U.S. patent application number 10/106646 was filed with the patent office on 2003-03-13 for method of manufacturing fine metal particles, substance containing fine metal particles, and paste solder composition.
This patent application is currently assigned to TAMURA KAKEN CORPORATION. Invention is credited to Iwabuchi, Mitsuru, Ohashi, Yuji, Ono, Takao, Takahashi, Yoshiyuki.
Application Number | 20030047034 10/106646 |
Document ID | / |
Family ID | 27346376 |
Filed Date | 2003-03-13 |
United States Patent
Application |
20030047034 |
Kind Code |
A1 |
Ono, Takao ; et al. |
March 13, 2003 |
Method of manufacturing fine metal particles, substance containing
fine metal particles, and paste solder composition
Abstract
There is provided an in-oil atomization method wherein a solder
is fused and dispersed in a heated particle dispersion medium, the
method being featured in that even if the quantity of the particle
dispersion medium to be employed is relatively small, fine solder
particles can be effectively obtained. Namely, this invention
provides a method of manufacturing fine particles, wherein solder
is fused in the heated particle dispersion medium to obtain a
molten solder, which is then dispersed by means of an agitator to
obtain molten solder particles which are subsequently cooled and
solidify, the method being characterized in that the above
dispersing step is performed in the presence of a particle
coalescence-preventing agent. This invention also provides a fine
metal particles-containing substance and a paste solder
composition.
Inventors: |
Ono, Takao; (Iruma-shi,
JP) ; Takahashi, Yoshiyuki; (Iruma-shi, JP) ;
Iwabuchi, Mitsuru; (Iruma-shi, JP) ; Ohashi,
Yuji; (Iruma-shi, JP) |
Correspondence
Address: |
MCKEE, VOORHEES & SEASE, P.L.C.
801 GRAND AVENUE
SUITE 3200
DES MOINES
IA
50309-2721
US
|
Assignee: |
TAMURA KAKEN CORPORATION
Iruma-shi
JP
|
Family ID: |
27346376 |
Appl. No.: |
10/106646 |
Filed: |
March 26, 2002 |
Current U.S.
Class: |
75/331 |
Current CPC
Class: |
B23K 35/0244 20130101;
B23K 35/025 20130101; B22F 9/06 20130101; B22F 2009/0864 20130101;
B22F 2009/0804 20130101 |
Class at
Publication: |
75/331 |
International
Class: |
B22F 009/06 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2001 |
JP |
2001-092273 |
Sep 21, 2001 |
JP |
2001-288778 |
Dec 27, 2001 |
JP |
2001-395566 |
Claims
What is claimed is:
1. A method of manufacturing fine metal particles, which comprises
the steps of: dispersing molten metal particles in a dispersion
medium by way of a process wherein a low melting point metal is
mixed with the dispersion medium to obtain a mixture which is
subsequently heated to melt the low melting point metal, and a
dispersing energy is applied to the dispersion medium to disperse
the low melting point metal in the dispersion medium to obtain a
molten metal particle-dispersed substance; and forming solid
particles by cooling the molten metal particle-dispersed substance
to thereby solidify the molten metal particles; wherein said step
of dispersing molten metal particles in a dispersion medium and
said step of forming solid particles are preceded by a step of
mixing the dispersion medium with a particle coalescence-preventing
agent which is capable of adsorbing onto and/or reacting with at
least the molten metal particles and also capable of preventing the
generation of coalescence at least among the molten metal
particles.
2. The method of manufacturing fine metal particles according to
claim 1, wherein said particle coalescence-preventing agent is
rosin and/or a derivative thereof.
3. The method of manufacturing fine metal particles according to
claim 1, wherein said particle coalescence-preventing agent is
rosin soap.
4. The method of manufacturing fine metal particles according to
claim 1, wherein said particle coalescence-preventing agent is a
metal salt of organic acid having carboxyl group.
5. The method of manufacturing fine metal particles according to
any one of claims 1 to 4, which further comprises a step of
removing the solidified metal particles obtained in said step of
forming solid particles from said dispersion medium, thereby
leaving a residual liquid, which is then recycled as a particle
dispersion medium.
6. The method of manufacturing fine metal particles according to
any one of claims 1 to 4, wherein the low melting point metal is
employed at a ratio of 0.1-100 g per long of the dispersion medium,
and the particle coalescence-preventing agent is employed at a
ratio of 0.01-100 g per 100 g of the dispersion medium.
7. The method of manufacturing fine metal particles according to
any one of claims 1 to 4, wherein the application of said
dispersing energy to the dispersion medium is performed by making
use of a high-speed agitator comprising a cup-shaped stator having
slits in the sidewall thereof, and a rotator mounted inside the
stator and having a rotary vane, wherein a fluid material is
permitted to be introduced through said slits into said stator, in
which the fluid material is subjected to a high shearing force
through an interaction between said stator and said rotator by
actuating said rotator to rotate at a high speed relative to said
stator, the fluid material being subsequently discharged from the
stator.
8. The method of manufacturing fine metal particles according to
claim 7, wherein the number of revolution of the high-speed
agitator is at least 5000 per minute, and the temperature of said
heating is at least 10.degree. C. higher than the melting point of
the low melting point metal.
9. The method of manufacturing fine metal particles according to
any one of claims 1 to 4, wherein the low melting point metal is
employed at a ratio of 0.1-100 g per 100 g of the dispersion
medium, the particle coalescence-preventing agent is employed at a
ratio of 0.01-10 g per 100 g of the dispersion medium, and the
application of said dispersing energy to the dispersion medium is
performed by making use of a high-speed agitator comprising a
cup-shaped stator having slits in the sidewall thereof, and a
rotator mounted inside the stator and having a rotary vane, wherein
a fluid material is permitted to be introduced through said slits
into said stator, in which the fluid material is subjected to a
high shearing force through an interaction between said stator and
said rotator by actuating said rotator to rotate at a high speed
relative to said stator, the fluid material being subsequently
discharged from the stator.
10. The method of manufacturing fine metal particles according to
any one of claims 1 to 4, wherein the low melting point metal is
employed at a ratio of 0.1-100 g per 100 g of the dispersion
medium, the particle coalescence-preventing agent is employed at a
ratio of 0.01-10 g per 100 g of the dispersion medium, and the
application of said dispersing energy to the dispersion medium is
performed by making use of a high-speed agitator comprising a
cup-shaped stator having slits in the sidewall thereof, and a
rotator mounted inside the stator and having a rotary vane, wherein
a fluid material is permitted to be introduced through said slits
into said stator, in which the fluid material is subjected to a
high shearing force through interaction between said stator and
said rotator by actuating said rotator to rotate at a high speed
relative to said stator, the fluid material being subsequently
discharged from the stator, and e number of revolution of the
high-speed agitator is at least 5000 r minute, and the temperature
of said heating is at least 10.degree. C. higher than the melting
point of the low melting point metal.
11. A fine metal particles-containing substance containing fine
metal particles obtained by a method according to any one of claims
to 4.
12. A paste solder composition containing fine metal particles to
employed for soldering, said fine metal particles being fine metal
particles-containing substance to be obtained by a method according
any one of claims 1 to 4.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a method of manufacturing
fine metal particles such as solder particles, to a fine metal
particles-containing substance containing such fine metal
particles, and to a paste solder composition comprising such a fine
metal particles-containing substance.
[0002] In recent years, concomitant with an increasing trend to
multi-functionalize the wiring board of electronic devices as well
as with an increasing trend of miniaturization, i.e. the reduction
of the size and weight of electronic devices, a surface mounting
technique has now been quickly advanced, so that it is now desired,
for the purpose of realizing a high density packaging such as the
surface mounting of electronic device, to develop a solder paste or
other kinds of soldering materials and a soldering method, which
are not only capable of performing a metal mask printing of a fine
pattern, but also excellent in solderability.
[0003] As for the solder paste, the configuration of soldering
particles should preferably be spherical rather than aspherical so
as to make it possible to perform the metal mask printing of a fine
pattern. It is also desired that the solder is made into as fine
particle as possible in order to meet the current demands that the
solder is also applicable to a refined wiring so as to make it
possible to directly solder an LSI chip onto the surface of wiring
board.
[0004] As for the method of making soldering particles into
spherical particles, there is generally employed an atomizing
method wherein a fused solder in a solder melt bath is sprayed into
an atmosphere, thereby pulverizing the fused solder in the
atmosphere.
[0005] This atomization method can be classified, according to
differences in spraying method thereof, into two kinds of methods,
i.e. a centrifugal atomization method wherein the centrifugal force
of rotary disc is utilized, and a gas atomization method wherein a
gas is ejected into a solder melt bath so as to disperse and
atomize the fused solder. There is also known an ultrasonic
atomization method wherein an ultrasonic vibration is applied to
the fused solder for achieving the atomization of the solder.
