JP2013168375A - Dendrite-like copper powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide new dendrite-like copper powder whose conductivity is further excellent by further developing branches extending from a main shaft to grow dendrite more than in the conventional one.SOLUTION: The present invention suggests dendrite-like copper powder mainly containing copper powder particles, which represents the dendrite shape to be constituted by extension of a plurality of branches from one shaft when copper powder particles are observed by using a scanning electron microscope (SEM), of which the thickness (a) of the shaft is 0.3-5.0 μm, the length b of the longest branch among the branches extended from one shaft is 0.6-10.0 μm.

Description

  The present invention relates to a copper powder that can be suitably used as a material such as a conductive paste, and more particularly to a copper powder containing copper powder particles having a dendritic shape (referred to as “dendritic copper powder”).

  The conductive paste is a fluid composition in which a conductive filler is dispersed in a vehicle composed of a resin binder and a solvent, and is widely used for forming an electric circuit, an external electrode of a ceramic capacitor, and the like.

  This type of conductive paste has a resin-cured type in which conductive filler is pressure-bonded by hardening of the resin to ensure conduction, and organic components are volatilized by firing and the conductive filler is sintered to ensure conduction. There are firing types.

  The former resin-curable conductive paste is generally a paste-like composition containing a conductive filler made of metal powder and an organic binder made of a thermosetting resin such as an epoxy resin, and is heated. As a result, the thermosetting resin is cured and shrunk together with the conductive filler, and the conductive fillers are pressure-bonded through the resin so as to be in contact with each other, thereby ensuring conductivity. This resin curable conductive paste can be processed in a relatively low temperature range from 100 ° C. to at most 200 ° C. and has little thermal damage, and is therefore mainly used for printed wiring boards and heat-sensitive resin boards.

On the other hand, the latter fired conductive paste is a paste-like composition in which a conductive filler (metal powder) and glass frit are generally dispersed in an organic vehicle. By firing at 500 to 900 ° C., organic Conductivity is ensured by volatilization of the vehicle and further sintering of the conductive filler. At this time, the glass frit has a function of adhering the conductive film to the substrate, and the organic vehicle functions as an organic liquid medium for enabling printing of the metal powder and the glass frit.
Firing-type conductive paste cannot be used for printed wiring boards or resin materials because of its high firing temperature, but it can be reduced in resistance because it is sintered and the metal is integrated. It is used for external electrodes.

  In both the resin curable conductive paste and the high-temperature fired conductive paste, silver powder has been conventionally used as a conductive filler, but it is cheaper to use copper powder and migration is less likely to occur. Since the soldering resistance is also excellent, conductive paste using copper powder is being widely used.

  By the way, it is known that the electrolytic copper powder particles obtained by the electrolytic method have a dendritic shape. If the copper powder particles have a dendritic shape, the number of contact points between the particles is larger than that of spherical particles. The characteristics can be enhanced. Therefore, for example, in the case of embedding in a wiring connection hole with a conductive paste in the manufacture of a semiconductor device, it is only necessary to be able to conduct an electric signal. Therefore, a dendrite-like shape can be obtained even with a smaller amount of conductive material. Copper powder particles are expected to be particularly effective.

  With respect to such a dendrite-like copper powder, for example, in Patent Document 1, as a copper powder for a conductive paint that can be soldered, it is a rod shape obtained by pulverizing a dendritic copper powder having a particle shape, and has an oil absorption amount. A copper powder characterized by (JIS K5101) of 20 ml / 100 g or less, a maximum particle size of 44 μm or less, an average particle size of 10 μm or less, and a hydrogen reduction weight loss of 0.5% or less is disclosed.

  In Patent Document 2, fats and oils are added to and mixed with dendritic electrolytic copper powder having an average particle size of 20 to 35 μm and bulk density of 0.5 to 0.8 g / cm 3, and the surface of the electrolytic copper powder is coated with fats and oils. There is disclosed a method for producing fine copper powder, characterized in that it is pulverized and pulverized by an impact plate jet mill.

