JP2002115001A - Fine copper powder for forming circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide circuit-forming fine copper powders having sharp particle- size distribution as well as an excellent filling property in conductive paste, by using the conductive paste of which a coated film having high film density can be formed and resultantly sintered density can be increased by sintering, a fine pattern can be formed and wiring density can be increased. SOLUTION: The fine copper powder for forming circuit satisfies the following conditions: when the average particle size by SEM observation and the standard deviation of particle size are represented by x (μm) and σ, respectively, the tap density (g/cm3) and the average particle size x satisfy inequality (tap density)>=4.83-1.99exp(-0.29x) and also the coefficient of variation CV determined by equation CV(%)=(σ/x)×100 becomes <=40%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine copper powder for forming a circuit, and more particularly, to a fine copper powder having an excellent filling property in a conductive paste and a sharp particle size distribution. By using a conductive paste containing copper fine powder, it is possible to form a coating film having a high film density,
The present invention relates to a copper fine powder for a conductive copper paste suitable for forming a circuit.

[0002]

2. Description of the Related Art Conventionally, as a method of forming an electric circuit (wiring conductor) for a wiring board or an electronic component, a conductive metal powder such as gold, silver, palladium, copper, or aluminum, a resin,
A so-called firing type paste method, in which a vehicle made of a solvent or the like, and a conductive paste formed by mixing an arbitrary component glass frit or the like into a paste form are applied or printed on the insulating substrate surface and fired to form a thick film, and Solvent-free thermosetting conductive paste made by mixing those conductive metal powders with resin and curing agent is applied or printed on the surface of the insulating substrate, or filled into via holes and heat-cured by heating and curing. The mold paste method is generally known.

[0003] Copper powder is relatively inexpensive;
In recent years, it has been widely used as a material for conductive pastes in place of noble metal powders such as gold, silver, and palladium because of the advantage of having excellent migration resistance and the like. The requirement for copper powder for conductive paste is that it is composed of copper fine particles having a uniform particle size, does not contain agglomerates or has low agglomeration degree (high dispersibility), And the like.

[0004] As such copper powder, generally,
Copper fine powder composed of copper fine particles having a particle diameter of 10 μm or less has been demanded. Recently, in order to cope with miniaturization of electronic equipment and high wiring density, it is composed of finer copper fine particles having a particle diameter of 1 μm or less. Demand for copper fine powder is increasing.

[0005] Conventionally, as a method for producing fine copper powder, a method of treating an aqueous solution of a copper salt or the like with a reducing agent such as hydrazine to reduce the copper salt or the like, or a method of heating a copper salt or a copper oxide in a reducing atmosphere. A reduction method, a method in which copper chloride vapor is treated with a reducing gas to reduce copper chloride, and the like are known. Among these methods, the reduction method using hydrazine is a method excellent in productivity in that it can be processed under atmospheric pressure.

[0006]

However, with respect to the copper fine powder obtained by the above-mentioned prior art, even if the dispersion of the particle diameter is large or the dispersion of the particle diameter is small, the conductive paste is not used when preparing the conductive paste. However, there are drawbacks such as low fillability of the copper fine powder therein, and the requirements for copper fine powder for conductive pastes have not been sufficiently satisfied. Further, in the copper fine powder according to the prior art, as the average particle diameter becomes smaller, the tap density becomes lower, and therefore, the filling property in the conductive paste becomes lower,
In order to cope with higher wiring density, there is a problem that it is difficult to use fine powder.

As described above, in the case of copper fine powder for circuit formation which can be used as a raw material such as a so-called conductive paste for forming an electric circuit (wiring conductor) for a wiring board or an electronic component, etc. It is important that the copper fine powder has a high filling property and a sharp particle size distribution. An object of the present invention is to provide a circuit-forming copper fine powder having excellent filling properties in a conductive paste as described above and having a sharp particle size distribution.

[0008]

Means for Solving the Problems The present inventors have analyzed various test data in order to achieve the above-mentioned object, and as a result of diligent examination, the tap density is relatively higher than the average particle diameter. If it is a specific copper fine powder having a specific particle size distribution,
The inventors have found that the above-mentioned problems can be solved, and have completed the present invention.

