JPH11283441A - Conductive paste and electronic part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide paste for preventing the occurrence of a crack and delamination by covering the surface of a base metal particle with nickel oxide. SOLUTION: Desirably in conductive paste, a base metal particle is a nickel particle, and nickel oxide is contained by 5 to 20 wt.% in the whole metal in metal conversion. Desirably in an electronic part having an internal conductor in a dielectric, nickel oxide exists on an interface between the dielectric and the internal conductor. A shape of the base metal particle is a spherical shape, a flake shape, a projection shape or an undefined shape, the average particle size of the base metal particle is 0.05 to 0.8 μm in a value found by a specific surface area diameter, and a thickness of the nickel oxide covering the surface of the base metal particle is desirably 50 to 300 nm. For example, a nickel oxide layer 3 exists on an interface between a dielectric layer 1 and an internal electride layer 2 in a multilayer ceramic capacitor. When the base metal particle is covered with the nickel oxide, a degree of sintering nickel is delayed, and the volume is also reduced since the nickel oxide is reduced to nickel to thin the internal conductor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste used for various electronic parts and an electronic part such as 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 laminated, and each dielectric layer is sandwiched between the internal electrode layers.

Here, the dielectric layer is formed by firing an unfired ceramic green sheet at a high temperature and sintering it.
The internal electrode layer is formed by firing a conductive paste at a high temperature to form a conductive metal thin film.

[0004] In recent years, the demand for lighter and smaller electronic components has become more severe, and in order to satisfy the demand, the sheet thickness per layer has been reduced, the number of layers has been further increased, and the laminated ceramic has been required. For capacitors,
In order to achieve a smaller size and a larger capacity, a dielectric material having a high relative dielectric constant is used, and the sheet thickness is further reduced.

Further, when the internal electrode layer is formed of a conductive paste for internal electrodes containing a noble metal such as palladium as a main component, the cost of forming the electrodes increases remarkably with an increase in the number of laminated layers. Has been developed, and a multilayer ceramic capacitor having an internal electrode layer formed with the paste has been put to practical use.

When a base metal such as nickel is used as the internal electrode layer, the base metal generally has a low equilibrium oxygen partial pressure, so that an oxide is formed when the base metal is fired at a high temperature and the conductivity is reduced. There's a problem. Therefore, firing must be performed in a non-oxidizing atmosphere in which nickel is not oxidized, and the dielectric material naturally requires reduction resistance.

A conventional multilayer ceramic capacitor using nickel as an internal electrode layer generally reduces the firing cost of an unsintered laminate in which a plurality of ceramic green sheets each having a surface coated with a conductive paste for an internal electrode layer are stacked. Therefore, after performing binder removal treatment (hereinafter, referred to as removal of binder) at 400 ° C. or higher in the atmosphere, sintering and integration are performed in a non-oxidizing atmosphere having a very low oxygen partial pressure such that the internal electrode layer is not oxidized, for example, a nitrogen atmosphere. It was produced by this.

It is necessary to select a conductive paste and a porcelain material for the internal electrode layer used in such an integral firing method which have close heat shrinkage characteristics in the firing process, otherwise delamination or cracks may occur. Cheap.

Conventionally, in order to make the heat shrinkage of the conductive paste close to that of the porcelain, the surface of the base metal is coated with palladium (Japanese Patent Laid-Open No. Hei 6-96997), or the same or similar porcelain material powder as the green sheet called co-material is used. Means for inclusion in conductive paste (JP-A-54-14096,
JP-A-57-30308) has been proposed.

[0010]

However, in the conventional manufacturing method, although the internal electrode layer is hardly oxidized in the sintering step, the nickel is partially removed from the atmosphere at 400 ° C. or higher from the viewpoint of sintering cost. Oxidation caused the internal electrode layer to expand, and delamination and cracks were generated in the laminate during de-buying. As a result, there is a problem that delamination and cracks occur in the obtained capacitor.

On the other hand, if the internal electrode layer is deburied at a temperature lower than 400 ° C. in order to prevent oxidative expansion of the internal electrode layer, the debuy cannot be performed completely, the binder component remains as carbon, and the internal electrode is removed during firing. The layer caused oversintering and the nickel was molten. As a result, there is a problem that nickel on the end face is blown out to the outside, capacity is lost, and the capacity is reduced. In addition, oversintering of the internal electrode layer causes nickel to become spherical, which causes the internal electrode layer to expand and generate internal stress, which causes a problem that cracks occur in the porcelain. Further, there is a problem that voids are generated in the sintered body after firing by remaining as carbon.

