Copper flake powder, method for producing copper flake powder, and conductive paste using copper flake powder

Abstract

The present invention is mainly for providing a flake copper powder for a conductive paste with particle properties which are defined by that the particle thickness is thinner being possible for use to form an electrode or a circuit, and a production process thereof. To achieve the object of producing the following particles, each powder particles shape is plastically processed into a flake-shape, wherein the flake copper powder has a cumulative particle diameter D50 of 10 μm or smaller measured with laser diffraction scattering particle size distribution method. The D10, D50 and D90 measured with the laser diffraction scattering particle size distribution method are illustrative and the SD / D50 value measured by the standard deviation of particle distribution with the laser diffraction scattering particle size distribution, is 0.55 or larger and / or a D90 / D10 of 4.5 or smaller. The flake copper powder is compressed with a high energy ball mill whose media beads having fine particle diameter which plastically deforms the copper particles into flake-shaped particles, so that stable flake copper powder is produced.

Description

TECHNICAL FIELD [0001] The present invention relates to flake copper powder, a method of producing flake copper powder and a conductive paste using the flake copper powder. BACKGROUND ART [0002] Conventionally flake copper powder has widely been used as raw material for a conductive paste. Also, conductive pastes have been typically applied to various electrical contacts in order to form a circuit of a printed-wiring board and an external electrode of a ceramic capacitor in order to ensure electrical conduction. [0003] Normal shape of flake copper powder is substantially spherical. When flake copper powder is processed to a conductive paste, some properties are required for such flake copper powder, in which viscosity of a conductive paste can be controlled to form a thinner electrode of chip material and enhance filling capability for a via-hole. When a conductive circuit is formed using a method of sintering and solidifying the circuit by drawing a conductive pattern with the cond...

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Benefits of technology

[0019] Additionally, a property of the flake copper powder of the present invention, when the cumulative particle diameter D50 through the laser diffraction scattering particle size distribution measurement method is defined by a standard value, has a maximum cumulative particle diameter Dmax value which will never exceed the standard value. The Dmax value is never more than five times the D50 value. Namely, the Dmax / D50 of a ratio of a cumulative particle diameter D50 to the maximum cumulative particle diameter Dmax determined through the laser diffraction scattering particle size distribution method is 5 or smaller. As a result, the product (the flake copper powder relating to the present invention) is a narrow distribution of particles, because there is no coarse particle that could be observed in the conventional flake copper powder.

[0025] If an object is merely to disperse copper into particles using several methods, it seems to be possible to use such methods as a high-energy ball mill, a high-speed conductive jet mill, an impact mill, a gauge mill, a media agitating mill, a high-pressured water type mill and so on. However, according to study by the inventors, the two types of dispersing methods mentioned below are preferable from an aspect of reliability in dispersing procedure. A common point between the two methods is to inhibit minimum that the particles of copper powder touch inside of the device, impeller and media to mill, which occurs when powder particles under agglomerate condition an crashed on each other in order to disperse them into individual powder particle form the agglomerate condition. In the other words, this can restrain if at all possible the touching of the inside of the device, impeller and media to mill, injuring the surface of powder particle and increasing the roughness of the surface of powder particle. Further, when a sufficient crash between each powder particle occurs, this can result in dispersing the powder particle under agglomerate condition, at the same time it can produce a smooth surface of powder particle through the crash of each powder particle.

[0036] Further, it is preferable to use media beads, wherein the gravity of each of the media beads is from 3.0 g / cm3 to 6.5 g / cm3. In case of a specific gravity of the media beads is smaller than 3.0 g / cm3, so that it takes a long time for compressive deformation because the gravity of media beads is too light. Considering productivity of flake copper powder, this is not a reasonable condition for production. On the contrary, in a case of specific gravity of the media exceeds 6.5 g / cm3, the gravity of media beads becomes heavier, so that compressive deformation force of each of particles of copper powder becomes large and it becomes easy to condensate each powder particle. Additionally, it is unable to have uniformed thickness of flake copper powder after the deformation. By obtaining flake copper powder using the above-mentioned method, products can be produced effectively providing powder properties relating to flake copper powder of the present invention. In addition, the producing conductive paste for which this flake copper powder is used has excellent performance. Therefore, when a conductor is produced using such flake copper powder, even if the thickness of conductor becomes thinner, such flake copper powder can maintain lower electronic resistance, and also its stability in a conductive configuration will be superior. Accordingly, it will be a suitable method for yielding sintering circuit of PWB, a sintered configuration of ceramic capacitor. Conductive Paste

[0037] When producing conductive paste with the above-mentioned flake copper powder of the present invention, controlling viscosity is easy. Simultaneously, the changing because of aging of conductive paste is diminished and easily providing thixotropic property being superior to a conductive paste. Therefore, regarding conductive paste using flake copper powder of the present invention, if kinds of organic vehicles in the conductive paste and the containing amount of the flake copper powder are as same as those of the conventional flake copper powder content, the quality of the present conductive paste is incomparably better than that of the conventional one.

Problems solved by technology

Further, the thickness of each of the powder particles is uneven and the particle distribution is uneven.

As apparent from the FIG. 2, thickness of conventional flake copper powder is thin and also the thickness is uneven; particularly the powder particle size is not only uniform but also unstable.

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