CA2506367A1

CA2506367A1 - Copper flake powder, method for producing copper flake powder, and conductive paste using copper flake powder

Info

Publication number: CA2506367A1
Application number: CA002506367A
Authority: CA
Inventors: Takahiko Sakaue; Kunihiko Yasunari; Katsuhiko Yoshimaru
Original assignee: Individual
Current assignee: Mitsui Mining and Smelting Co Ltd
Priority date: 2002-11-22
Filing date: 2003-08-11
Publication date: 2004-06-10
Also published as: CN1292861C; DE10393768T5; TWI236393B; JP4145127B2; US20060137488A1; TW200408475A; AU2003254924A1; KR100613033B1; WO2004048017A1; KR20040086853A; JP2004169155A; CN1642680A

Abstract

A copper flake powder for a conductive paste, which has a thin particle thickness and powder characteristics applicable to formation of a fine electrode or circuit, and a method for producing such a copper flake powder are provided. Particles of a copper powder are plastically deformed to form the copper flake powder, which is characterized in that the weight cumulative particle diameter D50 measured by a laser diffraction/scattering particle size distribution measuring method is 10 µm or less, the value of SD/D50 is 0.55 or less and the value of D90/D10 is 4.5 or less, which values are expressed by using the weight cumulative particle diameters D10, D50, D90 measured by a laser diffraction/scattering particle size distribution measuring method.and the standard deviation SD of the particle size distribution measured by a laser diffraction/scattering particle size distribution measuring method. The copper flake powder can be stably produced by plastically deforming, i.e.
compressing, medium beads of small particle size into flakes using a high-energy ball mill.

