JP2808639B2 - Conductive particles for electrodes of ceramic electronic components - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to conductive particles used for an electrode material of a ceramic electronic component.

2. Description of the Related Art Conventionally, conductive coatings composed of conductive particles, resins and solvents (including trace amounts of frit, metal oxides and organometallic oxides in some cases) have been widely used as electrode materials for various components. I have. Here, as the conductive particles, expensive noble metals such as gold, silver, platinum, and palladium are used. In order to reduce the cost of the electrode material, consider reducing the amount of the noble metal used or replacing it with a base metal material. Has been made.

Copper and nickel are used for the entire replacement with the base metal material, and silver-copper alloy is used for the partial replacement. Therefore, it is necessary to control the baking atmosphere and coat the electrode surface, resulting in a problem that the manufacturing process becomes complicated. On the other hand, in order to reduce the amount of noble metal used, a method of coating a noble metal with a base metal powder as a base material has been attempted (for example, Japanese Patent Publication No. 46-40593 and Japanese Patent Application Laid-Open No. 60-100679).

When a conductive paint using such a noble metal coated powder is applied to a ceramic material and baked in air to form an electrode, the coated noble metal is not sintered in a continuous state, and the base material is exposed. In addition, the oxide is generated, thereby lowering the conductivity. In order to prevent this, the thickness of the coating of the noble metal must be increased, and the effect of cost reduction is suppressed. Further, in order to suppress the exposure of the base material, the plating method for coating the noble metal has been improved (for example, Japanese Patent Publication No. 61-22028).

However, with respect to a powder obtained by coating a base metal powder with a noble metal as a base material, it is basically impossible to completely suppress the thermal diffusion of the base material to the coated metal when baking at a high temperature. In order to suppress this, the thickness of the coated noble metal must be increased, and a significant cost reduction cannot be expected.

Also, use of oxides such as silicon oxide, aluminum oxide, vanadium oxide, zirconium oxide, and barium titanate as expected substances has been studied (for example, Japanese Patent Publication Nos. 61-22029 and 48586).

However, when such an oxide is used, heat diffusion to the noble metal layer is suppressed as compared with the base metal, but since all of the above oxides are insulators, it is difficult to maintain conductivity as an electrode material. However, it is necessary to increase the coating thickness, and it is difficult to significantly reduce the material cost. Further, the specific resistance of the obtained electrode is high because the base is an insulator, and cannot be used as an electrode material of an electronic component requiring high-frequency characteristics.

Problems to be Solved by the Invention With respect to the conductive particles having the above-mentioned configuration and coated with a noble metal using a base metal or an oxide as a base material, in order to prevent exposure of the base material or reduction in conductivity due to baking treatment at a high temperature, However, there is a problem that the coating thickness must be thickened, the amount of the noble metal used increases, and the cost of the conductive particles cannot be significantly reduced.

The present invention has been made in view of the above, and has as its object to provide inexpensively conductive particles having excellent conductivity and excellent thermal stability.

Means for Solving the Problems In order to solve the above problems, the conductive particles of the present invention,
After the particle surface of the conductive composite oxide is activated with a palladium colloid, it is directly covered with a noble metal by electroless plating.

Here, as the conductive composite oxide, in particular, La _1-x Sr _x Co
O ₃ (0.1 ≦ x ≦ 0.8), Pr _1-x Sr _x CoO ₃ (0.2 ≦ x ≦ 0.8), Nd
_1-x Sr _x CoO ₃ (0.3 ≦ x ≦ 0.7), La _1-x Ba _x CoO ₃ (0.1 ≦ x ≦
0.5), Pr _1-x Ba _x CoO ₃ (0.2 ≦ x ≦ 0.5), having one or more compositions, or La _2-x Sr _x Cu
O ₄ (0.1 ≦ x ≦ 0.5), La _2-x Ba _x CuO ₄ (0.01 ≦ x ≦ 0.5) having one or more solid solution compositions, and furthermore, YBa ₂ Cu ₃ O Those having a composition of ₇ series or BiCaSrCu ₂ O _5.5 series are preferable.

Action The present invention has the above-described configuration, and since the base substance is a conductive oxide, diffusion to the coated noble metal layer is suppressed, and activation treatment with a noble metal colloid is performed.
The plating process can be simplified by eliminating the complexity of the process in the activation processing stage. In addition, since the precious metal colloid can be dried after the activation treatment, the process can be easily controlled. With this feature, it is possible to control the plating coating thickness and to reduce the process cost, so that the manufacturing cost can be significantly reduced. Another characteristic of the chemical stability of the coated noble metal layer is that when a ceramic material such as a dielectric material or a magnetic material is baked at a high temperature, the base material reacts with the ceramic material and the dielectric material of the ceramic material reacts. It is possible to suppress deterioration of characteristics or magnetic characteristics and deterioration of conductivity as an electrode.

