U.S. patent application number 10/056667 was filed with the patent office on 2002-10-24 for lead-free solder compositions.
This patent application is currently assigned to H-Technologies Group, Inc.. Invention is credited to Hwang, Jennie S..
Application Number | 20020155024 10/056667 |
Document ID | / |
Family ID | 27369074 |
Filed Date | 2002-10-24 |
United States Patent
Application |
20020155024 |
Kind Code |
A1 |
Hwang, Jennie S. |
October 24, 2002 |
Lead-free solder compositions
Abstract
Disclosed is a high temperature, high performance lead-free
solder alloy comprising effective amounts of tin, copper, silver,
bismuth, and antimony and having a liquidus temperature above
215.degree. C. More particularly, several lead-free solder alloys
are disclosed that comprise about (i) at least about 90% Sn, 0.2 to
5.0% Cu, 0.05 to 5.0% Bi; or (ii) at least about 75% Sn, 0.5 to
7.0% Cu, 0.05 to 18% Sb; or (iii) at least about 67% Sn, 3 to 15%
Ag, 0.01 to 18% Sb; (iv) at least about 78% Sn, 0.8 to 7.0% Cu, 4
to 15% Ag; (v) at least about 96% Sn, and at least one of 0.01 to
2.0% Ni, and 0.01 to 2.0% Co; (vi) at least about 90% Sn, 0.05 to
5.0% Bi, and 0 to 5.0% Sb; and (vii) at least about 90% Sn, 0.2 to
0.9% Cu, and 0.1 to 5.0% Bi.
Inventors: |
Hwang, Jennie S.; (Moreland
Hills, OH) |
Correspondence
Address: |
FAY, SHARPE, FAGAN, MINNICH & MCKEE, LLP
1100 SUPERIOR AVENUE, SEVENTH FLOOR
CLEVELAND
OH
44114
US
|
Assignee: |
H-Technologies Group, Inc.
|
Family ID: |
27369074 |
Appl. No.: |
10/056667 |
Filed: |
October 29, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60244506 |
Oct 31, 2000 |
|
|
|
60243796 |
Oct 27, 2000 |
|
|
|
Current U.S.
Class: |
420/561 ;
420/562 |
Current CPC
Class: |
C22C 13/02 20130101;
C22C 13/00 20130101; B23K 35/262 20130101 |
Class at
Publication: |
420/561 ;
420/562 |
International
Class: |
C22C 013/02 |
Claims
I claim:
1. A lead-free solder alloy selected from the group consisting of:
(i) an alloy including at least about 90% Sn, 0.2 to 5.0% Cu, and
0.05 to 5.0% Bi; (ii) an alloy including at least about 75% Sn, 0.5
to 7.0% Cu, 0.05 to 18% Sb; (iii) an alloy including at least about
67% Sn, 3 to 15% Ag, and 0.01 to 18% Sb; (iv) an alloy including at
least about 78% Sn, 0.8 to 7.0% Cu, and 4 to 15% Ag; (v) an alloy
including at least about 96% Sn, and at least one of 0.01 to 2.0%
Ni, and 0.01 to 2.0% Co; (vi) an alloy including at least about 90%
Sn, 0.05 to 5.0% Bi, and 0 to 5.0% Sb; and (vii) an alloy including
at least about 90% Sn, 0.2 to 0.9% Cu, and 0.1 to 5.0% Bi.
2. The lead-free solder alloy of claim 1 having a liquidus melting
temperature greater than 215.degree. C.
3. The lead-free solder alloy of claim 1, wherein the alloy is
alloy (i) and includes about 90 to 99% Sn, 0.2 to 5.0% Cu, and 0.05
to 5.0% Bi.
4. The lead-free solder alloy of claim 3, wherein the solder alloy
composition comprises about 96.0% Sn, 3.0% Cu, and 1.0% Bi.
5. The lead-free solder alloy of claim 1, wherein the alloy is
alloy (ii) and includes about 75 to 99% Sn, 0.5 to 7.0% Cu, and
0.05 to 18% Sb.
