U.S. patent application number 10/291572 was filed with the patent office on 2003-05-22 for lead-free solder alloy and a manufacturing process of electric and electronic apparatuses using such a lead-free solder alloy.
This patent application is currently assigned to Fujitsu Limited. Invention is credited to Fukushima, Yumiko, Kitajima, Masayuki, Moriya, Yasuo, Nemoto, Yoshinori, Takesue, Masakazu.
Application Number | 20030095888 10/291572 |
Document ID | / |
Family ID | 26400607 |
Filed Date | 2003-05-22 |
United States Patent
Application |
20030095888 |
Kind Code |
A1 |
Kitajima, Masayuki ; et
al. |
May 22, 2003 |
Lead-free solder alloy and a manufacturing process of electric and
electronic apparatuses using such a lead-free solder alloy
Abstract
A lead-free solder alloy composition containing Sn, Ag and Bi,
with respective concentrations set such that the lead-free solder
alloy has a melting temperature lower than a predetermined
heat-resistant temperature of a work to be soldered.
Inventors: |
Kitajima, Masayuki;
(Kawasaki-shi, JP) ; Takesue, Masakazu;
(Kawasaki-shi, JP) ; Moriya, Yasuo; (Kawasaki-shi,
JP) ; Nemoto, Yoshinori; (Kawasaki-shi, JP) ;
Fukushima, Yumiko; (Kawasaki-shi, JP) |
Correspondence
Address: |
ARENT FOX KINTNER PLOTKIN & KAHN
1050 CONNECTICUT AVENUE, N.W.
SUITE 400
WASHINGTON
DC
20036
US
|
Assignee: |
Fujitsu Limited
|
Family ID: |
26400607 |
Appl. No.: |
10/291572 |
Filed: |
November 12, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10291572 |
Nov 12, 2002 |
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09728120 |
Dec 4, 2000 |
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6521176 |
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09728120 |
Dec 4, 2000 |
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08526929 |
Sep 12, 1995 |
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6184475 |
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Current U.S.
Class: |
420/557 ;
420/562 |
Current CPC
Class: |
B23K 35/3615 20130101;
B23K 35/3613 20130101; B23K 35/3618 20130101; B23K 35/025 20130101;
B23K 35/264 20130101; H05K 3/3463 20130101; B23K 35/262 20130101;
B23K 35/3616 20130101 |
Class at
Publication: |
420/557 ;
420/562 |
International
Class: |
C22C 013/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 1994 |
JP |
6-235734 |
Mar 17, 1995 |
JP |
7-059561 |
Claims
What is claimed is:
1. A lead-free solder ally composition containing Sn, Ag and Bi,
with respective concentrations set such that said lead-free solder
alloy has a melting temperature lower than a predetermined
heat-resistant temperature of a work to be soldered.
2. A lead-free solder alloy composition as claimed in claim 1,
wherein said solder alloy composition contains Sn with an amount of
96.5.times.(100-X)/100 in wt % and Ag with an amount of
3.5.times.(100-X)/100 in wt %, wherein X represents the amount of
Bi represented in wt %.
3. A lead-free solder alloy composition as claimed in claim 1,
wherein said solder alloy composition contains Ag with an amount
not exceeding 4.0 wt %, Bi with an amount equal to or larger than
1.0 wt %, and Sn with an amount not exceeding 95.0 wt %.
4. A lead-free solder alloy composition as claimed in claim 1,
wherein said lead-free solder alloy composition contains Ag with an
amount between 1.0 wt % and 4.0 wt %, Bi with an amount between 1.0
wt % and 40.0 wt %, and Sn with an amount between 55.0 wt % and
95.0 wt %.
5. A lead-free solder alloy composition as claimed in claim 1,
wherein said lead-free solder alloy composition contains Ag with an
amount of approximately 3.3 wt %, Bi with an amount of
approximately 5.0 wt %, and Sn with an amount of approximately 91.7
wt %.
6. A lead-free solder alloy composition as claimed in claim 1,
wherein said lead-free solder alloy composition contains Ag with an
amount of approximately 3.1 wt %, Bi with an amount of
approximately 10.0 wt %, and Sn with an amount of approximately
86.9 wt %.
7. A lead-free solder alloy composition as claimed in claim 1,
wherein said lead-free solder alloy composition contains Ag with an
amount of 3.0 wt %, Bi with an amount of 15.0 wt %, and Sn with an
amount of 82.0 wt %.
8. A lead-free solder alloy composition as claimed in claim 1,
wherein said lead-free solder alloy composition contains Ag with an
amount of 2.8 wt %, Bi with an amount of 20.0 wt %, and Sn with an
amount of 77.2 wt %.
9. A lead-free solder composition as claimed in claim 1, wherein
said leadfree solder alloy composition contains Ag with an amount
of 2.4 wt %, Bi with an amount of 30.0 wt %, and Sn with an amount
of 67.6 wt %.
10. A lead-free solder alloy composition as claimed in claim 1,
wherein said lead-free solder alloy composition contains Ag with an
amount of 2.1 wt %, Bi with an amount of 40.0 wt %, and Sn with an
amount of 57.9 wt %.
11. A lead-free solder powder comprising: a plurality of lead-free
solder particles each having a generally spherical shape with a
diameter of 20-60 .mu.m; each of said lead-free solder particles
containing Sn, Ag and Bi, with respective concentrations set such
that said lead-free solder alloy has a melting temperature lower
than a predetermined heat-resistant temperature of a work to be
soldered.
12. A lead-free solder paste, comprising: a lead-free solder powder
comprising a plurality of lead-free solder particles each having a
generally spherical shape with a diameter of 20-60 .mu.m; each of
said lead-free solder particles containing Bi with a concentration
not exceeding 60.0 wt %; In with a concentration not exceeding 50.0
wt %; one or more elements selected from a group consisting of Ag,
Zn, Ge, Ga, Sb and P, with a concentration equal to or larger than
1.0 wt % but lower than 5.0 wt %; and Sn as a remaining component
of said solder alloy; said lead-free solder powder being contained
with a proportion of 80.0-95.0 wt %; and a mixture of an amine
halide, a polyhydric alcohol; and a polymer, with a proportion of
20.0-5.0 wt %.
13. A lead-free solder paste, comprising: a lead-free solder powder
comprising a plurality of lead-free solder particles each having a
generally spherical shape with a diameter of 20-60 .mu.m; each of
said lead-free solder particles containing Sn, Ag and Bi, with
respective concentrations set such that said lead-free solder
particle has a melting temperature lower than a predetermined
heat-resistant temperature of a work to be soldered; and a mixture
of an amine halide, a polyhydric alcohol and a polymer, with a
proportion of 20.0-5.0 wt %.
14. A lead-free solder paste, comprising: a lead-free solder powder
comprising a plurality of lead-free solder particles each having a
generally spherical shape with a diameter of 20-60 .mu.m; each of
said lead-free solder particles containing Sn, Bi and In, with
respective concentrations set such that said lead-free solder
powder has a melting temperature lower than a predetermined
heat-resistant temperature of a work to be soldered, said lead-free
solder powder being contained with a proportion of 80.0-95.0 wt %;
and a mixture of an organic acid, a polyhydric alcohol and a
polymer, with a proportion of 20.0-5.0 wt %.
15. A lead-free solder paste, comprising: a lead-free solder powder
comprising a plurality of lead-free solder particles each having a
generally spherical shape with a diameter of 20-60 .mu.m; each of
said lead-free solder particles containing Bi with a concentration
not exceeding 60.0 wt %; In with a concentration not exceeding 50.0
wt %; one or more elements selected from a group consisting of Ag,
Zn, Ge, Ga, Sb and P, with a concentration equal to or larger than
1.0 wt % but lower than 5.0 wt %; and Sn as a remaining component
of said solder alloy; said lead-free solder powder being contained
with a proportion of 80.0-95.0 wt %; and a mixture of an organic
acid, a polyhydric alcohol and a polymer, with a proportion of
20.0-5.0 wt %.
16. A lead-free solder paste, comprising: a lead-free solder powder
comprising a plurality of lead-free solder particles each having a
generally spherical shape with a diameter of 20-60 .mu.m; each of
said lead-free solder particles containing Sn, Ag and Bi, with
respective concentrations set such that said lead-free solder alloy
has a melting temperature lower than a predetermined heat-resistant
temperature of a work to be soldered; and a mixture of an organic
acid, a polyhydric alcohol and a polymer, with a proportion of
20.0-5.0 wt %.
17. A printed circuit board, comprising: a substrate; a conductor
pattern provided on said substrate; and a lead-free solder alloy
covering said conductor pattern, said lead-free solder alloy
containing: Sn, Ag and Bi, with respective concentrations set such
that said lead-free solder alloy has a melting temperature lower
than a predetermined heat-resistant temperature of a component to
be soldered upon said substrate.
