JP7170464B2 - Method for cleaning silver-coated metal powder, method for producing silver-coated metal powder, silver-coated copper powder, silver-coated copper alloy powder, method for producing conductive paste and conductive film, electronic component, and electric device - Google Patents

Description

The present invention relates to a method for cleaning silver-coated metal powder, and the like.

Conventionally, in order to form electrodes and wiring of electronic parts by printing methods, etc., conductive pastes made by mixing conductive metal powders such as silver powder and copper powder with solvents, resins, dispersants, etc. are used. there is Silver powder is excellent in electrical conductivity and oxidation resistance, but has problems such as high cost and susceptibility to migration. On the other hand, copper powder is excellent in conductivity and cost, and hardly causes migration, but has a problem of poor oxidation resistance.

Therefore, silver-coated copper powder has been developed in order to enjoy these merits (for example, Patent Document 1). Furthermore, in order to provide desired properties, a silver-coated copper alloy powder has been developed in which the core copper powder is a copper alloy powder (for example, Patent Document 2).

In the embodiment of the invention of Patent Document 3, after the silver-coated copper powder is produced, it is heated in a wet reducing atmosphere, then put into a solution of hydrazine hydrate and heated at 100° C. for 30 minutes while stirring. It is stated that it was processed separately.

Japanese Patent Application Laid-Open No. 2006-161081 JP 2014-005531 A JP 2003-105404 A

With respect to the silver-coated copper (alloy) powders disclosed in Patent Documents 1 and 2, it is extremely difficult to perform a uniform silver-coating reaction to completely cover the copper (alloy) core particles, and the core particles are exposed. There are concerns that there are places where It is believed that an oxide film is formed at such locations, adversely affecting the electrical conductivity of the silver-coated copper (alloy) powder. The conductivity refers to the conductivity of a conductive film formed by firing or curing the paste when this powder is used for the conductive paste. The same applies hereinafter.

An object of the present invention is to provide a method for making the silver-coated copper (alloy) powder described above more conductive, and such a silver-coated copper (alloy) powder having excellent conductivity.

As a result of intensive studies by the present inventors to solve the above problems, the silver-coated copper (alloy) powder was first washed with an aqueous solution containing a substance capable of complexing and removing copper oxide, and then containing a reducing agent. By performing a washing step of washing with an aqueous solution that dissolves, the oxygen content is reduced, the filling property is improved, and a silver-coated copper (alloy) powder with better conductivity can be obtained. reached.
That is, the present invention is as follows.

Ammonia, amine-based compounds and cyanides are used for silver-coated metal powders having a silver-coated layer on the particle surface of metal powders that are copper powders composed of copper and inevitable impurities, or copper alloy powders composed of copper, nickel, zinc and unavoidable impurities. and a washing step of washing the silver-coated metal powder washed in the washing step 1 with an aqueous solution containing a reducing agent. 2. A method for cleaning silver-coated metal powder.

In the washing step 1, it is preferable to wash the silver-coated metal powder with an aqueous solution containing 0.05 to 1 equivalent of a complex-forming compound with respect to copper in the silver-coated metal powder. The reducing agent is preferably at least one selected from the group consisting of hydrazine, sodium borohydride, oxalic acid and formic acid. The aqueous solution containing the complex-forming compound used in the washing step 1 is preferably aqueous ammonia.

In the washing step 2, it is preferable to wash the silver-coated metal powder with an aqueous solution containing 10 to 60 equivalents of a reducing agent with respect to copper in the silver-coated metal powder.

The volume-based cumulative 50% particle diameter (D ₅₀ ) of the silver-coated metal powder subjected to the washing step 1 measured by a laser diffraction particle size distribution analyzer is preferably 0.1 to 15.0 μm. . Further, when the metal powder is a copper alloy powder, the mass ratio of copper to the total mass of copper, nickel and zinc in the silver-coated metal powder is preferably 82% by mass or more.

The method for producing a silver-coated metal powder of the present invention comprises forming a silver coating layer on the surface of a metal powder, which is a copper powder containing copper and unavoidable impurities, or a copper alloy powder containing copper, nickel, zinc, and unavoidable impurities. A silver-coating step for obtaining a silver-coated metal powder; and an aqueous solution containing at least one complex-forming compound selected from the group consisting of ammonia, an amine-based compound, and a cyanide compound for the silver-coated metal powder obtained in the silver-coating step. and a washing step 2 of washing the silver-coated metal powder washed in the washing step 1 with an aqueous solution containing a reducing agent.

The volume-based cumulative 50% particle diameter (D ₅₀ ) of the metal powder measured by a laser diffraction particle size distribution analyzer is preferably 0.1 to 15.0 μm. When the metal powder is the copper alloy powder, the mass ratio of copper to the total mass of copper, nickel and zinc in the copper alloy powder is preferably 82% by mass or more.

The silver-coated copper powder of the present invention is a silver-coated copper powder having a silver coating layer on the surface of copper particles composed of copper and unavoidable impurities, and the reciprocal of the ratio of the tap density to the true density of the silver-coated copper powder (R _TAP ), the oxygen content (O) of the silver-coated copper powder _{, and the product (R TAP × OxD50} (% by mass/μm)) is 0.80 (% by mass/μm) or less. The product (R _TAP ×O×D ₅₀ (mass %·μm)) is preferably 0.30 to 0.75 (mass %·μm). The content of the silver-coated layer in the silver-coated copper powder is preferably 1 to 50% by mass. The cumulative 50% particle size (D ₅₀ ) of the silver-coated copper powder is preferably 0.1-15.0 μm.

The silver-coated copper alloy powder of the present invention is a silver-coated copper alloy powder having a silver coating layer on the surface of copper alloy particles composed of copper, nickel, zinc and unavoidable impurities, and the tap density of the silver-coated copper alloy powder is The reciprocal of the ratio to the true density (R _TAP ), the oxygen content (O) of the silver-coated copper alloy powder, and the volume-based cumulative 50% particle diameter measured by a laser diffraction particle size distribution analyzer of the silver-coated copper alloy powder ( D ₅₀ ) (R _TAP ×O×D ₅₀ (mass %·μm)) is 0.58 (mass %·μm) or less. The product (R _TAP ×O×D ₅₀ (mass %·μm)) is preferably 0.25 to 0.56 (mass %·μm). The content of the silver coating layer in the silver-coated copper alloy powder is preferably 1 to 50% by mass. In the silver-coated copper alloy powder, the mass ratio of copper to the total mass of copper, nickel, and zinc is 82 to 95 mass%, the mass ratio of nickel to the total is 1 to 8 mass%, and the mass ratio of nickel to the total is 1 to 8 mass%. It is preferable that the mass proportion of zinc is 1 to 17 mass %. The cumulative 50% particle diameter (D ₅₀ ) of the silver-coated copper alloy powder is preferably 0.1 to 15.0 μm.