That is, the copper fine powder for forming a circuit of the present invention is
When the average particle diameter by EM observation is x (μm) and the standard deviation of the particle diameter is σ, the tap density (g / cm ³ ) and the average particle diameter x satisfy the following expression (1). And the coefficient of variation CV obtained by the following equation (2) is 40%
It is characterized by the following. (Tap density) ≧ 4.83-1.99 exp (−0.29x) {(1) CV (%) = (σ / x) × 100} (2)

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the copper fine powder for circuit formation of the present invention, the tap density and the average particle diameter x are expressed by the following formula (1).
Needs to be satisfied. (Tap density) ≧ 4.83-1.99 exp (−0.29x) ‥‥ (1) When the tap density is smaller than the value calculated by the formula on the right side, the copper fine powder is compared with the average particle diameter. The tap density is relatively low, the cohesion is relatively high (the dispersibility is relatively low), and the filling property in the conductive paste is inferior. A coating film having a relatively low density is formed, and as a result, the sintering density during sintering becomes relatively low, which is inconvenient for forming a circuit.

Conversely, when the tap density is higher than or equal to the value calculated by the equation on the right side, the copper fine powder has a relatively higher tap density and a lower cohesion degree than the average particle diameter. It is excellent in the filling property in the conductive paste because it is low (the dispersibility is relatively high). When the conductive paste containing such copper fine powder is used, a coating film having a relatively high film density is formed. As a result, the firing density during firing is relatively high, which is convenient for circuit formation.

As described above, the copper fine powder of the present invention has a relatively low agglomeration degree (has a relatively high dispersibility) and therefore has excellent filling properties in a conductive paste. Low viscosity at the time. That is, the copper fine powder of the present invention has a lower viscosity of the conductive paste when the filling concentration of the copper fine powder is the same as compared with the conventional copper fine powder, and conversely, when the viscosity of the conductive paste is the same, The filling concentration of the fine powder can be increased. Since the conductive paste having a low viscosity has excellent filling properties into via holes, it is particularly suitable for forming via holes in a resin substrate for a multilayer printed wiring board. This is particularly useful when forming a circuit. In addition,
In the copper fine powder for circuit formation of the present invention, the tap density and the average particle diameter x preferably satisfy the following expression (3). (Tap density) ≧ 4.81-1.60exp (−0.49x) ‥‥ (3)

In the fine copper powder for circuit formation according to the present invention, the average particle diameter by SEM observation is x (μm),
When the standard deviation of the particle diameter is σ, it is necessary that the coefficient of variation CV determined by the following equation (2) is 40% or less. CV (%) = (σ / x) × 100 (2) When the CV exceeds 40%, the copper fine powder is broad because the particle size distribution is broader and the particle size varies. Is not suitable for forming fine patterns and increasing the wiring density.

Conversely, when the CV is 40% or less, the conductive paste containing such fine copper powder can form fine patterns because the particle size distribution is sharper and the variation in particle size is small. It is suitable for increasing the wiring density. The smaller the CV, the sharper the particle size distribution,
It is preferably at most 35%, more preferably at most 30%.

The copper fine powder for circuit formation of the present invention has an average particle diameter of 0.1 to 10 μm by SEM observation.
The conductive paste containing such fine copper powder is particularly suitable as a conductive paste for forming a circuit.

Further, in the copper fine powder for circuit formation of the present invention, it is preferable that the particle surface is coated with an organic compound. Examples of the organic compound used for this coating include saturated fatty acids, unsaturated fatty acids, benzotriazole and derivatives thereof, amide amine salts and amine salts of high molecular weight polyester acids, phosphate surfactants, and amines of polyether phosphate. And the like.

As described above, in the copper fine powder whose particle surface is coated with an organic compound, the tap density of such coated copper fine powder becomes relatively high as the amount of the organic compound coated increases. In addition, the filling property of the copper fine powder in the conductive paste is relatively increased, the oxidation of the copper fine powder is prevented, and the compatibility between the copper fine powder and the vehicle when preparing the conductive paste is improved. In addition, a coating film having a relatively high film density can be formed by using the conductive paste containing the copper fine powder coated as described above, and as a result, the firing density can be relatively increased by firing. It is easy to form a fine pattern and increase the wiring density.

The additional effects as described above are clearly exhibited when the coating amount of the organic compound is 0.01% by mass or more based on the mass of copper, and is remarkably exhibited when the coating amount is 0.05% by mass or more. . However, when the coating amount of the organic compound is further increased, and the paste is prepared using the copper fine powder having the increased coating amount of the organic compound, the dispersibility of the copper fine powder is hindered, and the viscosity of the paste is reduced. Undesirably increases. Therefore, the coating amount of the organic compound is not more than 0.1 based on the mass of copper.
It is preferably from 0.01 to 5% by mass, and more preferably from 0.05 to 1% by mass.