Description

DESCRIPTION
TITLE OF THE INVENTION
FLAKE COPPER POWDER, METHOD OF PRODUCING THE FLAKE COPPER
POWDER AND CONDUCTIVE PASTE USING THE FLAKE COPPER POWDER
TECHNICAL FIELD
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
Conventionally flake copper powder has widely been used as raw material for a conductive paste. Also a conductive paste has 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.
Normal shape of flake copper powder is substantially spherical. When flake copper powder is applied to a conductive paste, some properties are required for such flake copper powder, such that the 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 conductive paste, a high-layer-density is required that prevents an electric resistance in an electric circuit from being heightened. Simultaneously it has been desired to have ability of maintaining a configuration of the formed conductive circuit.
To meet market demands as above-mentioned, copper powder for producing a conductive paste is sometimes used as copper powder formed by not using the spherical particles of copper powder but using flaky particles powder (called ~~flake copper powder" hereinafter in the present description) has been considered. As apparent from a shape of each of particles of the flake copper powder, the shape is fish-scale-shaped or flat, resulting in that a specific surface area of each of the powder particles becomes larger, so that a contact area between the powder particles has also become wider resulting in that it is very effective for that flake copper powder to reduce electric resistance and enhance properties to maintain a configuration of the conductive circuit. The above-mentioned details are referred in Japanese Patent publications No. H06(1994)-287762 and No. H08(1996)-325612. These publications make easy to understand the above-mentioned contents.
However, such conventional flake copper powder has not had evenly-sized particle diameter and even thickness and there has been no existence of flake copper powder having fine particles while containing coarse particles at a constant rate.
Besides, some cracks could appear on a surface of each of particles of the flake copper powder. Also the conventional flake copper powder has been a product having the above-mentioned quality and also has had a very broad particle size distribution.
Viscosity of each particle of flake copper powder having such above-mentioned quality has been very difficult to control when the flake copper powder is processed into a conductive paste and there has been a difficult problem when handling the conductive paste. Also the viscosity of the conductive paste has been instable. The conventional flake copper powder has had defects regarding its thixotropic property of conductive paste being unstable. Particularly the thixotropic property is important when forming an electrode of a chip part using a dipping method. For one of example, upon producing an external electrode of a chip part for a multilayer ceramic capacitor, firstly the chip itself is dipped into a conductive paste and secondly the chip is lifted up from the conductive paste in order to apply a conductive paste onto the surface of the chip to form external electrodes.
In recent years, as a chip part becomes downsized, the more demand for a thinner layer of an external electrode . To meet the demands of forming the thinner layer, a quality of a conductive paste is required as follows. More specifically, when a chip part is dipped into a conductive paste, the conductive paste is thinly applied onto a surface of the chip part with excellent wettability. It has an evenly coated layer formed using the conductive paste. The layer is lifted from the conductive paste, and thereafter the surface of the chip part shows a superior thixotropic property that can prevent the coated layer formed by the conductive paste from being flown.
Further the other properties are required to maintain a condition of the coated layer as it stands during the above-mentioned process from the dipping step to a sintering step.
The conductive paste used for the conventional flake copper powder also can have the superior thixotropic property.
However the conventional flake copper powder can arrive at a mere certain level regarding the properties. However, when the conventional flake copper powder is processed into a conductive paste, a target of a certain level is required. The target is to enhance resistance on a sintered circuit using the conductive paste obtained from the conventional flake copper powder. Even if the target is achieved though the conductive paste having a limitation for lowering the electric resistance on the sintered circuit, it is impossible for the conventional flake copper powder to enhance the resistance because its layer density cannot be made to be greater. Further in a case of drawing a circuit using the conductive paste flake from the conventional flake copper powder or applying the dipping method thereto in order to form an electrode of a chip device, a conductive circuit having an electrode in the sintered process to be a fine-pitched circuit or a thinner layer formation cannot be obtained. Therefore the configuration stability and the surface condition regarding the conductive circuit or the electrode have the other problems. Therefore the conductive paste using the conventional copper powder has been used only for forming the conductive circuit having a thick and rough pattern of a circuit.
As apparent from the above-mentioned matters, the flake copper powder can be utilized not only for the conventional conductive circuit but also for a thinner and fine-pitched conductive circuit. Therefore such a type of flake copper powder has been demanded in a market.
BRIEF DESCRIPTION OF DRAWINGS
FIG.1 shows an observed image of a flake copper powder relating to the present invention through a scanning electron microscope.
FIG.2 shows a conventional observed image of a conventional copper powder in order to compare the present invention powder with the conventional powder through a scanning electron microscope.
DISCLOSURE OF THE INVENTION
Accordingly, the inventors had developed after-mentioned flake copper powder based on following reasons.
Coarse particles, each having a principal axis is mixed with the conventional flake copper powder, in which the principal axis of each of the coarse particles is five times or more as long as that of a diameter of particle of the conventional flake copper powder. Further thickness of each of the powder particles is uneven and the particle distribution is uneven.
The inventors had focused on the above-mentioned defects. In view of relationship between the properties of powder and a performance of thinningthe above-mentioned conductive circuit, and so on, the inventors had developed flake copper powder as below-mentioned. Followings will be explained about the present invention.
<Flake copper powder relating to the present invention>
The inventors had researched the conventional copper powder which had already existed, resulting in that the conventional one showed various properties having the conventional copper powder in Table 1. Herein, Dlo, Dso. D9o and Dmax are defined by particle diameter sizes by each of 100, 500 and 90o and maximum particle size regarding the volume cumulation, which can be obtained using a laser diffraction scattering particle size distribution measurement method.
Then the flake copper powder whose weight was O.lg was mixed with O.lo-aqueous solution of SN Dispersant 5468 (manufactured by San Nopco Limited) . After dispersing them by an ultrasonic homogenizer (manufactured by Nippon Seiki Co., Ltd. US-300T) for five minutes, then they were measured using a laser diffraction scattering particle size distribution apparatus, Micro Trac HRA 9320-X100 type (manufactured by Leeds and Northru Limited).
Table 1 Dio Dso 1 D9o 1. Dmax SD
-SAMPLE SD/Dso D9o/Dio (um) 1 10.13 26.15 46.77 104.70 18.31 0.70 4.62 2 2.88 6.28 14.09 44.00 4.15 0.66 4.89 3 2.71 5.87 13.14 52.33 3.86 0.66 4.85 4 2.81 8.20 21.38 52.33 7.17 0.87 7.61 As long as studying the results shown in the Table 1, the results show that the conventional flake copper powder also has various properties of the powder particles, and it seems that the conventional one can be changed depending on various properties of powder particles of raw materials and methods of process. In Table l, first, a value of standard deviation (SD) is notable. The standard deviation (SD) is an index to indicate scattering of the data of indicators of the entire particles diameter, which can be obtained with the laser diffraction scattering particle size distribution measurement method. As the values of the data become larger, variation of the data also becomes larger. Therefore the value of five lots standard deviation (SD) measured therein can be shown by scattering from 3.86 ~m to 18. 31 um, also as apparent from Table 1, scattering between the particles is incredibly large.
