JP2000340030A - Bonded copper particles and powder for conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain copper particles.powder showing high conductivity when dispersed in resin by preparing joined copper particles for conductive paste joined in neck parts of unit particles of the specified number of particles. SOLUTION: Two or more unit particles are joined. Preferably, the diameters of the unit particles are 0.5-10 μm, the diameter of the neck part is smaller than the diameter of unit particles on both sides of neck part, and copper powder for conductive paste is prepared with joined copper particles formed by joining two or more unit particles in the neck parts and unit particles having no neck part, and the number of the joined copper particles is 20-80% of the whole copper particles. Copper powder is manufactured in such a process that a copper salt aqueous solution and an alkali agent are reacted to deposit copper hydroxide, a reducing agent is added to suspension of the deposited copper hydroxide to intermediately reduce to cuprous oxide, and the cuprous oxide is finally reduced to metallic copper with a reducing agent in water, and in this manufacturing method, preferably, a process depositing copper hydroxide is conducted under an oxygen-containing atmosphere, and copper hydroxide is deposited in a aqueous solution having an iron concentration of 50 ppm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to metallic copper particles / powder for a conductive paste from which a conductive paste having good conductive performance can be obtained.

[0002]

2. Description of the Related Art For example, when a thick film circuit board is manufactured by screen-printing a conductive paste on an insulating substrate, a silver-based paste has been mainly used as the conductive paste.
Recently, copper-based pastes have also been used. This is because the copper-based paste has the following advantages over the silver-based paste.

(1) It is difficult to cause a short circuit because migration hardly occurs. (2) Since the conductor resistance and high-frequency loss are small, the circuit can be miniaturized. (3) High reliability due to excellent solder resistance. (4) Cost reduction is possible.

[0004] A copper paste having such advantages can be obtained by dispersing copper powder having a particle size of about 0.1 to 10 µm in a vehicle (resin).

As a method for producing copper powder, there are known a mechanical pulverizing method, an atomizing method in which molten copper is sprayed, an electrolytic deposition method on a cathode, an evaporation deposition method, a wet reduction method, and the like. Although each of these has its advantages and disadvantages, the wet reduction method is a main stream in the production of copper powder for conductive paste, since fine powder having a particle size suitable for paste can be obtained relatively easily. JP-A-4-116109, JP-A-2-197
No. 012 and Japanese Unexamined Patent Publication No. 62-99406 describe a method for producing copper powder by a wet reduction method.

[0006]

The performance as a copper-based paste can be evaluated from various viewpoints, but when used as a conductive paste, it is basically important to have excellent conductivity. Even when metallic copper powder of the same purity is dispersed in a resin, the electric resistance also shows different values due to differences in particle size distribution, particle shape, and the like.
In order to reduce the electrical resistance, it is important that the particles are in close contact with each other, in other words, that the copper particles are dispersed at a high filling rate in the resin so that the contact interface between the particles increases. Of course it is possible. However, it is not easy in practice to realize other properties required for the conductive paste, for example, to maintain appropriate fluidity and viscosity and to have appropriate strength.

[0007] In the conventional method of producing copper powder by the wet reduction method,
The particle size of the obtained copper powder is often determined empirically, and the distribution of the particle size generally increases as the particle size increases. Therefore, it was practically impossible to control the production method so as to obtain a copper powder that can be filled into a resin with a high filling rate and that has a large contact interface between particles.

An object of the present invention is to solve such a problem and to provide copper particles / powder having a high conductivity (low electric resistance) when dispersed in a resin.

[0009]

According to the present invention, there is provided a bonded copper particle for a conductive paste comprising two or more unit particles, preferably two or more and twenty or less unit particles bonded together with a neck portion. I do. Particularly, the particle size is 0.5 to 10 μm
Provided is a bonded copper particle for a conductive paste in which 2 to 20 unit particles having a degree are bonded to each other with a neck in an arbitrary three-dimensional direction.

Here, the neck portion refers to a portion where the unit particles are bonded to each other, and the diameter of the neck is smaller than at least one of the unit particles on both sides of the neck portion. It is smaller than the particle size of both unit particles on both sides. According to the present invention, there is provided a copper powder for a conductive paste comprising the bonded copper particles having such a neck portion and the unit particles having no neck portion. In this case, it is desirable that the number of bonded copper particles having a neck portion occupies 20 to 80% of the whole. By dispersing such metal copper powder in a resin, a conductive paste having good electric conductivity can be obtained. The resin can be a thermosetting resin such as a phenolic resin.

