JP6970609B2 - Silver-coated alloy powder and its manufacturing method, conductive paste and its manufacturing method, electronic parts, and electronic equipment - Google Patents

Description

The present invention has a silver-coated alloy powder suitable as a material for forming an external electrode of an electronic component and a method for producing the same, a conductive paste containing the powder and a method for producing the same, and an external electrode formed by using the conductive paste. The present invention relates to an electronic component and an electronic device provided with the electronic component.

As electronic components constituting electronic devices, there are those having external electrodes such as capacitors, capacitors, inductors, piezoelectric elements, varistores, and thermistors. Of these, capacitors, capacitors and inductors include, for example, a laminate in which dielectric layers and internal electrode layers are alternately laminated, and an external electrode formed on the side surface of the laminate and connected to the internal electrode. It has a structure.

Electronic components are mounted on a substrate and connected to other electrical elements. A typical means of connection is solder connection. For example, the solder paste is printed so that the electronic component (external electrode) and the electric element are connected, and the solder paste is reflowed at a temperature of about 200 to 350 ° C. to connect the solder paste.

In order for solder connection to be performed properly, first, the molten solder must be sufficiently wetted with the external electrode, and the solder and the external electrode must be sufficiently bonded (solder wettability). Secondly, it is required that the solder bite, which is considered to occur when the external electrode melts into the melted solder, does not occur (solder bite resistance).

The external electrode is formed of a fired conductive paste containing a conductive filler such as copper, but in order to make a good solder connection and improve reliability, Ni (Ni) is applied to the conductive film formed from the above paste. It is generally practiced to perform nickel) plating and Sn (tin) plating to obtain an external electrode (for example, Patent Document 1). It is also known to use a nickel-copper (Ni-Cu) alloy powder coated with silver (Ag) as a conductive filler (for example, Patent Documents 2 to 3).

Japanese Unexamined Patent Publication No. 2014-84267 Japanese Unexamined Patent Publication No. 2015-156083 Japanese Unexamined Patent Publication No. 2003-224028

However, there is room for improvement in terms of cost and manufacturing efficiency in the three-layer structure consisting of the conductive film, the Ni-plated layer, and the Sn-plated layer. Since it is necessary to consider the adhesion and contact resistance between the conductive film and the Ni-plated layer, and the Ni-plated layer and the Sn-plated layer), there are fewer layers than when an external electrode is formed by such a three-layer configuration. It is desirable to have a configuration. Further, since it is desired to reduce the thickness of the external electrode due to the recent trend toward miniaturization of electronic devices, such a layer structure is desirable from this point as well. Furthermore, conductivity is also important in applications such as capacitors and capacitors.

Therefore, an object of the present invention is to provide a metal powder that can be used as a conductive paste capable of forming an external electrode having excellent solder wettability and solder biting resistance while having a smaller layer structure.

The present inventors studied diligently to solve the above problems, and first examined the conventional silver-coated nickel-copper alloy powder disclosed in Patent Documents 2 and 3, and found that they were inferior in solder properties. .. As a result of further studies, the oxygen adhering to the particles constituting the silver-coated alloy powder and the alloy core particles before the silver-coated alloy powder was produced greatly affected the solder wettability and the solder biting resistance. I found out that I was there. The following aspects were created based on this finding.

That is, the first aspect is a silver-coated alloy powder having a coating layer containing silver on the surface of alloy core particles containing copper, nickel and unavoidable impurities, and the oxygen content (mass%) of the silver-coated alloy powder is rationalized. It is a silver-coated alloy powder having a value divided by a surface area Sm (m ² / g) of 2.5 (mass% · g / m ^{2) or less.}
The specific surface area Sm is calculated by the following formula (1).
Specific surface area Sm = 6 / (ρ × D ₅₀ ) ... (1)
Ρ is the specific gravity and composition ratio of copper, nickel and silver in the silver-coated alloy powder (when the total of copper, nickel and silver in the silver-coated alloy powder is 100% by mass, respectively). It is a density (g / cm ³ ) calculated from (mass ratio), and D ₅₀ is a volume-based cumulative 50% particle diameter (μm) obtained by measuring the silver-coated alloy powder with a laser diffraction type particle size distribution measuring device. ).

The second aspect is the first aspect.
The proportion of copper is 40 to 95% by mass and the proportion of nickel is 5 to 60% by mass in the total 100% by mass of copper and nickel in the alloy core particles.

The third aspect is the first or second aspect.
The value obtained by dividing the amount of oxygen (mass%) of the silver-coated alloy powder by the specific surface area BET (m ² / g) measured by the BET 1-point method of the silver-coated alloy powder is 1.50 (mass% g / m). ² ) The following.

The fourth aspect is any one of the first to third aspects.
The mass ratio of silver in the silver-coated alloy powder is 1 to 40% by mass.

The fifth aspect is any one of the first to fourth aspects.
_{The cumulative 50% particle size (D 50} ) based on the volume measured by the laser diffraction type particle size distribution measuring device of the silver-coated alloy powder is 0.1 to 10 μm.

The sixth aspect is any one of the first to fifth aspects.
The amount of oxygen in the silver-coated alloy powder is 0.05 to 0.40% by mass.

A seventh aspect is the conductive paste containing the silver-coated alloy powder and the curable resin according to any one of the first to sixth aspects.

The eighth aspect is the seventh aspect.
The content ratio of the curable resin in the conductive paste is 0.5 to 49% by mass.

The ninth aspect is the seventh or eighth aspect.
The curable resin is a phenol resin, a urea resin, a melamine resin, an epoxy resin, an unsaturated polyester resin, a silicone resin, a polyurethane resin, a polyvinyl butyral resin, a polyimide resin, a polyamide resin, a maleimide resin, a diallyl phthalate resin, an oxetane resin, ( Meta) At least one selected from the group consisting of acrylic resin, maleic acid resin, maleic anhydride resin, polybutadiene resin, alkyd resin, amino resin, polylactic acid resin, oxazoline resin, benzoxazine resin and fluororesin.

The tenth aspect is any one of the seventh to ninth aspects.
The content of the silver-coated alloy powder in the conductive paste is 50 to 98% by mass.

The eleventh aspect is an electronic component provided with an external electrode, wherein the external electrode contains the silver-coated alloy powder and the curable resin according to any one of the first to sixth aspects.

The twelfth aspect is the eleventh aspect.
After immersing the external electrode in the flux, it is immersed in a lead-free solder (having a metal composition of Sn96.5Ag3Cu0.5) at 260 ° C. for 1 second, then the external electrode is pulled up and observed using a laser microscope. When this is done, solder adheres to 65 area% or more of the entire upper surface of the external electrode.

The thirteenth aspect connects the substrate, the electric element formed on the substrate, the electronic component according to the eleventh or twelfth aspect mounted on the substrate, and the electronic component and the electric element. It is an electronic device provided with a solder member.

The fourteenth aspect is
A method for producing a silver-coated alloy powder having a coating layer containing silver on the surface of alloy core particles containing copper, nickel and unavoidable impurities.
It is a method for producing a silver-coated alloy powder, which comprises a step of performing an oxygen reduction treatment on the powder of the alloy core particles or the silver-coated alloy powder after the coating layer is formed on the surface of the alloy core particles. ..