[0006] The centrifugal atomization method is an atomization method
wherein a fused solder is poured onto the surface of a rotary disk
while keeping the rotary disk rotated, thereby enabling a thin film
to be formed on the surface of the rotary disk due to the
centrifugal force, the resultant film being allowed to disperse
from the peripheral portion of the disk, thus forming fine drops of
solder, which is then allowed to cool and solidify in the ambient
atmosphere to achieve the atomization of solder. It is possible,
according to this method, to minimize the average particle diameter
of the resultant solder particles by increasing the rotational
speed of the disk. However, since there is a limit in the
rotational speed of the motor employed for driving the rotary disk,
it is difficult, in industrial viewpoint, to control the average
particle diameter of the resultant solder particles to not less
than 10 m and to reliably make the solder particles into a
spherical configuration.
[0007] According to the gas atomization method, since the fused
solder is forced to disperse and atomize by the ejection of gas, it
will invite various problems, i.e. the distribution in particle
size of the resultant solder particles becomes relatively wide, and
so-called satellite particles where small particles are permitted
to adhere onto the surface of a relatively large solder particle is
caused to greatly generate, thereby not only deteriorating the
pulverization efficiency but also making it difficult to obtain
spherical particles. Further, although it is possible according to
this method to minimize the average particle diameter of the
resultant solder particles by enhancing the ejection pressure of
gas, the problem of the generation of satellite particles would
become more prominent, thus raising a serious problem and hence
making it increasingly difficult to obtain spherical fine
particles.
[0008] According to the ultrasonic atomization method on the other
hand, as the frequency of the ultrasonic vibrator becomes higher,
the average particle diameter of solder particles to be obtained
can be minimized. However, in order to increase the frequency of
the ultrasonic vibrator, the size of the ultrasonic vibrator is
required to be reduced, which however, invites the deterioration of
the efficiency of granulation. As a result, it is very difficult to
industrially manufacture solder particles having an average
particle diameter of not more than 10 micrometers.
[0009] As an alternative method to the aforementioned ejection
methods, there is proposed an in-oil atomization method wherein
lumps of solder are heated in a dispersion medium having a high
boiling point at a temperature higher than the melting point of the
solder to thereby melt the lumps of solder, the resultant molten
solder being subsequently agitated to disperse and transform the
molten solder into liquid granules, which are then cooled and
solidified to thereby obtain fine granular solder.
[0010] According to this in-oil atomization method, since a solder
is permitted to melt in a heated oily liquid dispersion medium to
obtain the molten solder which is then agitated to form liquid fine
particles, the liquid fine particles being subsequently permitted
to cool and solidify, it is possible to obtain fine solder
particles which are substantially spherical in configuration and
are free from the generation of aforementioned satellite particles
or deformed particles. Additionally, this in-oil atomization method
is also advantageous in that it is possible to relatively easily
obtain fine solder particles having an average particle diameter of
not more than 10 micrometers by increasing the rotational speed of
the agitation. Furthermore, since this in-oil atomization method is
a so-called wet system where the granulation of solder is performed
in an oily liquid dispersion medium, this in-oil atomization method
is substantially free from the problems to be raised as the
diameter of solder particles is increasingly minimized, such as the
adhesion of solder particles onto an atomizing apparatus, the
oxidation of solder particles, the deterioration in fluidity of the
resultant solder particles, the generation of dusts, etc., which
problems are inherently accompanied with the conventional so-called
dry system such as the aforementioned centrifugal atomizing method
where the granulation of solder is performed in a gas atmosphere.
Therefore, this in-oil atomization method is advantageous also in
treating fine solder particles in the manufacturing processes
thereof.
[0011] As explained above, although all of the aforementioned
centrifugal atomization method, gas atomization method and
ultrasonic atomization method are applicable to the manufacture of
solder particles having an average particle diameter of not less
than 10 .mu.m, these methods are not satisfactory in manufacturing
the solder particles having an average particle diameter of not
larger than 10 .mu.m and also may not be satisfactory in
manufacturing the solder particles having a spherical
configuration. Whereas, the in-oil atomization method is
advantageous in that it is capable of solving the aforementioned
problems.
[0012] However, this in-oil atomization method is accompanied with
the problem that when the concentration of the dispersed solder
particles (the volume ratio of the liquid particles of molten
solder to the dispersing medium) is increased, the liquid particles
of molten solder that have been once segmented and divided into
smaller particles by an agitator are permitted to immediately
return to the original size of liquid particles, or permitted to
generate the so-called coalescence of solder particles, thereby
preventing the molten solder particles from further being
granulated. There is also a problem that even if the granulation of
the solder particles is proceeded, when the liquid particles are
permitted to contact with each other due to the sedimentation
thereof, the coalescence. of liquid solder particles is caused to
take place, thereby resulting in an increased bulkiness of the
solder particles. In particular, the above problem would become
more prominent in the situations where a vegetable oil having a
high acid number is employed as a dispersion medium for the purpose
of obtaining solder particles exhibiting a modest surface
oxidation, or where an oily substance exhibiting a relatively low
viscosity is employed.
[0013] In order to avoid these problems, it has been conventionally
considered that the concentration of the dispersed solder particles
should be made as low as possible, and that the liquid particles of
molten solder that have been granulated by the agitation of the
molten solder should be prevented from being contacted with each
other. If these countermeasures are to be realized, a large
quantity of dispersing medium is required to be employed, and hence
the dispersing medium thus employed is required to be subsequently
removed in order to ultimately obtain solder particles.
Accordingly, if it is required to discard a large quantity of
dispersing medium, the consumption of the dispersing medium would
be inevitably increased, thus raising a problem that the
manufacturing cost of the solder particles would be caused to
increase.
BRIEF SUMMARY OF THE INVENTION
[0014] Therefore, a first object of this invention is to provide a
method of manufacturing fine metal particles, which makes it
possible to effectively manufacture fine metal particles in
industrial viewpoint, to provide a substance containing such fine
metal particles, and to provide a paste solder composition
containing such fine metal particles.
[0015] A second object of this invention is to provide a method of
manufacturing fine metal particles, which makes it possible to
effectively manufacture spherical fine metal particles in
industrial viewpoint, to provide a substance containing such
spherical fine metal particles, and to provide a paste solder
composition containing such spherical fine metal particles.
[0016] A third object of this invention is to provide a method of
manufacturing fine metal particles, which makes it possible to
minimize a component to be consumed in the manufacturing process
thereof, to provide a substance containing such fine metal
particles, and to provide a paste solder composition containing
such fine metal particles.
[0017] A fourth object of this invention is to provide a method of
manufacturing fine metal particles, which makes it possible to
reduce the manufacturing cost thereof, to provide a substance
containing such fine metal particles, and to provide a paste solder
composition containing such fine metal particles.
[0018] A fifth object of this invention is to provide a method of
manufacturing fine metal particles, which makes it possible to
apply them even to a fine soldering portion on the surface of
wiring board, to provide a substance containing such fine metal
particles, and to provide a paste solder composition containing
such fine metal particles.
[0019] As a result of intensive studies made by the present
inventors with a view to solve the aforementioned objects, it has
been found that when rosin having carboxyl group is incorporated in
a dispersion medium in the in-oil atomization method, the rosin is
permitted to be adsorbed on the surfaces of the fine particles of
fused solder through a chemical reaction to form a rosin film,
thereby making it possible to greatly inhibit the coalescence among
the fine particles, this effect of inhibiting the coalescence being
further promoted especially when a modified rosin is incorporated
in a dispersion medium, thus accomplishing the present
invention.
[0020] Namely, the present invention provides (1) a method of
manufacturing fine metal particles, which comprises the steps
of:
[0021] dispersing molten metal particles in a dispersion medium by
way of a process wherein a low melting point metal is mixed with
the dispersion medium to obtain a mixture which is subsequently
heated to melt the low melting point metal, and a dispersing
energy. is applied to the dispersion medium to disperse the low
melting point metal in the dispersion medium to obtain a molten
metal particle-dispersed substance; and
[0022] forming solid particles by cooling the molten metal
particle-dispersed substance to thereby solidify the molten metal
particles;
[0023] wherein said step of dispersing molten metal particles in a
dispersion medium and said step of forming solid particles are
preceded by a step of mixing the dispersion medium with a particle
coalescence-preventing agent which is capable of adsorbing onto
and/or reacting with at least the molten metal particles and also
capable of preventing the generation of coalescence at least among
the molten metal particles.
[0024] The present invention also provides (2) the method of
manufacturing fine metal particles according to the aforementioned
item (1), wherein said particle coalescence-preventing agent is
rosin and/or a derivative thereof.
[0025] The present invention also provides (3) the method of
manufacturing fine metal particles according to the aforementioned
item (1), wherein said particle coalescence-preventing agent is
rosin soap.
[0026] The present invention also provides (4) the method of
manufacturing fine metal particles according to the aforementioned
item (1), wherein said particle coalescence-preventing agent is a
metal salt of organic acid having carboxyl group.
[0027] The present invention also provides (5) the method of
manufacturing fine metal particles according to any one of the
aforementioned items (1) to (4), which further comprises a step of
removing the solidified metal particles obtained in said step of
forming solid particles from said dispersion medium, thereby
leaving a residual liquid, which is then recycled as a particle
dispersion medium.
[0028] The present invention also provides (6) the method of
manufacturing fine metal particles according to any one of the
aforementioned items (1) to (4), wherein the low melting point
metal is employed at a ratio of 0.1-100 g per 100 g of the
dispersion medium, and the particle coalescence-preventing agent is
employed at a ratio of 0.01-10 g per 100 g of the dispersion
medium.
