U.S. patent application number 12/081195 was filed with the patent office on 2008-11-27 for quaternary pb-free solder composition incorporating sn-ag-cu-in.
This patent application is currently assigned to KOREA INSTITUTE OF INDUSTRIAL TECHNOLOGY. Invention is credited to Jeong-Han Kim, Chang-Woo Lee, Jong-Hyun Lee.
Application Number | 20080292493 12/081195 |
Document ID | / |
Family ID | 39218967 |
Filed Date | 2008-11-27 |
United States Patent
Application |
20080292493 |
Kind Code |
A1 |
Lee; Jong-Hyun ; et
al. |
November 27, 2008 |
Quaternary Pb-free solder composition incorporating Sn-Ag-Cu-In
Abstract
Provided is a quaternary Pb-free solder composition
incorporating Sn--Ag--Cu--In, which can prevent a cost increase and
sufficiently ensure proccessability and mechanical property as a
solder material. To this end, indium (In) with appropriate amount
is added into the Pb-free solder composition, and the addition
amount of Ag is optimized, thus preventing a decrease in
wettability caused by a decrease in the amount of Ag and improving
resistance to a thermal cycling and a mechanical impact. The
quaternary Pb-free solder composition includes silver (Ag) of about
0.3 wt. % or more, and less than about 2.5 wt. %, copper (Cu) of
about 0.2 wt. % or more, and less than about 2.0 wt. %, indium (In)
of about 0.2 wt. % or more, and less than about 1.0 wt. % or less,
and a balance of tin (Sn).
Inventors: |
Lee; Jong-Hyun; (Incheon,
KR) ; Lee; Chang-Woo; (Gyeonggi-do, KR) ; Kim;
Jeong-Han; (Seoul, KR) |
Correspondence
Address: |
VENABLE LLP
P.O. BOX 34385
WASHINGTON
DC
20043-9998
US
|
Assignee: |
KOREA INSTITUTE OF INDUSTRIAL
TECHNOLOGY
Chungcheongnam-do
KR
|
Family ID: |
39218967 |
Appl. No.: |
12/081195 |
Filed: |
April 11, 2008 |
Current U.S.
Class: |
420/561 ;
420/560 |
Current CPC
Class: |
B23K 35/262 20130101;
C22C 13/02 20130101; C22C 13/00 20130101 |
Class at
Publication: |
420/561 ;
420/560 |
International
Class: |
C22C 13/02 20060101
C22C013/02; C22C 13/00 20060101 C22C013/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 25, 2007 |
KR |
10-2007-0050905 |
Claims
1. A quaternary lead (Pb)-free solder composition incorporating
tin-silver-copper-indium, comprising: silver (Ag) of about 0.3 wt.
% or more, and less than about 2.5 wt. %; copper (Cu) of about 0.2
wt. % or more, and less than about 2.0 wt. %; indium (In) of about
0.2 wt. % or more, and less than about 1.0 wt. %; and a balance of
tin (Sn).
2. The composition as recited in claim 1, wherein one or more
elements selected from phosphor (P), germanium (Ge), gallium (Ga),
aluminum (Al) and silicon (Si) are added into the quaternary
Pb-free solder composition in a weight percent range of about 0.001
wt. % to about 1 wt. % to improve anti-oxidation properties of the
Pb-free solder composition.
3. The composition as recited in claim 1, wherein one or more
elements selected from zinc (Zn) and bismuth (Bi) are added into
the quaternary Pb-free solder composition in a weight percent range
of about 0.001 wt. % to about 2 wt. % to improve interfacial
reaction properties and drop a melting point of the Pb-free solder
composition.
4. The composition as recited in claim 1, wherein one or more
elements, which are selected from nickel (Ni), cobalt (Co), gold
(Au), platinum (Pt), lead (Pb), manganese (Mn), vanadium (V),
titanium (Ti), chromium (Cr), niobium (Nb), palladium (Pd),
antimony (Sb), magnesium (Mg), tantalum (Ta), cadmium (Cd) and rare
earth metals, are added into the quaternary Pb-free solder
composition in a weight percent range of about 0.001 wt. % to about
1 wt. %.