6. The lead-free solder alloy of claim 5, wherein the solder alloy
composition comprises about 82% Sn, 3% Cu, and 15% Sb.
7. The lead-free solder alloy of claim 1, wherein the alloy is
alloy (iii) and includes about 67 to 97% Sn, 3 to 15% Ag, and 0.01
to 18% Sb.
8. The lead-free solder alloy of claim 7, wherein the solder alloy
composition comprises about 75% Sn, 10% Ag, and 15% Sb.
9. The lead-free solder alloy of claim 7, wherein the solder alloy
composition comprises about 93.5% Sn, 5% Ag, and 1.5% Sb.
10. The lead-free solder alloy of claim 1, wherein the alloy is
alloy (iv) and includes about 78 to 96% Sn, 0.8 to 7.0% Cu, and 4
to 15% Ag.
11. The lead-free solder alloy of claim 10, wherein the solder
alloy composition comprises about 87% Sn, 3% Cu, and 10% Ag.
12. The lead-free solder alloy of claim 1, wherein the alloy is
alloy (v) and includes about 96 to 99% Sn, and at least one of 0.01
to 2.0% Ni, and 0.01 to 2% Co.
13. The lead-free solder alloy of claim 12, wherein the solder
alloy composition comprises about 99.3% Sn, 0.2% Ni, and 0.5%
Co.
14. The lead-free solder alloy of claim 1, wherein the alloy is
alloy (vi) and includes about 90 to 99% Sn, 0.05 to 5.0% Bi, and 0
to 5.0% Sb.
15. The lead-free solder alloy of claim 14, wherein the solder
alloy composition comprises about 98.5% Sn, 1% Bi, and 0.5% Sb.
16. The lead-free solder alloy of claim 1, wherein the alloy is
alloy (vii) and includes about 90 to 99% Sn, 0.2 to 0.9% Cu, and
0.1 to 5.0% Bi.
17. The lead-free solder alloy of claim 16, wherein the solder
alloy composition comprises about 98.3% Sn, 0.7% Cu, and 1% Bi.
18. The lead-free solder alloy of claim 16, wherein the solder
alloy exhibits a tensile strength and fatigue life at 0.2% strain
greater than a Sn/Cu eutectic composition of 99.3Sn/0.7Cu.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application claims priority upon U.S. Provisional
application Serial No. 60/244,506 filed Oct. 31, 2000 and U.S.
Provisional application Serial No. 60/243,796 filed Oct. 29,
2000.
FIELD OF THE INVENTION
[0002] The present invention relates to lead-free solder alloys
that provide high temperature performance for microelectronics and
various other electronic applications. More particularly, the
present invention relates to lead-free compositions containing
effective amounts of tin, copper, silver, bismuth, antimony and
which exhibit a melting temperature (liquidus temperature) above
215.degree. C.
[0003] The present invention also relates to a surprising and
unexpected discovery concerning the effect of bismuth in lead-free
tin-copper compositions.
BACKGROUND OF THE INVENTION
[0004] Lead-containing solder alloys face a limited future due to
lead toxicity and the control or prohibition of the use of lead on
a global basis. Consequently, many efforts around the world have
been undertaken to find suitable lead-free alternatives to Pb--Sn
solder alloys. Some low and moderate temperature alloys (having
melting temperatures below 215.degree. C.) have been disclosed in
the art. However, there remains a need for Pb-free alloys with a
liquidus temperature above 215.degree. C. that can withstand high
temperature applications. In addition, there is a particular need
for high temperature Pb-free alloys that possess high strength and
high fatigue resistance in order to meet increasing performance
requirements for solder interconnections as advancements in
integrated circuit (IC) and related interconnections are made.
