JPH05226179A - Powder for conductive paste - Google Patents

Abstract

PURPOSE:To form a thin layer inner electrode in a high yield without applying severe printing and coating conditions by using flake-shaped conductive powder having a special ratio between a mean diameter of two axes to a mean thickness. CONSTITUTION:Powder for conductive paste is flake-shaped conductive powder having 15mum or less of mean diameter of two axes, 0.5mum or less of mean thickness and 3 or more of the ratio of the mean diameter of the two axes/the mean thickness. When the paste containing it is applied, the powder is superposed in a state oriented along a coated surface, and even if a thickness of a coated layer is reduced, excellent conductivity can be obtained. Accordingly, this conductive paste is useful for forming an inner electrode of a laminated ceramic capacitor.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a powder for conductive paste.

[0002]

2. Description of the Related Art A conductive paste is a composite of a binder mainly composed of synthetic resin and a conductive powder such as a conductive metal powder which is generally spherical in overall shape. For example, formation of electrodes in an IC chip, It is used for forming conductor circuits on circuit boards, manufacturing thin film resistors, and forming internal electrodes for laminated ceramic capacitors.

For example, FIG. 1 is a perspective view of a laminated ceramic capacitor manufactured using a conductive paste.
As shown in the figure, a plurality of internal electrodes 2 are provided in an electrically insulating ceramic bulk 1 at predetermined intervals.
2'are arranged in a comb shape, and a pair of electrodes 3, 3'for applying a voltage to each internal electrode 2, 2'is loaded on both sides of the ceramic bulk 1.

Such a multilayer ceramic capacitor is generally manufactured as follows. It will be described with reference to FIG. That is, first, seven ceramic green sheets having a desired thickness are prepared. A conductive paste is thinly printed and applied on the upper surface of the first green sheet through a mask having a predetermined pattern to form a conductive paste layer to be the internal electrode 2, and a second green sheet is further laid on it.
A conductive paste is thinly printed and applied on the upper surface of the green sheet to form a conductive paste layer to be the internal electrode 2 '. This operation is sequentially and alternately repeated to form a bulk body in which six conductive paste layers are arranged at equal intervals between seven green sheets.

Then, the obtained bulk body is fired at a predetermined temperature. The conductive paste layer is converted into the internal electrodes 2 and 2'having a desired thickness by the binder volatilizing and shrinking as a whole, and the conductive powders contacting each other, and each green sheet is also an electrically insulating ceramic layer. Converted, Figure 1
A monolithic ceramic capacitor having a structure as shown in is obtained. The thickness of the internal electrodes at this time is generally 5 to 8 μ.
It is about m.

[0006]

By the way, as the electronic parts are made lighter, thinner, shorter and smaller, it is required to make the internal electrodes of the above-mentioned laminated ceramic capacitor thin to a thickness of about 1 to 2 μm. Therefore, in the case of the conductive paste for forming the internal electrodes of the multilayer ceramic capacitor, the conductive powder dispersed in the binder is made into fine powder. When the conductive powder is spherical, specifically, fine powder having a particle size of 1 μm or less, preferably about 0.2 to 0.3 μm is required, and moreover, when the conductive paste is applied by printing on the surface of the green sheet. There is a demand for conductive powder in which 2 to 4 conductor powders are aligned and overlapped in the layer thickness direction of the paste layer.

However, since it is quite difficult to produce a conductive powder having a particle diameter in the range of 0.2 to 0.3 μm with a high yield, the obtained conductive paste becomes expensive. Will end up. In addition, when the conductive powder is to be aligned in the layer thickness direction as described above, in order to deal with it, suitable conditions such as the amount and the dispersed state of the conductive powder in the binder are considerably limited. Therefore, it is necessary to align the green sheet and the pattern mask when printing the conductive paste, and to rigorously adjust the conditions such as the squeegee feed speed and surface hardness used during printing. It gets complicated.
Therefore, defects such as lack of conductivity of the formed internal electrode or a thickness not reaching a target value are likely to occur, resulting in a problem that overall yield is deteriorated.

The present invention solves the above problems in the conventional conductive paste, and when it is used for forming an internal electrode of a laminated ceramic capacitor, a strict print coating condition is applied to a thin layer internal electrode of about 1 to 2 μm. Without
An object of the present invention is to provide a powder for a conductive paste that can be formed with a high yield.

[0009]

To achieve the above object, in the present invention, the biaxial average diameter is 15 μm or less, the average thickness is 0.5 μm or less, and the biaxial average diameter / average thickness is 3 or more. There is provided a powder for a conductive paste, which is a scale-shaped conductive powder. The powder of the present invention has a scaly shape that can be expressed by the shape characteristics described above.

That is, the projected image of the powder in a stable state is observed under a microscope, and the shortest interval in the projected image is a,
If the longest distance perpendicular to it is b, then (a + b)
A powder having a biaxial average diameter (d) expressed by / 2 of 15 μm or less and an average thickness value (h) of 0.5 μm or less. Further, d / h is 3 or more. When d is larger than 15 μm, when the powder is dispersed in a binder to prepare a conductive paste, the stringiness of the paste is poor and the print coating operation cannot be performed well, and the powder and the binder separate from each other. The life of the paste is easily shortened, and further, the separation of the powder and the binder causes uneven distribution of the powder at the interface with the substrate, resulting in poor adhesion, which is inconvenient. Further, when h is thicker than 0.5 μm, it becomes difficult to form a thin layer electrode having a thickness of about 1 to 2 μm when the internal electrodes of the multilayer ceramic capacitor are formed using the conductive paste.