Description
CROSS-REFERENCE(S) TO RELATED APPLICATIONS
[0001] The present invention claims priority of Korean patent
application number 10-2007-0050905, filed on May 25, 2007, which is
incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a lead (Pb)-free solder
composition, and more particularly, to a quaternary Pb-free solder
composition incorporating tin-silver-copper-indium
(Sn--Ag--Cu--In), which can reduce the amount of silver by using
indium.
[0003] A Sn--Ag--Cu-based composition is most popularly used as a
Pb-free solder composition at present, and its representative
composition may be expressed as Sn-3.0Ag-0.5Cu. To improve
anti-oxidation properties of such a Pb-free solder composition,
phosphor (P), germanium (Ge), gallium (Ga), aluminum (Al), silicon
(Si), or the like may be added at a concentration of several tens
to several thousands of ppm. Furthermore, to enhance mechanical
properties and interfacial reaction properties, nickel (Ni), cobalt
(Co), iron (Fe), bismuth (Bi), gold (Au), platinum (Pt), lead (Pb),
manganese (Mn), vanadium (V), titanium (Ti), chromium (Cr), niobium
(Nb), palladium (Pd), antimony (Sb), magnesium (Mg), tantalum (Ta),
cadmium (Cd), rare earth metal, or the like, of which each
concentration is in the range of several tens to several thousands
of ppm, may be added into the Pb-free composition.
[0004] However, as there are ongoing demands and efforts to reduce
fabrication cost in packaging electronic devices, several attempts
are being made to reduce the amount of silver (Ag) because Ag is
the most expensive among additive elements. For example, a
Sn-2.5Ag-0.5Cu or Sn-1.0Ag-0.5Cu composition is applied to the
Pb-free solder. Further, a Sn-0.3Ag-0.5Cu composition has been
recently suggested and its properties are being analyzed whether it
is suitable for the Pb-free solder.
[0005] Variations in metallurgical and mechanical properties of a
Sn--Ag--Cu based solder according to the amount of Ag are
summarized as followings.
[0006] 1) As the addition amount of Ag decreases, a difference
between a liquidus temperature and a solidus temperature increases,
resulting in an increase of a pasty range or mush zone.
[0007] 2) As the addition amount of Ag decreases, wettability
decreases due to the increase of the pasty range or mush zone.
[0008] 3) As the addition amount of Ag decreases, the strength and
creep resistance of the alloy decrease.
[0009] 4) As the amount of Ag decreases, the fracture speed of a
solder joint according to a thermal cycling test increases because
the strength and creep resistance of the alloy decrease.
[0010] 5) As the amount of Ag decreases, the elongation of an alloy
increases, and the fracture speed of the solder joint according to
a mechanical impact test decreases.
[0011] Herein, the case 1) represents a variation in metallurgical
properties depending on the amount of Ag in the solder. Even in the
case of reducing the amount of Ag, therefore, the appropriate
addition amount of Ag should be determined. Moreover, although the
amount of Ag is reduced, the solder composition should have
wettability similar to that of the typical Sn-3.0Ag-0.5Cu
composition in order for this composition to be used as a solder
material with low fabrication cost.
[0012] The cases 4) and 5) represent opposite characteristics
according as the amount of Ag decreases in the Pb-free solder.
Hence, the appropriate addition amount of Ag should be determined
in consideration of these opposite characteristics. In addition to
the appropriate amount of Ag, mechanical properties of the Pb-free
solder composition should also be improved for example, by adding
alloy metals, which allows the solder composition to have
resistance to both a thermal cycling and a mechanical impact.
Accordingly, an ideal solder composition with high reliability can
be achieved and further fabrication cost can be reduced through a
decrease in the addition amount of Ag.
[0013] However, such a Pb-free solder composition satisfying the
above conditions has not been developed yet.