[0029] The present invention also provides (7) the method of
manufacturing fine metal particles according to any one of the
aforementioned items (1) to (4), wherein the application of said
dispersing energy to the dispersion medium is performed by making
use of a high-speed agitator comprising a cup-shaped stator having
slits in the sidewall thereof, and a rotator mounted inside the
stator and having a rotary vane, wherein a fluid material is
permitted to be introduced through said slits into said stator, in
which the fluid material is subjected to a high-shearing effect
through an interaction between said stator and said rotator by
actuating said rotator to rotate at a high speed relative to said
stator, the fluid material being subsequently discharged from the
stator.
[0030] The present invention also provides (8) the method of
manufacturing fine metal particles according to the aforementioned
item (7), wherein the number of revolution of the high-speed
agitator is at least 5000 per minute, and the temperature of said
heating is at least 10.degree. C. higher than the melting point of
the low melting point metal.
[0031] The present invention also provides (9) the method of
manufacturing fine metal particles according to any one of the
aforementioned items (1) to (4), wherein the low melting point
metal is employed at a ratio of 0.1-100 g per 100 g of the
dispersion medium, the particle coalescence-preventing agent is
employed at a ratio of 0.01-10 g per 100 g of the dispersion
medium, and the application of said dispersing energy to the
dispersion medium is performed by making use of a high-speed
agitator comprising a cup-shaped stator having slits in the
sidewall thereof, and a rotator mounted inside the stator and
having a rotary vane, wherein a fluid material is permitted to be
introduced through said slits into said stator, in which the fluid
material is subjected to a high-shearing effect through an
interaction between said stator and said rotator by actuating said
rotator to rotate at a high speed relative to said stator, the
fluid material being subsequently discharged from the stator.
[0032] The present invention also provides (10) the method of
manufacturing fine metal particles according to any one of the
aforementioned items (1) to (4), wherein the low melting point
metal is employed at a ratio of 0.1-100 g per 100 g of the
dispersion medium, the particle coalescence-preventing agent is
employed at a ratio of 0.01-10 g per 100 g of the dispersion
medium, and the application of said dispersing energy to the
dispersion medium is performed by making use of a high-speed
agitator comprising a cup-shaped stator having slits in the
sidewall thereof, and a rotator mounted inside the stator and
having a rotary vane, wherein a fluid material is permitted to be
introduced through said slits into said stator, in which the fluid
material is subjected to a high-shearing effect through an
interaction between said stator and said rotator by actuating said
rotator to rotate at a high speed relative to said stator, the
fluid material being subsequently discharged from the stator, and
the number of revolution of the high-speed agitator is at least
5000 per minute, and the temperature of said heating is at least
10.degree. C. higher than the melting point of the low melting
point metal.
[0033] The present invention also provides (11) a fine metal
particles-containing substance containing fine metal particles
obtained by a method according to any one of the aforementioned
items (1) to (4).
[0034] The present invention also provides (12) a paste solder
composition containing fine metal particles to be employed for
soldering, said fine metal particles being fine metal
particles-containing substance to be obtained by a method according
to any one of the aforementioned items (1) to (4).
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0035] FIG. 1 is an illustration showing the front view and bottom
view of the generator representing one example of the present
invention;
[0036] FIG. 2 is a partial cross-sectional view of the front side
of the generator shown in FIG. 1;
[0037] FIG. 3 is a cross-sectional view of an apparatus where the
generator of FIG. 1 is employed; and
[0038] FIGS. 4 is a bottom view which corresponds to that shown in
FIG. 1 illustrating the structure of a generator representing
another example of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0039] In the description of this invention, the expression of "a
low melting point metal" is intended to mean at least one kind
material selected from low melting point pure metals and low
melting point alloys, so that it may be selected only from low
melting point pure metals or only from low melting point alloys, or
may contain both of them.
[0040] As for the low melting point pure metals, it is possible to
employ Ga (29.8.degree. C. (melting point, hereinafter the same)),
In (156.degree. C.), Li (186.degree. C.), Se (217.degree. C.), Sn
(232.degree. C), Bi (271.degree. C.), Tl (302.degree. C.), Pb
(327.degree. C.), Zn (419.degree. C.) and Te (452.degree. C.). It
is also possible to employ Cd, Cs, Rb, K and Na.
[0041] As for the low melting point alloys, it is possible to
employ 67Ag/33Te (351.degree. C.), 97.2Ag/2.8Tl (291.degree. C),
45.6Ag/54.4Zn (258.degree. C.), 95.3Ag/4.7Bi (262.degree. C.),
52.7Bi/47.3In (110.degree. C.), 47.2In/52.8Sn (117.degree. C.),
95.3Ag/4.7Pb (304.degree. C.), 86.6Ag/3.4Li (154.degree. C.) and
8.1Bi/91.9Zn (254.5.degree. C.).
[0042] As for the examples of the low melting point metals, solder
is well known. Especially, a Pb/Sn eutectic solder is commonly
employed a bonding material in electronic industries and other
industrial fields. Specifically, in addition to 100% Sn
(2320.degree. C.), it is also possible to employ Pb--Sn type
solders, such as 37Pb/63Sn (183.degree. C.), 4OPb/6OSn (183.degree.
C.), 5OPb/50Sn (212.degree. C.), 44Pb/56Sn (125.degree.C.) etc.;
Pb--In type solders, such as 5OPb/50In (198.degree. C.), etc.;
Sn--In type solders, such as 49Sn/51In (120.degree. C.), 48Sn/52In
(117-120 .degree. C.), 65Sn/35In (162.degree. C.), etc.; Sn--Bi
type solders, such as 43Sn/57Bi (139.degree. C.), 42Sn/58Bi
(138.degree. C.), etc.; Sn--Ag type solders, such as 98Sn/2Ag
(221-226.degree. C.), 96.5Sn/3.5Ag (221.degree. C.), 96Sn/4Ag
(232.degree. C.), 95Sn/5Ag (232.degree. C.), etc.; Sn--Zn type
solders, such as 91Sn/9Zn (199-203.degree. C.), 30Sn/70Zn, etc.;
Sn--Cu type solders, such as 99.3Sn/0.7Cu (2270.degree. C.), etc.;
Cd--Zn type solders, such as 60Cd/30Zn, etc.; Sn--Sb type solders,
such as 95Sn/5Sb (238.degree. C.), etc. Ag--In type solders, such
as 3Ag/97In (141.degree. C.), etc.; Au--Sn type solders, such as
80Au/20Sn (283.degree. C.), etc.; Sn--Cd--Ag type solders, such as
10Sn/85Cd/5Ag, etc.; Sn--Ag--In type solders, such as
95.5Sn/3.5Ag/Iln, etc.; Sn--Zn--In type solders, such as
86Sn/9Zn/5In (192.degree. C.), 81Sn/9Zn/10In (178.degree. C.),
etc.; Sn--Ag--Cu type solders, such as 95.5Sn/0.5Ag/4Cu
(216.degree. C.), 96.5Sn/3.0Ag/0.5Cu, etc.; Sn--Pb--Bi type
solders, such as 16Sn/32Pb/52Bi (99.50.degree. C.), 19Sn/3lPb/50Bi
(96.degree. C.), 34Sn/20Pb/46Bi (100.degree. C.), 43Sn/43Pb/14Bi
(136-166.degree. C.), etc.; Sn--Pb--Sb type solders, such as
35Sn/64.5Pb/0.5Sb, 32Sn/66Pb/2Sb, etc.; Sn--Bi--In type solders,
such as 17Sn/57Bi/26In, etc.; Pb--Ag type solders, such as
97.5Sn/2.5Ag, etc.; Sn--Bi--Ag type solders, such as
90.5Sn/7.5Bi/2Ag (207-212.degree. C.), 41.0Sn/58Bi/1.0Ag, etc.; and
Sn--Zn--Bi type solders, such as 89.0Sn/8.0Zn/3.0Bi.
[0043] As for the "particle dispersion medium" to be employed in
the present invention, it is possible to employ any kinds of
organic compounds as long as the usable upper limit temperature,
i.e. a boiling point or a decomposition temperature thereof is
higher than the melting point (melting temperature) of a low
melting point metal to be employed, and they are capable of
dispersing the molten particles of a low melting point metal to be
employed. Specific examples of them include silicon oil; mineral
oil to be produced through petroleum refining; engine oil;
industrial lubricants such as spindle oil, machine oil, cylinder
oil, gear oil, etc.; and synthetic lubricants to be produced by way
of a chemical synthesis (the chemical components thereof are:
hydrocarbons including polyolefin such as polybutene and alkyl
aromatic compound such as alkylbenzene; and non-hydrocarbons
including polyglycol, polyether such as phenyl ether, e.g.
polyphenyl ether and alkyldiphenyl ether, diester, polyol ester,
ester such as natural fats and oils (triglyceride), phosphorus
compounds such as phosphate, and polyether fluoride of these
compounds). It is also possible to employ, as the particle
dispersion medium, a vegetable oil such as coconut oil, palm oil,
olive oil, sunflower oil, castor oil, soybean oil, linseed oil,
rapeseed oil, tung oil and cotton oil; whale oil; beef tallow;
higher hydrocarbon compounds such as decane, dodecane, tetradecane,
hexadecane, octadecane, undecane, etc.; glycols such as glycerin,
ethylene glycol, diethylene glycol, triethylene glycol,
polyethylene glycol, polypropylene glycol, etc. (the glycols may be
called polyalkylene glycol and include not only the aforementioned
triol type and diol type, but also mono-ol type (Nissan Unilube MB
series (non-water soluble type); such as MB-7, MB-11, MB-22
(tradename)); derivatives of these glycols; phosphates such as
trimethyl phosphate and triethyl phosphate, tributyl phosphate;
substituted phenols such as octyl phenol, trichlorophenol and
nonylphenol; organic heating media such trichloroaniline, diphenyls
and triphenyls; phenyl imidazole; undecyl imidazole; heptadecyl
imidazole. It is preferable, in view of avoiding fire, to select
those which are free from inflammability.