18. An electronic component, comprising: an electronic component
body; an electrode projecting from said electronic component body;
and a lead-free solder alloy covering said conductor pattern, said
lead-free solder alloy containing: Sn, Ag and Bi, with respective
concentrations set such that said lead-free solder alloy has a
melting temperature lower than a predetermined heat-resistant
temperature of a component to be soldered upon said substrate.
19. An electronic apparatus, comprising: a substrate; a conductor
pattern provided on said substrate; an electronic component mounted
upon said substrate in electrical connection with said conductor
pattern, said electronic component having an electrode projecting
therefrom; and a lead-free solder alloy connecting said electrode
to said conductor pattern, said lead-free solder alloy containing
Sn, Ag and Bi, with respective concentrations set such that said
lead-free solder alloy has a melting temperature lower than a
predetermined heat-resistant temperature of said electronic
component.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention generally relates to manufacturing of
electric and electronic apparatuses and more particularly to a
solder alloy of various forms used for soldering electric and
electronic components, as well as to a soldering process and
further to a rig used for such a soldering process. In particular,
the present invention relates to a lead-free solder alloy that
contains no substantial amount of lead (Pb).
[0002] Solder alloys are characterized by low melting temperatures
and provide excellent electric as well as mechanical properties.
Thus, solder alloys of various forms, including solder powders and
solder pastes, are used for mounting electronic components on a
printed circuit board.
[0003] Meanwhile, conventional solder alloys contain Pb. As Pb is
toxic against biological bodies, it has been necessary to take
precautionary measure when conducting such a soldering process,
while such a precautionary measure increases the cost of the
products produced as a result of the soldering. Thus, there is a
demand for a lead-free solder alloy that is suitable for use in
various soldering processes including automated soldering
process.
[0004] In the automated soldering process of electronic components,
several types of solder alloys are used conventionally. A
representative example is a solder alloy known as Sn63-Pb37,
wherein the solder alloy contains 63 wt % of Sn and 37 wt % of Pb.
This material causes an eutectic melting at a melting temperature
of 183.degree. C. Another typical example is a solder alloy known
as Sn62-Pb36-Ag2, wherein the solder alloy contains 62 wt % of Sn,
36 wt % of Pb and 2 wt % of Ag. The solder alloy forms an eutectic
system characterized by a melting temperature of 179.degree. C. As
these solder alloys have low melting temperatures and provide
excellent mechanical properties in terms of tensile strength and
elongation as well as excellent electrical properties such as low
resistance, they are used extensively for various automated
soldering processes.
[0005] Meanwhile, there is a tendency of increasing public
regulations against the use of Pb in view of human health and in
view of environmental protection. Under such circumstances, various
efforts have been made for developing a substitute solder alloy
that is free from Pb.
[0006] As the material for use in assembling electric and
electronic apparatuses, such a substitute solder alloy is required
to have a low melting temperature such that the soldered electric
or electronic component experiences little degradation of
performance caused by the heat at the time of soldering. Further,
such a substitute solder alloy should have an excellent mechanical
strength comparable to that of a conventional solder alloy that
contains Pb.
SUMMARY OF THE INVENTION
[0007] Accordingly, it is a general object of the present invention
to provide a novel and useful solder alloy of various forms as well
as a soldering process wherein the foregoing problems are
eliminated.
[0008] Another and more specific object of the present invention is
to provide a solder alloy free from Pb and still having a
sufficiently low melting temperature, high conductivity and high
mechanical strength.
[0009] Another object of the present invention is to provide a
lead-free solder alloy composition comprising Sn, Bi and In, said
solder alloy containing Sn, Bi and In with respective
concentrations set such that said lead-free solder alloy
composition has a melting temperature lower than a predetermined
heat-resistant temperature of a work to be soldered.
[0010] Another object of the present invention is to provide a
method for soldering a work, comprising the steps of:
[0011] reflowing a lead-free solder alloy containing therein Sn, Bi
and In with respective contents set such that said solder alloy has
a melting temperature lower than a predetermined heat-resistant
temperature of said work, said step of reflowing including a step
of heating said solder alloy to a temperature higher than said
melting temperature; and
[0012] cooling said work at a part where a soldering has been made
to solidify said lead-free solder alloy.
[0013] Another object of the present invention is to provide a
lead-free solder alloy composition containing: Bi with a
concentration not exceeding 60.0 wt %; In with a concentration not
exceeding 50.0 wt %; one or more elements selected from a group
consisting of Ag, Zn, Ge, Ga, Sb and P, with a concentration equal
to or larger than 1.0 wt % but lower than 5.0 wt %; and Sn as a
balancing component of said lead-free solder alloy.
[0014] Another object of the present invention is to provide a
soldering process of a work, comprising the steps of:
[0015] reflowing a leadfree solder alloy containing therein: Bi
with a concentration not exceeding 60.0 wt %; In with a
concentration not exceeding 50.0 wt %; one or more elements
selected from a group consisting of Ag, Zn, Ge, Ga, Sb and P, with
a concentration equal to or larger than 1.0 wt % but lower than 5.0
wt %; and Sn as a remaining component of said solder alloy; and
[0016] cooling said work at a part where a soldering is made to
solidify said lead-free solder alloy.
[0017] Another object of the present invention is to provide a
lead-free solder alloy composition containing Sn, Ag and Bi, with
respective concentrations set such that said lead-free solder alloy
has a melting temperature lower than a predetermined heat-resistant
temperature of a work to be soldered.
[0018] Another object of the present invention is to provide a
method of soldering a work, comprising the step of:
[0019] reflowing a lead-free solder alloy containing therein Sn, Ag
and Bi with respective contents set such that said lead-free solder
alloy has a melting temperature lower than a predetermined
heat-resistant temperature of said work, said step of reflowing
including a step of heating said lead-free solder alloy to a
temperature higher than said melting temperature; and
[0020] cooling said work at a part where a soldering is made to
solidify said lead-free solder alloy.
[0021] Another object of the present invention is to provide a
lead-free solder powder comprising:
[0022] a plurality of lead-free solder particles each having a
generally spherical shape with a diameter of 20-60 .mu.m;
[0023] each of said lead-free solder particles containing Sn, Bi
and In, with respective concentrations set such that said lead-free
solder particle has a melting temperature lower than a
predetermined heat-resistant temperature of a work to be
soldered.
[0024] Another object of the present invention is to provide a
lead-free solder powder comprising:
[0025] a plurality of lead-free solder particles each having a
generally spherical shape with a diameter of 20-60 .mu.m;
[0026] each of said lead-free solder particles containing Bi with a
concentration not exceeding 60.0 wt %; In with a concentration not
exceeding 50.0 wt %; one or more elements selected from a group
consisting of Ag, Zn, Ge, Ga, Sb and P, with a concentration equal
to or larger than 1.0 wt % but lower than 5.0 wt %; and Sn as a
remaining component of said lead-free solder particle.
[0027] Another object of the present invention is to provide a
lead-free solder powder comprising:
[0028] a plurality of lead-free solder particles each having a
generally spherical shape with a diameter of 20-60 .mu.m;
[0029] each of said lead-free solder particles containing Sn, Ag
and Bi, with respective concentrations set such that said lead-free
solder alloy has a melting temperature lower than a predetermined
heat-resistant temperature of a work to be soldered.
[0030] Another object of the present invention is to provide
lead-free solder paste, comprising:
[0031] a lead-free solder powder comprising a plurality of
lead-free solder particles each having a generally spherical shape
with a diameter of 20-60 .mu.m; each of said lead-free solder
particles containing Sn, Bi and In, with respective concentrations
set such that said lead-free solder particle has a melting
temperature lower than a predetermined heat-resistant temperature
of a work to be soldered, said solder powder being contained with a
proportion of 80.0-95.0 wt %; and
[0032] a mixture of an amine halide, a polyhydric alcohol and a
polymer, with a proportion of 20.0-5.0 wt %.
[0033] Another object of the present invention is to provide a
lead-free solder paste, comprising:
[0034] a lead-free solder powder comprising a plurality of
lead-free solder particles each having a generally spherical shape
with a diameter of 20-60 .mu.m; each of said lead-free solder
particles containing Bi with a concentration not exceeding 60.0 wt
%; In with a concentration not exceeding 50.0 wt %; one or more
elements selected from a group consisting of Ag, Zn, Ge, Ga, Sb and
P, with a concentration equal to or larger than 1.0 wt % but lower
than 5.0 wt %; and Sn as a remaining component of said solder
alloy; said leadfree solder powder being contained with a
proportion of 80.0-95.0 wt %; and
[0035] a mixture of an amine halide! a polyhydric alcohol and a
polymer, with a proportion of 20.0-5.0 wt %.
