JPS6229843B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for producing a conductive material, particularly a conductive material for forming internal electrodes of a multilayer ceramic capacitor.

Background of the Technology Multilayer ceramic capacitors are manufactured by stacking a plurality of raw sheets printed with conductive paste (conductive material for forming internal electrodes) to form external electrodes, and then firing this.

Prior Art and Problems Silver-palladium alloys have conventionally been used as this type of conductive material, but the internal composition thereof has been fine powders of silver and palladium with a particle size of 1 μm or less.

However, in this case, although uniformity during printing can be obtained, expansion and contraction during firing are large, making it difficult to match the firing shrinkage of ceramic sheets. This is because when palladium is heated in air, an oxidation reaction occurs at about 500℃, and then at about 850℃.
This is because a reduction reaction occurs, and the volume change at that time is large, causing delamination and cracking. Furthermore, if the powder is too small, the so-called shrinkage during sintering will be large, causing electrode breakage.

Purpose of the Invention The present invention is intended to solve the above-mentioned various problems, and is a silver-palladium conductive material that reduces the above-mentioned reactions, improves compatibility with ceramic sheets, and prevents interlayer delamination and cracking. The purpose is to provide a method for manufacturing materials.

Embodiments of the invention Hereinafter, embodiments of the invention will be described with reference to the drawings.

The present invention utilizes the effect that when the effective surface area of silver powder is made larger than that of palladium and ball mill kneading is performed, the palladium powder is completely coated with silver, resulting in more uniform alloying. The aim is to accelerate the reaction and reduce the redox reaction of palladium powder, and during ball mill kneading, plastic balls and plastic pots are used to prevent unnecessary inorganic impurities from being mixed in. In this case, it is necessary to appropriately select the particle size of palladium and silver powder in order to obtain the desired effect.
Next, the experimental results will be explained.

The conductive paste consists of silver (Ag) with a particle size of 0.7 μm and palladium (Pd) of various diameters in a weight ratio of Pd and Ag.
Two types were prepared: one in which Pd was added at a ratio of 60:40, and another in which Pd of various diameters was added in the same ratio to Ag with a particle size of 3 μm. In each case, MEK methyl ethyl ketone and a dispersant were added and kneaded in a ball mill for 24 hours, and then ethyl cellulose and polyvinyl butyral as binders and terpineol as a high boiling point solvent were added to prepare an Ag-Pd paste.

On the other hand, we prepared a dielectric ceramic paste (which can be fired at 1250℃) with BaTiO ₃ as its basic composition, used this and the above-mentioned paste to prototype various 40-layer multilayer ceramic capacitors, and conducted boiling tests on the finished products. The quality of the internal electrodes was evaluated. According to the boiling test, if there is delamination or cracking between layers, the insulation resistance deteriorates due to water absorption, and the quality of the electrode can be evaluated. Figures 1 and 2 show the IR (insulation resistance) defect rate and capacity defect rate after the boiling test. Curve A in Figure 1 and curve C in Figure 2 are
Curve B in FIG. 1 and curve D in FIG. 2 show the case where the Ag powder particle size is 0.7 μm, and the curve B in FIG. 2 shows the case where the Ag powder particle size is 3 μm.

From FIG. 1, it is clear that the IR defect rate is low when the Pd powder particle size is 1 to 3 μm, and that the Ag powder particle size of 0.7 μm is better.

In addition, from Figure 2, when the Pd powder particle size becomes 1 μm or less, the capacity defect rate becomes extremely high.
It is clear that the Ag powder particle size of 0.7 μm is superior.

The reason why such a result was obtained is considered to be due to the following reasons.

(1) If both the Pd powder particle size and the Ag powder particle size are too small, shrinkage during firing will increase and electrode breakage will easily occur.

(2) When the effective surface area of Pd powder is large (when the particle size is small), the volume change during the redox reaction is large, so each defect rate becomes large.

(3) When the Ag powder particle size is comparable to the Pd powder particle size, the effect of covering the Pd powder with Ag is low. Ag
A good coating effect can be obtained when the powder particle size is smaller than the Pd powder particle size.

(4) When Ag is coated around Pd powder, which has a larger Young's modulus than Ag, it prevents the redox reaction of Pd and promotes the homogeneous alloying reaction.

Figure 3 shows how Pd powder is coated with Ag powder. In FIG. 3, a shows the state before kneading with a ball mill, and FIG. 3b shows a state after kneading with a ball mill. In the figure, 1 is Pd
2 is Ag powder, and 3 is Ag coating layer.

In the above experiment, the weight ratio of Pd and Ag was 60:40, but the results would not change even if the weight ratio was other than that. When used to form internal electrodes for multilayer ceramic capacitors, this weight ratio may be determined in consideration of the firing temperature of the ceramic, and the higher the Pd content, the higher the firing temperature.

Effects of the Invention As described above, since the method for manufacturing a conductive material according to the present invention uses palladium powder coated with silver as the main component, it is possible to uniformize the alloying reaction of silver and palladium and to achieve appropriate shrinkage during firing. Furthermore, since the oxidation-reduction reaction during firing of palladium can be reduced, when used for forming internal electrodes for multilayer ceramic capacitors, the compatibility is excellent and the yield of finished products can be improved.

[Brief explanation of the drawing]

The drawings show examples of the present invention. Figure 1 shows a conductive material obtained by mixing silver powder with an average particle size of 0.7 μm and 3 μm with palladium powder of various average particle sizes, and kneading the mixture in a ball mill. A graph showing the IR failure rate after boiling of various multilayer ceramic capacitors used for forming internal electrodes. Figure 2 is a graph showing the capacity failure rate after boiling of similar multilayer ceramic capacitors. Figures 3a and b show that palladium powder FIG. 3 is an explanatory diagram showing how the film is coated with silver powder. In the figure, 1 is palladium powder, 2 is silver powder, and 3 is a silver coating layer.

Claims (1)

[Claims] 1. Mix silver powder with an average particle size of 3 μm or less to palladium powder with an average particle size of 1 to 3 μm, which is the main component,
A method for producing a silver palladium conductive material, which comprises coating palladium powder with silver powder by kneading the material with an organic solvent using a plastic ball.