SUMMARY OF THE INVENTION
[0014] Embodiments of the present invention are directed to
providing a quaternary lead (Pb)-free solder composition
incorporating tin-silver-copper-indium (Sn--Ag--Cu--In), which can
prevent a cost increase and sufficiently ensure proccessability and
mechanical property as a solder material. To this end, indium (In)
with appropriate amount is added into the Pb-free solder
composition, and the addition amount of Ag is optimized, thus
preventing a decrease in wettability caused by a decrease in the
amount of Ag and improving resistance to a thermal cycling and a
mechanical impact.
[0015] In accordance with an aspect of the present invention, there
is provided a quaternary Pb-free solder composition incorporating
tin-silver-copper-indium, including: silver (Ag) of about 0.3 wt. %
or more, and less than about 2.5 wt. %; copper (Cu) of about 0.2
wt. % or more, and less than about 2.0 wt. %; indium (In) of about
0.2 wt. % or more, and less than about 1.0 wt. %; and a balance of
tin (Sn).
[0016] In the Pb-free solder composition of the present invention,
the amount of Ag is reduced to save fabrication cost. Therefore, to
improve reliability on a thermal cycling and a mechanical impact
and also prevent a decrease in wettability caused by the decrease
in the addition amount of Ag, indium (In) is added into the Pb-free
solder composition. Accordingly, it is possible to provide a
high-quality Pb-free solder composition with low price.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a graph illustrating an endothermic peak of a
conventional solder composition in a heating state.
[0018] FIG. 2 is a graph illustrating an endothermic peak of a
solder composition of the present invention in a heating state.
[0019] FIG. 3 is a graph illustrating an exothermic peak of a
conventional solder composition in a cooling state after being
melted.
[0020] FIG. 4 is a graph illustrating an exothermic peak of a
solder composition of the present invention in a cooling state
after being melted.
[0021] FIG. 5 is a graph illustrating a zero cross time value
versus a soldering temperature in a conventional solder
composition.
[0022] FIG. 6 is a graph illustrating a zero cross time value
versus a soldering temperature in a solder composition of the
present invention.
[0023] FIG. 7 is a graph illustrating a wetting force at 2 seconds
versus a soldering temperature in a conventional solder
composition.
[0024] FIG. 8 is a graph illustrating a wetting force at 2 seconds
versus a soldering temperature in a solder composition of the
present invention.
[0025] FIG. 9 is a graph illustrating a final wetting force versus
a soldering temperature in a conventional solder composition.
[0026] FIG. 10 is a graph illustrating a final wetting force versus
a soldering temperature in a solder composition of the present
invention.
[0027] FIG. 11 is a graph illustrating test results obtained from
tensile specimens having conventional solder compositions of
Sn-3.0Ag-0.5Cu, Sn-1.0Ag-0.5Cu and Sn-1.2Ag-0.5Cu-0.05Ni.
[0028] FIG. 12 is a graph illustrating test results obtained from
tensile specimens having solder compositions of
Sn-1.2Ag-0.5Cu-0.4In, Sn-1.2Ag-0.5Cu-0.2In, Sn-1.2Ag-0.5Cu-0.6In,
Sn-1.2Ag-0.5Cu-0.8In and Sn-1.0Ag-0.5Cu-1.0In in accordance with
the present invention.
[0029] FIG. 13 is a graph illustrating a zero cross time value
versus a soldering temperature, which compares the
Sn-0.3Ag-0.7Cu-0.2In composition of the present invention with the
conventional compositions of Sn-3.0Ag-0.5Cu, Sn-1.0Ag-0.5Cu and
Sn-0.3Ag-0.7Cu.
[0030] FIG. 14 is a graph illustrating a wetting force at 2 seconds
versus a soldering temperature, which compares the
Sn-0.3Ag-0.7Cu-0.2In composition of the present invention with the
conventional compositions of Sn-3.0Ag-0.5Cu, Sn-1.0Ag-0.5Cu and
Sn-0.3Ag-0.7Cu.
