US005658528A
United States Patent [191
[111 Patent Number:
Ninomiya et a].
[45]
[54] LEAD-FREE SOLDER
Date of Patent:
FOREIGN PATENT DOCUTVIENTS
[75] Inventors: Ryuji Ninomiya; Junichi Matsunaga.
6-344180
1211994
Japan ................................... .. 420/557
115725
7/1982
Poland ................................. .. 420/557
both of Ageo. Japan
OTHER PUBLICATIONS
[73] Assignee: Mitsui Mining & Smelting Co., Ltd..
Tokyo, Japan
Artaki. I. and Jackson. A.M., Evaluation of Lead-Free
Solder Joints in Electronic Assemblies, Journal of Electronic
Materials, v01. 23. No. 8. Aug. 1994.
[21] Appl. No.: 712,678
[22] Filed:
Sep. 13, 1996
Primary Examiner-Sikyin Ip
Attorney, Agent, or Firm-Flynn. Thiel. Boutell & Tanis.
Related US. Application Data
[63]
[30]
5,658,528
Aug. 19, 1997
RC.
Continuation of Ser. No. 619,155, Mar. 21, 1996, aban
doned, which is a continuation of Ser. No. 417,911, Apr. 6,
[57]
1995, abandoned.
A lead-free solder consisting of l to 4 Wt % of Ag, at least
one of Bi and In in respective amounts meeting the condi
tions that the value of expression (1), A, is equal to or greater
than 5.00 and that the value of expression (2), B, is equal to
or less than 6.90. and Sn for the balance:
Foreign Application Priority Data
Nov. 2, 1994
[JP]
Japan .................................. .. 6-293880
Feb. 21, 1995
[JP]
Japan .................................. .. 7056691
[51]
Int. Cl.6 ................................................... .. C22C 13/02
[52]
[58]
US. Cl. ........................... .. 420/562; 420/557; 148/22
Field of Search ................................... .. 420/557. 562;
ABSTRACT
148/22
[56]
This solder has a tensile strength and an elongation as high
as those of conventional Pb—Sn solder without containing
References Cited
neither lead nor cadmium, which can cause environmental
U.S. PATENT DOCUMENTS
contamination.
5,256,370 10/1993 Slattery et a1. .
420/557
5,328,660
7/1994 Gonya et a1.
420/562
5,393,489
2/1995 Gonya et al. ......................... .. 420/561
1 Claim, 2 Drawing Sheets
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in CONTENT (wt°/°)
Agi 3wt% (Sni BALANCE)
10
US. Patent
Aug. 19, 1997
Sheet 1 0f 2
5,658,528
FIG. I
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U.SQ Patent
Aug. 19, 1997
Sheet 2 of 2
5,658,528
FIG. 3
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1 n CONTENT (wt %)
AL N E
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FIG. 4
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1
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LEAD-FREE SOLDER
DESCRIPTION OF THE PREFERRED
ENIBODIMENTS
This application is a continuation of US. Ser. No. 08/619
155, ?led Mar. 21, 1996, now abandoned, which is a
In the present invention, silver has the e?’ects of improv
ing the heat resistance. lowering the fusing temperature, and
increasing the strength. spreadability and brightness of the
continuation of US. Ser. No. 08/417 911, ?led Apr. 6, 1995,
now abandoned.
solder with only a small amount contained therein. The
silver content appropriate for this purpose is equal to or
greater than 1 wt %. The upper limit of the silver content is
BACKGROUND OF THE INVENTION
a) Field of the Invention
4 wt %, taking into account the expansiveness of silver.
This invention relates to a lead-free solder which has
The Bi and In contents are within the ranges such that the
combination of their contents fall in the hatched area in
mechanical properties as good as those of conventional
Pb—Sn solder.
FIGS.1to4forlwt%,2wt%,3wt%and4wt%.
b) Description of the Prior Art
respectively, which can be de?ned by the conditions that the
value of expression (1). A, is equal to or greater than 5.00
and that the, value of expression (2), B. is equal to or less
Pb—Sn alloys of eutectic or near-eutectic composition are
well known as representative solders. Zn-Cd alloys. which
have a greater strength than Pb—Sn eutectic solders. are also
than 6.90, where expressions (1) and (2) represent the upper
known. Amid the increased concern with environmental
and lower boundary lines of the hatched area in FIG. 3.
protection in recent years, the harmfulness of lead and the
noxious effect of vaporized cadmium on workers have
become a problem with the former and latter solders,
respectively, and a solder replacing them is needed
To meet this need, zinc or tin base solders, which contain
If the value of expression (1), A, is smaller than 5.00, the
tensile strength of the solder is lower than 4.0 kgflmmz. If
the value of expression (2), B, is greater that 6.90, on the
other hand, the elongation of the solder is lower than 30%.
