat-treated at 200 to 500 ° C. to form magnesium oxide on the surface of the particles.

In order to enhance the adhesion between the nickel metal particles and the magnesium oxide layer, before coating the magnesium oxide, the nickel powder is heat-treated at 260 to 300 ° C. in the air to oxidize the surface of the nickel particles. It is desirable to form a nickel oxide layer beforehand.

The surface of the nickel particles is coated with a specific thickness of magnesium oxide. The magnesium oxide coating layer may contain magnesium metal or magnesium hydroxide.

Further, the thickness of the magnesium oxide coating layer is desirably 10 to 100 nm. If the coating thickness is greater than 100 nm, the particles in the conductive paste are likely to aggregate with each other, and the dispersibility of the particles is reduced. Therefore, the amount of the organic binder necessary for dispersing the nickel particles increases, and the binder removal treatment is performed. In addition to the difficulty, magnesium oxide exists alone as a large number of particles, and the connection between nickel particles deteriorates, so that the resistivity of the internal electrode layer increases. Conversely, if the coating thickness is less than 10 nm, the effect of reducing the cracks of magnesium and the effect of improving the moisture resistance load characteristics are not sufficiently exhibited, and the nickel particles that are the cores of the particles are oxidized during the binder removal treatment. Cracks may occur, and the oxidized nickel remains as nickel oxide even after firing, increasing the resistance value of the internal electrode layer.

It is important that the content of magnesium oxide covering the surface of the nickel particles is 0.05 to 1% by weight in terms of magnesium metal in the nickel particles. That is, if the content of magnesium oxide is less than 0.05% by weight in terms of metal, it is impossible to completely cover the nickel particles, and if it is more than 1% by weight, a large amount of magnesium oxide remains inside the internal electrode layer. This is because the resistance value of the internal electrode layer increases.

When the conductive paste is applied to the surface of the ceramic green sheet and fired simultaneously, a predetermined amount of raw material powder such as the same material as the ceramic green sheet may be added as a common material. As a result of improving the adhesion to the green sheet and approximating the shrinkage and thermal expansion coefficient due to firing of the ceramic and conductor, cracks and delamination at the interface and end of the internal electrode layer are prevented. Can be.

Further, the conductive paste may contain various organic binders and solvents for forming the paste, or various dispersants for preventing agglomeration and poor dispersion of particles.

Specific examples of the organic binder resin include cellulose resins, rosin resins, polyvinyl resins, butyral resins, polyester resins, acrylic resins, epoxy resins, polyamide resins, polyurethane resins, and alkyds. Resin, maleic acid resin, polyamide resin, petroleum resin, etc., and these resins can be used alone or in combination. Among them, a cellulose resin is desirable from the viewpoint of good compatibility with other organic resins and solvents, and suppression of aggregation of particles and improvement of dispersion.

As the dispersant, any surfactant generally used for preparing a paste can be used.
A polymer surfactant is desirable from the viewpoint of stabilizing the paste.

The solvent is not particularly limited as long as it is compatible with the organic binder resin used. Examples thereof include alcohols such as ethanol, carbitol, toluene, acetate, and xylene, hydrocarbons, and esters. , Ether alcohols, ketones, chlorinated hydrocarbons and the like can be used. Further, when preparing a homogeneous solution of a desired amount of organic additives and a solvent, a surfactant, a plasticizer, an antistatic agent, an antifoaming agent, an antioxidant, a lubricant, a curing agent, and the like may be used, if necessary, as an auxiliary agent. It can be used as appropriate.

The conductive paste is obtained by mixing the above-mentioned metal powder (40 to 50% by weight) and the above-mentioned organic component (50 to 60% by weight) and kneading them with a three-roll mill or the like.

