JP4230017B2 - Method for producing fine copper powder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a fine copper powder, and more particularly to a method for producing a fine copper powder which exhibits suitable characteristics when used in a conductive paste or a conductive adhesive, and which is inexpensive and simple.
[0002]
[Prior art and problems to be solved by the invention]
In recent years, conductive metal powders or flakes mainly composed of silver or silver-palladium are used as conductive pastes used in the field of chip components, contact materials, etc. in electronic component mounting technology such as OA equipment and portable communication equipment. Some are blended with resin binder or glass frit. Furthermore, the conductive paste is also used for through holes in printed wiring boards, wiring crossovers, electrodes, and the like. Conductive metal powder or conductive paste using flakes mainly composed of silver or silver-palladium is excellent in conductivity and oxidation resistance, but metal powder such as silver and palladium is expensive. In addition, stable acquisition is difficult, and there is a problem in migration resistance. Therefore, in place of expensive silver and palladium, there is an increasing demand for inexpensive and excellent conductive copper powder.
[0003]
An atomizing method, an electrolytic method, a wet synthesis method, or the like is employed as a method for producing the copper powder. Among these production methods, the copper powder obtained by the atomizing method and the electrolytic method is mainly used for powder metallurgy, and the average particle size is about several tens of μm. On the other hand, in the wet synthesis method, copper powder having a narrow particle size distribution with an average particle size of about 0.2 to 4 μm can be obtained, but it is expensive and has a problem in economic efficiency.
[0004]
Along with the downsizing and weight reduction of electronic devices, etc., the conductive circuit has become finer pitch, and with this, the copper powder used for the conductive paste for through-holes of printed wiring boards has become even smaller. Specifically, copper powder having an average particle size of 10 μm or less, preferably about 3 to 5 μm is required. As described above, in the wet synthesis method, copper powder having such an average particle diameter can be obtained, but it is economically disadvantageous and is difficult to say as an industrial production method. Moreover, the average particle diameter of the copper powder obtained by the atomization method is generally several tens of μm as described above. When the copper powder of 10 μm or less is classified from this, the yield is poor, resulting in high cost. It becomes.
[0005]
In order to meet the above requirements, copper powder having an average particle size of about 8 μm is obtained by pulverizing electrolytic copper powder having an average particle size of about 20 to 35 μm with an atomizer. Something is required. Moreover, by using a high-pressure water atomizer, copper powder having an average particle size of about 5 μm can be obtained, but the production yield is poor, which is economically disadvantageous.
[0006]
JP-A-62-299705 and JP-A-2-182809 describe that electrolytic copper powder is pulverized and pulverized by collision between copper powder particles to obtain fine copper powder having an average particle size of 10 μm or less. Has been. That is, a method is described in which electrolytic copper powder is pulverized and pulverized using a jet mill in which particles collide with each other. However, in this method, there is a problem that the obtained conductive paste using the fine copper powder is inferior in properties such as conductivity.
[0007]
Accordingly, an object of the present invention is to provide a method for producing fine copper powder that is suitable for use in conductive pastes and conductive adhesives, particularly exhibits good conductivity, and is inexpensive and simple. It is in.
[0008]
[Problems to be solved by the invention]
As a result of the study, the present inventors have found that the above-mentioned object can be achieved by pulverizing and pulverizing the dendritic electrolytic copper powder coated with oil and fat with a collision plate type jet mill.
[0009]
The present invention has been made on the basis of the above knowledge, and fats and oils are added to and mixed with a dendritic electrolytic copper powder having an average particle diameter of 20 to 35 μm and a bulk density of 0.5 to 0.8 g / cm ^3. The present invention provides a method for producing fine copper powder characterized in that after the surface is coated with fats and oils, it is pulverized and pulverized by a collision plate type jet mill.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The dendritic electrolytic copper powder used in the present invention has an average particle size of 20 to 35 μm and a bulk density of 0.5 to 0.8 g / cm ³ , preferably 0.60 to 0.75 g / cm ^3. . When the average particle size is out of the above range, good fine copper powder cannot be obtained. The bulk density is less than 0.5 g / cm ³ may result in out burning during grinding, fine copper powder having an average particle size 3~5μm exceeds 0.8 g / cm ³ can not be obtained.