The conductive paste of the present invention is obtained by dispersing the above silver-coated copper powder and/or silver-coated copper alloy powder in a solvent and/or a resin binder. In the method for producing a conductive film of the present invention, the conductive paste is applied onto a substrate to form a coating film, and the coating film is baked or cured to form a conductive film on the substrate. be.

An electronic component according to the present invention is an electronic component provided with an external electrode, wherein the external electrode contains the above silver-coated copper powder and/or silver-coated copper alloy powder and a curable resin. Further, an electric device of the present invention comprises a substrate, an electric element formed on the substrate, the electronic component mounted on the substrate, and a solder member for connecting the electronic component and the electric element. is.

ADVANTAGE OF THE INVENTION According to this invention, the silver-coated copper (alloy) powder which is excellent in electroconductivity compared with the past is provided.

The present invention will be described in detail below. As used herein, individual "particles" constitute "powder", and "powder" refers to a collection of "particles". In the following description, as a general rule, the term "particles" is used when focusing on the individual constituents of the powder, and the term "powder" or "particle powder" when focusing on the aggregate of particles as a whole. use the word. It should be noted that it is not intended to strictly distinguish individual particles from aggregated powders.

[Method for cleaning silver-coated metal powder]
<Silver-coated metal powder>
The silver-coated metal powder to be subjected to a predetermined cleaning step in the embodiment of the method for cleaning a silver-coated metal powder of the present invention (hereinafter also referred to as the "cleaning method of the present invention") is a copper powder containing copper and inevitable impurities, Alternatively, a metal powder, which is a copper alloy powder composed of copper, nickel, zinc and unavoidable impurities, is used as core particle powder, and the particle surface has a silver coating layer.

The silver coating layer enhances the electrical conductivity of the silver-coated metal powder, and since copper in the metal powder is poor in oxidation resistance, the silver coating layer enhances the oxidation resistance of the core particles. The silver coating layer preferably consists essentially of silver. Moreover, it is rare for the silver coating layer to completely cover the entire particle surface of the metal powder, and usually part of the core particle is exposed. The silver-coated layer may be alloyed with the core particles by heat treatment or the like, but in this case silver is unevenly distributed near the particle surface layer of the silver-coated metal powder.

From the viewpoint of conductivity, the content of the silver coating layer in the silver-coated metal powder is preferably 1-50% by mass, more preferably 3-40% by mass, and still more preferably 15-30% by mass. The content of the silver coating layer is the mass ratio of silver to the total mass of silver and copper when the metal powder is copper powder, and silver, copper, nickel and zinc when the metal powder is copper alloy powder. shall be obtained as the mass ratio of silver to the total mass of Moreover, the content of the silver coating layer is preferably 2 to 12% by mass from the viewpoint of the production cost of the silver-coated metal powder.

<Metal powder>
(Inevitable impurities)
The unavoidable impurities in the metal powder (copper powder or copper alloy powder) in the silver-coated metal powder are trace amounts (based on the weight of the silver-coated metal powder preferably about 0.1 to 1000 ppm), examples of which include iron, sodium, potassium, calcium, palladium, magnesium, oxygen, carbon, nitrogen, phosphorus, silicon and chlorine. The unavoidable impurities include trace elements added at a level of about 1000 ppm or less (usually 0.1 ppm or more) based on the weight of the silver-coated metal powder in order to achieve a given purpose. .

(copper alloy powder)
When the metal powder is a copper alloy powder, the silver-coated metal powder is useful, for example, as a metal powder component in a conductive paste for forming a solder-connected conductive film. Specifically, copper, which constitutes the copper alloy powder, has excellent conductivity, nickel has excellent resistance to solder erosion, and the presence of zinc improves the silver coating of the copper alloy powder (of the particle surface of the metal powder, , so that a large percentage of the area is covered with silver), leading to excellent electrical conductivity and solder wettability. The solder erosion resistance refers to the phenomenon of solder erosion, which is thought to occur when a conductive film melts into melted solder, but this phenomenon is difficult to occur.

In addition, from the viewpoint that various properties such as conductivity and solder erosion resistance described above are exhibited in a well-balanced manner and the effects of the embodiment of the cleaning method of the present invention are favorably exhibited, the metal powder is a copper alloy powder. In the silver-coated metal powder, the mass ratio of copper to the total mass of copper, nickel, and zinc is preferably 82% by mass or more. From the same point of view, more preferably, the mass ratio of copper is 82 to 95% by mass, the mass ratio of nickel is 1 to 8% by mass, and the mass ratio of zinc is 1 to 17% by mass with respect to the total. More preferably, the mass ratio of copper is 84 to 93% by mass, the mass ratio of nickel is 1.5 to 7.5% by mass, and the mass ratio of zinc is 1.5 to 14% with respect to the total. 0.5 mass %.

<Surface treatment layer>
The silver-coated metal powder used in the embodiment of the cleaning method of the present invention may have a surface treatment layer on the particle surface. Thereby, the filling property of the powder can be improved and the electrical conductivity can be improved. The surface treatment layer can be formed by treating the silver-coated metal powder with a surface treatment agent.

Examples of the surface treatment agent constituting the surface treatment layer include saturated or unsaturated fatty acids having 1 to 32 carbon atoms, saturated or unsaturated amines having 1 to 32 carbon atoms, and heterocyclic compounds having 5 to 12 ring atoms. mentioned. The fatty acid or amine may have a cyclic structure, and the heterocyclic compound may be saturated or unsaturated, and may have a condensed ring structure. The surface treatment layer may be composed of one of these compounds, or may be composed of a combination of two or more.

<Average particle size ( _D50 )>
The volume-based cumulative 50% particle diameter (D ₅₀ ) of the silver-coated metal powder used in the embodiment of the cleaning method of the present invention measured by a laser diffraction particle size distribution analyzer is From the viewpoint of enabling formation, the thickness is preferably 0.1 to 15.0 μm, more preferably 1.0 to 10 μm, and particularly preferably 1.5 to 6.5 μm.

<Shape>
The shape of the silver-coated metal powder is not particularly limited, and may be spherical, approximately spherical, granular, flaky, or amorphous.

<Washing step 1>
In an embodiment of the cleaning method of the present invention, first, the silver-coated metal powder is subjected to a cleaning step 1 of cleaning with a predetermined cleaning liquid. As a result, it is believed that the copper oxide on the particle surface of the silver-coated metal powder where the core particles are exposed and not covered with the silver coating layer is complexed and removed together with oxygen.

The washing liquid is an aqueous solution containing at least one complex-forming compound selected from the group consisting of ammonia, amine-based compounds and cyanide compounds. Examples of the amine compound include monoamines having 1 to 18 carbon atoms (preferably 2 to 10) such as hexylamine and aniline, and diamines having 1 to 18 carbon atoms (preferably 2 to 10) such as ethylenediamine. Cyan compounds include various metal salts of cyanide ions (examples of metals include metals belonging to Group 1 of the periodic table, such as sodium and potassium). Among the complex-forming compounds described above, ammonia is preferable from the viewpoint of cost and ability to remove copper oxide.