Focusing on a result of SD/Dso value being a coefficient of variation, the result of scattering from 0.66 to 0.87 is obtained, and D9o/Dlo value shows scattering from 4.62 to 7.61.
Further Dmax value can be obtained using the laser diffraction scattering particle size distribution measurement method, which is the maximum particle diameter and also includes a coarse particle such as 104.70 um at maximum. FIG.2 shows the conventional flake copper powder (three types) observed by a scanning electron microscope. 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. Of course it depends on what extent of forming flake is. Some spherical copper powder seems to remain, which had not been processed into flake copper powder. As a result, distribution of the conventional particle size shown in FIG.2 becomes extremely broad.
When a conductive paste is produced, external electrodes of a ceramic capacitor and a sintered circuit made of a low temperature sintered ceramic material using the conventional flake copper powder having copper powder properties, the following matters occur. Namely, the shape is not uniform, additionally, it is impossible to make thinner the thickness of the external electrode and the sintered circuit mentioned above.
The inventors had devoted themselves to study and shown some facts as follows. If properties of a particle of flake copper powder as defined by that "a cumulative particle diameter DSO is l0um or smaller; SD/DSO value is 0. 55 or smaller;
and D9o/Dlo value is 4.5 or smaller; in which SD is a standard deviation of particle distribution measured by a laser diffraction scattering particle size distribution method, and Dlo. Dso and D9o are cumulative particle diameters measured thereby", as recited in the claims, when the flake copper powder is processed into a conductive paste then drawing a circuit under the conditions described above, a layer thickness of the circuit can be thinner, also the layer density is splendid and it is possible to acquire a well-quality-balanced thixotropic property which can properly perform a binder removing method as a conductive paste. In case of using such a conductive paste, followings are shown: it can prevent a resistance of conductor from being higher; simultaneously the conductor can be enhanced in its shape without heightening resistance of the conductor.
In FIG.1, the flake copper powder (two types) relating to the present invention can be shown, which are observed using the scanning electron microscope. As apparent from comparing FIG.1 with FIG.2, powder particle sizes of flake copper powder in FIG.l are uniform and have more microscopical shape in comparison with flake copper powder in FIG.2. Even at a level being clearly visible by the scanning electron microscope, it is easy to understand that the particle distribution may be sharp.
Here, the reason why "cumulation particle size DSO is 10 um or smaller with the laser diffraction scattering particle size distribution measurement" has been proved by eager researching and developing by the inventors, owing that if a cumulation particle size DSO is 10 um or smaller, it is impossible to stably make thinner the thickness of conductor of a circuit drawn by the conductive paste using the flake copper powder and also it is impossible to enhance a filing ability of a via-hole. In particular, in the case where a cumulation particle DSO is 7 um or smaller, it can be possible to acquire an adequate thixotropic property when the copper powder is processed into a conductive paste. In a case of drawing a circuit after the copper powder is processed into a conductive paste, the thickness of a layer can be thinner and the layer density is superior, further, it has well-quality-balance that is able to perform a binder removing method as a conductive paste. It is noted that it has especially high quality stability as a conductive paste.
Optionally, it is noted that thickness of conductive shape cannot be thinner resulting in increasing electric resistance of a formed sintered circuit due to inferiority of layer density of inside of the conductor, breaking linearity of the edge surface of the sintered circuit and roughening of the surface condition of a sintered circuit, even if thinner conductor is formed using a conductive paste, the thin layer is not formed successfully because of existence of coarse particles and inferiority of thixotropic property. Additionally, it is considerable that measurement of cumulative particle diameter DSO using this method of measuring the laser diffractive scattering particle size distribution measurement method is a length at a major axis direction of particle of flake copper powder affected and flattened by plastic deformation.
It is more preferable that an aspect ratio (average major axis/average thickness) of the powder particle is from 3 to 200.
The aspect ratio herein is determined by depending on a processing degree of the powder particle. Generally, as an aspect ratio is higher, a thickness of flake copper powder tends to become thinner. On the other hand, the aspect ratio is smaller, the flake copper powder tends to become thick and large.
Therefore it is remarkable if the range of the aspect ratio (average major axis/average thickness) is 3 or shorter, the thixotropic property will be apparently lack with respect to the viscosity property when the flake copper powder is processed into a conductive paste. However, when the aspect ratio (average major axis/average thickness) is over 200, a defect occurs such that a shape of a powder particle itself is folded and cracked on a surface of a powder particle. A range of the particle distribution will be very broad and the thickness of flake copper powder will also be too much thin.
This thin flake copper powder cannot be mixed evenly with organic vehicles when a flake copper powder is processed as a conductive paste.
Additionally as properties of flake copper powder relating to the present invention, when the cumulative particle diameter DSO through the laser diffraction scattering particle size distribution measurement method is defined by a standard value, a maximum cumulative particle diameter Dmax value will never exceed the standard value, Dmax value is not five times as much as DSO value. Namely, Dmax/DSO of a ratio of a cumulative particle diameter DSO to the maximum cumulative particle diameter Dmax 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 sharp product regarding the distribution for particles, because there is no coarse particle that could be observed in the conventional flake copper powder.
Also the above-mentioned flake copper powder obtained by that the conventional copper powder particle having a substantially spherical shape is mechanically changed by plastic deformation, then to be flake-shaped. As a result, scattering upon producing will generally occur at a certain rate. Then the inventors have studied eagerly as follows. If the product contains the flake copper powder by 70 wt o or larger in existence rate provided with above-mentioned fine powder properties, even if the powder properties of the other remaining flake copper powder do not meet above-mentioned assumption, the flake copper powder produces the properties sufficiently by maintaining stability of the circuit configuration by processing a conductive paste and reducing the thickness of drawing a circuit.
<Method of producing flake copper powder relating to the present invention>
It is impossible to stably produce above-mentioned flake copper powder, even if the conventional producing process is used. Namely, the conventional flake copper powder, substantially spherical copper powder obtained with wet method such as a typified hydrazine reduction method with dry method and a typified atomizing method, is directly milled with a mill such as a ball mill, a beads mill or the like in order to mill utilizing balls or beads used as medias for a mill, and then the processed powder particle is changed by plastic deformation to be flattened and flake-shaped.
However in the case of performing such producing process, usually-spherical copper powder itself used at the first step, is under a predetermined agglomerate condition, even if conducting compressed deformation without being destroyed the agglomerate condition, the condition will be compressed by deformation, maintaining agglomerate condition, as a result that producing process gave flake copper powder under the same agglomerate condition as above-mentioned, further powder particles will not be mutually dispersed.
Therefore the inventors have reached a conclusion that firstly the agglomerate condition of substantially spherical powder particle is dispersed, secondly the powder particle is forced to be flaked-shaped by compressing and deformation.

