Note: Descriptions are shown in the official language in which they were submitted.
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Pb-free Solder Alloy Compositions Comprising Essentially Tin (Sn), Silver (AM,
Copper (Cu), Nickel (Ni), Phosphorus (P) and/or Rare Earth: Cerium (Ce) or
Lanthanum (La)
Background of the Invention
1. Field of the Invention
Despite Pb is a component of solder alloys in widespread use in the electronic
industry, there is a drive to replace the use of Pb metal, because of its
toxic nature. In
addition to the toxicity of Pb, there are other problems concerning continued
widespread
use of the Sn-Pb and Pb-based solders. In United States, Canada, most of the
Europe,
and in Japan, the use of Pb in all commercial products, such as: vehicles,
electronic toys,
computers and appliances, shall all be banned.
2. Description of the Prior Art
The excellent metallurgical wetting of 63% Sn and 37% Pb is thought to be
promoted by the instantaneous formation of a thin layer of a very stable
intermetallic
compound at the molten solder interface. The interfacial inter-metallic
compound that
aids solder wetting is always based on Sn, not Pb. The role of Pb in promoting
solderability is much less understood, but seems related to its ability to
strongly suppress
the liquid surface tension of the solder alloy, lowering the contact angel of
the molten
solder which leads to better spreading and more interacting surface area for
the solder
joint to form. The eutectic solidification reaction of 63% Sn and 37% Pb also
generates a
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highly refined mixture of Sn and Pb phases that produces unusual strength from
rather
weak constituents.
In response to the possibility of a governmental ban or excessive taxation of
Pb
use, manufacturers and users of Pb-bearing solder for electronic and circuit
joining
applications recently have attempted to developed Pb-free solders as direct
replacements
for the conventional Sn-Pb solders in conventional hand/wave/reflow soldering
processes
employing general heating of an electronic wiring board to temperatures of 240-
250
degree Celsius. Moreover, there is a need for such a solder that would be
competitive in
cost and as readily available as conventional Sn-Pb eutectic solders for high
volume use.
A ternary, off-eutectic Sn-Ag-Cu solder alloy has been developed by the
plumbing industry as a Pb-free solder with 96 weight % Sn, 3.5 weight % Cu,
and 0.5
weight % Ag. This plumbing solder has a 227 degree Celsius of solidus
temperature and
260 degree Celsius liquidus temperature, which would be considered not
suitable for
electronics manufacturers.
Recent developments of Pb-free solder alloys mainly involve the use of Ag, Bi,
Cu, In, Sn, and Zn. Special attentions have been drawn on the solder
composition
comprising Sn, Ag, and Cu. Anderson et. al. of Iowa State University Research
have
reported the eutectic Pb-free solder comprising 93.6Sn/4.7Ag/1.7Cu and
Sn/Ag/Cu/Ni/Fe,
respectively.
Summary of the Invention
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This present invention provides a Pb-free solder comprising a compositions
consisting
essentially of Sn, Ag, Cu, Ni, P, and/or Ce or La, having a melting
temperature of 221-
233 degree Celsius.
In one embodiment of the invention, the Pb-free solder consists essentially of
0.3 weight
% Ag, 0.7 weight % Cu, 0.3 weight % Ni, 0.05 weight % P, 0.05 weight % Ce or
La, and
balance of weight % Sn. To the Sn/0.3Ag/0.7Cu/0.3Ni/0.05P, 0.05 weight % of Ce
or La
is added to improve better micro-structural stability and hence reduce grain
size of Sn in
the solder composition, and the melting temperature is 223-230 degree Celsius.
In another embodiment of the invention, the Pb-free solder consists
essentially of 0.4
weight % Ag, 0.6 weight % Cu, 0.3 weight % Ni, 0.05 weight % P, 0.05 weight %
Ce or
La, and balance of weight % Sn. To the Sn/0.4Ag/0.6Cu/0.3Ni/0.05P, 0.05 weight
% Ce
or La is added to improve better micro-structural stability and hence reduce
grain size of
Sn in the solder composition, and the melting temperature is 221-229 degree
Celsius.
The solder of the invention described here-above can be used as a replacement
for Pb-
containing solder in solder wave and other hand soldering processes in
widespread use in
the electronic and other industries.
The solder of the invention is advantageous not only from an environmental
standpoint
but also from the cost and availability standpoint in that the alloy compounds
(Sn, Ag, Cu,
Ni, P and/or Ce or La) are readily available at lower cost than the Pb-free
solders
including large amount of Bi, In, Zn, or Ga proposed to-date. Large volume
solder
applications especially will benefit from the low cost, high performance
solder of the
invention having the aforementioned advantages not possesses heretofore by
other Pb-
free solders.