The fifteenth aspect is the fourteenth aspect.
The step of performing oxygen reduction treatment on the powder of the alloy core particles and
After the step, the step of forming the coating layer on the surface of the alloy core particles and the step of forming the coating layer.
Have.

The sixteenth aspect is the fourteenth or fifteenth aspect.
The oxygen reduction treatment is hydrogen reduction in an atmosphere containing hydrogen.

The seventeenth aspect is
A method for producing a conductive paste, which comprises a step of mixing the silver-coated alloy powder obtained by the production method according to any one of the fourteenth to sixteenth aspects with a curable resin.

According to the present invention, a metal powder (silver-coated alloy powder) that can be used as a conductive paste capable of forming an external electrode having excellent solder wettability and solder biting resistance while having a smaller layer structure and a method for producing the same are available. Provided. Further, a conductive paste and a method for producing the same, electronic components, and electronic devices using this silver-coated alloy powder are also provided.

Hereinafter, the present invention will be described in detail. In addition, in this specification, "~" means a predetermined value or more and a predetermined value or less.

[Silver coated alloy powder]
<Composition of silver-coated alloy powder>
The silver-coated alloy powder of the present invention has a coating layer containing silver (silver or a silver compound) on the surface of alloy core particles containing copper, nickel and unavoidable impurities. The silver-containing coating layer (hereinafter referred to as silver-coating layer) contributes to the excellent conductivity and solder wettability of the external electrode formed from the silver-coated alloy powder (containing conductive paste), and the alloy core particles are copper. The silver-coated layer enhances the oxidation resistance of the alloy core particles because the silver-coated layer is inferior in oxidation resistance. The silver-coated layer is preferably composed substantially only of silver and has a good coating on the alloy core particles, but does not necessarily cover the entire surface of the alloy core particles and a part of the alloy core particles. It may be exposed. In the alloy core particles, copper contributes to the excellent conductivity of the silver-coated alloy powder. Nickel imparts excellent solder-eating resistance to the silver-coated alloy powder. Specifically, the silver-coated layer on the surface of the silver-coated alloy powder is eaten by solder, but the alloy core particles have nickel, so that the alloy core. It is thought that the solder is eaten by the particles to stop the phenomenon.

The silver content (mass ratio) in such a silver-coated alloy powder is preferably 1 to 40% by mass, more preferably 8 to 30% by mass, from the viewpoint of good conductivity and solder wettability. .. From the viewpoint of the production cost of the silver-coated alloy powder, the silver content is preferably 2 to 12% by mass. Regarding the alloy core particles, the proportion of copper in the total 100% by mass of copper and nickel is preferably 40 to 95% by mass, more preferably 65 to 90% by mass from the viewpoint of good conductivity. be. In the total 100% by mass, the proportion of nickel is preferably 5 to 60% by mass, more preferably 10 to 35% by mass, from the viewpoint of good solder bite resistance.

The shape of the silver-coated alloy powder is not particularly limited, and may be spherical or substantially spherical, granular, flaky (flake-shaped), or amorphous. The flake-shaped silver-coated alloy powder can be produced by appropriately adjusting the production conditions of the powder, or by mechanically plastically deforming and flattening a spherical silver-coated alloy powder with a ball mill or the like. You can also do it.

Silver coated cumulative 50% particle diameter on a volume basis as measured by a laser diffraction particle size distribution measuring apparatus of the alloy powder (D _50), from the viewpoint of enabling the formation of a conductive or thin external electrode, preferably 0.1 It is 10 μm, more preferably 1 to 9 μm, and particularly preferably 2 to 6.5 μm.

Silver coated alloy measured specific surface area BET by BET1 point method of powder ^(m 2 / g), from the viewpoint of exhibiting good conductivity, preferably 0.08~1.0m ² / g, more preferably 0.08~0.50m a ² / g, particularly preferably 0.08~0.30m ² / g.

The TAP density of the silver-coated alloy powder is preferably 3.0 to 7.5 g / cm ³ and more preferably 4.6 to 6. from the viewpoint of increasing the packing density of the powder and exhibiting good conductivity. a 5 g / cm ^3, more preferably from 5.2~6.4g / cm ^3.

Alloy core particles in silver-coated alloy powder may contain trace amounts of unavoidable impurities due to the influence of the manufacturing raw materials and equipment / substances used in the manufacturing process. Examples thereof include iron, sodium, potassium, calcium, and palladium. Examples include magnesium, oxygen, carbon, nitrogen, phosphorus, silicon and chlorine.

Among these, oxygen is considered to adversely affect the conductivity of the silver-coated alloy powder. From this point, the oxygen content of the silver-coated alloy powder (determined by analyzing the silver-coated alloy powder with an oxygen / nitrogen analyzer (unit: mass%); the same shall apply hereinafter) is preferably 0.05 to 0.40 mass. %, More preferably 0.15 to 0.30% by mass.

In the present embodiment, the amount of oxygen in the silver-coated alloy powder mentioned above is adjusted to the following predetermined range, and as shown in the items of Examples described later, soldering has a smaller layer structure. It is possible to realize a metal powder that can be used as a conductive paste capable of forming an external electrode (furthermore, an external electrode having excellent conductivity) having excellent wettability and solder biting resistance. Hereinafter, the regulation will be described in detail.

The silver-coated alloy powder of the present embodiment is a silver-coated alloy powder having a coating layer containing silver on the surface of alloy core particles containing copper, nickel and unavoidable impurities, and has an oxygen content (% by mass) of the silver-coated alloy powder. , The value divided by the specific surface area Sm (m ² / g) (hereinafter, also referred to as O / Sm) is 2.5 (mass% · g / m ² ) or less (hereinafter, the unit of O / Sm). May be omitted).
The specific surface area Sm is calculated by the following formula (1).
Specific surface area Sm = 6 / (ρ × D ₅₀ ) ... (1)
Ρ is the specific gravity and composition ratio of copper, nickel and silver in the silver-coated alloy powder (the mass ratio of each when the total of copper, nickel and silver in the silver-coated alloy powder is 100% by mass). ) Is the density (g / cm ³ ) calculated from), and D ₅₀ is the cumulative 50% particle diameter (μm) based on the volume obtained by measuring the silver-coated alloy powder with a laser diffraction type particle size distribution measuring device. .. The detailed calculation method of the formula (1) and ρ will be described later in the item of the example.
The O / Sm is preferably 0.8 to 2.2, preferably 1.35 to 2.0, from the viewpoint of being able to form an external electrode having excellent solder wettability and solder biting resistance. More preferably, it is more preferably 1.5 to 2.0.

_{Incidentally, in the present embodiment, the specific surface area Sm is obtained from D 50} obtained by the laser diffraction type particle size distribution measuring device, and O / Sm is obtained by using this specific surface area Sm. Here, there is a reason why ^{the specific surface area BET (m 2} / g) measured by the BET 1-point method of the silver-coated alloy powder is not adopted.
The reason is that the specific surface area BET may fluctuate depending on the amount of oxygen in the silver-coated alloy powder. In that case, if an O / BET is to be set, the denominator will depend on the numerator. Rather, by _{obtaining the specific surface area Sm from D 50} , the dependence of the silver-coated alloy powder on the Sm is reduced, and then the ratio of the oxygen amount of the silver-coated alloy powder to the specific surface area Sm is specified. The present inventors thought that it was better to do so.
As a result of considering the above reasons, in the present invention, the oxygen content of the silver-coated alloy powder is defined as O / Sm, and by setting this within a predetermined range, the silver-coated alloy powder can solve the above-mentioned problems. ..