[0011]
Such dendritic electrolytic copper _{powder, CuSO 4 · 5H 2 O:} 5~50g / l, H 2 SO 4: in a liquid composition of 50 to 150 g / l, the electrolyte density 5~10A / dm ^2, a liquid temperature 20 It can be obtained by directly depositing on the cathode under the condition of -60 ° C. The dendritic electrolytic copper powder obtained by electrolysis is subjected to treatments such as pickling and rinsing.
[0012]
Thereafter, fats and oils are added to and mixed with the dendritic electrolytic copper powder for rust prevention treatment, and the surface of the electrolytic copper powder is uniformly coated with the fats and oils. As for the addition amount of fats and oils, it is desirable that it is 0.1 to 5 weight% with respect to electrolytic copper powder. As such fats and oils, saturated fatty acids or unsaturated fatty acids are preferably used. Examples of saturated fatty acids include lauric acid, palmitic acid, and stearic acid, and examples of unsaturated fatty acids include oleic acid and linoleic acid.
[0013]
Next, in the present invention, dendritic electrolytic copper powder whose surface is coated with fats and oils is pulverized and pulverized by a collision plate type jet mill. In this collision plate type jet mill, the supplied electrolytic copper powder is made to collide with the collision plate in the pulverization chamber by compressed air to be pulverized and pulverized. The pulverized and pulverized copper powder is classified by a classifier, and the target fine copper powder is discharged and collected by a cyclone or a bag filter. On the other hand, the coarse copper powder is fed back to the crushing chamber and pulverized and pulverized again. As such a collision plate type jet mill, an IDS type jet mill manufactured by Nippon Pneumatic Industry Co., Ltd. can be exemplified.
[0014]
JP-A-62-199705 and JP-A-2-182809 described above use a jet mill that collides particles with each other, such as a PJM jet mill manufactured by Nippon Pneumatic Industry Co., Ltd. It describes that the electrolytic copper powder is pulverized and pulverized. However, in this method, compared to the case of using a collision plate type jet mill, when the same raw material is used, a small particle size cannot be obtained, and the obtained fine copper powder is used for a conductive paste or the like. At times, problems such as inability to obtain good conductivity arise.
[0015]
The fine copper powder having a desired average particle diameter can be obtained by appropriately adjusting the speed of supplying the electrolytic copper powder and the setting of the classifier in the pulverizer. For example, by reducing the supply speed and setting the classifier setting to the fine powder side, a fine copper powder can be obtained. Moreover, a fine copper powder can also be obtained by using an electrolytic copper powder having a low bulk density as a raw material. In order to obtain a fine copper powder having an average particle diameter of 3 to 5 μm, it is desirable to slow the supply rate. Moreover, what is necessary is just to increase a supply rate, in order to obtain the fine powder exceeding average particle diameter 5 micrometers.
[0016]
The fine copper powder thus obtained is granular or a mixture of grains and branches, and the average particle diameter is preferably 3 to 5 μm.
[0017]
The fine copper powder obtained by the production method of the present invention is used alone or in combination with other copper powders for conductive pastes and conductive adhesives for through-hole substrates and electronic component electrodes. In particular, it is suitably used as a conductive paste for through-hole substrates that accompanies fine pitches in conductive circuits.
[0018]
【Example】
Hereinafter, the present invention will be specifically described based on examples and the like.
