U.S. patent application number 11/422782 was filed with the patent office on 2007-03-29 for low melting temperature compliant solders.
This patent application is currently assigned to Indium Corporation of America. Invention is credited to Benlih Huang, Hong-Sik Hwang, Ning-Cheng Lee.
Application Number | 20070071634 11/422782 |
Document ID | / |
Family ID | 37894223 |
Filed Date | 2007-03-29 |
United States Patent
Application |
20070071634 |
Kind Code |
A1 |
Huang; Benlih ; et
al. |
March 29, 2007 |
LOW MELTING TEMPERATURE COMPLIANT SOLDERS
Abstract
Low melting temperature compliant solders are disclosed. In one
particular exemplary embodiment, a low melting temperature
compliant solder alloy comprises from about 91.5% to about 97.998%
by weight tin, from about 0.001% to about 3.5% by weight silver,
from about 0.0% to about 1.0% by weight copper, and from about
2.001% to about 4.0% by weight indium.
Inventors: |
Huang; Benlih; (New
Hartford, NY) ; Hwang; Hong-Sik; (Clinton, NY)
; Lee; Ning-Cheng; (New Hartford, NY) |
Correspondence
Address: |
HUNTON & WILLIAMS LLP;INTELLECTUAL PROPERTY DEPARTMENT
1900 K STREET, N.W.
SUITE 1200
WASHINGTON
DC
20006-1109
US
|
Assignee: |
Indium Corporation of
America
Utica
NY
|
Family ID: |
37894223 |
Appl. No.: |
11/422782 |
Filed: |
June 7, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60720039 |
Sep 26, 2005 |
|
|
|
Current U.S.
Class: |
420/560 |
Current CPC
Class: |
C22C 13/00 20130101;
B23K 35/262 20130101 |
Class at
Publication: |
420/560 |
International
Class: |
C22C 13/00 20060101
C22C013/00 |
Claims
1. A low melting temperature compliant solder alloy consisting
essentially of from about 91.5% to about 97.998% by weight tin,
from about 0.001% to about 3.5% by weight silver, from about 0.0%
to about 1.0% by weight copper, and from about 2.001% to about 4.0%
by weight indium.
2. The low melting temperature compliant solder alloy of claim 1,
wherein the alloy comprises at most about 3.0% by weight
indium.
3. The low melting temperature compliant solder alloy of claim 1,
wherein the alloy comprises at most about 2.5% by weight
indium.
4. The low melting temperature compliant solder alloy of claim 1,
wherein the alloy includes traces of impurities.
5. The low melting temperature compliant solder alloy of claim 1,
wherein the alloy does not include traces of impurities.
6. The low melting temperature compliant solder alloy of claim 1,
further consisting of from about 0.01% to about 3.0% by weight at
least one dopant selected from the group consisting of zinc (Zn),
nickel (Ni), iron (Fe), cobalt (Co), germanium (Ge), phosphorus
(P), aluminum (Al), antimony (Sb), cadmium (Cd), tellurium (Te),
bismuth (Bi), platinum (Pt), rare earth elements, and combinations
thereof to improve oxidation resistance and increase physical
properties and thermal fatigue resistance.
7. The low melting temperature compliant solder alloy of claim 6,
wherein the rare earth elements are selected from the group
consisting of cerium (Ce), lanthanum (La), praseodymium (Pr),
neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu),
gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho),
erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), actinium
(Ac), thorium (Th), protactinium (Pa), and combinations
thereof.
8. A low melting temperature compliant solder alloy consisting
essentially of from about 89.7% to about 94.499% by weight tin,
from about 3.5% to about 6.0% by weight silver, from about 0.0% to
about 0.3% by weight copper, and from about 2.001% to about 4.0% by
weight indium.
9. The low melting temperature compliant solder alloy of claim 8,
wherein the alloy comprises at most about 3.0% by weight
indium.
10. The low melting temperature compliant solder alloy of claim 8,
wherein the alloy comprises at most about 2.5% by weight
indium.
11. The low melting temperature compliant solder alloy of claim 8,
wherein the alloy includes traces of impurities.
12. The low melting temperature compliant solder alloy of claim 8,
wherein the alloy does not include traces of impurities.