If O / BET is specified, it will be as follows. That is, the value obtained by dividing the oxygen content (mass%) of the silver-coated alloy powder by the specific surface area BET (m ² / g) measured by the BET 1-point method of the silver-coated alloy powder is 1.50 (mass% g / m). ^{2 ) It is preferably 1} ) or less, more preferably 1.40 (mass% · g / m 2) or less, and further preferably 1.00 (mass% · g / m ² ) or less. The O / BET is usually 0.20 (mass% · g / m ² ) or more.

In addition, carbon becomes a source of gas such as carbon dioxide during (heat) curing, and the adhesion between the external electrode and the layer in contact with it may deteriorate. Therefore, the amount of carbon in the silver-coated alloy powder may be small. Preferably, specifically, it is preferably 0.5% by mass or less, and more preferably 0.35% by mass or less. The amount of carbon is determined by analyzing the silver-coated alloy powder with a carbon / sulfur analyzer.

In the silver-coated alloy powder of the present invention, the TAP density is increased by improving the dispersibility in the conductive paste described later, the conductivity of the external electrode is enhanced, and the oxidation resistance is imparted to the silver-coated alloy powder. A surface treatment may be applied in order to reduce the change with time. The surface treatment agent is preferably a fatty acid or a triazole compound. These fatty acids include butyric acid, valeric acid, caproic acid, enanthic acid, capric acid, pelargonic acid, cabric acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, palmitreic acid, margaric acid, stearic acid, oleic acid, bacenoic acid. , Linol acid, linolenic acid, arachidic acid, eikosazienoic acid, eikosatrienic acid, eikosatetraenoic acid, arachidonic acid, behenic acid, lignoseric acid, nervonic acid, serotic acid, montanic acid, melicic acid, etc. can be used. Although possible, it is preferred to use palmitic acid, stearic acid or oleic acid. Examples of the above-mentioned triazole compound include benzotriazole.

The amount of the surface treatment agent added is preferably 0.1 to 7 parts by mass, preferably 0.3 to 6 parts by mass with respect to 100 parts by mass of the silver-coated alloy powder (not surface-treated). It is more preferably 0.3 to 5 parts by mass, and most preferably 0.3 to 5 parts by mass.

Next, the L * value (measured in the SCE mode) of the silver-coated alloy powder of the present invention can be a measure of the uniformity of the silver coating, and it is preferable that the particle size distribution is close to the L * value of the similar silver powder. .. Specifically, the L * value of the silver-coated alloy powder is preferably 45 to 81.6, more preferably 63 to 81.6.

<Manufacturing method of silver-coated alloy powder>
Next, a method for producing the silver-coated alloy powder of the present invention will be described.

(Manufacturing method of alloy core particles)
First, a method for producing alloy core particles will be described. In the present invention, the alloy core particles are preferably produced by a water atomizing method. Alloy core particles can be produced by rapidly cooling and solidifying the molten metal by spraying high-pressure water having a predetermined water pressure while dropping the molten metal in which copper and nickel are dissolved from the tundish. It is also possible to dissolve copper-nickel alloy and copper.

The temperature of the molten metal is preferably 1100 to 1700 ° C, more preferably 1200 to 1700 ° C. When the temperature of the molten metal is raised, alloy core particles having a small particle size tend to be obtained, and by coating the alloy core particles with silver, a silver-coated alloy powder having a small particle size can be produced.

Water atomization can be carried out in the atmosphere or in a non-oxidizing atmosphere such as argon, nitrogen, carbon monoxide, or hydrogen. It is considered that water atomization in a non-oxidizing atmosphere can prevent the oxidation of copper, which is susceptible to oxidation. Further, the molten metal may be prepared in the atmosphere or in a non-oxidizing atmosphere. Further, in order to reduce the amount of oxygen in the alloy core particles, a reducing agent such as carbon black or charcoal may be added to the molten metal.

The water pressure of the high-pressure water used for water atomization is preferably 30 to 200 MPa, and when the water pressure is increased, alloy core particles having a small particle size can be obtained. Further, as the high-pressure water, pure water, weakly acidic water (pH about 5.0 to 6.5) or alkaline water (pH about 8 to 12) can be used.

When alloy core particles are produced from molten metal by the water atomization method, copper and nickel in the alloy core particles are adjusted by adjusting the amount of each constituent metal charged in the molten metal (or the amount of copper-nickel alloy and copper charged). The ratio of can be adjusted.

Further, by spraying high-pressure water while dropping the molten metal to quench and solidify it, a slurry in which alloy core particles are dispersed in water can be obtained. This is solid-liquid separated, and the obtained solid material is dried to dry the alloy core. Particles can be obtained. If necessary, the solid matter obtained by solid-liquid separation may be washed with water before drying, crushed after drying, or classified to adjust the particle size.

(Removal of oxygen by oxygen reduction treatment)
In the present embodiment, the powder of the alloy core particles produced as described above is subjected to oxygen reduction treatment. This oxygen reduction treatment is for removing at least a part of oxygen (typically existing in the form of an oxide film) on the surface of the alloy core particles. By performing this oxygen reduction treatment, as shown in the items of Examples described later, an external electrode having excellent solder wettability and solder biting resistance (further, an external electrode having excellent conductivity) while having a smaller layer structure. ) Can be realized as a metal powder that can be used as a conductive paste.

The reason for this is speculated, but the following can be considered.
First, as shown in Comparative Example 1 described later, the solder wettability of the silver-coated alloy powder is not good when the oxygen reduction treatment is not performed. It is presumed that this is because the alloy core particles are not sufficiently coated with silver (excellent in solder wettability) in the silver-coated alloy powder.
On the other hand, by performing oxygen reduction treatment on the powder of the alloy core particles, it is possible to remove at least a part of oxygen existing on the surface of the alloy core particles. By doing so, the silver coating is less likely to be hindered by the oxygen present on the surface of the alloy core particles, and the silver coating is performed better, resulting in solder wettability and solder bite resistance in the silver coated alloy powder. It is thought that it will improve.

Further, as shown in Example 2 described later, not only the alloy core particles before being coated with silver are subjected to oxygen reduction treatment, but also the silver-coated alloy powder after being coated with silver is subjected to oxygen reduction treatment. The effect of the present invention is also obtained when the above oxygen reduction treatment is performed. In the following, an example of oxygen reduction treatment of alloy core particle powder will be described.

As a specific method of the oxygen reduction treatment here, a known method can be adopted as long as it is a treatment capable of removing at least a part of oxygen on the surface of the alloy core particles or the silver-coated alloy powder. For example, hydrogen reduction treatment in an atmosphere containing hydrogen, reduction treatment using another gas (for example, carbon monoxide), pickling using an acidic liquid, etc. may be applied, but alloy core particles or silver coating may be applied. From the viewpoint of suppressing deterioration of the alloy powder, the reduction treatment using a gas is preferable, and from the viewpoint of not containing carbon, the hydrogen reduction treatment is preferable.