[0036] Another object of the present invention is to provide a
lead-free solder paste, comprising:
[0037] a lead free solder powder comprising a plurality of
lead-free solder particles each having a generally spherical shape
with a diameter of 20-60 .mu.m; each of said lead-free solder
particles containing Sn, Ag and Bi, with respective concentrations
set such that said lead-free solder particle has a melting
temperature lower than a predetermined heat-resistant temperature
of a work to be soldered; and
[0038] a mixture of an amine halide, a polyhydric alcohol and a
polymer, with a proportion of 20.0-5.0 wt %.
[0039] Another object of the present invention is to provide a
lead-free solder paste, comprising:
[0040] a lead-free solder powder comprising a plurality of
lead-free solder particles each having a generally spherical shape
with a diameter of 20-60 .mu.m; each of said lead-free solder
particles containing Sn, Bi and In, with respective concentrations
set such that said lead-free solder powder has a melting
temperature lower than a predetermined heat-resistant temperature
of a work to be soldered, said lead-free solder powder being
contained with a proportion of 80.0-95.0 wt %; and
[0041] a mixture of an organic acid, a polyhydric alcohol and a
polymer, with a proportion of 20.0-5.0 wt %.
[0042] Another object of the present invention is to provide a
lead-free solder paste, comprising:
[0043] a lead-free solder powder comprising a plurality of
lead-free solder particles each having a generally spherical shape
with a diameter of 20-60 .mu.m; each of said lead-free solder
particles containing Bi with a concentration not exceeding 60.0 wt
%; In with a concentration not exceeding 50.0 wt %; one or more
elements selected from a group consisting of Ag, Zn, Ge, Ga, Sb and
P, with a concentration equal to or larger than 1.0 wt % but lower
than 5.0 wt %; and Sn as a remaining component of said solder
alloy; said leadfree solder powder being contained with a
proportion of 80.0-95.0 wt %; and
[0044] a mixture of an organic acid, a polyhydric alcohol and a
polymer, with a proportion of 20.0-5.0 wt %.
[0045] Another object of the present invention is to provide a
lead-free solder paste, comprising:
[0046] a lead-free solder powder comprising a plurality of
lead-free solder particles each having a generally spherical shape
with a diameter of 20-60 .mu.m; each of said lead-free solder
particles containing Sn, Ag and Bi, with respective concentrations
set such that said lead-free solder alloy has a melting temperature
lower than a predetermined heat-resistant temperature of a work to
be soldered; and
[0047] a mixture of an organic acid, a polyhydric alcohol and a
polymer, with a proportion of 20.0-5.0 wt %.
[0048] Another object of the present invention is to provide a
printed circuit board, comprising:
[0049] a substrate;
[0050] a conductor pattern provided on said substrate; and
[0051] a lead-free solder alloy covering said conductor pattern,
said lead-free solder alloy containing Sn, Bi and In, with
respective concentrations set such that lead-free said solder alloy
has a melting temperature lower than a predetermined heat-resistant
temperature of a component to be soldered upon said substrate.
[0052] Another object of the present invention is to provide
printed circuit board, comprising:
[0053] a substrate;
[0054] a conductor pattern provided on said substrate; and
[0055] a lead-free solder alloy covering said conductor pattern,
said lead-free solder alloy containing: Bi with a concentration not
exceeding 60.0 wt %; In with a concentration not exceeding 50.0 wt
%; one or more elements selected from a group consisting of Ag, Zn,
Ge, Ga, Sb and P, with a concentration equal to or larger than 1.0
wt % but lower than 5.0 wt %; and Sn as a remaining component of
said lead-free solder alloy.
[0056] Another object of the present invention is to provide a
printed circuit board, comprising:
[0057] a substrate;
[0058] a conductor pattern provided on said substrate; and
[0059] a lead-free solder alloy covering said conductor pattern,
said lead-free solder alloy containing: Sn, Ag and Bi, with
respective concentrations set such that said lead-free solder alloy
has a melting temperature lower than a predetermined heat-resistant
temperature of a component to be soldered upon said substrate.
[0060] Another object of the present invention is to provide an
electronic component, comprising:
[0061] an electronic component body;
[0062] an electrode projecting from said electronic component body;
and
[0063] a lead-free solder alloy covering said electrode, said
lead-free solder alloy containing Sn, Bi and In, with respective
concentrations set such that said lead-free solder alloy has a
melting temperature lower than a predetermined heat-resistant
temperature of said electronic component.
[0064] Another object of the present invention is to provide an
electronic component, comprising:
[0065] an electronic component body;
[0066] an electrode projecting from said electronic component body;
and
[0067] a lead-free solder alloy covering said electrode, said
lead-free solder alloy containing: Bi with a concentration not
exceeding 60.0 wt %; In with a concentration not exceeding 50.0 wt
%; one or more elements selected from a group consisting of Ag, Zn,
Ge, Ga, Sb and Pi with a concentration equal to or larger than 1.0
wt % but lower than 5.0 wt %; and Sn as a remaining component of
said lead-free solder alloy.
[0068] Another object of the present invention is to provide an
electronic component, comprising:
[0069] an electronic component body;
[0070] an electrode projecting from said electronic component body;
and
[0071] a lead-free solder alloy covering said conductor pattern,
said lead-free solder alloy containing: Sn, Ag and Bi, with
respective concentrations set such that said lead-free solder alloy
has a melting temperature lower than a predetermined-heat-resistant
temperature of a component to be soldered upon said substrate.
[0072] Another object of the present invention is to provide an
electronic apparatus, comprising:
[0073] a substrate;
[0074] a conductor pattern provided on said substrate;
[0075] an electronic component mounted upon said substrate in
electrical connection with said conductor pattern, said electronic
component having an electrode projecting therefrom; and
[0076] a lead-free solder alloy connecting said electrode to said
conductor pattern, said lead-free solder alloy containing Sn, Bi
and In, with respective concentrations set such that said lead-free
solder alloy has a melting temperature lower than a predetermined
heat-resistant temperature of said electronic component.
[0077] Another object of the present invention is to provide an
electronic apparatus, comprising:
[0078] a substrate;
[0079] a conductor pattern provided on said substrate;
[0080] an electronic component mounted upon said substrate in
electrical connection with said conductor pattern, said electronic
component having an electrode projecting therefrom; and
[0081] a lead-free solder alloy connecting said electrode to said
conductor pattern, said lead-free solder alloy containing: Bi with
a concentration not exceeding 60.0 wt %; In with a concentration
not exceeding 50.0 wt %; one or more elements selected from a group
consisting of Ag, Zn, Ge, Ga, Sb and P, with a concentration equal
to or larger than 1.0 wt % but lower than 5.0 wt %; and Sn as a
remaining component of said lead-free solder alloy.
[0082] Another object of the present invention is to provide
an-electronic apparatus, comprising:
[0083] a substrate;
[0084] a conductor pattern provided on said substrate;
[0085] an electronic component mounted upon said substrate in
electrical connection with said conductor pattern, said electronic
component having an electrode projecting therefrom; and
[0086] a lead-free solder alloy connecting said electrode to said
conductor pattern, said lead-free solder alloy containing Sn, Ag
and Bi, with respective concentrations set such that said lead-free
solder alloy has a melting temperature lower than a predetermined
heat-resistant temperature of said electronic component.
[0087] Another object of the present invention is to provide a
soldering rig for soldering a work, comprising:
[0088] soldering unit for soldering a work by causing a reflow of a
lead-free solder; and
[0089] a cooling unit for cooling said work at a part where a
soldering has been made, to solidify said lead-free solder.
[0090] According to the present invention as set forth above, one
can obtain a solder alloy free from Pb while maintaining excellent
mechanical strength in the solidified solder alloy. Thereby, the
problem of hazard to biological bodies as well as the problem of
environmental pollution are successfully eliminated. Further, by
optimizing the composition of the solder alloy, it is possible to
reduce the melting temperature of the solder alloy lower than a
melting temperature of a conventional solder alloy that contains
Pb, while maintaining sufficient mechanical strength. Thereby, the
damage applied to the work or electronic component as a result of
soldering is reduced. Associated with the reduced temperature of
soldering, the preparation of the work for soldering is
substantially simplified, and the cost of the work is also reduced
by using less expensive materials. By cooling the solder alloy
rapidly, it is possible to maximize the elongation of the
solidified solder alloy.
