JPH02217479A - Production of conductive grain - Google Patents

Abstract

PURPOSE:To produce conductive grains having superior electric conductivity and excellent in thermal and chemical stability at a low cost by directly coating the surface of the grains of conductive multiple component oxide having a specific composition with noble metal in an electroless plating bath without exerting activating treatment. CONSTITUTION:A powder of conductive multiple component oxide having a solid solution-type composition consisting of one or >=2 kinds among La1-xSrxCoO3 (0.1<=x<=0.8), Pr1-xSrxCoO3 (0.2<=x<=0.8), Nd1-xSrxCoO3 (0.3<=x<=0.7), La1-xBaxCoO3 (0.1<=x<=0.5), and Pr1-xBaxCoO3 (0.2<=x<=0.5) is prepared. The surface of the grains of the above conductive multiple component oxide is directly coated with noble metal in an electroless plating bath without being previously subjected to activating treatment. By this method, the conductive grains in which high electric conductivity can be provided even if the thickness of the noble metal coating is reduced and, as a result, costs can be remarkably reduced can be obtained.

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.

BACKGROUND OF THE INVENTION Conventionally, conductive paints consisting of conductive particles, resin and solvent, in some cases trace amounts of frit, metal oxides and organometallic oxides have been widely used as electrode materials for various parts. The above-mentioned conductive particles include gold, silver, platinum,
In order to reduce the cost of electrode materials, studies are being made to reduce the amount of precious metals used or replace them with base metal materials.

Here, copper and nickel are used for full replacement with base metal materials, and silver-steel alloys are used for partial replacement, but in both cases, silicon oxides are formed by baking in air or by leaving them. The problem is that the baking process requires controlling the atmosphere and coating the electrode surface, complicating the manufacturing process.

In addition, attempts have been made to reduce the amount of precious metal used by using base metal powder as a base material and coating it with noble metal. (For example, Japanese Patent Publication No. 46-40593, Japanese Patent Application Laid-Open No. 60-100679) A conductive paint using such Kikai 4 coating powder was applied to a ceramic material and baked in air to form an electrode. In this case, the coated noble metal is not sintered in a continuous state, the base material is exposed, and oxides are generated, resulting in a decrease in conductivity. In order to prevent this, the coating thickness of the noble metal must be increased, and the cost reduction effect is suppressed. In addition, in order to suppress the exposure of the base material, your company I! Improvements have also been made to the plating method used for coating (for example, Japanese Patent Publication No. 61-22028).
.

However, when baking a base metal powder coated with a noble metal as a base material, it is basically impossible to completely suppress heat diffusion from the base material to the coated metal, so exposure of the base material is avoided. To suppress K, it is necessary to increase the thickness of the coated precious metal, and a significant cost reduction cannot be expected.

In addition, the base material may include silicon oxide, aluminum oxide, acid f.
The use of warming substances such as hypanadium, zirconium oxide, or barium titanate is also being considered. (For example, Japanese Patent Publication No. 61-22029, AASAE Publication) However, when oxides are used, heat diffusion into the noble metal layer is suppressed compared to base metals, but all of the above oxides are insulators. Therefore, in order to maintain conductivity as an electrode material, 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 substrate 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 conductive particles coated with a base metal or oxide having the above-mentioned structure, baking at high temperatures may result in exposure of the base material or conductivity due to processing. In order to prevent a decrease in the conductive particles, the thickness of the coating must be increased, which results 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 safely provide conductive particles that have excellent conductivity and excellent thermal stability.

Means for Solving the Problems In order to solve the above problems, 1. The method for producing conductive particles of the present invention is to produce conductive particles directly in an electroless plating solution without activating the particle surface of a conductive composite oxide. It is equipped with a structure that covers four parts of the body.

Here, as the conductive composite oxide, especially La, -, 5
rxCoo, (0.1≦X≦o, s), pr, -
xsrxcoo.

(0.2≦X≦0.8), N(1,-xSrxC
od, (Oβ≦X≦α7).

La, -XBaXCoO, (0.1≦X≦o, s).

A composition having one or more of Pr, -XBaXCoO, (02≦X≦05), or La, xSrxCub4 (o, 1≦X≦o, s).

Those having a solid solution composition of one or more of La, xBaxCuO4 (o, o 1≦X≦0.6), as well as YBa2Cu, O, system, BiCaSrC
It is preferable to have a composition of u2O5.5rCu20.5 system.

Function: Due to the above-described structure, the base material is a conductive oxide, which suppresses diffusion into the coated noble metal layer, and also has self-activation properties, eliminating the need for activation treatment in electroless plating. This allows the process to be simplified. This feature allows the coating thickness to be made very thin and the process cost to be reduced, resulting in a significant cost reduction.