  Patent Document 3 and Patent Document 4 disclose electrolytic copper powder particles having a dendritic shape as a heat pipe constituent raw material.

  In Patent Document 5, in order to obtain an electrolytic copper powder that can be molded to a higher strength with improved moldability than conventional electrolytic copper powder without unnecessarily developing the branches of the electrolytic copper powder, a current is supplied to the electrolytic solution. In the method for producing electrolytic copper powder in which electrolytic copper powder is deposited by flowing, the electrolytic solution is added with one or more selected from tungstate, molybdate and sulfur-containing organic compound in an aqueous copper sulfate solution A method is disclosed.

Japanese Patent Laid-Open No. 06-158103 JP 2000-80408 A JP 2008-122030 A JP 2009-047383 A JP 2011-58027 A

  In Patent Document 5, when the dendrite is further grown by developing a branch of electrolytic copper powder, the electrolytic copper powder is entangled more than necessary, and agglomeration is likely to occur. A point has been pointed out. However, when dendrite is further grown by developing a tree of electrolytic copper powder, it can be expected that the number of contact points between particles is further increased and the conductive properties can be further enhanced.

  Therefore, the present invention is intended to provide a new dendrite-like copper powder that contains copper powder particles exhibiting dendrite growth suitable for obtaining excellent electrical conductivity, and is further excellent in electrical conductivity.

  The present invention is provided with a single main axis when the copper powder particles are observed using a scanning electron microscope (SEM), and a plurality of branches are obliquely branched from the main axis, and are two-dimensional or three-dimensional. It has a dendrite-like shape, has a main axis thickness a of 0.3 μm to 5.0 μm, and the longest branch length b among the branches extending from the main axis is 0.6 μm to 10.0 μm. A dendrite-like copper powder mainly containing copper powder particles having a dendrite-like shape is proposed.

  The dendrite-like copper powder proposed by the present invention exhibits a dendrite shape having characteristics different from those of conventionally known dendrite-like copper powder, and the dendrite shape is suitable for obtaining excellent conductivity. Compared with conventional products, it is possible to obtain more excellent conductivity. Therefore, the dendritic copper powder proposed by the present invention can be used particularly effectively as a material such as a conductive paste, particularly as a material such as a conductive paste embedded in a wiring connection hole when a semiconductor device is manufactured.

It is a model figure of the particle shape of the copper powder particle which constitutes the dendritic copper powder of the present invention. It is a SEM photograph at the time of observing a part of powder arbitrarily selected from the electrolytic copper powder obtained in Example 1 at 12,000 times magnification using a scanning electron microscope (SEM).

  Hereinafter, although the embodiment of the present invention is described in detail, the scope of the present invention is not limited to the following embodiment.

  The copper powder according to the present embodiment (referred to as “present copper powder”) is a copper powder containing dendritic copper powder particles (referred to as “present copper powder particles”).

(Dendrite-like copper powder particles)
In the present copper powder, “dendritic copper powder particles”, as shown in FIG. 1, have a single main axis when observed with an electron microscope (500 to 20,000 times). This means copper powder particles that have two-dimensional or three-dimensional growth, with multiple branches branching diagonally, with wide leaves gathering together to form a pinecone, and many needle-shaped parts are radial It does not include those that are elongated.

