U.S. patent application number 17/417205 was filed with the patent office on 2022-02-10 for soldering alloy, soldering paste, preform solder, soldering ball, wire solder, resin flux cored solder, solder joint, electronic circuit board, and multi-layer electronic circuit board.
This patent application is currently assigned to SENJU METAL INDUSTRY CO., LTD.. The applicant listed for this patent is SENJU METAL INDUSTRY CO., LTD.. Invention is credited to Naoko IZUMITA, Takashi SAITO, Shunsaku YOSHIKAWA.
Application Number | 20220040802 17/417205 |
Document ID | / |
Family ID | 1000005971069 |
Filed Date | 2022-02-10 |
United States Patent
Application |
20220040802 |
Kind Code |
A1 |
SAITO; Takashi ; et
al. |
February 10, 2022 |
SOLDERING ALLOY, SOLDERING PASTE, PREFORM SOLDER, SOLDERING BALL,
WIRE SOLDER, RESIN FLUX CORED SOLDER, SOLDER JOINT, ELECTRONIC
CIRCUIT BOARD, AND MULTI-LAYER ELECTRONIC CIRCUIT BOARD
Abstract
A soldering alloy includes an alloy composition consisting of
13-22 mass % of In, 0.5-2.8 mass % of Ag, 0.5-5.0 mass % of Bi,
0.002-0.05 mass % of Ni, and a balance Sn. A soldering alloy, a
soldering paste, a preform solder, a soldering ball, a wire solder,
a resin flux cored solder and a solder joint, each of which is
composed of the soldering alloy. An electronic circuit board and a
multi-layer electronic circuit board joined by using the solder
joint.
Inventors: |
SAITO; Takashi; (Tokyo,
JP) ; YOSHIKAWA; Shunsaku; (Tokyo, JP) ;
IZUMITA; Naoko; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SENJU METAL INDUSTRY CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
SENJU METAL INDUSTRY CO.,
LTD.
Tokyo
JP
|
Family ID: |
1000005971069 |
Appl. No.: |
17/417205 |
Filed: |
May 11, 2020 |
PCT Filed: |
May 11, 2020 |
PCT NO: |
PCT/JP2020/018837 |
371 Date: |
June 22, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05K 3/3457 20130101;
B23K 2101/42 20180801; C22C 13/00 20130101; H05K 1/0298 20130101;
B23K 35/262 20130101 |
International
Class: |
B23K 35/26 20060101
B23K035/26; C22C 13/00 20060101 C22C013/00; H05K 1/02 20060101
H05K001/02; H05K 3/34 20060101 H05K003/34 |
Foreign Application Data
Date |
Code |
Application Number |
May 27, 2019 |
JP |
2019-098427 |
Claims
1. A soldering alloy comprising an alloy composition consisting of
13-22 mass % of In, 0.5-2.8 mass % of Ag, 0.5-5.0 mass % of Bi,
0.002-0.05 mass % of Ni, and a balance Sn.
2. The soldering alloy according to claim 1, wherein the alloy
composition further contains at least one selected from P, Ge and
Ga in total of 0.09 mass % or less.
3. The soldering alloy according to claim 1, wherein the alloy
composition further contains 0.005-0.1 mass % of Sb.
4. The soldering alloy according to claim 1, wherein the content of
In is 15-20%.
5. The soldering alloy according to claim 4, wherein an upper limit
of the content of In is 17%.
6. The soldering alloy according to claim 1, wherein the content of
Ag is 1.0-2.5%.
7. The soldering alloy according to claim 1, wherein the content of
Bi is 1.0-2.5%.
8. The soldering alloy according to claim 1, wherein the content of
Ni is 0.003-0.04%.
9. The soldering alloy according too claim 1, wherein the content
of In, Ag, Bi, and Ni satisfies the following equation (1),
0.9.ltoreq.(In.times.Ni).times.(Ag+Bi).ltoreq.3.4 (1) wherein, in
the relationship (1), In, Ni, Ag, and Bi represent each content of
the respective elements.
10. The soldering alloy according to claim 1, wherein a solidus
temperature is 160.degree. C. or more and a liquidus temperature is
210.degree. C. or less.
11. The soldering alloy according to claim 10, wherein the solidus
temperature is 165.degree. C. or higher and the liquidus
temperature is 200.degree. C. or lower.
12. A soldering paste consisting of the soldering alloy according
to claim 1.
13. A preform solder consisting of the soldering alloy according to
claim 1.
14. A soldering ball consisting of the soldering alloy according to
claim 1.
15. A wire solder consisting of the soldering alloy according to
claim 1.
16. A resin flux cored solder consisting of the soldering alloy
according to claim 1.
17. A solder joint consisting of a soldering alloy comprising an
alloy composition consisting of 13-22 mass % of In, 0.5-2.8 mass %
of Ag, 0.5-5.0 mass % of Bi, 0.002-0.05 mass % of Ni, and a balance
Sn, wherein the solder joint does not include another soldering
alloy other than the soldering alloy comprising the alloy
composition.
18. An electronic circuit board comprising an electronic part
joined by using the solder joint according to claim 17.
