JP2002246256A - Conductive paste and multiplayer capacitor using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive paste or multiplayer capacitors that has improved thin film formation capacity and electric conductivity, and has small manufacturing costs, and to provide a multiplayer capacitor using the conductive paste. SOLUTION: Nickel powder where a titanium compound is reduced as a reducing agent from solution containing nickel ions is mixed with an organic binder such as an epoxy resin to obtain conductive paste. Further, the conductive paste is printed and applied to a ceramic dielectric layer, is laminated in a number of layers, and then is burned at approximately 1000 deg.C, thus forming the multiplayer capacitor.

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 a multilayer capacitor and a multilayer capacitor using the same.

[0002]

2. Description of the Related Art In recent years, like other electronic components, multilayer capacitors have been further required to be smaller, have higher capacity, have higher reliability, and have lower cost. In order to respond to this demand, development of a material having a high dielectric constant, a defect-free dielectric layer, a thin film, a reduction in the cost of an internal electrode material, and the like are being advanced.

A multilayer capacitor has a multilayer structure in which thin dielectric ceramic layers and internal electrode layers obtained by firing a conductive paste are alternately stacked.

Conventionally, noble metals such as palladium and platinum have been mainly used as materials for internal electrodes of multilayer capacitors. However, in order to increase the capacity of the capacitor, the number of layers increases, and there is a problem in that the use of the above-mentioned noble metals increases the cost of raw materials. Recently, nickel powder has been frequently used to reduce costs. I have.

[0005] Nickel powder is dispersed in an organic binder to form a paste, printed and coated on a substrate, stacked with a derivative ceramic layer to form a multilayer, and fired in a reducing atmosphere while being pressed to form a capacitor. In recent years, as capacitors have become smaller and have higher capacities, it has become necessary to form thin films on the electrodes. However, if the electrodes are made thinner, there is a problem of deterioration in reliability due to dielectric breakdown. This is because the dielectric layer becomes thinner as the thickness of the dielectric layer becomes thinner as the film becomes thinner.

[0006] If the particle size of the nickel powder used as the material for the internal electrode is small and uniform, the dispersibility by the organic binder is improved, projections on the electrode surface are less likely to occur, and reliability is reduced due to dielectric breakdown. . If the particle size of the nickel powder is small and uniform, the packing density with respect to the organic binder can be increased, and a good electric conductive film can be obtained.

Further, as the thickness of the internal electrode is reduced, the electric conductivity of the metal used for the internal electrode also becomes a problem. When the electric conductivity of the metal used for the internal electrode is low, Joule heat is generated each time charge and discharge are repeated, resulting in poor energy conversion efficiency. Also, the temperature of the internal electrode increases, the electrical conductivity of that part decreases,
The capacitance when designed as a multilayer capacitor cannot be secured. In order to improve the electric conductivity, it is necessary to refine the metal used for the internal electrodes.

As a method for producing a metal powder having a small particle size,
For example, JP-A-11-302709 describes a method of reducing and depositing metal ions with a reducing agent such as hydrazine or a hydrazine compound, alkali hypophosphite, or alkali borohydride to obtain a nickel powder of 0.01 to 3 μm. Have been. Japanese Patent Application Laid-Open No. 11-80816 discloses a method for producing spherical nickel powder having a particle size of 0.1 μm to 1.0 μm by a gas phase reduction reaction.

However, the nickel powder obtained by these methods has problems of impurities and production costs.
When a reducing agent such as alkali hypophosphite or alkali borohydride is used in the method disclosed in JP-A-11-302709, phosphorus and boron are co-deposited in the metal, and the resulting metal powder Electric conductivity decreases. Hydrazine or hydrazine compounds are dangerous substances, and when they are used as a reducing agent, strict control of handling is required, which increases the production cost. The nickel powder obtained by the method described in JP-A-11-80816 contains 500 ppm of sulfur.
From 2000 to 2000 ppm, the electric conductivity is lowered.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a conductive paste for a multilayer capacitor which is excellent in thin film forming ability and electric conductivity and low in production cost, and a multilayer capacitor using the same.