Especially, when this copper powder particle | grain is observed with an electron microscope (500-20,000 times), it is preferable to exhibit the dendrite shape which has the following predetermined characteristics.
It is important that the thickness a of the main shaft is 0.3 μm to 5.0 μm, especially 0.4 μm or more or 4.5 μm or less, especially 0.5 μm or more or 4.0 μm or less. preferable. When the thickness a of the dendrite is 0.3 μm or less, branches are difficult to grow because the main axis is not solid. On the other hand, when the thickness is larger than 5.0 μm, the particles tend to aggregate and become pine cones. End up.
-The longest branch length b (referred to as "branch length b") among the branches extending from the main axis indicates the degree of dendrite growth, and it is important that the length is 0.6 μm to 10.0 μm. In particular, 0.7 μm or more or 9.0 μm or less, more preferably 0.8 μm or more or 8.0 μm or less. If the branch length b is less than 0.6 μm, it cannot be said that the dendrite has grown sufficiently. On the other hand, when the branch length b exceeds 10.0 μm, the fluidity of the copper powder is lowered and the handling becomes difficult.
The number of branches relative to the major axis L of the main axis (number of branches / major axis L) indicates the number of dendrite branches, and is preferably 0.5 / μm to 4.0 / μm. .6 / μm or more or 3.5 / μm or less, more preferably 0.8 / μm or more or 3.0 / μm or less. If the number of branches / major axis L is 0.5 / μm or more, the number of branches is sufficiently large and sufficient contact can be secured, while if the number of branches / major axis L is 4.0 / μm or less, It can prevent that the fluidity | liquidity of copper powder becomes inferior because there are too many branches.

  However, when observed with an electron microscope (500 to 20,000 times), if many of them are occupied by the dendritic particles as described above, the dendritic particles as described above may be used even if particles of other shapes are mixed. The effect similar to the copper powder which consists only of can be acquired. Therefore, from this point of view, when the present silver-coated copper powder is observed with an electron microscope (500 to 20,000 times), the dendrite-like copper powder particles are preferably 80% or more of the total copper powder particles, preferably As long as it occupies 90% or more, non-dendritic copper powder particles that are not recognized as dendritic may be included.

(Oxygen concentration)
If the oxygen concentration of the present copper powder particles is 0.20% by mass or less, the conductivity can be maintained well. Therefore, the oxygen concentration of the present copper powder particles is preferably 0.20% by mass or less, more preferably 0.18% by mass or less, and more preferably 0.15% by mass or less.
In order to control the oxygen concentration of the present copper powder particles to 0.20% by mass or less, the oxygen concentration and the drying temperature in the drying atmosphere may be controlled.

(D50)
The central particle diameter (D50) of the present copper powder, that is, the volume cumulative particle diameter D50 measured by a laser diffraction / scattering particle size distribution measuring apparatus is preferably 5 μm to 50 μm, more preferably 8 μm or more or 45 μm or less, and more preferably 10 μm. More preferably, it is 40 μm or less, and more preferably 25 μm or less. If D50 is 5 μm or more, the viscosity can be easily adjusted, and if it is 50 μm or less, it can be applied to various conductive pastes, which is preferable.

(Specific surface area)
The specific surface area of the copper powder measured by the BET single point method is preferably 0.30 to 1.50 m ² / g. If it is remarkably smaller than 0.30 m ² / g, the branch is not developed and it becomes close to a pinecone to a sphere, so that the dendrite shape of the present invention cannot be exhibited. On the other hand, if it is significantly larger than 1.50 m ² / g, the dendrite branch becomes too thin, and there is a possibility that the branch breaks in the paste processing step, thereby impeding conductivity.
Therefore, the specific surface area as measured by single point method BET of the copper powder is 0.30~1.50m ² / g at and even good properly, inter alia 0.40 m ² / g or more or 1.40 m ² / g or less, Among these, it is more preferable that it is 1.00 m < ² > / g or less especially.

(Production method)
This copper powder can be manufactured by a predetermined electrolytic method.
As an electrolysis method, for example, an anode and a cathode are immersed in a sulfuric acid electrolytic solution containing copper ions, and a direct current is passed through the electrolyte to conduct electrolysis. An example is a method of producing electrolytic copper powder by scraping and collecting by an electric method, washing, drying, and passing through a sieving step as necessary.