[0091] Other objects and further features of the present invention
will become apparent from the following detailed description when
read in conjunction with the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0092] FIG. 1 is a diagram summarizing the effect of In added to a
solder alloy of a Sn--Bi eutectic system in the form of a
table;
[0093] FIG. 2 is a diagram summarizing the effect of Bi added to a
solder alloy of a Sn--Bi--In ternary system in the form of a
table;
[0094] FIG. 3 is a diagram summarizing the effect of various
elements added to a solder alloy of a Sn--Bi--In ternary system in
the form of a table;
[0095] FIG. 4 is a diagram summarizing the effect of Bi added to a
solder alloy of a Sn--Ag eutectic system in the form of a
table;
[0096] FIGS. 5A-5I are diagrams showing a particle of a lead-free
solder powder according to an embodiment of the present
invention;
[0097] FIG. 6 is a diagram showing the composition of a lead-free
solder paste according to another embodiment of the present
invention in the form of a table;
[0098] FIG. 7 is a diagram showing the composition of a lead-free
solder paste according to other embodiment of the present invention
in the form of a table;
[0099] FIG. 8 is a diagram showing the construction of a printed
circuit board according to still other embodiment of the present
invention;
[0100] FIG. 9 is a diagram showing the construction of a printed
circuit board according to still other embodiment of the present
invention;
[0101] FIG. 10 is a diagram showing the construction of a
semiconductor device mounted upon a printed circuit board according
to still other embodiment of the present invention;
[0102] FIG. 11 is a diagram showing the mechanical property of the
lead-free alloy of various embodiments of the present invention in
the form of a table;
[0103] FIG. 12 is a diagram showing the detailed experimental
result conducted for a sample included in FIG. 11, in the form of a
table;
[0104] FIG. 13 is a diagram showing the detailed experimental
result conducted for another sample included in FIG. 11, in the
form of a table;
[0105] FIG. 14 is a diagram showing the detailed experimental
result conducted for other sample included FIG. 11, in the form of
a table;
[0106] FIG. 15 is a diagram showing the detailed experimental
result conducted for other sample included in FIG. 11, in the form
of a table;
[0107] FIG. 16 is a diagram showing the detailed experimental
result conducted for other sample included in FIG. 11, in the form
of a table;
[0108] FIG. 17 is a diagram showing the relationship between the
elongation and the load for the sample of FIG. 12;
[0109] FIG. 18 is a diagram showing the relationship between the
elongation and the load for the sample of FIG. 13;
[0110] FIG. 19 is a diagram showing the relationship between the
elongation and the load for the sample of FIG. 14;
[0111] FIG. 20 is a diagram showing the relationship between the
elongation and the load for the sample of FIG. 15;
[0112] FIG. 21 is a diagram showing the relationship between the
elongation and the load for the sample of FIG. 16;
[0113] FIG. 22 is a diagram showing the state of fracture of the
sample of FIG. 12;
[0114] FIG. 23 is a diagram showing the state of fracture of the
sample of FIG. 13;
[0115] FIG. 24 is a diagram showing the state of fracture of the
sample of FIG. 14;
[0116] FIG. 25 is a diagram showing the state of fracture of the
sample of FIG. 15;
[0117] FIG. 26 is a diagram showing the state of fracture of the
sample of FIG. 16;
[0118] FIG. 27 is a diagram showing the soldering process according
to still other embodiment of the present invention in the form of a
flowchart;
[0119] FIG. 28 is a diagram showing a soldering rig according to a
still other embodiment of the present invention;
[0120] FIG. 29 is a diagram showing the construction of a cooling
unit of the soldering rig of FIG. 28;
[0121] FIG. 30 is a diagram showing the construction of another
cooling unit of the soldering rig of FIG. 28; and
[0122] FIG. 31 is a diagram showing the construction of still other
cooling unit of the soldering rig of FIG. 28.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0123] Hereinafter, the present invention will be described with
reference to the preferred embodiments.
[0124] In the present invention, the inventor has conducted a
series of experiments to prepare various solder alloys free from Pb
and to examine the properties thereof. As a result, it has been
discovered that a lead-free solder alloy containing Sn, Bi and In
as well as a lead-free solder alloy containing Sn, Ag and Bi, show
mechanical as well as electrical properties comparable or even
superior to those of the conventional solder alloy that contains
Pb.
[0125] Thus, the inventor of the present invention has conducted
detailed experiments on the lead-free solder alloy containing Sn,
Bi and In as well as on the lead-free solder alloy containing Sn,
Ag and Bi in search of the optimum composition of the solder alloy.
Further, experiments have been conducted also on the alloys in
which other metal or non-metal elements are added.
[0126] First, a description will be made on the experiments about
the solder alloy of the Sn--Bi--In ternary system with reference to
FIGS. 1 and 2, wherein FIGS. 1 and 2 are tables that summarize the
result of the experiments on the tensile strength, percentage of
elongation, time-to-failure, fracture surface morphology and the
melting temperature for various compositions of the solder alloy.
Further, FIG. 3 shows a table summarizing the result of the similar
experiments conducted for solder alloys in which other metal as
well as non-metal elements are added.
[0127] Before going to the evaluation of the experimental results,
explanation will be made on the testing process and testing
apparatuses used in the experiments.
[0128] In the experiments, standard test pieces prescribed in the
JIS (Japanese Industrial Standard) were produced from solder alloys
of various compositions, and the test pieces thus produced were
subjected to a tensile test for mechanical properties such as
tensile strength, percentage of elongation, time-to-failure and
fracture surface observation. Further, the melting temperature of
the solder alloy was measured by using a thermocouple.
[0129] More specifically, the test pieces were produced according
to the JIS type 7 prescription for tensile tests. The test piece
thus produced had a cross sectional area of 40 mm.sup.2 and a gauge
length of 30 mm. The test pieces were prepared by melting an alloy
of Sn, Bi and In or an alloy containing further impurity elements
in a furnace held at 400.degree. C., wherein the molten solder
alloy thus prepared was poured into a mold carrying therein a
cavity with a shape corresponding to the JIS type 7 test piece
prescription.
[0130] In the tensile test, a test rig of Instron Model 4206 was
used. The test piece was set on the rig, and the test was conducted
by pulling the test piece with a fixed rate of 0.5 mm/min while
recording the tensile load and the elongation of the test piece.
Upon occurrence of the failure, the tensile strength and the
percentage of elongation were calculated based upon the record.
Further, a discrimination was made whether the fracture was a
ductile one or brittle one based upon the observation of the
fracture surface morphology.
[0131] The measurement of the melting temperature or liquidus
temperature of the solder alloy, on the other hand, was made by
causing a melting of the solder alloy, followed by a natural
cooling. During the process of natural cooling, the temperature
profile was measured by means of a thermocouple inserted into the
molten solder alloy.
[0132] As already noted, FIGS. 1 through 3 summarize the result of
the test in terms of the tensile strength, elongation,
time-to-failure, fracture surface and the melting temperature. When
the properties observed were satisfactory for a solder alloy, an
open circle mark was given as an indication of positive evaluation.
When the properties were unsatisfactory, on the other hand, a cross
mark was given as an indication of negative evaluation. In the
present test, the evaluation was made based upon a standard that:
(1) the solder alloy should have a tensile strength of at least 2
kg/mm.sup.2; (2) the solder alloy should have an elongation of at
least 30%; and (3) the solder alloy should have a melting
temperature equal to or lower than 155.degree. C.
[0133] Referring to FIG. 1, it will be noted chat the content of In
is changed variously in the ternary alloy of the Sn--Bi--In system
while maintaining the content of Bi generally constant. As will be
noted in FIG. 1, the solder alloy provides a satisfactory tensile
strength as long as the In content in the alloy is less than 50 wt
%. When the In content exceeds 50 wt % as in the case of the
comparative examples 3 and 4, on the other hand, the solder alloy
fails to provide a satisfactory tensile strength. About the
elongation, it should be noted that the solder alloy containing In
with a content less than 0.5 wt % as in the case of the comparative
examples 1 and 2 does not provide a satisfactory result, while the
solder alloy containing In with a content of 0.5 wt % or more
provides a satisfactory result.
[0134] About the melting temperature, all of the test samples in
FIGS. 1-3 satisfy the requirement that the melting temperature
should be lower than 155.degree. C. It should be noted that
electronic components are generally designed to have a
heat-resistant temperature of 183.degree. C. in view of use of
conventional solder alloy that contains Pb. By using the solder
alloy of the present invention, on the other hand, it is possible
to conduct the soldering process at a temperature lower than the
temperature used conventionally, and the problem of thermal damage
to the electronic components is minimized. Further, it is possible
to reduce the cost of the electronic apparatus by simplifying the
preparation process of soldering as well as by using inexpensive
materials for the electronic components.
[0135] It should be noted that FIG. 1 further shows a tendency that
the melting temperature of the solder alloy decreases with
increasing In content. In other words, FIG. 1 indicates that one
can control the melting temperature of the solder alloy by
controlling the In content. Thereby, any necessary change of the
soldering temperature depending upon the electronic component such
as a semiconductor device, is easily attended to.
[0136] With regard to the time-to-failure, it will be noted that no
satisfactory result is obtained when the In content is less than
0.5 wt % as in the case of the comparative examples 1 and 2 or when
the In content exceeds 50 wt % as in the case of the comparative
example 3. It is noted that there is an exception in the case of
the comparative example 4 in which the time-to-failure falls in the
satisfactory range of 40-60 minutes even when the In content
exceeds 50 wt %. It is believed that this exception is caused
because of the Bi-free composition of the solder alloy that has
resulted in an increase of the time-to-failure.
