JPH0266101A - Electric conductive particles and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain electric conductive particles having excellent electric conductivity and improved solderability and wettability at a low cost by coating surface of base metal particles with different kinds of two or more layers of noble metals. CONSTITUTION:The base metal particles consisting of one or more kinds among Fe, Co, Ni, Cu, Al, Mo and W or alloys thereof are prepared. Then, on the surface of the base metal particles, a first layer is formed by coating with the noble metal, which does not react with oxygen or the oxygen does not permeate there through, for example, one or more kinds among Au, Pt, Ag and Ir or alloys thereof. Successively, by applying the coating layer of Pd or Pd alloy on the first layer, hence the objective electric conductive particles are obtd. The noble metal layer on the first layer has effect preventing oxidization of the base metal layer by heat treatment. Further, the noble metal layer being the second layer has effect giving solderability and solder pitting resistance as an electrode material. Then, at the time of using the resultant electric conductive particles for the electrode of electronic parts, the parts having high performance can be provided at a low cost.

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 oxides have been widely used as electrode materials for various parts. .

Expensive precious metals such as gold, silver, platinum, and palladium are used as the conductive particles.In order to reduce the cost of electrode materials, the amount of precious metals used is reduced.1. Name of the invention: Conductive particles and their manufacturing method. 2. Claims (1) Conductive particles characterized in that the surfaces of base metal particles are coated with two or more layers of different noble metals.

(2) The conductive particles according to claim 1, wherein the base metal particles have a composition of at least one of iron, cobalt, nickel, copper, aluminum, molybdenum, and tungsten, or an alloy thereof. .

(3) The first noble metal layer in contact with the surface of the base metal particles has a composition of at least one of gold, platinum, silver, and iridium or an alloy thereof. conductive particles.

(4) The conductive particle according to claim 1, wherein the noble metal layer of the surface layer has a composition of palladium or an alloy containing palladium.

(5) Considerations have been made to electroless plating the particle surfaces of base metal particles or replacing them with base metal materials.

Copper and nickel are used for full replacement with base metal materials, and silver-steel alloys are used for partial replacement.
In both cases, oxides are formed when baked or left in the air, reducing conductivity. Baking poses a problem in that controlling the atmosphere and storing methods become complicated.

Furthermore, attempts have been made to coat base metal particles with noble metals (for example, Japanese Patent Publication No. 46-40593 and Japanese Patent Application Laid-Open No. 60-100679). A conductive paint using such precious metal-coated particles is applied to a ceramic material,
When electrodes are formed by baking in air, an interlayer corresponding to each noble metal emerges.

For example, in the method as shown in Japanese Patent Publication No. 61-22028, when the noble metal is silver, migration of silver becomes a problem when used as an electrical component, and problems remain in terms of reliability. However, when a palladium coating film is provided and heat treated in the air, palladium turns into palladium oxide at around 400°C, oxidizing the base metal particles that are the core of the particles and increasing electrical resistance. Ta.

Furthermore, when coating with gold or platinum, there are problems in that it is too expensive and the gold tends to be eaten by solder.

Problems to be Solved by the Invention Regarding conductive particles having base metal particles having the above-described structure as cores and coated with noble metals, silver migration, gold solder eating, palladium oxidation due to high temperature heat treatment, and the accompanying base metal particles occur. There is a problem that the cost of conductive particles cannot be significantly reduced because there are interlayers such as oxidation of the conductive particles and deterioration of solder resistance properties, and a complicated process that exceeds the material cost is required.

The present invention has been made in view of the above, and an object of the present invention is to provide, at a low cost, conductive particles that have excellent conductivity, improved solderability, and wettability.

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 base metal particles is coated with two or more layers of noble metals, and furthermore, the conductive particles of the present invention have a structure in which the particle surface of base metal particles is coated with two or more layers of noble metals. The structure uses an electroless plating method. Here, the base metal particles preferably have an alloy composition of one or more of iron, cobalt, nickel, copper, aluminum, molybdenum, and tungsten. However, the noble metal in the first layer coated on the base metal particles is made of a material that does not react with oxygen or does not allow oxygen to pass therethrough. Specifically, it may be an alloy of at least one or two or more of gold, platinum, silver, and iridium. The uppermost surface layer is composed of palladium or an alloy containing palladium.