19. The electronic circuit board according to claim 18, further
comprising a high thermal resistance electronic part which has a
higher thermal resistance temperature than the electronic part,
wherein the high thermal resistance electronic part is joined by
using another alloy having a melting point higher than the liquidus
temperature of the soldering alloy included in the solder
joint.
20. The electronic circuit board according to claim 18, further
comprising a low thermal resistance electronic part which has a
lower heat resistance temperature than the electronic part, wherein
the low thermal resistance electronic part is joined by using
another solder joint including another soldering alloy having a
melting point lower than the solidus temperature of the soldering
alloy.
21. A multi-layer electronic circuit board, comprising: a first
board including an electronic part joined by using a solder joint
consisting of a soldering alloy comprising an alloy composition
consisting of 13-22 mass % of In, 0.5-2.8 mass % of Ag, 0.5-5.0
mass % of Bi, 0.002-0.05 mass % of Ni, and a balance Sn, wherein
the solder joint does not include another soldering alloy other
than the soldering alloy; and a second board including a high
thermal resistance electronic part which is laminated on the first
board and has a higher thermal resistance temperature than the
electronic part, wherein the high thermal resistance electronic
part and the second board are joined by using another solder joint
including another soldering alloy having a melting point higher
than the liquidus temperature of the soldering alloy included in
the solder joint.
22. A multi-layer electronic circuit board, comprising: a first
board including an electronic part joined by using the solder joint
according to claim 17; and a second board including a low thermal
resistance electronic part which is laminated on the first board
and has a lower thermal resistance temperature than the electronic
part, wherein the low thermal resistance electronic part and the
second board are joined by using another solder joint including
another soldering alloy having a melting point lower than the
solidus temperature of the soldering alloy included in the solder
joint.
Description
FIELD
[0001] The present invention relates to a soldering alloy of which
a main component is Sn, a use of the soldering alloy, and an
electronic circuit board in which the soldering alloy is used.
BACKGROUND
[0002] In recent years, lead-free soldering alloy that does not
contain lead has been used in consideration of environment.
Examples of the lead-free soldering alloy include SAC305
(Sn-3.0Ag-0.5Cu). A melting point of SAC305 is about 220.degree. C.
During a soldering with SAC305, a peak temperature of a reflow oven
is generally set to an intermediate temperature range of about
250.degree. C.
[0003] On the other hand, in order to suppress thermal loads on a
miniaturized electronic part, the soldering performed in a low
temperature range has also been required. In the soldering in the
low temperature range, the lead-free soldering alloy having a low
melting point is used. Such the soldering alloy include Sn-58Bi and
Sn-521n. The melting point of Sn-58Bi is about 140.degree. C. That
of Sn-52In is about 120.degree. C. During the soldering performed
in the low temperature range, the peak temperature of the reflow
oven is generally set to 150-160.degree. C.
[0004] Incidentally, in a step-soldering where the soldering is
performed in multiple stages, the soldering is expected to be
performed at an intermediate temperature range between the
above-mentioned intermediate temperature and low temperature.
Examples of prior arts related to the lead-free soldering alloy
having the melting point in such the intermediate temperature range
include Patent Document 1. Patent Document 1 discloses a lead-free
soldering alloy consisting of three elements of Sn, Ag and In. This
conventional soldering alloy has a solidus temperature of
167-212.degree. C. and a liquidus temperature of 179-213.degree.
C.
[0005] Examples of the prior arts related to the present
application include Patent Document 2. Patent Document 2 discloses
a lead-free soldering alloy consisting of Sn, In, Ag and Cu. Patent
Document 2 discloses several examples in which these essential
elements are different in content. Each of the solidus temperature
of these examples is about 120.degree. C.
[0006] Another example of the prior art related to the present
application includes Patent Document 3. Patent Document 3 discloses
a lead-free soldering alloy consisting of 0.5 to 5 mass % of Ag,
0.5 to 20 mass % of In, 0.1 to 3 mass % of Bi, 3 mass % or less of
an additive element, and balance Sn. The additive element is at
least one element selected from Sb, Zn, Ni, Ga, Ge and Cu. Patent
Document 3 discloses examples of the alloys that contain 0.5 and
1.5 weight % of Ni as the additive element.
CITATION LIST
Patent Literature
[0007] [PTL 1] JPH6-15476A [0008] [PTL 2] JP2013-198937A [0009]
[PTL 3] JP2004-188453A
SUMMARY
Technical Problem
[0010] The lead-free soldering alloy that simply has the low
melting point is not suitable for a step-soldering including the
soldering performed in the above-mentioned intermediate temperature
range. That is, the property that melts at a temperature below the
melting point of the low-temperature soldering alloy represented by
Sn-58Bi leads to a possibility of being re-melted in the soldering
step of the low-temperature soldering alloy. Therefore, the
soldering alloy of Patent Document 2 having the solidus temperature
lower than the melting point of the low-temperature soldering alloy
cannot be subjected to the soldering step that is different from
the soldering step of the said low-temperature soldering alloy.
[0011] In addition, the soldering alloy of Patent Document 3 has
not been developed focusing on its melting point. Therefore, it is
not known whether or not the soldering alloy of Patent Document 3
is suitable for the soldering performed in the above-mentioned
intermediate temperature range.
