U.S. patent application number 10/536012 was filed with the patent office on 2006-06-29 for copper flake powder, method for producing copper flake powder, and conductive paste using copper flake powder.
This patent application is currently assigned to Mitsui Mining and Smelting Co., Ltd.. Invention is credited to Takahiko Sakaue, Kunihiko Yasunari, Katsuhiko Yoshimaru.
Application Number | 20060137488 10/536012 |
Document ID | / |
Family ID | 32375760 |
Filed Date | 2006-06-29 |
United States Patent
Application |
20060137488 |
Kind Code |
A1 |
Sakaue; Takahiko ; et
al. |
June 29, 2006 |
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 D.sub.50 of 10 .mu.m or smaller
measured with laser diffraction scattering particle size
distribution method. The D.sub.10, D.sub.50 and D.sub.90 measured
with the laser diffraction scattering particle size distribution
method are illustrative and the SD/D.sub.50 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 D.sub.90/D.sub.10 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.
Inventors: |
Sakaue; Takahiko;
(Shimonoseki-shi, Yamaguchi, JP) ; Yasunari;
Kunihiko; (Shimonoseki-shi, JP) ; Yoshimaru;
Katsuhiko; (Shimonoseki-shi, JP) |
Correspondence
Address: |
ROTHWELL, FIGG, ERNST & MANBECK, P.C.
1425 K STREET, N.W.
SUITE 800
WASHINGTON
DC
20005
US
|
Assignee: |
Mitsui Mining and Smelting Co.,
Ltd.
11-1, Osaki 1-chome, Shinagawa-ku
Tokyo
JP
141-8584
|
Family ID: |
32375760 |
Appl. No.: |
10/536012 |
Filed: |
August 11, 2003 |
PCT Filed: |
August 11, 2003 |
PCT NO: |
PCT/JP03/10192 |
371 Date: |
February 9, 2006 |
Current U.S.
Class: |
75/255 ;
257/E23.075 |
Current CPC
Class: |
B22F 2999/00 20130101;
H01L 2924/0002 20130101; B22F 1/0011 20130101; H05K 1/095 20130101;
H01L 2924/0002 20130101; B22F 2998/00 20130101; H01L 2924/09701
20130101; B22F 2999/00 20130101; B22F 1/0007 20130101; B22F 1/0055
20130101; B22F 2998/00 20130101; B22F 1/0007 20130101; H01L
23/49883 20130101; B22F 1/0055 20130101; H01L 2924/00 20130101;
B22F 9/04 20130101 |
Class at
Publication: |
075/255 |
International
Class: |
B22F 1/00 20060101
B22F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 22, 2002 |
JP |
2002-338990 |
Claims
1. Flake copper powder processed by plastic deformation of each of
particles of copper powder characterized in that: a cumulative
particle diameter D.sub.50 is 10 .mu.m or smaller; a SD/D.sub.50
value is 0.55 or smaller; and a D.sub.90/D.sub.10 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 D.sub.10, D.sub.50 and D.sub.90 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, wherein
Dmax/D.sub.50 of a ratio of a cumulative particle diameter D.sub.50
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 claim 1 by 70 wt % or larger in existence rate.
5. A manufacturing method of the flake copper powder according to
claim 1 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 0.5 mm 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/cm.sup.3 to 6.5 g/cm.sup.3.
7. A conductive paste produced using said flake copper powder
according to claim 1.
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 conductive paste, a high-layer-density is required
that prevents an increase in the electric resistance in an electric
circuit. Simultaneously it is desired to have the ability of
maintaining a configuration of the formed conductive circuit.
[0004] To meet the market demands as above-mentioned, the copper
powder used for producing a conductive paste is sometimes a copper
powder formed by not using the spherical particles of copper powder
but using flaky particles of powder (hereinafter called "flake
copper powder" in the present description) has been considered. As
apparent from the shape of each of the 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. Thus, the contact area between the powder particles
has also become wider resulting in that the flake copper powder is
very effective in reducing electric resistance and enhance
properties to maintain the configuration of the conductive circuit.
The above-mentioned details are referred in Japanese Patent
publications Nos. H06(1994)-287762 and H08(1996)-325612. These
publications clarify the above-mentioned description.
[0005] However, such conventional flake copper powder has not had
evenly-sized particle diameter and even thickness. Further, there
has been no existence of flake copper powder having fine particles
while containing coarse particles at a constant ratio. 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 in addition to
having a very broad particle size distribution.
[0006] The viscosity 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 the
conductive paste is difficult to handle. Also the viscosity of the
conductive paste has been unstable. The conventional flake copper
powder has had defects regarding the instability of the thixotropic
property of the conductive paste. The thixotropic property is
particularly important when forming an electrode of a chip part
using a dipping method. For example, upon producing an external
electrode of a chip part for a multilayer ceramic capacitor, first
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.
[0007] In recent years, as a chip part becomes miniaturized, there
is an increase in demand for a thinner layer of external electrode.
To meet the demands of forming the thinner layer, the 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 flowing of the coated layer
formed by the conductive paste. Further, 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.
[0008] The conductive paste using the conventional flake copper
powder can also have the superior thixotropic property. However,
the conventional flake copper powder can arrive only at a 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
although 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 increased. Further, in case of
drawing a circuit using the conductive paste 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 are a problem. 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.