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The above brief description sets forth rather broadly the more important
features of the
present invention in order that the detailed description thereof that follows
may be better
understood, and in order that the present contributions to the art may be
better
appreciated. There are, of course, additional features of the invention that
will be
described hereinafter and will form the subject matter of the claims appended
hereto.
In this respect, before explaining the preferred embodiments of the invention
in detail, it
is to be understood that the invention is not limited in its application to
the details of the
construction and to the arrangements of the components set forth in the
following
description. The invention is capable of other embodiments and of being
practiced and
camed out in various ways. Also, it is to be understood, that the phraseology
and
terminology employed herein are for the purpose of description and should not
be
regarded as limiting.
As such, those skilled in the art will appreciate that the conception, upon
which this
disclosure is based, may readily be utilized as a basis for designing other
structures,
methods and systems for carrying out the several purposes of the present
invention. It is
important, therefore, that the claims be regarded as including such equivalent
constructions insofar as they do not depart from the spirit and scope of the
present
invention.
Further, the purpose of the foregoing Abstract is to enable the Intellectual
Property Office
and the public generally, and especially the scientists, engineers and
practitioners in the
art who are not familiar with patent or legal terms of phraseology, to
determine quickly
from a cursory inspection the nature and essence of the technical disclosure
of the
application. Accordingly, the Abstract is neither intended to defme the
invention or the
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application, which only is measured by the claims, nor is it intended to be
limiting as to
the scope of the invention in any way.
It is therefore an object of the present invention to provide a new and
improved
composition of an environmental friendly Pb-free solder alloy, which has all
of the
advantages of the prior art and yet keep our environment green.
It is another object of the present invention to provide a new and improved
composition
of an environmental friendly Pb-free solder alloy, which may be efficiently
manufactured
and marketed.
An even further object of the present invention is to provide a new and
improved
composition of an environmental friendly Pb-free solder alloy, which is
susceptible of a
low cost of manufacture with regard to both materials and labor, and which
accordingly
is then susceptible of low prices of sale to the consuming public, thereby
making such
composition available to the buying public.
Still yet a further object of the present invention is to provide a new and
improved
composition of an environmental friendly Pb-free solder alloy, which can be
used to
make Pb-free solder bar, wire, paste, BGA ball and anode in electronics
industries.
These together with still other objects of the invention, along with the
various features of
novelty, which characterize the invention, are pointed out with particularity
in the claims
forming a part of this disclosure. For a better understanding of the
invention, its
operating advantages and the specific objects attained by its uses, reference
should be
made to the following detailed description of the preferred embodiments of the
invention.
Description of the preferred Embodiment
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The Pb-free solder of the present invention is based on a composition
essentially of about
0.3-0.4 weight % Ag, 0.6-0.7 weight % Cu, 0.01-1.0 weight % Ni, 0.01-0.3
weight % P,
0.001-0.3 weight % Ce or La, and balance weight % Sn, with the additional of
Ce or La,
not exceeding 0.3 weight % of the overall composition, to enhance better micro-
structural
stability and to reduce grain size of the resultant solder joints. With the
presence of Ni,
the thermal stability of the alloy is improved. Further, addition of Ni causes
fine crystal
texture (forming the Ni-Sn inter-metallic compound), thereby improving
strength and
thermal fatigue characteristic. Still further, when soldering onto a Cu
substrate, addition
of Ni suppresses formation of an inter-metallic compound (Cu3Sn), of which Cu-
Sn
would degrade the soldering strength.
Preferably, for electronic solder applications using the solder wave process,
the melting
temperature range of the solder should not exceed 10 degree Celsius. This
present
invention has a solder melting range of 10 degree Celsius.
A preferred Pb-free solders of the invention are listed below, exhibiting off-
eutectic
melting temperatures:
(1). A electrical conductor Pb-free solder composition consisting essentially
of 0.3 %
weight % Ag, 0.7 weight % Cu, 0.3 weight % Ni, 0.05 weight % P, 0.05 weight %
Ce or La, balance Sn and unavoidable impurities, based on the weight of
composition. The melting temperature of the solder is in the range of 223 to
230
degree Celsius.
(2). A electrical conductor Pb-free solder composition consisting essentially
of 0.4 %
weight % Ag, 0.6 weight % Cu, 0.3 weight % Ni, 0.05 weight % P, 0.05 weight %
Ce or La, balance Sn and unavoidable impurities, based on the weight of
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composition. The melting temperature of the solder is in the range of 221 to
229
degree Celsius.
The Pb-free solder of the present invention includes at least one non-metallic
component
consisting essentially of P, in an amount not exceeding 0.3 weight %.