[0044] Preferably, this "particle dispersion medium" should be
employed under the conditions wherein the heating temperature is
not higher than the usable upper limit temperature thereof but
higher than the melting temperature of the low melting point metal
to be employed, and the heating is performed in an inert gas
atmosphere. For example, the usable temperature thereof may be
selected from the range of 120 to 470.degree. C. The usable
temperature of the particle dispersion medium however is usually
not higher than the decomposition temperature of the aforementioned
organic materials.
[0045] It is preferable to incorporate an anti-oxidant into the
particle dispersion medium in order to prevent the oxidation of the
particle dispersion medium on the occasion of heating it, thereby
making it possible to prevent the oxidation of the particle
dispersion medium by the oxygen that may be included in a very
small quantity even in an inert gas atmosphere.
[0046] As for the anti-oxidant, those which are commonly employed
in fats and oils, rubber or synthetic resins can be employed. For
example, a phenol-based anti-oxidant, a bis-phenol-based
anti-oxidant, apolymer-basedanti-oxidant,
asulfur-basedanti-oxidant, a phosphorus-based anti-oxidant, etc.
can be employed. Otherwise, imidazols having an
oxidation-suppressing effect may be used singly or together with
the aforementioned anti-oxidants. Specific examples of these
anti-oxidants useful in the present invention are set forth in
Japanese Patent Unexamined Publication (Kokai) H9-49007.
[0047] Although the "particle coalescence-preventing agent" to be
employed in the present invention is designed to prevent the
coalescence among the molten metal particles that may be caused to
occur due to the fusion of the molten metal particles with each
other, the particle coalescence-preventing agent may be also
designed to prevent the coalescence among the solidified metal
particles to be obtained from the solidification of the molten
metal particles, or to prevent the coalescence between the molten
metal particles and the solidified metal particles to be obtained
from the solidification of the molten metal particles.
[0048] In the case of a dispersed material where a dispersing
material (material to be dispersed) (particles) is dispersed in a
dispersing medium such as emulsion, the process where the dispersed
material is getting gradually instabilized is considered to proceed
generally according to the following stages. At first, a phenomenon
of creaming (a phenomenon where particles are floated upward or
settled downward due to a difference in specific gravity between
the particles and the dispersing medium) is caused to occur, which
is followed by a phenomenon of aggregation (a phenomenon where
particles approaching to each other are caused to bond to each
other due to the attractive force thereof), resulting finally in
the coalescence thereof (a phenomenon where the particles are
integrated with each other). When an activating agent or a polymer
is adsorbed onto the surfaces of particles, particles are caused to
contact with each other through this adsorbed film at the stage of
the aggregation. Therefore, it is important to form a very strong
adsorptive layer on the surfaces of particles for the purpose of
preventing the aforementioned coalescence, thereby making it
possible to prevent the adsorbed layer from being peeled off or
pushed aside due to a shearing stress to the surfaces of the
particles, thus preventing the particles from being directly
contacted with each other and hence from generating the coalescence
of particles. For this purpose, it is important that a material
having a strong affinity not only to the particle but also to the
dispersing medium is employed for the adsorbed layer, and that the
resultant adsorbed layer is excellent in surface viscosity as well
as in surface elasticity ("Chemistry on Interfacial Phenomena",
Sankyo Publishing Co. Ltd., pp16-18).
[0049] In this viewpoint, a compound which is capable of adsorbing
onto and/or reacting with the surface of a metal particle,
especially, a molten metal particle is employed as a "particle
coalescence-preventing agent". More specifically, the following
materials can be employed.
[0050] (i) Rosin and/or the derivatives thereof (Rosins)
[0051] (a) Examples of rosin: Tall oil rosin, gum rosin, wood
rosin, etc.
[0052] (b) Examples of rosin derivatives: Hydrogenated rosin,
polymerized rosin, heterogeneous rosin, acrylic acid-modified
rosin, maleic acid-modified rosin, rosin alcohol, rosin amine,
rosin soap, etc.
[0053] All of the tall oil rosin, gum rosin, wood rosin comprises,
as a main component, abietic acids (abietic acid, dehydroabietic
acid, neoabietic acid) and, as a constituent component, pimaric
acid, parastearic acid, isopimaric acid or other resin acids, the
component ratios thereof being different from each other among
these rosins.
[0054] Rosin soap is a metal salt of rosin or a metal salt of rosin
derivative having carboxyl group, wherein the metal thereof is
selected from the group consisting of Na, K, Li, Ca, Mg, Al, Zn,
Sn, Pb, Ni, Cu, Co, Mn, Fe, In, Bi and Ag. Among them, Sn salt is
most preferable among them for using it as a solder material. On
the other hand, in terms of the effect to prevent the coalescence
of particles as a "particle coalescence-preventing agent", it is
preferable for the rosin or rosin derivatives having carboxyl group
to have as many carboxyl groups as possible. Among these metal
salts, it is preferable to employ a metal salt of monobasic
acid-modified rosin, more preferably, a metal salt of dibasic
acid-modified rosin.
[0055] (c) It is possible to employ a colorless rosin derivative
that can be employed through a hydrogenation reaction of an
addition reaction product to be obtained from the reaction between
a refined rosin and a,a-unsaturated monocarboxylic acid and/or
,-unsaturated dicarboxylic acid (Japanese Patent Unexamined
Publication (Kokai) H5-86334).
[0056] Although at least one kind of material selected from the
aforementioned groups (a) to (c) is employed, it is more preferable
to select from those excellent in affinity (adsorptivity and/or
reactivity) to the surface of metal particle, in particular, molten
metal particle. Among them, it is especially preferable to employ
monobasic acid (acrylic acid, methacrylic acid, crotonic acid,
etc.)-modified rosin, glycolic acid-modified rosin, dibasic acid
(maleic acid, maleic anhydride, fumaric acid, etc. )-modified rosin
or metal salts thereof.
[0057] (ii) Triazoles
[0058] Benzotriazole and/or derivatives thereof
[0059] (iii) Imidazole and/or derivatives thereof
[0060] (iv) Amine compounds
[0061] Aromatic amine (aniline, o-toluidine, m-toluidine,
p-toluidine), aliphatic amine and cyclic ketoamine, etc.
[0062] (v) Organic acids having carboxyl group such as fatty acids
and/or metal salts thereof
[0063] A fatty acid having at least 8 (8 or more) carbon atoms such
as dicarboxylic acid, polycarboxyl acid, hydroxycarboxylic acid
(for example, 12-hydroxy stearic acid, licinolic acid), aromatic
carboxylic acid, aminocarboxylic acid, a higher fatty acid (oleic
acid, stearic acid, etc.), etc.; acrylic acid; polyacrylic acid;
and metal salts thereof.
[0064] In this case, the metal salts of each of these organic acids
are generally called a metal soap, wherein the metal thereof is
selected from the group consisting of Na, K, Li, Ca, Mg, Al, Zn,
Sn, Pb, Ni, Cu, Co, Mn, Fe, In, Bi and Ag. Among them, Sn salt is
most preferable among them for using it as a solder material. On
the other hand, in terms of the effect to prevent the coalescence
of particles as a "particle coalescence-preventing agent", the
metal salts of organic acid having carboxyl group (carboxylic acid)
should preferably be selected from metal salts of linear fatty
acids or of hydroxy fatty acids each having at least 8 (8 or more)
carbon atoms. It is especially preferable to employ metal salts of
stearic acid, metal salts of 12-hydroxy stearic acid and metal
salts of licinolic acid. By the way, the metal salts of the
derivatives of fatty acid or of 12-hydroxy stearic acid can be
deemed to fall within the definition of the fatty acid soap.
[0065] (vi) Hydrazines
[0066] Hydrated hydrazine and alkyl hydrazine compound (benzyl
hydrazine, tert -butyl hydrazine hydrochloride, isopropyl hydrazine
sulfate and hydrazinomethyl acetate hydrochloride).
[0067] (vii) Pyrazoles
[0068] (viii) Azo compounds
[0069] (ix) Thermoplastic resin such as acrylic resin and phenol
resin.
[0070] (x) Alcohols such as propyl alcohol, butyne diol, hexynol
and pethylacrosinol.