Such a metallic copper powder is prepared by reacting an aqueous solution of a copper salt with an alkali agent to add a reducing agent to a suspension in which copper hydroxide is precipitated, and intermediate-reduced to cuprous oxide, and further reduced. In the method for producing copper powder that is finally reduced to metallic copper in water with an agent, the step of precipitating copper hydroxide is carried out in an oxygen-containing gas atmosphere. The production can be advantageously carried out in an aqueous solution having an Fe concentration of 50 ppm or less, and further by blowing an oxygen-containing gas into the suspension of cuprous oxide after the intermediate reduction.

[0012]

1 and 2 show electron micrograph images (SEM images) of the copper metal powder according to the present invention obtained in the following Examples.
FIG. 2 is an enlarged view of the central part of FIG. The central copper particles in FIG. 2 have a particle size of 2.5 to 5 μm.
It can be seen that seven unit particles of the order are joined with a neck in a three-dimensional random direction, and each neck has a diameter smaller than the diameter of the unit particles on both sides of the neck.
And, besides such bonded copper particles of seven unit particles,
As can be seen in FIG. 1, one unit particle (independent without joining), two joined, three joined,... N joined (in FIG. 1, n is Up to about 20
About). In any case, the neck is different from the one where the particles are only in point contact with each other.
Unit particles are bonded with a certain bonding area,
It has a neck strength such that it does not separate at the neck under natural impact such as when the powder flows. It was found that when a conductive paste was prepared from copper powder containing bonding copper particles bonded with such a neck portion, the electrical resistance was significantly lower than that without the bonding copper particles.

FIGS. 3 and 4 are electron micrograph images (SEM images) of the metallic copper powder obtained by the comparative method described later, and FIG.
It is an enlargement of the one slightly above the center. It can be seen that this copper powder has no bonded copper particles having a neck portion smaller in diameter than the particle size, and those having a particle size of 2 to 10 μm in a substantially spherical shape (ball shape) are almost uniformly distributed. The average particle size is about 6.0 μm.

When the electric resistance (volume resistance of the dried coating film) of the paste in which the same amount of both metal copper powders and the same resin were dispersed in the same resin was measured under the same conditions, as shown in the examples described later, the former paste was used. Is 3.12 × 10 ⁻³ Ω · cm and the latter paste is 2.76 × 10 ⁻² Ω · cm, and the former shows a value smaller by one order and has remarkably good conductivity. Although the reason is not exactly known, the connection between the unit particles is assured because of the large number of bonded copper particles.
Therefore, the number of contact interfaces between the particles increases, and the smaller copper particles or single unit particles intervene between the bonded copper particles, so that the resin can be better filled as a whole. Is mentioned. However, even in the former case, it is preferable to use a bonded copper particle in which the number of bonded unit particles exceeds 20, since the number of necks is too large, the dispersibility in the resin becomes inferior, and a state of aggregation occurs. is not. Similarly, dispersibility may be inferior if it is composed of only bonded copper particles. For example, if the number of bonded copper particles exceeds 80% of the total, the dispersibility will be poor, and it is better that independent unit particles exist. The number of copper particles should be in the range of 20-80% of the whole. Further, it is preferable that the unit particles forming the bonded copper particles have a particle size of about 0.5 to 10 μm. On the other hand, when the latter is made of copper particles without a neck (ball-shaped), the contact interface between the particles is the same as that of the former, even if it has a good particle size distribution for filling. As a result, the conductivity will be inferior to that of the former.

The metal copper powder in which bonded copper particles having an appropriate number of necks are distributed as in the former method is further improved by controlling the atmosphere during the initial copper hydroxide production process in the production of metal copper powder by the wet reduction method. Was found to be able to be produced by controlling impurities in the process of producing the copper hydroxide. That is,
A conventional method in which a reducing agent is added to a suspension in which copper hydroxide is precipitated by reacting an aqueous solution of a copper salt with an alkali agent to intermediately reduce to cuprous oxide, and finally reduce to metallic copper in water with a reducing agent. In the production of copper powder, the process of precipitating copper hydroxide was previously performed under an inert atmosphere such as nitrogen, but it can be changed to a process performed in an oxygen-containing gas, typically air.
Further, M coexisting in the solution for precipitating the copper hydroxide is used.
It was found that when the concentration of impurities such as g, Ca, Zn, Na, Al, and Fe was reduced, bonded copper particles having the above-described number of necks could be obtained. In addition, an oxygen-containing gas, typically air, is blown into the cuprous oxide suspension after the intermediate reduction to cuprous oxide and before the final reduction to metallic copper. It was also found that the particle size and particle size distribution of the resulting copper powder could be controlled.

