Note: Descriptions are shown in the official language in which they were submitted.
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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.
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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
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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
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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.
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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.
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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.
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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
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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.
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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.
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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
CA 02506367 2005-05-16
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
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CA 02506367 2005-05-16
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
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CA 02506367 2005-05-16
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
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CA 02506367 2005-05-16
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
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CA 02506367 2005-05-16
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
CA 02506367 2005-05-16
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
26
CA 02506367 2005-05-16
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.
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CA 02506367 2005-05-16
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
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CA 02506367 2005-05-16
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.
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CA 02506367 2005-05-16
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
CA 02506367 2005-05-16
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
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CA 02506367 2005-05-16
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
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CA 02506367 2005-05-16
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.
33