[0071] (xi) Isocyanates
[0072] (xii) Sulfur-containing compounds
[0073] Heterocyclic compounds having a thiourea-based compound such
as thiourea and N-substituted alkyl thiourea, and -SH group
(mercapto group) in the molecule thereof (2-mercaptobenzothiazole,
2-mercaptobenzoimdazole- , etc.).
[0074] (xiii) High-molecular amine compounds
[0075] Poly(4-vinyl pyridine), etc.
[0076] The compounds set forth in these items (i) through (xiii)
may be employed singly or in combination thereof, which are
selected from the same item or different items.
[0077] As for the effects of the carboxyl group (--COOH) on the
metals, it can be classified into a case where a chemical
adsorption is taken place on the surface of a metal as represented
by--COO--Me (metal) --OOC--, and a case where a physical adsorption
due to the attractive force of electric charge is taken place on
the surface of a metal as in the case of --OH as represented by
--O.sup.-H.sup.+/Me.sup.-+/--O.sup.---H.sup.+. Since the former
case is accompanied with a chemical reaction, a large quantity of
adsorption heat is generated, so that it requires a high activating
energy which is higher than that of the physical adsorption,
indicating that the adsorption force in the chemical adsorption is
relatively strong, thus preventing the particle
coalescence-preventing agent from being easily desorbed at a high
temperature.
[0078] As for the mixing ratio of these components in the particle
dispersion medium, the content of the low melting point metal
should be within the range of 0.1 to 100 g, preferably 1 to 50 g,
more preferably 2 to 20 g per 100 g of the particle dispersion
medium, and the content of the particle coalescence-preventing
agent should preferably be within the range of 0.01 to 100 g per
100 g of the particle dispersion medium. When the mixing ratio of
the low melting point metal is smaller than the aforementioned
lower limit, the manufacturing efficiency of the fine metal
particles would be deteriorated. Whereas when the mixing ratio of
the low melting point metal is larger than the aforementioned upper
limit, the effects of preventing the coalescence of the molten
metal particles that have been once dispersed in the particle
dispersion medium would be deteriorated in the same manner as in
the case where the content of the particle coalescence-preventing
agent is lower than the aforementioned lower limit thereof. On the
other hand, when the content of the particle coalescence-preventing
agent is larger than the aforementioned upper limit thereof, the
coalescence-preventing effects thereof would be no longer enhanced,
indicating the saturation of the coalescence-preventing
effects.
[0079] The processing liquid (liquid to be processed) that has been
obtained through the mixing of these constituent components is then
subjected to a dispersion treatment. In this case, the expression
of "a dispersing energy is applied to the dispersion medium to
disperse the low melting point metal, as particles, in the
dispersion medium" is intended to indicate a process wherein a lump
or a coarse particle is atomized to obtain fine particles, to which
a mechanical energy is applied for preventing the fine particles
from being aggregated or coalesced. Therefore, this dispersion
treatment includes not only a situation where a molten body of the
low melting point metal is split and dispersed as fine particles in
the particle dispersion medium, but also a situation where a lump
or powder of the low melting point metal is dispersed as fine
particles in the particle dispersion medium. Alternatively, both of
these situations may be intermingled with other. In the latter
situation where a lump or powder of the low melting point metal is
dispersed as fine particles in the particle dispersion medium, the
fine particles are heated during or subsequent to the dispersion
process so as to melt and disperse the fine particles, thereby
obtaining a dispersion of molten metal particles. It is preferable
to perform this dispersion treatment in such a way that a lump or
powder of the low melting point metal is mixed with a particle
dispersion medium, the resultant mixture being subsequently heated
and dispersed, or in such a way that a lump or powder of the low
melting point metal is mixed with a heated particle dispersion
medium, the resultant mixture being subsequently dispersed.
However, the present invention is not limited to these dispersion
treatments.
[0080] As for the means for applying a dispersing energy to the
dispersion medium, it is possible to employ an agitation/dispersion
apparatus comprising a generator consisting of a rotator and a
stator, an ultrasonic dispersion apparatus, a high-pressure
homogenizer or high-speed agitators which are disclosed in Japanese
Patent Unexamined Publications (Kokai) H9-75698; H10-161667; and
H11-347388.
[0081] As for the agitation/dispersion apparatus comprising a
generator consisting of a rotator and a stator, it is possible to
employ the apparatus shown in FIGS. 1 and 2. Referring to FIGS. 1
and 2, the apparatus comprises a concave stator (a cup-shaped body)
1 having a plurality of slits 4 in the sidewall thereof, the slits
4 being radially provided along the sidewall. A rotator 2 (having a
couple of vanes on both sides of the axis thereof) is mounted
inside the stator 1 so as to be rotated at a high-speed relative to
the stator 1, thereby enabling the processing liquid (or a mixed
solution where the particle coalescence-preventing agent and the
low melting point metal are fused in the particle dispersion
medium) to be sucked into the stator 1. The processing liquid thus
sucked into the stator 1 is then subjected to a high-shearing
effect acting between the stator 1 and the rotator 2 to thereby
split and granulate the molten body of the low melting point mental
in the processing liquid, the dispersion liquid medium for the
molten metal particles being subsequently discharged from the slits
4. The reference numeral 5 denotes a rotation axis.
[0082] The high-shearing apparatus shown in FIG. 1 is disposed in
the inner bottom portion of a processing tank 6 in such a manner
that the high-shearing apparatus is spaced apart from the bottom
surface of the processing tank 6. The rotation axis 5 (not shown in
FIG. 3) of the high-shearing apparatus is inserted into a
cylindrical body which is hermetically pierced through a top board
7, thereby enabling the torque from a motor 8 (the rotational speed
thereof is enabled to be controlled by a rotational speed
controller 8a) to be transmitted to the rotation axis 5. The top
board 7 which is hermetically and detachably mounted on the
high-shearing apparatus is provided with an inlet port and with an
outlet port (as shown by an arrow) so as to enable an inert gas to
always pass through the interior of the processing tank 6, whereby
the interior of the processing tank 6 can be kept in an inert gas
atmosphere. When the bottom portion and opposite-sidewalls of the
processing tank 6 are heated by heaters 10 disposed around thereof,
a mixed liquid filled so as to immerse the high-shearing apparatus
therein and composed of a solution "a" comprising the particle
dispersion medium and the particle coalescence-preventing agent,
and also containing a low melting point metal "b" is heated up to a
suitable processing temperature to fuse the low melting point metal
"b" with the rotator 2 being rotated at a low speed if required,
which is followed by a high-speed rotation of the rotator 2 to
thereby obtain the aforementioned processing liquid.
[0083] On this occasion, the temperature of the processing liquid
is detected by means of a thermocouple 11 so as to enable a
temperature controller 12 to control the heat quantity of the
heaters 10, thereby making it possible to suitably control the
temperature of the processing liquid. Between the processing tank 6
and the heaters 10, there is disposed a copper pipe so as to
surround the processing tank 6. This copper pipe is mounted so as
to enable a cooling water to flow therein, thereby preventing the
temperature of the processing liquid from rising higher than a
predetermined value during the stirring thereof, and also allowing
the processing liquid to cool down to the ordinary temperature
after finishing the stirring thereof. By the way, a baffle plate 9
is disposed so as to prevent a gas from being entrapped in the
processing liquid as a central portion of the liquid surface is
depressed due to the generation of a revolving flow of the
processing liquid. The reference numeral 13 denotes a processing
tank-receiving body which is lined with a heat resistant material
having the aforementioned heaters buried therein.
[0084] Although it is preferable to employ the apparatus shown in
FIGS. 1 and 2, it is also possible to employ the Kady mill set
forth in Japanese Patent No. 2555715. This Kady mill is constructed
as shown in FIG. 4 which illustrates a plan view of the structure
of the generator thereof. Namely, this Kady mill comprises a stator
1' having a plurality of slits 4' radially disposed, and a rotator
2' having a plurality of slits 3' which are radially disposed, the
edges of these slits 3' being inclined in a direction opposite to
the rotational direction thereof. When the rotator 2' is rotated at
a high speed relative to the stator 1, the processing liquid is
sucked into the stator 1. The processing liquid thus sucked into
the stator 1 is then subjected to a high-shearing effect acting
between the stator 1' and the rotator 2' to thereby split and
granulate the molten body of the low melting point mental in the
processing liquid, the dispersion liquid medium for the molten
metal particles being subsequently discharged from the slits 4'.
The reference numeral 5' denotes a rotation axis. The Kady mill may
be of any kind as long as the generator is constructed as described
above.
[0085] Further, the ultrasonic dispersion apparatus is designed to
apply an ultrasonic energy to the processing liquid while the
processing liquid is kept agitated by means of a homogenizer or
other kinds of agitators. Thus, it is possible, even in this case,
to treat the processing liquid under a heated condition, thereby
enabling a molten body of the low melting point metal to be split
and granulated. As for the means to generate an ultrasonic
vibration, it is possible to employ a separation type vibrator
where an oscillator and a vibrator are separated, an integrated
type vibrator where these component members are integrated with
each other, an immersion type vibrator, or a planar type vibrator.