[0019]
[Example 1]
After adding 1 part by weight of oil (oleic acid) to 100 parts by weight of dendritic electrolytic copper powder having an average particle size of 28.2 μm and a bulk density of 0.63 g / cm ³ , mixing for 2 hours, a collision plate type jet mill (Nippon Pneumatic Industrial Co., Ltd. IDS jet mill, IDS-5) was pulverized and pulverized under the conditions of a pulverization pressure of 6 kg / cm ³ and a supply rate of 3.4 kg / hr to obtain a fine copper powder. . The obtained fine copper powder was almost granular, the average particle size was 3.37 μm, and the recovery rate was 89%. Scanning electron micrographs of the dendritic electrolytic copper powder used as a raw material and the obtained fine copper powder are shown in FIGS. 1 and 2, respectively.
[0020]
After adding 85 parts by weight of the fine copper powder thus obtained, 16 parts by weight of a resol type phenolic resin, 6 parts by weight of a solvent (butyl cellosolve) and making a paste with a three roll mill, screen printing on a glass epoxy substrate, Thermal curing was performed at 150 ° C. for 30 minutes in an air oven. The specific resistance of this conductive paste was 1.2 × 10 ⁻⁴ Ω · cm.
[0021]
[Comparative Example 1]
1 part by weight of oil (oleic acid) is added to 100 parts by weight of dendritic electrolytic copper powder having an average particle size of 14.4 μm and a bulk density of 1.34 g / cm ³ , and mixed for 2 hours. (Nippon Pneumatic Industry Co., Ltd. IDS jet mill, IDS-5) was pulverized and pulverized under the conditions of a pulverization pressure of 6 kg / cm ³ and a supply rate of 1.2 kg / hr to obtain copper powder. The obtained copper powder was almost granular, but the average particle size was 11.2 μm and a fine copper powder was not obtained. The recovery rate was as low as 78%.
[0022]
[Comparative Example 2]
Fine copper powder in the same manner as in Example 1 except that instead of the collision plate type jet mill, a jet mill (PJM type jet mill manufactured by Nippon Pneumatic Industry Co., Ltd.) that collides particles with each other was used. Got. This fine copper powder had an average particle size of 5.8 μm and a recovery rate of 60%. The fine copper powder thus obtained was used to form a paste in the same manner as in Example 1, and then screen-printed on a glass epoxy substrate and thermally cured in an air oven. The specific resistance of this conductive paste was 3.0 × 10 ⁻⁴ Ω · cm.
[0023]
[Example 2]
1 part by weight of fat (oleic acid) is added to 100 parts by weight of dendritic electrolytic copper powder having an average particle size of 30.3 μm and a bulk density of 0.74 g / cm ³ , and mixed for 2 hours. (Nippon Pneumatic Kogyo Co., Ltd. IDS jet mill, IDS-5) was pulverized and pulverized under conditions of a pulverization pressure of 6 kg / cm ³ and a supply speed of 6.7 kg / hr to obtain a fine copper powder. . The obtained fine copper powder was a mixture of particles and branches, the average particle size was 4.43 μm, and the recovery rate was 97%.
[0024]
After adding 86 parts by weight of the fine copper powder thus obtained, 14 parts by weight of a resol-type phenol resin, and 6 parts by weight of a solvent (butyl cellosolve), a paste was formed in the same manner as in Example 1 and then screen-printed on a glass epoxy substrate. And heat-cured in an air oven. The specific resistance of this conductive paste was 1.0 × 10 ⁻⁴ Ω · cm.
[0025]
【The invention's effect】
As described above, by the production method of the present invention, a fine copper powder exhibiting suitable characteristics, particularly good conductivity, when used in a conductive paste, a conductive adhesive or the like can be obtained inexpensively and easily. It is done.
[Brief description of the drawings]
1 is a scanning electron micrograph of dendritic electrolytic copper powder in Example 1. FIG.
FIG. 2 is a scanning electron micrograph of the fine copper powder in Example 1.

Claims (1)

Oil and fat 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 oil and fat. A method for producing a fine copper powder, characterized in that the fine copper powder is pulverized and pulverized.

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