That is, in the case where the binder is removed in the atmosphere, it is difficult to completely scatter and remove the organic binder used for the green sheet and the organic binder used for the conductive paste, or the capacity as designed cannot be obtained. Problems such as voids in the sintered body, cracks in the sintered body, or oxidative expansion of the internal electrode layer, causing delamination and cracks in the multilayer ceramic capacitor Was.

When the base metal surface is coated with palladium, the heat shrinkage can be adjusted. However, when the palladium is removed at 400 ° C. or more in the air atmosphere, palladium becomes palladium oxide at about 400 ° C. or more. The base metal particles, which are the cores of the particles, are oxidized to increase the electric resistance, and the multilayer ceramic capacitor has problems such as delamination and cracks. On the other hand, at a temperature lower than 400 ° C., the de-buying could not be completely performed for the above-mentioned reason.

Further, when the above-mentioned co-material is contained in the conductive paste, the heat shrinkage can be adjusted. However, when the de-buying temperature is 400 ° C. or higher, the base metal is oxidized and the internal electrode layer expands. However, there is a fear that cracks may occur in the laminated body during de-buying, and at temperatures lower than 400 ° C., de-buying cannot be performed completely. Further, in the fired capacitor, there is a problem that the portion where the upper and lower dielectric layers are connected via the common material contained in the internal electrode layer increases, and the electrode layer is cut off in the middle.

An object of the present invention is to provide a conductive paste and an electronic component which can be removed at a temperature lower than 400 ° C. and can prevent the occurrence of cracks and delamination.

[0016]

The conductive paste of the present invention is a conductive paste containing base metal particles as a main component, and the surface of the base metal particles is coated with nickel oxide. Here, the base metal particles are desirably nickel particles. Further, it is desirable that nickel oxide be contained in an amount of 5 to 20% by weight of all metals in terms of metal.

Further, the electronic component of the present invention is an electronic component having an internal conductor in a dielectric, wherein a nickel oxide layer is present at an interface between the dielectric and the internal conductor.

[0018]

In the conductive paste of the present invention, since the surface of the base metal is coated with nickel oxide, even in the case of de-buying at a temperature lower than 400 ° C. in the air, oxygen in the air and oxygen of the nickel oxide are removed. Thereby, carbon, which is a decomposition product of the organic binder, can be effectively oxidized and removed.

Since the surface of the base metal particles is coated with nickel oxide and there is no contact between the base metal particles, the temperature at which shrinkage due to sintering of the internal conductor is increased by the amount or thickness of the coated nickel oxide. The shrinkage behavior during firing can be made closer to that of a dielectric, and delamination and cracks can be prevented. Since the nickel oxide covering the base metal surface is reduced to almost metallic nickel by firing in a non-oxidizing atmosphere, the thickness of the internal conductor layer is reduced due to the volume reduction, and the occurrence of delamination and cracks is further reduced. In addition to suppressing the internal conductor, the thickness of the internal conductor can be reduced.

Further, nickel oxide is reduced to nickel metal by firing in a non-oxidizing atmosphere, and when the base metal particles are nickel, nickel metal alone is used.
When the base metal particles are other than nickel, since nickel and the base metal are almost alloyed, the electric resistance of the internal conductor does not increase and the characteristics of the dielectric are not adversely affected. In addition, when the base metal particles are other than nickel, the base metal and nickel are alloyed to be less oxidized than when the base metal is made of a base metal. And reliability can be improved.

That is, when the surface of the base metal particles is coated with nickel oxide, the residual carbon content of the internal conductor after the production of a multilayer ceramic capacitor or the like can be reduced even if debuying is performed at a temperature lower than 400 ° C. in the atmosphere. Can be
Cracks and delamination can be prevented, and the internal conductor can be made thinner.

Further, in the conventional conductive paste, the onset temperature of shrinkage due to sintering is lower than that of the green sheet, the shrinkage ratio is large, and the property of becoming spherical by sintering is strong. Although there were problems such as voids in the electrode layer due to sintering, such a problem was also raised because the surface of the base metal particles was coated with nickel oxide. In addition, since the grain growth of the base metal can be suppressed, and the nickel oxide is reduced to metallic nickel and the volume is reduced, a continuous internal electrode layer can be formed. Even when the base metal particles are other than nickel, by increasing the coating thickness, a continuous internal electrode layer can be formed as in the case where the base metal particles are nickel.