The corresponding method according to claim is that "a producing method of the flake copper powder comprises the steps of : dispersing a copper powder under an agglomerate condition;
using the copper powder having superior dispersity whose agglomerate degree is 1.6 or smaller after completion of dispersion; and forming and plastically deforming particles of the copper powder in a flake manner by compressing the particles of the copper powder with a high energy ball mill using media beads, each whose particle diameter is 0.5mm or smaller".
Copper powder under agglomerate condition is defined by that even if the inventors use wet method being typified hydrazine reduction, or dry method being typically atomizing method, the certain agglomerate condition of copper powder will be formed, then, that is the reason why used the term "agglomerate condition" in the descriptions. Especially, applying wet method thereto tends to be formed under agglomerate condition of particle of copper powder. Because a general producing method of copper powder with wet method uses copper sulfate solution as starting material, and then utilizes sodium hydroxide solution to be reacted in order to obtain copper oxide. That copper oxide is undertaken with so-called hydrazine reduction, and then given methods below, such as cleaning, filtering and drying. The method will provide copper powder to be under dry condition, though if wet method is used in order to gain particle of copper powder, it will tend to produce a certain agglomerate condition in the producing process. Additionally, a copper powder slurry as below is defined by that powder comes up in a so-called hydrazine reduction and further such copper powder slurry conditions are established, containing the above-mentioned powder. The operation that agglomerate particles are dispersed under initial particles as much as possible is so-called "dispersing".
If an object is merely to disperse copper into each particle using several methods, it seems to be possible to use such 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 eager study by the inventors, two types of below-mentioned dispersing methods are preferable from an aspect of reliability in dispersing procedure. A common point between the two methods is to inhibiting it at the minimum that particles of copper powder touch inside of the device, impeller and media to mill, to utilize powder particle generated when powder particles under agglomerate condition is crashed each other in order to disperse them into individual powder particle form the agglomerate condition. In the other words, that can restrain if at all possible to touch inside of the device, impeller and media to mill, to injure the surface of powder particle and to increase roughness of the surface of powder particle. Further, occurring sufficient crash between each powder particle can realize to disperse powder particle under agglomerate condition, at the same time can produce smooth of the surface of powder particle utilizing the crash of each powder particle.
As one of methods for dispersing procedure, dried copper powder under agglomerate condition can be dispersed into each particle of copper powder with a wind power circulator. "Wind power circulator utilizing centrifugal force" herein, first of all, to blow air and then blow up copper powder in concentrated condition like drawing a circumference of track in order to circulate. To use centrifugal force occurred at the time set forth, each powder particle is forced to be crushed in the air in order to be dispersed. In this case, it is possible to use commercial force of wind classification machine. The object of the machine is not to be classified but the object is to take a role as a circulator to blow up air and then concentrated status copper powder is blown up in the air like drawing circumference of track.
Another method of dispersing copper powder into particle, copper powder slurry that contains copper powder under agglomerate condition is under a procedure with fluid mill used centrifugal force. The object of use of "fluid mill used centrifugal force" here in, first of all, to flow copper powder slurry in high speed to draw a circumference of track, and then each particle of copper powder to crash them each other in solvent with centrifugal force which occurred at the time due to a dispersing procedure.
According to the above-mentioned dispersing procedure, it can be conducted repeatedly to meet the requirements, and also to meet the products quality, and level for dispersing procedure of particle can be selected optionally. The copper powder being finished a dispersing procedure, was destroyed under its concentrate condition and has new properties as a powder particle. From now on, there will be explanation about agglomerate value set in the description. Using the obtained DSO value, with the laser diffraction scattering particle size distribution measurement and average particle diameter DIA
obtained an image analysis with a scanning electron microscope, and then an agglomerate value of DSO/DIA shown by the above value, DSO and DIA, that should be 1. 6 or smaller is the most preferable value to be settled. That's why an almost perfect condition of mono-disperse could be established, even if the agglomerate value became 1.6 or smaller.