(Covered with silver)
A coating layer (silver coating layer) containing silver is formed on the surface of the alloy core particles subjected to the oxygen reduction treatment as described above. As a method for forming this coating layer, a method of precipitating silver or a silver compound on the surface of the alloy core particles by a substitution method using a substitution reaction between a constituent metal of the alloy core particles and silver or a reduction method using a reducing agent is used. Can be used. In the above substitution method, for example, a method of precipitating silver or a silver compound on the surface of the alloy core particles by stirring a solution containing the alloy core particles and silver or a silver compound in a solvent can be adopted. Further, a solution containing alloy core particles and an organic substance (for example, a chelating agent described later) in a solvent and a solution containing silver or a silver compound and an organic substance (for example, a chelating agent described later) in the solvent are mixed and stirred. Therefore, a method of precipitating silver or a silver compound on the surface of the alloy core particles can be adopted.

As the solvent used in the substitution method or the reduction method, water, an organic solvent, or a solvent obtained by mixing these can be used. When using a solvent in which water and an organic solvent are mixed, it is necessary to use an organic solvent that becomes liquid at room temperature (20 to 30 ° C.), but the mixing ratio of water and the organic solvent depends on the organic solvent used. It can be adjusted as appropriate. Further, as the water used as the solvent, distilled water, ion-exchanged water, industrial water and the like can be used as long as there is no risk of impurities being mixed.

Since silver ions need to be present in the solution as a raw material for the silver coating layer (coating layer composed of silver or a silver compound), it is preferable to use silver nitrate having high solubility in water and many organic solvents. .. Further, in order to carry out the silver coating reaction as uniformly as possible, it is preferable to use a silver nitrate solution in which silver nitrate is dissolved in a solvent (water, an organic solvent or a solvent obtained by mixing them) instead of solid silver nitrate. The amount of the silver nitrate solution to be used, the concentration of silver nitrate in the silver nitrate solution, and the amount of the organic solvent can be determined according to the amount of the target silver coating layer.

A chelating agent may be added to the solution to form the silver coating layer more uniformly. As the chelating agent, it is recommended to use a chelating agent having a high complex stability constant with respect to copper ions, etc., so that copper ions, etc., which are by-produced by the substitution reaction between silver ions and alloy core particles, do not reprecipitate. preferable. In particular, since the alloy core particles of the silver-coated alloy powder contain copper as a main component, it is preferable to select the chelating agent while paying attention to the illusion stability constant with copper. Specifically, as the chelating agent, a chelating agent selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid, diethylenetriamine, triethylenediamine and salts thereof can be used.

A pH buffer may be added to the solution in order to carry out the silver coating reaction stably and safely. As this pH buffering agent, ammonium carbonate, ammonium hydrogencarbonate, aqueous ammonia, sodium hydrogencarbonate and the like can be used.

In the silver coating reaction, the alloy core particles are put into the solution and stirred before adding the silver salt, and the solution containing the silver salt is added in a state where the alloy core particles are sufficiently dispersed in the solution. It is preferable to do. The reaction temperature during this silver coating reaction may not be the temperature at which the reaction solution solidifies or evaporates, but is preferably in the range of 15 to 80 ° C, more preferably 20 to 75 ° C, and most preferably 20 to 70 ° C. Set. The reaction time varies depending on the coating amount of silver or the silver compound and the reaction temperature, but can be set in the range of 1 minute to 5 hours.
For example, after the silver coating reaction is carried out as described above to obtain a silver coated alloy powder, the oxygen reduction treatment may be performed as described above.

(surface treatment)
As described above, the silver-coated alloy powder of the present invention may be surface-treated in order to improve the conductivity of the external electrode. The surface treatment may be performed by mixing the alloy powder coated with the silver-containing layer and the surface treatment agent, or by adding and mixing the surface treatment agent to the slurry of the alloy powder coated with the silver-containing layer. ..

[Conductive paste]
Next, the conductive paste containing the silver-coated alloy powder of the present invention will be described. The conductive paste contains a curable resin in addition to the silver-coated alloy powder. The conductive film formed by curing the conductive paste (curable resin inside) has excellent solder wettability and solder biting resistance, and also has excellent conductivity, so that it is external (solder-connected). It is suitable as a material for forming an electrode. Further, the conductive paste of the present invention can be used for forming other electrodes, circuits, bonding layers and the like.

In the conductive paste of the present invention, two or more kinds of silver-coated alloy powders having different types in terms of particle size, shape and other points, which correspond to the silver-coated alloy powder of the present invention, may be used in combination. The content of the silver-coated alloy powder in the conductive paste is preferably 50 to 98% by mass, more preferably 70 to 70, from the viewpoint of obtaining an external electrode having appropriate solder wettability, solder biting resistance and conductivity. It is 97% by mass.

The curable resin used for the conductive paste includes a thermosetting resin and a photocurable resin.
Examples of the thermosetting resin include phenol resin, urea resin, melamine resin, epoxy resin, unsaturated polyester resin, silicone resin, polyurethane resin, polyvinyl butyral resin, polyimide resin, maleimide resin, diallyl phthalate resin, oxetane resin and (meth). Acrylic resin can be mentioned.
The photocurable resin may be a resin having at least one unsaturated bond in one molecule that causes a cross-linking reaction by light, and specific examples thereof include (meth) acrylic resin, maleic acid resin, and 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 resin and fluorine. Resin is mentioned.

These curable resins can be used alone or in combination of two or more. Further, the content ratio of the curable resin in the conductive paste is preferably 0. From the viewpoint of sufficiently curing to form an external electrode and at the same time appropriately exhibiting solder wettability, solder biting resistance and conductivity. It is 5 to 49% by mass, more preferably 1 to 29% by mass.

The conductive paste of the present invention may contain copper powder, silver powder, aluminum powder, nickel powder, zinc powder, tin powder, bismuth powder, phosphorus powder, etc., depending on the required properties, as long as the effects of the present invention are not impaired. , Metal powders other than the silver-coated alloy powder of the present invention may be added. The content of the metal powder in the conductive paste is preferably 1 to 48% by mass, more preferably 1 to 28% by mass. Further, the metal powder may be used alone or in combination of two or more.

The total content of the silver-coated alloy powder and the metal powder in the conductive paste of the present invention is preferably 51 to 99% by mass from the viewpoint of exhibiting appropriate solder wettability, solder biting resistance and conductivity. , More preferably 71 to 98% by mass.

When the paste is cured by heating, a thermal polymerization initiator may be added to the conductive paste of the present invention in order to cure or accelerate the curing. Examples of the thermal polymerization initiator include hydroperoxides, dialkyl peroxides, peroxyesters, diacyl peroxides, peroxycarbonates, peroxyketals, and ketone peroxides. These thermal polymerization initiators may be used alone or in combination of two or more.

Further, in order to accelerate curing, a curing agent such as a polyamine, an acid anhydride, a boron trihalogenated compound, an amine complex salt of a boron trihalogenated compound, an imidazole compound, an aromatic diamine compound, or a carboxylic acid compound is added. May be good. These may be used alone or in combination of two or more.

