JPH0268805A - Conductive particle and manufacture thereof - Google Patents

Abstract

PURPOSE:To make it possible to provide conductive particle excellent in its conductivity and thermal stability inexpensively by composing the particle surface of a conductive composite oxide being coated with a precious metal wherein a nonelectrodeposition plating method is used as the method of precious metal coating. CONSTITUTION:The particle surface of a conductive composite oxide is coated with a precious metal by a nonelectrodeposition plating method. In this case, the dispersion to the precious metal coat layer is retrained since the basic material is oxide, and it is possible to retrain the basic material from being exposed on the particle surface by a high temp. baking process even if the thickness of coating is made thin. Moreover, it is possible to restrain the decrease in the conductivity, even if the exposure occurs, since the basic material is conductive. It is thus possible to produce conductive particle excellent in conductivity, thermal and mechanical stability inexpensively.

Description

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

Conventional Technology Conventionally, conductive paints made of conductive particles, resins, solvents, and in some cases trace amounts of frit, metal oxides, and organometallic compounds have been widely used as electrode materials for various parts. . Here, as the conductive particles,
Expensive precious metals such as silver, gold, platinum, and palladium are used, and in order to reduce the cost of electrode materials, reduction of the amount of precious metals used 1. Title of the invention Conductive particles and method for manufacturing the same 2. Claims ( 1) Conductive particles characterized in that the particle surface of a conductive composite oxide is coated with a noble metal.

(2) The conductive composite oxide is La, -xSrxCo
o, (0,1<X<O,B), Pr1-xSr
xCoo5(0,2<x<:0.8), Nd1-
xSrxCoo, (0,3<X<:0.7),
3, La5. BaxCoo, (0,1<:x(:0.
5), pr,, BaxCoo5(0,2<X<
2. The conductive particles according to claim 1, having a solid solution composition of one or more of the following: 0.5).

(3) The conductive composite oxide is La2-xBaxCub4
(0,1<x<o,es), La2-xBaxG
2. The conductive particles according to claim 1, having a solid solution composition of one or two of um4 (0.01<, x<0.6).

(Brown) Considerations have been made to replace the conductive composite oxide with a conductive or base metal material according to claim 1, characterized in that the conductive composite oxide has a composition of YB&2Cu, O, system.

Copper and nickel are used for full replacement with base metal materials, and silver-copper alloys are used for partial replacement, but in both cases, oxides are formed by baking or exposure in the air, resulting in poor conductivity. In order to prevent baking, the atmosphere must be controlled and the electrode surface must be coated, complicating the manufacturing process.

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 Publication No. 60-
100679 Publication) 0 When an electrode is formed by applying a conductive paint using such noble metal coated powder to a ceramic material and baking it in air, the coated noble metal is not sintered in a continuous state, In order to prevent the conductivity from decreasing due to exposure of the base material and generation of oxides, the coating thickness of the noble metal must be increased, and the effect of cost reduction is suppressed. In addition, in order to suppress the exposure of the base material, improvements have been made to plating methods when coating precious metals (for example, Japanese Patent Publication No. 61-22028
Publication No.). However, with respect to powders made of base metal powder coated with noble metals, it is basically impossible to completely suppress heat diffusion from the base material to the coated metal when baking at high temperatures, so exposure of the base material is avoided. In order to suppress this, the thickness of the coated precious metal must be increased, and a significant cost reduction cannot be expected. Also, silicon oxide is used as the base material.

The use of oxides such as aluminum oxide, zirconium oxide, titanium dioxide, or barium titanate has also been considered (for example, Japanese Patent Publication No. 61-22029, Japanese Patent Publication No. 81-48586). However, when using oxides, thermal diffusion to the noble metal layer is suppressed compared to base metals, but since all of the above oxides are insulators, they are no longer sufficient to maintain conductivity as electrode materials. However, the thickness of the coating must be increased, making it difficult to significantly reduce material costs.

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 is necessary to prevent the base material from being exposed or the conductivity from decreasing due to processing. However, there is a problem in that the coating thickness must be increased, and therefore the amount of precious metal used increases, making it impossible to significantly reduce the cost of the conductive particles.

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 conductive particles of the present invention have a structure in which the particle surface of a conductive composite oxide is coated with a noble metal. The structure uses an electroless plating method.