Then, on the surface of the above-mentioned dielectric sheet,
This conductive paste is applied to the internal electrode layer pattern by a known printing method such as a screen printing method, a gravure printing, or an offset printing method. The thickness is 2 μm or less, particularly 1 μm, from the viewpoint of miniaturization and high reliability of the capacitor.
It is desirable that:

Then, a plurality of dielectric sheets to which the conductive paste is applied are laminated and pressure-bonded, and the laminated molded body is placed in the atmosphere at 250 to 300 ° C. or in a low oxygen atmosphere having an oxygen partial pressure of 0.1 to 1 Pa to 500 to 800. After binder removal at ℃
Baking is performed at 1100 to 1200 ° C. for 2 to 3 hours in a non-oxidizing atmosphere. Further, if desired, the oxygen partial pressure is 0.1 to 10
^-4 Pa at low oxygen partial pressure, about 900 ~ 1100 ℃, 3 ~
By performing the reoxidation treatment for 10 hours, the reduced dielectric layer is oxidized to form a dielectric layer having good insulating properties.

Finally, a paste such as silver or indium-gallium is applied to each end face of the obtained laminated sintered body,
By forming external electrodes electrically connected to the internal electrode layers, a multilayer ceramic capacitor can be manufactured.

[0041]

EXAMPLES (Examples) Values (BE) determined as specific surface area diameters
(T value), a nickel powder having an average particle size of 0.2 μm was heat-treated at 500 ° C. for 30 minutes in nitrogen,
C. for 10 minutes to oxidize the surface of the nickel particles.
The treated nickel particles were introduced into a vacuum chamber, sprayed on the surfaces of the Ni particles using a magnesium organic compound, and heat-treated at 400 ° C. to obtain nickel particles coated with magnesium oxide. As a result of observation by a transmission electron microscope and a crystal structure analysis, it was confirmed that the surface layer of the base metal particles was covered with 50 to 100 nm of magnesium oxide.

With respect to 45% by weight of the obtained coated metal powder,
5.5% by weight of ethylcellulose and α-terpineol 9
An electrically conductive paste was prepared by kneading 55% by weight of an organic vehicle consisting of 4.5% by weight with a three-roll mill.

On the other hand, 97.5 mol% of BaTiO ₃ and Ca
0.5 mol% of Y ₂ O ₃ is added to 100 mol% of a composition composed of 2.0 mol% of ZrO ₃ and 0.5 mol% of MnO.
The ceramic slurry having the added composition was formed on a belt-shaped carrier film made of a synthetic resin such as polyester or polypropylene by a doctor blade method, dried, and then, the ceramic green sheet was peeled off from the carrier film to have a thickness of 10 μm. After forming a belt-shaped ceramic green sheet, the ceramic green sheet
mm, 200 mm wide.

The conductive paste described above was printed on one main surface of the obtained ceramic green sheet in a pattern of internal electrode layers using a screen printing apparatus. A plurality of ceramic green sheets to which the paste was applied were laminated to obtain a laminated molded body.

Next, the obtained laminated molded body was placed in air at 300
After heating to 500 ° C. in an oxygen / nitrogen atmosphere at 500 ° C. or 0.1 Pa to perform a binder removal treatment, baking is performed at 1200 ° C. for 2 hours in an oxygen / nitrogen atmosphere at 10 ⁻⁷ Pa, and then 10 ^−2. Reoxidation was performed at 900 ° C. in an oxygen-nitrogen atmosphere of Pa to obtain a ceramic sintered body. After firing, an indium-gallium paste was applied to each end surface of the obtained ceramic sintered body to form external electrodes electrically connected to the internal electrode layers.

The external dimensions of the multilayer ceramic capacitor thus obtained are 1.6 mm in width and 3.2 m in length.
m, the thickness was 1.0 mm, and the thickness of the dielectric ceramic layer interposed between the internal electrode layers was 8 μm. The effective number of laminated dielectric ceramic layers was 50, and the area of the opposed internal electrode layer per layer was 2.1 mm ² .

The multilayer ceramic capacitors obtained as described above were hardened with a resin for each of 100 samples and polished, and the cross section of the capacitors was observed with a metal microscope at 400 times magnification to check for cracks. Table 1 shows the number of porcelains having cracks. In addition, the presence / absence and type of the metal oxide layer at the interface between the dielectric layer and the internal electrode layer were confirmed by micro-portion X-ray diffraction measurement. Further, scanning electron microscope (SEM) observation was performed to measure the thickness of the internal electrode layer and the internal electrode layer interface.