[0031] FIG. 15 is a graph illustrating a final wetting force versus
a soldering temperature, which compares the Sn-0.3Ag-0.7Cu-0.2In
composition of the present invention with the conventional
compositions of Sn-3.0Ag-0.5Cu, Sn-1.0Ag-0.5Cu and
Sn-0.3Ag-0.7Cu.
DESCRIPTION OF SPECIFIC EMBODIMENTS
[0032] Hereinafter, a quaternary lead (Pb)-free composition
incorporating tin-silver-copper-indium (Sn--Ag--Cu--In) in
accordance with the present invention will be described in detail
with reference to the accompanying drawings. Herebelow, specific
descriptions for a related well-known function or construction will
be omitted when it is deemed that they make the gist of the present
invention vague unnecessarily.
[0033] In a Pb-free solder composition of the present invention,
the weight percent of Ag is less than about 2.5 wt. % but not less
than about 0.3 wt. %. If the weight percent of Ag is less than 0.3
wt. %, a liquidus temperature hardly drops, leading to an increase
in a melting point of a solder and a packaging process temperature.
On the contrary, if the weight percent of Ag is 2.5 wt. % or more,
the fabrication cost increases unfavorably. Consequently, the
weight percent of Ag should be less than about 2.5 wt. % but not
less than about 0.3 wt. %, preferably about 1.2 wt. %.
[0034] The Pb-free solder composition of the present invention
includes Cu of which weight percent is less than about 2.0 wt. %
but not less than about 0.2 wt. %. If the weight percent of Cu is
less than 0.2 wt. %, the liquidus temperature drops little and a
fraction of Cu.sub.6Sn.sub.5 phase is extremely small, which
reduces the strength of a solder alloy excessively. In contrast, if
the weight percent of Cu is 2.0 wt. % or more, a difference between
the liquidus temperature and solidus temperature increases and thus
a pasty range or mush zone increases. This leads to an increase in
a fraction of Cu.sub.6Sn.sub.5 phase, thus intensifying the
mechanical properties of the solder alloy in excess and increasing
a growth rate of an interfacial reaction layer. Consequently, the
weight percent of Cu should be less than about 2.0 wt. % but not
less than about 0.2 wt. %, preferably about 0.5 wt. %.
[0035] The Pb-free solder composition of the present invention
further includes In of which weight percent is less than about 1.0
wt. % but not less than about 0.2 wt. %. If the weight percent of
In is less than 0.2 wt. %, wettability and mechanical properties
are not enhanced substantially. If the weight percent of In is 1.0
wt. % or more, wettability and mechanical properties are not
enhanced in proportion to the addition amount of In, but a price of
the solder alloy increases drastically. Therefore, the weight
percent of In should be less than about 1.0 wt. % but not be less
than about 0.2 wt. %, preferably about 0.4 wt. %.
[0036] In accordance with a desirable ratio of each additive
element, most preferable Pb-free solder composition is
Sn-1.2Ag-0.5Cu-0.4In. The most preferable composition of
Sn-1.2Ag-0.5Cu-0.4In, other research compositions and conventional
compositions of Sn-3.0Ag-0.5Cu, Sn-1.0Ag-0.5Cu and
Sn-1.2Ag-0.5Cu-0.05Ni are respectively tested under the same
conditions and then evaluated, of which results are shown in FIGS.
1 to 11.