13. The low melting temperature compliant solder alloy of claim 8,
further consisting of from about 0.01% to about 3.0% by weight at
least one dopant selected from the group consisting of zinc (Zn),
nickel (Ni), iron (Fe), cobalt (Co), germanium (Ge), phosphorus
(P), aluminum (Al), antimony (Sb), cadmium (Cd), tellurium (Te),
bismuth (Bi), platinum (Pt), rare earth elements, and combinations
thereof to improve oxidation resistance and increase physical
properties and thermal fatigue resistance.
14. The low melting temperature compliant solder alloy of claim 13,
wherein the rare earth elements are selected from the group
consisting of cerium (Ce), lanthanum (La), praseodymium (Pr),
neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu),
gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho),
erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), actinium
(Ac), thorium (Th), protactinium (Pa), and combinations thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application claims priority to U.S. Provisional
Patent Application No. 60/720,039, filed Sep. 26, 2005, which is
hereby incorporated by reference herein in its entirety.
FIELD OF THE DISCLOSURE
[0002] The present disclosure relates generally to solder
compositions and, more particularly, to low melting temperature
compliant solders.
BACKGROUND OF THE DISCLOSURE
[0003] As feature sizes of semiconductor devices continue to
shrink, low dielectric constant (low K) materials are more
frequently employed to replace conventional insulators (e.g.,
silicon oxide) in the manufacturing of semiconductor devices.
Currently, carbon-doped silicon oxide (SiOC) (K.about.2.5-3) is the
industry's primary choice for a low K material in the manufacturing
of semiconductor devices.
[0004] Carbon-doped silicon oxide (SiOC) typically comprises
numerous air pockets to improve low K performance. However, these
air pockets make this low K material very brittle and susceptible
to fracture. Consequently, during electronic packaging and assembly
processes, this low K material is known to crack due to stresses
generated during soldering processes. In particular, solder paste
reflow processes require reflow temperatures approximately
20-30.degree. C. above the liquidus temperatures of solder alloys.
For example, for a conventional Sn63Pb37 solder paste, the reflow
temperature is typically around 210-230.degree. C. However, the
recent conversion to Sn--Ag--Cu lead free solder alloys has
resulted in a great increase in reflow temperatures to typically
around 235-260.degree. C. The liquidus temperatures and yield
strengths of some of these Sn--Ag--Cu lead free solder alloys is
summarized in the table of FIG. 1.
[0005] Due to the higher liquidus temperatures (>218.degree. C.)
of the Sn--Ag--Cu lead free solder alloys and mismatches in
coefficients of thermal expansion between these Sn--Ag--Cu lead
free solder alloys and low K materials, high stresses develop in
low K materials during cooling from high temperature reflow
processes and thus cause cracking and failures in the low K
materials. In light of the above, solder alloys with lower melting
temperatures are required.
[0006] In addition to the requirement for solder alloys with low
liquidus temperatures, the ability of a solder to deform to
accommodate possible stresses or impact loading is critical to the
reliability of electronic devices employing low k materials. In
general, solders with low yield strengths are softer and easier to
deform so as to relieve stresses. Common low melting temperature
solder alloys presently consist mainly of generic 91Sn9Zn solder
alloy and patented Sn--Ag--In and Sn--Ag--Cu--In solder alloys.
However, in comparison with Sn--Ag--Cu solder alloys, these common
low melting temperature solder alloys are at least 50% greater in
yield strength and rigidity. A brief summary of these common low
melting temperature solder alloys is provided in the table of FIG.
2.
[0007] As shown in FIG. 2, 91Sn9Zn solder has a melting point of
199.degree. C., and this solder is very strong (yield strength of
9.1 ksi) and very rigid. As also shown in FIG. 2, patented
Sn--Ag--In and Sn--Ag--Cu--In solder alloys are also very strong
and rigid. Specifically, U.S. Pat. No. 5,580,520 discloses a solder
alloy with (71.5-91.9)% Sn, (2.6-3.3)% Ag, and (4.8-25.9)% In,
which has a melting point below 213.degree. C., but is too strong
for use in low K material embedded semiconductor devices. Also,
U.S. Pat. No. 6,176,947 discloses a solder alloy with (76-96)% Sn,
(0.2-2.5)% Cu, (2.5-4.5)% Ag, and (6-12)% In, which has a liquidus
temperature below 215.degree. C., but has proven too rigid for use
with low K material embedded semiconductor devices. Similarly, U.S.