Here, as the conductive composite oxide, especially La, -xS
rxCoo5(0,1<x<,0.8), Pr
, -,5rx)Coo, (0,2:<X≦o-s
) + Nd, -xsrxcoos (o-3<, X
<, 0.7), La+-xBaxCoo5(0,1
<X <0.5) IPr, -xBaxCoo,
One or two of (0, 2 x <: 0.5)
Those having a solid solution composition of more than one species, or La2-
xSrxCub4(o, 1<, x (, o, s )
.

L&2−xBaxCub, (o, o 1<x<
o, s), and furthermore, YBa2Cu, O, system, BiC
Preferably, the material has a composition based on aSrCu2O55.

Effect The present invention has the above-described structure, and since the base substance is an oxide, diffusion into the coated precious metal layer is suppressed.Even if the thickness of the coating is reduced, baking at high temperatures will cause the base substance to reach the particle surface due to processing. Exposure can be suppressed. Also,
Since the base material is electrically conductive, a decrease in electrical conductivity can be suppressed even when exposed.

The reason why a composite oxide is used as the base material here is that a composite oxide is superior in terms of conductivity and cost compared to an oxide containing a single metal element. In particular, La,
-xSrxCoo, (0,1<, !≦0.8)
.

Pr, , -xSrxCoo5(0,2<x<:0.
8), Nd1-xSr.

Coo5 (0,3≦X≦0.7), Lz, -xB
zxCoo5(o, 1≦x<, o, rs),
Pr,−,Ba,Coo, (0,2<x riO,es
), or La2-xSrxC:uo4(o, 1
<xrio,s), LIL2-xBaxCub4
(o, o 1 <
Cu30. system, BiCaSrCu2O5. .

All of the particles having the above-mentioned composition have excellent electrical conductivity, and high electrical conductivity can be obtained even if the thickness of the noble metal coating is thin, making it possible to significantly reduce the cost of the electrically conductive particles. The method for coating the base material with precious metals is as follows:
There are electroplating methods, electroless plating methods, pyrolysis methods, vapor deposition methods, etc., but the electroless plating method is the best in terms of equipment scale and mass productivity, and it allows the production of precious metal coated powders at low cost. becomes possible. Precious metals that can be coated with this electroless plating method include silver, gold, and platinum.

Examples include palladium, rhodium, iridium, 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) La205.5rCO, Go, 04f As starting materials, the required amounts of each were weighed, mixed in ethanol for 12 hours, dried and calcined at 900°C. After pulverizing this calcined powder, it was fired at 1000°C for 2 hours to obtain Lao, sSro
A powder having a composition of 5CoO was obtained.

On the other hand, the above powder is immersed in an activation solution containing neutral type palladium ions to activate the powder. Separately, palladium chloride is dissolved in concentrated ammonia water, and hydrochloric acid is added to this to adjust the pH to 8.6. A prepared palladium plating solution was prepared. Hydrazine was added to this palladium plating solution, all of the powder that had been subjected to the above activation treatment was added, and the powder surface was plated with palladium by stirring. After this plating treatment, it was washed with water by decantation and dried to obtain a palladium-coated powder. L of the powder thus obtained
The weight ratio of ILo5Sro5CoO5 and palladium is 70
/30.

100 parts by weight of the above palladium-coated powder, 5-type strained glass frit, and 2 parts by weight of ethyl cellulose.

A mixture consisting of 10 parts by weight of terpineol was kneaded with three rolls to form a paste, and after screen printing on an alumina substrate, the entire process was carried out by baking at 1000° C. for 10 minutes. The electrical resistance value of the thick film baked in this way is 4X
The resistance was 10-'Ω·α, indicating excellent conductivity.

On the other hand, in the case of a thick film formed on an alumina substrate by the same method as above using LILo5Sr, 5Coo, powder without palladium coating, 7 to 9 × 10 Ω・
In all cases, the resistance value of α was significantly increased compared to the case where palladium-coated powder was baked. This is because the boundary between the baked thick film and the alumina substrate is colored blue, and it is thought that the resistance value increases due to the reaction of La, 5Sr, and 5Coo5 with alumina. Therefore, by coating with palladium, the conductivity of the powder is increased, and at the same time, the base material L&. 5
It is thought that the two effects of suppressing the reaction between "0.5"05 and the substrate material combine to form a thick film with excellent conductivity on the alumina substrate.