The D5o value obtained through the laser diffraction scattering particle size distribution measurement method will not be considered to really observe a powder particle each by each. Almost copper powder particle is not individual perfectly, so-called mono-dispersed. The copper powder was comprised of several particles that lies in agglomerate condition. The laser diffraction scattering particle size distribution measurement method is to regard each of the agglomerate powder particles as a single particle (the condition of such particle is under agglomerate), and then calculates the value of cumulative particle diameter.
On the contrary, an average diameter value DIA with SEM
(Scanning Electron Microscope) to observe a copper powder observation image and process the observation image into image data, is directly obtained from SEM observation image. An image of an initial particle can be perceived surely using the laser diffraction scattering particle size distribution measurement.
On the other hand, it is not reflected thereon that there exist powder particles under agglomerate condition.
In view of the above-mentioned content, the inventors used D5o being the value of cumulative particle diameter to get the laser diffraction scattering particle size distribution measurement and an average particle diameter DIA obtained through an image analysis to determine the value as agglomerate value, which can be calculated as DSO~DIA. In other words, the inventors presume that copper powder from the same lot, DSO and DIA values can be measured with the same accuracy, considering over the above-mentioned theory, D5o value is meant by reflection of the concentrated condition over a value to be measured, so that DSO value may be higher than DIA value.

If agglomerate particles of copper powder become individual perfectly, Dso value will be infinitely closer to DIA value and the concentrated degree Dso/DIA w111 be close to 1. When the concentrated value becomes l, then it can be said that there is completely no agglomerate condition of powder particles, and as a result, those particles are completely dispersed individually. However, in reality, sometimes the concentrated value indicates being smaller than 1.
Theoretically considering over when a particle is completely spheroid, in fact the value is not smaller than 1. However, if a particle whose shape is not spheroid, the value being smaller than 1 can be obtained. Further the image analysis using scanning electron microscope in the description relating to the present invention, using IP-1000PC manufactured by Asahi Engineering, sensitivitythreshold value 10, overlapped extend value is regarded as 20 by circular-shaped-particle analyzing.
The average particle diameter is obtained as DIA.
The substantially spherical copper powder after completion of dispersion is processed with a high energy ball mill. The particle of copper powder is performed by plastic deformation and produce flake copper powder. Therefore the cumulated particle diameter Dso of laser diffraction scattering particle size distribution measurement of the flake copper powder as the final product on the procedure mentioned above is 10 ~m or smaller. First of all, DSO can be employed as a standard using the laser diffraction scattering particle size distribution measurement of the flake copper powder is before compressive deformation and after disperse treatment (hereinafter referred as "original powder"), considering over a processed extend of flake of copper powder. To consider over these matters, Dso can be used as an estimation index.

The "high energy ball mil" herein is a generic term used to refer a device whenever employing media beads to compress copper powder into plastic deformation, e. g. , using a ball mill, attoritor and so on, regardless of under wet condition or under slurry of copper powder condition. Regarding the present invention, selecting a particle diameter of each of media beads and quality of material are very important.
Firstly, it should be used media beads each whose particle diameter is 0.5 mm or smaller. The reasons why a diameter of each of the media beads is defined based on followings. If the size of diameter of media beads is over 0.5 mm, it is easy that flake copper powder can be easily agglomerate when the media beads are compressed by plastic deformation. As a result, coarse flake powder particles are generated due to change shapes of agglomerate particles by compressive plastic deformation. The flake copper powder cannot be obtained that has shape and superior dispersibility particle size distribution, because particle size distribution became broad.
Further it is preferable to use media beads wherein a gravity of each of the media beads is from 3. 0 g/cm3 to 6. 5 g/cm3.
In a case of specific gravity of media beads being 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 over productivity of flake copper powder, it is not reasonable condition to produce it . On the contrary, in a case where specific gravity of the media exceed 6.5g/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, producing conductive paste used for this flake copper powder 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 conductive configuration stability will be superior. Accordingly, it will be suitable method for yielding sintering circuit of PWB, a sintered configuration of ceramic capacitor.
<Conductive Paste>
When producing conductive paste with above-mentioned flake copper powder of the present invention, controlling viscosity is facility, simultaneously, changing based on aging of conductive paste is lessened and easy to provide 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.
Solutions against which level can be defined as thixotropic property and how the conductive paste should be generally used in accordance with the intentioned usage as above-mentioned, appropriate measures will be determined, considering over variations of organic vehicles in the conductive paste, flake copper powder content and particle diameter having particle of flake copper powder.