The washing step 1 can be carried out, for example, by adding the silver-coated metal powder to the washing solution and stirring the obtained mixed solution. The temperature at which this cleaning step 1 is performed is preferably 10 to 40°C, more preferably 15 to 35°C, from the viewpoint of oxygen removal efficiency. The implementation time of the washing step 1 (the stirring time when the mixed solution is stirred) is preferably 10 to 80 minutes, more preferably 15 to 60 minutes, from the viewpoint of oxygen removal efficiency.

The amount of the complex-forming compound used in the washing step 1 is preferably 0.05 to 1 equivalent, more preferably 0.08 to 0.5 equivalent, relative to copper in the silver-coated metal powder, from the viewpoint of oxygen removal efficiency. 0.8 equivalents. Note that one equivalent is the amount of the complex-forming compound required to form a complex with copper oxide. For ammonia, for example, the ratio is 6 mol of ammonia per 1 mol of copper. Further, the concentration of the complex-forming compound in the cleaning liquid is preferably 0.1 to 50% by mass, more preferably 0.5 to 30% by mass, and still more preferably 1 to 50% by mass, from the viewpoint of copper oxide removal efficiency. 10% by mass.

<Washing step 2>
Impurities such as complex-forming compounds adhere to the silver-coated metal powder washed with a predetermined washing liquid in the washing step 1, and it is desirable to wash these impurities. If it is washed with pure water at this time, it is thought that oxidation occurs at the portions where the core particles are exposed without being covered with silver, which adversely affects the electrical conductivity.

In an embodiment of the cleaning method of the present invention, in order to avoid such a situation, the silver-coated metal powder cleaned in the cleaning step 1 is washed with an aqueous solution containing a reducing agent (hereinafter also referred to as "aqueous reducing agent solution"). (washing step 2). Oxidation of the silver-coated metal powder during cleaning is prevented by containing a reducing agent in the cleaning liquid used for cleaning. In addition, although the mechanism is unknown, by carrying out these washing steps 1 and 2, the filling property of the silver-coated metal powder is also improved.

In the washing step 2, for example, the silver-coated metal powder is placed on a filter paper and suction-filtered while adding an aqueous reducing agent solution, or the silver-coated metal powder is added to an aqueous reducing agent solution, and the resulting mixture It can be carried out by stirring.

Reducing agents that can be used in washing step 2 are not particularly limited, but examples thereof include hydrazine, sodium borohydride, oxalic acid and formic acid. These may be used individually by 1 type, or may be used in combination of 2 or more type. Among these reducing agents, hydrazine is preferable because of its cost and because it hardly remains as an impurity in the silver-coated metal powder.

The amount of the reducing agent used in the washing step 2 is preferably 5 to 60 equivalents, more preferably 8 to 60 equivalents, relative to the copper in the silver-coated metal powder, from the viewpoint of the effect of the reducing agent and cost. 60 equivalents, more preferably 10 to 60 equivalents, more preferably 10 to 40 equivalents. One equivalent is the number of moles of the reducing agent required to reduce copper (II) to metallic copper.

Further, the concentration of the reducing agent in the reducing agent aqueous solution is preferably 12 to 80% by mass, more preferably 15 to 30% by mass, from the viewpoint of the effect of the reducing agent and cost.

<Other processes>
Through the washing steps 1 and 2 described above, a silver-coated metal powder having a reduced oxygen content and excellent conductivity is obtained. Alternatively, a pulverization or classification step may be performed to adjust the particle size of the powder.

[Method for producing silver-coated metal powder]
The silver-coated metal powder to be subjected to the cleaning step 1 in the cleaning method of the present invention can be obtained by a known method. It can be obtained by carrying out a silver coating step of forming a silver coating layer on. When the cleaning steps 1 and 2 are carried out after carrying out the silver coating step, the present invention can also be regarded as a method for producing a silver-coated metal powder.

The specific implementation method of the silver coating step is not particularly limited. The silver coating step can be carried out by a reduction method that deposits silver on the grain surface.

[Silver-coated metal powder]
Next, embodiments of the silver-coated metal powder of the present invention will be described. This silver-coated metal powder is obtained, for example, by carrying out the cleaning method of the present invention, and has reduced oxygen content, improved powder filling properties, and excellent electrical conductivity.

Specifically, this silver-coated metal powder has a silver coating layer on the surface of metal particles, and the reciprocal of the ratio of the tap density to the true density of the silver-coated metal powder (R _TAP ) and the oxygen content (O) and the volume-based cumulative 50% particle diameter (D ₅₀ ) measured by a laser diffraction particle size distribution analyzer (R _TAP ×O×D ₅₀ (mass %·μm)) is within a predetermined range. The structure of this silver-coated metal powder will be described below.

<Metal particles>
Specifically, the metal particles are copper particles composed of copper and inevitable impurities, or copper alloy particles composed of copper, nickel, zinc and inevitable impurities. These copper particles and copper alloy particles are the same as the copper powder and copper alloy powder (particles constituting the same) described in the cleaning method of the present invention, respectively. That is, the inevitable impurities in these particles are iron, sodium, etc., and the content thereof is preferably about 0.1 to 1000 ppm based on the weight of the silver-coated metal powder. Regarding the copper alloy particles, the mass ratio of copper to the total mass of copper, nickel, and zinc is preferably 82 from the viewpoint that various properties such as conductivity and resistance to solder erosion are expressed in a well-balanced manner in the silver-coated metal powder. % by mass or more. From the same point of view, more preferably, the mass ratio of copper is 82 to 95% by mass, the mass ratio of nickel is 1 to 8% by mass, and the mass ratio of zinc is 1 to 17% by mass with respect to the total. More preferably, the mass ratio of copper is 84 to 93% by mass, the mass ratio of nickel is 1.5 to 7.5% by mass, and the mass ratio of zinc is 1.5 to 14% with respect to the total. 0.5 mass %.

<Silver coating layer>
The silver coating layer that coats the surface of the metal particles is the same as the silver coating layer that constitutes the silver-coated metal powder in the embodiment of the cleaning method of the present invention. That is, the silver coating layer has an effect such as enhancing electrical conductivity. From this viewpoint, the content of the silver coating layer in the embodiment of the silver-coated metal powder of the present invention is preferably 1 to 50% by mass. It is preferably 3 to 40% by mass, more preferably 15 to 30% by mass. Moreover, the content of the silver coating layer is preferably 2 to 12% by mass from the viewpoint of the production cost of the silver-coated metal powder.

