JP4136106B2 - Flat micro copper powder and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a flat fine copper powder and a method for producing the same, and more specifically, a flat fine copper powder exhibiting suitable characteristics when used in a conductive paste and a conductive adhesive, and an inexpensive and simple production method thereof. About.
[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 the copper powder used in the conductive paste for through-holes on printed circuit boards has also become smaller. Requires copper powder having an average particle size of 10 μm or less, preferably about 3 to 5 μm. 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-62-199705 and JP-A-2-182809 describe that electrolytic copper powder is pulverized and pulverized by collision between copper powder particles to obtain copper powder having an average particle size of 10 μm or less. ing. That is, a method is described in which electrolytic copper powder is pulverized and pulverized using a jet mill that collides with each other to obtain copper powder having an average particle size of 10 μm or less. Moreover, the fine copper powder with an average particle diameter of 3-5 micrometers can also be obtained by grind | pulverizing and pulverizing electrolytic copper powder with a collision board type jet mill.
[0007]
However, in this method, the obtained fine copper powder was granular or a mixture of granular and branched shapes. As the fine copper powder used for the conductive paste, not only granular particles but also flat ones are desired from the viewpoint of preventing sagging and improving conductivity.
[0008]
Accordingly, an object of the present invention is to provide a flat fine copper powder having suitable characteristics when used in a conductive paste and a conductive adhesive, particularly good conductivity and anti-sagging effect, and its inexpensive and simple production. It is to provide a method.
[0009]
[Problems to be solved by the invention]
As a result of the study, the present inventors have found that the above object can be achieved by flattening the granular fine copper powder with a medium stirring mill.
[0010]
The present invention has been made on the basis of the above-mentioned knowledge, and is based on a resinous electrolytic copper powder obtained by an electrolysis method. The average major axis diameter is 4 to 10 μm, the flatness is 2 to 20, and the bulk density is 2 to 4 g / cm ^3. , there is provided a Bian Tairajo fine copper powder you being a BET specific surface area of 0.4~1.5m ² / g.
[0011]
Further, in the present invention, as a preferable method for producing the above-described flat micro copper powder, the resinous electrolytic copper powder obtained by the electrolysis method is pulverized and refined by a collision plate type or a jet mill of a type in which particles collide with each other. , to obtain a granular fine copper powder having an average particle size of 3 to 5 [mu] m, then the particulate fine copper powder by introducing a copper slurry dispersed in water medium stirrer mill, Bian Tairajo minute flattening the fine small copper powder A method for producing copper powder ,
A method for producing a flat micro copper powder in which the medium stirring mill is a bead mill, beads used in the bead mill are zirconia beads having a diameter of 0.3 to 1.0 mm, and an operation time is 30 minutes to 2 hours. It is to provide.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The flat fine copper powder of the present invention needs to have an average major axis diameter of 4 to 10 μm and a flatness ratio of 2 to 20. By having an average major axis diameter and flatness in this range, when used in a conductive paste, good conductivity can be obtained, and the effect of preventing sagging can be obtained.
[0013]
Moreover, it is desirable that the flat fine copper powder of the present invention has a bulk density of ^{2 to 4} g / cm ³ and a BET specific surface area of 0.4 to 1.5 m ² / g. By having the properties in this range, suitable flattening can be achieved, and when the conductive paste is obtained, good conductivity is obtained and sagging is prevented.
[0014]
Next, the manufacturing method of this invention is demonstrated.
In the present invention, granular fine copper powder having an average particle diameter of 3 to 5 μm is dispersed in water to form a copper slurry. The fine copper powder used here is not particularly limited and may be obtained by an atomizing method or a wet synthesis method. From an economical point of view, a dendritic electrolytic copper powder obtained by an electrolytic method is used as an impingement plate type or a particle mutual type. Are obtained by pulverizing and refining with a jet mill of a collision type, and those obtained by pulverization and pulverization with a collision plate type jet mill are particularly preferred from the characteristics of the finally obtained conductive paste. In addition, the term “granular” as used herein includes not only those mainly composed of grains but also those in which grains and branches are mixed. The reason why the average particle size is in the above range is that if the average particle size is out of the above range, flat micro copper powder having a desired major axis diameter and flatness cannot be obtained. The granular fine copper powder is desirably uniformly coated with fats and oils such as stearic acid and oleic acid.
[0015]
It is desirable to disperse the fine particulate copper powder in water and add a lubricant such as a fatty acid salt or a dispersant to the copper slurry. By adding a lubricant or a dispersant to the copper slurry, it is possible to prevent the particle size from increasing due to adhesion between the fine copper powders. Examples of the fatty acid salt as the lubricant include sodium oleate. Moreover, as a dispersing agent, Emulgen 910 (made by Kao Corporation) etc. are illustrated.