In the conductive paste of the present invention, nickel oxide is contained in an amount of 5 to 20% by weight of the total metal in terms of metal, thereby preventing oxidation of the base metal particles at the time of de-buying and reducing the sintering temperature of the internal conductor. And the oversintering of the internal conductor can be suppressed. Even when the base metal particles are other than nickel, the alloying of nickel and the base metal becomes optimal by containing nickel oxide in an amount of 5 to 20% by weight based on the total metal.

A multilayer ceramic capacitor manufactured using the conductive paste of the present invention, for example, has a nickel oxide layer at the interface between the dielectric layer and the internal electrode layer, so that it is fired to improve the characteristics. Oxidation of the internal electrode layer is also prevented by the re-oxidation treatment, so that an increase in conduction resistance does not occur.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The conductive paste of the present invention contains base metal particles whose surface is coated with nickel oxide as a main component. As the base metal, there are nickel, cobalt, copper or an alloy of two or more of them. Nickel is preferable because the firing temperature of the metal matches the firing temperature of a general dielectric and the cost is low. . The shape of these base metal particles is spherical, flake-like, protruding or irregular, and is not particularly limited. The average particle diameter of the base metal particles is 0.05 as a value obtained from the specific surface area diameter because the thickness of the internal electrode layer is reduced and the thickness variation is reduced.
0.8 μm is desirable.

The coating thickness of the nickel oxide coating the surface of the base metal particles is desirably 50 to 300 nm. If the coating thickness is larger than 300 nm, the particles having the coating layer tend to agglomerate and the dispersibility of the particles decreases. Or the amount of binder solution for dispersing the particles increases.

On the other hand, if the coating thickness is less than 50 nm,
There is a possibility that the base metal particles as the core may be oxidized. In order to coat the surface of the base metal particles with nickel oxide, the base metal particles which have been heat-treated at a high temperature in the air are introduced into a vacuum chamber, and nickel oxide is vapor-deposited.

The nickel oxide layer is formed by simply oxidizing the surface of the nickel particles. In this case, NiO and Ni ₂
O ₃ is generated, and when a capacitor is manufactured using such particles, the de-buying property is good, but Ni ₂ O ₃ causes oversintering at the time of firing, and the surface of the Ni particles is subjected to oxidation treatment. Since the control is difficult, the thickness of the oxide layer varies, for example, the particles become completely NiO particles, and the shrinkage occurs, and the internal electrode layer is interrupted and the capacitance decreases. On the other hand, when the nickel oxide is coated by vapor deposition or the like, the nickel oxide layer can be formed uniformly on the surface of the base metal particles, almost no shrinkage variation occurs, and a good internal electrode layer can be formed. This is because the capacitance can be improved.

The conductive paste contains, as a main component, base metal particles coated with nickel oxide. The conductive paste is made of a common material, for example, in order to improve the adhesiveness with a ceramic green sheet when producing a multilayer ceramic capacitor. Alternatively, a predetermined amount of the same raw material powder as the ceramic green sheet may be added. Further, in order to prevent the occurrence of a short circuit between the electrodes due to agglomeration of the particles or poor dispersion, it is desirable that the powder used is sufficiently dispersed. Therefore, various resins, dispersants and the like are used in various combinations as organic additives.

As the resin, a cellulose resin, a rosin resin, a polyvinyl resin, a butyral resin,
There are polyester resin, acrylic resin, epoxy resin, polyamide resin, polyurethane resin, alkyd resin, maleic resin, polyamide resin, petroleum resin, etc., and these resins may be used alone or in combination. it can. As a resin that suppresses agglomeration of particles and improves dispersion, because of compatibility with other resins and solvents,
Cellulosic resins are desirable.

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 additive to be used. Examples thereof include alcohols such as ethanol, carbitol, toluene, acetate, and xylene, hydrocarbons, and the like. Esters, ether alcohols, ketones, chlorinated hydrocarbons and the like can be used.

Further, in preparing a homogeneous solution of a desired amount of an organic additive and a solvent, a surfactant, a plasticizer, an antistatic agent, an antifoaming agent, an antioxidant, a lubricant, a curing agent may be used, if necessary, as an auxiliary agent. Agents and the like can be appropriately used.

Further, in the conductive paste of the present invention, it is desirable that the nickel oxide coated with the base metal particles be contained in an amount of 5 to 20% by weight based on the total metal.

