JPH0437009A - Conductive paste for forming terminal electrode of laminated type capacitor - Google Patents

Abstract

PURPOSE:To obtain conductive paste which can form an external electrode in which a crack scarcely occurs in a capacitor element by incorporating 2-15 wt.% of granular TiO2 in 100 pts.wt. of silver conductive powder. CONSTITUTION:In conductive powder, metal powder of Pd, Ni, Cu, etc., is slightly mixed with silver-palladium alloy. Its means particle size is about 0.2-2 mum. Borosilicate glass powder is used, and its mean particle size is about 1-6 mum. As organic binder, ethylcellulose is, for example, used, and its mixing amount is normally set to about 3-7 wt.%. As organic solvent, alpha-terpineol is used, and its mixing amount is normally about 15-30 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a conductive paste, particularly a conductive paste for forming terminal electrodes of a multilayer capacitor.

[Conventional technology]

As electronic devices become smaller, electronic components used in electronic devices are also becoming smaller. For example, among ceramic capacitors, small and lightweight multilayer ceramic capacitors have been developed. This multilayer ceramic capacitor is, for example,
It has a capacitor element in which internal electrode layers with a thickness of several μm and ceramic dielectric layers with a thickness of several tens of μm are alternately laminated and integrally fired, and an external electrode. Here, the external electrodes are formed using conductive paste. Furthermore, in order to improve solder heat resistance and enable mounting on a printed circuit board, a Ni film or a Sn film is formed on the surface of the multilayer ceramic capacitor by electroplating.

Conventional conductive pastes for forming external electrodes are mainly composed of silver-based conductive powder, glass frit, organic binder, and organic solvent (for example, Japanese Patent Publication No. 62-60
(Refer to Publication No. 802), external electrodes are formed using a conductive paste by applying the above-mentioned conductive paste to the end face of a capacitor element, and baking the conductive powder and glass frit in the paste to integrate it with the capacitor element. This is done by

[Problem to be solved by the invention]

Multilayer ceramic capacitors using the conventional conductive paste are prone to cracks on the capacitor element side at the interface between the external electrode and the capacitor element.This is because the coefficient of thermal expansion of the capacitor element is 8°5 = 10 ．． 5 x 10
"/"C, whereas the coefficient of thermal expansion of the external electrode is 19.
This is because there is a large difference in the coefficient of thermal expansion between the two. In particular, if the capacitor element is large (for example, 3.2 wa > (1,6+++m or more))
In multilayer ceramic capacitors.

As mentioned above, the rack is easy to live in.

An object of the present invention is to provide a conductive paste for forming terminal electrodes of multilayer capacitors, which can form external electrodes that are less likely to cause cracks in capacitor elements.

[Means to solve the problem]

The conductive paste for forming terminal electrodes of a multilayer capacitor of the present invention contains a silver-based conductive powder, a glass solid, an organic binder, and an organic solvent. It is characterized by.

* * The conductive powder used in the present invention is a component for forming an electrode after baking the conductive base.

As the conductive powder, for example, silver, a powder of an alloy containing silver as a main component, or a mixture of silver powder and powder of another type of conductive metal is used. Examples of such conductive powder7 include silver-basidium-based alloys such as Pa, Ni,
An example is a mixture of metal powders such as Cu (4) to some extent (7). The average particle size of the conductive powder is preferably about 0.2 to 2 μm. When the average diameter of the conductive powder is 2 μm, the sintering speed of the conductive powder tends to be slow. Note that the conductive powder is usually mixed into the conductive paste in an amount of about 65 to 755 times.

The glass fluoride used in the present invention is an inorganic binder component that bonds the C1' conductive powder to the body of the multilayer capacitor during firing of the conductive base. As a glass frit, Inuba ZnO is used.

B, 0. , S iOi , Na, o, Lj, 0. Ba
O1i' b 01CaO1S r O,T i Ox
An example is a borosilicate-based glass powder prepared by mixing the following in a desired ratio. The average particle size of the glass powder is 1 to 6 μm.
About m is preferable. If the average particle size is larger than 6 μm, firing blisters will occur during firing, and the adhesion between the terminal electrodes and the capacitor body will deteriorate.