Pat. No. 6,843,862 discloses an alloy composition with (88.5-93.5)%
Sn, (3.5-4.5)% Ag, (2-6)% In, (0.3-1)% Cu, and up to 0.5% of an
anti-oxidant and anti-skinning additive. This alloy is also too
strong and rigid for use in low K material embedded semiconductor
devices. In addition, U.S. Pat. No. 6,689,488 reveals a solder
alloy with (1-3.5)% Ag, (0.1-0.7)% Cu, (0.1-2)% In, balanced with
Sn, but this alloy composition has shown to be either too high in
melting temperature or too rigid for use in low K material embedded
semiconductor devices.
[0008] In view of the foregoing, it would be desirable to provide
low melting temperature compliant solders which overcome the
above-described inadequacies and shortcomings.
SUMMARY OF THE DISCLOSURE
[0009] Low melting temperature compliant solders are disclosed. In
one particular exemplary embodiment, a low melting temperature
compliant solder alloy comprises from about 91.5% to about 97.998%
by weight tin, from about 0.001% to about 3.5% by weight silver,
from about 0.0% to about 1.0% by weight copper, and from about
2.001% to about 4.0% by weight indium.
[0010] In accordance with other aspects of this particular
exemplary embodiment, the low melting temperature compliant solder
alloy may comprise at most about 3.0% by weight indium.
[0011] In accordance with further aspects of this particular
exemplary embodiment, the low melting temperature compliant solder
alloy may comprise at most about 2.5% by weight indium.
[0012] In accordance with still further aspects of this particular
exemplary embodiment, the low melting temperature compliant solder
alloy may further comprise traces of impurities.
[0013] In accordance with still further aspects of this particular
exemplary embodiment, the low melting temperature compliant solder
alloy does not comprise traces of impurities.
[0014] In accordance with additional aspects of this particular
exemplary embodiment, the low melting temperature compliant solder
alloy may further comprise from about 0.01% to about 3.0% by weight
at least one dopant selected from the group consisting of zinc
(Zn), nickel (Ni), iron (Fe), cobalt (Co), germanium (Ge),
phosphorus (P), aluminum (Al), antimony (Sb), cadmium (Cd),
tellurium (Te), bismuth (Bi), platinum (Pt), rare earth elements,
and combinations thereof to improve oxidation resistance and
increase physical properties and thermal fatigue resistance.
[0015] In accordance with still additional aspects of this
particular exemplary embodiment, the rare earth elements may be
selected from the group consisting of cerium (Ce), lanthanum (La),
praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm),
europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy),
holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium
(Lu), actinium (Ac), thorium (Th), protactinium (Pa), and
combinations thereof.
[0016] In another particular exemplary embodiment, a low melting
temperature compliant solder alloy comprises from about 89.7% to
about 94.499% by weight tin, from about 3.5% to about 6.0% by
weight silver, from about 0.0% to about 0.3% by weight copper, and
from about 2.001% to about 4.0% by weight indium.
[0017] In accordance with other aspects of this particular
exemplary embodiment, the low melting temperature compliant solder
alloy may comprise at most about 3.0% by weight indium.
[0018] In accordance with further aspects of this particular
exemplary embodiment, the low melting temperature compliant solder
alloy may comprise at most about 2.5% by weight indium.
[0019] In accordance with still further aspects of this particular
exemplary embodiment, the low melting temperature compliant solder
alloy may further comprise traces of impurities.
[0020] In accordance with still further aspects of this particular
exemplary embodiment, the low melting temperature compliant solder
alloy does not comprise traces of impurities.
[0021] In accordance with additional aspects of this particular
exemplary embodiment, the low melting temperature compliant solder
alloy may further comprise from about 0.01% to about 3.0% by weight
at least one dopant selected from the group consisting of zinc
(Zn), nickel (Ni), iron (Fe), cobalt (Co), germanium (Ge),
phosphorus (P), aluminum (Al), antimony (Sb), cadmium (Cd),
tellurium (Te), bismuth (Bi), platinum (Pt), rare earth elements,
and combinations thereof to improve oxidation resistance and
increase physical properties and thermal fatigue resistance.