Best Mode for Carrying Out the Invention The following examples specifically show the present invention.
Example l:
In this example, copper powder obtained from raw material powder with a below-mentioned method is used, as original powder with the producing process of the present invention to produce flake copper powder.
Powder properties of original powder utilized in this example, the cumulative particle diameter; DSO was 0.35 um, which was obtained using a laser diffraction scattering particle size distribution measurement method and average particle diameter; DIA was 0. 20 pm obtained by an image analysis .
Accordingly an agglomerate value calculated on DSO/DIA was 1. 75.
The above-mentioned original powder under agglomerate condition was circulated on the number of revolution at 6500 rpm, with a Turbo classifier manufactured by Nissei Engineering Limited, which is a commercial pneumatic classification device to perform an operation by which agglomerate particles were made to be a single one to collide against the powder particle each other.
As a result, the cumulative particles diameter of copper powder (original powder) completed as single particles, i.e., DSO was 0.30 um using the laser diffraction scattering particle size distribution measurement method and an average diameter DIA was 0.20 ~m obtained from the image analysis so that the agglomerate value calculated on DSO/DIA was 1.50. The fact showed that the above-mentioned dispersion operation was performed sufficiently.

Next, the original powder having 300 g weight containing a singular particle using a DISPERMAT D-5226 manufactured VMG-GETZMANN and zirconia' s beads 800 g, as media beads, each whose specific gravity of zirconia's beads was 5.8 g/cm3, and its diameter was 0.3 mm. As a solvent, methanol 120 g mixed with capric acid 5g was used and then treated them using Turbo classifier, under a condition of the number of revolution of 2000 rpm for 3 hrs . and then particles of original powder converting were compressed into plastic deformation resulting in changing the spherical original powder into the flake copper powder.
The obtained flake copper powder' s properties using the above-mentioned method were as follows. The maximum particle diameter was 1.64 um or smaller, and there was no coarse particle, in which an average particle diameter DSO of the ratio of Dmax/Dso was 4.1, but there was no coarse particle whose Dmax/D5o value was 5 or larger as below-mentioned, and the agglomerate values showed D1o (0.26 um), D5o (0.40 um) and D9o (0.67 um) measured using the laser diffraction scattering particle size distribution measurement method, SD/Dso value was 0.38 and Dgo/Dlo value was 2.58 by the standard deviation SD
(0.15 ~Zm) of particle size distribution with the laser diffraction scattering particle size distribution measurement method.
And the average thickness of powder particle of the flake copper powder was 0.05 um. The thickness was significant to determine using the following method having the steps of producing sample made of flake copper powder being solidified using epoxy resin and observing that sample with the scanning electron microscope (at X10000-magnification) to monitor the sample in order to the thickness directly, and then the total of thickness of the flake copper powder in the field of microscope view was divided into the total number of flake copper powder. And yet, in the below-mentioned examples and the comparative example, magnification of the microscope was applied up to the thickness of copper powder for monitoring being available to determine the thickness as well as the above-mentioned methods. Further the average particle diameter (major axis) being observed directly this flake copper powder was 0.39 Vim. Here, the powder particle was observed using the scanning electron microscope (at X5000-magnification) , and then the average value of major axis for flake copper powder, which could be confirmed from observation image obtained using the above-mentioned method was required. Regarding as the major axis of flake copper powder, the magnification, by which the major axis of flake copper powder could be observed at pleasure in the following examples and the comparative example, it will be the major axis of flake copper powder as well. The average aspect ratio was 7.8. The average aspect ratio was required as the above-mentioned [average particle size]/[average thickness].
Accordingly, it could be shown that the facts were satisfied which flake copper powder of the present invention should meet the requirements.
Additionally the inventors produced conductive paste which belonged to a terpineol group used for flake copper powder, and measured the change rate of viscosity of a conductive paste.
The composition of the conductive paste belongs to a terpineol group produced in the present invention constituted by 65wto flake copper powder and the rest of composition is organic vehicle used for binder resin, milling those in order to gain the conductive paste of the terpineol group. Organic vehicle utilized in this method had the composition constituted by terpineol 93wt% and ethylcellulose 7wto. The viscosity of conductive paste of terpineol group being obtained using the above-mentioned method, immediately after produced, was measured.
The viscosity in this descrption, was measured using RE-10 which was a viscometer manufactured from Toki Sangyo Co. , Ltd. at revolution of 0.1 rpm and 1.0 rpm. The following, measured at revolution, 0.1 rpm, is called [A viscosity], measured at revolution, 1.0 rpm is called [B viscosity]. A
viscosity was 380 Pa ~ s and B viscosity was 160 Pa ~ s . Besides, in order to require the viscosity ratio (=[A viscosity]/ [B
viscosity]), used for the index to show thixotropix property of a conductive paste, as defined by 2.4. As the viscosity ratio was larger, thixotropix property of conductive paste might be preferable.
Example 2:
In this example, copper powder obtained from raw material powder with the below-mentioned method was used, as original powder with a producing process of the present invention to produce flake copper powder.
Powder properties of original powder utilized in this example, the cumulative particle diameter, i . e. , D5o value was 0.85 um, in which the value was obtained using the laser diffraction scattering particle size distribution measurement method, and an average particle diameter, i.e., DIA value was 0.48 um, which was obtained by image analysis. Accordingly, an agglomerate value calculated based on D5o/DIA value was 1.77.
Regarding as the above-mentioned original particles powder under the agglomerate condition, the powder was used in purified water as copper powder slurry, and then circulated by the number of revolution by 3000 rpm, with a fine flow mill manufactured by Pacific Machinery & Engineering Co. , Ltd. which is a commercial fluid mill using a centrifugal force to perform an operation that changed agglomerate powder particles into single ones to collide against the powder particle each other.
As a result, the cumulative powder particle diameter of copper powder (original powder) completed after conducting to be a single particle, DSO value was 0.73 um with the laser diffraction scattering particle size distribution measurement method, and an average diameter DIA was 0. 49 um obtained by image analysis so that the agglomerate value calculated on DSO/DIA
value was 1.49. The fact showed that the above-mentioned operation was conducted sufficiently.
Next, while using original powder 500g treated after dispersion of particles, by using the same method in Example 1, powder particles of original powder were compressed and plastically deformed, so as to spherical original powder to be flake copper powder. However, a media dispersion mill, the DISPERMAT D-5226, manufactured by VMG-GETAMANN in Example l, changed only an processing time by 10 hours for the treatment, and then compressed powder particles of original powder by plastic deformation, finally substantially spherical original particles powder was compressed and plastically deformed into flake copper powder.
The obtained flake copper powder' s properties using the above-mentioned method, the maximum particle diameter was 15.56 Vim, and there was no coarse particle such that Dmax/DSo was 4.7 or larger but 5 or smaller as below-mentioned, and the agglomerate values show Dlo value (1. 51 yam) , DSO value (3.33 um) and D9O value(6.03 um) with the laser diffraction scattering particle size distribution measurement method, SD/DSO value was 0.50 and D9o/Dlo value was 3.99 to be shown by standard deviation SD ( 1 . 68 Vim) of particle size distribution with the laser diffraction scattering particle size distribution measurement method. And the average thickness of powder particle of the flake copper powder was 0.02 um, the average particle diameter (major axis) directly observed of this flake copper powder was 2.8 um, and an average aspect ratio was 140.
Accordingly, the fact that flake copper powder of the present invention met the requirements.
Besides, the inventors produced a conductive paste that belonged to terpineol groups using flake copper powder, and providing an organic vehicle by mix at ratio in the same way as in Example 1, then measured the rate of viscosity of the conductive paste. As a result, a viscosity was 600 Pa~s, B
viscosity was 143 Pa~s. Therefore the viscosity ratio (=[A
viscosity]/ [B viscosity]) was 4.2.
Example 3:
In this example, copper powder obtained from raw material powder with a below-mentioned method was used, as original powder with a producing process of the present invention to produce flake copper powder. Raw material and original powder utilized in this example were applied in the same way as in Example 2. Therefore, to omit duplicate explanation about properties of powder particle and the same after finishing the treatment, the explanation is not omitted herein.
Next, the original powder 500g constituted by single particles in the same way as in Example 1 to compress powder particles of original powder and deforming them by plastic deformation, so as to obtain substantially spherical original particles powder and flake copper powder. However, a media dispersion mill called the DISPERMAT D-5226 manufactured by VMG-GETAMANN was used by merely changing the processing time in Example 1 as 7 hours for the treatment, and then the powder particles of original powder were compressed to be converted them by plastic deformation, finally the substantially spherical original particles powder was changed into flake copper particles powder.
The obtained flake copper powder' s properties using the above-mentioned method, the maximum particle diameter was smaller than 5.36 um, and there was no coarse particle whose average particle diameter was defined as DSO, then Dmax/D5o value showed larger than 3.6 but smaller than 5 as below-mentioned, and the values show Dlo value(0.67 um), D5o value (1. 50 um) and D9O value (2. 80 um) with the laser diffraction scattering particle size distribution measurement method.
The SD/DSO value was 0.53 and the D9O/Dio value was 4.18 using the standard deviation SD (0.79 ~zm) of particle size distribution with the laser diffraction scattering particle size distribution measurement method. The average thickness of the powder particle of the flake copper powder was 0.08 Vim, the average particle diameter (major axis) observed directly through this flake copper powder was 1.3 ~zm, and an average aspect ratio was 18.8. Accordingly the fact showed that the flake copper powder of the present invention met the requirements.
Further the inventors produced a conductive paste which belonged to a terpineol group used for flake copper powder, providing organic vehicle at mixed ratio in the same way as in Example l, then the rate of viscosity of the conductive paste was measured. As a result, A viscosity was 420 Pa~s and B