[0137] With regard to the fracture surface of the tested samples,
it is noted that a brittle fracture occurs when the In content of
the solder alloy is less than 5.0 wt %. When the In content is
equal to or larger than 5.0 wt %, a ductile fracture occurs. While
the type of fracture of the solder alloy may not affect the
property thereof as a solder, it is more preferable that the solder
alloy shows ductile fracture than brittle fracture in view point of
the mechanical strength.
[0138] Summarizing the result of FIG. 1, it is concluded that one
can obtain a solder alloy of desirable property by incorporating In
into a solder alloy of the Sn--Bi eutectic system with a proportion
of 0.5 wt % or more but less than 50.0 wt %. In FIG. 1, the samples
1-1-1-5 provide such desirable properties.
[0139] In the sample 1-5, it should be noted that, while the
tensile strength is slightly larger than the acceptable lower
limit, the solder alloy provides a much larger elongation over
other samples as well as comparative examples cited in the table of
FIG. 1. Thus, by setting the composition of the solder alloy such
that the solder alloy contains Sn with a proportion of about 34.0
wt %, Bi with a proportion of about 46.0 wt % and In with a
proportion of about 20.0 wt %, it is possible to obtain a solder
alloy having an excellent elongation. Such a solder alloy
composition is particularly suitable for soldering components upon
a flexible substrate where the solder alloy experiences large
deformation.
[0140] In the description above, the representation of the
composition such as "about 34.0 wt %," "about 20.0 wt %," and the
like, is used, in view of possible error in the composition of the
solder alloy that can reach as much as .+-.1 wt % for Sn and Bi and
.+-.0.1 wt % for In.
[0141] Next, the result of FIG. 2 will be explained. As already
noted, FIG. 2 shows the properties of various solder alloys all
included in the ternary eutectic system of Sn--Bi--In but with
various Bi contents and a generally common In content.
[0142] Referring to FIG. 2, it will be noted that a satisfactory
tensile strength is obtained when the Bi content has exceeds 5.0 wt
%. About the elongation, no satisfactory result is obtained when
the Bi content is equal to or larger than 60.0 wt % as in the case
of the comparative examples 12-15, while the solder alloy
containing Bi with a proportion less than 60.0 wt % provides a
satisfactory elongation. About the melting temperature, all of the
solder alloy compositions, except for the example in which the Bi
content is 100%, satisfy the requirement. In other words, it is
demonstrated that the melting temperature or liquidus temperature
is reduced in the solder alloy that contains Sn, Bi and In.
[0143] The result of FIG. 2 further indicates the tendency that the
melting temperature increases with increasing Bi content. Thus, by
adjusting the Bi content, it is possible to control the melting
temperature of the solder alloy.
[0144] About the time-to-failure, it will be noted that the solder
alloys containing Bi with less than 5.0 wt %, as in the comparative
examples 10 and 11, as well as the solder alloys containing Bi with
60.0 wt % or more, as in the case of the comparative experiments
12-15, provide a reduced time-to-failure and hence an
unsatisfactory durability. Further, the observation of the fracture
surface indicates that the solder alloy shows a ductile fracture
when the Bi content is less than 55.0 wt %, while the fracture
becomes brittle when the Bi content in the solder alloy is equal to
or larger than 55.0 wt %.
[0145] Summarizing the result of FIG. 2, it is concluded that a
solder alloy suitable for soldering electric and electronic
components is obtained by adding Bi to a solder alloy of the Sn--In
eutectic system, with a proportion that exceeds 5.0 wt % but
smaller than 60.0 wt % as in case of the examples 2-1 and 2-2 of
FIG. 2.
[0146] Further, the results of FIGS. 1 and 2 collectively indicate
that a solder alloy suitable for soldering electric and electronic
components is obtained by setting the Bi content to be less than
60.0 wt %, the In content less than 50.0 wt %, and by balancing the
rest of the solder alloy by Sn. Particularly, one obtains a solder
alloy of optimum composition by setting the Sn content to about
40.0 wt %, the Bi content to about 55.0 wt %, and the In content to
about 5.0 wt %. As already noted, the phrase "about" is used in
view of the possible error in the composition when forming the
alloy. The error can be as large as .+-.1 wt % for Sn and Bi and
.+-.0.1 wt % for In.
[0147] Next, a description will be made on the experiments
conducted by the inventor with reference to FIG. 3, wherein FIG. 3
shows the result of the experiments conducted upon a solder alloy
based upon the Sn--Bi--In eutectic system, except that other metal
elements, particularly Ag and Zn, are added to the foregoing
ternary system.
[0148] It will be noted that the solder alloy does not satisfy the
requirement about elongation when Ag and Zn are added to the solder
alloy of the Sn--Bi--In ternary eutectic system with a proportion
of 5.0 wt % or more for each of Ag and Zn. On the other hand, when
the proportion of one of Ag and Zn is set to 1.0 wt %, the
requirement for elongation is satisfied.
[0149] Further, it will be noted in FIG. 3 that all of the samples
satisfy the requirement about melting temperature. The result of
FIG. 3 indicates that one can reduce the melting temperature and
hence the liquidus temperature by incorporating Ag and Zn to the
ternary solder ally of the Sn--Bi--In eutectic system.
[0150] The result of FIG. 3 clearly indicates that the solder alloy
containing Ag and Zn with a proportion of 1.0 wt % or more but
below 5.0 wt %, such as the examples 3-1 and 3-2, satisfies the
requirement imposed upon a solder alloy, with every respect of the
requirement. Further, it should be noted that the content of Bi and
In in FIG. 3 falls in the optimum range derived from the result of
FIGS. 1 and 2. In other words, the content of Bi does not exceed
60.0 wt % and the content of In does not exceed 50.0 wt %.
[0151] Summarizing the result of FIG. 3, a solder alloy suitable
for soldering is obtained from a ternary alloy of the Bi--In--Sn
eutectic system by setting the proportion of Bi and In such that
the Bi content does not exceed 60.0 wt %, the In content does not
exceed 50.0 wt % and by incorporating Ag or Zn with a proportion
equal to or larger than 1.0 wt % but smaller than 5.0 wt %. The
rest of the alloy composition is balanced by Sn. In the embodiment
of FIG. 3, it should be noted that other metal elements such, as Ge
or Ga may be used in place of Ag and Zn. Further, non-metal
elements such as P may also be used for this purpose.
[0152] In the ternary alloy composition of the Sn--Bi--In eutectic
system shown in FIG. 3, it is also possible to incorporate Sb as an
additional metal element. By adding Sb, the problem of elemental
diffusion to a Sn--Pb plating is successfully eliminated. When Pb
and Bi are contacted with each other, there tends to occur a
problem of diffusion, which in turn results in a bulging or
coming-off of the solder metal. Thereby, the reliability of the
soldering deteriorates significantly. In the lead-free solder alloy
of the present invention, such a problem of degradation of the
solder alloy is successfully eliminated by incorporating Sn as
noted above. Thereby, it is preferable to control the Sn content in
the solder alloy to fall in the range of 1.0-5.0 wt %. The Sn
content is optimized in this range in view of the tensile strength
and the elongation of the solder alloy.
[0153] Next, a solder alloy of the Sn--Ag--Bi system will be
described with reference to FIG. 4 that shows the result of the
test conducted upon the tensile strength, elongation,
time-to-failure, fracture surface morphology and the melting
temperature for the solder alloy of various compositions. As the
tests conducted upon the solder alloys of FIG. 4 are identical with
the tests described already, further description thereof will be
omitted. Similarly to FIGS. 1-3, FIG. 4 cites the evaluation about
the tensile strength, elongation, time-to-fracture and the melting
temperature. When the evaluation is positive, a designation is made
by an open circle mark. When the evaluation is negative, on the
other hand, a designation is made by a cross mark.
[0154] In the test of FIGS. 4, a standard is imposed such that a
satisfactory solder alloy should have a tensile strength of 7
kg/mm.sup.2 or more, an elongation of 7.0% or more and a melting
temperature of 220.degree. C. or less. It will be noted that this
standard is different from the standard applied to the solder alloy
containing Sn, Bi and In. The reason of using a such different
standard is to meet the demand for a solder alloy having a
particularly large tensile strength. Such a demand on the other
hand does not require a high elongation as in the case of the
foregoing solder alloy of the Sn--Bi--In system.
[0155] Referring to FIG. 4, the table shows the properties of the
ternary solder alloy of the Sn--Ag--Bi eutectic system for various
contents of Bi while maintaining the Ag content substantially
constant.
[0156] From the result of FIG. 4, it will be noted that the solder
alloy of the examples 4-1-4-6 satisfies the foregoing standard. On
the other hand, the comparative example 30 that contains Pb has a
lower tensile strength and does not satisfy the foregoing standard,
contrary to the ternary alloy of the Sn--Ag--Bi system. A similar
result was obtained also for the example 31 for the binary alloy of
the Sn--Bi eutectic system and for the example 32 for the binary
alloy of the Sn--Ag eutectic system.