[0022] In accordance with still additional aspects of this
particular exemplary embodiment, the rare earth elements may be
selected from the group consisting of cerium (Ce), lanthanum (La),
praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm),
europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy),
holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium
(Lu), actinium (Ac), thorium (Th), protactinium (Pa), and
combinations thereof.
[0023] The present disclosure will now be described in more detail
with reference to exemplary embodiments thereof as shown in the
accompanying drawings. While the present disclosure is described
below with reference to exemplary embodiments, it should be
understood that the present disclosure is not limited thereto.
Those of ordinary skill in the art having access to the teachings
herein will recognize additional implementations, modifications,
and embodiments, as well as other fields of use, which are within
the scope of the present disclosure as described herein, and with
respect to which the present disclosure may be of significant
utility.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] In order to facilitate a fuller understanding of the present
disclosure, reference is now made to the accompanying drawings, in
which like elements are referenced with like numerals. These
drawings should not be construed as limiting the present
disclosure, but are intended to be exemplary only.
[0025] FIG. 1 is a table showing the liquidus temperatures and
yield strengths of several Sn--Ag--Cu lead free solder alloys.
[0026] FIG. 2 is a table showing the liquidus temperatures and
yield strengths of several common low melting temperature solder
alloys.
[0027] FIG. 3 is a graph showing the effect of adding indium (In)
to standard Sn--Ag--Cu (SAC) alloys.
[0028] FIG. 4 is a table showing the liquidus temperatures and
yield strengths of indium (In) added Sn-1Ag-0.5Cu alloy
compositions with respect to the concentration of indium (In).
[0029] FIG. 5 is a table showing the liquidus temperatures and
yield strengths of indium (In) added Sn-2Ag-0.5Cu alloy
compositions with respect to the concentration of indium (In).
[0030] FIG. 6 is a table showing the liquidus temperatures and
yield strengths of indium (In) added Sn-2.5Ag-0.5Cu alloy
compositions with respect to the concentration of indium (In).
[0031] FIG. 7 is a table showing the liquidus temperatures and
yield strengths of indium (In) added Sn-3Ag-0.5Cu alloy
compositions with respect to the concentration of indium (In).
[0032] FIG. 8 is a table showing the liquidus temperatures and
yield strengths of indium (In) added Sn-4Ag-0.2Cu alloy
compositions with respect to the concentration of indium (In).
[0033] FIG. 9 is a graph showing the yield strengths of
Sn--Ag--Cu--In alloys with respect to the concentration of indium
(In).
[0034] FIG. 10 shows a scanning electron microscopy (SEM) snapshot
where energy dispersive spectrometry (EDS) is used to identify
major strengthening particles in an indium (In) added Sn--Ag--Cu
alloy composition.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0035] Referring to FIG. 3, there is shown a graph showing the
effect of adding indium (In) to standard Sn--Ag--Cu (SAC) alloys.
As shown in FIG. 3, the addition of indium (In) to the standard
Sn--Ag--Cu (SAC) alloys results in a decrease of liquidus
temperature. Specifically, when indium (In) is added to the
standard Sn--Ag--Cu (SAC) alloys in an amount greater than 2%, the
liquidus temperatures of the resultant Sn--Ag--Cu--In alloys are
reduced to below the liquidus temperatures of the standard
Sn--Ag--Cu (SAC) alloys. Thus, it may be advantageous to utilize
Sn--Ag--Cu--In alloys with indium (In) concentrations greater than
2% in semiconductor devices using low K materials.
[0036] However, adding indium (In) to the standard Sn--Ag--Cu (SAC)
alloys also results in a rapid increase of the yield strength due
to solution hardening, and high strength Sn--Ag--Cu--In alloys may
cause high stresses and unacceptable high defects. Thus, it would
be beneficial to determine compositional ranges for Sn--Ag--Cu--In
alloys that result in low liquidus temperatures, low yield
strength, and low rigidity. Indeed, the present disclosure is
directed to Sn--Ag--Cu--In alloy compositions exhibiting low
liquidus temperatures, low yield strength, and low rigidity. Such
Sn--Ag--Cu--In alloy compositions include Ag(0.001-3.5)%, Cu(0-1)%,
In(2.001-4)%, balanced with Sn, and Ag(3.5-6)%, Cu(0-0.3)%,
In(2.001-4)%, balanced with Sn. These Sn--Ag--Cu--In alloy
compositions were derived through a series of multiple
experimentations as exemplified below.