Effect of the Invention Due to the above-described structure, the present invention enables heat treatment in the presence of oxygen without oxidizing the base metal, even though the base particles are made of a base metal.

In order to achieve this, oxidation of the base metal particles can be prevented by the first layer of noble metal coated on the surface of the base metal particles. It is important that this first layer be a dense film, and the covering layer may be thin.

Furthermore, the second coating layer made of palladium or palladium alloy can prevent solder from being eaten away by solder dipping and solder reflow, and can improve adhesive strength and reliability with solder. Furthermore, when silver is used in the first layer, it also serves as a barrier to prevent migration.

Here, if the palladium layer alone is used as an electrode material and is baked in air, as the temperature increases, the
Since it becomes palladium oxide at a temperature of 100°C, it does not act as an oxygen barrier and oxidizes base metal particles. In addition, the purpose of using base metals for the base particles is that they are superior in terms of conductivity and cost, and if heat treatment can be performed in air, it will no longer be necessary to perform heat treatment while controlling the complicated atmosphere. This makes it possible to lower the total cost. Furthermore, the parts (ceramics) on which the electrodes are formed are often fired in the air, and in order to make atmosphere firing possible, restrictions such as the need to have reduction resistance are required. The invention satisfies this need as described above.

Furthermore, methods for coating the base metal powder with noble metals include electroplating, thermal decomposition, vapor deposition, and electroless plating. Among these methods, the electroless plating method has the best coating properties, and this makes it possible to produce noble metal coated powder at low cost.

Example Hereinafter, the present invention will be explained in detail using examples.

<Example 1> 10 g of commercially available copper powder was mixed with ammonia; 2 occ/l.

Add Potassium I T971 and silver nitrate; 1o9/71 and stir and mix well to disperse. Add 0.1N of homorin to glucose as a reducing agent to the solution adjusted to this level.
Added with 10CG of ammonia at a ratio of 3g/l,
Stir well. Copper powder coated with silver then precipitates. The weight ratio of silver and copper obtained by filtering this was 1:2.

Next, 10 g of commercially available copper powder was added to gold potassium cyanide; 129/
1. Potassium cyanide: Pour it into a 7 og/l solution with stirring and perform immersion plating. Then, copper powder coated with gold precipitates. The weight ratio of gold and copper obtained by filtering this was approximately 1:1.

Further, in order to form a second layer of palladium film, the plated copper powder is separately immersed in an activation solution containing neutral palladium ions to perform an activation treatment. Next, an electroless plating solution is prepared by dissolving palladium chloride in aqueous ammonia and adding hydrochloric acid to adjust the pH to 5. When the activated powder is immersed in this electroless plating solution and hydrazine sulfate is added and stirred and mixed, palladium-plated copper powder is precipitated.

In this way, conductive particles on which a copper powder-silver plating layer-palladium plating layer were formed and conductive particles on which a copper powder-gold plating layer-palladium plating layer were formed were obtained.

Further, as a conventional example, when 10 g of commercially available copper powder is treated by silver mirror reaction, copper powder covered with silver is precipitated. The weight ratio of silver and copper obtained by filtering this was 1:2. Then, in order to form a palladium film on the copper powder, the copper powder is immersed in an activation solution containing neutral palladium ions to perform an activation treatment. Next, an electroless plating solution is prepared by dissolving palladium chloride in aqueous ammonia and adding hydrochloric acid to adjust the pH to 8.5.

When the activated powder is immersed in this electroless plating solution and hydrazine sulfate is added and stirred and mixed, palladium-plated copper powder is precipitated.

The thus obtained conductive particles 5I of the present invention and the conventional example were used as a glass frit, and borosilicate lead glass: 2.0 wt%, and ethyl cellulose was used as a binder.
A mixture of 1-5 cc of TVNEO-7V as a solvent was thoroughly kneaded using three rolls to form a paste.

96% of the paste obtained in this way was screen printed.
After printing on an alumina substrate and drying at 105℃ for 10 minutes, it was placed in a firing furnace and baked in air under the following firing conditions: 700'C for 10 minutes, 8cc℃ for 10 minutes, and 900℃ for 10 minutes. Fired.