More specifically, in the step of reacting an aqueous solution of a copper salt with an alkali agent to precipitate copper hydroxide, an aqueous solution of copper sulfate is used as the aqueous solution of copper salt, and an aqueous solution of NaOH is used as the alkali agent. It can be used normally, and in some cases, the former may be an aqueous solution of copper chloride, copper carbonate, copper nitrate, etc., and the latter can be used as long as it has no influence on other substances. Precipitation of copper hydroxide by separately preparing a copper salt aqueous solution and an alkaline aqueous solution having a predetermined concentration and mixing the two solutions and immediately stirring the mixture vigorously, or by continuously adding the aqueous alkali solution to the copper salt aqueous solution with stirring. The reaction can proceed, but when this atmosphere is changed from the conventional inert gas atmosphere to an oxygen-containing gas atmosphere (air) to precipitate copper hydroxide, the intermediate reduction , Nitrous oxide, copper of a relatively large particle size,
Typically, cuprous oxide having a particle size of about 0.5 to 1.5 μm is obtained. On the other hand, when copper hydroxide is precipitated under the same conditions except that a nitrogen atmosphere is used, cuprous oxide having a small particle size of about 0.3 μm is obtained. In the case of cuprous oxide having such a small particle size, it is difficult to obtain metallic copper powder having the above-mentioned neck.

At this time, Mg, Ca, Zn, N
If the concentration of impurities such as a, Al, and Fe is high, it is difficult to obtain cuprous oxide having such a large particle size. In particular, Fe in the liquid has a strong effect of preventing obtaining cuprous oxide having a large particle size. Therefore, the concentration of these impurities should be as low as possible, and the content of Fe should be 50 ppm or less, and the total impurities should be 70 ppm or less, preferably 50 ppm or less. Such impurities are usually entrained in the starting copper salt, and it is therefore advisable to use a copper salt of the highest purity possible.

When a reducing agent is added to the precipitated copper hydroxide suspension to reduce (intermediately reduce) cuprous oxide, glucose (glucose) can be used as the reducing agent. This intermediate reduction step is preferably performed while raising the temperature in an inert gas atmosphere. After the completion of the intermediate reduction treatment, the atmosphere gas is replaced with an oxygen-containing gas, and the oxygen-containing gas is preferably bubbled in the liquid.

By performing such an oxidation treatment after the intermediate reduction, the pH of the solution becomes 5 to 9. However, as the amount of the oxygen-containing gas to be blown in increases, the particle size of the copper unit particles at the time of final reduction increases. Tends to be large. The blowing amount of the oxygen-containing gas is determined by the flow rate and the blowing time. By adjusting the flow rate and the blowing time, the particle size of the unit particles can be controlled. The width of the particle size distribution is narrowed to obtain unit particles with a uniform particle size.
It turned out to be a ball. It is preferable to adjust the flow rate and the blowing time so that the oxygen-containing gas is blown at a rate of at least 0.1 mole or more per mole of copper in the solution. The upper limit of the blowing amount is not particularly limited. However, even if the blowing amount is too large, the effect is saturated. Therefore, depending on the blowing method, when the oxygen amount is 20 mol or less per mol of copper in the liquid. Depending on the case, it may be 10 mol or less. As the oxygen-containing gas to be blown, the use of air is most convenient. Unless otherwise specified, air at room temperature may be blown into the suspension at room temperature. Of course, oxygen-enriched air or pure oxygen gas can also be used.

Next, the suspension was decanted under an inert gas atmosphere, and the supernatant was removed to collect a precipitate, and the precipitate was suspended in fresh water.
Final reduction to metallic copper using hydrazine hydrate as reducing agent. The metallic copper in the liquid thus obtained is separated from the liquid, and is subjected to a surface treatment for imparting oxidation resistance or dried without being subjected to the method, thereby obtaining a metallic copper powder having a neck according to the present invention. be able to.