Further, when the conductive paste of the present invention is photopolymerized, a photopolymerization initiator is contained in the conductive paste. As the photopolymerization initiator, a photoradical generator or a photocationic polymerization initiator is usually used. These photopolymerization initiators may be used alone or in combination of two or more.

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

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

Further, in addition to the photocationic polymerization initiator, a curing agent for curing the polymerizable monomer may be added to the conductive paste. Examples of the curing agent include amine compounds, compounds such as polyaminoamide compounds synthesized from amine compounds, tertiary amine compounds, imidazole compounds, hydrazide compounds, melamine compounds, acid anhydrides, phenol compounds, and thermal latent cationic polymerization catalysts. , Dicianamide and derivatives thereof.

It is also possible to add a photosensitizer to the conductive paste. Specific examples of the photosensitizer include pyrene, perylene, acridine orange, thioxanthone, 2-chlorothioxanthone and benzoflavin.

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

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

The method for preparing the conductive paste described above is not particularly limited, but for example, each component is weighed and placed in a predetermined container, and a kneading defoaming machine, a frothing machine, a universal stirrer, a kneader, or the like is used. It can be prepared by pre-kneading and then main-kneading with three rolls. Also, if necessary, then organic solvents (eg, texanol (2,2,4-trimethyl-1,3-pentanediol 2-methylpropanolate), tarpineol, carbitol acetate (diethylene glycol monoethyl ether acetate), etc. Ethylene glycol, dibutyl acetate or diethylene glycol monobutyl ether acetate) may be added to adjust the viscosity.

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

[Electronic components]
Next, an electronic component that can be manufactured by using the conductive paste of the present invention will be described. The electronic component is not particularly limited as long as it has an external electrode. Among them, it is more preferable that the device has an external electrode and is connected to another electric element by soldering. Specific examples thereof include capacitors (for example, multilayer ceramic capacitors: MLCC (Multi-Layered Ceramic Capacitor)), capacitors, inductors, laminated wiring boards (for example, printed wiring boards), piezoelectric elements, varistor, thermistors and resistors. In addition, semiconductor chips and the like can also be mentioned.

The conductive paste of the present invention is applied to a place where an external electrode of a member constituting an electronic component should be formed, and is treated under the condition that the curable resin is cured to become an external electrode. The conductive paste is applied by a printing method such as dipping, screen printing and transfer printing. For example, if the electronic component is a capacitor or a capacitor, the member constituting the electronic component is composed of a laminated body in which a dielectric layer and an internal electrode layer having different polarities are alternately laminated, and the inside of the laminated body. External electrodes are formed at both ends from which the electrode layers are alternately drawn out.

For the coated conductive paste, for example, in the case of thermosetting, the temperature is preferably 100 to 300 ° C, more preferably 120 to 250 ° C, still more preferably 150 to 220 ° C, preferably 10 to 120 minutes. It is preferably heated for 15 to 90 minutes, more preferably 20 to 60 minutes.

When the conductive paste is photocured, the amount of radiation irradiated during curing is arbitrary as long as the photopolymerization initiator generates radicals, but the composition of the curable resin and the type of photopolymerization initiator And, depending on the amount, ultraviolet rays having a wavelength of 200 to 450 nm are irradiated, preferably in the range of ^{0.1 to 200 J / cm 2.} The radiation may be divided into a plurality of times and irradiated. Specific examples of the light source lamp to be used include a metal halide lamp, a high-pressure mercury lamp, and an ultraviolet LED lamp. In addition, for the purpose of promptly completing the polymerization, the photopolymerization and the thermal polymerization as described above may be carried out at the same time.

When the curable resin in the conductive paste is cured by the thermosetting or photocuring described above, the resin forms a cured product, and the silver-coated alloy powder contained therein is in contact with each other due to the curing shrinkage of the resin and conducts. And becomes an external electrode. When the conductive paste contains a volatile substance such as an organic solvent, at least a part of the volatile substance is volatilized in the curing reaction. As described above, an electronic component provided with an external electrode can be obtained.

In the formed external electrode, the ratio of the silver-coated alloy powder to the total of the silver-coated alloy powder and the curable resin (cured product) is almost the same as the ratio in the conductive paste, preferably 60 to 99% by mass. Yes, more preferably 70-97% by mass. Similarly, in the external electrode, the ratio of the curable resin (cured product) in the above total is preferably 1 to 40% by mass, more preferably 3 to 30% by mass.

It is considered that a large amount of silver-coated alloy powder is present on the surface of the external electrode that comes into contact with the solder. The silver-coated alloy powder has an O / Sm in a predetermined range, and when the alloy core particles are subjected to oxygen reduction treatment in the production thereof, it is considered that the silver-coated alloy powder has a good silver coating. Although the reason is unknown when the silver-coated alloy powder is subjected to the oxygen reduction treatment, the external electrode has excellent solder wettability. Furthermore, since the alloy core particles inside the silver coating layer have excellent resistance to solder biting, it is considered that even if the silver coating layer on the surface is eaten by the solder biting phenomenon, it can be stopped to some extent by the alloy core particles. The external electrode is solder-eating and has excellent resistance. Further, the external electrode is also excellent in conductivity due to the presence of the silver coating layer and the copper of the alloy core particles.
Therefore, when the solder wettability is quantitatively expressed, the external electrode is immersed in a flux, then immersed in a lead-free solder (having a metal composition of Sn96.5Ag3Cu0.5) at 260 ° C. for 1 second, and then the above-mentioned. When the external electrode is pulled up and observed using a laser microscope, it is preferable that solder adheres to 65 area% or more of the entire upper surface of the external electrode. When the solder biting resistance is quantitatively expressed, the external electrode is immersed in a flux, then immersed in a lead-free solder (having a metal composition of Sn96.5Ag3Cu0.5) at 260 ° C. for 30 seconds, and then the above-mentioned. When the external electrode is pulled up and observed using a laser microscope, it is preferable that solder adheres to 60 area% or more of the entire upper surface of the external electrode. These more detailed observation methods will be described in Examples.

[Electronics]
As described above, the external electrode included in the electronic component of the present invention is excellent in solder wettability, solder bite resistance, and conductivity, so that it can be satisfactorily solder-connected to other electric elements. The electronic device of the present invention has a configuration including a substrate, an electric element formed on the substrate, an electronic component mounted on the substrate, and a solder member connecting the electronic component and the electric element, and is necessary. Other members and elements may be provided accordingly. Examples of the electronic device include MLCC, MLCI, wireless IC tag, and the like. Further, examples of the electric element include electric circuits and electrodes such as wirings, leads, terminals, and antenna circuits.

The electric element may be formed directly on the substrate, or may be formed, for example, via an intermediate layer for enhancing the adhesion between the electric element and the substrate. Electronic components are usually mounted on a substrate by being connected to an electrical element by a solder member.

The substrate is not particularly limited, but 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 co-fired ceramic substrate).