[0157] About the observed elongation, all of the examples of FIG. 4
satisfy the required standard. It is known that the elongation and
the tensile strength tend to contradict with each other. Thus,
there is a tendency that an alloy having a large tensile strength
shows a small elongation. Under such circumstances, the solder
alloy of the present embodiment provides a particularly high
tensile strength while sacrificing the elongation. For example, the
samples 4-1-4-6 shows a tensile strength higher than that of the
comparative examples 30-32 and an elongation smaller than that of
the comparative examples 30-32.
[0158] With regard to the melting temperature, all of the examples
shown in the table of FIG. 4 satisfy the required standard.
Particularly, the examples 4-1-4-6 show a melting temperature
falling in the range of 139.degree. C.-220.degree. C. It has been
practiced, in the conventional lead-containing solder alloys, to
adjust the composition of the alloy such that the melting
temperature is held low in view of the endurable temperature of
183.degree. C. of the electronic components to be soldered. On the
other hand, there also are demands for a solder alloy composition
having a higher melting temperature such as 220.degree. C. or more.
In order to meet such a demand, there exist a group of solder
alloys in which the melting temperature is adjusted higher than
220.degree. C. According to the present embodiment as set forth in
the table of FIG. 4, one can provide a lead-free solder alloy that
is suitable for the purpose while simultaneously maintaining a
sufficient tensile strength.
[0159] With regard to the time-to-failure, there is a tendency that
the time-to-failure increases with increasing elongation. Thus, the
examples 4-1-4-6 provide a relatively small time-to-failure value
as compared with the comparative examples 30-32. Even then, the
solder alloys of the examples 4-1-4-6 provides a satisfactory
time-to-failure of 230-670 seconds while maintaining a large
tensile strength.
[0160] With regard to the fracture surface, the solder alloy of the
present embodiment shows a feature of brittle fracture. As the
solder alloy of the present embodiment is intended to provide a
high tensile strength, the evidence that the solder alloy shows a
brittle fracture does not cause any serious consequence.
[0161] Summarizing the result of FIG. 4, it will be noted that the
ternary solder alloy of the Sn--Ag--Bi system provides a superior
tensile strength over the eutectic solder alloys of other
compositions described previously such as the examples 30-32, as
clearly demonstrated in the examples 4-1-4-6. Further, it is
possible to adjust the melting temperature as desired within the
temperature range conventionally used for soldering. Thus, it is
possible to carry out the soldering at various temperatures
optimized for the components to be soldered while simultaneously
maintaining a high tensile strength, by selecting the composition
of the lead-free solder alloy according to the purpose.
[0162] In the examples 4-1-4-6 of FIG. 4, it should be noted that
the ratio of the Sn wt % to the Ag wt % is held constant and only
the Bi content is changed. In other words, the solder alloy
composition of the examples 4-1 4-6 is represented as
96.5.times.(100-X)/100 for Sn, 3.5.times.(100-X)/100 for Ag, and X
for Bi, all represented in terms of wt %.
[0163] From FIG. 4, it is concluded that the following compositions
are suitable for the solder alloy having a large tensile strength:
a solder alloy containing Ag with an amount not exceeding 4.0 wt %,
Bi with an amount equal to or larger than 1.0 wt %, and Sn with an
amount not exceeding 95.0 wt %; a solder alloy containing Ag with
an amount between 1.0 wt % and 4.0 wt %, Bi with an amount between
1.0 wt % and 40.0 wt %, and Sn with an amount between 55.0 wt % and
95.0 wt %, a solder alloy containing Ag with an amount of
approximately 3.3 wt %, Bi with. an amount of approximately 5.0 wt
%, and Sn with an amount of approximately 91.7 wt %; a solder alloy
containing Ag with an amount of approximately 3.1 wt %, Bi with an
amount of approximately 10.0 wt %, and Sn with an amount of
approximately 86.9 wt %; a solder alloy containing Ag with an
amount of 3.0 wt %, Bi with an amount of 15.0 wt %, and Sn with an
amount of 82.0 wt %; a solder alloy containing Ag with an amount of
2.8 wt %, Bi with an amount of 20.0 wt %, and Sn with an amount of
77.2 wt %; a solder alloy containing Ag with an amount of 2.4 wt %,
Bi with an amount of 30.0 wt %, and Sn with an amount of 67.6 wt %;
a solder alloy containing Ag with an amount of 2.1 wt %, Bi with an
amount of 40.0 wt %, and Sn with an amount of 57.9 wt %, and the
like.
[0164] FIGS. 5A-5I are diagrams showing the examples of solder
particles forming a solder powder.
[0165] Referring to FIG. 5A, the solder alloy of the examples 1-1
-1-5 shown in FIG. 1 or the solder alloy of the examples 2-1 or 2-2
of FIG. 2, is used to form a generally spherical solder particle
having a diameter of 20-60 .mu.m. FIG. 5B, on the other hand, shows
a solder particle formed of the solder alloy of the example 3-1 or
3-2 of FIG. 3, wherein the solder particle has a generally
spherical form and a diameter of 20-60 .mu.m. Further, FIG. 5C
shows a solder particle formed of the solder alloy of the examples
4-1-4-6 of FIG. 4, wherein the solder particle has a generally
spherical form and a diameter of 20-60 .mu.m.
[0166] FIG. 5D, on the other hand, shows a composite solder
particle, in which a core particle, formed of the solder alloy of
any of the examples 1-1-1-5 of FIG. 1 or 2-1-2-2 of FIG. 2, is
covered by Sn or an alloy of Sn containing Ge with a proportion of
0.1-5.0 wt %, wherein the composite solder particle as a whole has
a generally spherical form and a diameter of 20-60 .mu.m.
[0167] FIG. 5E, on the other hand, shows another composite solder
particle; in which a core particle, formed of the solder alloy of
any of the examples 3-1 and 3-2 of FIG. 3, is covered by a similar
alloy that contains Sn or Ge further with a proportion of 0.1-5.0
wt %, wherein the composite solder particle as a whole has a
generally spherical form and a diameter of 20-60 .mu.m.
[0168] Further, FIG. 5F shows another composite solder particle, in
which a core particle of the solder alloy of any of the examples
4-1-4-6 of FIG. 4, is covered by a similar alloy that contains Sn
or Ge further with a proportion of 0.1-5.0 wt %, wherein the
composite solder particle as a whole has a generally spherical form
and a diameter of 20-60 .mu.m.
[0169] FIG. 5G shows another composite solder particle, in which a
core particle of the solder alloy of any of the examples 1-1-1-5 of
FIG. 1 or the examples 2-1 and 2-2 of FIG. 2 is covered by a
similar alloy containing Sn and Bi with respective proportions
exceeding 20.0 wt % and less than 60.0 wt %, wherein the composite
solder particle as a whole has a generally spherical form and a
diameter of 20-60 .mu.m.
[0170] FIG. 5H shows a still other composite solder particle, in
which a core particle of the solder alloy of any of the examples
3-1 and 3-2 of FIG. 3 is covered by a similar alloy that contains
Sn and Bi with respective proportions exceeding 20.0 wt % and less
than 60.0 wt %, wherein the composite solder particle as a whole
has a generally spherical form and a diameter of 20-60 .mu.m.
[0171] FIG. 5I shows a still other composite solder particle, in
which a core particle of the solder alloy of any of the examples
4-1-4-6 of FIG. 4 is covered by a similar alloy containing Sn and
Bi with respective proportions exceeding 20.0 wt % and less than
60.0 wt %, wherein the composite solder particle as a whole has a
generally spherical form and a diameter of 20-60 .mu.m.
[0172] In any of the embodiments in FIGS. 5A-5I, it is possible to
form a solder paste from the solder powder formed of the solder
particles. Further, in the embodiments of FIGS. 5D-5I, it is
possible to eliminate the problem of oxidation of the solder alloy
by covering the solder alloy by an alloy containing Sn or Ge with a
proportion of 0.1-0.5 wt % or by an alloy containing Sn and Bi with
the proportion of Sn exceeding 20.0 wt % and the proportion of Bi
not exceeding 60.0 wt %.
[0173] Hereinafter, the solder paste that uses the solder powder of
the previous embodiments will be described.
[0174] The inventor of the present invention has prepared various
solder paste compositions, the first series of compositions being a
mixture of a solder powder, an amine halide, a polyhydric alcohol
and a polymer compound, wherein first series composition contains
the solder powder with a proportion of 80.0-95.0 wt %. Thus, the
solder paste composition of the first series contains, as the
remaining component, the amine halide, the polyhydric alcohol and
the polymer compound with a proportion of 20.0-5.0 wt %. The second
series composition is a mixture of a solder powder, an organic
acid, polyhydric alcohol and a polymer compound, wherein the second
series composition contains the solder powder with a proportion of
80.0 wt %-95.0 wt %. Thus, the solder paste composition of the
second series contains, as the remaining component, the organic
acid, the polyhydric alcohol and the polymer compound with a
proportion of 20.0-5.0 wt %.