[0037] FIGS. 1 and 2 are graphs illustrating endothermic peaks of
solder compositions in a heating state. Specifically, FIGS. 1 and 2
show endothermic peaks observed by the use of a differential
scanning calorimeter (DSC) when a solder composition (about 8 mg)
is heated up at a heating rate of 10.degree. C./min and at a
nitrogen flow rate of 50 ml/min. As shown in FIG. 1, the
Sn-3.0Ag-0.5Cu composition has an endothermic peak at about
217.degree. C. to about 218.degree. C., which is substantially
equal to a melting point of this alloy. On the contrary, the
Sn-1.0Ag-0.5Cu composition has a first endothermic peak at about
218.degree. C. to about 219.degree. C. and a second endothermic
peak at about 226.degree. C., which are respectively observed as a
liquidus temperature and a solidus temperature. Therefore, it can
be observed that a pasty range or mush zone significantly
increases. The Sn-1.2Ag-0.5Cu-0.05Ni composition has a first
endothermic peak at about 219.degree. C. to about 220.degree. C.
and a second endothermic peak at about 225.degree. C. to about
226.degree. C., which are respectively observed as a liquidus
temperature and a solidus temperature. Therefore, it can be
observed that a pasty range or a mush zone also significantly
increases.
[0038] As shown in FIG. 2, the Sn-1.0Ag-0.5Cu-1.0In composition has
a first endothermic peak at about 216.degree. C. and a second
endothermic peak at about 224.degree. C. to about 225.degree. C.,
which are respectively observed as a liquidus temperature and a
solidus temperature. In this case, it can be observed that a pasty
range or mush zone also increases considerably but the liquidus
temperature and the solidus temperature are relatively lowered in
totality. Such a transition of the liquidus and solidus lines to a
low temperature provides an excellent effect in solder wettability
at a low temperature. The Sn-1.0Ag-0.5Cu-0.5In composition has a
first endothermic peak at about 217.degree. C. and a second
endothermic peak at about 225.degree. C., which are respectively
observed as a liquidus temperature and a solidus temperature. In
this case, it can be observed that a pasty range or a mush zone
also increases considerably but the liquidus temperature and the
solidus temperature are relatively lowered in totality.
[0039] The Sn-1.2Ag-0.5Cu-0.8.about.0.4In composition has a first
endothermic peak at about 217.degree. C. to about 218.degree. C.
and a second endothermic peak at about 224.degree. C. to about
225.degree. C., which are respectively observed as a liquidus
temperature and a solidus temperature. In this case, it can be
observed that a pasty range or a mush zone also increases
considerably but the liquidus temperature and the solidus
temperature are relatively lowered in totality. The
Sn-1.2Ag-0.5Cu-0.2In composition has a first endothermic peak at
about 219.degree. C. to about 220.degree. C. and a second
endothermic peak at about 226.degree. C., which are respectively
observed as a liquidus temperature and a solidus temperature. In
this case, it can be observed that a pasty range or a mush zone
also increases considerably but the liquidus temperature and the
solidus temperature are not lowered in comparison with the
Sn-1.0Ag-0.5Cu composition. From this result, it can be appreciated
that the solder wettability of the Sn-1.2Ag-0.5Cu-0.2In composition
in a low temperature range is not much improved compared to that of
the Sn-1.0Ag-0.5Cu composition.
[0040] FIGS. 3 and 4 are graphs illustrating first exothermic peaks
of solder compositions in a cooling state after being melted.
Specifically, FIGS. 3 and 4 show exothermic peaks observed through
a DSC when a solder composition (about 8 mg) is cooled down after
it is heated up to 250.degree. C. at a heating rate of 10.degree.
C./min and at a nitrogen flow rate of 50 ml/min. As shown in FIG.
3, the Sn-3.0Ag-0.5Cu composition has a first exothermic peak at
about 194.degree. C., which means an actual solidification
temperature of this alloy. Metallurgically, a difference between a
melting temperature and an actual solidification temperature of an
alloy, that is, a temperature difference of about 23.degree. C. to
24.degree. C. in this case, is called `undercooling` or
`supercooling`. The degree of undercooling increases according to
the amount of Ag in the alloy. For instance, the Sn-1.0Ag-0.5Cu
composition has a first exothermic peak at about 188.degree. C.,
which proves that the degree of undercooling is increased. In
contrast, the Sn-1.2Ag-0.5Cu-0.05Ni composition has a first
exothermic peak at about 206.degree. C. to about 207.degree. C.