If the nickel oxide content is less than 5% by weight of the total metal in terms of metal, the coated base metal particles are liable to be oxidized at the time of de-buying, which may cause cracks. If the content is more than 10% by weight, the nickel oxide is not reduced and the resistance is increased. If the base metal particles are other than nickel, nickel and the base metal (except nickel) are alloyed to reduce the sintering temperature. Because it goes down,
This is because the internal electrode may be over-sintered and may be in the shape of a ball to cause cracks and delamination. Nickel oxide is reduced to nickel in a reducing atmosphere,
From the reason that nickel and the base metal are alloyed, it is desirable to contain 10 to 15% by weight of the total amount.

In the electronic component of the present invention, for example, in a multilayer ceramic capacitor, dielectric layers and internal electrode layers are alternately laminated, and as shown in FIG.
A nickel oxide layer 3 exists at the interface between the electrode and the internal electrode layer 2. Nickel hydroxide may be present in the nickel oxide layer 3 in some cases.

When a multilayer ceramic capacitor is manufactured using the conductive paste of the present invention, it is necessary to fire in a reducing atmosphere. However, even in this reducing atmosphere, part of the nickel oxide on the surface of the base metal particles is reduced. This is because they remain without being moved to the dielectric layer side and sandwich the internal electrode layer made of the base metal, and thus the internal electrode layer made of the base metal is sandwiched by the nickel oxide layer. Since the passivation is formed on the surface of the internal electrode layer, the internal electrode layer is not oxidized by the re-oxidation treatment after firing, and the conduction can be improved.

The thickness of the nickel oxide layer at the interface between the dielectric layer and the internal electrode layer is preferably from 0.02 to 0.15 μm, and particularly from the viewpoint of increasing the oxidation resistance.
10 μm is desirable.

The electronic component may be any as long as it has an internal conductor in a dielectric, and includes, for example, a multilayer ceramic capacitor, a resonator, an actuator and the like, and also includes a substrate having an internal conductor.

A method for manufacturing a multilayer ceramic capacitor using the conductive paste of the present invention will be described. First, a ceramic green sheet having a predetermined composition is
It is manufactured by a pulling method, a doctor blade method, a reverse roll coater method, a gravure coater method, a screen printing method, a gravure printing method or the like. The thickness of the green sheet is desirably 0.5 to 50 μm for reasons of miniaturization and large capacity.

The conductive paste is formed on the ceramic green sheet by a screen printing method, an extrusion method, a gravure printing method, an offset printing method, or another method. The thickness thereof is 2 μm or less from the viewpoint of miniaturization and high reliability. In particular, it is desirable that the thickness be 1 μm or less.

Then, a plurality of green sheets to which the conductive paste is applied are laminated, and the laminated molded body is exposed to air in air.
It is obtained by removing the temperature at a temperature lower than 0 ° C., for example, 350 ° C., and baking in a non-oxidizing atmosphere at 1100 to 1350 ° C. for 2 to 3 hours. After firing, if necessary, reoxidation is performed at 900 to 1100 ° C. for 3 to 10 hours under a low oxygen partial pressure of about 10 ⁻⁶ to 10 ⁻¹⁰ to obtain a multilayer ceramic capacitor.

[0043]

EXAMPLE First, 0.2 μm Ni powder was added to 260-35 Ni powder.
Heat treatment was performed at 0 ° C. to oxidize the surface of the nickel particles. The treated nickel particles were introduced into a vacuum chamber and sprayed with nickel oxide to obtain nickel particles coated with nickel 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 nickel oxide.

Next, 45% by weight of base metal powder composed of base metal particles coated with nickel oxide, and 55% by weight of a vehicle composed of 5.5% by weight of ethylcellulose and 94.5% by weight of α-terpineol were kneaded with three rolls. Thus, a conductive paste was prepared. The amount of nickel oxide in the paste in terms of metal was changed by changing the coating thickness of the nickel oxide.

Next, 97.5 mol% of BaTiO ₃ and C
aZrO ₃ 2.0 mol% and with respect to 100 moles of the main component parts consisting of MnO0.5 mol%, the ceramic slurry composition having a Y ₂ O ₃ was added 0.5 parts by mole, synthetic resin such as polyester or polypropylene A belt-like ceramic green sheet was obtained by forming a film on a belt-like carrier film formed by a doctor blade method and drying the film. Next, the ceramic green sheet was peeled from the carrier film and punched into a size of 200 mm in length and 200 mm in width. The thickness of the ceramic green sheet was 10 μm.