The material of the solder member is not particularly limited, but for example, the solder member includes at least one metal selected from the group consisting of tin, lead, silver, copper, zinc, bismuth, indium and aluminum. Further, since lead-free solder is desirable in recent years due to the problem of environmental load, it is preferable that the solder member does not substantially contain lead. Examples of the lead-free solder member 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 on, for example, an electric element, and electronic components are placed on the printed solder paste (electric elements and electronic components are subjected to flux cleaning as necessary). Alternatively, the solder paste may contain flux). Then, by heating at a temperature of about 200 to 350 ° C. by the reflow process, the solder is melted and the electric element and the electronic component are electrically and physically connected. In this way, the electronic device of the present invention is manufactured, and other members and elements are formed or mounted on the substrate as needed.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.
In Production Example 1 described below, the alloy powder was subjected to a reduction treatment (that is, an oxygen reduction treatment for removing oxygen) before the alloy powder was coated with silver. Then, the silver coating treatment and the surface treatment were performed in this order.
Further, in Production Example 2, after the alloy powder was coated with silver, the silver-coated alloy powder was subjected to surface treatment and oxygen reduction treatment in this order.
Further, in Production Example 3, after the alloy powder was coated with silver, the silver-coated alloy powder was subjected to an oxygen reduction treatment, and further surface-treated with palmitic acid.
On the other hand, in Production Comparative Example 1, the oxygen reduction treatment was not performed.
In summary, the difference in the process order of each manufacturing example is as follows.
Production Example 1: Oxygen reduction treatment → Silver coating treatment → Surface treatment Production Example 2: Silver coating treatment → Surface treatment → Oxygen reduction treatment Production Example 3: Silver coating treatment → Oxygen reduction treatment → Surface treatment Production Comparative Example 1: Silver coating treatment → Surface treatment

[Manufacturing Example 1]
<Manufacturing of alloy core particles>
In an air atmosphere, carbon powder is added as a reducing agent to a molten metal obtained by heating 28 kg of copper and 12 kg of nickel to 1300 ° C in a tundish furnace, and the molten metal is dropped from the lower part of the tundish furnace in the air by a water atomizing device. High-pressure water (water pressure: 70 MPa, water volume: 160 L / min, pH: 5.8) is sprayed to quench and solidify, and the obtained alloy powder is filtered, washed with water, dried, crushed, and the alloy powder a. (Copper-nickel powder a) was obtained.

<Oxygen reduction treatment>
The alloy powder a (copper-nickel powder a) thus obtained was heated at 350 ° C. for 10 hours in a hydrogen atmosphere (100% hydrogen) to reduce hydrogen to the alloy powder b (copper-nickel powder b). Got

<Silver coating reaction>
A solution (solution 1) in which 0.17 kg of EDTA-2Na dihydrate and 0.17 kg of ammonium carbonate are dissolved in 1.9 kg of pure water, and 0.37 kg of EDTA-2Na dihydrate and 0.18 kg of ammonium carbonate are pure. A solution (solution 2) obtained by adding a solution of 0.06 kg of silver nitrate in 0.19 kg of pure water to a solution of 1.5 kg of water was prepared.
Next, in a nitrogen atmosphere, 0.35 kg of the obtained alloy powder b as a powder of the alloy core particles to be coated was added to the solution 1 and the temperature was raised to 25 ° C. with stirring. Solution 2 was added to the solution in which the alloy powder b was dispersed, and the mixture was stirred for 1 hour, filtered, washed with water, and dried to obtain an alloy powder coated with silver.

<Surface treatment>
Next, 80 g of the obtained silver-coated alloy powder and 0.24 g of palmitic acid (0.3 parts by mass with respect to 100 parts by mass of the unsurface-treated silver-coated alloy powder) were placed in a cutter mill and crushed for 20 seconds. Was performed twice to obtain a substantially spherical silver-coated alloy powder surface-treated with palmitic acid.

[Manufacturing Example 2]
<Manufacturing of alloy core particles>
An alloy powder a (copper-nickel powder a) was obtained by the same method as in Production Example 1.

<Silver coating reaction>
A silver coating reaction was carried out on the alloy powder a (copper-nickel powder a) by the same method as in Production Example 1.

<Surface treatment>
The silver-coated alloy powder after the silver-coated reaction was surface-treated by the same method as in Production Example 1. Then, a substantially spherical silver-coated alloy powder surface-treated with palmitic acid was obtained.

<Oxygen reduction treatment>
In this example, the silver-coated alloy powder thus obtained is heated at 200 ° C. for 10 hours in a hydrogen atmosphere (100% hydrogen), and 80 g of the hydrogen-reduced alloy powder is placed in a cutter mill for 20 seconds. Was crushed twice to obtain a silver-coated alloy powder.

[Manufacturing Example 3]
<Manufacturing of alloy core particles>
An alloy powder a (copper-nickel powder a) was obtained by the same method as in Production Example 1.

<Silver coating reaction>
A silver coating reaction was carried out on the alloy powder a (copper-nickel powder a) by the same method as in Production Example 1.

<Oxygen reduction treatment>
In this example, the silver-coated alloy powder thus obtained is heated at 200 ° C. for 10 hours in a hydrogen atmosphere (100% hydrogen), and 80 g of the hydrogen-reduced alloy powder is placed in a cutter mill for 20 seconds. Was crushed twice to obtain a silver-coated alloy powder.

<Surface treatment>
Next, 80 g of the obtained silver-coated alloy powder and 0.24 g of palmitic acid (0.3% by mass based on the silver-coated alloy powder) were placed in a cutter mill and crushed twice for 20 seconds to obtain palmitic acid. A substantially spherical silver-coated alloy powder surface-treated with acid was obtained.

[Manufacturing Comparative Example 1]
<Manufacturing of alloy core particles>
An alloy powder a (copper-nickel powder a) was obtained by the same method as in Production Example 1.

<Silver coating reaction>
The alloy powder a (copper-nickel powder a) was subjected to a silver coating reaction and surface treatment in the same manner as in Production Example 1 to obtain a substantially spherical silver-coated alloy powder surface-treated with palmitic acid.
In this example, the oxygen reduction treatment was not performed either after the production of the alloy core particles or after the silver coating reaction.

[Characteristic evaluation]
For each of the metal powders obtained in Production Examples 1 to 3 and Production Comparative Example 1, the mass ratio of silver in the entire metal powder, the mass ratio of each metal element to the total of (silver and) copper and nickel in the metal powder, The specific surface area BET, TAP density, oxygen content, carbon content, and particle size distribution were determined. More specifically, each characteristic was measured as follows.

Weight ratio of silver (weight method): After dissolving the metal powder with nitric acid, the precipitate of silver chloride (AgCl) produced by adding hydrochloric acid was dried and weighed.
Weight ratio of each metal element to the total of (silver and) copper and nickel: Metal powder (about 2.5 g) is spread in a vinyl chloride ring (inner diameter 3.2 cm x thickness 4 mm), and then tablet-molded and compressed. A metal powder pellet was prepared by applying a load of 100 kN using a machine (model number BRE-50 manufactured by Maekawa Test Mfg. Co., Ltd.), and this pellet was placed in a sample holder (opening diameter 3.0 cm) to be a fluorescent X-ray analyzer. (XRF) Set at the measurement position in (RIX2000 manufactured by Rigaku Co., Ltd.), the measurement atmosphere was reduced to (8.0 Pa), and the X-ray output was 50 kV and 50 mA. The measurement was carried out by automatic calculation with the software of.
Then, from the mass ratio of the metal element obtained here, a value (converted value 1) converted into each mass ratio when the total of copper and nickel was 100% by mass was obtained. Further, when the mass ratio of silver obtained by the gravimetric method is subtracted from 100 mass% and the balance is allocated to copper and nickel at the ratio of the conversion value 1 to make the total of these three elements 100 mass%. The values converted into the mass ratios of each (copper, nickel and silver) were also obtained.

