JPH02243768A - Production of electrically conductive particles - Google Patents

Abstract

PURPOSE:To improve the electrical conductivity and thermal stability of particles of an electrically conductive multiple oxide by coating the surfaces of the particles with a noble metal by electroless plating after activation with Pd colloid. CONSTITUTION:Pd colloid is adsorbed on the surfaces of particles of an electrically conductive multiple oxide as a base material to activate the surfaces and the activated surfaces are directly coated with a noble metal such as Au, Ag, Pd or Pt in an electroless plating soln. The multiple oxide is preferably one or more among La1-xSrxCoO3 (0.1<=x<=0.8), Pr1-xSrxCoO3 (0.2<=x<=0.8), Nd1-xSrxCoO3 (0.3<=x<=0.7), Lax-1BaxCoO3 (0.1<=x<=0.5) and Pr1-xBaxCoO3 (0.2<=x<=0.5) each having the compsn. of a solid soln. Since the oxides have superior electrical conductivity, high electrical conductivity is obtd. even in the case of a small thickness of the noble metal coats.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing conductive particles used as electrode materials.

Conventional Technology Conventionally, conductive paints consisting 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 parts. There is. Here, as the conductive particles,
Expensive precious metals such as gold, silver, platinum, and palladium are used, and there are 3 bases of electricity.

In order to reduce the cost of electrode materials, consideration is being given to reducing the amount of precious metals used or replacing them with base metal materials.

Copper and nickel have been used for full replacement with base metal materials, and silver-copper alloys have been used for partial replacement, but in both cases oxides are formed when baked in air or left unattended. To prevent the conductivity from decreasing, the atmosphere must be controlled and the electrode surface must be coated to prevent burning.
There is a problem that the manufacturing process becomes complicated. On the other hand, in order to reduce the amount of precious metals used, attempts have been made to use base metal powder as a base material and coat it with precious metals (for example, Japanese Patent Publication No. 46-40593, Japanese Patent Application Laid-Open No. 60-100
Publication No. 679).

Conductive paint using such noble metal coated powder is Cera d.
When an electrode is formed by applying the coating to a solid material and baking it in the air, the coated precious metal is not sintered in a continuous state, the base material is exposed, and oxides are generated, making it conductive. Sexuality decreases. In order to prevent this, the coating thickness of the precious metal must be increased, and the effect of cost reduction will be suppressed. In addition, improvements have been made to plating methods for noble metal coating in order to suppress exposure of the base material (for example, Japanese Patent Publication No. 61-22028).

However, when baking at high temperatures, powders made of base metal powder coated with noble metals,
Basically, it is impossible to completely suppress heat diffusion from the base material to the coated metal, so in order to suppress the exposure of the base material, the thickness of the coated noble metal must be increased.
After all, significant cost reductions cannot be expected.

Furthermore, the use of oxides such as silicon oxide, aluminum oxide, vanadium oxide, zirconium oxide, or barium titanate as the base material is also being considered (for example, Japanese Patent Publications No. 61-22029 and No. 48586).
.

However, when such oxides are used, thermal diffusion into the noble metal layer is suppressed compared to base metals, but since all of the above oxides are insulators, the conductivity of the electrode material 5 vane material is reduced. To maintain this, the thickness of the coating must be increased, making it difficult to significantly reduce material costs. Furthermore, the specific resistance of the obtained electrode is high because the base is an insulator, and it cannot be used as an electrode material for electronic components that require high frequency characteristics.

Problems to be Solved by the Invention Regarding the conductive particles having the above-mentioned structure, in which the base material is a base metal or an oxide and is coated with a noble metal, baking at high temperatures prevents the base material from being exposed or the conductivity from decreasing due to processing. In order to achieve this, the thickness of the coating must be increased, resulting in the problem that the amount of precious metal used is large and the cost of the conductive particles cannot be reduced significantly.

The present invention has been made in view of this point, and an object of the present invention is to provide conductive particles having excellent conductivity and thermal stability at a low cost.

Means for Solving the Problems In order to solve the above problems, the method for producing conductive particles of the present invention includes activating the particle surface of a conductive composite oxide with 6-page palladium colloid, and then directly electroless plating. It has a structure in which it is coated with a precious metal.

Here, as the conductive composite oxide, especially La1-xS
rxCoO3 (0.3 (0.1≦X≦0.8), Pr
1-1srzco05 (0.2≦X≦0.s),
Nd1-xSrXCob3≦x≦0.7).

La1)[BIL][CO03((1,1≦X≦0.
5), Pr, zBaxCOQ5(0.2≦X≦0
．． 5), or La2-xSrxCub4 (0.1≦X≦
0.5), La2zBaxCuO4(0.01
≦X≦0.5), and YBa2Cu30. It is preferable to have a composition of BiCaSrCu205.5 system or BiCaSrCu205.5 system.