In addition, as a characteristic due to the chemical stability of the coated noble metal layer, when baking with ceramic materials such as dielectric materials and magnetic materials at high temperatures, the substrate substance reacts with the ceramic material due to processing, and the dielectric properties of the ceramic material Alternatively, it is possible to suppress deterioration of magnetic properties and deterioration of conductivity as an electrode.

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

In particular, LIL, -xSrx Coo, (o, 1≦X≦O
,B).

Pr,,5rxCoo, (0.2≦X≦o,a)
.

Nd, xSrxCoo, (0.3Thx≦0.7
).

La, XBaXCoO, (0.16X l-0.5
).

Pr, -XBaXCoO, (0.2≦X≦0.6)
Those having one or more of the following compositions, or La, 5rxCub4 (0.1≦X≦0.5
).

Those having a solid solution composition of one or more of La2-xBaxCub4 (0.01≦X≦0.6), as well as YBa2Cu3O7 system, BiCaSrC
u2O5.5rCu20 All those with s and s compositions have excellent conductivity, and high conductivity can be obtained even if the thickness of the coating material is thin, so the cost of conductive particles can be significantly reduced. Is possible.

Examples of noble metals that can be coated include gold, silver, palladium, platinum 20dium, /1/thenium, and alloys thereof. Also.

When coating with noble metals, it is also possible to coat with two or more of the above noble metals in multiple layers.

Example The present invention will be explained in detail below using examples.

(Example 1) La O, 5rCO,, Go, 04 was used as a starting material.

The required amount of each was weighed, mixed in ethanol for 12 hours, dried and calcined at 900''C. This calcined powder was crushed and calcined at 1100''C for 2 hours.

A powder having a composition of La, Sr [L5CjoO, was obtained.

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

The above La (L5Sr, 5Co) is added to this palladium plating solution.
o.

A powder having the following composition was added while being dispersed using a magnetic stirrer. Next, hydrazine as a reducing agent was added and stirred to plate the powder surface with palladium. After plating, it is washed with water using the decantation method.

After drying, a palladium-coated powder was obtained. LIL of the powder thus obtained, 5Sr, 5G00. The weight ratio of the sample and the palladium plating film was as shown in Table 1 below. 100 parts of the above palladium coated powder.

6 parts by weight of glass frit, 2 parts by weight of ethyl cellulose,
A mixture consisting of 10 parts by weight of α-televinol was kneaded using three rolls to form an electrode paste.

This electrode paste was screen printed on an alumina substrate and then baked at 1000'C for 10 minutes. The electrical resistance value of the thick film baked in this manner was as shown in Table 1, indicating excellent electrical conductivity. On the other hand, LIL15S
r[L5CoO3 with m-
It was evaluated as an electrode paste under the above conditions.

From these results, it can be seen that when only La, 5Sr, and 5Coo are used as an electrode, they do not have sufficient stability during sintering in terms of stability for one reaction. Therefore, by coating palladium, the conductivity of the powder is increased, and the reaction between the base material and the alumina substrate, which is the substrate material, is suppressed, which are two effects that combine to create a thick film with excellent conductivity on the alumina substrate. is formed.

(Example 2) La20. , PF60. , , Nd2O,,B
aC0. , 5r00. .

Using Cjo, 04 as the starting material, the same method as in Example 1), La, -xSrxCoo, , Pr,
-xSrxCoo, .

Ha, xSrICoo, , La, -XBaXCo
O.

Pr,, Ba! Powders having different compositions of OoO and X were prepared. Using these powders as basic materials, plating treatment was performed in the same manner as in Example 1 to obtain palladium-coated powders having a weight ratio of base material to palladium of 10/1.

Using this powder, a multi-conductor paste was prepared in the same manner as in Example 1, and the paste was baked onto an alumina substrate and the electrical resistance was measured. The results of converting the measured values into units of 0.01 are shown in [Table 2] below.

(Margin below) From the results in Table 2, it can be seen that the electrical resistance value of the baked thick film is determined not only by the coated palladium but also by the composition of the base material. here,
Palladium plays a role in preventing reactions with ceramic materials.

In order to obtain excellent conductivity, the composition of the base material must be La, -, 5rxCod3 (o, 1≦X≦O, s
).

Pr, -xsrxcoo, (0.2≦X≦0.8)
.

N(1,−,5rxCoo, (0.3≦X≦0.7
).

Laf-xBILxCO03 (α1≦X≦o, s)
.

Pr, -xBaxCod, (0.2≦X≦0.6) is suitable.

Next, using an oxide that is a composite of the above materials as a base material, it is coated with palladium by plating in the same manner as above, and the electrical resistance of the resulting thick film is measured. The result.

Excellent conductivity was confirmed as shown in Table 3 below.