[0175] As the amine halide for use in the solder paste, one may
select one or more from the group of: acrylic amine hydrochloride,
aniline hydrochloride, diethylamine hydrochloride, cyclohexylamine
hydrochloride, monomethylamine hydrochloride, dimethylamine
hydrochloride, trimethylamine hydrochloride, phenylhydrazine
hydrochloride, n-butylamine hydrochloride, O-methylhydrazine
hydrochloride, ethylamine oxalate, cyclohexyl oxalate,
2-aminoethylbromide oxalate, and tri-n-butylamine oxalate.
[0176] As the organic acid for use in the solder paste, one may
select one or more from the group of: oxalic acid, malonic acid,
succinic acid, glutaric acid, adipic acid, pimelic acid, suberic
acid, azelaic acid, sebacic acid, maleic acid, tartaric acid,
benzoic acid, acetic acid, hydroxyacetic acid, propionic acid,
butyric acid, n-veleric acid, n-caproic acid, enanthic acid,
n-capric acid, lauric acid, myristic acid, palmitic acid, stearic
acid, and the like.
[0177] FIG. 6 shows an example of the solder paste composition that
uses a solder alloy described in one of the examples shown in FIGS.
1 through 3 as a solder powder, while FIG. 7 shows an example of
the solder paste composition that uses a solder alloy described in
one of the examples shown in FIG. 4.
[0178] It should be noted that the amine halides or organic acids
described above act as an activating agent. Further, one may use
abietic acid, dehydroabietic acid, .alpha.-terpineol, and the like,
for the base of the paste. The solder paste may further contain a
polymer compound such as cured castor oil as a thixotropic agent.
Further, a polyhydric alcohol such as 2-methyl 2,4-pentadiol may be
added as a solvent.
[0179] The solder paste composition described above is naturally
free from Pb and can be used for a hazard-free reflowing process
that does not require precautionary measure against toxicity of Pb.
Thereby, the efficiency of production of the electronic apparatuses
is improved.
[0180] FIG. 8 shows an example of application of the lead-free
solder alloy upon a conductor pattern on a printed circuit
board.
[0181] Referring to FIG. 8, a printed circuit board 1 includes a
base member 2 of a glass-epoxy, wherein the base member 2 carries
thereon an electrode 3 of Cu for external connection. On the
electrode 3, a leadfree solder alloy selected from any of the
examples described in FIGS. 1-3 is applied, such that a film 4 of
the solder alloy covers the electrode 3. It was confirmed that such
a construction provides an excellent junction or adherence between
the solder alloy and the electrode 3 of Cu, and the film of the
solder alloy 4 covers the electrode 3 uniformly.
[0182] FIG. 9 shows an example in which the solder alloy is applied
to coat a lead 7 of an electronic component 5 that may be a
semiconductor device having a resin package body 6.
[0183] Referring to FIG. 9, the lead 7 may be formed of any of Cu,
42-alloy (containing Ni 42 wt %, Co 0.5 wt %, Mn 0.8 wt % and
balancing Fe) and Covar, and the lead-free solder alloy of various
compositions selected from the examples in FIGS. 1-3 covers the
lead 7. It was confirmed that such a construction provides an
excellent junction or adherence between the lead 7 and the solder
alloy, and a solder alloy film 8 is formed on the lead 7 with a
uniform thickness.
[0184] As described above, the lead-free solder alloy successfully
coat the conductor patterns on the printed circuit board as well as
the terminals of electronic components, and one can achieve a
reliable electrical as well as mechanical connection between the
electronic components and the printed circuit board.
[0185] FIG. 10 shows an example of using the lead-free solder alloy
of the present invention for the solder bumps that form an external
connection terminal of an electronic apparatus such as a
semiconductor device 9.
[0186] Referring to FIG 10, the semiconductor device 9 includes a
substrate 13 carrying thereon a semiconductor element not
illustrated, wherein the semiconductor element is embedded in a
resin package body 14 provided on the substrate 13. Further, the
substrate 13 carries a plurality of solder bumps 11 on a lower
major surface thereof for external connection. Upon placing the
semiconductor device 9 on a printed circuit board 12, the solder
bumps 11 engage with corresponding conductor patterns provided on
the printed circuit board 12. Thus, there occurs a reflowing of the
solder bumps 11 upon passage of the printed circuit board 12
through a furnace, and a reliable electrical as well as mechanical
connection is achieved thereby according to the flip-chip process,
without using a lead-containing solder alloy.
[0187] Next, the soldering process as well as the soldering rig
developed for the lead-free solder alloy of the present invention
will be described.
[0188] In the foregoing experimental result summarized in FIGS.
1-4, it will be noted that there are examples that show anomalously
large elongation as in the case of the examples 1-5 of FIG. 1, 3-2
of FIG. 3 and 4-1 of FIG. 4. Further, it was rather frequently
observed that the lead-free solder alloys containing Sn and Bi show
a rather remarkable increase of elongation.
[0189] The inventor of the present invention at first attributed
this effect to the effect of the impurities contained in the solder
alloy. Thus, a chemical analysis was conducted upon the solder
alloys that showed anomalous elongation by way of the XRF (X-ray
fluorescent) analysis and by way of the induction plasma
spectroscopy. The result of the chemical analysis, however, clearly
showed that the solder alloy is essentially formed of Sn and Bi and
that there is no substantial contamination of the solder alloy by a
third element.
[0190] Based upon the result of the chemical analysis above, the
inventor of the present invention has set a working hypothesis that
the anomalous elongation occurs as a result of the process of
preparing the test specimen, particularly the cooling rate when
molding the test piece used for the test piece of the specimen.
[0191] Thus, the inventor has conducted a series of experiments to
mold the test pieces with various cooling rates, and test the
pieces thus formed were subjected to tests for various mechanical
properties such as tensile strength, elongation, time-to-fracture,
fracture surface observation as well as tests for various
metallurgical properties such as the surface state and
metallurgical texture. In the experiments, a binary eutectic alloy
having a composition of 42.0 wt % for Sn and 58.0 wt % for Bi was
used throughout.
[0192] When molding the test pieces, three different cooling
processes, i.e., natural cooling process, water cooling process and
gradual cooling process, were employed. In the natural cooling
process, a molten alloy was left in the room temperature
environment together with a mold. Thereby, test pieces 5-1-5-3 were
obtained according to such a natural cooling process. In the water
cooling process, the mold was cooled compulsorily by water after
molding the test piece from the molten solder alloy. Thereby, a
test piece 5-4 was obtained. In the gradual cooling process, the
molten alloy in the mold was gradually cooled by holding the mold
in a thermally insulated environment. Thereby, a test piece 5-5 is
obtained.
[0193] By employing various cooling processes, the cooling rate of
the solder alloy at the time of molding the test piece is changed
variously. Particularly, the molding according to the natural
cooling process is conducted by setting the mold at various initial
temperatures such as 200.degree. C. in the case of the example 5-1,
100.degree. C. in the case of the example 5-2, and 25.degree. C. in
the case of the example 5-3.
[0194] In the results of FIG. 11, it should be noted that the
mechanical properties shown in each of the examples represent the
average of three measurements conducted upon three test pieces.
Thereby, the effect of scattering of individual measurement is
eliminated.
[0195] FIG. 12 shows the results of the measurement conducted upon
the three test pieces for the example 5-1. Further, FIG. 13 shows
the measurement conducted upon the three test pieces for the
example 5-2, FIG. 14 shows the results of the measurement conducted
upon the three test pieces for the example 5-3, FIG. 15 shows the
results of the measurement conducted upon the three test pieces for
the example 5-4, and FIG. 16 shows the results of the measurement
conducted upon the three test pieces for the example 5-5.
[0196] FIG. 17 shows the relationship between the load and
elongation observed for the test piece of the example 5-1, wherein
the relationship of FIG. 17 is for one of the three test pieces
that has shown the result closest to the average. Similarly, FIG.
18 shows the relationship between the load and elongation observed
for the test piece of the example 5-2, wherein the relationship of
FIG. 18 is for one of the three test pieces that has shown the
result closest to the average. FIG. 19 shows the relationship
between the load and elongation observed for the test piece of the
example 5-3, wherein the relationship of FIG. 19 is for one of the
three test pieces that has shown the result closest to the average.
FIG. 20 shows the relationship between the load and elongation
observed for the test piece of the example 5-4, wherein the
relationship of FIG. 20 is for one of the three test pieces that
has shown the result closest to the average. Further, FIG. 21 shows
the relationship between the load and elongation observed for the
test piece of the example 5-5, wherein the relationship of FIG. 21
is for one of the three test pieces that has shown the result
closest to the average.