[0005] In electronics manufacturing, solder alloy is used to
metallurgically join bare chips or packaged chips onto an adjacent
level of a substrate and to connect leadframe or various other
leads. This enables electronic devices to be constructed through
the formation of a desirable band of intermetallics. In forming
reliable solder joints, it is important that the solder alloy
readily flows and wets commonly used metallization pads such as Cu,
Ag, Au, Pd, Ni and other metallic surfaces in the assembly. These
requirements are particularly important in view of today's
high-speed automated manufacturing processes that employ mild
fluxes that are compatible with electronic systems.
[0006] It would be beneficial to provide a class of solder
compositions with a critical physical property, i.e., a high enough
melting temperature to accommodate interconnection requirements
without approaching a melting state during multiple-step production
operations as well as while the product is in service. This high
temperature performance is particularly important for chip level
interconnections. Exposing solder compositions to temperatures near
the melting temperatures of the compositions, causes product
malfunction or a catastrophic failure. In order to avoid such
interconnecting disruption and failure, the melting temperature of
this class of solder compositions must be above 215.degree. C.
[0007] A Cu--Sn eutectic with a composition of 99.3% Sn, 0.7% Cu is
considered a viable Pb-free alloy. However, the strength and
fatigue resistance of the Cu--Sn eutectic is significantly inferior
to 63Sn/37Pb that has been most widely used in electronic
assemblies, particularly surface mount printed circuit boards. It
would be desirable to provide a new class of solder compositions
that exhibit dramatically increased strength and fatigue life as
compared to currently known comparable solder compositions.
[0008] Solder joints perform as electrical, thermal, and mechanical
interconnections in many electronic systems such as
telecommunication, computer, avionics and automotive electronics.
During the service life of electronic components, solder joints are
inevitably exposed to thermal stresses as the result of temperature
fluctuation, power on/off switching, and/or harsh environmental
conditions. This coupled with mismatched thermal expansion
characteristics in the interconnected materials of semiconductor,
ceramic, metal, and polymeric materials in the system, may result
in thermo-mechanical fatigue in solder joints. Furthermore, as
electronic circuitry becomes increasingly denser and the clock
speed of microprocessors continues to reach ever-higher
frequencies, one of the design objectives of electronic systems is
increased heat dissipation.
[0009] In addition, the number of solder joints on each printed
circuit board (PCB) continues to rise. The presence of several
thousands or tens of thousands of solder joints in a typical
electronic circuit is not uncommon. As will be appreciated, a
single solder joint failure can result in a failed system.
Consequently, requirements on the strength and fatigue resistance
of solder joints are heightened. The recent developments in high
pin count integrated circuit (IC) packages such as ball grid array
(BGA), chip scale package (CSP), and direct-chip-attach
technologies such as "flip chip" further demand higher performance
in fatigue resistance for solder alloys.
[0010] A number of lead-free solders have been proposed in the art.
A summary of these lead-free alloys is outlined in Chapter 15 of
the book "Modern Solder Technology for Competitive Electronics
Manufacturing", authored by Dr. J. S. Hwang and published by
McGraw-Hill. Although satisfactory in many respects, these alloys
do not exhibit high enough liquidus temperatures to satisfy high
temperature performance either during multiple-step circuitry
manufacturing or for certain end-use applications. Therefore, there
is an acute need for a new class of lead-free solder compositions
that exhibit a melting point of at least 215.degree. C. and/or that
exhibit improved strength and fatigue resistance over comparable
currently known solder compositions.
SUMMARY OF THE INVENTION
[0011] Accordingly, it is a primary object of the present invention
to provide a lead-free solder. It is an advantage of this invention
to provide a lead-free solder that is capable of withstanding the
high temperature production steps and/or exposure to high
temperatures in microelectronic and electronic applications.
[0012] It is a further advantage of this invention to provide a
lead-free solder that has a melting temperature range above
215.degree. C.
[0013] It is a further advantage of this invention to provide a
lead-free solder that is readily adaptable to established or
conventional electronic manufacturing processes and infrastructure
without requiring major changes in materials, processes and
components.