<Product (R _TAP × O × D ₅₀ (% by mass · μm))>
The embodiment of the silver-coated metal powder of the present invention is considered to have appropriately removed the oxide film on the particle surface, and has a small amount of oxygen (O). Since the oxygen content (O) tends to increase as the particle size decreases, the oxygen content (O) was multiplied by the particle diameter ( _D50 ). In addition, although the mechanism of this embodiment of the silver-coated metal powder is unknown, as shown in the examples below, the silver-coated metal powder in which the amount of oxygen is reduced to the same extent by a method different from the cleaning method of the present invention is used. also has good powder packing and high tap density (which leads to good electrical conductivity). Therefore, the ratio of the tap density to the true density is also high, and its reciprocal (R _TAP ) is small. The embodiment of the silver-coated metal powder of the present invention has a small product of the R _TAP explained above, the oxygen content (O) and the particle diameter (D ₅₀ ). Therefore, the product of these (R _TAP ×O×D ₅₀ (mass %·μm)) is also small.

Specifically, when the metal particles are copper particles, the product of the silver-coated metal (copper) powder (R _TAP ×O×D ₅₀ (mass %·μm)) is 0.80 (mass %·μm) or less. be. From the viewpoint of further reducing the oxygen content and increasing the conductivity, the product (R _TAP ×O ×D ₅₀ (mass% · μm)) is preferably 0.30 to 0.75 (mass% · μm), more preferably is 0.40 to 0.72 (% by mass/μm).

When the metal particles are copper alloy particles, the product of the silver-coated metal (copper alloy) powder (R _TAP ×O×D ₅₀ (mass %·μm)) is 0.58 (mass %·μm) or less. From the viewpoint of further reducing the oxygen content and increasing the conductivity, the product (R _TAP ×O ×D ₅₀ (mass% · μm)) is preferably 0.25 to 0.56 (mass% · μm), more preferably is 0.30 to 0.55 (% by mass/μm).

The method of obtaining the true density necessary for obtaining _RTAP is as follows. The elemental composition of the silver-coated metal powder is measured by an X-ray fluorescence spectrometer (XRF), and from the results, when the metal particles are copper particles, the total mass ratio of silver and copper is 100% by mass, and the metal particles are In the case of copper alloy particles, the mass ratio of each element is calculated with the sum of the mass ratios of silver, copper, nickel, and zinc set to 100% by mass. Then, the true density of the silver-coated metal powder is obtained by multiplying the determined mass ratio by the density of each element and adding them together.

<Tap density>
The tap density of the embodiment of the silver-coated metal powder of the present invention is preferably 3.0 to 7.5 g/cm ³ , more preferably 3.0 to 7.5 g/cm 3 from the viewpoint of increasing the packing density of the powder and exhibiting good electrical conductivity. is 4.2-6.5 g/cm ³ .

<Average particle size ( _D50 )>
The volume-based cumulative 50% particle diameter (D ₅₀ ) (average particle diameter) measured by the laser diffraction particle size distribution analyzer of the embodiment of the silver-coated metal powder of the present invention is From the viewpoint of making it possible, it is preferably 0.1 to 15.0 μm, more preferably 1.0 to 10 μm, and particularly preferably 1.5 to 6.5 μm.

<Oxygen content>
The oxygen content of the embodiment of the silver-coated metal powder of the present invention is preferably 0.05 to 0.60% by mass, more preferably 0.08 to 0.25% by mass, from the viewpoint of conductivity. .

<Carbon content>
The amount of carbon in the embodiment of the silver-coated metal powder of the present invention is preferably 0.10 to 0.65% by mass, more preferably 0.18 to 0, from the viewpoint of preventing gas generation when heated. .45 mass %.

<BET specific surface area>
The specific surface area (BET specific surface area) measured by the BET single-point method of the embodiment of the silver-coated metal powder of the present invention is preferably 0.08 to 1.50 m ² /g from the viewpoint of exhibiting good conductivity. more preferably 0.10 to 1.00 m ² /g, particularly preferably 0.15 to 0.80 m ² /g.

<Shape>
The shape of the embodiment of the silver-coated metal powder of the present invention is not particularly limited, and may be spherical, substantially spherical, granular, flaky, or irregular.

[Conductive paste]
Next, an embodiment of the conductive paste of the present invention will be described. This conductive paste contains an embodiment of the silver-coated metal powder of the present invention, and since the powder has a reduced oxygen content and excellent conductivity, it is suitable for use in forming a conductive film. There are two types of conductive paste: one is a sintering type conductive paste that is fired at a high temperature to decompose and volatilize the solvent and resin components in the paste and then sinters the metal powder together, and the other is a sintering type conductive paste that is heated at a lower temperature than the sintering type. There is a resin-curing conductive paste in which the components are cured and contraction of the resin at the time of curing brings the metal powders into contact with each other to achieve electrical continuity. The electrically conductive paste embodiments of the present invention can be used as any type of electrically conductive paste, including one or both of a solvent and a resin binder. When a resin curing paste is used, a resin binder, which is a curable resin, is included as an essential component.

In the embodiment of the conductive paste of the present invention, two or more silver-coated metals different in particle size, metal composition of the core particles to be silver-coated, and other points, which correspond to the silver-coated metal powder of the present invention. Combinations of powders may also be used. The content of the silver-coated metal powder in the conductive paste is preferably 50 to 98% by mass, more preferably 70 to 97% by mass, from the viewpoint of forming a conductive film having appropriate conductivity.

Also, the content of the resin binder in the conductive paste is preferably 1 to 49% by mass, more preferably 2 to 29.5% by mass. As a resin binder, resin can be used individually by 1 type or in combination of 2 or more types.

Curing resins used in conductive paste include thermosetting resins and photo-curing resins.
Thermosetting resins include phenol resins, urea resins, melamine resins, epoxy resins, unsaturated polyester resins, silicone resins, polyurethane resins, polyvinyl butyral resins, polyimide resins, maleimide resins, diallyl phthalate resins, oxetane resins and (meth) acrylic resins,
The photocurable resin may be a resin having one or more functional groups such as unsaturated bonds that cause a cross-linking reaction by light in one molecule. Specific examples thereof include (meth)acrylic resins and maleic acid resins. , maleic anhydride resin, polybutadiene resin, unsaturated polyester resin, polyurethane resin, epoxy resin, oxetane resin, phenol resin, polyimide resin, polyamide resin, alkyd resin, amino resin, polylactic acid resin, oxazoline resin, benzoxazine resin , silicone resins and fluorine resins.

In the embodiment of the conductive paste of the present invention, when the paste is cured by heating, a thermal polymerization initiator may be added for curing or accelerating curing. Thermal polymerization initiators include, for example, hydroperoxides, dialkyl peroxides, peroxyesters, diacyl peroxides, peroxycarbonates, peroxyketals, and ketone peroxides. These thermal polymerization initiators may be used singly or in combination of two or more.

In addition, in order to accelerate curing, curing agents such as polyamines, acid anhydrides, boron trihalide compounds, amine complex salts of boron trihalide compounds, imidazole compounds, aromatic diamine compounds, and carboxylic acid compounds are added. good too. These may be used individually by 1 type, or may be used in combination of 2 or more type.