It is also possible to a joint type vibrator where a plurality of
ultrasonic vibrations differing in frequency are jointly used.
[0086] Further, the high-pressure homogenizer is designed such that
a processing liquid is enabled to pass through a narrow gap under a
pressure, and then, the processing liquid thus pressurized is
instantaneously lowered to a lower pressure, thereby generating
cavitation, whose effect is then utilized so as to granulate the
low melting point metal.
[0087] It is possible, through the application of a high energy to
the processing liquid for the dispersion thereof, e.g. through an
increase of rotational speed or of the number of vibration in each
of the aforementioned dispersion apparatus, to control the average
particle diameter of the molten metal particles to a preferable
range of not more than ten and several micrometers, more
preferably, not more than ten micrometers.
[0088] The processing liquid where the molten metal particles are
dispersed in the particle dispersion medium containing a particle
coalescence-preventing agent as described above is then cooled down
to a temperature which is not higher than the solidification point
of the molten metal to thereby enable the molten metal particles to
be solidified to form solid metal particles. As for the cooling
method to be employed in this case, although the molten metal
particles may be water-cooled as shown in FIG. 3, or air-cooled in
a vessel of the dispersion apparatus, the processing liquid may be
pooled and then, quenched by pouring a cooling medium into the
pooled processing liquid. Alternatively, the processing liquid may
be continuously poured into a cooling medium. This cooling medium
may be the aforementioned particle dispersion medium, or other
kinds of cooling medium, for instance, a volatile cooling
medium.
[0089] Thereafter, the solid metal particles are isolated from the
particle dispersion medium by means of gravitational sedimentation,
centrifugal sedimentation or filtration. Then, in order to discard
matters other than the solid metal particles, a slurry obtained in
this manner is washed with a solvent and dried to obtain a metallic
powder. However, if it is desired to obtain a solder powder, a
rosin-based material employed as a particle coalescence-preventing
agent is not required to be completely removed from the slurry.
[0090] The configuration and particle diameter of the solid metal
particles to be obtained in this manner would be determined
depending on the configuration and particle diameter of the molten
metal particles that have been dispersed in the heated particle
dispersion medium. In this case, since the molten metal particles
formed are almost perfectly spherical, the solid metal particles
would become also almost perfectly spherical. On the other hand, if
it is desired to obtain fine solid particles, the molten metal
particles should be formed into fine particles. In order to realize
this, the rotational speed or the number of vibration in each of
the aforementioned dispersion apparatus should be increased as
mentioned above, and at the same time, the operation conditions of
these dispersion apparatus such as the time for applying a
dispersion energy, the heating temperature of the processing
liquid, and the processing time, as well as the kinds and mixing
ratios of components to be employed such as the low melting point
metal, the particle dispersion medium and the particle
coalescence-preventing agent should be suitably selected, thereby
making it possible to obtain molten fine metal particles having an
average particle diameter ranging from 2 to 30 .mu.m.
[0091] In the present invention, the definition of the "fine metal
particles-containing substance" includes a composition comprising
the fine metal particles (powder) obtained in this manner and the
aforementioned particle coalescence-preventing agent adhered to the
fine metal particles.
[0092] The fine metal particles (powder) obtained by the
aforementioned manufacturing method can be employed at a ratio of
85-92% by weight (flux: 8-15% by weight) based on a solder paste.
Since the fine metal particles are spherical in shape, it is suited
for use in a reflow solder to be employed in the manufacture of the
current printed circuit board wherein the pitch of solder lands is
increasingly narrowed.
[0093] As for the flux to be employed in this case, rosin-based
resin can be employed. As for the examples of the rosin-based
resin, it is possible to employ derivatives of rosin and of
modified rosin. These derivatives may be co-used. More
specifically, it is possible to employ gum rosin, wood rosin,
polymerized rosin, phenol-modified rosin, and the derivatives
thereof. The content of the rosin-based resin may be in the range
of 30 to 70% by weight based on so-called flux or all of the solder
paste components excluding the solder powder. If the content of the
rosin-based resin is less than this lower limit, so-called
solderability of the solder paste (i.e. the ability of the solder
paste to prevent the oxidation of copper surface of soldering land
to thereby improving the wettability thereof to the fused solder)
would be deteriorated, thus giving rise to the generation of solder
balls. On the other hand, if the content of the rosin-based resin
is larger than this upper limit, the quantity of residue would be
increased.
[0094] As for the activating agent to be incorporated in the flux,
it is possible to employ hydrohalogenates of organic amine and
organic acid. More specifically, it is possible to employ diphenyl
guanidine hydrobromate, cyclohexyl amine hydrobromate, diethyl
amine hydrobromate, triethanol amine hydrobromate, monoethanol
amine hydrobromate, adipic acid, sebacic acid, etc. The content of
these activating agent should preferably be in the range of 0.1 to
3% by weight based on the flux in terms of inhibiting the
generation of corrosion by the effects of the residue thereof, and
of preventing the generation of damage to the insulation
resistance, and in terms of solderability and of preventing the
generation of solder balls.
[0095] A thixotropic agent may be employed for adjusting the
viscosity of a solder paste so as to optimize the printing
characteristics of the solder paste. For instance, hydrogenated
castor oil, fatty acid amides and oxyfatty acids may be employed
for this purpose, the mixing ratio of which being preferably in the
range of 3 to 15% by weight based on the flux.
[0096] As for the solvent, those which are commonly employed for
the solder paste can be employed. For instance, hexylcarbitol
(boiling point: 260.degree. C.), butylcarbitol (boiling point:
230.degree. C.), etc. can be employed, the mixing ratio of which
being preferably in the range of 30 to 50% by weight based on the
flux.
[0097] This invention will be further explained with reference to
the following examples which are not intended to limit this
invention. The "%" in these examples is expressed on the basis of
weight.
[0098] In the following examples, there is exemplified a method of
manufacturing fine metal particles, wherein a low melting point
metal is melted and dispersed in a heated particle dispersion
medium (dispersion medium) while applying a dispersion energy to
obtain fine metal particles which are subsequently cooled to
solidify the fine metal particles, the resultant solid fine metal
particles being subsequently separated to obtain fine; wherein said
step of dispersing molten metal particles in a dispersion medium
and said step of forming solid particles are preceded by a step of
mixing the dispersion medium with a particle coalescence-preventing
agent which is capable of adsorbing onto and/or reacting with at
least the molten metal particles and also capable of preventing the
generation of coalescence at least among the molten metal
particles, thereby making it possible to obtain solid fine metal
particles.
[0099] Further, it is possible to manufacture solder fine particles
or solder fine powder by making use of a high-speed agitator
(rotation speed: 5000 rpm or more, for example 5000 rpm-2000 rpm)
comprising a stator and a rotator as shown in FIG. 1, by suitably
selecting the kinds of the solder, the kinds of rosin and/or the
derivatives thereof, the kinds of fatty acid soap (including metal
salts of hydroxycarboxylic acid of the derivatives of fatty acid),
and by using polyalkylene glycol or vegetable oil as a particle
dispersion medium. In this case, the mixing ratio between the
solder powder and the dispersion medium should preferably be 1:100
to 1:2 (weight ratio, the same hereinafter), and the mixing ratio
between the rosin and/or the derivatives thereof, or the fatty acid
soap and the dispersion medium should preferably be 1:2000 to 1:20.
As for the heating temperature, it should preferably be "the
melting point of the solder +10.degree. C. or so". As for the
residue to be left behind after the removal of the solidified fine
particles of low melting point metal from the dispersion medium, it
can be recycled as a particle dispersion medium after, preferably,
removing floating matters from the dispersion medium.
[0100] The fine particles or powder thus obtained is substantially
perfectly spherical in configuration (average particle diameter: 15
.mu.m or less, for instance 8-13 .mu.m). A solder paste can be
manufactured by making use of the fine particles, and the solder
paste thus obtained can be applied to a fine soldering portion of
wiring board.
Example 1
[0101] A mixture consisting of 90 g of Sn--Pb eutectic alloy lump
(63Sn/37Pb) (solder alloy), 882 g of Unilube MB-22 (polyalkylene
glycol; Nippon Yushi Co., Ltd.) (dispersion medium), and 18 g of
hydrogenated acrylic acid-modified rosin (KE-604, Arakawa Chemical
Industries Ltd.) (a particle coalescence-preventing agent) (the
mixing ratio of the particle coalescence-preventing agent is 2%
based on the total weight of the dispersion medium plus the
particle coalescence-preventing agent) was placed in a 10 mL
separable flask, which was then set in an agitator (HG-92 type, SMT
Co., Ltd.) and the agitator was hermetically closed. Thereafter,
nitrogen gas was introduced into this separable flask to thereby
turn the interior of the flask into an inert gas atmosphere.
[0102] Under this condition, the separable flask was heated up to
190.degree. C. by means of a mantle heater. On this occasion, in
order to dissolve the KE-604 in the Unilube MB-22 at the initial
stage of this heating, the agitator was rotated at a low speed. At
the moment when the KE-604 was dissolved and the temperature of the
mixture was stabilized at a temperature of 190.degree. C., the
agitator was rotated at a high speed of 10,000 rpm for 10
minutes.