From this result, it can be appreciated that small addition amount
of Ni reduces the degree of undercooling drastically.
[0041] The results obtained by adding In into compositions are
shown in FIG. 4. From FIG. 4, it can be observed that the
Sn-1.0Ag-0.5Cu-1.0In composition has a first exothermic peak at
about 200.degree. C. and the Sn-1.0Ag-0.5Cu-0.5In composition has a
first exothermic peak at about 190.degree. C. to about 191.degree.
C. Therefore, the addition of In also reduces the degree of
undercooling greatly. Further, it can be observed that the
Sn-1.2Ag-0.5Cu-0.8In composition has a first exothermic peak at
about 192.degree. C. to about 193.degree. C., the
Sn-1.2Ag-0.5Cu-0.6In composition has a first exothermic peak at
about 197.degree. C. to about 198.degree. C., the
Sn-1.2Ag-0.5Cu-0.4In composition has a first exothermic peak at
about 200.degree. C. to about 201.degree. C., and the
Sn-1.2Ag-0.5Cu-0.2In composition has a first exothermic peak at
about 202.degree. C. to about 203.degree. C.
[0042] FIGS. 5 and 6 are graphs illustrating a zero cross time
value versus a soldering temperature. In one-time wettability test,
a zero cross time value, a wetting force at 2 seconds and a final
wetting force are measured at once, and following results are mean
values obtained from test results of 10 or more times. A specimen
used in the wettability test was a Cu piece having 3 mm in width
and 10 mm in length. A water-soluble type flux of SENJU Company was
coated on a surface of the Cu piece and it was then charged into a
melted solder, wherein a charging depth was 2 mm. Each of a
charging speed and a separating speed of the Cu piece was 5 mm/sec.
As shown in FIG. 5, the Sn-1.2Ag-0.5Cu-0.05Ni composition and the
Sn-1.0Ag-0.5Cu composition are much greater in zero cross time
value than the Sn-3.0Ag-0.5Cu composition. In particular, it can be
observed that the zero cross time value is more increased in a low
temperature range of about 230-240.degree. C. On the contrary, if
In is added into the composition as illustrated in FIG. 6, it can
be observed that the zero cross time value is significantly reduced
and the zero cross time value is more effectively reduced in a low
temperature range of 230-240.degree. C. Especially, the
representative composition of the present invention, i.e., the
Sn-1.2Ag-0.5Cu-0.4In composition, has the zero cross time value
similar to or better than that of the Sn-3.0Ag-0.5Cu composition.
Therefore, it can be confirmed that the Sn-1.2Ag-0.5Cu-0.4In
composition of the present invention has very excellent wettability
as a solder material.
[0043] FIGS. 7 and 8 are graphs illustrating a wetting force at 2
seconds versus a soldering temperature. As shown in FIG. 7, the
Sn-1.0Ag-0.5Cu composition and the Sn-1.2Ag-0.5Cu-0.05Ni
composition have wetting forces at 2 seconds, which are lower than
that of the Sn-3.0Ag-0.5Cu composition. Particularly, the wetting
forces at 2 seconds of the Sn-1.0Ag-0.5Cu composition and the
Sn-1.2Ag-0.5Cu-0.05Ni composition are significantly decreased in a
low temperature range of 230-240.degree. C. In contrast, if In is
added into compositions as shown in FIG. 8, the wetting force at 2
seconds is remarkably increased, and the wetting force at 2 seconds
in a low temperature of 230-240.degree. C. is more effectively
increased. In especial, it can be confirmed that the representative
composition of the present invention, i.e., the
Sn-1.2Ag-0.5Cu-0.4In composition, has the wetting force at 2
seconds which is similar to or better than that of the
Sn-3.0Ag-0.5Cu composition.
[0044] From the results above, the composition of the present
invention has excellent wettability in spite of very low price, and
thus it is very suitable for a soldering material. Accordingly, the
Pb-free solder composition of the present invention is used in
fabricating a solder paste, a solder ball, a solder bar, a solder
wire, a solder bump, a solder foil, a solder powder, and a solder
perform. Herein, the solder perform may include a solder pellet, a
solder granule, a solder ribbon, a solder washer, a solder ring and
a solder disk.