When copper powder is produced by the electrolytic method, the copper ions in the electrolyte solution are consumed as copper is deposited, so the copper ion concentration in the electrolyte solution near the electrode plate is reduced, and the electrolytic efficiency decreases as it is. End up. Therefore, normally, in order to increase the electrolysis efficiency, the electrolyte solution in the electrolytic cell is circulated so that the copper ion concentration of the electrolyte solution between the electrodes does not become thin.
However, it has been found that in order to develop the dendrite of each copper powder particle, in other words, in order to promote the growth of branches extending from the main axis, it is preferable that the copper ion concentration in the electrolyte solution near the electrode is low. Therefore, in the production of the present copper powder, the size of the electrolytic cell, the number of electrodes, the distance between the electrodes, and the circulation amount of the electrolytic solution are adjusted, and the copper ion concentration of the electrolytic solution in the vicinity of the electrode is adjusted to be low. It is preferable to adjust so that the copper ion concentration of the electrolyte solution between electrodes is always thinner than the copper ion concentration of the electrolyte solution at the bottom.

Here, when introducing a model case, the size of the electrolytic cell is 2m ³ through 10m ^3, the electrode number is 10 to 40 sheets, when the inter-electrode distance is 5Cm～50cm, copper ion concentration 1 g / Dendrites can be developed and the present copper powder can be obtained by adjusting the circulating amount of the electrolytic solution of L to 50 g / L to 10 to 100 L / min.

In order to adjust the particle size of the dendritic copper powder particles, conditions may be set as appropriate based on common general technical knowledge within the range of the above conditions. For example, if it is intended to obtain dendritic copper powder particles having a large particle size, the copper concentration is preferably set to a relatively high concentration within the above preferred range, and the current density is relatively low within the above preferred range. The density is preferably set, and the electrolysis time is preferably set to a relatively long time within the above preferable range. If it is intended to obtain dendritic copper powder particles having a small particle size, it is preferable to set the respective conditions based on the opposite concept. As an example, the copper concentration may be 1 g / L to 10 g / L, the current density may be 100 A / m ^{2 to} 1000 A / m ² , and the electrolysis time may be 5 minutes to 3 hours.

If necessary, the surface of the electrolytic copper powder particles may be subjected to an oxidation resistance treatment using an organic material to form an organic material layer on the surface of the copper powder particles. It is not always necessary to form the organic layer, but it is more preferable that the organic layer is formed in consideration of the change over time due to oxidation of the copper powder particle surface.
The organic substance used for this oxidation resistance treatment is not particularly limited, and examples thereof include glue, gelatin, organic fatty acid, and a coupling agent.
The oxidation-resistant treatment method, that is, the organic layer forming method may be a dry method or a wet method. In the case of a dry method, a method of mixing an organic substance and a core material with a V-type mixer or the like, and in the case of a wet method, a method of adding an organic substance to a water-core material slurry and adsorbing it on the surface can be exemplified. However, it is not limited to these. For example, after washing the slurry after electrolytic copper powder deposition, a method of adhering the organic substance to the copper powder surface by mixing an aqueous solution containing a copper powder cake and a desired organic substance with an organic solvent is a preferred example.

(Use)
Since this copper powder has excellent conductive properties, it is used as a main constituent material of various conductive materials such as conductive pastes and conductive adhesives, and conductive paints. It can be used suitably.

For example, in order to produce a conductive paste, the copper powder can be mixed with a binder and a solvent, and further, if necessary, a curing agent, a coupling agent, a corrosion inhibitor, etc. to produce a conductive paste.
In this case, examples of the binder include liquid epoxy resins, phenol resins, unsaturated polyester resins, and the like, but are not limited thereto.
Examples of the solvent include terpineol, ethyl carbitol, carbitol acetate, butyl cellosolve and the like.
Examples of the curing agent include 2-ethyl 4-methylimidazole.
Examples of the corrosion inhibitor include benzothiazole and benzimidazole.

The conductive paste can be used to form a circuit pattern on a substrate to form various electric circuits. For example, it is possible to form a printed wiring board, an electric circuit of various electronic components, external electrodes, and the like by applying or printing on a fired substrate or an unfired substrate, heating, pressurizing and baking as necessary.
In particular, the copper powder particles of the present copper powder have particularly developed dendrites, the number of contacts between the particles is increased, and excellent conductive properties can be obtained even if the content of the conductive powder is reduced. It is suitable as a conductive paste material used for the purpose of embedding the inside of a wiring connection hole when manufacturing a semiconductor device.