viscosity was 130 Pa's. Therefore the viscosity ratio (=[A
viscosity]/ [B viscosity]) was 3.2.
Example 4:
In this example, copper powder obtained from raw material powder with a below-mentioned method was used, as original powder with a producing process of the present invention to produce flake copper powder. Raw material and original powder utilized in this example were applied in the same way as in Example 2. Therefore, to avoid duplicate explanation about properties of powder particle and the same after being finished treatment, the explanation is not omitted herein.
Next, original powder 5008 constituted by single particles, providing the same method in a same way as in Example 1 to compress powder particles of original powder and converting them by plastic deformation, so as to change spherical original powder into flake copper powder. However, a media dispersion mill called the DISPERMAT D-5226 manufactured by VMG-GETAMANN in Example 1, to change only the time as 7 hours for the treatment, and then compressing powder particles of original powder and converting them by plastic deformation, finally changing the spherical particles original powder to flake copper powder.
The obtained flake copper powder' s properties using the method as mentioned-above were as follows, the maximum particle diameter Dmax was 1.44, and there was no coarse particle having an average particle diameter DSO, Dmax/D5o value was 1.5, but there was no coarse particle whose Dmax/Dso value was 5 or larger as below-mentioned, and the agglomerate values show Dlo value (0.51 um), DSO value (0.95 um) and D9o value(1.43 um) with the laser diffraction scattering particle size distribution measurement method. The SD/DSO value was 0.45 and the D9o/Dlo value was 2.80 to be shown by using the standard deviation SD
(0.79 ~zm) of a particle size distribution with the laser diffraction scattering particle size distribution measurement method. The average thickness of the powder particle of the flake copper powder was 0.19 um, the average particle diameter (major axis) obtained directly using this flake copper powder was 0. 9 um, and the average aspect ratio was 4.7. Accordingly the fact showed that flake copper powder of the present invention met the requirements. Further the inventors produced a conductive paste which belonged to a terpineol group used for flake copper powder, and applying organic vehicle and mixed ratio in the same way as in Example 1, then measured at the rate of viscosity of the conductive paste. As a result, a viscosity was 350 Pa ~ s and B viscosity was 125 Pa ~ s.
Therefore, the viscosity ratio (_ [A viscosity] / [B viscosity] ) was defined by 2.8.
Example 5:
In this example, copper powder obtained from raw material powder using a below-mentioned method was used, as original powder with a producing process of the present invention to produce flake copper powder.
Regarding as powder properties of original powder utilized in this example, the cumulative particle diameter, i.e.,Dso, was 6.84 um, which was obtained using the laser diffraction scattering particle size distribution measurement method, and average particle diameter; DIA was 4.20 um. The value was obtained by image analysis. Accordingly, an agglomerate value was calculated, so that Dso/DrA value was 1.63.

Above-mentioned original powder under agglomerate condition was circulated by the number of revolution by 6500rpm, with Turbo classifier manufactured by Nissei Engineering Limited using a commercial pneumatic classification device to perform an operation that made agglomerate particles to be a single one to collide against the powder particle each other.
As a result, the cumulative particle diameter of copper powder (original powder) was completed after conducting to be a singular particle, Dso value was 4.92 um with the laser diffraction scattering particle size distribution measurement method, and an average diameter DIA was 4.10 um obtained from image analysis so that the agglomerate value calculated on Dso/Dza value was 1.20. The fact showed that the above-mentioned operation was conducted sufficiently.
Next, original powder 500g was treated as single particles in the same way as in Example 1. The compressed powder particles of original powder converted them by plastic deformation, so as to change spherical original powder to be flake copper powder. However, a media dispersion mill called DISPERMAT D-5226 manufactured by VMG-GETAMANN in Example 1 was used to change only the processing time as 10 hours for the treatment, and then compressing particles of original powder converting them by plastic deformation, finally changed spherical original powder to flake copper powder.
The obtained flake copper powder' s properties using the above-mentioned method, the maximum particle diameter, Dmax was smaller than 40.00 Vim, and there was no coarse particle whose average particle diameter regarded as Dso. Then Dmax/D5o value is 4.2. There is no coarse particle whose size is 5 or larger, and the agglomerate values show Dlo ( 4 . 75 um) , Dso ( 9 . 50 pm) and D9o (12.83 Vim) using the laser diffraction scattering particle size distribution measurement method, the SD/DSO value was 0.34 and the D9o/Dlo value was 2.70 used for standard deviation SD (3.23 um) of particle size distribution with the laser diffraction scattering particle size distribution measurement method. And the average thickness of the powder particle of the flake copper powder was 0.80 ~m and the average particle diameter (major axis) observed directly by this flake copper powder was 9.2 um, and the average aspect ratio was 11 . 5.
Accordingly, the fact showed that flake copper powder of the present invention met the requirements.
Additionally, the inventors produced a conductive paste, which belonged to a terpineol group using flake copper powder, and providing organic vehicle at mixed ratio in the same way as in Example 1, then measured the rate of viscosity of a conductive paste. As a result, A viscosity was 90Pa ~ s and B
viscosity was 60 Pa's. Therefore the viscosity ratio (=[A
viscosity]/ [B viscosity]) was 1.5.
Example 6:
In this example, copper powder obtained from raw material powder with a below-mentioned method was used, as original powder with a producing process of the present invention to produce flake copper powder.
Powder properties of original powder used in this example, the cumulative particle diameter; DSO was 4.24 Vim, in which the value was obtained with the laser diffraction scattering particle size distribution measurement method and DIA of the average particle diameter was 2.10 um, in which the value was obtained by image analysis. Accordingly, the agglomerate value obtained by DSO/DIA was 2.02.