Furthermore, in the present invention, the reason why the composite oxide is used as the base substance is that the composite oxide is superior to the oxide containing a single metal element in terms of conductivity and cost.

In particular, La _1-x Sr _x CoO ₃ (0.1 ≦ x ≦ 0.8), Pr _1-x Sr _x CoO ₃
(0.2 ≦ x ≦ 0.8), Nd _1-x Sr _x CoO ₃ (0.3 ≦ x ≦ 0.7), La
_1-x Ba _x CoO ₃ (0.1 ≦ x ≦ 0.5), Pr _1-x Ba _x CoO ₃ (0.2 ≦ x ≦
0.5), La2 _-x Sr _x CuO ₄ (0.1 ≦ x ≦ 0.5), La _2-x Ba _x C
uO ₄ (0.01 ≦ x ≦ 0.5) having one or more solid solution compositions, furthermore, YBa ₂ Cu ₃ O ₇ or B
All those having the composition of iCaSrCu ₂ O _5.5 system are excellent in conductivity, and high conductivity can be obtained even if the thickness of the coated noble metal is thin, so it is possible to drastically reduce the cost of conductive particles .

Further, as the noble metal that can be coated, gold, silver, palladium, platinum, rhodium, ruthenium, or an alloy thereof can be used. Further, at the time of coating the noble metal, it is possible to coat the two or more kinds of noble metals in a multilayer.

Examples Hereinafter, the present invention will be described in detail with reference to examples.

(Example 1) Using La ₂ O ₃ , SrCO ₃ , and Co ₃ O ₄ as starting materials, each required amount was weighed, mixed in ethanol for 12 hours, dried, and then dried.
It was calcined at ℃. Next, the calcined powder was pulverized and calcined at 1100 ° C. for 2 hours to obtain a powder having a composition of La _0.5 Sr _0.5 CoO ₃ .

On the other hand, palladium chloride
Dissolve in water with a molar amount of sodium chloride.

Next, a surfactant is added while stirring the solution, and then an aqueous solution of sodium borohydride is added dropwise, whereby a palladium colloid is instantaneously generated, and a black color is formed. Here, any of cationic, anionic and nonionic surfactants may be used. In this example, as a nonionic surfactant, a nonionic surfactant manufactured by Lion Oil & Fat Co., Ltd. (trade name: LD-110)
1% by weight. The above La
_The conductive particles having a composition of _0.5 Sr _0.5 CoO ₃ are introduced while being decomposed by a magnetic stirrer. And
The solution obtained by stirring and mixing for about 1 hour is transparent, and the palladium colloid is adsorbed on the conductive particles. After the adsorption of the palladium colloid, the resultant was washed with water by a decantation method and dried to obtain palladium colloid-activated particles.

On the other hand, palladium chloride was dissolved in concentrated aqueous ammonia as a plating solution, and hydrochloric acid was added to the solution to prepare a palladium plating solution adjusted to pH 8.5. The powder activated by the noble metal colloid having the composition of La _0.5 Sr _0.5 CoO ₃ is poured into this palladium plating solution while being dispersed by a magnetic stirrer. Next, hydrazine as a reducing agent was added, and the mixture was stirred to perform palladium plating on the powder surface. After the plating treatment, the resultant was washed with water by a decantation method and dried to obtain a palladium-coated powder. The weight ratio of La _0.5 Sr _0.5 CoO ₃ to the palladium plating film of the powder thus obtained was as shown in Table 1 below. Next, a mixture consisting of 100 parts by weight of the palladium-coated powder, 5 parts by weight of glass frit, 2 parts by weight of ethyl cellulose, and 10 parts by weight of α-terpinol was kneaded with a three-roll mill to prepare an electrode paste. After screen printing this electrode paste on an alumina substrate, baking treatment was performed at 1000 ° C. for 10 minutes. The electrical resistance of the thick film thus baked is as shown in Table 1 and showed excellent conductivity. On the other hand, La _0.5 Sr _0.5 CoO ₃ was evaluated as an electrode paste under the above conditions using a powder not coated with palladium.

From these results, it can be seen that when LaSrCoO ₃ alone is used as an electrode, it does not have sufficient stability during sintering in terms of reaction stability. Therefore, the effect of suppressing the reaction between the base material and the alumina substrate, which is a substrate material, is enhanced by applying the palladium coating to increase the conductivity of the powder,
It can be seen that a thick film having excellent conductivity is formed on the alumina substrate.