[0016]
Next, the copper slurry in which the particulate fine copper powder is dispersed is introduced into a medium type stirring mill, and the fine copper powder is flattened. A typical example of the medium type agitation mill is a bead mill. The copper slurry supply rate is preferably 0.5 to 1.0 liter / minute when this volume is 1.4 liter. Further, beads having a diameter of 0.3 to 1.0 mm are used, and ceramics such as zirconia and alumina, glass, stainless steel and the like are used. In order to prevent the particle size from increasing due to adhesion between copper powders, it is desirable to use a material having a small diameter and a small specific gravity. The operation time for flattening is generally 30 minutes to 2 hours, although it depends on the flattening ratio to be obtained.
[0017]
In this way, the flat micro copper powder is obtained. The flat micro copper powder 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]
30 parts by weight of granular copper powder having an average particle size of 3.25 μm obtained by pulverizing and pulverizing electrolytic copper powder with a collision plate type jet mill, 70 parts by weight of water, and 0.2 weight of lubricant (sodium oleate) Parts and a dispersing agent (Emulgen 910 manufactured by Kao Corporation) 0.1 parts by weight were mixed, stirred and dispersed to prepare a copper slurry. This copper slurry was put into a bead mill to flatten the granular fine copper powder. As the bead mill, a dyno mill (KDL-PILOT type, void volume: 1.4 liters) manufactured by WTB Switzerland was used, and zirconia beads having a diameter of 0.5 mm (filling density in beads was 80%) were used. The supply rate of the copper slurry was 0.7 liter / minute, the operation time was 1 kg / hr, and the copper slurry was circulated between the container and the bead mill while being stirred in the container. As a result, a flat micro copper powder having an average particle size of 5.97 μm, a flatness ratio of 10, a bulk density of 2.57 g / cm ³ and a BET specific surface area of 0.89 m ² / g was obtained. A scanning electron micrograph of the obtained flat micro copper powder is shown in FIG.
[0020]
After adding 74 parts by weight of the obtained flat micro copper powder, 26 parts by weight of a resol type phenol resin, and 9 parts by weight of a solvent (butyl cellosolve), the mixture was made into a paste with a three roll mill and then screen-printed on a glass epoxy substrate. And heat-cured at 150 ° C. for 30 minutes in an air oven. The specific resistance of this conductive paste was 0.9 × 10 ⁻⁴ Ω · cm.
[0021]
[Example 2]
A flat fine copper powder was obtained in the same manner as in Example 1 except that granular fine copper powder having an average particle size of 4.43 μm was used. This flat micro copper powder had an average particle size of 7.01 μm, a flatness ratio of 10, a bulk density of 3.28 g / cm ³ , and a BET specific surface area of 0.76 m ² / g.
[0022]
Example 3
Except for using fine particulate copper powder with an average particle size of 3.25 μm, using non-alkali glass beads with a diameter of 1.0 mm (filling density within beads of 83%) as beads, and operating time of 2.0 kg / hr, In the same manner as in Example 1, a flat fine copper powder was obtained. This flat micro copper powder had an average particle size of 5.36 μm, a flatness ratio of 10, a bulk density of 2.38 g / cm ³ , and a BET specific surface area of 0.90 m ² / g.
[0023]
Example 4
39 parts by weight of the flat fine copper powder obtained in Example 1, 39 parts by weight of granular fine copper powder having an average particle size of 4.78 μm, 22 parts by weight of a resol type phenol resin, and 9 parts by weight of a solvent (butyl cellosolve) were added. After pasting in the same manner as in Example 1, it was screen-printed on a glass epoxy substrate and thermally cured in an air oven. The specific resistance of this conductive paste was 0.8 × 10 ⁻⁴ Ω · cm.
[0024]
[Comparative Example 1]
After adding 78 parts by weight of fine particulate copper powder having an average particle size of 4.78 μm, 22 parts by weight of a resol type phenol resin, and 9 parts by weight of a solvent (butyl cellosolve), a paste was formed in the same manner as in Example 1, and then a screen was placed on a glass epoxy substrate. It was printed 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, the flat fine copper powder of the present invention has good conductivity and can prevent sagging when used in a conductive paste, a conductive adhesive, or the like. Moreover, the said flat fine copper powder is cheap and can be obtained simply by the manufacturing method of this invention.
[Brief description of the drawings]
1 is a scanning electron micrograph of a flat micro copper powder in Example 1. FIG.

Claims (2)

Resinous electrolytic copper powder obtained by the electrolysis method is used as a raw material, average major axis diameter of 4 to 10 μm, flatness of 2 to 20 , bulk density of 2 to 4 g / cm ³ , BET specific surface area of 0.4 to 1.5 m ² / Bian Tairajo fine copper powder it is a g. The resinous electrolytic copper powder obtained by the electrolysis method is pulverized and refined by a jet mill of a collision plate type or a collision type of particles to obtain a granular fine copper powder having an average particle size of 3 to 5 μm , and then the granular fine copper powder copper powder method for manufacturing a copper slurry dispersed in water is introduced into the medium stirrer mill, Bian Tairajo fine copper powder you flattening the fine small copper powder,
A method for producing a flat micro copper powder, wherein the medium stirring mill is a bead mill, beads used in the bead mill are zirconia beads having a diameter of 0.3 to 1.0 mm, and an operation time is 30 minutes to 2 hours .

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