In addition, we conducted the same experiment as above by changing the thickness of the palladium coating, and even when the weight ratio of LILo5Sro5COO5 and palladium was 80/20, the same excellent conductivity as above was confirmed, and the amount of precious metal used was significantly reduced. It has become clear that reductions are possible.

(Example 2) La20. Pr60. , , Nd2O5,BaC0
,,5rCO5゜Co,04 as the starting material, L a + -x S r x
Co Os * P r + −x S rx Co
Os TNd, -xSrxCoo, , La, -x
BaxCoo5. Powders with different X of each composition system of Pr, -, and BaxCoo were prepared.

Using these powders as a base material, plating was performed in the same manner as in Example 1 to obtain a palladium-coated powder having a weight ratio of base material to palladium of 70,730. Using this powder, a conductor paste was prepared in the same manner as in Example 1, and the paste was baked on an alumina substrate and the electrical resistance value was measured. The results of converting this measured value into units of Ω/mouth are shown in Table 1 below.

(Hereinafter in the margin) From the results of Coating 1 above, it can be seen that the electrical resistance value of the baked thick film is not determined only by the coated palladium, but is influenced by the composition of the base material. In order to obtain excellent conductivity, the composition of the base material should be La, -xSrxCoo 5 (0,1<X<,
0.8), Pr,-,5rxCoo5(0,2≦
X<:0.8), Nd, -xSrxCoo5(o
, s<x<0.7).

La + -x Bax C0Os (0-1≦x<
0.5), Pr, -xBaxCoo, (0-,2<
, ! <:0.6) is suitable.

Next, palladium plating, pasting, and baking were performed in the same manner as above using an oxide that is a composite of the above materials as a base material.The electrical resistance value of the obtained thick film was measured, and the results are shown in the table below. As shown in Figure 2, excellent conductivity was confirmed.

(Example 3) Using 25 l 5 of LaO5rCO, BaCO3, and CuO as starting materials, the required amount of each was weighed, mixed in ethanol for 12 hours, dried, and calcined at 900'C for 12 hours.
L 2L 2-x S rxC by heat treatment in oxygen at ℃
ub4. La, xBaxCub4 xf Powders having various compositions were obtained.

On the other hand, the above powder was activated by immersing it in an activation solution containing neutral palladium ions, and a plating solution consisting of platinum chloride, aqueous ammonia, and hydrochloric acid was separately prepared, and this plating solution was added with hydrazine and activated. Add the processed powder,
The powder surface was plated with platinum by stirring. After this plating treatment, it was washed with water by decantation and dried to obtain a platinum-coated powder. The weight ratio of the base substance and platinum in the powder thus obtained was 70/30.

Using the above platinum-coated powder, a conductive paste was prepared in the same manner as in Example 1, and placed on an alumina substrate at 900°C.
The electrical resistance was measured at a temperature of . The results of converting this measured value into units of Ω·α are shown in Table 3 below.

(Left below) From the results of Cloth 3 above, in order to obtain excellent conductivity, the composition of the base material must be La 2-. 5rxCuO4(0
,1<,X<,0.5), La2-xBaxC
ub4(0,01<.

It can be seen that xkuo,s) is suitable.

Next, using an oxide that is a composite of the above materials as a base material,
Platinum plating, pasting, and baking were performed in the same manner as above, and the electrical resistance of the thick film thus obtained was measured, and as a result, excellent conductivity was confirmed as shown in Table 4 below.

(Left below) (Example 4) Y OBaC0, CuO, Bi OCaC0,, 5rC
0゜2 5' 5
Using 25' as a starting material, the required amount of each was weighed, mixed in ethanol for 12 hours, dried, and heated at 850°C for 12 hours.
After baking for an hour, heat-treated in oxygen at 600°C, Y
Ba2Cu30. and BiCaSrCu2O5.
A total powder having the composition was obtained.

On the other hand, the above powder was immersed in an activation solution containing neutral type palladium ions for activation treatment, and separately 4NIL of gold cyanide and ethylenediaminetetraacetic acid (EDT) was applied.
A plating solution consisting of salt and hydrochloric acid was prepared, sodium ascorbate and activated powder were added to this plating solution, and the powder surface was plated with gold by stirring.