  When a semiconductor device is manufactured, a large number of wiring grooves (trench) for connecting elements and wiring connection holes (via holes or contact holes) for electrically connecting multilayer wirings are provided. Conventionally, aluminum has been used as a conductive material embedded in these wiring grooves and wiring connection holes, but due to high integration and miniaturization of semiconductor devices, instead of the conventional aluminum, the electrical resistivity is low, Copper having excellent electromigration resistance has attracted attention and is being put to practical use, and a conductive paste containing copper powder as an electric material is used for embedding in wiring connection holes. In this type of application, it is not necessary to energize a large amount of current, and it is sufficient that an electric signal can be energized.

(Explanation of words)
In the present specification, when expressed as “X to Y” (X and Y are arbitrary numbers), “X is preferably greater than X” or “preferably more than Y” with the meaning of “X to Y” unless otherwise specified. The meaning of “small” is also included.
In addition, when expressed as “X or more” (X is an arbitrary number), it means “preferably larger than X” unless otherwise specified, and expressed as “Y or less” (Y is an arbitrary number). In the case, unless otherwise specified, the meaning of “preferably smaller than Y” is included.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

<Observation of particle shape>
With a scanning electron microscope (2,000 times), the shape of 500 particles was observed in 100 arbitrary fields of view, and the thickness of the main axis a (“main axis thickness a”) and the branch extending from the main axis The longest branch length b (“branch length b”) and the number of branches with respect to the major axis of the main axis (“number of branches / major axis L”) were measured, and the average values are shown in Table 1.

<Particle size measurement>
Take a measurement sample (copper powder) in a small amount of beaker, add a few drops of 3% Triton X solution (manufactured by Kanto Chemical Co., Ltd.), and blend it into the powder. 50 mL was added, and then a measurement sample was prepared by dispersing for 2 minutes using an ultrasonic disperser TIPφ20 (manufactured by Nippon Seiki Seisakusho).
This sample for measurement was measured for volume accumulation standard D50 using a laser diffraction / scattering particle size distribution measuring device MT3300 (manufactured by Nikkiso), and is shown in Table 1.

<Measurement of specific surface area>
The specific surface area was measured by the BET single-point method using a monosorb manufactured by Yuasa Ionics, and shown in Table 1 as BET.

<Measurement of oxygen concentration>
The copper powders (samples) obtained in Examples and Comparative Examples were heated and melted in a He atmosphere using “EMGA-820ST” manufactured by Horiba, Ltd., and the oxygen concentration (wt%) was measured. .

<Example 1>
In an electrolytic cell having a size of 2.5 m × 1.1 m × 1.5 m (about 4 m ³ ), 9 cathode plates (1.0 m × 1.0 m) and an insoluble anode plate (DSE (Permelec) Electrode))) is suspended so that the distance between the electrodes is 5 cm, a copper sulfate solution as an electrolytic solution is circulated at 30 L / min, and an anode and a cathode are immersed in the electrolytic solution, and a direct current is supplied thereto. To conduct electrolysis to deposit powdered copper on the cathode surface.
At this time, the electrolytic solution to be circulated was adjusted to a Cu concentration of 5 g / L, a sulfuric acid (H ₂ SO ₄ ) concentration of 100 g / L, and a current density of 100 A / m ² for electrolysis for 1 hour.
During electrolysis, the copper ion concentration of the electrolyte solution between the electrodes was always kept lower than the copper ion concentration of the electrolyte solution at the bottom of the electrolytic cell.