EXAMPLE 1
[0037] The liquidus temperatures and yield strengths of indium (In)
added Sn-1Ag-0.5Cu alloy compositions with respect to the
concentration of indium (In) are shown in the table of FIG. 4. The
yield strengths of the resultant alloy compositions increased
rapidly as the concentration of indium (In) increased.
EXAMPLE 2
[0038] The liquidus temperatures and yield strengths of indium (In)
added Sn-2Ag-0.5Cu alloy compositions with respect to the
concentration of indium (In) are shown in the table of FIG. 5.
[0039] The yield strengths of the resultant alloy compositions
remained about constant as the concentration of indium (In)
increased up to 2.5%. However, when the concentration of indium
(In) exceeded 2.5%, the yield strengths increased as the
concentration of indium (In) increased.
EXAMPLE 3
[0040] The liquidus temperatures and yield strengths of indium (In)
added Sn-2.5Ag-0.5Cu alloy compositions with respect to the
concentration of indium (In) are shown in the table of FIG. 6. The
yield strengths of the resultant alloy compositions remained
approximately constant as the concentration of indium (In)
increased up to about 2.5%. However, when the concentration of
indium (In) exceeded 2.5%, the yield strengths increased as the
concentration of indium (In) increased.
EXAMPLE 4
[0041] The liquidus temperatures and yield strengths of indium (In)
added Sn-3Ag-0.5Cu alloy compositions with respect to the
concentration of indium (In) are shown in the table of FIG. 7. The
yield strengths of the resultant alloy compositions decreased
slightly as the concentration of indium (In) increased up to about
2.5%. However, when the concentration of indium (In) exceeded 2.5%,
the yield strengths increased as the concentration of indium (In)
increased.
EXAMPLE 5
[0042] The liquidus temperatures and yield strengths of indium (In)
added Sn-4Ag-0.2Cu alloy compositions with respect to the
concentration of indium (In) are shown in the table of FIG. 8. Due
to a high yield strength (>6 ksi) developed because of a high
silver (Ag) concentration (>3.5%), a lower copper (Cu)
concentration (0.2%) with respect to standard Sn--Ag--Cu (SAC)
alloys (i.e., 0.5%) was employed. The yield strengths of the
resultant alloy compositions decreased (approximately 20%) as the
concentration of indium (In) increased up to about 2.5%. However,
when the concentration of indium (In) exceeded 2.5%, the yield
strengths increased as the concentration of indium (In)
increased.
[0043] The yield strengths of the Sn--Ag--Cu--In alloys with
respect to the concentration of indium (In) are shown in the graph
of FIG. 9. As shown in FIG. 9, it is clear that the yield strengths
of the indium (In) added Sn-1Ag-0.5Cu alloy compositions increased
very rapidly as the concentration of indium (In) increased, and
thus these alloy compositions are unacceptable for use in low K
material embedded semiconductor devices. However, with higher
silver (Ag) concentrations, the yield strengths of the indium (In)
added Sn--Ag--Cu alloy compositions either remained about constant
or decreased slightly as the concentration of indium (In) increased
up to about 2.5%, after which the yield strengths increased as the
concentration of indium (In) increased. For example, the yield
strengths of the indium (In) added Sn-2Ag-0.5Cu, Sn-2.5Ag-0.5Cu and
Sn-3Ag-0.5Cu alloy compositions resulted in a slight decrease in
yield strength as the concentration of indium (In) increased up to
about 2.5-3%. However, as the silver (Ag) concentration increased
to 4% and the copper (Cu) concentration decreased to 0.2% (i.e.,
Sn-4Ag-0.2Cu), the reduction in yield strength was very significant
(approximately 20%), although this low yield strength compositional
range was shortened very significantly. By the same token, it is
reasonable to expect that as the silver (Ag) concentration becomes
greater than 4% (e.g., Sn-6Ag-0.2Cu), an even more significant
reduction in yield strength would be produced, but the low yield
strength compositional range would become even shorter. These
results indicate that the yield strengths of indium (In) added
Sn-(0-2)% Ag-0.5Cu alloy compositions increase as the concentration
of indium (In) increases, but the yield strengths of indium (In)
added Sn-(2-3.5)% Ag-0.5Cu alloy compositions decrease as the
concentration of indium (In) increases (i.e., (2.001-4)% In). The
latter alloy compositions give rise to the low melting temperature
compliant solders of the present disclosure for use in low K
material embedded semiconductor devices. In addition, when the
copper (Cu) concentration is further reduced to 0.2%, the yield
strengths of indium (In) added Sn-(3.5-6)% Ag-0.2Cu alloy
compositions are most significantly reduced.