Also, JISC 5102 for 300 pieces
Table 1 shows the number of cracks generated by a stereoscopic microscope after holding at a temperature of 40 ° C., a relative humidity of 90 to 95%, and a rated voltage of 10 V for 500 hours.

(Comparative Example) The value (B
(ET value) nickel powder having an average particle size of 0.2 μm and a value (BET value) determined as a specific surface area diameter of 10 μm
An internal electrode layer and a capacitor were manufactured using a powder obtained by mixing m magnesium powder, and the same evaluation was performed.

[0050]

[Table 1]

From the results shown in Table 1, it is found that the sample No. As for No. 8, many cracks were generated by the binder removal treatment and firing of the capacitor. In addition, the internal electrode layer was oxidized by the re-oxidation treatment, and the resistance value of the internal electrode layer was high, and the load property under humidity and humidity was deteriorated. Sample No. 3 in which the coating amount of magnesium oxide was less than 0.05% by weight. Even in Examples 1 and 2, no metal oxide layer was formed or the thickness was less than 0.05 μm. The internal electrode layer was oxidized by the reoxidation treatment, the resistance value of the internal electrode layer was high, and the wet and medium load characteristics were poor. Further, in Sample No. in which the thickness of the metal oxide layer exceeded 0.2 μm. In No. 7, the resistance value of the internal electrode layer was high, and the capacitance of the capacitor was reduced.

The sample No. to which MgO powder was added was used. 9
However, although MgNiO ₂ was generated, the composite oxide layer could not be formed scattered. As a result, the wet and medium load characteristics were poor, and the resistance of the internal electrode layer was increased.

On the other hand, in the sample of the present invention, no cracks were generated after firing, the capacity was 1.1 μF or more, the insulation resistance was 0.9 GΩ or more, and the wet and medium load characteristics were good.

[0054]

As described in detail above, according to the present invention,
By using a powder in which nickel particles are coated with a specific amount of magnesium oxide as a conductive paste for forming the internal electrode layer, cracks and delamination during firing can be prevented and the internal electrode layer and the dielectric layer A composite oxide layer containing nickel and magnesium can be formed at the interface, and the moisture load resistance can be improved. In addition, a low-resistance internal electrode layer can be formed without the internal electrode layer being oxidized by the reoxidation treatment.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view illustrating the structure of a multilayer ceramic capacitor.

FIG. 2 is an enlarged view of a main part for describing the structure of the multilayer ceramic capacitor of the present invention.

[Explanation of symbols]

 Reference Signs List 1 dielectric layer 2 internal electrode layer 3 external electrode 4 metal oxide layer

Claims (4)

[Claims] 1. A multilayer ceramic capacitor comprising a nickel-containing internal electrode layer between at least two dielectric layers having reduction resistance, wherein said internal electrode layer has a weight of 0.05 to 1%. % Of magnesium and 0.05% at the interface between the internal electrode layer and the dielectric layer.
A multilayer ceramic capacitor comprising a metal oxide layer containing nickel and magnesium having a thickness of about 0.2 μm. 2. The multilayer ceramic capacitor according to claim 1, wherein the metal oxide containing nickel and magnesium is MgNiO ₂ . 3. The method according to claim 1, wherein the surface of the nickel particles has a metal content of 0.05 to 0.05.
A step of preparing a conductive paste containing a metal powder coated with 1% by weight of magnesium oxide; and a step of applying the conductive paste to a surface of a dielectric sheet made of a dielectric material having reduction resistance. Laminating a plurality of the dielectric sheets, baking the laminate in a reducing atmosphere, and forming external electrode layers on both end surfaces of the sintered body. Manufacturing method of ceramic capacitor. 4. The coating thickness of said magnesium oxide is 10 to 10.
4. The method according to claim 3, wherein the thickness is 100 nm.