As shown in Table 1 below, the resistivity of the electrode obtained in the above manner is sufficiently low.On the other hand, with conventional coated powder, base metal particles are oxidized, making it difficult for practical use. It is clear that this is not preferable as an electrode material that requires resistance. Further, although silver-coated base metal particles have sufficient electrical properties, they are insufficient to prevent the electrode from being eaten away by solder immersion in the obtained electrode material, and cannot be put to practical use. The same thing happens with gold coatings, and it is necessary to have a sufficient thickness of the coating layer, which does not provide any cost advantage.

As described above, by coating base metal particles with gold or silver and then coating them with a palladium layer as a second layer, an electrode material that can be heat-treated in air was obtained. Here, we experimented with gold and silver as the precious metals for the first layer.
It is clear that the same results can be obtained with platinum and iridium.

<Example 2> Nickel particles were obtained by forming a silver plating layer and a palladium plating layer on 6 g of commercially available nickel powder using the same method as in Example 1. On the other hand, the same nickel powder: 5! ! platinum chloride,
A platinum plating layer is formed by immersing it in a hydrochloric acid solution and stirring and mixing the reducing agent. Next, the palladium layer is plated with nickel powder in the same manner as in Example 1.

Conductive particles on which nickel powder, silver plating layer, and palladium plating layer were formed by such a method, and nickel powder.
Conductive particles on which a platinum plating layer and a palladium plating layer were formed were obtained.

Conductive particles thus obtained: 5y, lead borosilicate glass as a glass frit: 2.0 wt%, ethyl cellulose as a binder: 1. c) wt%, TVNeo-/I/:1.2CC as a solvent, and thoroughly kneaded with three rolls to form a paste. The paste obtained in this way was printed on an alumina substrate by screen printing, dried at 105°C for 10 minutes, and then placed in a firing furnace for 80 minutes.
Firing was carried out in the air under conditions of holding at 00 to 1000C for 10 to 30 minutes. The specific resistance of the electrode obtained as described above is sufficiently low as shown in Table 2 below, and in the case of coated powder as in the conventional example, oxidation of base metal particles occurs, and low resistance is required for practical purposes. It can be seen that it is not suitable as an electrode material. Furthermore, it can be seen that the base metal particles coated with silver are not sufficient to prevent the electrode from being eaten away by immersion of the obtained electrode material in solder, and cannot be put to practical use as a solder resistance property during mounting. Here, as a conventional example, it was produced under exactly the same conditions as described in Example 1 except that the copper powder was replaced with nickel powder.

As described above, by coating base metal particles with silver or platinum and then coating them with a palladium layer as a second layer, an electrode material that can be heat-treated in the atmosphere was obtained.

<Example 3> Conductive particles used in Example 1: 5 g of lead borosilicate glass having a softening point Hs3oc as a glass frit;
5. Qwt%, ethyl cellulose as binder;
1. Qwt%, terpineol as solvent; 12cc
The following composition is thoroughly kneaded using three rolls to form a paste.

On the other hand, the resistor is made by making a paste of thenium oxide and screen-printing it on an alumina substrate on which an electrode band made of palladium electrodes is formed. At this time, the alumina substrate is pre-grooved so that it can be divided into chip sizes (32×1.6 mm). Further, the resistor is fired under firing conditions of 850° C. for 10 minutes and designed to have a desired resistance value. In order to achieve mechanical strength of the end face of such a chip resistor, the above conductive particles are made into a paste and applied as a terminal electrode. After that, 105C
After drying for -10 minutes, baking is performed in the air at 550°C for 10 minutes. The thus obtained chip resistor had stable resistance characteristics due to ruthenium oxide and the structure of the terminal electrode according to the method of the present invention, resulting in an inexpensive and high-performance chip resistor.

<Example 4> Lead borosilicate glass having a softening point of 650° C. using 5 g of the conductive particles used in Example 2 as a glass frit; 1.
Qwt%, three rows/VK with a composition of 1,100 ethyl cellulose-sterepineol as a binder
Mix well to make a paste. On the other hand, dielectric ceramic is a material whose main component is BaTi05 with a diameter of 10 mmφ.
After molding to a thickness of 1,000 mm and sintering at 1,320°C to 120 minutes, the paste-formed conductive particles were applied to both sides of the capacitor porcelain and dried.
The heat treatment was carried out under the conditions of baking at -10 minutes. The capacitor thus obtained had a dielectric constant of 1200°.