Next, a preferred method for producing the copper fine powder for circuit formation of the present invention will be described. The copper fine powder for circuit formation of the present invention is obtained by adding an alkali hydroxide to a copper salt aqueous solution to generate cupric oxide, and then adding a reducing sugar to precipitate cuprous oxide to form a slurry. After filtering and washing the cuprous copper, it is dispersed in water to make a slurry again,
A hydrazine-based reducing agent is added to this slurry to generate copper fine powder, and the obtained copper fine powder is subjected to a pulverization treatment by a specific pulverization treatment apparatus.

In the method for producing a fine copper powder for forming a circuit according to the present invention, it is important to use a fine copper powder obtained by a wet reaction as the fine copper powder to be subjected to the crushing treatment. Generally, copper fine powder is produced by heat reducing copper salts or copper oxide in a reducing atmosphere, or by treating copper chloride vapor with a reducing gas to reduce copper chloride. There is also a dry reaction method typified by such a method, etc., since the copper fine powder obtained by the dry reaction has a broad particle size distribution, even if such a particle size distribution is subjected to a pulverization treatment to a broad copper fine powder. It is extremely difficult to obtain the copper fine powder of the present invention.

In the above preferred production method, it is important to filter and wash cuprous oxide from the cuprous oxide slurry in the middle of the process, and then disperse the slurry in water to form a slurry. Reduces the agglomeration of cuprous oxide particles and suppresses agglomeration during reduction with a hydrazine-based reducing agent. As a result, the low agglomeration degree (dispersibility) of the copper fine powder
Can be further improved. The particle size of the copper fine powder is controlled by appropriately adjusting the concentration of the aqueous copper salt solution, the rate of addition of the reducing sugar during the production of cuprous oxide, and the rate of addition of the hydrazine-based reducing agent during the reduction reaction. It can be carried out.

In the method for producing a fine copper powder for forming a circuit according to the present invention, it is important to carry out a pulverization treatment by a specific pulverization treatment apparatus. By performing the pulverization treatment with this specific pulverization treatment apparatus, the degree of aggregation of the aggregated particles can be reduced, and at the same time, the filling property of the copper fine powder in the conductive paste can be improved.

As the pulverization processing in the above specific pulverization processing apparatus, high-speed rotary collision pulverization processing in which copper fine powder is caused to collide with a rotating part rotating at high speed and pulverized, slurry containing copper fine powder Media stirring type pulverization process in which the slurry is stirred with beads or the like, a high water pressure type pulverization process in which a slurry containing copper fine powder is crushed by colliding from two directions with high water pressure, and a jet abutment process. As a classification, a high-speed moving body collision type air flow type pulverizer, an impact type pulverizer, a cage mill, a medium agitation type mill, an axial flow mill, a jet abutment device and the like can be used. Specifically, a super hybrid mill (manufactured by Ishikawajima-Harima Heavy Industries), a jet mill (manufactured by Seishin Enterprise), a supermass colloider (manufactured by Masuko Sangyo), a bead mill (manufactured by Irie Shokai), an optimizer (manufactured by Sugino Machine), an NC mill ( Ishii Pulverizer Co., Ltd., Disintegrator (Otsuka Iron Works), ACM Pulverizer (Hosokawa Micron), Turbo Mill (Matsubo), Supermicron (Hosokawa Micron), Micros (Nara Machinery), New Cosmo Smizer (Nara Machinery) Made),
Fine Victor Mill (manufactured by Hosokawa Micron), Ecobrex (manufactured by Hosokawa Micron), CF Mill (manufactured by Ube Industries), Hybridizer (manufactured by Nara Machinery), Bin Mill (manufactured by Alpinay), Pressure Homogenizer (manufactured by Nippon Seiki Seisakusho),
Harel homogenizer (manufactured by Domestic Seiko), Mechanofusion system (manufactured by Hosokawa Micron) and the like.

[0024]

The present invention will be specifically described below based on examples and comparative examples. Example 1 Dissolving 100 kg of copper sulfate (pentahydrate) in warm water to prepare 200 L
And maintained at 60 ° C. 125 L of a 25% by weight aqueous sodium hydroxide solution is added to this aqueous solution,
The mixture was stirred for 1 hour while maintaining the temperature at 60 ° C., and reacted to produce cupric oxide.