Therefore, according to the present invention, a reducing agent is added to a suspension in which copper hydroxide is precipitated by reacting an aqueous solution of a copper salt with an alkali agent, intermediate reduction is performed to cuprous oxide, and then reducing agent is added. In the method for producing copper powder which is finally reduced to metallic copper in water by water, the step of precipitating copper hydroxide is carried out in an oxygen-containing gas atmosphere, and the F
The present invention provides a method for producing copper powder comprising metallic copper particles having a neck, characterized in that the e concentration is set to 50 ppm or less, and furthermore, an intermediate reduction to cuprous oxide is performed and then an oxidation treatment is performed by blowing an oxygen-containing gas. .

[0022]

EXAMPLES Example 1 The following aqueous copper sulfate solution A and aqueous alkali solution B were prepared. Copper sulfate aqueous solution A: [CuSO ₄ .5H ₂ O: 0.6925 kg] + [pure water:
2.20 Kg] Alkaline aqueous solution B: [48.1% NaOH aqueous solution: 0.545 Kg] +
[Pure water: 4.15 kg]

The alkaline aqueous solution B maintained at a temperature of 27 ° C.
Then, the entire amount of the aqueous solution of copper sulfate A at a temperature of 29 ° C. is added in the air atmosphere, followed by vigorous stirring. The Fe concentration in the liquid is 50 ppm or less, and other impurities are present only in traces. The temperature of the liquid A + B rises to 32 ° C. due to heat generation, and a suspension in which copper hydroxide is precipitated is obtained. The pH of this solution is 13.2. As for the mixing ratio of the liquid A and the liquid B, the equivalent ratio of caustic soda to copper in the liquid is 1.20.

To a total amount of the obtained copper hydroxide suspension, a glucose solution obtained by dissolving 0.9935 kg of glucose in 1.41 kg of pure water was added.
After heating to 0 ° C., hold for 15 minutes. The pH of the liquid at this time is 7.8. This treatment is performed in a nitrogen atmosphere.

Next, air is bubbled through the solution at a flow rate of 0.7 liter / min for 420 minutes to oxidize the solution. As a result, the pH of the liquid becomes 5.76. The particle size of cuprous oxide is approximately 0.7 μm.

After the suspension was allowed to stand in a nitrogen atmosphere for 2 days, the supernatant (pH 5.99) was removed, and almost all of the precipitate of cuprous oxide was collected, and 0.55 kg of pure water was added thereto. Add. 0.074 kg of hydrazine hydrate is added in several portions to the total amount of the cuprous oxide suspension. Due to the exothermic reaction, the temperature of the liquid is raised from 50 ° C. to finally 80 ° C., and the reaction is completed. After the completion of the reaction, the suspension is subjected to solid-liquid separation, a powder is collected, and dried in a nitrogen atmosphere at 120 ° C. to obtain a copper powder.

Electron microscope SE of the copper powder obtained by this method
The M images are shown in FIGS. As described in the text, this copper powder is a copper powder containing bonded copper particles in which unit particles having a particle size of 2.5 to 5.0 μm are bonded together with a neck. The number of copper particles was approximately 40% of the total particles.

According to the same processing method as that of the conventional copper-based conductive paste, 30 g of this copper powder and 7.5 g of a phenolic resin are kneaded to prepare a paste, which is formed into a film having a thickness of 30 μm on a glass substrate. After drying, the electrical resistance was measured. As a result, the volume resistance of the coating film was 3.12 × 10 ⁻³ Ω.
Cm.

Comparative Example 1 The following aqueous copper sulfate solution A and alkaline aqueous solution B 'were prepared. Copper sulfate aqueous solution A: [CuSO ₄ .5H ₂ O: 0.6925 kg] + [pure water:
2.20 Kg] Alkaline aqueous solution B: [NaOH aqueous solution with a concentration of 49.0%: 0.541 kg] +
[Pure water: 4.15 kg]

To the aqueous alkali solution B ′ maintained at a temperature of 27 ° C., the entire aqueous copper sulfate solution A at a temperature of 29 ° C. is added in a nitrogen gas atmosphere, followed by vigorous stirring. Fe concentration in liquid is 50p
pm or less, and only traces of other impurities are present. The temperature of the solution A + B 'rises to 32.9 ° C. due to heat generation, and a suspension in which copper hydroxide is precipitated is obtained. The pH of this solution is 12.9. As for the mixing ratio of the liquid A and the liquid B ', the equivalent ratio of caustic soda to copper in the liquid is 1.19.