[0011]

In order to achieve the above-mentioned object, the present invention relates to a conductive material for a multilayer capacitor in which nickel powder obtained by precipitating a titanium compound as a reducing agent from an aqueous solution containing nickel ions is mixed with an organic binder. Use a conductive paste. Further, a multilayer capacitor is formed using the conductive paste.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The titanium compound used as a reducing agent of the present invention can be used as long as it contains a trivalent titanium ion. Particularly, titanium trichloride which is industrially easily available is preferably used. it can. Further, a mixture of titanium tetrachloride and citric acid added to the titanium trichloride is also preferably used.

Further, any nickel ions can be used as long as they are derived from at least one nickel compound selected from the group consisting of nickel sulfate, nickel chloride and nickel carbonate. Nickel sulfate can be suitably used because it has little adverse effect due to solubility and accumulation of remaining anions.

The nickel powder used in the conductive paste of the present invention reduces nickel ions dissolved in an aqueous solution by transfer of electrons when trivalent titanium is oxidized to tetravalent, and is precipitated as metallic nickel. When depositing nickel powder, a phosphoric acid compound or hydrazine has too large a reducing ability, so that precipitation occurs continuously on nickel powder once deposited, so that particle growth occurs. We have found a reducing agent containing titanium ions as a condition under which nickel deposition is unlikely to occur continuously. Also, after or during the deposition of nickel, oxidized tetravalent titanium ions can be reduced to trivalent titanium ions by performing a cathodic reduction treatment in an electrolytic cell. That is, by replenishing nickel ions, the reducing agent containing titanium ions can be used semipermanently, and low cost can be expected. Titanium ion, which is a reducing agent, has a very high ionization tendency and cannot be present in an aqueous solution since it is metallic titanium. Therefore, titanium derived from titanium ions is not substantially contained in nickel powder (100 ppm or less), and is extremely high. Of purity. Therefore,
The electrical conductivity is not impaired. For this reason, the multilayer capacitor manufactured using the conductive paste of the present invention also shows excellent electric characteristics.

[0015] The nickel powder used in the conductive paste of the present invention is characterized in that it has a small particle size, is spherical and has a narrow particle size distribution. For this reason, this nickel powder is excellent in dispersibility by an organic binder, the electrode surface formed from the conductive paste of the present invention is smooth, has few protrusions, and is unlikely to cause dielectric breakdown.

The particle size can be changed by appropriately selecting the type of nickel ions, the concentration of the reducing agent, and the deposition rate. In the present invention, nickel powder having an average particle size of 10 nm to 300 nm is preferably used. The average particle diameter is the average diameter of the primary particles, using a high-resolution scanning electron microscope.
When observed at a magnification of 100,000 times, when the major axis of the sphere is a and the minor axis is b, it is determined by (a + b) / 2.

As the average particle diameter decreases, the influence of the oxide film on the surface increases, and the conductivity is impaired. From these, the average particle size is preferably 10 nm or more.
On the other hand, when the average particle size is larger than 300 nm, the gap between the powders when the conductive paste is applied becomes large, in other words, the filling amount per unit volume becomes small, so that the conductivity becomes poor. Therefore, the nickel powder used in the conductive paste of the present invention preferably has an average particle size of 10 nm to 300 nm. Further, the average particle size is more preferably 40 to 100 nm. The influence of the oxide film on the surface is small,
A conductive paste having a higher filling amount and more excellent conductivity can be obtained.

The conductive paste of the present invention is obtained by mixing the above nickel powder with a known organic binder. As the organic binder, a resin obtained by adding a solvent as necessary to a resin such as an epoxy resin, an acrylic resin, or a phenol resin is used. The mixing ratio varies depending on the type of the organic binder, but since the nickel powder of the present invention is excellent in dispersibility, a conductive paste containing 80% by weight of the nickel powder is also possible.

