JPH0696994A - Conductive paste composition - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an internal electrode composition for a ceramic capacitor, which effectively suppresses delamination by suppressing the oxidation of palladium at a high temperature. [Composition] A conductive paste composition characterized by being coated with a heat-resistant resin having a decomposition start temperature, for example, an average particle size of 0.3 μm.
After mixing and mixing the palladium powder, the polyimide precursor, and normal methylpyrrolidone as a solvent, the mixture is made into a polyimide and pulverized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paste composition suitable for an internal electrode of a laminated ceramic capacitor.

[0002]

2. Description of the Related Art A general method for manufacturing a monolithic ceramic capacitor is as follows: barium titanate, lead titanate, a composite perovskite compound containing lead, etc. As a material, palladium or an alloy powder of palladium and silver, or
Screen printing a paste containing a metal powder containing a mixed powder of palladium powder and silver powder, etc., a plurality of the printed green sheets, then cut into a predetermined size, in the air or nitrogen atmosphere, 800-1400
It is baked at ℃.

However, palladium once undergoes a phase change to palladium oxide which is a thermodynamically stable phase at a temperature of 400 to 820 ° C., and then returns to palladium again at 820 ° C. or higher. When changing to palladium oxide, the electrode layer expands, and when returning to palladium, the electrode layer contracts. For this reason, stress may be generated in the dielectric layer and the electrode layer due to the difference in thermal expansion, and the electrode layer may be lifted up or cracks may be generated in the dielectric layer to cause defects. This defect is usually called delamination. Therefore, if the oxidation of palladium can be suppressed, the contraction at the time of reduction can also be suppressed and the occurrence of delamination can be prevented.

Several improved methods have been proposed to prevent such rapid shrinkage and oversintering of palladium. For example, it has been proposed to delay the firing shrinkage rate of palladium by adding an iridium organic resin salt or a rhodium organic resin salt to the palladium paste (JP-A-3-80513). However, there is a problem in that the wettability between these metals and the dielectric is poor and the adhesive strength between the electrode and the dielectric is weakened.

On the other hand, a method of delaying the sintering of palladium by adding a clay component containing montmorillonite as a main component to a palladium paste has been proposed (Japanese Patent Laid-Open No. 57-121072). However, this method has a problem that the silica component and the alumina component, which are clay components, diffuse into the dielectric and deteriorate the dielectric properties. Further, since the clay component remaining in the palladium electrode has an insulating property, the resistance value of the electrode itself is increased, and the high frequency characteristics of the multilayer capacitor are deteriorated.

Therefore, there is no rapid sintering shrinkage at high temperature,
The development of a paste that does not cause delamination has been earnestly desired.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a conductive paste composition capable of suppressing the oxidation of palladium at high temperature and effectively preventing delamination.

[0008]

[Means for Solving the Problems] Palladium-containing powder,
The above object can be achieved by coating with a heat-resistant resin having a thermal decomposition initiation temperature of 400 ° C. or higher.

[0009]

The palladium-containing powder may be any one of palladium simple substance powder, palladium-silver alloy powder, palladium-gold alloy powder, or the like, and these may be mixed and used.

A part or the whole of the surface of these powders is coated with these heat-resistant resins. The coating method is not particularly specified, for example, after immersing the metal powder in a solution in which the precursor of the heat-resistant resin is dissolved, take out the metal powder by a method such as filtration,
A method of heating and curing the heat-resistant resin and then pulverizing it, or a method of mixing the metal powder, the heat-resistant resin and, if necessary, a polymerizing agent, curing and then pulverizing may be used.

It is preferable that the heat decomposition starting temperature of these heat-resistant resins is at least 400 ° C., more preferably at least 450 ° C., at which the oxidation of palladium is severe.
The thermal decomposition start temperature referred to here is JIS K71.
20 (thermogravimetric measurement method for plastics). Polyimide resin and polytetrafluoroethylene are suitable as the heat-resistant resin, but polymers such as polyvinyl fluoride, polyvinylidene fluoride and poly-para-xylene, which have a high thermal decomposition initiation temperature, can also be used.
For example, when the thermal decomposition characteristics of the polyimide resin are examined using a thermogravimetric analyzer (TGA) in air, it is found that there is almost no weight loss up to about 550 ° C.

Since the heat-resistant resin decomposes during firing,
The coating amount of the heat-resistant resin does not need to be specified, but is preferably 20 to 100 parts by weight per 100 parts by weight of palladium.

A paste is prepared by kneading the metal powder and the vehicle, if necessary, with glass frits by a three-roll mill or the like. The vehicle is obtained by dissolving a resin serving as a binder in a solvent, and examples of the resin used include cellulosic resins such as ethyl cellulose and nitrocellulose, and acrylic resins such as butyl methacrylate and methyl methacrylate. Examples of the solvent include alcohol solvents such as terpineol and decanol, naphtha solvents such as mineral spirit and supersol, and ketone solvents such as methyl ethyl ketone.

Since the weight of the palladium-containing metal powder increases when it is oxidized, the degree of oxidation of the palladium-containing metal powder is
It can be evaluated by measuring the weight change of the palladium powder during heating.

[0015]

Example: Palladium powder (average particle size 0.3 μm, spherical)
And polyimide precursor (Toray brand name Semicofine)
And normal methylpyrrolidone as a solvent were mixed as shown in Table 1, thoroughly mixed, and then vacuum dried at 100 ° C. for 4 hours to volatilize normal methylpyrrolidone.
The polyimide precursor was polyimidized by heating in the air at 0 ° C. for 1 hour to obtain a dried body. The dried product was crushed in a mortar to obtain a palladium powder coated with a polyimide resin. The amount of polyimide resin coated on the palladium powder was calculated from the difference in weight before and after the coating treatment.

Next, the oxidized weight of this powder was measured by TGA using a heating rate of 20 ° C./min and a measuring temperature of 25 to 1100.
The measurement was carried out under the conditions of ℃ and air flow rate of 1000 ml / min.
The maximum rate of increase in oxidative weight depends on the maximum oxidative weight during measurement and 105
It was calculated by the ratio of the difference in weight of oxidation at 0 ° C. and the weight of oxidation at 1050 ° C. In addition, as a comparative example, those not coated with the resin were similarly tested, and are also shown in Table 1. It is shown that the lower the maximum rate of increase in oxidation is, the more the oxidation of palladium is suppressed.

[0017]

[Table 1]

According to Table 1, in each of the examples, the maximum oxidation weight increase rate is lower than that of the comparative example, and it is understood that the oxidation of the palladium powder is suppressed.

[0019]

As described above, according to the conductive paste composition of the present invention, shrinkage during firing is small, and delamination can be effectively prevented.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location C25B 11/08 Z 9046-4K H01B 1/22 Z 7244-5G H01G 1/01 9174-5E

Claims (2)

[Claims] 1. A conductive paste composition comprising a palladium-containing powder coated with a heat-resistant resin having a thermal decomposition initiation temperature of 400 ° C. or higher. 2. The coating amount of the heat-resistant resin is palladium 1
The conductive paste composition according to claim 1, which is 20 to 100 parts by weight per 00 parts by weight.