On the other hand, if it is smaller than 1/7 m, the viscosity stability of the paste deteriorates and workability tends to decrease. In addition, in the present invention, the glass powder is usually contained in the conductive paste in an amount of 2 to 7% by weight.
Mixed to some degree.

The organic binder used in the present invention C is a component for imparting viscoelasticity that can be applied to the conductive P4 base,
For example, ethyl cellulose, rosin resin, etc. are used. The amount of the organic binder mixed in the conductive paste is appropriately set depending on the coating conditions of the conductive base I, etc., but is usually set to about 3 to 7%.

The organic solvent used in the present invention is a component for dissolving the above-mentioned organic binder component and imparting desired viscosity to the conductive base. Examples of the organic solvent include α
-Terpineol, 2,2.4 trimethyl~ i,3-
Pentanedi-A-Lumonoisobutyrate, Bunalcaldito-Ruacetate I.

(BCA) etc. are used. Conductivity of organic solvents・−～・
- The amount of mixture in the coating is set as appropriate based on the 4 conditions for applying the conductive base, but it is usually set to about 15% to 30%.

The conductive base plate of the present invention contains 11 glass components and particulate TiOx (-titanium oxide) as a different filler. T i O, is the difference between the coefficient of thermal expansion of the terminal electrode obtained by firing the conductive base and the coefficient of thermal expansion of the capacitor body, which is 4. Prevents cracks from forming. Here, since the thermal expansion coefficient of 1゛102 is 7.6 It is possible to approach the expansion rate. Note that the particle size of TiO7 is 1.4. ~3.0μ- is preferred.

In the present invention, 'T'i02 is added in 2 to 15 parts by weight per 100 parts by weight of the above-mentioned silver-based conductive powder.

If the amount of TiO□ added is less than 2 parts by weight, no effect will be produced by adding TiO□;
If the amount exceeds 5 parts by weight, cracks are likely to occur in the terminal electrode obtained by firing the conductive paste, and there is a risk that the plating solution will enter the terminal electrode during the plating process.

In addition to the above-mentioned components, the conductive paste of the present invention may contain a small amount of colloid of an organic noble metal such as organic platinum, organic rhodium, organic gold, or organic silver. It can promote knotting.

Next, a method of using the conductive paste of the present invention will be explained.

First, FIGS. 1 and 2 show an example of a multilayer ceramic capacitor in which the conductive paste of the present invention is adopted.
The figure is a perspective view of a multilayer ceramic capacitor, and FIG. 2 is a cross-sectional view taken along the line -■ in FIG. 1.

In the figure, a multilayer ceramic capacitor 1 includes a rectangular parallelepiped main body 2 and a pair of external electrodes 3a and 3b arranged to face each other at both ends of the main body 20.

The main body 2 is constructed by laminating a large number of green sheets made of a dielectric ceramic material such as barium titanate, and firing them to integrate them. Inside the main body part 2, an internal electrode 4a is provided.

4b are arranged alternately. The internal electrode 4a is connected to the external electrode 3a disposed on the right end surface of the main body 2 in the figure, and is insulated from the external electrode 3b disposed on the left end surface. On the other hand, the internal electrode 4b is connected to the external electrode 3b and is insulated from the external electrode 3a. Also,
Internal electrode 4a.

4b are arranged in parallel.

The external electrodes 3a, 3b are constructed using the conductive paste of the present invention. Therefore, the external electrodes 3a and 3b include a silver-based conductive material, glass frit, and T i O.

In this multilayer ceramic capacitor 1, charges are accumulated in internal electrodes 4a and 4b that face each other via a fired ceramic material. And an external electrode 3a.

3b serve as input/output terminals of capacitors configured within the main body portion 2, respectively.

Here, a method for manufacturing the above-described multilayer ceramic capacitor 1 will be described while referring to a method for using the conductive paste of the present invention.