The Pb-free solder of the present invention, which comprises Sn/(0.3-
0.4)Ag/(0.6-
0.7)Cu/(0.05-0.5)Ni/(not exceeding 0.1)P/(0.001-0.1)Ce or La, is similar as
the
conventional Pb-free solder comprising Sn/3.OAg/0.5Cu in welding performance,
conductivity, mechanical property, pliability and so on. But since the content
of Ag of the
Pb-free solder of the present invention is about one-tenth of other Pb-free
solder
comprising Sn/3.OAg/0.5Cu (Ag is trend to react with chemical agents, such as
acid or
alkali and so on, thereby to produce noxious substance), so the Pb-free solder
of the
present invention is more safe, and has no adverse effect to living beings and
environments in potential. In addition, the content of Ag [less than 0.5%] of
the Pb-free
solder of the present invention, which comprises Sn/(0.3-0.4)Ag/(0.6-
0.7)Cu/(0.01-
l.0)Ni/(not exceeding 0.3)P/(0.001-0.3)Ce or La, is less than that of
conventional Pb-free
SnAgCu solder, so the silver compounds which are generated in the reaction
between
silver and halogen component of the soldering flux, are not easy to form, as a
result, the
phenomenon of changing to black is slight.
The method for preparing 500 Kg of the Pb-free solder of the present invention
is
shown below:
1. 3.5 Kg of pure Cu, 1.5 Kg of pure Ni, 250 g Ce or La and 200 Kg of pure Sn
are
added into a steel kettle, then heated to the temperature of 400 degree
Celsius, and stirred
for about 45 minutes;
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2. The resulting mixture is cooled to the temperature of 300 degree Celsius,
then 293
Kg pure Sn is added into the steel kettle and stirred for about 45 minutes;
3. 1.5 Kg of pure silver is added into the steel kettle, then heated to the
temperature
of 370 degree Celsius, and stirred for about 45 minutes;
4. 250 g P is pulverized and added into the steel kettle and stirred for about
45
minutes at the temperature of 370 degree Celsius.
The solder of the present invention can be provided in many forms as needed
for
particular solder applications. The solder of the present invention can be
provided as
solder wire, solder bar, solder ingot, and solder powder. The solder bar and
ingot can be
manufactured by convention solder smelting technique. The smelting solder
should be
stirred 360 30 degree Celsius for 45 minutes, then let drop to 300 degree
Celsius. The
solder the can be chilled cast, from 300 degree Celsius to 65 10 degree
Celsius, into
suitable steel molds to produce bars or ingots having high purity and
compositional
accuracy. The solder wire can be extruded from ingot into hollow wire, which
is then
filled with core flux.
The above brief description sets forth rather broadly the more important
features of
the present invention in order that the detailed description thereof that
follows may be
better understood, and in order that the present contributions to the art may
be better
appreciated. There are, of course, additional features of the invention that
will be
described hereinafter and will form the subject matter of the claims appended
hereto.
In this respect, before explaining the preferred examples of the invention in
detail, it
is to be understood that the invention is not limited in its application to
the details of the
construction and to the arrangements of the components set forth in the
following
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description. The invention is capable of other embodiments and of being
practiced and
carried out in various ways. Also, it is to be understood, that the
phraseology and
terminology employed herein are for the purpose of description and should not
be
regarded as limiting.
It is an object of the present invention to provide a Sn-Ag-Cu Pb-free solder
alloy,
addition of Ni (0.01-1.0 weight %), trace amount of P(0.01-0.3 weight %) and
trace
amount of rare earth (Ce or La in the range 0.001-0.3 weight %), can improve
thermal
stability, better micro-structural stability and reduce joint oxidation rate,
hence, reduce
the formation of course grain solder joint. Furthermore, the surface of
soldering tin is not
trend to change black, so the amount of metal oxide produced in the steel
kettle of solder
can be reduced, and the defective fraction rate can be reduced during electro
wiring board
soldering.
Example 1
The Pb-free solder of this example consists of the following components, based
on
the weight %: 0.3 weight % Ag, 0.7 weight % Cu, 0.3 weight % Ni, 0.05 weight %
Ce or
La, 0.05 weight % P, and balance Sn.
Example 2
The Pb-free solder of this example consists of the following components, based
on
the weight %: 0.4 weight % Ag, 0.6 weight % Cu, 0.3 weight % Ni, 0.05 weight %
Ce or
La, 0.05 weight % P, and balance Sn.
The raw materials, weights thereof, processing steps and processing conditions
for
preparing the Pb-free solder have been described in detail in foregoing
paragraphs. Now,
the example 1 and 2 are listed in table 1. [see table 1]