[0103] Then, the agitation and the heating were suspended, and a
cooling water was allowed to flow through a water-cooling pipe
which was interposed between the separable flask and the mantle
heater to thereby cool the mixture in the flask. This cooling step
was continued for 20 minutes, after which the separable flask was
opened, and a supernatant liquid was removed and the precipitated
matter settled on the bottom of the flask was taken out. Then, this
precipitated matter was immersed in ethyl acetate, and dissolved
phase was removed together with the ethyl acetate. This decantation
operation was repeated, and then, the ethyl acetate was removed by
means of vacuum drying to obtain fine solder particles. By the way,
it is also possible to employ the aforementioned precipitated
matter as it is as a paste solder material.
[0104] When the fine solder particles obtained in this manner was
observed by means of a scanning electronic microscope (SEM), the
fine solder particles are found perfectly spherical and completely
free from the generation of satellite particles. Further, when the
average particle diameter thereof and the distribution of particle
size thereof were measured by means of a laser diffraction method,
the average particle diameter thereof was found 12.4m, and the
distribution of particle size thereof was found 0.61 as the
particle size distribution was represented by
.epsilon.=(D.sub.90,-D.sub.10)/D.sub.50, (D.sub.90, D.sub.10,
D.sub.50 represent respectively the diameter of particle when the
quantity of the particles is counted at 90%, 10% and 50%,
respectively, as the entire particles are arranged in order of
diameter from smaller one to larger one). Further, the yield of the
fine solder particles obtained was 90%. The smaller the value of
.ang. is, the narrower, i.e. the more sharp is the distribution of
particle size.
[0105] By the way, the following Table 1 shows the measured results
together with the kinds of particle dispersion medium (dispersion
medium (base oil)), the kinds of the hydrogenated acrylic
acid-modified rosin (additive rosin), the quantity of the rosin
added, the rotational speed of the agitator (rotational speed for
agitation), and the temperature of the mixture comprising a solder
alloy, a dispersion medium and a particle coalescence-preventing
agent (stirring temperature).
EXAMPLES 2 to 11
[0106] Fine solder particles were manufactured in the same manner
as in Example 1 except that the kinds of dispersion medium, the
quantity of the rosin, the rotational speed for agitation, and the
stirring temperature were altered as shown in Table 1. Table 1
shows the results which were measured in the same manner as in
Example 1.
EXAMPLES 12 to 16
[0107] Fine solder particles were manufactured in the same manner
as in Example 1 except that the composition of alloy, the kinds of
dispersion medium, the kinds of the rosin, and the stirring
temperature were altered as shown in Table 1. Table 1 shows the
results which were measured in the same manner as in Example 1.
Comparative Examples 1 and 2
[0108] Fine solder particles were manufactured in the same manner
as in Example 1 except that the kinds of dispersion medium was
altered as shown in Table 1. Table 1 shows the results which were
measured in the same manner as in Example 1.
1TABLE 1 Dispersion Alloy Comp. medium Quantity (wt %) (base oil)
Rosins (wt %) Exam- ple 1 Sn63Pb37 Unilube MB-22 KE-604 2.0 2
Sn63Pb37 Unilube MB-11 KE-604 2.0 3 Sn63Pb37 Unilube MB-7 KE-604
2.0 4 Sn63Pb37 Unilube MB-22 KE-604 0.5 5 Sn63Pb37 Unilube MB-22
KE-604 0.2 6 Sn63Pb37 Refined castor oil KE-604 2.0 (acid value:
0.8) 7 Sn63Pb37 Refined castor oil KE-604 0.5 (acid value: 0.8) 8
Sn63Pb37 Refined castor oil KE-604 0.2 (acid value: 0.8) 9 Sn63Pb37
Unilube MB-22 KE-604 2.0 10 Sn63Pb37 Unilube MB-11 KE-604 2.0 11
Sn63Pb37 Refined castor oil KE-604 2.0 (acid value: 0.8) 12
Sn96.5Ag3.5 Unilube MB-22 Harimack 2.0 AS-5 13 Sn96.5Ag3.5 Refined
castor oil Harimack 2.0 (acid value: 0.8) AS-5 14 Sn41.0Bi58BiAg1.0
Unilube MB-22 Harimack 2.0 AS-5 15 Sn89.0Zn8.0Bi3.0 Unilube MB-22
KE-604 2.0 16 Sn96.5Ag3.0Cu0.5 Refined castor oil Harimack 2.0
(acid value: 0.8) AS-5 Comp. Ex. 1 Sn63Pb37 Unilube MB-22 None -- 2
Sn63Pb37 Refined castor oil None -- (acid value: 0.8) Rotational
Temperature Time Average Yield speed (rpm) (.degree. C.) (min) size
(.mu.m) .epsilon. (%) Example 1 10,000 190 10 12.4 0.61 90 2 10,000
190 10 10.3 0.62 92 3 10,000 190 10 9.4 0.56 94 4 10,000 190 10
12.3 0.60 90 5 10,000 190 10 12.7 0.63 90 6 10,000 190 10 11.5 0.70
95 7 10,000 190 10 12.1 0.92 93 8 10,000 190 10 12.4 1.26 90 9
12,500 190 10 10.0 0.78 90 10 12,500 190 10 7.7 0.55 92 11 12,500
190 10 8.8 0.63 94 12 10,000 230 10 13.2 0.54 96 13 10,000 230 10
11.9 0.73 91 14 10,000 150 10 12.9 0.57 85 15 10,000 210 10 13.3
0.61 88 16 10,000 230 10 12.0 0.60 92 Comp. Ex. 1 10,000 190 10
Failed to granulate 2 10,000 190 10 Failed to granulate
[0109] In Table 1, Unilube MB-22, Unilube MB-11 and Unilube MB-7
dename, NOF Corporation) represent polyalkylene glycol, and mac
AS-5 (tradename, Harima Chemicals Inc.) represents dibasic (maleic
acid)-modified rosin.
[0110] It will be seen from the results shown in Table 1 that
Comparative Examples 1 and 2 where a particle
coalescence-preventing agent (additive rosin) was not employed were
found defective in that the solder was left remain in the form of
lumps, thus failing to granulate the solder. Whereas in the case of
all of the above Examples, it was possible to obtain fine particles
having an average diameter of 13.3 .mu.m or less. In particular, it
was found that when the rotational speed for the agitation was
increased up to 12500 rpm, fine metal particles having an average
particle size of not more than 10 m could be obtained. This result
can be attributed to the fact that due to the presence of the
particle coalescence-preventing agent, the molten fine solder
particles in the particle dispersion medium were prevented from
being coalesced with each other. By the way, even in these
Comparative Examples, when the concentration of the molten fine
solder particles in the particle dispersion medium is decreased,
the solder can be granulated without necessitating the employment
of the particle coalescence-preventing agent. In the cases of above
Examples however, since a particle coalescence-preventing agent was
employed, it was possible to effectively obtain fine solder
particles even if the quantity of the particle dispersion medium
employed was relatively small. As a result, the quantity of the
particle dispersion medium required to be removed for isolating the
fine solder particles can be minimized, thus making it possible not
only to save the consumption of the components but also to improve
the production efficiency.
EXAMPLE 17
[0111] Fine solder particles were manufactured in the same manner
as in Example 1 except that the quantity of the rosin was altered
as shown in Table 2. Table 2 shows the results which were measured
in the same manner as in Example 1.
[0112] Further, the supernatant (the residual liquid to be left
remained after the removal of precipitated matters from a cooled
liquid subsequent to the processing thereof) obtained in the same
manner as in Example 1 was subjected to a centrifugal separation
(treated at a rotational speed of 10,000 rpm (centrifugal
acceleration: 7,600-16,900 G) for 5 minutes by making use of CR22F,
R12 rotor (Hitachi Kohki Co., Ltd.)) to thereby remove floating
matters. When the quantity of the clarified liquid thus obtained
was measured for determining the recovery ratio of the original
dispersion medium (the ratio of the clarified liquid relative to
the original quantity thereof), the result was 94%. The results are
also shown in Table 2.
EXAMPLES 18-26
[0113] A fresh dispersion medium corresponding in quantity to a
deficient quantity of 6% ((Unilube MB-22)+2% KE-604) (2% of KE-604
out of this deficient quantity of 6%, the balance being Unilube
MB-22, the same hereinafter) was supplemented to the recovered
dispersion medium which was obtained in Example 17 (a clarified
liquid which was recovered after the employment of a mixed liquid
consisting of Unilube MB-22 and KE-604), thereby obtaining a mixed
liquid. Subsequently, fine solder particles of Example 18 were
manufactured in the same manner as in Example 17 except that the
aforementioned mixed liquid was employed as a dispersion medium.
Table 2 shows the results which were measured in the same manner as
in Example 17.
[0114] Likewise, in each of Examples 19-26, a fresh dispersion
medium ((Unilube MB-22)+2% KE-604) corresponding in quantity to a
deficient quantity of dispersion medium that was resulted from the
immediately preceding Example was supplemented to the recovered
dispersion medium which was recovered from the immediately
preceding Example at the recovery ratio as shown in Table 2,
thereby obtaining a mixed liquid. Then, fine solder particles of
each of these Examples were manufactured in the same manner as in
Example 17 except that the aforementioned mixed liquid was employed
as a dispersion medium. Table 2 shows the results which were
measured in the same manner as in Example 17.