Moreover, when the embodiment of the conductive paste of the present invention is photopolymerized, the conductive paste is made to contain a photopolymerization initiator. As the photopolymerization initiator, a photoradical generator or a photocationic polymerization initiator is usually used. These photoinitiators may be used individually by 1 type, or may be used in combination of 2 or more types.

As the photoradical generator, a known compound known to be used for this purpose can be used. For example, benzophenone, benzoin methyl ether, benzoin propyl ether, diethoxyacetophenone, 1-hydroxycyclohexylphenyl ketone, 2,6-dimethylbenzoyldiphenylphosphine oxide, and 2,4,6-trimethylbenzoyldiphenylphosphine oxide can be used. is.

The photocationic polymerization initiator is a compound that initiates cationic polymerization by irradiation with radiation such as ultraviolet rays and electron beams. Examples thereof include aromatic sulfonium salts, aromatic iodonium salts, aromatic diazonium salts and aromatic ammonium salt.

Further, thermoplastic resins such as ethyl cellulose, ethylhydroxyethyl cellulose, rosin, phenoxy resin, and polyacetal resin can be added to the embodiment of the conductive paste of the present invention, if necessary. These thermoplastic resins may be used singly or in combination of two or more.

Additives such as surfactants, dispersants, stabilizers, plasticizers, and metal oxide powders may be added to the embodiment of the conductive paste of the present invention, if necessary.

The preparation method of the embodiment of the conductive paste described above is not particularly limited. It can be prepared by preliminarily kneading using a kneader or the like and then performing main kneading with three rolls. Further, if necessary, an organic solvent may be added thereafter to adjust the viscosity. Organic solvents include texanol (2,2,4-trimethyl-1,3-pentanediol 2-methylpropanoate), terpineol, carbitol acetate (diethylene glycol monoethyl ether acetate), ethylene glycol, dibutyl acetate and diethylene glycol mono Polar solvents such as butyl ether acetate are included.

The viscosity at 25° C. measured by the E-type viscometer of the embodiment of the conductive paste of the present invention is preferably 80 to 200 Pa·s from the viewpoint of the printability of the conductive paste.

[Method for producing conductive film]
Next, an embodiment of the method for producing a conductive film according to the present invention will be described. The conductive paste described above is applied to a substrate (such as a ceramic substrate) in a predetermined pattern by dipping or printing (such as screen printing or inkjet printing) to form a coating film, which is then fired (the conductive paste is A conductive film can be formed on the substrate by sintering) or curing (when the conductive paste is a resin curing type). When the conductive paste is applied by dipping, the substrate is dipped in the conductive paste to form a coating film, and unnecessary portions of the conductive film obtained by baking or curing are removed from the coating film, A conductive film having a predetermined pattern shape can be formed on the substrate.

Firing of the conductive paste applied on the substrate may be performed in a non-oxidizing atmosphere such as nitrogen, argon, hydrogen, or carbon monoxide. The firing temperature of the conductive paste is preferably about 600 to 1000.degree. C., more preferably about 700 to 900.degree. In addition, volatile components such as a solvent in the conductive paste may be removed by performing pre-drying such as vacuum drying before baking the conductive paste. Further, when the conductive paste contains a resin binder, it is preferable to heat the conductive paste at a low temperature of 250 to 400° C. as a debindering step to reduce the content of the resin binder before baking the conductive paste.

On the other hand, when curing a coating film (in the case of a resin curing conductive paste), for example, when curing by heat, the temperature is preferably 100 to 300 ° C., more preferably 120 to 250 ° C., and still more preferably 150 to 220 ° C. , preferably 10 to 120 minutes, more preferably 15 to 90 minutes, still more preferably 20 to 60 minutes.

When the coating film is photocured, the amount of radiation irradiated during curing is arbitrary as long as the photopolymerization initiator generates radicals. Depending on the dose, UV radiation with a wavelength of 200-450 nm is preferably applied in the range of 0.1-200 J/cm ² .

[Electronic parts]
Next, electronic components that can be manufactured using the conductive paste (resin-curing conductive paste) of the present invention will be described. The electronic component is not particularly limited as long as it has external electrodes and is connected to other electrical elements by soldering. Specific examples of electronic components include capacitors, capacitors, inductors, laminated wiring boards, piezoelectric elements, varistors, thermistors, resistors, and semiconductor chips.

The conductive paste of the present invention is applied to a portion of a member constituting an electronic component where an external electrode is to be formed, and the formed coating film is treated, for example, under the heat-curing or photo-curing conditions described above. , become an external electrode (conductive film). A member constituting an electronic component, for example, if the electronic component is a capacitor or a capacitor, has a laminate structure in which dielectric layers and internal electrode layers with different polarities are alternately laminated. External electrodes are formed at both ends where the electrode layers are alternately drawn.

When the curable resin in the conductive paste is cured, the resin forms a cured product, and the silver-coated metal powder contained inside comes into contact with each other due to curing shrinkage of the resin and becomes an external electrode. . If the conductive paste contains a volatile substance such as an organic solvent, at least part of it volatilizes during the curing reaction. As described above, an electronic component having external electrodes is obtained.

In the formed external electrodes, the ratio of the silver-coated metal powder in the total of the silver-coated metal powder and the curable resin (cured product thereof) is approximately the same as the ratio in the conductive paste, preferably 50 to 98% by mass. Yes, more preferably 70 to 97% by mass. Similarly, in the external electrodes, the ratio of (a cured product of) the curable resin in the above total is preferably 1 to 49% by mass, more preferably 2 to 29.5% by mass.

[Electrical device]
The external electrodes included in the electronic component of the present invention are soldered to other electrical elements. An electrical device of the present invention comprises a substrate, an electrical element formed on the substrate, an electronic component mounted on the substrate, and a solder member for connecting the electronic component and the electrical element. Other members and elements may be provided accordingly. Examples of the electric elements include wiring, leads, terminals, electric circuits, and electrodes.

The electric element may be formed directly on the substrate, or may be formed via an intermediate layer for enhancing adhesion between the electric element and the substrate, for example. An electronic component is mounted on a substrate by being connected to an electric element with a solder member.

Although the substrate is not particularly limited, it is preferably a paper phenol substrate, a paper epoxy substrate, a glass epoxy substrate, a polymer film, a glass substrate, or a ceramic substrate (including a low temperature fired ceramic substrate).

The material of the solder member is not particularly limited, but for example the solder member contains at least one metal selected from the group consisting of tin, lead, silver, copper, zinc, bismuth, indium and aluminum. In recent years, lead-free solder has become desirable due to the environmental burden, so it is preferable that the solder member does not substantially contain lead. Examples of lead-free solder members include Sn/Ag/Cu solder, Sn/Zn/Bi solder, Sn/Cu solder, Sn/Ag/In/Bi solder and Sn/Zn/Al solder.