[0009] 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, there has been a demand in the
market for such type of flake copper powder.
BRIEF DESCRIPTION OF DRAWINGS
[0010] FIG. 1 shows an observed image of a flake copper powder
relating to the present invention through a scanning electron
microscope.
[0011] 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
[0012] Accordingly, the inventors have developed subsequent flake
copper powder based on following reasons. Coarse particles, each
having a principal axis are mixed with the conventional flake
copper powder, in which the principal axis of each of the coarse
particles is five times or more longer than the diameter of a
particle of the conventional flake copper powder. Further, the
thickness of each of the powder particles is uneven and the
particle distribution is uneven. The inventors have focused on the
above-mentioned defects. In view of the relationship between the
properties of the powder and a process of thinning the
above-mentioned conductive circuit the inventors have developed
flake copper powder as follows. Below the present invention will be
described.
Flake Copper Powder Relating to the Present Invention
[0013] The inventors have researched the conventional copper powder
which already existed, resulting in the various properties of the
conventional copper powder shows in Table 1. Herein, D.sub.10,
D.sub.50, D.sub.90 and Dmax are defined by particle diameter sizes
by each of 10%, 50% and 90% and maximum particle size regarding the
volume cumulation, which can be obtained using a laser diffraction
scattering particle size distribution measurement method. Then, 0.1
g of flake copper powder was mixed with 0.1%-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, they were
measured using a laser diffraction scattering particle size
distribution apparatus, Micro Trac HRA 9320-X100 type (manufactured
by Leeds and Northrup Limited). TABLE-US-00001 TABLE 1 D.sub.10
D.sub.50 D.sub.90 Dmax SD SAMPLE (.mu.m) SD/D.sub.50
D.sub.90/D.sub.10 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
[0014] As far as observing the results of Table 1, the results show
that the conventional flake copper powder also has various
characteristics of the powders, and it seems that the conventional
flake copper powder can be changed depending on various properties
of powder particles of raw materials and methods of process. In
Table 1, 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 all particle diameters, 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
lots with a standard deviation (SD) measured therein can be shown
by scattering from 3.86 .mu.m to 18.31 .mu.m. Also apparent is,
that there is a significant scattering of particle size between
lots. Focusing on a result of SD/D.sub.50 value being a coefficient
of variation, the result of scattering from 0.66 to 0.87 is
obtained, and D.sub.90/D.sub.10 value shows scattering from 4.62 to
7.61. Further, the Dmax value can be obtained using the laser
diffraction scattering particle size distribution measurement
method, which is the maximum particle diameter and it can be noted
that coarse particles as much as 104.70 .mu.m in diameter are
included. 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
to what extend the flake is formed. 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.
[0015] 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
these 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.
[0016] The inventors have devoted themselves to study and shown
some facts as follows. If properties of a particle of flake copper
powder as defined by a cumulative particle diameter D.sub.50 of 10
.mu.m or smaller; a SD/D.sub.50 value of 0.55 or smaller; and a
D.sub.90/D.sub.10 value of 4.5 or smaller; in which the SD is a
standard deviation of particle distribution measured by a laser
diffraction scattering particle size distribution method, and
D.sub.10, D.sub.50 and D.sub.90 are cumulative particle diameters
measured thereby", as recited in the claims, and when the flake
copper powder is processed into a conductive paste then layer
thickness of the circuit can be thinner drawing a circuit under the
conditions described above. Further, the layer density is excellent
and it is possible to acquire a well-quality-balanced thixotropic
property which can easily remove a binder contained in a conductive
paste. In case of using such a conductive paste, the following can
be shown: it can prevent on increase in conductivity resistance;
simultaneously the conductivity can be enhanced by its shape
without increasing conductivity resistance. In FIG. 1, the flake
copper powder (two types) relating to the present invention is
shown, which is observed using the scanning electron microscope. As
apparent from comparing FIG. 1 with FIG. 2, the powder particle
sizes of flake copper powder in FIG. 1 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.
[0017] Here, the reason why "cumulation particle size D.sub.50 is
10 .mu.m 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 D.sub.50 is 10 .mu.m or smaller, it is impossible to
stably decrease 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 D.sub.50 is 7
.mu.m 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 stability as a conductive paste optionally, it is noted that
thickness of the conductive figure cannot be thinner resulting in
increasing electric resistance of a formed sintered circuit due to
the inferiority of the layer density 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
a thinner conductor is formed using a conductive paste, the thin
layer is not formed successfully because of existence of coarse
particles and inferior thixotropic property. Additionally, one can
consider that measurement of cumulative particle diameter D.sub.50
using this method of measuring the laser diffractive scattering
particle size distribution may be a reflection of the length at a
major axis of the particle of flake copper powder affected and
flattened by plastic deformation.
[0018] 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 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, when the aspect ratio is smaller, the flake
copper powder tends to become thick and large. Therefore, it is
remarkable that if the range of the aspect ratio (average major
axis/average thickness) is 3 or shorter, the thixotropic property
will be apparently lacking with respect to the viscosity property
when the flake copper powder is processed into a conductive paste.