While maintaining the above reaction product at 60 ° C., 80 L of an aqueous glucose solution having a concentration of 450 g / L was added thereto for 20 hours.
Added quantitatively over a period of one minute to produce a cuprous oxide slurry. After the slurry was filtered and washed, warm water was added to re-slurry to obtain a 320 L slurry. 1.5 kg of aminoacetic acid and 0.7 kg of gum arabic were added to the slurry, stirred, and the temperature was maintained at 50 ° C. To this slurry was added 50 L of 20% hydrazine hydrate.
It was added quantitatively over time to produce a fine copper powder. The obtained copper fine powder slurry was filtered, sufficiently washed with pure water, filtered, and dried to obtain a copper fine powder. Table 1 shows the addition time of the aqueous glucose solution, the presence / absence of slurry washing, the addition time of hydrazine, the presence / absence of crushing treatment, and the presence / absence of organic compound coating.

The copper fine powder thus obtained was put into a pulverizer AP-1SH type (manufactured by Hosokawa Micron) equipped with a knife-type hammer, and was subjected to granulation at 2500 rpm for 15 minutes to obtain a copper fine powder. Various properties of the copper fine powder thus obtained were evaluated according to the following methods. The results were as shown in Table 2.

(1) Average Particle Size Observed by SEM Observation The sample was observed with a 2000-times SEM, and the Feret diameters of 500 particles in a total of three randomly selected visual fields were measured, and the average value was determined. . (2) Tap Density Using a 200 g sample, powder density was measured with a powder tester PT-E type (manufactured by Hosokawa Micron).

(3) CV Using the average particle diameter x obtained by the above SEM observation and the standard deviation σ obtained from 500 particle diameter data, the CV was calculated by the following equation (2). CV (%) = (σ / x) × 100 (2)

A vehicle consisting of 3.5 parts by mass of ethylcellulose and 46.5 parts by mass of terpineol was added to 50 parts by mass of the above-mentioned copper fine powder, and these were mixed and kneaded with a roll mill to prepare a conductive paste. The prepared conductive paste was printed on a polyimide (PI) film (UPILEX manufactured by Ube Industries, Ltd .: 125 μm) using a 380 mesh screen mask made of Tetron (printing pattern: 4 cm × 4 cm). Print the PI film at room temperature
After leveling for 5 minutes, temporary drying was performed for 30 minutes in a hot air circulation type constant temperature dryer set at 60 ° C. Further 120
It was transferred to a hot-air circulation type constant temperature dryer set to ° C., and main curing was performed for 60 minutes. After being taken out of the dryer and allowed to cool to room temperature, the film density (g / cm ³ ) was measured. The result is the second
As shown in the table.

Further, 3.5 parts by mass of ethyl cellulose and 46.5 parts by weight of terpineol were added to 50 parts by mass of the copper fine powder.
After adding a vehicle consisting of parts by mass and mixing them,
The conductive paste was prepared by kneading with a roll mill. The degree of dispersion of the copper fine powder in the conductive paste (copper fine particles) was determined for the prepared conductive paste in accordance with JIS K 5400 by using a 0-25 μm crush gauge and reading a portion where dense crushes began to appear by a granularity. Was measured. The results were as shown in Table 2.

Examples 2 to 6 Except that the addition time of an aqueous glucose solution, the presence or absence of slurry washing, the addition time of hydrazine, the presence or absence of a granulation treatment, and / or the presence or absence of an organic compound coating were changed as shown in Table 1. Copper fine powder was obtained in the same manner as in Example 1.

Various properties of the obtained copper fine powder were evaluated in accordance with the method described in Example 1. Further, the film density formed using the conductive paste containing the copper fine powder and the degree of dispersion of the copper fine powder in the conductive paste (cohesion of copper fine particles) were measured. The results were as shown in Table 2.

Example 7 25 kg of the copper fine powder obtained in Example 2 was
25 kg of methanol in which 25 kg is dissolved is poured, and the mixture is sufficiently stirred. Then, the excess solution is removed by suction filtration, dried at 70 ° C. for 5 hours, and the organic compound whose particle surface is coated with oleic acid A coated copper fine powder was obtained.

With respect to the organic compound-coated copper fine powder thus obtained, various characteristics were evaluated in accordance with the method described in Example 1. Further, the film density formed using the conductive paste containing the copper fine powder and the degree of dispersion of the copper fine powder in the conductive paste (cohesion of copper fine particles) were measured.
The results were as shown in Table 2.

Example 8 An organic compound-coated copper fine powder was obtained in the same manner as in Example 7, except that the copper fine powder obtained in Example 5 was used. Various characteristics of the thus obtained organic compound-coated copper fine powder were evaluated in accordance with the method described in Example 1. Further, the film density formed using the conductive paste containing the copper fine powder and the degree of dispersion of the copper fine powder in the conductive paste (cohesion of copper fine particles) were measured. The results were as shown in Table 2.