[0197] FIG. 22 shows a representative state of fracture of the test
piece for the example 5-1. Similarly, FIG. 23 shows a
representative state of fracture of the test piece for the example
5-2. Further, FIG. 24 shows a representative state of fracture of
the test piece for the example 5-3, FIG. 25 shows a representative
state of fracture of the test piece for the example 5-4, and FIG.
26 shows a representative state of fracture of the test piece for
the example 5-5.
[0198] It should be noted that FIG. 11 summarizes the foregoing
experimental results in FIGS. 12-25.
[0199] Hereinafter, the relationship between the cooling condition
and the mechanical property of the solder alloy will be described
with reference to the experimental results shown in FIG. 11.
[0200] First, the effect of cooling process upon the mechanical
property will be examined for the case where the mold temperature
is set to 200.degree. C., based upon the examples 5-1, 5-4 and
5-5.
[0201] Referring to FIG. 11, it is clearly indicated that the
solder alloy provides the smallest elongation of 20.44% when the
gradual cooling process is employed in which the cooling rate is
minimum. With increasing cooling rate, the elongation increases
such that an elongation of 33.67% is obtained as a result of the
natural cooling process. When a water cooling is employed, an
elongation of 89.48% is obtained. The foregoing results indicate
that one obtains an increased elongation with increasing cooling
rate.
[0202] Next, the effect of the mold temperature on the elongation
will be explained based upon the examples 5-1-5-3 in which the
natural cooling is used throughout but with various initial mold
temperatures.
[0203] Referring to FIG. 11, it will be noted that the highest
initial mold temperature of 200.degree. C., which provides the
smallest cooling rate, results in the smallest elongation of
33.67%, while the lower initial mold temperature of 100.degree. C.
provides an increased elongation of 137.50%. When the mold
temperature is set to 25.degree. C., it is possible to achieve an
elongation of 218.33%. This result also supports the conclusion
that the elongation increases with increasing cooling rate.
[0204] Summarizing the experimental results above, the mechanical
properties of a solder alloy can change variously depending upon
the cooling rate, even when the composition of the solder alloy is
fixed. With increasing cooling rate, the elongation of the solder
alloy increases, and the solder alloy shows the evidence of ductile
fracture.
[0205] As will be noted in FIG. 11, the fracture surface of the
test pieces that provide a large elongation, as in the case of the
examples 5-2-5-4, do not exhibit a scale-like pattern that is
typically observed in the fracture surface of an Sn42-Bi58 alloy
cooled slowly. Further, the microscopic observation of the fracture
surface indicates that there is a coarsening of texture in the
examples 5-2-5-4. Thus, it is believed that such a coarsening is
responsible for the increase of the elongation of the alloy.
[0206] As already noted, the remarkable increase of the elongation
occurs not only in the solder alloy containing Sn and Bi, but also
in the alloy of other compositions. Thus, it is believed that such
an increase of the elongation results from the coarsening of
texture of the alloy, caused by the large cooling rate.
[0207] It should be noted that such a solder alloy composition
having a large elongation is particularly useful in flexible
printed circuit boards in which the conductor patterns including
the solder patterns experience deformation.
[0208] Hereinafter, a soldering process as well as a soldering rig
that carries out such a soldering process will be described.
[0209] FIG. 27 shows the soldering process that uses the lead-free
solder alloy of any of the previous embodiments for soldering an
electric or electronic component upon a substrate such as a printed
circuit board. Of course, the substrate is not limited to the
printed circuit board.
[0210] Referring to FIG. 27, a step 10 is conducted at first in
which a flux is applied to the part of the printed circuit board on
which the soldering is to be made. The flux is applied for
improving the wetting by the solder alloy, wherein a suitable flux
is selected in view of the composition of the lead-free solder
alloy to be used.
[0211] Next, in the step 12, a preheating is conducted upon the
printed circuit board for eliminating inhomogeneity of soldering
caused by localized cooling and associated solidifying of the
molten solder alloy.
[0212] Further, a step 14 is conducted subsequently, wherein the
pre-heated printed circuit board is dipped in a bath of molten
solder alloy of any of the foregoing compositions, and the molten
alloy covers the exposed conductor pattern as well as the lead or
electrode of the electric or electronic components. Thereby, the
soldering is achieved. The steps 10-14 are substantially the same
as the conventional soldering process that uses a lead-containing
solder alloy.
[0213] Next, in the following step 16, the printed circuit board is
pulled up from the solder bath and cooled by suitable external
cooling means, such that the solder alloy experiences a rapid
cooling or quenching. As a result of such a rapid cooling, the
solder alloy shows an improved elongation as explained already. As
the external cooling means, one may employ a jet of cooling medium
such as a coolant gas or volatile organic solvent. Such a jet of
cooling medium can be applied selectively to the part where the
soldering has just been made.
[0214] FIG. 28 shows the construction of a soldering rig 20
according to an embodiment of the present invention for conducting
the soldering process of FIG. 27. It should be noted that the
soldering rig 20 is designed primarily to carry out a soldering of
a sheet-like or plate-like object such as a printed circuit board.
However, the soldering rig is by no means limited to such a
soldering of printed circuit boards but is applicable to~various
soldering processes.
[0215] Referring to FIG. 27, it will be noted that the soldering
rig 20 includes a flux coating unit 21, a pre-heating unit 22, a
soldering unit 23, a transport conveyer 24 and a cooling unit 25
that characterizes the rig 20 of the present invention, each of
which will be explained below.
[0216] The transport conveyer 24 carries a printed circuit board 26
placed thereon and transports the same in a direction indicated by
an arrow. Further, the flux coating unit 21, the pre-heating unit
22, the soldering unit 23 and the cooling unit 25 are disposed
consecutively along the transport conveyer 24 in the transport
direction of the conveyer 24.
[0217] Thus, the flux coating unit 21 applies a flux upon the
printed circuit board 26 and the preheating unit 22 preheats the
printed circuit board 26 thus applied with the flux. Further, the
soldering unit 23 carries out the soldering by means of the
lead-free solder alloy described previously.
[0218] After the soldering, the printed circuit board 26 is
forwarded to the cooling unit 25 by the transport conveyer 24.
Thereby, the cooling unit 25 rapidly cools the high temperature
solder alloy applied by-the soldering unit 23. As a result of such
a rapid cooling, it is possible to increase the elongation of the
solidified solder alloy as explained already.
[0219] FIGS. 29-31 show the construction of the cooling unit
25.
[0220] Referring to FIG. 29 showing an example 25A of the cooling
unit 25 that uses liquid nitrogen as a cooling medium, the cooling
unit 25A includes a tank 27 for containing liquid nitrogen wherein
the liquid nitrogen in the tank 27 is supplied to an evaporator 28
that evaporates the liquid nitrogen and forms a low temperature
nitrogen gas. The low temperature nitrogen gas thus formed, in
turn, is supplied along a pipe 29 to which one or more gas nozzles
30 are connected. Thereby, the low temperature nitrogen is injected
upon the location of soldering on the printed circuit board for
cooling the high temperature solder alloy.
[0221] FIG. 30 shows another example 25B of the cooling unit 25,
wherein the cooling unit 25B uses a volatile freon gas as a cooling
medium.
[0222] Referring to FIG. 30, the cooling unit 25B includes a tank
31 of freon to which a supply pipe 33 of freon is connected.
Further, one or more nozzles 32 are connected to the pipe 33 for
injecting the freon upon the printed circuit board 26 on the
conveyer 24 at the location where the soldering has just been made.
Thereby, the high temperature solder alloy experiences a rapid
cooling upon the evaporation of freon.
[0223] FIG. 31 shows another example 25C of the cooling unit 25
that is designed to cool a cylindrical or tubular object after
soldering. As the cooling unit 25C of FIG. 31 employs the
construction of FIG. 29, those parts corresponding to the parts
shown in FIGS. 29 are designated by the same reference numerals and
the description thereof will be omitted.
[0224] Referring to FIG. 31, the cooling unit 25C includes an
annular nozzle element 35 in which a plurality of nozzles 36 are
provided. The nozzle element 35 is disposed in a tube 37 adapted
for passing a cylindrical object 34 that has experienced soldering,
for example by means of a soldering iron 38 that uses a lead-free
solder alloy 39 of the Sn--Bi eutectic system. Thereby, the object
34 is cooled upon passage through an inner space of the annular
nozzle element 35. As the nozzles 36 are disposed with a generally
uniform interval on the nozzle element 35, the seam of the
cylindrical object 34 where the soldering has been made,
experiences a uniform cooling by the low temperature nitrogen gas
injected from the nozzles 36.
[0225] Further, the present invention is by no means limited to the
embodiments described heretofore, but various variations and
modifications may be made without departing from the scope of the
invention.
* * * * *