To the total amount of the obtained copper hydroxide suspension, a glucose solution in which 0.9935 kg of glucose was dissolved in 1.41 kg of pure water was added.
After heating to 0 ° C., hold for 15 minutes. The pH of the liquid at this time is 7.8. This treatment is performed in a nitrogen atmosphere.

Next, air is bubbled into the liquid at a flow rate of 0.7 liter / min for 420 minutes to oxidize the liquid. As a result, the pH of the solution becomes 5.80. The particle size of cuprous oxide is approximately 0.3 μm.

After the suspension was allowed to stand in a nitrogen atmosphere for 2 days, the supernatant (pH 6.02) was removed, and almost all of the precipitate of cuprous oxide was collected, and 0.55 kg of pure water was added thereto. Add. 0.074 kg of hydrazine hydrate is added in several portions to the total amount of the cuprous oxide suspension. Due to the exothermic reaction, the temperature of the liquid is raised from 50 ° C. to finally 80 ° C., and the reaction is completed. After the completion of the reaction, the suspension is subjected to solid-liquid separation, a powder is collected, and dried in a nitrogen atmosphere at 120 ° C. to obtain a copper powder.

Electron microscope SE of copper powder obtained by this method
The M images are shown in FIGS. As described in the text, the copper powder is composed of ball-shaped particles having an average particle diameter of approximately 6.0 μm and has no neck.

In the same manner as in Example 1, 30 g of this copper powder
Was mixed with 7.5 g of a phenolic resin to prepare a paste, which was coated on a glass substrate with a thickness of 30 μm, dried, and then measured for electrical resistance. As a result, the volume resistance of the coating film was 2.76 × 10 ⁻² Ω · cm.

[0036]

As described above, according to the present invention,
A copper powder for a conductive paste capable of forming a coating film having excellent electric conductivity can be provided.

[Brief description of the drawings]

FIG. 1 is an electron micrograph image of metallic copper powder obtained in Example 1 of the present invention.

FIG. 2 is an electron micrograph image of an enlarged particle portion in the center of FIG.

FIG. 3 is an electron micrograph image of the metallic copper powder obtained in Comparative Example 1 of the present invention.

FIG. 4 is an electron micrograph image in which a particle portion slightly above the central portion in FIG. 3 is enlarged.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05K 3/12 610 H05K 3/12 610B // B22F 1/00 B22F 1/00 L B23K 35/30 310 B23K 35/30 310C (72) Inventor Hiromasa Miyoshi 1-8-2 Marunouchi, Chiyoda-ku, Tokyo F-term in Dowa Mining Co., Ltd. 4J038 DA041 EA011 HA066 KA20 NA20 4K017 AA03 BA05 CA07 DA01 DA07 EH03 EH16 FB05 4K018 AA03 BA02 BB04 BB10 BC09 BD10 HA10 KA33 5E343 BB24 BB72 GG13 5G301 DA06 DA55 DD01 DE10

Claims (11)

[Claims] 1. Bonded copper particles for a conductive paste comprising two or more unit particles bonded together with a neck portion. 2. Bonded copper particles for a conductive paste comprising two or more and twenty or less unit particles bonded together with a neck portion. 3. The bonded copper particle according to claim 1, wherein the diameter of the unit particle is 0.5 to 10 μm. 4. The bonded copper particles for a conductive paste according to claim 1, wherein the diameter of the neck portion is smaller than the diameter of the unit particles on both sides of the neck portion. 5. A copper powder for a conductive paste comprising a bonded copper particle formed by bonding two or more unit particles with a neck portion and a unit particle having no neck portion. 6. The copper powder for a conductive paste according to claim 5, wherein the number of bonding copper particles is 20 to 80% of the whole. 7. A reducing agent is added to a suspension in which an aqueous copper salt solution and an alkali agent are reacted to precipitate copper hydroxide, and the intermediate is reduced to cuprous oxide. A method for producing copper powder having bonded copper particles, wherein the step of precipitating copper hydroxide is carried out in an oxygen-containing gas atmosphere in the method for producing copper powder to be finally reduced in (1). 8. The method for producing copper powder according to claim 7, wherein the step of depositing copper hydroxide is performed in an aqueous solution having an Fe concentration of 50 ppm or less. 9. The method for producing copper powder according to claim 7, wherein an oxygen-containing gas is blown into the suspension of cuprous oxide after the intermediate reduction. 10. A conductive paste obtained by dispersing the copper powder for a conductive paste according to claim 1 in a resin. 11. The conductive paste according to claim 10, wherein the resin is a phenolic resin.