Specific surface area BET: Using a BET measuring instrument (4 Sorb US manufactured by Yuasa Ionics Co., Ltd.), nitrogen gas was flowed into the measuring instrument at 105 ° C. for 20 minutes to degas, and then a mixed gas of nitrogen and helium (mixed gas of nitrogen and helium) ( N _2: 30 vol%, the He: while flowing 70 vol%) was measured by a BET1 point method.

TAP density: Similar to the method described in JP-A-2007-263860, a metal powder layer is filled with metal powder up to 80% of its volume in a bottomed cylindrical die having an inner diameter of 6 mm and a height of 11.9 mm. ^{Is formed, a pressure of 0.160 N / m 2} is uniformly applied to the upper surface of the metal powder layer, and the metal powder is compressed until the metal powder is no longer densely packed, and then the height of the metal powder layer is measured. The density of the metal powder was obtained from the measured value of the height of the metal powder layer and the weight of the filled metal powder, and this density was defined as the TAP density of the metal powder.

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

Carbon content: Measured with a carbon / sulfur analyzer (EMIA-220V manufactured by HORIBA, Ltd.).

Particle size distribution (D ₁₀ , D ₅₀ , D ₉₀ ): Dispersion pressure 5 bar using a laser diffraction type particle size distribution measuring device (Hellos particle size distribution measuring device (HELOS & RODOS (air flow type drying module)) manufactured by SYSTEMTEC). Measured at.

・・・（２）
で求められる。
この式より物体の直径をＤとすると、

・・・（３）
となり、レーザー回折式粒度分布測定装置にて求めたＤ_５０を式（３）のＤに代入することで、比表面積Ｓｍを求めた。 Specific surface area Sm: Obtained by the following formula (1).
Specific surface area Sm = 6 / (ρ × D ₅₀ ) ・ ・ ・ (1)
The equation (1) was calculated as follows. First, assuming that an object is a true sphere, its volume is V, its density is ρ (calculated by composition ratio), and its surface area is S, the specific surface area Sm is

... (2)
Is sought after.
If the diameter of the object is D from this equation,

... (3)
Then, the specific surface area Sm was obtained by substituting _{D 50} obtained by the laser diffraction type particle size distribution measuring device into D of the formula (3).

Density ρ of silver-coated alloy powder: Based on specific gravity of copper, nickel and silver (at room temperature) and composition ratio (each mass ratio when the total of copper, nickel and silver in silver-coated alloy powder is 100% by mass) I asked for it as follows. For example, in Manufacturing Example 1, ρ is obtained as follows.
ρ = (Cu specific density) × (Cu composition ratio) + (Ni specific gravity) × (Ni composition ratio) + (Ag specific gravity) × (Ag composition ratio)
= 8.94 (g / cm ³ ) x 0.622 + 8.908 (g / cm ³ ) x 0.275 + 10.49 (g / cm ³ ) x 0.103
= 9.09 (g / cm ³ )

Tables 1 and 2 below summarize the various parameters obtained by the above-mentioned apparatus or method in Production Examples 1 to 3 and Production Comparative Example 1 of this example. Table 1 is a table summarizing various parameters for the alloy core particle powder. Table 2 is a table summarizing various parameters for the silver-coated alloy powder. In Table 2, Comparative Example 1 is placed above in consideration of the ease of comparison in the table.

[Resistance evaluation]
<Preparation of Conductive Pastes of Examples 1 to 3 and Comparative Example 1>
9.3 g of each metal powder obtained in Production Examples 1 to 3 and Production Comparative Example 1 and 0.82 g of bisphenol F type epoxy resin (Adecaledin EP-491E manufactured by ADEKA Co., Ltd.) as a thermosetting resin, and cured. After mixing 0.041 g of boron trifluoride monoethylamine as an agent, 0.25 g of diethylene glycol monobutyl ether acetate as a solvent, and 0.01 g of oleic acid as a dispersant with a kneading and defoaming machine, three rolls are passed 5 times. Then, diethylene glycol monobutyl ether acetate was added to the obtained kneaded product and mixed to adjust the viscosity at 25 ° C. to about 100 Pa · s, and the conductivity of Examples 1 and 2 and Comparative Example 1 were obtained. A sex paste was obtained.

<Resistance evaluation>
This conductive paste is printed on an alumina substrate by a screen printing method (in a pattern having a line width of 500 μm and a line length of 37.5 mm), and then heated in the air at 200 ° C. for 40 minutes to be cured to form a conductive film (a conductive film). A film thickness of about 20 μm) was formed, and the volume resistivity (initial resistance) of the obtained conductive film was calculated.

[Evaluation of solder wettability and solder biting resistance]
The 2 mm square conductive film (simultaneously formed by screen printing at the time of resistance evaluation) on the alumina substrate formed from the conductive pastes of Examples 1 to 3 and Comparative Example 1 obtained as described above is as follows. The solder wettability and solder bite resistance were evaluated.

<Solder wettability>
After immersing the conductive film formed on the above-mentioned alumina substrate in ESR-250T4 (flux, manufactured by Senju Metal Industry Co., Ltd.), lead-free solder at 260 ° C. (Eco Solder M705 (Sn96.5Ag3Cu0.5 solder)) , (Manufactured by Senju Metal Industry Co., Ltd.)) After immersing in a tank for 1 second, the alumina substrate was pulled up and soldered.
Then, the surface shape of the solder on the 2 mm square conductive film was measured using a laser microscope VK-9710 (manufactured by KEYENCE). Using the obtained height data, the unevenness is measured using the attached software, and it is assumed that the solder adheres to the part where the height threshold is 40 μm or more from the substrate, and the entire area of the upper surface of the conductive film is covered. The area ratio (%) was calculated.
However, in Example 2, since the area ratio increased up to the immersion time of 10 seconds, the area ratio at 10 seconds was evaluated as the wettability.

<Solder bite resistance>
The area ratio to which the solder adhered was determined in the same manner as in the evaluation of the solder wettability except that the solder was immersed in the lead-free solder bath for 10 seconds or 30 seconds.

<Result>
The evaluation results of the above solder wettability and solder bite resistance are shown in Table 3 below together with the above resistance evaluation results.

上記の表３が示すように、実施例１〜３は比較例１に比べ、半田濡れ性及び半田食われ耐性に優れており、更には初期抵抗においても好適な値を示していた。特に実施例１においてはこれらの特性を顕著に発揮した。

As shown in Table 3 above, Examples 1 to 3 were superior in solder wettability and solder biting resistance as compared with Comparative Example 1, and further showed suitable values in the initial resistance. In particular, in Example 1, these characteristics were remarkably exhibited.