[Table 3] (Example 3) La20. , 5rCO, , BaC0. , CuO as a starting material, weigh the required amount of each, and add 1 ml of each in ethanol.
After mixing for 2 hours, drying, and baking at 9oO℃ for 2 hours,
Heat treated in oxygen at aoo°C to form La, xSrxOur4. La2-xBaxCub4
A powder having a composition in which X was changed to species 4 was obtained. This powder was separately added to a plating solution consisting of platinum chloride, aqueous ammonia, and hydrochloric acid together with hydrazine, and the powder surface was plated with platinum by stirring. After the plating treatment, the plate was washed with water using the decanty silon method and dried to obtain a platinum-coated powder. The powder thus obtained had a weight ratio of base material to platinum of 7 o/30. A conductive paste was prepared in the same manner as in Example 1 using the platinum plating powder described in L.

It was baked on an alumina substrate at a temperature of eoo'C, and the electrical resistance was measured. The results of converting this measured value into units of Ω·1 are shown in [Table 4] below.

(Left below) From the results in Table 4, in order to obtain excellent conductivity, the composition of the base material should be LIL, -xSrxCuO.

(0.1≦X≦o, s), La2-xBaxCu
It can be seen that O4 (Q01≦X≦06) is suitable.

Next, platinum 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 basic substance, 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) T O, BaC0, CuO, Bi2's, O & CjO
s.

Using SrCO as a starting material, weigh the required amount of each,
After mixing in ethanol for 12 hours and drying.

After firing for 2 hours in sso"c, heat treatment in oxygen at 600°C results in more affiCu, O, and 81Ca8rC.
A powder having a composition of u20a5 was obtained. On the other hand, gold cyanide and IEDTM (ethylenediaminetetraacetate)
A plating solution consisting of a 4N solution and hydrochloric acid was prepared, and the above powder and sodium ascorbate were simultaneously added to the plating solution and stirred to adhere gold plating to the powder surface. The powder thus obtained had a weight ratio of base material to gold of 60/40.

Using the above gold-coated powder, a conductive paste was prepared by the same method as in Example 1, and was placed on an alumina substrate at 850'.
It was baked at a temperature of C and the electrical resistance was measured. As a result, when the basic materials are YBa, Cu, and O, the electrical resistance value is 8.
X 10-'Ω・1.1casrcu20cL5
In this case, the resistance was 8×10-'Ω·1, and excellent conductivity was confirmed.

(Example 6) Magnesium lead niobate (P b (M g 1/3
Dielectric powder 100 whose main component is Nb2A)03)
Parts by weight, 8 parts by weight of polyvinyl butyler/I/resin, 4 parts by weight of dibutyl phthalate, 40 parts by weight of trichloroethane, and 26 parts by weight of butyl acetate were added, followed by ball milling. The dielectric slurry thus obtained was formed into a sheet with a thickness of 40 μm using the reverse throw μ method.

Next, in the same manner as in Example 1, La, 5Sr, 5C
oo.

Powder whose particle surface is coated with palladium (Laas,k
r, scOOs and palladium weight ratio: so/so).

Ethyl cellulose and α-terepinol were added to this and kneaded with a triple roll to prepare an electrode paste. This electrode paste is cut into desired dimensions on the dielectric sheet.
It was fired at 100'C for 2 hours.

On the side surface of the sintered body thus obtained where the electrodes are exposed,
Palladium-coated La, 5Sr, 5Coo, (LallL5Sra5C) prepared in the same manner as in Example 1
An electrode paste consisting of glass frit, ethyl cellulose, and α-terebinolt was applied and baked at 80°C. The capacitance value of the multilayer chip capacitor obtained in this way agrees well with the design value calculated from the dielectric constant (ε=1'2000), and the palladium-coated L&
, 5SrI15Coo, was confirmed to be practical. 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 compound powder used in the above example had 0
．． Although the particle size was in the range of 1 to 5.0 μm, the particle size and shape are not particularly defined.

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

Effects of the Invention As described above, the present invention provides conductive particles coated with a precious metal directly in an electroless plating solution without activating the surface of the particles of a conductive composite oxide. Excellent,
Moreover, conductive particles with excellent thermal and chemical stability can be manufactured in Yasukuni, and both values are extremely large in practical use.

Claims (5)

[Claims] (1) A method for producing conductive particles, characterized in that the surface of conductive composite oxide particles is directly coated with a noble metal in an electroless plating solution without activation treatment. (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.
6), 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≦0.6. (3) The conductive composite oxide is La_2_-_XSr_XC
uO_4 (0.1≦X≦0.5), La_2_-_XB
1 of a_XCuO_4 (0.01≦X≦0.5)
2. The method for producing conductive particles according to claim 1, wherein the conductive particles have a solid solution composition of one species or two or more species. (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.