The above-mentioned original powder under agglomerate condition was circulated on the number of revolution by 6500 rpm, with Turbo classifier from Nissei Engineering Limited, used for a commercial pneumatic classification device to perform an operation that made agglomerate powder particles to be single ones to collide against the powder particle each other.
As a result, the cumulative particle diameter of copper powder (original powder) was completed after conducting to be single particles. Dso value was 2.80 ~m using the laser diffraction scattering particle size distribution measurement method, and the average diameter DIA was 2.00 um obtained from image analysis, so that the agglomerate value calculated by Dso/DIA value was 1.40. The fact showed that the above-mentioned operation was sufficiently performed.
Next, the original powder 5008 constituted by single particles was provided in the same way as in Example 1 to compress powder particles of original powder and convert them by plastic deformation, so as to convert spherical original particles powder into flake copper powder. However, a media dispersion mill, the DISPERMAT D-5226 manufactured by VMG-GETAMANN in Example l, to change only the processing time as 7 hours for the treatment, and then compressing powder particles of original powder and converting them by plastic deformation, resulting in that substantially spherical original powder was changed into flake copper powder.
The obtained flake copper powder' s properties using the method as above-mentioned, the maximum particle diameter, Dmax was 20.73 um or smaller, and there was no coarse particle whose average particle diameter was Dso , whose Dmax/Dso was the ratio of the Dso was 2.8 but there was no coarse particle whose Dso was 5 or larger described below, and the agglomerate values show Dlo ( 3 . 87 um) , DSO ( 7 . 30 um) and D9o ( 8 . 51 um) with the laser diffraction scattering particle size distribution measurement method, SD/DSO value was 0.50 and D9o/Dlo value was 2.20 using for standard deviation SD (2.34 um) of particle size distribution with the laser diffraction scattering particle size distribution measurement method. And that the average thickness of the powder particle of the flake copper powder was 0.70 ~zm, the average particle diameter (major axis) observed directly this flake copper powder was 7.2 um, and the average aspect ratio was 10.3. The fact showed that flake copper powder of the present invention met the requirements.
Accordingly the inventors produced a conductive paste which belonged to a terpineol group used for flake copper powder, and applying organic vehicle at mixed ratio in the same way as in Example 1, then measured the rate of viscosity of the conductive paste. As a result, A viscosity was 112Pa~s and B viscosity was 70 Pa ~ s. Therefore the viscosity ratio (_[A
viscosity]/ [B viscosity]) was showed by 1.6.
Comparative Example:
In this comparative example, dried material powder under agglomerate condition was employed in Example 1, without a dispersing operation in the same way as in Example 1, using a Dyno-mill manufactured by Willy A. Bachofen AG Maschinenfabrik, KDL type, and then compressing powder particles of original powder and converting them into plastic deformation with 0.7 mm diameter beads, then finally change spherical original powder into flake copper powder. As a result, the obtained powder properties of flake copper powder as above-mentioned were shown in Table 1, labeled as sample number 4. This flake copper powder contains coarse particles, in which the maximum diameter was five times as long as average diameter Dso.
Now, powder properties of flake copper powder to be labeled as the sample number 4 will be described. The agglomerate values show Dlo (2. 81 um) , DSO (8. 20 pm) , D9o (21. 38 um) and the maximum particle diameter size Dmax (52.33 Vim), Dmax/DSO was 6.4 and the value of it was 5 or larger. Further SD/DSo value was 0.87 by the value of the standard deviation, SD (7. 17 um) , and D9o/Dlo value was 4 . 04. The average thickness of the powder particle of the flake copper powder was 0.75 um, and an average particle (major axis) to be observed directly was 7.8 um, an average ratio was 10.4. Alternatively, the fact showed that flake copper powder of the present invention met the requirements. Using such flake copper powder to product conductive paste, even if the composition of organic vehicle were altered in order to be difficult to control the viscosity of the conductive paste, such flake copper powder could not be applied to drawing of a printed circuit by a high density.
Therefore the inventors measured the viscosity of conductive paste to utilize flake copper powder, the sample number 4, and to apply organic vehicle and mixing ratio thereof to produce conductive paste in a terpineol group. As a result, A viscosity was 250 Pa ~ s and B viscosity was 227 Pa ~ s. The viscosity ratio (=[A viscosity] / [B viscosity] ) was defined by 1.1. Owing to the result, only thixotropic property thereof especially seemed to be inferior in comparison with the above-mentioned conductive paste, though there might be no extraordinary difference between both. Alternatively the conventional flake copper powder could have the thixotropic property and produce thinner the thickness of particle of flake copper powder, while the powder particle distribution became broad, and if the average particle diameter was regarded as a standard so that it had extraordinary coarse particles, it means that that kind of powder particles could not be used for forming the electrode and circuit being thinner, also having high layer density.
Industrial Applicability The viscosity of conductive paste can be controlled by using flake copper powder by the present invention, and thereby it can provide a thixotropic property having a good balance with respect to viscosity, forming conductive pastes being thinner into such the conductive paste, enhancing the layer density, without losing electrical resistance. Also a conductor shape is easy to control, resulting in that a thinner and/or fined circuit pattern can be established, which had been able to be obtained. Further usage of the producing method of the present invention makes to be possible to produce flake copper powder efficiently. Also through the flake copper powder having the powder properties of the present invention, the particle distribution of fine particle is splendid, which had not exist.
Also a production yield of the flake copper powder having the splendid powder properties can be much more enhanced.
Apparent from the above-mentioned descriptions, the flake copper powder of the present invention whose particle distribution is much sharper than conventional and the aspect ratio thereof can be easy to be changed using the producing method of the present invention. As a result, the most preferable way can be designed for thixotropic property of flake copper powder.

Claims

1. Flake copper powder processed by plastic deformation of each of particles of copper powder characterized in that:
a cumulative particle diameter D50 is 10µm or smaller;
a SD/D50 value is 0.55 or smaller;
and a D90/D10 value is 4.5 or smaller;
in which SD is a standard deviation of a particle distribution measured by a laser diffraction scattering particle size distribution method, and D10, D50 and D90 are cumulative particle diameters measured thereby.

2. The flake copper powder according to claim 1, wherein an aspect ratio (average major axis / average thickness) of said powder particle is from 3 to 200.

3. The flake copper powder according to claim 1 or claim 2, wherein Dmax / D50 of a ratio of a cumulative particle diameter D50 to the maximum cumulative particle diameter Dmax by the laser diffraction scattering particle size distribution method is 5 or smaller.

4. Flake copper powder including said flake copper powder according to one selected from claim 1 to claim 3 by 70 wt% or larger in existence rate.

5. A manufacturing method of the flake copper powder according to one selected from claim 1 to claim 4 comprising the steps of:
dispersing a copper powder under an agglomerate condition;
using the copper powder having superior dispersity whose agglomerate degree is 1.6 or smaller after completion of dispersion; and forming and plastically deforming particles of said copper powder in a flake manner by compressing said particles of said copper powder with a high energy ball mill using media beads, each whose particle diameter is 0.5mm or smaller.

6. The manufacturing method of flake copper powder according to claim 5 wherein a gravity of each of the media beads is from 3.0 g/cm3 to 6.5 g/cm3.

7. A conductive paste produced using said flake copper powder according to any of claim 1 to claim 4.