[0014] It is a further advantage of this invention to provide a
lead-free solder that offers high-strength and high fatigue
resistance. Such characteristics would enable the solder to
withstand the increasingly adverse and harsh conditions associated
with many microelectronic and electronic applications.
[0015] Additional objects and advantages of the invention will be
set forth in part in the description which follows.
[0016] To achieve the foregoing objects and in accordance with this
invention, as embodied and broadly described herein, the solder
alloys of this invention have Sn as a major constituent and
effective amounts of Cu, Ag, Bi, or Sb. The solder demonstrates
compatible and desired melting temperature, good strength and
fatigue resistance. The solder alloys of this invention also
exhibit significant improvements in strength by using Bi as a
doping constituent in the Cu--Sn matrix. The solder exhibits
compatible melting temperature, high strength, and high fatigue
resistance.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] While the present invention will be described in connection
with several preferred embodiments, it will be understood that such
description is not intended to limit the invention to those
embodiments.
[0018] The present invention provides a high temperature, high
performance lead-free solder alloy that exhibits a melting
temperature that is compatible with established component and
circuitry manufacturing techniques. The preferred solder alloys are
as follows:
[0019] (i) at least about 90% Sn, 0.2 to 5.0% Cu, and 0.05 to 5.0%
Bi;
[0020] (ii) at least about 75% Sn, 0.5 to 7.0% Cu, and 0.05 to 18%
Sb;
[0021] (iii) at least about 67% Sn, 3 to 15% Ag, and 0.01 to 18%
Sb;
[0022] (iv) at least about 78% Sn, 0.8 to 7.0% Cu, and 4 to 15%
Ag;
[0023] (v) at least about 96% Sn, at least one of 0.01 to 2.0% Ni,
and 0.01 to 2.0% Co;
[0024] (vi) at least about 90% Sn, 0.05 to 5.0% Bi, and 0 to 5.0%
Sb; and
[0025] (vii) at least about 90% Sn, 0.2 to 0.9% Cu, and 0.1 to 5.0%
Bi.
[0026] All compositions are expressed in weight percent.
[0027] The upper limit of Sn in each of the compositions (i)-(vii)
varies with each composition. However, these upper limits are
generally as follows. Solder alloy (i) may contain Sn up to about
99%. Solder alloy (ii) may contain Sn up to about 99%. Solder alloy
(iii) may contain Sn up to about 97%. Solder alloy (iv) may contain
Sn up to about 96%. Solder alloy (v) may contain Sn up to about
99%. Solder alloy (vi) may contain Sn up to about 99%. Solder alloy
(vii) may contain Sn up to about 99%.
[0028] In yet another preferred embodiment of the invention, there
is provided a solder alloy containing about 96.0% Sn, 3.0% Cu, and
1.0% Bi. The alloy has a liquidus temperature at 304.degree. C. (a
melting temperature from about 225.degree. C. to 304.degree. C.).
The tensile strength and fatigue life of the alloy are 55 MPa and
4215 cycles, respectively.
[0029] In another preferred embodiment of the invention, there is
provided a solder alloy containing about 82% Sn, 3% Cu, and 15% Sb.
The alloy has a liquidus temperature at 295.degree. C. (a melting
range from about 240.degree. C. to 295.degree. C.). The tensile
strength and fatigue life of the alloy are 87 MPa and 5881 cycles,
respectively.
[0030] In a further preferred embodiment of the invention, there is
provided a solder alloy containing about 90% Sn and 10% Ag. The
alloy has a liquidus temperature at 275.degree. C. (a melting
temperature from about 224.degree. C. to 275.degree. C.). The
tensile strength and fatigue life of the alloy are 52 MPa and 9821
cycles, respectively.
[0031] In yet another preferred embodiment of the invention, there
is provided a solder alloy containing about 85% Sn and 15% Sb. This
alloy may contain relatively minor amounts of copper. The alloy has
a liquidus temperature at 290.degree. C. (a melting temperature
from about 240.degree. C. to 290.degree. C.). The tensile strength
and fatigue life of the alloy are 73 MPa and 7619 cycles,
respectively.