Further, when d / h is less than 3, the flatness of the powder is small, so that the orientation of the powder when the conductive paste is applied by printing is poor, and as a result, defects may occur in the conductivity. is there. The powder of the present invention is produced from a material having conductivity, and in particular, at least one selected from Cu, Ag, and Au belonging to Group Ib of the periodic table, and Ru, Os, and Group VIII belonging to Group VIII of the periodic table. Co, Rh,
At least 1 selected from Ir, Ni, Pd, Pt, etc.
A single elemental metal of the species or an alloy obtained by appropriately combining them has excellent conductivity, so that even if formed into a thin layer, good conductivity is ensured, which is preferable.

Powders of these elemental metals or alloys can be produced by using, for example, a ball mill. In that case, it is preferable that the balls to be used have a small diameter of about 0.5 to 7 mm. If you use a too large diameter,
This is because the production yield of the scale-shaped powder represented by the above-mentioned shape characteristics is reduced, which is economically disadvantageous.

A conductive paste is prepared by dispersing the conductive powder of the present invention in a binder. The binder is not particularly limited and, for example, ethyl cellulose can be used. The amount of the conductive powder dispersed in the binder is preferably in the range of 60 to 90% by weight. When the dispersion amount is less than 60% by weight, sufficiently good conductivity cannot be obtained, and when it is more than 90% by weight, the viscosity of the conductive paste increases to make it difficult to apply by printing, for example, to a uniform thickness. Because it will be.

The viscosity of the conductive paste may be adjusted by blending a predetermined amount of a solvent such as butyl carbitol acetate, terpineol or butyl carbitol.

[0015]

Examples of the invention

Example 1 Ag-Pd with d = 3 μm, h = 0.1 μm, and d / h = 30
Alloy (Pd content in alloy 30% by weight) Flake powder 58
A paste was prepared by kneading 0 part by weight, 4.8 parts by weight of ethyl cellulose and 36.2 parts by weight of butyl carbitol acetate for 16 hours with a rye crusher. The average diameter measured with a grain gauge was 2.0 μm.

This paste was applied by printing onto an alumina substrate having a thickness of 1 mm so that the paste thickness would be 15 μm, and then heated from room temperature to 250 ° C. over 2 hours to give 250
Hold at ℃ for 3 hours, further heat to 950 ℃ for 4 hours, hold at 950 ℃ for 2 hours, then 850 for 1 hour.
After cooling to ℃, the alumina substrate was taken out. A uniform film having a thickness of 2.0 μm was formed on the substrate.

Comparative Example 1 A paste was prepared in the same manner as in Example 1 using a spherical Ag—Pd alloy having a particle diameter of 1 μm (Pd content in the alloy was 30% by weight). The average diameter of the grain gauge was 10 μm. This paste was applied by printing onto an alumina substrate and baked in the same manner as in Example 1. The Ag—Pd alloy was scattered on the alumina substrate in an island shape and could not be applied as an electrode.

Comparative Example 2 A paste was prepared in the same manner as in Comparative Example 1. However, it was prepared by extending the kneading time from 16 hours to 50 hours. The average diameter of the grain gauge was 7 μm. Example 1 of this paste
In the same manner as above, printing coating was performed on an alumina substrate and firing. The Ag—Pd alloy was formed in a mesh shape on the alumina substrate and had a thickness of 5 to 7 μm. Even if it could be applied as an electrode, thinning of the electrode could not be achieved.

Comparative Example 3 A spherical Ag-Pd alloy having a particle diameter of 0.3 μm (Pd in the alloy was used)
A paste was prepared in the same manner as in Example 1 using the content of 30% by weight). However, it was prepared by extending the kneading time from 16 hours to 50 hours. The average diameter of the grain gauge was 5 to 6 μm. This paste was applied by printing onto an alumina substrate and baked in the same manner as in Example 1. Ag- on the alumina substrate
The Pd alloy was scattered like islands and could not be applied as an electrode.

Comparative Example 4 Spherical Ag—Pd alloy having a particle size of 0.3 μm (Pd in the alloy was used)
Content 30% by weight) 54 parts by weight, ethyl cellulose 5.
A paste was prepared by kneading 2 parts by weight and 40.8 parts by weight of butyl carbitol acetate for 50 hours using a rye crusher. The average diameter of the grain gauge was 2-3 μm. This paste was applied by printing onto an alumina substrate and baked in the same manner as in Example 1. The Ag—Pd alloy was scattered on the alumina substrate in an island shape and could not be applied as an electrode.

[0021]

As is clear from the above description, the conductive powder of the present invention has a scale-like shape expressed by the above-mentioned shape characteristics, and therefore has excellent orientation, and the conductive powder in which it is dispersed. When the pastes are applied by printing, the pastes are flatly oriented by the squeeze action of the printing roller and overlap each other.

Therefore, good conductivity can be obtained even when the conductive paste layer applied by printing is thin.
Therefore, when the conductive paste containing the powder for conductive paste of the present invention is used, the degree of freedom in controlling the thickness of the conductive paste layer is increased while ensuring the target conductivity.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a multilayer ceramic capacitor.

[Explanation of symbols]

 1 Ceramic bulk 2, 2'Internal electrode 3 Electrode

Claims (2)

[Claims] 1. A biaxial average diameter of 15 μm or less and an average thickness of
A conductive paste powder, which is a scale-shaped conductive powder having a diameter of 0.5 μm or less and a biaxial average diameter / average thickness of 3 or more. 2. The conductive paste powder according to claim 1, wherein the conductive powder is a powder of any one of elemental metals belonging to Group Ib or Group VIII of the Periodic Table or alloys thereof.