On the other hand, in times when the aspect ratio (average major
axis/average thickness) exceeds 200, the shape of the powder
particle itself folded, a defective shape occurs, and cracks on the
surface of the powder particle occur. The range of the particle
distribution will be very broad and the thickness of flake copper
powder will be much too thin. This thin flake copper powder cannot
be mixed evenly with organic vehicles when a flake copper powder is
processed as a conductive paste.
[0019] Additionally, a property of the flake copper powder of the
present invention, when the cumulative particle diameter D.sub.50
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
D.sub.50 value. Namely, the Dmax/D.sub.50 of a ratio of a
cumulative particle diameter D.sub.50 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.
[0020] Also the above-mentioned flake copper powder is obtained
through a process where the conventional copper powder particle
having a substantially spherical shape is mechanically changed to
be flake-shaped by plastic deformation. As a result, scattering
upon producing will generally occur at a certain rate. Then the
inventors have studied as follows. If the product contains 70% or
more of the flake copper powder 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
[0021] It is impossible to stably produce the above-mentioned flake
copper powder, even if the conventional production process is used.
In other words, the conventional flake copper powder, the
substantially spherical copper powder obtained with wet method such
as the 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. Then the processed powder
particle is changed by plastic deformation to be flattened and
flake-shaped.
[0022] However, in the case of performing such production process,
usually-spherical copper powder itself used at the first step, is
under a predetermined agglomerate condition, and even if conducting
compressed deformation without destroying the agglomerate
condition, the condition will be compressed by deformation,
maintaining the agglomerate condition. As a result of the
production process, the flake copper powder an produced under the
same agglomerate condition as above-mentioned, and additional
powder particles will not be mutually dispersed.
[0023] Therefore, the inventors have reached a conclusion that at
first the agglomerate condition of substantially spherical powder
particle be dispersed, and secondly the powder particle is forced
to change by compressing and deformation to be flake-shaped. The
corresponding method according to claim is that "a production
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 of which the
particle diameter is 0.5 mm or smaller".
[0024] Copper powder under agglomerate condition is defined such
that even if the inventors use the wet method being the typified
hydrazine reduction, or the dry method being typically atomizing
method, a certain agglomerate condition of copper powder will be
formed, which is the reason why the term "agglomerate condition" is
used in the descriptions. Especially, applying wet method tends to
induce of the agglomerate condition particle of copper powder.
This, because in general the production method of copper powder
with wet method uses copper sulfate solution as starting material.
Then a sodium hydroxide solution is utilized to be reacted in order
to obtain copper oxide. This copper oxide goes through the
so-called hydrazine reduction, and then produces with the methods
below, such as cleaning, filtering and drying. The method will
provide copper powder to be under dry condition, though if the wet
method is used in order to gain particles 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 copper powder comes up in the so-called hydrazine
reduction and such copper powder slurry conditions are established
containing the above-mentioned copper powder. The operation that
agglomerate particles are dispersed under initial particles as much
as possible is so-called "dispersing".
[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.
[0026] As one of the methods for the dispersing procedure, of dried
copper powder under agglomerate condition can be dispersed into
each particle of copper powder with a wind power circulator. The
"wind power circulator utilizing centrifugal force" defined herein,
first of all, to blow air and then blow up copper powder in
concentrated condition like drawing an orbit of circumference of
track in order to circulate. To use the centrifugal force occurred
as 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 a wind classification machine. The object of
the machine is not to classify but the object is to take a role as
a circulator to blow up air and then in concentrated status the
copper powder is blown up in the air like drawing circumference of
track.
[0027] Another method of dispersing copper powder into particles,
was copper powder slurry containing copper powder under agglomerate
condition in a procedure with a fluid mill using centrifugal force.
The object is to use the "fluid mill used centrifugal force" here
in, first of all, to flow copper powder slurry in high speed to
drawn orbit of circumference, and then each particle of copper
powder to crash these with each other in a solvent with centrifugal
force which occurred at the time due to the dispersing
procedure.
[0028] Accordingly, the above-mentioned dispersing procedure, 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 finished in
a dispersing procedure, has new properties as a powder particle
after the concentrate condition is destroyed. Following is an
explanation about the agglomerate value set in the description.
Using the D.sub.50 obtained value, with the laser diffraction
scattering particle size distribution measurement and an average
particle diameter which is a D.sub.IA, defined by calculation from
a size of the picture image by SEM, and then an agglomerate value
of D.sub.50/D.sub.IA shown by the above value, D.sub.50 and
D.sub.IA, 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.
[0029] The D.sub.50 value, obtained through the laser diffraction
scattering particle size distribution measurement method, will not
be considered to really observe a powder particle one by one. Most
copper powder particles are not individual perfectly, so-called
mono-dispersed. The copper powder are comprised of several
particles of the agglomerate condition. The laser diffraction
scattering particle size distribution measurement method is to
regard each of the agglomerate powder particles as a single
particle, and then calculates the value of cumulative particle
diameter.
[0030] On the contrary, an average diameter value D.sub.IA with SEM
(Scanning Electron Microscope) observes a copper powder image and
processes the observation image into image data, as is directly
obtained from the SEM observation image. An image of 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.