Effect of the present invention Due to the above-described structure, since the base material is a conductive oxide, diffusion into the coated precious metal layer is suppressed, and the process at the activation treatment stage is prevented by activation treatment with noble metal colloid. By eliminating complications, the plating process can be simplified. Further, since the noble metal colloid can be dried after being activated, the process can be easily managed. This feature makes it possible to control the plating thickness and reduce process costs, resulting in a significant reduction in manufacturing costs. In addition, a feature derived from the chemical stability of the coated noble metal layer is that when baking is performed with ceramic materials such as dielectric materials and magnetic materials at high temperatures, the base substance reacts with the ceramic material, causing the ceramic material to react with the ceramic material. It is possible to prevent further deterioration of the dielectric properties or magnetic properties of the electrode and the deterioration of the conductivity as an electrode.

Further, in the present invention, a composite oxide is used as the base material because the composite oxide is superior in terms of conductivity and cost compared to an oxide containing a single metal element.

In particular, La1-xSrxCo03 (0.1≦X≦0.
s).

Pr1-. 5rxCo03 (0.2≦X≦0.s)
.

Nd1zsrxCoo3≦x≦0.7).

La1. BaXCoO3 (0.1≦X≦0.s).

Pr 1-X Ba X Go O5 (0.2≦X≦0
．． 6), or La2-1srxCuO4 (0.1≦X≦
0. es).

Those having a solid solution composition of one or more of La2-1BaxGuO4 (001≦X≦0.5), as well as YBa2Cu3O7 system, BiCaSr
All of the Cu 205,5-based compositions have excellent electrical conductivity, and high electrical conductivity can be obtained even if the noble metal coating is thin, making it possible to significantly reduce the cost of electrically conductive particles. .

Furthermore, examples of noble metals that can be coated include gold, silver, palladium, platinum, rhodium, ruthenium, and alloys thereof. In addition, when coating with noble metals, it is also possible to coat with two or more of the above noble metals in multiple layers.

Example Hereinafter, the present invention will be explained in detail with reference to Examples.

(Example 1) Required amounts of each of La203.5rC05 and Co3O4 total 3O raw materials were weighed, mixed in ethanol for 12 hours, and then calcined at 900°C after drying. Next, after pulverizing the calcined powder, it was fired at 1000°C for 2 hours to obtain LIL 0
．． A powder with the composition s Sr p,5 Go O5 was obtained.

On the other hand, palladium chloride as a palladium colloid is dissolved in water together with 5 moles of sodium chloride.

Next, a surfactant is added to the mixture while stirring, and then an aqueous solution of sodium borohydride is added dropwise to the mixture. Palladium colloid is instantaneously produced, giving it a black color. Here, as the surfactant, any type of cationic, anionic, or nonionic surfactant may be used. In this example, the nonionic surfactant used was a nonionic surfactant manufactured by Lion Yushi Co., Ltd. (trade name: LD-11).
0) is added by weight. Conductive particles having the composition of Lag, 5 Sr 0.5 Co 03 are dispersed into this colloidal solution using a magnetinox stirrer. After stirring and mixing for about 1 hour, the solution becomes transparent, and the palladium colloid is adsorbed on the conductive particles. This palladium colloid absorbs 10...
- After deposition, the particles were washed with water by decantation and dried to obtain palladium colloid activated particles.

On the other hand, a palladium plating solution was prepared by dissolving palladium chloride in concentrated ammonia water and adding hydrochloric acid to adjust the pH to 8.5.

This palladium plating solution was added with the above LaO,5Sr (
, 5CoO3 powder activated with a noble metal colloid is introduced while being dispersed with a magnetic stirrer. Next, hydrazine as a reducing agent was added and stirred to plate the powder surface with palladium. After the plating treatment, the plate was washed with water by decantation and dried to obtain a palladium-coated powder. The thus obtained powder La O,5Sr (15Co
The weight ratio of O5 to the palladium plating film 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-terepinol was kneaded using three rolls to form an electrode paste. After screen printing this electrode paste on an alumina substrate,
11 4-D Baking treatment was performed at 100° C. for 10 minutes.

The electrical resistance value of the thick film baked in this way is as shown in Table 1, indicating excellent electrical conductivity. On the other hand, La
O,5 Sr O. An electrode paste was evaluated under the above conditions using 5 Co O 3 powder not coated with palladium.