[0045] FIGS. 9 and 10 are graphs illustrating a final wetting force
versus a soldering temperature. As shown in FIG. 9, the
Sn-1.0Ag-0.5Cu composition and the Sn-1.2Ag-0.5Cu-0.05Ni
composition have final wetting forces which are lower than that of
the Sn-3.0Ag-0.5Cu composition. Particularly, the final wetting
force is significantly decreased in a low temperature range of
230-240.degree. C. In contrast, the addition of In brings
interesting results as shown in FIG. 10. That is, when the addition
amount of In is high, e.g., 0.8 wt. %, in the Sn-1.2Ag-0.5Cu-xIn
composition, the final wetting force is enhanced little due to a
low surface tension of melted indium; and when the addition amount
of In is low, e.g., 0.2 wt. %, wettability is improved little so
that the final wetting force is not improved. In contrast, it can
be confirmed that the representative composition of the present
invention, i.e., Sn-1.2Ag-0.5Cu-0.4In composition has a final
wetting force that is similar to or somewhat worse than that of the
Sn-3.0Ag-0.5Cu composition. Particularly, it can be observed that
the Sn-1.2Ag-0.5Cu-0.4In composition has a more excellent final
wetting force in a low temperature range of 230-240.degree. C. than
other compositions with small amount of Ag.
[0046] FIG. 11 is a graph illustrating test results obtained from
tensile specimens having conventional solder compositions of
Sn-3.0Ag-0.5Cu, Sn-1.0Ag-0.5Cu and Sn-1.2Ag-0.5Cu-0.05Ni. The
tensile specimen was prepared as a proportional specimen based on
the Korean Standard (KS) 13A, of which a thickness was 2 mm and a
length is 27 mm. A tensile test is performed in a room temperature
at a tensile test speed of 7.8 mm/min. As shown in FIG. 11, the
Sn-3.0Ag-0.5Cu composition has a high strength but a low
elongation. From this, when the Sn-3.0Ag-0.5Cu composition is used
as a solder joint material, it is expected that the composition is
excellent in resistance to a thermal cycling but poor in resistance
to a mechanical impact. On the contrary, the elongation of the
Sn-1.0Ag-0.5Cu composition is increased slightly but its strength
is too small. Therefore, the Sn-1.0Ag-0.5Cu composition is expected
to be better in resistance to a mechanical impact but poorer in
resistance to a thermal cycling than the Sn-3.0Ag-0.5Cu
composition. The Sn-1.2Ag-0.5Cu-0.05Ni composition exhibits medium
characteristics between the Sn-3.0Ag-0.5Cu composition and the
Sn-1.0Ag-0.5Cu composition.
[0047] FIG. 12 is a graph illustrating test results obtained from
tensile specimens having solder compositions of
Sn-1.2Ag-0.5Cu-0.4In, Sn-1.2Ag-0.5Cu-0.2In, Sn-1.2Ag-0.5Cu-0.6In,
Sn-1.2Ag-0.5Cu-0.8In and Sn-1.0Ag-0.5Cu-1.0In in accordance with
the present invention. From FIG. 12, it can be observed that the
Sn-1.2Ag-0.5Cu-0.4In composition has a greater strength and a
higher elongation than a similar composition, e.g., Sn-1.0Ag-0.5Cu
composition. That is, the toughness of the Sn-1.2Ag-0.5Cu-0.4In
composition is improved in comparison with the Sn-1.0Ag-0.5Cu
composition. From this result, it is expected that the
Sn-1.2Ag-0.5Cu-0.4In composition has the most excellent resistance
to a mechanical impact and also has good resistance to a thermal
cycling. Therefore, the Sn-1.2Ag-0.5Cu-0.4In composition is
suitably used as a bonding material for electronics inside
automobiles and mobile products which are subject to a mechanical
shock or vibration. In the Sn-1.2Ag-0.5Cu-0.2In composition, the
intensification of a metal due to the addition of In decreases so
that its strength is lowered. In the Sn-1.2Ag-0.5Cu-0.6In
composition and the Sn-1.2Ag-0.5Cu-0.8In composition, the
elongation gradually decreases as the addition amount of In
increases. The Sn-1.0Ag-0.5Cu-1.0In composition, however, does not
exhibit good strength in spite of great addition amount of In.