[0031] In view of the above-mentioned content, the inventors used
D.sub.50 being the value of cumulative particle diameter to get the
laser diffraction scattering particle size distribution measurement
and an average particle diameter D.sub.IA obtained through an image
analysis to determine the agglomerate value, which can be
calculated as D.sub.50/D.sub.IA. In other words, the inventors
presume that in copper powder from the same lot, the D.sub.50 and
D.sub.IA values can be measured with the same accuracy, considering
the above-mentioned theory. The D.sub.50 value is meant by
reflection of the concentrated condition over a value to be
measured, so that D.sub.50 value may be higher than D.sub.IA
value.
[0032] If the agglomerate particles of copper powder become
perfectly individual, the D.sub.50 value will be infinitely closer
to the D.sub.IA value and the concentrated degree D.sub.50/D.sub.IA
will be close to 1. When the concentrated value becomes 1, then it
can be said that there is completely no agglomerate condition of
powder particles, and as a result, those particles are completely
dispersed. However, in reality, sometimes the concentrated value is
indicated as smaller than 1. Theoretically, when considering a
particle is completely spheroid, in fact the value is not smaller
than 1. However, if a particle whose shape is not spheroid, a 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, which sensitivity threshold value of 10, overlaps
extending the value which is regarded as 20 by
circular-shaped-particle analyzing. The average particle diameter
is obtained as D.sub.IA.
[0033] The substantially spherical copper powder after completion
of the dispersion is processed with a high energy ball mill. The
particle of copper powder is formed by plastic deformation and
produces flake copper powder. Therefore the cumulated particle
diameter D.sub.50 of laser diffraction scattering particle size
distribution measurement of the flake copper powder as the final
product on the procedure mentioned above is 10 .mu.m or smaller.
First of all, D.sub.50 can be employed as a standard using the
laser diffraction scattering particle size distribution measurement
of the flake copper powder as before compressive deformation and
after the dispersion treatment (hereinafter referred as "original
powder"), compared with a processed flake of copper powder. To
consider these matters, D.sub.50 can be used as an estimation
index.
[0034] The "high energy ball mil" herein is a generic term used to
refer to a device which employs media beads to compress copper
powder into plastic deformation, e.g., using a ball mill, agitator
and so on, regardless whether under wet condition or under slurry
copper powder condition. Regarding the present invention, selecting
a particle diameter of each of the media beads and quality of
material is very important.
[0035] Firstly, media beads should be used which particle diameter
is 0.5 mm or smaller. The reasons why a diameter of each of the
media beads is defined based on the following. 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 a change in shapes of agglomerate
particles by compressive plastic deformation. The flake copper
powder cannot be obtained that has a narrow and superior
dispersibility particle size distribution, because the particle
size distribution became broad.
[0036] Further, it is preferable to use media beads, wherein the
gravity of each of the media beads is from 3.0 g/cm.sup.3 to 6.5
g/cm.sup.3. In case of a specific gravity of the media beads is
smaller than 3.0 g/cm.sup.3, 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/cm.sup.3, 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.
[0038] The level of thixotropic character of conductive paste
should depend on the intended purpose and usage. In general,
appropriate measures are determined with the consideration over
variations of organic vehicles in the conductive paste, flake
copper powder content, and the diameter of the particle of flake
copper powder.
BEST MODE FOR CARRYING OUT THE INVENTION
[0039] The following examples specifically show the present
invention.
EXAMPLE 1
[0040] In this example, copper powder obtained from raw material
powder by a below-mentioned method is used, as starting powder for
the production process of the present invention to produce flake
copper powder.
[0041] The powder properties of the original powder utilized in
this example are defined in that, the cumulative particle diameter;
D.sub.50 was 0.35 .mu.m, which was obtained using a laser
diffraction scattering particle size distribution measurement
method and average particle diameter; D.sub.IA was 0.20 .mu.m
obtained by an image analysis. Accordingly, an agglomerate value
calculated on D.sub.50/D.sub.IA was 1.75.
[0042] The above-mentioned original powder under agglomerate
condition was circulated 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 singular by colliding the
powder particles against each other.
[0043] As a result, the cumulative particle diameter of copper
powder (starting powder) completed as single particles, i.e.,
D.sub.50 was 0.30 .mu.m using the laser diffraction scattering
particle size distribution measurement method and an average
diameter D.sub.IA was 0.20 .mu.m obtained from the image analysis
so that the agglomerate value calculated on D.sub.50/D.sub.IA was
1.50. This fact showed that the above-mentioned dispersion
operation was performed sufficiently.
[0044] Next, 300 g of starting powder containing a singular
particle was used in using a DISPERMAT D-5226 manufactured
VMG-GETZMANN with 800 g of zirconia's beads, as media beads, each
whose specific gravity of zirconia's beads was 5.8 g/cm.sup.3, and
its diameter was 0.3 mm. As a solvent, methanol 120 g mixed with
cupric acid 5 g was used and then these were treated them using
Turbo classifier, under a condition of 2000 rpm for 3 hrs., and
then particles of original powder were converted by compression
through plastic deformation, resulting in changing the spherical
starting powder into the flake copper powder.