<Table 1> From these results, it can be seen that when using only La Sr Go O 3 as an electrode, it does not have sufficient stability during sintering in terms of reaction stability. Therefore, the palladium coating increases the conductivity of the powder and suppresses the reaction between the base material and the alumina substrate, which is the substrate material.The combination of these two effects results in the formation of an alumina substrate with excellent conductivity. It can be seen that a thick film is formed.

(Example 2) La203, Pr6011, Nd203, Ba
Using CO3, SrCO3, C0504 as starting materials,
By the same method as in Example 1, La1 zsrxCoo
3, Pr1zsrXCoo3, Nd,, SrxCo0
3, La1zBaxCoo5, Pr,zBayc003
Powders with different X of each composition system were created. These powders were used as base materials and subjected to coating treatment in the same manner as in Example 1 to obtain palladium-coated powders having a weight ratio of base material to palladium of 2/1.

Using this powder, a conductive paste was prepared in the same manner as in Example 1, and the conductive paste was baked onto an alumina substrate and the electrical resistance value was measured. The results of converting this measured value into Ωcm are shown in Table 2 below.

(Margin below) 13A-ノ〒■, 11111× × × × × Dimensions■ ■ 〒 〒 〒 〒の. 11111O × × × × × ■ ω pus■ 〒 〒 〒 ト． ○ １１１１× × × × × 唖■ 小唖唖〒 〒 〒 〒 〒 10. 11111× × × × × size■ ■ ■ 〒 〒 〒 〒 〒 ■． 11111× × × × × 唖■ To the 〒 〒 of the size. ○ 11111 × × × × × ω Issun■ 1〒 『．． O /0 11111 × × × × × 1 1 0. 1111 × × × × × ■ ■ 唖ト■ / R P ~ 14,,. , From the results in Table 2 above, the electrical resistance value of the baked thick film is determined not only by the coated palladium, but also by
It can be seen that it is determined by the composition of the base material. Palladium also plays a role in preventing reaction with the ceramic material.

In addition, in order to obtain excellent conductivity, the composition of the base material should be La 1 -x Sr x Go O 3 (0.1
≦X≦o. s), Pr1, SrXCoQ3(0.
2≦X≦o,s), Nd4-xSrxCoo5(
03≦X≦07), La1, BaxCoo, (01≦
X≦05), Pr1-xBaxCo03 (0.2≦X
≦05), is JL. Next, using the oxide that is a composite of the above materials as a base material, it was coated with palladium by plating in the same manner as above, and the electrical resistance value of the obtained thick film was measured. Excellent conductivity was confirmed as shown in Table 3 below.

(Leaving space below) Table 3 (Example 3) Using La203.5rCO, BaCO3, and CuO as starting materials, the required amounts of each were weighed, and 12% of each was weighed in ethanol.
After mixing for hours, drying and baking at 900℃ for 2 hours, 60oC
La2 zsrzcu04La by heat treatment in oxygen at ℃
Powders having compositions in which X of 2-4Ba4Cu04 was varied were obtained. After activating this powder with the same palladium colloid solution as in Example 1, this powder was separately put into a plating solution consisting of platinum chloride, aqueous ammonia, and hydrochloric acid together with hydrazine, and by stirring, platinum was applied to the powder surface. plated. After the plating process, the plate was washed with water by decantation and dried to obtain a platinum-coated powder. The weight ratio of the base material and platinum of the powder thus obtained was 70/
It was 30. A conductive paste was prepared using the above platinum plating powder in the same manner as in Example 1, baked on an alumina substrate at a temperature of 900° C., and the electrical resistance was measured. The results of converting this measured value into Ωcm are shown in Table 4 below.

(Hereafter, extra white) 17 ・ He-no 18A,.

From the results in Table 4, in order to obtain excellent conductivity, the composition of the base material must be La2.5rxCub4 (0
．． 1≦X≦0.5), Laz-xBaxCu04
It can be seen that (0.o1≦X≦0.5) is suitable.

Next, platinum plating, pasting, and baking were performed in the same manner as above using an oxide that was a composite of the above materials as a base material, and as a result of measuring the electrical resistance value of the obtained thick film, the following results were obtained. As shown in Table 6, excellent conductivity was confirmed.