[0032] In another preferred embodiment of the invention, there is
provided a solder alloy containing about 75% Sn, 10% Ag, and 15%
Sb. The alloy has a liquidus temperature at 290.degree. C. (a
melting temperature from about 235.degree. C. to 290.degree. C.).
The tensile strength and fatigue life of the alloy are 98 MPa and
3752 cycles, respectively.
[0033] In a still further preferred embodiment of the invention,
there is provided a solder alloy containing about 87% Sn, 3% Cu,
and 10% Ag. The alloy has a liquidus temperature at 288.degree. C.
(a melting temperature from about 218.degree. C. to 288.degree.
C.), and the tensile strength and fatigue life of the alloy are 75
MPa and 4355 cycles, respectively.
[0034] In another preferred embodiment of the invention, there is
provided a solder alloy containing about 93.5% Sn, 5% Ag, 1.5% Sb.
The alloy has a liquidus temperature at 223 C., and the tensile
strength and fatigue life of the alloy are 57 MPa and 16424 cycles,
respectively.
[0035] In another preferred embodiment of the invention, there is
provided a solder alloy containing about 99.3% Sn, 0.2% Ni, 0.5%
Co. The alloy has a liquidus temperature at 231 C., and the tensile
strength and fatigue life of the alloy are 42 MPa and 4350 cycles,
respectively.
[0036] In another preferred embodiment of the invention, there is
provided a solder alloy containing about 98.5% Sn, 1% Bi, 0.5% Sb.
The alloy has a liquidus temperature of 232 C., and the tensile
strength and fatigue life of the alloy are 36 MPa and 3891 cycles,
respectively.
[0037] The present invention also provides a lead-free solder alloy
that is significantly superior to a Cu--Sn eutectic composition in
strength and fatigue resistance. The solder alloy of this aspect of
the present invention comprises at least about 90% Sn, 0.2 to 0.9%
Cu, and 0.1 to 5.0% Bi.
[0038] For reference purposes, it is believed that 63Sn/37Pb solder
has generally been measured with the ultimate tensile strength
being 47 MPa and the low-cycle fatigue life at 0.2% strain being
3650 cycles. The tensile strength and fatigue life of a solder
alloy of 99.3Sn/0.7Cu are 24 MPa and 1125 cycles, respectively,
which is well below that for a 63Sn/37Pb composition that has been
used as the industry standard for surface mount assemblies.
[0039] The present invention solder alloy demonstrates a higher
strength and fatigue life than a Sn/Cu eutectic composition.
[0040] In a preferred embodiment of this aspect of the invention,
there is provided a solder alloy containing about 98.3% Sn, 0.7%
Cu, and 1% Bi. The tensile strength and fatigue life of the alloy
are 48 MPa and 9165 cycles, respectively. The fatigue life of this
composition is 770% higher than that of 99.3Sn/0.7Cu, and the
tensile strength is 200% higher than that of 99.3Sn/0.7Cu.
[0041] It will be appreciated that all of the solder alloy
compositions of the present invention may contain a variety of one
or more elements. Examples of such elements include, but are not
limited to Ga, Se, Te, Ba, Ca, Mg, Zn, Si, Sb, In, Au, Ag, Pd, Pt,
Fe, Ni, Co, Ti and combinations thereof. Generally, the amounts of
such elements are less than 1% collectively.
[0042] The previously noted lead-free solder alloys of this
invention can be prepared at the molten states of the major
constituents by general heating techniques known in the art. The
alloys can also be used in various physical forms such as pastes,
powders, bars and wires or in any soldering processes such as
reflow oven soldering, wave machine soldering and hand soldering or
in any materials fabrication such as various deposition and coating
techniques.
[0043] While the invention has been described with respect to its
preferred embodiments, it is to be understood that variations and
modifications thereof will become apparent to those skilled in the
art. The foregoing disclosure is not intended or to be construed to
limit the scope of the invention described herein.
* * * * *