A solder paste containing such solder is printed, for example, on an electrical element, and an electronic component is placed on the printed solder paste (for the electrical element and electronic component, flux cleaning is performed as necessary. Alternatively, the solder paste may contain flux). Then, by heating at a temperature of about 200 to 350° C. by a reflow process, the solder melts and the electric element and the electronic component are electrically and physically connected. Thus, the electric device of the present invention is manufactured, and steps such as forming or mounting other members and elements on the substrate are carried out as necessary.

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these.

<Comparative Example 1> [Production of silver-coated copper powder 1]
(Production of copper powder)
315 kg of copper (purity of 99.99 mass% or more) heated to 1500 ° C in a nitrogen atmosphere is dropped from the bottom of the melting furnace, and high-pressure water (water pressure: 150 MPa, water volume: 160 L / min) is generated in the atmosphere by a water atomizer. , pH: 10) was sprayed to rapidly cool and solidify, the obtained slurry was filtered, and the obtained solid matter was washed with water, dried and pulverized to obtain a substantially spherical copper powder. For this copper powder, BET specific surface area, tap density, mass ratio of each element with respect to the total mass of silver and copper, true density, oxygen content, carbon content, particle size distribution, water content in the same manner as described below , was measured.

(Production of silver-coated copper powder 1)
A solution (solution 1) in which 3.67 kg of EDTA-2Na dihydrate and 3.67 kg of ammonium carbonate were dissolved in 42.66 kg of pure water, and 8.08 kg of EDTA-2Na dihydrate and 4.04 kg of ammonium A solution (solution 2) was prepared by adding a solution of 2.85 kg of silver nitrate dissolved in 2.66 kg of pure water to a solution of 32.20 kg of water.

Next, in a nitrogen atmosphere, 7.70 kg of the copper powder obtained above was added to solution 1 as a core powder to be coated, and the temperature was raised to 25° C. while stirring. Solution 2 is added to the copper powder-dispersed dispersion and stirred for 1 hour, followed by filtration. The obtained solid is washed with water, dried, and pulverized to obtain approximately spherical silver-coated copper. A powder (silver-coated copper powder 1) was obtained.

(Evaluation of silver-coated copper powder 1)
The BET specific surface area, tap density, mass ratio of each element to the total mass of silver and copper, true density, oxygen content, carbon content, particle size distribution, moisture content, and conductivity of the silver-coated copper powder 1 obtained above The resistance when made into a flexible paste was measured. The results are shown in Table 1 below. Moreover, the specific method of each measurement is as follows.

BET specific surface area: Using a BET specific surface area measuring device (Macsorb manufactured by Mountec Co., Ltd.), nitrogen gas was flowed into the measuring device at 105 ° C. for 20 minutes to deaerate, and then a mixed gas of nitrogen and helium (N ₂ : 30% by volume, He: 70% by volume) was measured by the BET one-point method.

Tap density: In the same manner as the method described in JP-A-2007-263860, silver-coated copper powder 1 was filled into a bottomed cylindrical die with an inner diameter of 6 mm and a height of 11.9 mm up to 80% of the volume. A coated copper powder layer is formed, and a pressure of 0.160 N/m ² is uniformly applied to the upper surface of this silver-coated copper powder layer, and with this pressure, the silver-coated copper powder 1 is compressed until the silver-coated copper powder 1 is no longer densely packed. After compressing the copper powder layer, the height of the silver-coated copper powder layer is measured, and from the measured value of the height of the silver-coated copper powder layer and the weight of the filled silver-coated copper powder 1, the silver-coated copper The density of the powder 1 was determined and used as the tap density of the silver-coated copper powder 1.

Mass ratio of each element to the total mass of silver and copper: After spreading silver-coated copper powder 1 (about 2.5 g) in a vinyl chloride ring (inner diameter 3.2 cm × thickness 4 mm), tablet molding compression Machine (model number BRE-50 manufactured by Mayekawa Test Co., Ltd.) to prepare pellets of silver-coated copper powder with a load of 100 kN, put the pellets in a sample holder (opening diameter 3.0 cm) and perform fluorescent X-ray. An analyzer (XRF) (RIX2000 manufactured by Rigaku Co., Ltd.) was set at the measurement position, the measurement atmosphere was reduced (8.0 Pa), and the X-ray output was 50 kV and 50 mA. was automatically calculated using the software attached to the
Then, from the mass ratios of the metal elements determined here, values converted into respective mass ratios when the sum of the masses of silver and copper is 100% by mass were determined.

True density: Obtained by multiplying the respective densities of silver and copper by the mass ratios of silver and copper obtained above and adding them together.

Oxygen content: Measured with an oxygen/nitrogen analyzer (EMGA-920 manufactured by Horiba, Ltd.).

Carbon content: Measured with a carbon/sulfur analyzer (EMIA-920V2 manufactured by Horiba, Ltd.).

Particle size distribution: Measured at a dispersion pressure of 5 bar using a laser diffraction particle size distribution analyzer (HELOS & RODOS (airflow dispersion module) manufactured by SYMPATEC).

Moisture content: Measured by the Karl Fischer method using a coulometric titration automatic moisture analyzer (AQ-2250 (vaporizer EV-2010) manufactured by Hiranuma Sangyo Co., Ltd.).

Resistance when used as a conductive paste: 9.3 g of silver-coated copper powder 1, 0.82 g of bisphenol F type epoxy resin (ADEKA Co., Ltd. ADEKA RESIN EP-4901E) as a thermosetting resin, and three curing agents. After mixing 0.041 g of boron fluoride monoethylamine, 0.25 g of diethylene glycol monobutyl ether acetate as a solvent, and 0.01 g of oleic acid as a dispersant in a kneading and defoaming machine, the mixture is uniformly mixed by passing through a triple roll five times. Diethylene glycol monobutyl ether acetate was added to the resulting kneaded product and mixed to adjust the viscosity at 25° C. to about 100 Pa·s to obtain a conductive paste.
After printing this conductive paste on an alumina substrate by screen printing (in a line pattern with a line width of 500 μm and a line length of 37.5 mm), a conductive film was formed by heating and curing in the air at 200° C. for 40 minutes. (film thickness of about 20 μm) was formed, and the volume resistivity (initial resistance) of the obtained conductive film was calculated.

<Comparative Example 2>
(ammonia cleaning)
After adding 1233.30 g of pure water to the reaction tank, the temperature was adjusted to 25° C., and while stirring at 640 rpm, N ₂ was added until the oxygen concentration meter (GX-8000 manufactured by Riken Keiki Co., Ltd.) indicated 0.0%. A purge was performed (the _N2 purge was continued thereafter to maintain the reactor oxygen concentration at 0.0%). When the oxygen concentration in the reaction tank reached 0.0%, 120 g of the silver-coated copper powder 1 obtained in Comparative Example 1 was added, and 92.57 g of ammonia water having an ammonia concentration of 28% by mass (special grade manufactured by Nacalai Rusk) was added. was added and the mixture was stirred for 30 minutes. The amount of ammonia added was 0.15 equivalent (0.9 mol per 1 mol of copper) with respect to copper in the silver-coated copper powder.