This was the same for the two types of conductive particles in Example 2. Further, in this example, it was used as a surface electrode of a disk-shaped ceramic capacitor, but it is easily thought that good results can be obtained by using it as a terminal electrode of a chip capacitor. Furthermore, BaTi05 is used as a mold material.
It goes without saying that it can also be used for the terminal electrodes of ceramic capacitors using materials other than the high dielectric constant material having a perovskite structure mainly composed of SrTi03pbo, as well as materials having a low dielectric constant such as Ti02 type.

<Example 6> To 5 g of the conductive particles used in Example 1, 1.5 g of glass frit) and ethylcetate (swt%) were added as a binder. o wt%, terpineol 1.20C as solvent
The following composition is thoroughly kneaded using three rolls to form a printing paste. The thus obtained paste is printed into a desired circuit pattern by screen printing. Then, after drying, it was baked at 900° C. for 10 minutes.

The electrodes of the circuit pattern thus obtained had low resistance and good solderability. Also.

This electrode could be put to practical use as a conductor electrode for hybrid integrated circuits and a land electrode for chip components.

<Example 6> 5 g of the conductive particles used in Example 2 were mixed into a paste using ethyl cellulose and terpineol. On the other hand, as magnetic particles, Ni with a particle size of 1 to 3/1 m
- Make Zn ferrite powder into a paste using the above method. After that, magnetic paste and electrode paste are printed alternately to form the electrodes into a spikele shape. This has a structure in which magnetic particles are embedded in spiral-shaped electrodes.

The printed material is then sintered under firing conditions of 1000° C. for 120 minutes. The inductor component thus obtained was a chip inductor having an inductance of 100 mH.

Here, in the above embodiment, the case where copper or nickel was used as the base metal particles was explained, but in addition to this, iron, cobalt, aluminum, molybdenum, tungsten, etc. can also be used.
Furthermore, it may have a composition based on an alloy thereof.

Furthermore, as the noble metal in the first layer in contact with the surface of the base metal particles, one of gold, platinum, silver, and iridium can be used, as described above, but this may be based on alloys of these metals. It may have the following composition.

Furthermore, although palladium has been described as the noble metal of the surface layer (second layer), it may also be composed of an alloy containing palladium.

Effects of the Invention As described above, the present invention provides conductive particles in which the surface of a base metal is coated with two or more layers of different noble metals, and the base metal particles have at least one of gold, platinum, silver, and iridium as the first layer. Alternatively, by providing a coating layer having a composition of alloys thereof, and further providing a coating layer having a composition of palladium or an alloy containing palladium as a surface layer, the first noble metal layer can be heat treated as a base metal layer. The second noble metal layer, as an electrode material, is effective in imparting solderability, chipping resistance, and solder attack resistance. By giving these respective noble metal layers different roles, the coating thickness of the noble metal layer can be made as thin as possible. Furthermore, since heat treatment can be performed in air, a high-performance electrode material can be provided without using an electric furnace or atmospheric gas that requires complicated atmosphere control.

Furthermore, when these conductive particles are used in electrodes of electronic components, inexpensive and high-performance components can be provided.

Claims (6)

[Claims] (1) Conductive particles characterized in that the surfaces of base metal particles are coated with two or more layers of different noble metals. (2) The conductive particles according to claim 1, wherein the base metal particles have a composition of at least one of iron, cobalt, nickel, copper, aluminum, molybdenum, and tungsten, or an alloy thereof. (3) The first noble metal layer in contact with the surface of the base metal particles has a composition of at least one of gold, platinum, silver, and iridium or an alloy thereof. conductive particles. (4) The conductive particle according to claim 1, wherein the noble metal layer of the surface layer has a composition of palladium or an alloy containing palladium. (5) coating the particle surface of the base metal particles with a composition containing at least one of gold, platinum, silver, and iridium or an alloy system thereof as a first layer by electroless plating;
A method for producing conductive particles, characterized in that the second layer is coated with palladium or a palladium alloy, and the second layer is coated with two or more different noble metals. (6) An electrode for electronic components using the conductive particles according to claim 1.