[0045] The properties of the flake copper powder obtained as
described above, are that the maximum particle diameter is 1.64
.mu.m, and the below mentioned Dmax/D.sub.50, a ratio of average
particle diameter D.sub.50 equals 4.1, and there are no observances
of particles over 5; and the number of SD/D.sub.50 is 0.38
calculated with laser deffraction scattering particle size
distribution measurement method of weight accumulation of D.sub.10
(0.26 .mu.m), D.sub.60 (0.40 .mu.m), D.sub.90 (0.67 .mu.m), and
using the particle distribution, normal deviation SD (0.15 .mu.m)
calculated through laser diffraction scattering particle size
distribution measurement method, and number represented with
D.sub.90/D.sub.10 is 2.58.
[0046] And the average thickness of powder particle of the flake
copper powder was 0.05 .mu.m. The thickness was significantly
determined using the following method having the steps of producing
a 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 determine the thickness directly. Then, the total of thickness
of the flake copper powder in the field of microscope view was
divided into the total number of flake of 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 of
this flake copper powder was 0.39 .mu.m. Here, the powder particle
was observed using the scanning electron microscope (at
X5000-magnification), and then the average value of major axis for
the flake copper powder, which could be confirmed from observation
of the image obtained using the above-mentioned method was
required. Comparing he magnification of the major axis of flake
copper powder, by which the major axis of the flake copper powder
could be observed at pleasure, the following can be viewed in
examples and the comparative example. The average aspect ratio was
7.8. The average aspect ratio was required in the above-mentioned
[average particle size]/[average thickness]. Accordingly, it could
be shown that the requirement were satisfied which the flake copper
powder of the present invention should meet.
[0047] 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 65 wt % of flake
copper powder and the rest of a composition which is an organic
vehicle used as binder resin, and milling those in order to gain
the conductive paste of the terpineol group. The organic vehicle
utilized in this method had the composition constituted by
terpineol 93 wt % and ethylcellulose 7 wt %. The viscosity of
conductive paste of terpineol group being obtained using the
above-mentioned method, was measured immediately after
produced.
[0048] The viscosity in this description, was measured using RE-10
which was a viscometer manufactured from Toki Sangyo Co., Ltd. at
0.1 rpm and 1.0 rpm. The following, measured at 0.1 rpm, is called
[A viscosity], and measured at 1.0 rpm is called [B viscosity]. A
viscosity was 380 Pas and B viscosity was 160 Pas. Besides, in
order to require the viscosity ratio ([A viscosity]/[B viscosity]),
used for the index to show the thixotropic property of a conductive
paste, as defined by 2.4. It can be said that the larger the
viscosity ratio, the thixotropic property of the conductive paste
might be preferable.
EXAMPLE 2
[0049] In this example, copper powder obtained from raw material
powder with the below-mentioned method was used, as starting powder
in a production process of the present invention to produce flake
copper powder.
[0050] Powder properties of the original powder utilized in this
example are defined in that, the cumulative particle diameter,
i.e., D.sub.50 value was 0.85 .mu.m, in which the value was
obtained using the laser diffraction scattering particle size
distribution measurement method, and an average particle diameter,
i.e., D.sub.IA value was 0.48 .mu.m, which was obtained by image
analysis. Accordingly, an agglomerate value calculated based on
D.sub.50/D.sub.IA value was 1.77.
[0051] With respect to the above-mentioned original particles
powder under agglomerate condition, the powder was used in purified
water as a copper powder slurry, and then circulated at 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 converts agglomerate
powder particles into singular particles by colliding the powder
particles against each other.
[0052] As a result, the cumulative powder particle diameter of the
copper powder (starting powder), completed after conversion to a
single particle, the D.sub.50 value was 0.73 .mu.m measured with
the laser diffraction scattering particle size distribution method,
and an average diameter D.sub.IA was 0.49 .mu.m obtained by image
analysis. Thus the agglomerate value calculated for the
D50/D.sub.IA value was 1.49. This fact showed that the
above-mentioned operation was conducted sufficiently.
[0053] Next, 500 g starting powder, treated after dispersion of
particles, was used in the same method as in Example 1, wherein the
powder particles of the starting powder were compressed and
plastically deformed, so that the spherical starting powder was
converted to flake copper powder. However, in the media dispersion
mill, the DISPERMAT D-5226, manufactured by VMG-GETAMANN in Example
1, only the processing time was changed to 10 hours for this
treatment, and thus compressing the powder particles of the
starting powder by plastic deformation, and finally the
substantially spherical starting powder particular were compressed
and plastically deformed into flake copper powder.
[0054] The obtained flake copper powder's properties using the
above-mentioned method, are that the maximum particle diameter was
15.56 .mu.m, and there were no coarse particle such that the
Dmax/D.sub.50 was equal to or larger than 4.7 but also equal to or
smaller than 5 as mentioned below. The agglomerate values show a
D.sub.10 value (1.51 .mu.m), a D.sub.50 value(3.33 .mu.m) and a
D.sub.90 value(6.03 .mu.m) measured with the laser diffraction
scattering particle size distribution method. The SD/D.sub.50 value
was 0.50 and the D.sub.90/D.sub.10 value was 3.99 showing a
standard deviation SD (1.68 .mu.m) of the particle size
distribution measured with the laser diffraction scattering
particle size distribution method. The average thickness of the
powder particle of the flake copper powder was 0.02 .mu.m, the
average particle diameter (major axis) directly observed of this
flake copper powder was 2.8 .mu.m, and an average aspect ratio was
140. Accordingly, the fact that flake copper powder of the present
invention met the requirements.