[0048] Another quaternary Pb-free solder composition of the present
invention, i.e., Sn-0.3Ag-0.7Cu-0.2In composition, is compared with
the conventional Sn-3.0Ag-0.5Cu composition, Sn-1.0Ag-0.5Cu
composition and Sn-0.3Ag-0.7Cu composition through the same
experimental procedure as described above. Results of wetting
properties are illustrated in FIGS. 13 to 15.
[0049] FIG. 13 is a graph illustrating a zero cross time value
versus a soldering temperature, FIG. 14 is a graph illustrating a
wetting force at 2 seconds versus a soldering temperature, and FIG.
15 is a graph illustrating a final wetting force versus a soldering
temperature. As shown in FIGS. 13 to 15, the Sn-0.3Ag-0.7Cu-0.2In
composition with small amount of In is excellent in the
above-described wetting properties at a temperature above
240.degree. C., compared to the Sn-0.3Ag-0.7Cu composition. That
is, the Sn-0.3Ag-0.7Cu-0.2In composition exhibits similar wetting
properties to those of the Sn-1.0Ag-0.5Cu composition. From this
result, it can be also confirmed that the Pb-free solder
composition with an appropriate amount of indium in accordance with
the present invention can minimize cost increase and prevent a
decrease in wettability caused by a reduction in Ag content.
[0050] To improve anti-oxidation properties of the quaternary
Pb-free solder composition incorporating Sn--Ag--Cu--In, one or
more elements selected from phosphor (P), germanium (Ge), gallium
(Ga), aluminum (Al) and silicon (Si) may be added into the
quaternary Pb-free solder composition in a weight percent range of
about 0.001 wt. % to about 1 wt. %.
[0051] In addition, one or more elements selected from zinc (Zn)
and bismuth (Bi) may be added into the quaternary Pb-free solder
composition in a weight percent range of about 0.001 wt. % to about
2 wt. % to improve interfacial reaction properties and drop a
melting point of the quaternary Pb-free solder composition
incorporating Sn--Ag--Cu--In.
[0052] Further, to improve mechanical properties and interfacial
reaction properties of the quaternary Pb-free solder composition
incorporating Sn--Ag--Cu--In, one or more elements, which are
selected from nickel (Ni), cobalt (Co), gold (Au), platinum (Pt),
lead (Pb), manganese (Mn), vanadium (V), titanium (Ti), chromium
(Cr), niobium (Nb), palladium (Pd), antimony (Sb), magnesium (Mg),
tantalum (Ta), cadmium (Cd) and rare earth metals, may be added
into the quaternary Pb-free solder composition in a weight percent
range of about 0.001 wt. % to about 1 wt. %.
[0053] The reason that additional remarks as above are made is to
clarify that the quaternary Pb-free solder composition
incorporating Sn--Ag--Cu--In with other element(s) added, which are
intended to avoid the patent of the quaternary Pb-free solder
composition in accordance with the present invention, also falls
within the technical idea of the present invention
[0054] As described above, in accordance with the present
invention, by reducing the amount of Ag but adding In, it is
possible to complement the wettability due to a decrease in amount
of Ag and improve resistance to both a thermal cycling and a
mechanical impact. Therefore, it is possible to provide a
high-quality Pb-free solder composition with low price.
[0055] While the present invention has been described with respect
to the specific embodiments, it will be apparent to those skilled
in the art that various changes and modifications may be made
without departing from the spirit and scope of the invention as
defined in the following claims.
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