<Table 5> (Example 4) Y2O2, BaCO3, CuO, Bi2O3, CaCO
Using 3゜SrCO3 as a starting material, weigh out the required amount of each, mix in ethanol for 12 hours, dry and sinter at 850°C for 2 hours, then heat treat at 197, - in oxygen at 600°C. YBa2Cu3O7 and B1Ca5rC
A powder having a composition of u2055 was obtained. After activating this powder with the same palladium colloid solution as in Example 1, the above powder and sodium ascorbate were placed in an electroless plating solution consisting of a 4N solution of gold cyanide, EDTA (ethylenediaminetetraacetate), and hydrochloric acid. were added at the same time and stirred to adhere a gold plating layer to the powder surface. The powder thus obtained had a weight ratio of base material to gold of 60/40. A conductive paste was prepared using the above gold-coated powder in the same manner as in Example 1, and baked on an alumina substrate at a temperature of 850"C, and the electrical resistance was measured. As a result, it was found that the base material was YBa2Cu.
The electrical resistance value in the case of 3O7 (7) is 6 x 10Ωcm, B1
In the case of Ca5rCu205.5, the resistance was 8×10 3 Ωcm, and excellent conductivity was confirmed.

(Example 5) Magnesium lead niobate CPb (Mg+/3Nb2
/3) 8 parts by weight of polyvinyl butyral resin, 4 parts by weight of dibutyl phthalate, 40 parts by weight of trichloroethane, and 25 parts by weight of butyl acetate were added to 100 parts by weight of dielectric powder mainly composed of 03), and the mixture was heated in a ball mill for 20 hours. Mixed. The dielectric slurry thus obtained was formed into a sheet with a thickness of 40 μm using a reverse roll method. Next, by the same method as in Example 1, LaO,5SrO,5Co
03 Powder whose particle surface was coated with palladium (La
), 5Sr0.50003' and palladium weight ratio: 50150), and added ethyl cellulose and α
- An electrode paste was prepared by adding terepinol and kneading with three rolls. This electrode paste was printed on the dielectric sheet, cut into desired dimensions, and baked at 1000° C. for 2 hours. The side surface of the thus obtained sintered body where the electrode is exposed is coated with palladium prepared in the same manner as in Example 1. LaO, 5SrO, 5Co03 (
), 5Sr (weight ratio of 15CoO3 and palladium = 7o/3o), glass frit, ethyl cellulose,
Apply an electrode paste consisting of α-terepinol,
Baked at 0°C. The capacitance value of the multilayer chip capacitor thus obtained is the dielectric constant (ε=12000
21A-), and the practicality of the electrode using palladium-coated LaO, 5SrO, 5CoO3 was confirmed. In addition to this example, it goes without saying that conductive composite oxide particles coated with noble metals have practical applications as electrodes for chip resistors, chip inductors, varistors, piezoelectric elements, and even ceramic multilayer wiring boards.

Since all of the composite oxides targeted by the present invention usually have oxygen vacancies, the composition of oxygen is not particularly defined. Furthermore, in order to control the chemical stability or electrical properties of the base material, metal elements or anionic elements other than the main component elements may be added to the base material. Furthermore, the composite oxide powder used in the above example had 0
．． Although the particle size was in the range of 1 to 50 μm, the particle size and shape are not particularly defined.

On the other hand, it goes without saying that silver, rhodium, iridium, ruthenium, and alloys thereof, which can be coated by electroless plating, and alloys thereof may be used in addition to the above embodiments as the noble metals to be coated.

Effects of the Invention As described above, the present invention provides conductive particles having a noble metal coating structure that is directly deposited in an electroless plating solution after activating the particle surface of a conductive composite oxide with a noble metal colloid.
Conductive particles with excellent conductivity and excellent thermal and chemical stability can be produced at low cost, and are of great practical value.

Claims (1)

[Scope of Claims] (1) A method for producing conductive particles, characterized in that the surface of conductive composite oxide particles is activated with palladium colloid and then directly coated with a noble metal in an electroless plating solution. . (2) The conductive composite oxide is La_1_-_xSr_xC
oO_3 (0.1≦x≦0.8), Pr_1_−_xS
r_xCoO_3 (0.2≦x≦0.8), Nd_1_
−_xSr_xCoO_3 (0.3≦x≦0.7), L
a_1_−_xBa_xCoO_3 (0.1≦x≦0.
5), Pr_1_−_xBa_xCoO_3 (0.2≦
2. The method for producing conductive particles according to claim 1, wherein the conductive particles have a solid solution composition of one or more of the following: x≦0.5. (3) The conductive composite oxide is La_2_-_xSr_xC
uO_4 (0.1≦x≦0.5), La_2_-xBa
2. The method for producing conductive particles according to claim 1, wherein the conductive particles have a solid solution composition of one or more of _xCuO_4 (0.01≦x≦0.5). (4) The method for producing conductive particles according to claim 1, wherein the conductive composite oxide has a YBa_2Cu_3O_7 composition. (5) The conductive composite oxide is BiCaSrCu_2O_5
＿． The method for producing conductive particles according to claim 1, characterized in that the conductive particles have a composition of _5 series. (6) An electrode for electronic components, characterized in that the conductive particles according to claim 1 are used.