[0055] Furthermore, the inventors produced a conductive paste
having a terpineol group using flake copper powder, and providing
an organic vehicle with mix at ratio in the same way as in Example
1. The rate of viscosity of the conductive paste was then measured.
As a result, the A viscosity was 600 Pa.s, the B viscosity was 143
Pa.s. Therefore the viscosity ratio ([A viscosity]/[B viscosity])
was 4.2.
EXAMPLE 3
[0056] In this example, copper powder obtained from raw material
powder with a below-mentioned method was used, as starting in a
production process of the present invention to produce flake copper
powder. The raw material and starting powder utilized in this
example were produced in the same way as in Example 2. Therefore,
to avoid duplicate explanation about the properties of powder
particle and similarly the properties after finishing the
treatment, the explanation is omitted.
[0057] Next, 500 g of starting powder constituted by single
particles in the same way as in Example 1 were used to compress
powder particles of the starting powder and deform them by plastic
deformation, so as to obtain from substantially spherical starting
powder particles and the flake copper powder. However, in the media
dispersion mill called the DISPERMAT D-5226 manufactured by
VMG-GETAMANN used the processing time was only changed from Example
1 to 7 hours in this treatment. Then the powder particles of the
starting powder were compressed to be converted by plastic
deformation, to finally convert the substantially spherical
starting powder particles into flake copper powder particles.
[0058] The obtained flake copper powder's properties using the
above-mentioned method are, that the maximum particle diameter was
smaller than 5.36 .mu.m, and there were no coarse particle whose
average particle diameter was defined as D.sub.50, The resulting
Dmax/D.sub.50 value was larger than 3.6 but smaller than 5 as
mentioned below, and the results show a D.sub.10 value(0.67 .mu.m),
a D.sub.50 value (1.50 .mu.m) and D.sub.90 value(2.80 .mu.m)
measured with the laser diffraction scattering particle size
distribution method. The SD/D.sub.50 value was 0.53 and the
D.sub.90/D.sub.10 value was 4.18 using the standard deviation SD
(0.79 .mu.m) of particle size distribution measured with the laser
diffraction scattering particle size distribution method. The
average thickness of the powder particle of the flake copper powder
was 0.08 .mu.m, the average particle diameter (major axis) observed
directly for this flake copper powder was 1.3 .mu.m, and an average
aspect ratio was 18.8. Accordingly, these facts show that the flake
copper powder of the present invention met the requirements.
[0059] Further, the inventors produced a conductive paste which has
a terpineol group using flake copper powder, providing an organic
vehicle at mixed ratio similar to that in Example 1. The rate of
viscosity of the conductive paste was then measured. As a result,
the A viscosity was 420 Pa.s and the B viscosity was 130 Pa.s.
Therefore, the viscosity ratio ([A viscosity]/[B viscosity]) was
3.2.
EXAMPLE 4
[0060] In this example, copper powder obtained from raw material
powder with a below-mentioned method was used, as starting powder
in a production process of the present invention to produce flake
copper powder. The raw material and starting powder utilized in
this example were produced in the same way as in Example 2.
Therefore, to avoid duplicate explanation about the properties of
the powder particle and similarly the properties after finishing
treatment, the explanation is omitted.
[0061] Next, 500 g of starting powder constituted by single
particles, provided by the same method as in Example 1 were used to
compress powder particles of the starting powder and were converted
by plastic deformation, so as to convert spherical starting powder
into flake copper powder. However, in the media dispersion mill
called the DISPERMAT D-5226 manufactured by VMG-GETAMANN in Example
1, only the treatment time was changed to 7 hours, followed by
compressing the powder particles of starting powder and converting
them by plastic deformation, finally converting the spherical
starting powder particles to flake copper powder.
[0062] The obtained flake copper powder's properties using the
above-mentioned method were as follows, the maximum particle
diameter Dmax was 1.44, and there were no coarse particles having
an average particle diameter D.sub.50. The Dmax/D.sub.50 value was
1.5, but there were no coarse particles whose Dmax/D.sub.50 value
was 5 or larger as mentioned below, and the agglomerate values show
a D.sub.10 value (0.51 .mu.m), a D.sub.50 value (0.95 .mu.m) and a
D.sub.90 value (1.43 .mu.m) measured with the laser diffraction
scattering particle size distribution measuring method. The
SD/D.sub.50 value was 0.45 and the D.sub.90/D.sub.10 value was 2.80
observed by using the standard deviation SD (0.79 .mu.m) of a
particle size distribution measured with the laser diffraction
scattering particle size distribution measuring method. The average
thickness of the powder particle of the flake copper powder was
0.19 .mu.m. The average particle diameter (major axis) obtained
directly using this flake copper powder was 0.9 .mu.m, and the
average aspect ratio was 4.7. Accordingly these facts show that
flake copper powder of the present invention met the requirements.
Further the inventors produced a conductive paste which has a
terpineol group using the flake copper powder, and applying organic
vehicle and mixed ratio similar to that in Example 1. The rate of
viscosity of the conductive paste was then measured. As a result,
the A viscosity was 350 Pa.s and the B viscosity was 125 Pa.s.