Example 2 La _1-x Sr _{x was obtained in} the same manner as in Example 1 using La ₂ O ₃ , Pr ₆ O ₁₁ , Nd ₂ O ₃ , BaCO ₃ , SrCO ₃ , and Co ₃ O ₄ as starting materials. CoO ₃ , Pr
_1-x Sr _x CoO ₃ , Nd _1-x Sr _x CoO ₃ , La _1-x Ba _x CoO ₃ , Pr _1-x Ba _x CoO ₃
, Powders having different x of each composition system were prepared. Using these powders as a substrate material, plating was performed in the same manner as in Example 1 to obtain a palladium-coated powder having a weight ratio of the substrate material to palladium of 2/1. Using this powder, a conductor paste was prepared in the same manner as in Example 1 and baked on an alumina substrate to measure the electric resistance value. The results of converting the measured values into Ωcm are shown in Table 2 below.

From the results in Table 2 above, it can be seen that the electrical resistance of the baked thick film is not determined solely by the coated palladium, but by the composition of the substrate material. Palladium plays a role in preventing a reaction with the ceramic material. In order to obtain excellent conductivity, the composition of the base material is La _1-x Sr _x CoO ₃ (0.1 ≦ x
≦ 0.8), Pr _1-x Sr _x CoO ₃ (0.2 ≦ x ≦ 0.8), Nd _1-x Sr _x CoO ₃
(0.3 ≦ x ≦ 0.7), La _1-x Ba _x CoO ₃ (0.1 ≦ x ≦ 0.5), Pr
_1-x Ba _x CoO ₃ (0.2 ≦ x ≦ 0.5) is suitable. Next, using an oxide obtained by compounding the above materials as a base material, palladium coating was performed by plating in the same manner as described above, and a paste was formed and baked, and the electrical resistance value of the obtained thick film was measured. As shown in Table 3 below, excellent conductivity was confirmed.

(Example 3) Using La ₂ O ₃ , SrCO ₃ , BaCO ₃ , and CuO as starting materials, each required amount was weighed, mixed in ethanol for 12 hours, and dried.
After calcination at 900 ° C for 2 hours, heat treatment in oxygen at 600 ° C
Powders having compositions in which x of x _-X Sr _x CuO ₄ and La _2-x Ba _x CuO ₄ were variously changed were obtained. After activating this powder with the same palladium colloid solution as in Example 1, this powder was separately put together with hydrazine into a plating solution composed of platinum chloride, aqueous ammonia and hydrochloric acid, and stirred to form platinum on the powder surface. Was plated. Then, after the plating treatment, washing with water was performed by a decantation method, followed by drying to obtain a platinum-coated powder.
The weight ratio between the base material and platinum of the powder thus obtained was 70.
/ 30. Using the powder coated with platinum plating, a conductive paste was prepared in the same manner as in Example 1 and baked on an alumina substrate at a temperature of 900 ° C., and the electrical resistance was measured. The results of converting the measured values into Ωcm are shown in Table 4 below.

From the results in Table 4, in order to obtain excellent conductivity, the composition of the base material must be La _2-x Sr _x CuO ₄ (0.1 ≦ x ≦
0.5), La _2-x Ba _x CuO ₄ (0.01 ≦ x ≦ 0.5) is suitable. Next, platinum plating, pasting and baking were performed in the same manner as described above using the oxide obtained by compounding the above materials as a base material, and the electrical resistance of the obtained thick film was measured. 5>, excellent conductivity was confirmed.

(Example 4) Starting amounts of Y ₂ O ₃ , BaCO ₃ , CuO, Bi ₂ O ₃ , CaCO ₃ , and SrCO ₃ are weighed, required amounts are mixed in ethanol for 12 hours, and dried at 850 ° C. And then heat-treated in oxygen at 600 ° C. to obtain a powder having a composition of YBa ₂ Cu ₃ O ₇ and BiCaSrCu ₂ O _5.5 . After activating this powder with the same palladium colloid solution as in Example 1, gold cyanide and EDTA
The above-mentioned powder and sodium ascorbate were simultaneously charged into an electroless plating solution consisting of a 4N solution of (ethylenediaminetetraacetate) and hydrochloric acid, and a gold plating layer was adhered to the surface of the powder by stirring. The weight ratio of the base material to gold in the powder thus obtained was 60/40. Using the above gold-coated powder, in the same manner as in Example 1,
A conductor paste was prepared and baked on an alumina substrate at a temperature of 850 ° C., and the electric resistance was measured. As a result, when the base material was YBa ₂ Cu ₃ O ₇ , the electrical resistance was 6 × 10 ³ Ωcm,
In the case of SrCu ₂ O _5.5 , it was 8 × 10 ³ Ωcm, and excellent conductivity was confirmed.