First, the main body part 2 is prepared. The main body part 2 has an internal electrode 4a
, 4b is obtained by laminating a plurality of ceramic green sheets printed with conductive paste and firing them. Note that the ends of the internal electrodes 4a or 4b are exposed at both ends of the main body 2 obtained by firing.

Next, both end surfaces of the obtained main body part 2, that is, the internal electrodes 4
External electrode 3a is provided on the surface where a and 4b are exposed.

3b is formed. In forming the external electrodes 3a and 3b, first, a conductive paste of the present invention is applied to both end surfaces of the main body part 20 in an amount of 100 to 100%.
Apply to a thickness of about 120 μm. The conductive paste is applied by, for example, a dipping method, a transfer method, or the like. After applying the conductive paste, the conductive paste is dried. At this time, the solvent in the conductive paste evaporates. Next, the conductive paste is fired. Firing temperature is usually 700~
The temperature is set at approximately 850°C. In the firing process, first 30
The resin component in the paste volatilizes at around 0° C., and when baking is continued, a sintering reaction of the conductive powder, softening of the glass frit, and plastic flow occur. In this reaction, the glass frit concentrates on the surface side of the conductive paste and the main body 2 side,
As the firing temperature increases, a glass-rich surface layer is formed on the bonding surface between the main body 2 and the conductive powder. Thereby, a multilayer ceramic capacitor 1 in which the main body portion 2 and the external electrodes 3a, 3b are firmly joined is obtained. Note that the Tie in the conductive paste does not react with either the conductive powder or the glass frit during the baking reaction of the paste, and is maintained uniformly in the form of particles in the thickness direction of the external electrodes 3a, 3b.

External electrode 3a of the obtained multilayer ceramic capacitor 1,
3b is plated with Ni. Further, 5n-Pb solder plating is applied thereon. As a result, a multilayer ceramic material 9 having good solder scratch resistance and solder heat resistance is obtained.

〔Example〕

100 parts by weight of S-conductive powder, 3.5 parts by weight of borosilicate curved lead gauze, 3.5 parts by weight of borosilicate curved lead, 3.5 parts by weight of utilyl cellulose,
3.5 parts by weight of rosin resin and Tie in the proportions shown in the table.
Knead with a mixer and add CS'α terpineol to adjust the viscosity to about 5,000 voids 1°7 to prepare a conductive paste. As the conductive powder, a mixture of 50% by weight of spherical Ag powder with an average particle diameter of 0.2 to 0.3 μyni71 and 50% by weight of scaly Ag powder was used. In addition, glass solid I□ contains Zn02O mol%,
820.28 mol%, S 1 O2 31 mol%, Ba0
(i mol%, Nax06.5 mol% and AI<z 03
2. A 5 mol% mixture was used.

Next, a 3225 type porcelain Nifundensa body (manufactured by Kyocera ■) having a thickness of 0.85 m was prepared, and a conductive base F was coated thereon by a dipping method. This conductive 1'1 base I was heated at a rate of 50°C/min.
From Jo and C: "-, a laminated Simic capacitor with an electrode formed thereon was manufactured. The linear thermal expansion coefficient of the external electrode was investigated for the obtained laminated Simic capacitor, and The occurrence of cracks was quickly investigated.The occurrence of clutter was evaluated by the number of cracks that had occurred in 100 manufactured multilayer ceramics.The results are shown in the table below. (.In addition,
In the table, sample number 2.3.4 is Example ζ of the present invention,
Sample number 1°5 is a comparative example.

1... Multilayer ceramic capacitor, 3a, 3b...
external electrode.

Patent applicant: Kyocera Corporation Agent: Patent Attorney Yoshio Miyagawa

Claims (1)

[Claims] (1) A conductive paste for forming terminal electrodes of a multilayer capacitor containing a silver-based conductive powder, a glass frit, an organic binder, and an organic solvent, based on 100 parts by weight of the silver-based conductive powder. 2 to 1 particulate TiO_2
5 parts by weight of a conductive paste for forming terminal electrodes of a multilayer capacitor.