Then, the copper deposited on the cathode surface was mechanically scraped and collected, and then washed to obtain a hydrated copper powder cake equivalent to 1 kg of copper powder. This cake was dispersed in 3 L of water, 1 L of an industrial gelatin (made by Nitta Gelatin Co., Ltd.) 10 g / L aqueous solution was added, stirred for 10 minutes, filtered through a Buchner funnel, washed, and then under reduced pressure (1 × 10 ⁻³ Pa) at 80 ° C. for 6 hours to obtain electrolytic copper powder.
When the electrolytic copper powder thus obtained was observed using a scanning electron microscope (SEM), at least 90% or more of the copper powder particles had one main axis, and a plurality of branches were oblique from the main axis. It was confirmed that it had a dendritic shape that was branched into three-dimensionally.

<Example 2>
An electrolytic copper powder was obtained in the same manner as in Example 1 except that the electrolysis time was 40 minutes and the circulating fluid amount was 20 L / min.
When the obtained electrolytic copper powder was observed using a scanning electron microscope (SEM), at least 90% or more of the copper powder particles had one main axis, and a plurality of branches were oblique from the main axis. It was confirmed that it had a dendritic shape that branched and grew three-dimensionally.

<Example 3>
An electrolytic copper powder was obtained in the same manner as in Example 1 except that the electrolysis time was 40 minutes, the Cu concentration of the electrolytic solution was 1 g / L, and the amount of circulating liquid was 10 L / min.
When the obtained electrolytic copper powder was observed using a scanning electron microscope (SEM), at least 90% or more of the copper powder particles had one main axis, and a plurality of branches were oblique from the main axis. It was confirmed that it had a dendritic shape that branched and grew three-dimensionally.

<Example 4>
In an electrolytic cell having a size of 5.0 m × 1.1 m × 1.5 m (about 8 m ³ ), 19 cathode plates (1.0 m × 1.0 m) and insoluble anode plates (DSE (Permelec) Electrode))) is suspended so that the distance between the electrodes is 10 cm, a copper sulfate solution as an electrolytic solution is circulated at 40 L / min, and an anode and a cathode are immersed in the electrolytic solution, and a direct current is supplied thereto. To conduct electrolysis to deposit powdered copper on the cathode surface.
At this time, electrolysis was carried out for 1 hour by adjusting the Cu concentration of the circulating electrolyte to 5 g / L, the sulfuric acid (H ₂ SO ₄ ) concentration to 200 g / L, and the current density to 200 A / m ² .
During electrolysis, the copper ion concentration of the electrolyte solution between the electrodes was always kept lower than the copper ion concentration of the electrolyte solution at the bottom of the electrolytic cell.

The copper deposited on the cathode surface was mechanically scraped and collected, and then washed to obtain a hydrous copper powder cake equivalent to 1 kg of copper powder. This cake was dispersed in 6 L of water, 2 L of an industrial gelatin (made by Nitta Gelatin) 10 g / L aqueous solution 2 L was added, stirred for 10 minutes, filtered through a Buchner funnel, washed, and then under reduced pressure (1 × 10 ^-3 Pa) at 80 ° C. for 6 hours to obtain electrolytic copper powder.
When the obtained electrolytic copper powder was observed using a scanning electron microscope (SEM), at least 90% or more of the copper powder particles had one main axis, and a plurality of branches were oblique from the main axis. It was confirmed that it had a dendritic shape that branched and grew three-dimensionally.

<Example 5>
An electrolytic copper powder was obtained in the same manner as in Example 4 except that the Cu concentration was 1 g / L, the electrolysis time was 30 minutes, and the circulating fluid amount was 20 L / min.
When the obtained electrolytic copper powder was observed using a scanning electron microscope (SEM), at least 90% or more of the copper powder particles had one main axis, and a plurality of branches were oblique from the main axis. It was confirmed that it had a dendritic shape that branched and grew three-dimensionally.