Therefore, the viscosity ratio ([A viscosity]/(B viscosity]) was
defined by 2.8.
EXAMPLE 5
[0063] In this example, copper powder obtained from raw material
powder using the method mentioned below was used, as starting
powder in a production process of the present invention to produce
flake copper powder.
[0064] With respect to the powder properties of starting powder
utilized in this example, the cumulative particle diameter, i.e.,
D.sub.50, was 6.84 .mu.m, which was obtained using the laser
diffraction scattering particle size distribution measurement
method, and the average particle diameter; D.sub.IA was 4.20 .mu.m.
This value was obtained by image analysis. Accordingly, an
agglomerate value was calculated, so that D.sub.50/D.sub.IA value
was 1.63.
[0065] The above-mentioned starting powder under agglomerate
condition was circulated at 6500 rpm, in a Turbo classifier
manufactured by Nissei Engineering Limited using a commercial
pneumatic classification device to perform an operation that made
the agglomerate particles singular by colliding the powder
particles against each other.
[0066] As a result, the cumulative particle diameter of copper
powder (starting powder) was measured after completion of the
conversion to singular particles, the D.sub.50 value was 4.92 .mu.m
as measured with the laser diffraction scattering particle size
distribution method, and an average diameter D.sub.IA was 4.10
.mu.m obtained from image analysis, so that the agglomerate value
calculated on D.sub.50/D.sub.IA value was 1.20. This fact shows
that the above-mentioned operation was conducted sufficiently.
[0067] Next, 500 g of starting powder comprising single particles
was treated in the same way as in Example 1. The compression of the
powder particles of the powder converts these by plastic
deformation, so as to convert spherical starting powder to flake
copper powder. However, in the media dispersion mill called
DISPERMAT D-5226 manufactured by VMG-GETAMANN as was used in
Example 1 the only change made was the processing time to 10 hours
for this treatment, following by compression of starting powder
particles converting them by plastic deformation, thereby changing
spherical starting powder to flake copper powder.
[0068] The obtained flake copper powder's properties using the
above-mentioned method are that, the maximum particle diameter,
Dmax was smaller than 40.00 .mu.m, and there were no coarse
particles having an average particle diameter of D.sub.50. The
Dmax/D.sub.50 value was 4.2 and there is no coarse particle whose
size is 5 or larger, and the agglomerate values show a D.sub.10
(4.75 .mu.m), a D.sub.50 (9.50 .mu.m) and a D.sub.90 (12.83 .mu.m)
using the laser diffraction scattering particle size distribution
measurement method. The SD/D.sub.50 value was 0.34 and the
D.sub.90/D.sub.10 value was 2.70 using a standard deviation SD
(3.23 .mu.m) of the particle size distribution measured with the
laser diffraction scattering particle size distribution method. The
average thickness of the powder particle of the flake copper powder
was 0.80 .mu.m and the average particle diameter (major axis)
observed directly by this flake copper powder was 9.2 .mu.m, and
the average aspect ratio was 11.5. Accordingly, these facts show
that the flake copper powder of the present invention met the
requirements.
[0069] Additionally, the inventors produced a conductive paste,
which has a terpineol group using flake copper powder, and
providing an organic vehicle at a mix ratio in the same way as in
Example 1. The rate of viscosity of the conductive paste was then
measured. As a result, the A viscosity was 90 Pa.s and the B
viscosity was 60 Pa.s. Therefore the viscosity ratio ([A
viscosity]/[B viscosity]) was 1.5.
EXAMPLE 6
[0070] In this example, copper powder obtained from raw material
powder was used in the method below, wherein as starting powder was
used in the production process of the present invention to produce
flake copper powder.
[0071] The powder properties of starting powder used in this
example were, that the cumulative particle diameter; D.sub.50 was
4.24 .mu.m, in which the value was obtained with the laser
diffraction scattering particle size distribution measurement
method and the D.sub.IA of the average particle diameter was 2.10
.mu.m, in which the value was obtained by image analysis.
Accordingly, the agglomerate value obtained by D.sub.50/D.sub.IA
was 2.02.
[0072] The above-mentioned starting powder under agglomerate
condition was circulated at 6500 rpm, Turbo classifier from Nissei
Engineering Limited, used for a commercial pneumatic classification
device to perform an operation that made the agglomerate powder
particles singular by colliding the powder particle against each
other.
[0073] As a result, the cumulative particle diameter of copper
powder (starting powder) completed after conversion conducting to
single particles was measured. The D.sub.50 value was 2.80 .mu.m
using the laser diffraction scattering particle size distribution
measurement method, and the average diameter D.sub.IA was 2.00
.mu.m obtained from image analysis, so that the agglomerate value
calculated by D.sub.50/D.sub.IA value was 1.40. These facts show
that the above-mentioned operation was sufficiently performed.
[0074] Next, 500 g of the starting powder constituting single
particles was provided in the same way as in Example 1 to compress
powder particles of starting powder converting them by plastic
deformation, so as to convert spherical starting particles powder
into flake copper powder. However, in the media dispersion mill,
the DISPERMAT D-5226 manufactured by VMG-GETAMANN as in Example 1,
only the processing time was changed to 7 hours for this treatment,
followed by compression of the powder particles of the starting
powder and converting them by plastic deformation, resulting in
that the substantially spherical starting powder was changed into
flake copper powder.