(Example 5) 8 parts by weight of polyvinyl butyral resin and 4 parts by weight of dibutyl phthalate were added to 100 parts by weight of a dielectric powder mainly composed of magnesium / lead niobate [Pb (Mg _1/3 Nb _2/3 ) O ₃ ]. , 40 parts by weight of trichloroethane and 25 parts by weight of butyl acetate were added and mixed by a ball mill for 20 hours. The dielectric slurry thus obtained was formed into a sheet having a thickness of 40 μm by a reverse roll method. Next, in the same manner as in Example 1, La
_0.5 Sr _0.5 CoO ₃ Particle surface coated with palladium (La
_0.5 Sr _0.5 CoO ₃ and palladium weight ratio: 50/50)
Ethyl cellulose and α-terpinol were added thereto, and kneaded with a three-roll mill to prepare an electrode paste. This electrode paste was printed on the dielectric sheet, cut into desired dimensions, and fired at 1100 ° C. for 2 hours. La _0.5 Sr _0.5 coated with palladium prepared in the same manner as in Example 1 was applied to the side of the thus obtained sintered body where the electrodes were exposed.
An electrode paste composed of CoO ₃ (La _0.5 Sr _0.5 CoO ₃ and palladium in a weight ratio of 70/30), glass frit, ethyl cellulose, and α-terpinol was applied and baked at 800 ° C. The capacitance value of the multilayer chip capacitor thus obtained is in good agreement with the design value calculated from the dielectric constant (ε12000) of the dielectric, and the palladium-coated La _0.5 Sr
The practicality of the electrode using _0.5 CoO ₃ was confirmed. In addition to the present embodiment, it is needless to say that the conductive composite oxide particles coated with the noble metal have practical use as electrodes for chip resistors, chip inductors, varistors, piezoelectric elements, and ceramic multilayer wiring boards.

Since the composite oxides targeted by the present invention usually have oxidation defects, the composition of oxygen is not particularly limited. Further, in order to control the chemical stability or the electrical characteristics of the base material, a metal element or an anion element other than the main component element may be added to the base material. Further, the composite oxide powder used in the above examples,
Although it had a particle diameter in the range of 0.1 to 5.0 μm, there is no particular limitation on the particle diameter and particle shape. on the other hand,
It goes without saying that silver, rhodium, iridium, ruthenium and alloys thereof which can be coated by electroless plating may be used as the coated noble metal in addition to the above embodiments.

Effect of the Invention As described above, the present invention is a conductive particle having a configuration in which a particle surface of a conductive composite oxide is activated with a noble metal colloid and then directly coated with a noble metal in an electroless plating solution. Conductive particles having excellent heat resistance and chemical stability can be produced at low cost, and the practical value thereof is extremely large.

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Koji Kawakita 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-62-207875 (JP, A) JP-A-48-56591 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 18/44 C23C 18 / 31 H01B 1/22

Claims (5)

(57) [Claims] An electroconductive particle for an electrode of a ceramic electronic component, wherein a particle surface of an electroconductive composite oxide serving as a base material is activated by a palladium colloid and then directly coated with a noble metal by electroless plating. 2. The method according to claim 1, wherein the conductive composite oxide is La _1-x Sr _x CoO ₃ (0.1 ≦
x ≦ 0.8), Pr _1-x Sr _x CoO ₃ (0.2 ≦ x ≦ 0.8), Nd _1-x Sr _x CoO
₃ (0.3 ≦ x ≦ 0.7), La _1-x Ba _x CoO ₃ (0.1 ≦ x ≦ 0.5), Pr
The composition of one or more of _1-x Ba _x CoO ₃ (0.2 ≦ x ≦ 0.5) as a solid solution.
The conductive particles for electrodes of the ceramic electronic component according to the above. 3. The method according to claim 1, wherein the conductive composite oxide is La _2-x Sr _x CuO ₄ (0.1 ≦
x ≦ 0.5), one of La _2-x Ba _x CuO ₄ (0.01 ≦ x ≦ 0.5)
2. The conductive particles for an electrode of a ceramic electronic component according to claim 1, wherein the conductive particles have one or more kinds of solid solution compositions. 4. The conductive particles for an electrode of a ceramic electronic component according to claim 1, wherein the conductive composite oxide has a YBa ₂ Cu ₃ O ₇ system composition. 5. The conductive particles for an electrode of a ceramic electronic component according to claim 1, wherein the conductive composite oxide has a composition of BiCaSrCu ₂ O _5.5 system.