After this plating treatment, it was washed with water using a decantation method and dried to obtain a gold-coated powder. The weight ratio of the base material and gold of the powder thus obtained was f30/40.Next, a multi-conductor paste was prepared in the same manner as in Example 1 using the above gold-coated powder, and an alumina substrate was prepared. 85 on top
It was baked at 0'C and the electrical resistance was measured. As a result, when the base material is YBa2Cu30a, the electrical resistance value is 6×
10 Ω-cat, and in the case of BiCaSrCu2O,5, it was 8×10 Ω·α, confirming excellent conductivity.

(Example 6) Magnesium lead niobate (Pb (Mgv3NbH)
0. ), 8 parts by weight of polyvinyl butyral resin, 4 parts by weight of dibutyl phthalate, 40 parts by weight of trichloroethane, and 26 parts by weight of butyl acetate were added and kneaded in a ball mill for 20 hours. The dielectric slurry thus obtained was subjected to a reverse roll method to
It was formed into a sheet with a thickness of μm.

Next, by the same method as in Example 1, LΔ was determined. 5SrO,
50003 Powder whose particle surface is coated with palladium (La
o5Sro5Coo, and palladium weight ratio 260
/60) was prepared, ethyl cellulose and terpineol were added thereto, and the mixture was kneaded with three rolls to prepare an electrode <-7. This electrode paster is printed in a desired pattern on the dielectric main sheet and laminated to produce a laminate in which electrodes and dielectrics are alternately laminated. C. Baked for 2 hours.

On the side of the sintered body thus obtained where the electrodes are exposed,
Palladium-coated L prepared in the same manner as in Example 1
ao5Sro5Coo, (Lao, 5Sro5Co0
An electrode paste consisting of 5 and palladium (weight ratio: 70/30), glass frit, ethyl cellulose, and terpineol was applied and baked at 800''C.The capacitance value of the multilayer chip capacitor thus obtained was , which is in good agreement with the design value calculated from the dielectric constant (ε~12000), and the palladium-coated La
The practicality of the electrode using o5Sr o5Co05 was confirmed.

In addition to non-example J, conductive composite oxide particles coated with precious metals are used for chip resistors and chip inductors.

Needless to say, it is useful as an electrode for 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 was 5
．． Although the particle size was in the range of 0 to 0.1 μm, the particle size and shape are not particularly defined.

On the other hand, in addition to the above-mentioned examples, silver, rhodium, and iridium, which can be plated electrolessly, can be used as coated noble metals.

It goes without saying that ruthenium and alloys thereof may also be used.

Effects of the Invention As described above, the present invention provides conductive particles having a structure in which the particle surface of a conductive composite oxide is coated with a noble metal, and furthermore, an electroless plating method is used as a method for coating the noble metal. Excellent conductivity and thermal properties.

Conductive particles with excellent chemical stability can be produced at low cost, and are of great practical value.

Claims (7)

[Claims] (1) Conductive particles characterized in that the particle surface of a conductive composite oxide is coated with a noble metal. (2) The conductive composite oxide is La_1_-_XSr_X
CoO_3 (0.1≦X≦0.8), Pr_1_-_X
Sr_XCoO_3 (0.2≦X≦0.8), Nd_1
____XSr_XCoO_3 (0.3≦X≦0.7),
La_1_−_XBa_XCoO_3 (0.1≦X≦0
．． 5), Pr_1_−_XBa_XCoO_3(0.2
The conductive particles according to claim 1, having a solid solution composition of one or more of the following: ≦X≦0.5. (3) The conductive composite oxide is La_2_-_XBa_X
CuO_4 (0.1≦X≦0.5), La_2_−_X
The conductive particles according to claim 1, having a solid solution composition of one or two of Ba_XCuO_4 (0.01≦X≦0.5). (4) The conductive composite oxide is YBa_2Cu_3O_7
2. The conductive particles according to claim 1, having a composition of: (5) The conductive composite oxide is BiCaSrCu_2O_5
＿． The conductive particles according to claim 1, having a composition of _5 series. (6) A method for producing conductive particles, which comprises coating the surface of conductive composite oxide particles with a noble metal by electroless plating. (7) An electrode for electronic components, characterized in that the conductive particles according to claim 1 are used.