[0075] The obtained flake copper powder's properties using the
method as mentioned above, has a maximum particle diameter, Dmax of
20.73 .mu.m or smaller, and there were no coarse particles having
an average particle diameter of D.sub.50. The Dmax/D.sub.50 ratio
was 2.8 but there were no coarse particles whose D.sub.50 was 5 or
larger as described below, and the agglomerate values show a
D.sub.10 (3.87 .mu.m), a D.sub.50 (7.30 .mu.m) and a D.sub.90 (8.51
.mu.m) measured with the laser diffraction scattering particle size
distribution method. The SD/D.sub.50 value was 0.50 and the
D.sub.90/D.sub.10 value was 2.20 using the standard deviation SD
(2.34 .mu.m) of the particle size measured distribution with the
laser diffraction scattering particle size distribution method. The
average thickness of the powder particle of the flake copper powder
was 0.70 .mu.m, the average particle diameter (major axis) observed
directly of this flake copper powder was 7.2 .mu.m, and the average
aspect ratio was 10.3. The facts show that the flake copper powder
of the present invention met the requirements.
[0076] Accordingly, the inventors produced a conductive paste
having terpineol groups using the flake copper powder, and applying
an organic vehicle at a mix ratio in the same way as in Example 1.
The rate of viscosity of the conductive paste was then measured. As
a result, the A viscosity was 112 Pa.s and the B viscosity was 70
Pa.s. Therefore, the viscosity ratio ([A viscosity]/[B viscosity])
was shown to be 1.6.
COMPARATIVE EXAMPLE
[0077] In this comparative example, dried material powder under
agglomerate condition was employed as in Example 1, without a
dispersing operation similar to that in Example 1, using a
Dyno-mill manufactured by Willy A. Bachofen A G Maschinenfabrik,
KDL type, followed by compressing the powder particles of the
starting powder and converting them by plastic deformation with 0.7
mm diameter beads, thus converting spherical starting powder into
flake copper powder. As a result, the obtained powder properties of
flake copper powder were shown as mentioned above 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 the average diameter D.sub.50.
[0078] Now, the powder properties of the flake copper powder
labeled as sample number 4 will be described. The agglomerate
values show a D.sub.10 (2.81 .mu.m), a D.sub.50 (8.20 .mu.m), a
D.sub.90 (21.38 .mu.m) and the maximum particle diameter size Dmax
(52.33 .mu.m), a resulting Dmax/D.sub.50 was 6.4 and the value of
it was 5 or larger. Further, the SD/D.sub.50 value was 0.87 with
the value of the standard deviation, SD (7.17 .mu.m), and the
D.sub.90/D.sub.10 value was 4.04. The average thickness of the
powder particle of the flake copper powder was 0.75 .mu.m, and an
average particle (major axis) to be observed directly was 7.8
.mu.m, an average ratio was 10.4. Alternatively, these facts show
that only the flake copper powder of the present invention meets
the requirements. Using such above flake copper powder to produce a
conductive paste, even if the composition of an organic vehicle
were altered in order to control the viscosity of the conductive
paste is difficult wherein, such flake copper powder could not be
applied to drawing of a printed circuit by a high density.
[0079] Therefore, the inventors measured the viscosity of
conductive paste utilizing this flake copper powder, of sample
number 4, and applying an organic vehicle and mixing thereof to
produce conductive paste with a terpineol group. As a result, the A
viscosity was 250 Pa.s and the B viscosity was 227 Pa.s. The
viscosity ratio ([A viscosity]/[B viscosity]) was defined by 1.1.
Owing to this result, the thixotropic property alone thereof seemed
to be especially inferior in comparison with the above-mentioned
conductive paste, though there might be no extraordinary difference
between both. This is to say, that the conventional flake copper
powder was acquiring a thixotropic performance by diminishing the
thickness of the particles of flake copper powders, but because the
particle distribution of particles has broadened, and since it
included especially large particles based on the average particle
diameter, it can not be used for forming thin, electrode and small
circuits having high layer density.
INDUSTRIAL APPLICABILITY
[0080] The viscosity of conductive pastes can be controlled by
using flake copper powder of the present invention, and thereby it
can provide a thixotropic property having a good balance with
respect to the viscosity, forming conductive pastes which are
thinner, and enhancing the layer density, without losing electrical
resistance. Also the conductor shape is more easily controlled,
resulting in that a thinner and/or fined circuit pattern can be
established can be obtained. Further, usage of the production
method of the present invention makes possible to produce flake
copper powder efficiently. Also, through the flake copper powder
having powder properties of the present invention, the particle
distribution of fine particle is excellent, which before did not
exist. Also, the production yield of the flake copper powder having
the excellent powder properties can be enhanced much more.
[0081] It is apparent from the above-mentioned descriptions, that
the flake copper powder of the present invention has a particle
distribution which is much narrower than that of the conventional
copper powder and the aspect ratio of the flake copper powder can
be easily changed using the producing method of the present
invention. As a result, the most preferable thixotropic
characteristics can be designed of flake copper powder.
* * * * *