[0044] In order to obtain a better understanding of the above
results, scanning electron microscopy (SEM) and energy dispersive
spectrometry (EDS) were performed on the above mentioned alloys.
For example, FIG. 10 shows an SEM snapshot where EDS is used to
identify major strengthening particles in an indium (In) added
Sn--Ag--Cu alloy composition. As shown in FIG. 10, the major
strengthening particles of this indium (In) added Sn--Ag--Cu alloy
composition is identified using EDS to be
Sn.sub.66.6Ag.sub.29.4In.sub.4. Specifically, the bright domains
may be identified as Sn--Ag--In within the composition
Sn.sub.66.6Ag.sub.29.4In.sub.4, and the dark grey matrix may be
identified as a solid solution of indium (In) in tin (Sn). This is
in contrast to the well established microstructure of the standard
Sn--Ag--Cu (SAC) alloys where the major strengthening Ag.sub.3Sn
particles (the minor strengthening particles are Cu.sub.6Sn.sub.5
due to copper (Cu)) are homogeneously distributed in the tine (Sn)
matrix. That is, because of the addition of indium (In) to the
stoichiometric Ag.sub.3Sn, the indium (In) doped
Sn.sub.66.6Ag.sub.29.4In.sub.4 particles are disordered and
off-stoichiometric. More specifically, these off-stoichiometric
Sn.sub.66.6Ag.sub.29.4In.sub.4 particles do not strengthen the
solder as much as Ag.sub.3Sn particles do due to a softer nature of
the off-stoichiometric compounds and a loss of coherency in the tin
(Sn) matrix.
[0045] In addition, it has been discovered that solution hardening
of indium was typically the main mechanism for strengthening
Sn--Ag--Cu--In solder alloys. However, in the Sn--Ag--Cu--In
compositions of the present disclosure, indium (In) is removed from
the solution, thus reducing the solution hardening effect, and
instead forms the off-stoichiometric Sn.sub.66.6Ag.sub.29.4In.sub.4
particles, which did not strengthen the alloy as much as the
replaced stoichiometric Ag.sub.3Sn particles. As a result of the
above-mentioned effects, the yield strengths of the presently
disclosed indium (In) added Sn--Ag--Cu alloy compositions decrease
as the concentration of indium (In) increases (i.e., between
(2.001-4)% In).
[0046] FIG. 10 also reveals that as the concentration of silver
(Ag) decreases below 2%, Sn.sub.66.6Ag.sub.29.4In.sub.4 particles
are found to be sparsely distributed because less indium (In) is
removed from the solution, and the softening effect is negligible.
In contrast, as the concentration of silver (Ag) exceeds 6%, indium
(In) available to form Sn.sub.66.6Ag.sub.29.4In.sub.4 particles is
exhausted. Nevertheless, the number of Ag.sub.3Sn particles
continues to increase due to the increasing amount of available
silver (Ag), rendering the softening effect less conspicuous and
the low strength compositional range shorter. In accordance with
the present disclosure, further reduction of yield strength is
achieved by reducing the number of the minor strengthening
particles of Cu.sub.6Sn.sub.5 by reducing the copper (Cu)
concentration, thereby resulting in even more advantageous alloy
compositions.
[0047] The present disclosure is not to be limited in scope by the
specific embodiments described herein. Indeed, other various
embodiments of and modifications to the present disclosure, in
addition to those described herein, will be apparent to those of
ordinary skill in the art from the foregoing description and
accompanying drawings. Thus, such other embodiments and
modifications are intended to fall within the scope of the present
disclosure. Further, although the present disclosure has been
described herein in the context of a particular implementation in a
particular environment for a particular purpose, those of ordinary
skill in the art will recognize that its usefulness is not limited
thereto and that the present disclosure may be beneficially
implemented in any number of environments for any number of
purposes. Accordingly, the claims set forth below should be
construed in view of the full breadth and spirit of the present
disclosure as described herein.
* * * * *