[Reference example: Silver-coated copper-nickel-zinc alloy powder]
Carbon powder is added as a reducing agent to a molten metal obtained by heating 34.0 kg of copper, 2.0 kg of nickel and 4.0 kg of zinc to 1200 ° C. in an air atmosphere, and the molten metal is dropped from the lower part of the tundish furnace. High-pressure water (water pressure: 150 MPa, water volume: 160 L / min, pH: 5.8) is sprayed in the air to quench and solidify, and the obtained alloy powder is filtered, washed with water, dried, and crushed. Then, a copper-nickel-zinc alloy powder was obtained.

The copper-nickel-zinc alloy powder thus obtained was subjected to a silver coating reaction in the same manner as in Production Example 1, solution 2 was added, and the reaction solution was stirred for 1 hour, and then stearic acid was added to the reaction solution. It was added at a ratio of 0.3 parts by mass with respect to 100 parts by mass of the coated copper-nickel-zinc alloy powder, stirred for 40 minutes, filtered, washed with water, and dried. As a result, a substantially spherical silver-coated copper-nickel-zinc alloy powder surface-treated with stearic acid was obtained.

For this silver-coated copper-nickel-zinc alloy powder, the mass ratio of each metal element to the total of silver, copper, nickel and zinc in the powder, specific surface area BET, TAP density, oxygen content and carbon content are the same as in the above embodiment. , The particle size distribution was obtained, and the resistance and solder wettability were further evaluated. Regarding the powder characteristics, the above copper-nickel-zinc alloy powder was also measured.

As a result, for the copper-nickel-zinc alloy powder, the specific surface area BET is 0.69 m ² / g, the TAP density is 4.4 g / cm ³ , and the oxygen content is 0.59 mass% (for this reason). O / BET is calculated as 0.85% by mass · g / m ² ), the carbon content is 0.01% by mass, D ₁₀ is 0.8 μm, D ₅₀ is 1.9 μm, and D. ₉₀ was 3.3 μm.

For the silver-coated copper-nickel-zinc alloy powder, the specific surface area BET is 0.38 m ² / g, the TAP density is 5.7 g / cm ³ , and the oxygen content is 0.15% by mass (hence O). / BET is calculated as 0.39% by weight · g / m ² ), the carbon content is 0.19% by weight, D ₁₀ is 0.9 _{μm, D 50} is 2.3 μm, and D _90. Was 4.1 μm. The ratio of copper to the total of copper, nickel and zinc is 85.8% by mass, the ratio of nickel is 5.5% by mass, the ratio of zinc is 8.7% by mass, and copper, nickel, zinc. And the ratio of copper to the total of silver is 76.6% by mass, the ratio of nickel is 4.9% by mass, the ratio of zinc is 7.8% by mass, and the ratio of silver is 10.7% by mass. %, The volume resistance was 120 μΩ · cm, and the solder wettability was 86 area% with a dipping time of 1 second.

Claims (17)

It is a silver-coated alloy powder having a coating layer containing silver on the surface of alloy core particles composed of copper, nickel and unavoidable impurities, and the oxygen content (mass%) of the silver-coated alloy powder is the specific surface area Sm (m ² / g). ) Is 2.5 (mass% · g / m ² ) or less, a silver-coated alloy powder.
The specific surface area Sm is calculated by the following formula (1).
Specific surface area Sm = 6 / (ρ × D ₅₀ ) ・ ・ ・ (1)
Ρ is the specific gravity and composition ratio of copper, nickel and silver in the silver-coated alloy powder (when the total of copper, nickel and silver in the silver-coated alloy powder is 100% by mass, respectively). It is a density (g / cm ³ ) calculated from (mass ratio), and D ₅₀ is a volume-based cumulative 50% particle diameter (μm) obtained by measuring the silver-coated alloy powder with a laser diffraction type particle size distribution measuring device. ). The silver-coated alloy powder according to claim 1, wherein the proportion of copper is 40 to 95% by mass and the proportion of nickel is 5 to 60% by mass in the total 100% by mass of copper and nickel in the alloy core particles. .. The value obtained by dividing the oxygen content (mass%) of the silver-coated alloy powder by the specific surface area BET (m ² / g) measured by the BET 1-point method of the silver-coated alloy powder is 1.50 (mass% g / m). ² ) The silver-coated alloy powder according to claim 1 or 2, which is as follows. The silver-coated alloy powder according to any one of claims 1 to 3, wherein the mass ratio of silver in the silver-coated alloy powder is 1 to 40% by mass. The silver coating according to any one of claims 1 to 4, wherein _{the cumulative 50% particle diameter (D 50} ) on a volume basis measured by the laser diffraction type particle size distribution measuring device of the silver coating alloy powder is 0.1 to 10 μm. Alloy powder. The silver-coated alloy powder according to any one of claims 1 to 5, wherein the amount of oxygen in the silver-coated alloy powder is 0.05 to 0.40% by mass. A conductive paste containing the silver-coated alloy powder and the curable resin according to any one of claims 1 to 6. The conductive paste according to claim 7, wherein the content ratio of the curable resin in the conductive paste is 0.5 to 49% by mass. The curable resin is a phenol resin, a urea resin, a melamine resin, an epoxy resin, an unsaturated polyester resin, a silicone resin, a polyurethane resin, a polyvinyl butyral resin, a polyimide resin, a polyamide resin, a maleimide resin, a diallyl phthalate resin, an oxetane resin, ( Meta) At least one selected from the group consisting of acrylic resin, maleic acid resin, maleic anhydride resin, polybutadiene resin, alkyd resin, amino resin, polylactic acid resin, oxazoline resin, benzoxazine resin and fluororesin. Item 7. The conductive paste according to Item 7. The conductive paste according to any one of claims 7 to 9, wherein the content of the silver-coated alloy powder in the conductive paste is 50 to 98% by mass. An electronic component including an external electrode, wherein the external electrode contains the silver-coated alloy powder and the curable resin according to any one of claims 1 to 6. After immersing the external electrode in the flux, it is immersed in a lead-free solder (having a metal composition of Sn96.5Ag3Cu0.5) at 260 ° C. for 1 second, then the external electrode is pulled up and observed using a laser microscope. The electronic component according to claim 11, wherein the solder adheres to 65 area% or more of the entire upper surface of the external electrode. An electronic device including a substrate, an electric element formed on the substrate, an electronic component according to claim 11 or 12 mounted on the substrate, and a solder member connecting the electronic component and the electric element. A method for producing a silver-coated alloy powder having a coating layer containing silver on the surface of alloy core particles composed of copper, nickel and unavoidable impurities.
A method for producing a silver-coated alloy powder, which comprises a step of performing an oxygen reduction treatment on the powder of the alloy core particles or the silver-coated alloy powder after the coating layer is formed on the surface of the alloy core particles. The step of performing oxygen reduction treatment on the powder of the alloy core particles and
After the step, the step of forming the coating layer on the surface of the alloy core particles and the step of forming the coating layer.
The method for producing a silver-coated alloy powder according to claim 14. The method for producing a silver-coated alloy powder according to claim 14 or 15, wherein the oxygen reduction treatment is hydrogen reduction in an atmosphere containing hydrogen. A method for producing a conductive paste, which comprises a step of mixing the silver-coated alloy powder obtained by the production method according to any one of claims 14 to 16 with a curable resin.