This conductive paste is printed and coated on, for example, a ceramic dielectric layer, and after laminating a large number, a temperature of about 1000 ° C.
To form a multilayer capacitor.

[0020]

EXAMPLES (Example 1) The plating solutions shown in Table 1 were prepared, and ammonia was added while maintaining the bath temperature at 60 ° C. to adjust the pH to 9.
It was adjusted to 0 to precipitate nickel powder. It was taken out of the bath, washed with tap water and pure water, and dried to obtain a nickel powder having an average particle size of 20 nm. 70% by weight of this powder, 7% by weight of bis-A epoxy resin (Araldite AER grade 6051N75 manufactured by Asahi Chiba Co., Ltd.), 7% by weight of bis-F epoxy resin (Epicoat 815 manufactured by Yuka Shell Epoxy Co., Ltd.), and other epoxy resins A conductive paste was obtained by mixing 15% by weight and 1% of a curing agent. Furthermore, 400 layers of this conductive paste were laminated by a screen printing method so as to be alternated with the ceramic layers, and then fired to produce a multilayer capacitor. 100 multilayer capacitors were prepared, and the capacitance of each was measured, and a 120 V DC short circuit between the electrodes was examined.

[0021]

[Table 1]

Example 2 The plating solutions shown in Table 1 were adjusted to a bath temperature of 50 ° C. and a pH of 9.2 to obtain nickel powder having an average particle size of 50 nm. Using this powder, a conductive paste and a multilayer capacitor were produced in the same manner as in Example 1.

(Comparative Example 1) Nickel chloride was evaporated in a CVD reactor, and the amount of nickel chloride in the carrier gas was adjusted to 5.0 g / liter using a carrier gas (nitrogen gas). A nickel powder having an average particle size of 800 nm was produced by a gas phase method of reducing at a temperature of ° C. Using this powder, a conductive paste and a multilayer capacitor were produced in the same manner as in Example 1.

[0024]

[Table 2]

The film thickness was measured by embedding the sample in a resin, polishing the cross section, and then observing it with an electron microscope. The surface roughness was measured based on JIS B0601-1994, and the average capacitance was measured with a coulomb meter. The short defect rate was determined by inspecting 100 pieces.

Conventionally, a multilayer capacitor formed of 400 layers is 0.8 mm.
In Example 1, (dielectric + conductive layer) / 2 was used.
Dielectric breakdown did not occur even when the thickness was reduced to 1.8 μm, and as a result, a capacitor with a 400-layer stack could be manufactured with a thickness of 0.45 mm. Furthermore, it has been found that by making the nickel powder particle size finer, dielectric breakdown when a direct current is applied is also suppressed. The multilayer ceramic capacitor of Comparative Example 1 having a large particle size could not secure the designed capacitance of 100 nF. In Examples 1 and 2, the capacitance satisfied the design value, the defect rate could be reduced to 3% at an average particle diameter of 20 nm, and no insulation failure occurred at 50 nm.

[0027]

As described above, the conductive paste of the present invention is excellent in thin film forming ability and electric conductivity and low in production cost. Thus, a multilayer capacitor that is superior in cost can be manufactured.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shinji Inazawa 1-3-1 Shimaya, Konohana-ku, Osaka-shi F-term in Sumitomo Electric Industries, Ltd. Osaka Works 5E001 AB03 AH01 AH09 AJ01 AJ02 5E082 AA01 AB03 EE04 EE23 EE35 FF05 FG26 FG46 5G301 DA10 DD01

Claims (4)

[Claims] 1. A conductive paste for a multilayer capacitor, wherein nickel powder obtained by depositing a titanium compound as a reducing agent from an aqueous solution containing nickel ions is mixed with an organic binder. 2. The conductive paste according to claim 1, wherein the titanium content of the nickel powder is 100 ppm or less. 3. The nickel powder has an average particle size of 10 nm to 300 nm.
The conductive paste for a multilayer capacitor according to claim 1, wherein: 4. A multilayer capacitor using the conductive paste according to claim 1.