<Comparative Example 1>
In an electrolytic cell having a size of 2.5 m × 1.1 m × 1.5 m (about 4 m ³ ), 9 cathode plates (1.0 m × 1.0 m) and an insoluble anode plate (DSE (Permelec) Electrode))) is suspended so that the distance between the electrodes is 5 cm, a copper sulfate solution as an electrolytic solution is circulated at 2 L / min, and an anode and a cathode are immersed in this electrolytic solution, and a direct current is supplied to this. To conduct electrolysis to deposit powdered copper on the cathode surface.
At this time, electrolysis was carried out for 5 hours while adjusting the Cu concentration of the electrolyte to be circulated to 100 g / L, the sulfuric acid (H ₂ SO ₄ ) concentration to 100 g / L, and the current density to 80 A / m ² .
During electrolysis, the copper ion concentration in the electrolyte solution between the electrodes was always higher than the copper ion concentration in the electrolyte solution at the bottom of the electrolytic cell.

  The copper deposited on the cathode surface was mechanically scraped and collected, and then washed to obtain a hydrous copper powder cake equivalent to 1 kg of copper powder. This cake was dispersed in 3 L of water, 1 L of an industrial gelatin (made by Nitta Gelatin) 10 g / L aqueous solution was added and stirred for 10 minutes, and then filtered through a Buchner funnel. It was dried for 6 hours to obtain electrolytic copper powder. The particle shape of the obtained electrolytic copper powder was pinecone-like, and the main shaft thickness, branch length, number of branches / long diameter L could not be measured.

<Comparative example 2>
In an electrolytic cell having a size of 5.0 m × 1.1 m × 1.5 m (about 8 m ³ ), 19 cathode plates (1.0 m × 1.0 m) and insoluble anode plates (DSE (Permelec) Electrode))) is suspended so that the distance between the electrodes is 10 cm, a copper sulfate solution as an electrolytic solution is circulated at 150 L / min, and an anode and a cathode are immersed in the electrolytic solution, and a direct current is supplied thereto. To conduct electrolysis to deposit powdered copper on the cathode surface.
At this time, the electrolytic solution to be circulated was adjusted to a Cu concentration of 70 g / L, a sulfuric acid (H ₂ SO ₄ ) concentration of 200 g / L, and a current density of 90 A / m ² for electrolysis for 6 hours.
During electrolysis, the copper ion concentration of the electrolyte solution between the electrodes was equal to the copper ion concentration of the electrolyte solution at the bottom of the electrolytic cell.

  The copper deposited on the cathode surface was mechanically scraped and collected, and then washed to obtain a hydrous copper powder cake equivalent to 1 kg of copper powder. This cake was dispersed in 6 L of water, 2 L of an industrial gelatin (made by Nitta Gelatin Co., Ltd.) 10 g / L aqueous solution 2 L was added, stirred for 10 minutes, filtered through a Buchner funnel, washed, and then washed at 120 ° C. in an air atmosphere. It was dried for 5 hours to obtain electrolytic copper powder. The particle shape of the obtained electrolytic copper powder was pinecone-like, and the main shaft thickness, branch length, number of branches / long diameter L could not be measured.

(Discussion)
Considering the above examples and the test results conducted so far, the thickness a of the main shaft is 0.3 μm to 5.0 μm, and the longest branch length among the branches extending from the main shaft is 0. It was found that if the copper powder particles have a dendrite shape of .6 μm to 10.0 μm, the dendrite has grown sufficiently and sufficiently to obtain excellent conductivity, and excellent conductivity can be obtained.

Claims (3)

  When observing copper powder particles using a scanning electron microscope (SEM), it has a single main axis, and a plurality of branches branch obliquely from the main axis and grow in two or three dimensions. It has a dendritic shape and has a main axis thickness a of 0.3 μm to 5.0 μm, and a longest branch length b among the branches extending from the main axis is 0.6 μm to 10.0 μm. Dendritic copper powder containing copper powder particles exhibiting   The copper powder particles having a dendritic shape according to claim 1, wherein the number of branches (the number of branches / long diameter L) is 0.5 / μm to 4.0 / μm with respect to the major axis L of the main axis. Item 4. A dendrite-like copper powder according to Item 1.   The dendrite-like copper powder according to claim 1 or 2, wherein the oxygen concentration is 0.20% or less.