2TABLE 2 Comp. of alloy Dispersion medium Quantity Example (wt %)
(base oil) Rosins (wt %) 17 Sn63Pb37 Unilube MB-22 KE-604 0.5 18
Sn63Pb37 Dispersion medium from Example 17 was recycled 19 Sn63Pb37
Dispersion medium from Example 18 was recycled 20 Sn63Pb37
Dispersion medium from Example 19 was recycled 21 Sn63Pb37
Dispersion medium from Example 20 was recycled 22 Sn63Pb37
Dispersion medium from Example 21 was recycled 23 Sn63Pb37
Dispersion medium from Example 22 was recycled 24 Sn63Pb37
Dispersion medium from Example 23 was recycled 25 Sn63Pb37
Dispersion medium from Example 24 was recycled 26 Sn63Pb37
Dispersion medium from Example 25 was recycled Rotational Av. speed
Temp. Time size Yield Recovery Example (rpm) (.degree. C.) (min)
(.mu.m) .ang. (%) (%) 17 10,000 190 10 12.1 0.63 89 94 18 10,000
190 10 12.2 0.64 89 96 19 10,000 190 10 12.1 0.63 89 96 20 10,000
190 10 11.8 0.62 90 96 21 10,000 190 10 11.9 0.64 92 96 22 10,000
190 10 11.6 0.65 92 97 23 10,000 190 10 12.1 0.63 92 97 24 10,000
190 10 12.4 0.65 91 96 25 12,500 190 10 12.4 0.64 93 96 26 12,500
190 10 11.9 0.64 93 96
[0115] It will be understood from the results shown in Table 2 that
even if a recovered dispersion medium is employed, almost the same
results as obtained in the aforementioned Examples 1-16 where a
fresh dispersion medium (particle dispersion medium) was employed
can be obtained.
EXAMPLES 27 to 30
[0116] Fine solder particles were manufactured in the same manner
as in example 1 except that the composition of alloy, the kinds of
dispersion medium, the kinds of the additive rosin, the quantity of
the rosin, the rotational speed for agitation, and the stirring
temperature were altered as shown in Table 3 (wherein "Rosin" is
replaced by "Coalescence-preventing agent") . Table 3 shows the
results which were measured in the same manner as in Example 1.
[0117] In Table 3, the coalescence-preventing agents represent
respectively an Sn salt of rosin derivatives such as Foral-AX
(complete hydrogenated rosin) , KE-604 (see Example 1) , Harimack
AS-5 (see Example 12), and Malkyd No.33 (maleic acid-modified
rosin). These Sn salts were manufactured according to the following
metathesis. (Method of manufacturing Sn salts of rosin derivatives
by means of metathesis)
[0118] To an ethanol solution of a rosin derivative was added KOH
to prepare an ethanol solution of a K (potassium) salt of rosin
derivative, which was then allowed to react with an ethanol
solution of SnCl.sub.2 at normal temperature to precipitate an Sn
salt of rosin derivative. Subsequently, this Sn salt was filtered
by means of Buchner funnel and washed with pure water, followed by
drying.
3TABLE 3 Exam- Alloy Dispersion medium Coalescence Quantity ple (wt
%) (base oil) preventive ag. (wt %) 27 Sn96.5Ag3.5 Refined castor
oil Foral-AX 1.0 (acid value: 0.8) Sn salt 28 Sn96.5Ag3.5 Refined
castor oil KE-604 1.0 (acid value: 0.8) Sn salt 29 Sn96.5Ag3.5
Refined castor oil Harimack AS-5 1.0 (acid value: 0.8) Sn salt 30
Sn96.5Ag3.5 Refined castor oil Malkyd No. 33 1.0 (acid value: 0.8)
Sn salt 31 Sn96.5Ag3.5 Refined castor oil Tin 12-hydroxy 1.0 (acid
value: 0.8) stearate 32 Sn96.5Ag3.5 Refined castor oil Tin stearate
1.0 (acid value: 0.8) Rotational Temperature Time Average Yield
Example speed (rpm) (.degree. C.) (min) size (.mu.m) .ang. (%) 27
10,000 230 10 11.3 0.68 96 28 10,000 230 10 11.6 0.62 97 29 10,000
230 10 11.9 0.59 97 30 10,000 230 10 11.2 0.64 95 31 10,000 230 10
12.7 0.61 95 32 10,000 230 10 12.4 0.57 98
[0119] It will be seen from the results shown in Table 3 that in
the case of all of the above Examples where a particle
coalescence-preventing agent (an Sn salt of rosin derivatives
having carboxyl group) was employed, it was possible to obtain fine
particles having an average diameter of 11.9 .mu.m or less.
EXAMPLES 31 and 32
[0120] Fine solder particles were manufactured in the same manner
as in Example 1 except that the composition of alloy, the kinds of
dispersion medium, the kinds of the additive rosin, the quantity of
the rosin, the rotational speed for agitation, and the stirring
temperature were altered as shown in Table 3 (wherein "Rosin" is
replaced by "Coalescence-preventing agent"). Table 3 shows the
results which were measured in the same manner as in Example 1.
[0121] In Table 3, the coalescence-preventing agents represent tin
12-hydroxy stearate and tin stearate, respectively, which are both
fatty acid soap (although the former is a soap of a fatty acid
derivative, it can be included in this definition). The former soap
was manufactured according to the aforementioned metathesis, while
the latter soap was procured from the market (Kishida Chemical Co.,
Ltd.).
[0122] It will be seen from the results shown in Table 3 that in
the case of all of the above Examples where a particle
coalescence-preventing agent (an Sn salt of hydroxycarboxylic acid
or an Sn salt of stearic acid) was employed, it was possible to
obtain fine particles having an average diameter of 12.7 .mu.m or
less.
EXAMPLE 33
[0123] A solder paste having the following composition was
prepared.
4 Hydrogenated rosin (rosin-based resin) 55.0 g Adipic acid
(activating agent) 2.0 g Hydrogenated castor oil (thixotropic
agent) 6.0 g Hexyl carbitol (solvent) 37.0 g Above being components
of a flux (total = 100 g) This flux 11.0 g Solder particles
(manufactured in Example 1) 89.0 g (Sn/Pb = 63/37) Above being
components of a solder paste (total = 100 g)
[0124] Then, the aforementioned flux and solder particles were
mixed together and agitated to obtain a solder paste. When the
viscosity of this solder paste was measured by making use of Malcom
viscometer, the viscosity thereof was found 230Pa.multidot.s
(measured at a temperature of 25.degree. C.).
[0125] Then, this solder paste was subjected to the following
tests, i.e. (1) Printability test (a test to examine if a thin spot
or bleeding can be visually recognized on a printed surface
produced by a screen printing where a metal mask having a thickness
of 0.15 mm was employed); (2) Viscosity test (a test based on JIS Z
3284 to examine the adhesive strength of the solder paste); (3)
Sagging resistance test under a heated condition (a test based on
JIS Z 3284 to examine any squeeze-out to be generated from a
predetermined place of a coated film under a heated condition); (4)
Insulation test (a test based on JIS Z 3284 to measure the
resistance of a flux film separated from a solder); (5)
Solderability test (a test to evaluate the solderability when a
main heating is performed at a temperature of 240.degree. C. for 30
seconds after a pre-heating which is performed at a temperature of
150.degree. C. for 120 seconds or at a temperature of 200.degree.
C. for 120 seconds in a reflow soldering apparatus, wherein the
solderability is evaluated by a five-grade method in which a state
where an unfused portion cannot be recognized at all in a
solidified solder after the fusion thereof is defined as being
grade 5, and a state where a lot of unfused portions can be
recognized in a solidified solder is defined as being grade 1,
grades 3 or more being considered as being practically useful). As
a result, all of the solder pastes were determined as being useful
in practical viewpoint.
[0126] By the way, when the solder pastes obtained in other
examples were subjected to the aforementioned tests, almost the
same results were obtained.
[0127] According to the present invention, it is possible to
provide a method of manufacturing fine metal particles, which makes
it possible to reduce the ratio of the quantity of the particle
dispersion medium relative to the quantity of a low melting point
metal, to effectively manufacture spherical fine metal particles in
industrial viewpoint, to reduce the quantity of the components to
be consumed in the manufacturing process to thereby make it
possible to save the manufacturing cost, to further reduce the
manufacturing cost by recovering and recycling the particle
dispersion medium, and to apply it to a fine soldering portion of a
wiring board. It is also possible according to the present
invention to provide a substance containing such fine metal
particles, and to provide a paste solder composition containing
such fine metal particles.
[0128] Further, it is also possible, through the employment of this
paste solder composition, to perform a metal mask printing of a
fine pattern. As a result, it is now possible to perform a high
density packaging such as the surface mounting of electronic
device, thereby making it possible to respond to the current
demands for the multifunctionization of the wiring board of
electronic devices as well as to the current demands for the
miniaturization, i.e. the reduction of the size and weight of
electronic devices.
* * * * *