The above-mentioned conductive paste was printed on one main surface of the obtained ceramic green sheet using a screen printing apparatus. A plurality of ceramic green sheets on which the coating film was formed were laminated to obtain a laminated molded body.

Next, the obtained laminated molded product was placed in the air at 380
Heated to a temperature of ° C. to burn the binder. At this time, the appearance of the 100 laminated molded articles after removing the binder was observed with a binocular microscope to check for cracks. Thereafter, firing was performed at 1200 ° C. for 2 hours in a reducing atmosphere, and reoxidation was performed at 900 ° C. in a nitrogen atmosphere (oxygen partial pressure 10 ⁻⁶ ) to obtain a ceramic sintered body. After firing, an indium-gallium paste was applied to each end face of the obtained ceramic sintered body to form an external electrode electrically connected to the internal electrode.

The external dimensions of the multilayer ceramic capacitor thus obtained were 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 electrodes was 8 μm. The effective number of laminated dielectric ceramic layers was 50, and the area of the opposed internal electrode per layer was 2.1 mm ² .

The multilayer capacitor obtained as described above was polished by solidifying 100 pieces of each sample with a resin, and a magnification of 40
A metallographic observation at a magnification of 0 was performed to check for cracks.

The internal electrode thickness was determined with a scanning electron microscope. Further, the thickness of the nickel oxide layer at the interface between the dielectric layer and the internal electrode layer was determined with an electron microscope for high magnification. X-ray photoelectron spectroscopy (ESCA) revealed that the nickel oxide layer was composed of nickel oxide and nickel hydroxide.

As a comparative example, a conductive paste was prepared using untreated nickel powder, and the same evaluation was performed.

Table 1 shows the state of occurrence of cracks (100) and the state of occurrence of cracks (100) after firing at 380 ° C. in an air atmosphere. The column of the amount of addition in Table 1 shows the amount of nickel oxide in the total amount of the paste in terms of metal, and the column of the oxide layer shows the thickness of the nickel oxide layer between the internal electrode and the dielectric ceramic layer and the column of the electrode thickness. Indicates the internal electrode thickness.

[0053]

[Table 1]

From Table 1, it can be seen that the sample No. With regard to No. 9, although nickel is oxidized and expanded during de-buying, cracks after de-buying and cracks after firing are large, but the amount of nickel oxide in terms of metal is 5% by weight.
It can be seen that cracks do not occur above this. On the other hand, in Samples 1 and 2 in which the amount of nickel oxide in terms of metal is less than 5% by weight, it can be seen that cracks after de-buying and cracking after firing are slightly generated.

Sample No. 2 in which the amount of nickel oxide in terms of metal was 25% by weight or more. No cracks were observed for Nos. 7 and 8, but it was found that the thickness of the nickel oxide layer in the capacitor was increased, the conduction of the internal electrodes was reduced, and the capacitance was reduced. Further, the sample No. As for No. 12, it can be seen that cracks increase due to oxidation of palladium.

On the other hand, in the sample of the present invention in which the amount of nickel oxide in terms of metal is 5 to 20% by weight, no cracks are generated after de-buying and after firing, and the capacitance is large. .

[0057]

As described above, according to the conductive paste and electronic component mainly composed of base metal particles whose surface is coated with nickel oxide, for example, in the case of a multilayer ceramic capacitor, the binder is removed from the atmosphere. Even after performing the binder removal at a temperature lower than 400 ° C., no crack or delamination occurs even after firing, and by coating the base metal particle surface with nickel oxide,
Nickel oxide can be reduced to nickel, the volume can be reduced, and the internal conductor can be made thinner.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an enlarged part of a multilayer ceramic capacitor manufactured using a conductive paste of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Dielectric layer 2 ... Internal electrode layer 3 ... Nickel oxide layer

Claims (4)

[Claims] 1. A conductive paste containing base metal particles as a main component, wherein the surface of the base metal particles is coated with nickel oxide. 2. The conductive paste according to claim 1, wherein the base metal particles are nickel particles. 3. Nickel oxide is 5-2 of all metals in metal conversion.
The conductive paste according to claim 1, wherein the conductive paste contains 0% by weight. 4. An electronic component having an internal conductor in a dielectric, wherein a nickel oxide layer is present at an interface between the dielectric and the internal conductor.