(water wash)
After stirring, the mixed solution was subjected to suction filtration using a filter bottle, a Buchner funnel, filter paper and an aspirator, and the silver-coated copper powder was collected on the filter paper. The silver-coated copper powder on the filter paper was washed by pouring 5 L of pure water while continuing suction filtration. This washing was repeated 10 times, and washing with a total of 50 L of pure water was performed. After washing, it was dried at 70° C. for 13.5 hours in a vacuum state and pulverized in a glove box in a nitrogen atmosphere (the display of the oxygen concentration meter (GX-8000 manufactured by Riken Keiki Co., Ltd.) was 0.0%). Thus, a substantially spherical silver-coated copper powder 2 was obtained. For this silver-coated copper powder 2, in the same manner as in Comparative Example 1, the BET specific surface area, tap density, mass ratio of each element to the total mass of silver and copper, true density, oxygen content, carbon content, particle size distribution, The water content and the resistance when made into a conductive paste were measured. The results are shown in Table 1 below.

<Comparative Example 3>
(water and hydrazine water wash)
120 g of the silver-coated copper powder 1 obtained in Comparative Example 1 was prepared. This was placed on a filter paper, and washed by pouring 5 L of pure water into the powder while sucking it using a filter bottle, a Buchner funnel and an aspirator. After repeating this washing nine times, 5 L of an aqueous hydrazine solution having a hydrazine concentration of 20% by mass was poured while suction filtration was continued. The amount of hydrazine used was 19 equivalents to copper in the silver-coated copper powder.

After this washing, it was dried at 70 ° C. for 13.5 hours in a vacuum state and dissolved in a glove box in a nitrogen atmosphere (the display of the oxygen concentration meter (GX-8000 manufactured by Riken Keiki Co., Ltd.) was 0.0%). It was pulverized to obtain approximately spherical silver-coated copper powder 3 . For this silver-coated copper powder 3, in the same manner as in Comparative Example 1, the BET specific surface area, tap density, mass ratio of each element to the total mass of silver and copper, true density, oxygen content, carbon content, particle size distribution, The water content and the resistance when made into a conductive paste were measured. The results are shown in Table 1 below.

(Example 1)
In Comparative Example 2 above, the pure water in the water washing was changed to an aqueous hydrazine solution having a hydrazine concentration of 20% by mass, and the number of washings was changed to one (as a result, the amount of hydrazine aqueous solution used for washing was 5 L). , to obtain a substantially spherical silver-coated copper powder 4 in the same manner. The amount of hydrazine used was 19 equivalents to copper in the silver-coated copper powder. For this silver-coated copper powder 4, in the same manner as in Comparative Example 1, the BET specific surface area, tap density, mass ratio of each element to the total mass of silver and copper, true density, oxygen content, carbon content, particle size distribution, The water content and the resistance when made into a conductive paste were measured. The results are shown in Table 1 below.

Silver-coated copper powder 4 obtained in Example 1, in which the cleaning method of the present invention was applied to silver-coated copper powder 1, had a lower oxygen content than silver-coated copper powder 1, and a higher tap density. . As a result, the resistance when made into a conductive paste was improved. In the case of Comparative Example 2 in which the silver-coated copper powder 1 was washed with aqueous ammonia, the amount of oxygen increased. In Comparative Example 3, in which the silver-coated copper powder 1 was washed with water and hydrazine water, a silver-coated copper powder 3 having a lower oxygen content than that of Example 1 was obtained. Compared to powder 4, the powder was inferior in powder filling properties (tap density and the ratio of tap density to true density), and was also inferior in resistance when made into a conductive paste.

<Comparative Example 4> [Production of silver-coated copper alloy powder 1]
(Production of copper alloy powder (CuNiZn))
In a nitrogen atmosphere, 17.5 kg of Cu70Ni30 (mass ratio) alloy, 44.23 kg of Cu65Zn35 (mass ratio) alloy, 50 kg of Cu80Ni10Zn10 (mass ratio) powder (coarse powder), and 88.72 kg of copper were heated to 1200 ° C. While dropping from the bottom of the dish, high-pressure water (water pressure: 150 MPa, water volume: 160 L/min, pH: 10) was sprayed in the air in the air by a water atomizer to rapidly cool and solidify, and the resulting slurry was filtered to obtain The solid matter was washed with water, dried and pulverized to obtain approximately spherical copper alloy powder (copper-nickel-zinc alloy powder). For this copper alloy powder, in the same manner as in Comparative Example 1, the BET specific surface area, tap density, mass ratio of each element to the total mass of copper, nickel and zinc, true density, oxygen content, carbon content, particle size Distribution and moisture content were measured.

(Production of silver-coated copper alloy powder 1)
A solution (solution 1) in which 0.357 kg of EDTA-2Na dihydrate and 0.357 kg of ammonium carbonate were dissolved in 4.155 kg of pure water, and 0.787 kg of EDTA-2Na dihydrate and 0.393 kg of ammonium carbonate were purified. A solution (solution 2) was prepared by adding a solution of 0.279 kg of silver nitrate dissolved in 0.257 kg of pure water to a solution of 3.136 kg of water.

Next, in a nitrogen atmosphere, 0.750 kg of the copper alloy powder obtained above was added to solution 1 as a core powder to be coated, and the temperature was raised to 25° C. while stirring. Solution 2 is added to the dispersion liquid in which the copper alloy powder is dispersed, and the mixture is stirred for 1 hour, filtered, and the obtained solid matter is washed with water, dried, and pulverized to obtain approximately spherical copper particles coated with silver. An alloy powder (silver-coated copper alloy powder 1) was obtained. For this silver-coated copper alloy powder 1, in the same manner as in Comparative Example 1, the BET specific surface area, tap density, mass ratio of each element to the total mass of silver, copper, nickel and zinc, true density, oxygen content, carbon The amount, particle size distribution, water content, and resistance as a conductive paste were measured. The results are shown in Tables 2 and 3 below.

<Example 2>
After adding 1233.30 g of pure water to the reaction tank, the temperature was adjusted to 25° C., and while stirring at 640 rpm, N ₂ was added until the oxygen concentration meter (GX-8000 manufactured by Riken Keiki Co., Ltd.) indicated 0.0%. A purge was performed (the _N2 purge was continued thereafter to maintain the reactor oxygen concentration at 0.0%). When the oxygen concentration in the reaction tank reached 0.0%, 120 g of the silver-coated copper alloy powder 1 obtained in Comparative Example 4 above was added, and ammonia water with an ammonia concentration of 28% by mass (special grade, manufactured by Nacalai Rusk) was added. 57 g was added and the mixture was stirred for 30 minutes. The amount of ammonia added was 0.17 equivalent to the copper in the silver-coated copper alloy powder 1.