Since the solder of the present invention may contain
neither harmful lead nor cadmium, were proposed. The
solders hitherto proposed. however, do not have mechanical
properties as good as conventional Pb—Sn solders. 3.5
Ag—-Sn solder. for example, has a problem of a low tensile
either one or both of Bi and In in the amounts as described
25
strength, though it has a satisfactory elongation. In this
present situation. a solder which does not contain harmful
lead or cadmium and has both a satisfactory high tensile
above, it may be a Sn-Ag-Bi or Sn—-Ag—In ternary‘
alloy or a Sn—Ag—Bi—In quarternary alloy,
When the solder is a Sn—Ag—-Bi ternary alloy without
In, expressions (1) and (2) become as follows:
30
strength and a satisfactory high elongation is desired.
SUMMARY OF THE INVENTION
From these expressions and the aforementioned range of
Ag, the Bi content is greater than 0.8 1 wt % and smaller than
The object of the present invention is to provide a solder
which does not contain harmful elements such as lead and 35 6.4 w %.
cadmium and still has both a tensile strength and an elon
If the Bi content is smaller than 0.81 Wt %. the tensile
gation as high as those of Pb—Sn solders.
The solder of the present invention consists of 1 to 4 wt
% Ag, either one or both of Bi and In of their respective
strength of the solder is lower than 4.0 kgflmmz. If greater
than 6.4 wt %, the elongation of the solder is lower than
30%.
When the solder is Sn-Ag-In ternary alloy without Bi,
expressions (1) and (2) become as follows:
amounts meeting the conditions that the value of expression
(1), A, is equal to or greater than 5.00 and that the value of
expression (2), B, is equal to or less than 6.90, and Sn for the
balance.
45
(2)
By this composition. the solder of the present invention
has a tensile strength equal to or greater than 4.0 kgf/mm2
and an elongation equal to or greater than 30% which are
mechanical properties as good as those of conventional
Pb—Sn solders.
50
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the relationship between the amounts of In
and Bi to be added when the Ag content is 1 wt % (Sn for
the balance).
FIG. 2 shows the relationship between the amounts of In
and Bi to be added when the Ag content is 2 wt % (Sn ?r the
balance Sn).
FIG. 3 shows the relationship between the amounts of In
and Bi to be added when the Ag content is 3 wt % (Sn for
55
From these expressions and the aforementioned range of
Ag, the In content is greater than 1.9 wt % and smaller than
12 wt %.
If the In content is smaller than 1.9 wt %. the tensile
strength of the solder is lower than 4.0. kgflmmz. If greater
than 12 wt %, the elongation of the solder is lower than 30%.
However, it is preferable to set the upper limit of the In
content to 4.0 wt % because In is expensive.
When the solder is a Sn——Ag--Bi—In quarternary alloy.
the Bi content is within the range of 0.81 to 5.0 wt % and the
In content is within the range of 1.9 to 12 wt % from
expressions (1) and (2) and the range of the Ag content.
EXAMPLES
Sn. Ag. Bi, In and Pb were weighed out to prepare
compositions listed in Table 1, each composition being 10
kg in total. These compositions were melted at 300° C. in an
electric furnace in the air using a graphite crucible. After all
FIG. 4 shows the relationship between the amounts of In 65 metals had melted. the molten metals were thoroughly
and Bi to be added when the Ag content is 4 wt % (Sn for
stirred to prevent segregation caused by gravity and cast into
solder pieces of 10 mm in thickness using a mold of 150
the balance).
the balance).
5 ,65 8,5 2 8
mm><60 mm with a height of 150 mm in inner dimensions.
Test samples were cut from the bottom part of the solder '
TABLE l-continued
pieces according to JIS 4 standards with a machine. and their
tensile strength and elongation were measured by the test
method de?ned by the HS Z2241 standards. The results are 5
shown in Table 1. The strength and the elongation of Pb-Sn
eutectic solders and 3.5 Ag—Sn solder are also shown in
Table l for comparison.
Chemical Co
Ag
Bi
4
4
4
1
2
2
ition wt %
3
0
1
Tensile Strength
elongation
Sn
(kgflmmz)
(%)
Hal.
E211.
Bal.
4.7
4.5
4.7
3 1.0
32. 1
30.4
3.9
4.9
3.9
4.9
3.8
37.5
29.4
37.0
28.8
38. 1
Comparative Example
10
TABLE 1
Chemical Co
Ag
Bi
sition wt %
Sn
Tensile Strength
elongation
(lief/1111112)
(‘70)
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