Comparative Example 1 Copper fine powder SFR-Cu manufactured by Nippon Atomize Processing Co., Ltd.
Various properties of the 3.5 micron product were evaluated according to the method described in Example 1. Further, the film density formed using the conductive paste containing the copper fine powder and the degree of dispersion of the copper fine powder in the conductive paste (cohesion of copper fine particles) were measured. The results were as shown in Table 2.

COMPARATIVE EXAMPLE 2 The procedure of Example 1 was repeated except that the step of filtering and washing the cuprous oxide slurry, adding hot water and re-slurrying the slurry, and not carrying out the pulverization treatment were performed. A copper fine powder was obtained in the same manner as in Example 1.

The copper fine powder thus obtained was evaluated for various properties according to the method described in Example 1. Further, the film density formed using the conductive paste containing the copper fine powder and the degree of dispersion of the copper fine powder in the conductive paste (cohesion of copper fine particles) were measured. The results were as shown in Table 2.

[0039]

[Table 1]

[0040]

[Table 2]

As is evident from the data in Table 2, the copper fine powders of the present invention of Examples 1 to 8 have a high tap density irrespective of the small average particle diameter, and have poor filling properties in the conductive paste. It turns out that it is excellent. In particular, the copper fine powders of Examples 1 and 4 have relatively high tap densities despite the fact that the average particle diameter is considerably small, and the film density when a coating film is formed by actually forming a conductive paste is also high. It is high and is suitable as a fine copper powder for circuit formation capable of coping with high wiring density.
Further, since the CV is small, the particle size distribution is sharp and the degree of dispersion (low agglomeration degree) in the conductive paste is sufficient, which is suitable for forming a fine pattern.

On the other hand, the commercially available copper fine powder of Comparative Example 1 was inferior in the degree of dispersion (cohesion of copper fine particles) of the copper fine powder in the conductive paste because the coefficient of variation CV was too large.
In addition, the copper fine powder of Comparative Example 2 has a formula (tap density) ≧ 4.83-1.99 exp (−0.2
9x), the film density was insufficient.

Test Example 1 To 82 parts by mass of the copper fine powder obtained in Example 2, 12.2 parts by mass of Epicoat 806 (manufactured by Yuka Shell Co.) and 6.8 parts by mass of Epomate B002 (manufactured by Yuka Shell Co., Ltd.) Was added and mixed, and then kneaded with a roll mill to prepare a conductive paste. The viscosity of the prepared conductive paste was measured at 0.5 rpm using a viscometer RE-105U manufactured by Toki Sangyo Co., Ltd. The results were as shown in Table 3. Further, a conductive paste was prepared in the same manner as described above using the copper fine powder obtained in Comparative Example 2 instead of the copper fine powder obtained in Example 2,
The viscosity was measured as above. The results were as shown in Table 3.

[0044]

As is evident from the data in Table 3, the conductive paste containing the copper fine powder of the present invention has a low viscosity, is excellent in filling the via holes, and can be used even when a circuit is formed without firing. Useful. On the other hand, the conductive paste containing the fine copper powder obtained in Comparative Example 2 has a high viscosity and is unsuitable for filling into via holes.

[0046]

The copper fine powder for circuit formation according to the present invention has a feature that the tap density is relatively high as compared with the average particle diameter, and thus the copper fine powder for circuit formation has excellent filling properties in the conductive paste. In addition, the particle size distribution is sharp, and a coating film having a high film density can be formed by using a conductive paste containing such copper fine powder, and as a result, the firing density can be increased, In addition, a fine pattern can be formed to increase the wiring density. Further, such a conductive paste is excellent in filling properties into via holes, and is useful for forming a circuit by non-firing.

Claims (3)

[Claims] 1. The average particle diameter by SEM observation is x (μm)
When the standard deviation of the particle diameter is σ, the tap density (g / cm ³ ) and the average particle diameter x satisfy the following expression (1) and are obtained by the following expression (2). A copper fine powder for circuit formation, wherein a coefficient of variation CV is 40% or less. (Tap density) ≧ 4.83-1.99 exp (−0.29x) {(1) CV (%) = (σ / x) × 100} (2) 2. An average particle size of 0.1 to 1 by SEM observation.
2. The fine copper powder for circuit formation according to claim 1, wherein the thickness is 0 [mu] m. 3. The fine copper powder for circuit formation according to claim 1, wherein the surface of the particles is coated with an organic compound.