After stirring, the mixed solution was subjected to suction filtration using a filter bottle, a Buchner funnel, filter paper and an aspirator, and the silver-coated copper alloy powder was collected on the filter paper. Then, the silver-coated copper alloy powder on the filter paper was washed by pouring 5 L of an aqueous solution having a hydrazine concentration of 20% by mass while continuing suction filtration (the amount of hydrazine used is the amount in the silver-coated copper alloy powder 43 equivalents to copper). After washing, it was dried at 70° C. for 13.5 hours in a vacuum state and pulverized in a nitrogen atmosphere glove box (the display of the oxygen concentration meter (GX-8000 manufactured by Riken Keiki Co., Ltd.) was 0.0%). Thus, a spherical silver-coated copper alloy powder 2 was obtained. For this silver-coated copper alloy powder 2, in the same manner as in Comparative Example 1, the BET specific surface area, tap density, mass ratio of each element to the total mass of silver, copper, nickel and zinc, true density, oxygen content, carbon The amount, particle size distribution, water content, and resistance as a conductive paste were measured. The results are shown in Tables 2 and 3 below.

By performing the cleaning method of the present invention (Example 2) on the silver-coated copper alloy powder 1 (Comparative Example 4), the oxygen content was reduced, and the filling properties of the powder (tap density and true density of tap density ratio) was improved, and the resistance was improved when it was made into a conductive paste.

Claims (20)

A silver-coated metal powder having a silver coating layer on the particle surface of a metal powder that is a copper powder composed of copper and inevitable impurities, or a copper alloy powder composed of copper, nickel, zinc, and inevitable impurities, and ammonia as a complex-forming compound. a washing step 1 for washing with an aqueous solution;
A method for cleaning a silver-coated metal powder, comprising a cleaning step 2 of cleaning the silver-coated metal powder cleaned in the cleaning step 1 with an aqueous solution containing hydrazine as a reducing agent. The silver-coated metal powder according to claim 1, wherein in said washing step 1, said silver-coated metal powder is washed with an aqueous solution containing 0.05 to 1 equivalent of a complex-forming compound with respect to copper in said silver-coated metal powder. A method for cleaning metal powder. 3. The silver-coated metal according to claim 1, wherein in said washing step 2, said silver-coated metal powder is washed with an aqueous solution containing 10 to 60 equivalents of a reducing agent with respect to copper in said silver-coated metal powder. Powder cleaning method. The metal powder is the copper alloy powder, and the mass ratio of copper to the total mass of copper, nickel and zinc in the silver-coated metal powder is 82% by mass or more, according to any one of claims 1 to 3 . method for cleaning the silver-coated metal powder of . Claims 1 to 1, wherein the silver-coated metal powder subjected to the washing step 1 has a volume-based cumulative 50% particle diameter (D50) measured by a laser diffraction particle size distribution analyzer of 0.1 to 15.0 μm. 5. The method for cleaning a silver-coated metal powder according to any one of 4 . a silver coating step of forming a silver coating layer on the surface of a metal powder, which is a copper powder containing copper and inevitable impurities or a copper alloy powder containing copper, nickel, zinc and inevitable impurities, to obtain a silver-coated metal powder;
a washing step 1 in which the silver-coated metal powder obtained in the silver-coating step is washed with an aqueous solution containing ammonia as a complex-forming compound;
A method for producing a silver-coated metal powder, comprising a washing step 2 of washing the silver-coated metal powder washed in the washing step 1 with an aqueous solution containing hydrazine as a reducing agent. 7. The silver-coated metal powder according to claim 6 , wherein the metal powder is the copper alloy powder, and the mass ratio of copper to the total mass of copper, nickel, and zinc in the copper alloy powder is 82% by mass or more. Production method. The production of the silver-coated metal powder according to claim 6 or 7 , wherein the metal powder has a volume-based cumulative 50% particle diameter (D50) measured by a laser diffraction particle size distribution analyzer of 0.1 to 15.0 µm. Method. A silver-coated copper powder having a silver coating layer on the surface of copper particles composed of copper and inevitable impurities,
The reciprocal of the ratio of the tap density to the true density of the silver-coated copper powder (R _TAP ), the oxygen content (O) of the silver-coated copper powder, and the volume basis of the silver-coated copper powder measured by a laser diffraction particle size distribution analyzer The product of the _{cumulative 50} % particle diameter (D ₅₀ ) of
does not contain fatty acids on its surface,
Silver-coated copper powder. 10. The silver-coated copper powder according to claim 9 , wherein the product (R _TAP ×O×D ₅₀ (mass %·μm)) is 0.30 to 0.75 (mass %·μm). The silver-coated copper powder according to claim 9 or 10, wherein the content of said silver-coated layer in said silver-coated copper powder is 1 to 50% by mass. The silver-coated copper powder according to any one of claims 9 to 11 , wherein said cumulative 50% particle size (D ₅₀ ) is 0.1 to 15.0 µm. A silver-coated copper alloy powder having a silver coating layer on the surface of copper alloy particles composed of copper, nickel, zinc and inevitable impurities,
The reciprocal of the ratio of the tap density to the true density of the silver-coated copper alloy powder (R _TAP ), the oxygen content (O) of the silver-coated copper alloy powder, and the silver-coated copper alloy powder measured by a laser diffraction particle size distribution analyzer The product of the volume-based cumulative 50% particle diameter (D ₅₀ ) (R _TAP × O × D ₅₀ (mass% · μm)) is 0.58 (mass% · μm) or less ,
In the silver-coated copper alloy powder, the mass ratio of copper to the total mass of copper, nickel, and zinc is 82 to 95 mass%, the mass ratio of nickel to the total is 1 to 8 mass%, and the mass ratio of nickel to the total is 1 to 8 mass%. The mass ratio of zinc is 1 to 17% by mass,
does not contain fatty acids on its surface,
Silver-coated copper alloy powder. 14. The silver-coated copper alloy powder according to claim 13 , wherein the product (R _TAP ×O×D ₅₀ (mass %·μm)) is 0.25 to 0.56 (mass %·μm). The silver-coated copper alloy powder according to claim 13 or 14 , wherein the content of said silver-coated layer in said silver-coated copper alloy powder is 1 to 50% by mass. The silver-coated copper alloy powder according to any one of claims 13 to 15 , wherein said cumulative 50% particle diameter (D ₅₀ ) is 0.1 to 15.0 µm. A conductive paste in which the silver-coated copper powder according to any one of claims 9 to 12 and/or the silver-coated copper alloy powder according to any one of claims 13 to 16 is dispersed in a solvent and/or a resin binder. . A method for producing a conductive film, comprising applying the conductive paste according to claim 17 to a substrate to form a coating film, and baking or curing the coating film to form a conductive film on the substrate. An electronic component comprising an external electrode, wherein the external electrode is the silver-coated copper powder according to any one of claims 9 to 12 and/or the silver-coated copper alloy powder according to any one of claims 13 to 16 , and an electronic component containing a curable resin. An electric device comprising a substrate, an electric element formed on the substrate, the electronic component according to claim 19 mounted on the substrate, and a solder member connecting the electronic component and the electric element.