[0012] It is important that the soldering alloy suitable for such
the step-soldering not only meets the requirement on the melting
point but also has excellent in a mechanical reliability.
Therefore, there is room to develop the soldering alloy focusing on
these viewpoints.
[0013] One object of the present invention is to provide a
soldering alloy which is suitable for the step-soldering including
the soldering performed in the intermediate to low temperature
range and which has excellent in the mechanical reliability.
Another object of the present invention is to provide a soldering
paste, a preform solder, a soldering ball, a wire solder, a resin
flux cored solder and a solder joint including such the soldering
alloy. It is yet another object of the present invention to provide
an electronic circuit board and a multi-layer electronic circuit
board to which such the soldering alloy is applied.
Solution to Problem
[0014] Inventors of the present invention started with a Sn--In
alloy consisting of two elements, Sn and In. When a content of In
exceeds a certain amount, this alloy forms an intermetallic
compound phase called a .gamma. phase composed of In and Sn.
However, since this .gamma. phase is brittle, there is a risk of
lowering a ductility of the soldering alloy. Therefore, the content
of In was set around 20 weight % such that a desired mechanical
property could be achieved without decreasing the ductility.
[0015] After determining the content of In, an additive element to
a soldering alloy having an appropriate melting point that is
subjected to the soldering with the intermediate to low temperature
range was investigated. Consequently, it was found that not only
the melting point is adjusted to the appropriate range but also the
mechanical property is improved by adding an appropriate amount of
Ag, Bi and Ni to the Sn--In based alloy. From the above
investigation, it was found that a soldering alloy obtained by
adding an appropriate amount of five elements of Sn, In, Ag, Bi and
Ni is an optimum soldering alloy for solving the above-described
problems.
[0016] A first invention is a soldering alloy having the following
features.
[0017] The soldering alloy includes an alloy composition consisting
of 13-22 mass % of In, 0.5-2.8 mass % of Ag, 0.5-5.0 mass % of Bi,
0.002-0.05% of Ni, and a balance of Sn.
[0018] A second invention has the following features in the first
invention.
[0019] The alloy composition further contains, at least one
selected from P, Ge and Ga in total of 0.09 mass % or less.
[0020] A third invention has the following features in the first or
second invention.
[0021] The alloy composition further contains 0.005-0.1 mass % of
Sb.
[0022] A fourth invention has the following features in any one of
the first to third inventions.
[0023] The content of In is 15-20%.
[0024] A fifth invention has the following features in the fourth
invention.
[0025] An upper limit of the content of In is 17%.
[0026] A sixth invention has the following features in any one of
the first to fifth inventions.
[0027] The content of Ag is 1.0-2.5%.
[0028] A seventh invention has the following features in any one of
the first to sixth inventions.
[0029] The content of Bi is 1.0-2.5%.
[0030] An eighth invention has the following features in any one of
the first to seventh inventions.
[0031] The content of Ni is 0.003-0.04%.
[0032] A ninth invention has the following features in any one of
the first to eighth inventions.
[0033] The content of In, Ag, Bi, and Ni satisfies the following
relationship (1).
0.9.ltoreq.(In.times.Ni).times.(Ag+Bi).ltoreq.3.4 (1)
[0034] In the relationship (1), In, Ni, Ag, and Bi represent each
content of the respective elements.
[0035] A tenth invention further has the following features in any
one of the first to ninth inventions.
[0036] A solidus temperature of the soldering alloy is 160.degree.
C. or more.
[0037] A liquidus temperature of the soldering alloy is 210.degree.
C. or less.
[0038] An eleventh invention further has the following features in
the tenth invention.
[0039] The solidus temperature is 165.degree. C. or higher.
[0040] The liquidus temperature is 200.degree. C. or less.
[0041] A twelfth invention is a soldering paste.
[0042] The soldering paste consists of the soldering alloy in any
one of the first to eleventh inventions.
[0043] A thirteenth invention is a preform solder.
[0044] The preform solder consists of the soldering alloy in any
one of the first to the eleventh inventions.
[0045] A fourteenth invention is a soldering ball.
[0046] The soldering ball consists of the soldering alloy in any
one of the first to eleventh inventions.
[0047] A fifteenth invention is a wire solder.
[0048] The wire solder consists of the soldering alloy in any one
of the first to eleventh inventions.
[0049] A sixteenth invention is a resin flux cored solder.
[0050] The resin flux cored solder consists of the soldering alloy
in any one of the first to eleventh inventions.
[0051] A seventeenth invention is a solder joint.
[0052] The solder joint includes the soldering alloy in any one of
the first to eleventh inventions (the solder joint does not include
a soldering alloy other than the soldering alloy in any one of the
first to eleventh inventions).
[0053] An eighteenth invention is an electronic circuit board.
[0054] The electronic circuit board is joined by using the solder
joint of the seventeenth invention.
[0055] A nineteenth invention further has the following features in
the eighteenth invention.
[0056] The electronic circuit board further includes a high thermal
resistance electronic part which has a higher thermal resistance
temperature than the electronic part.
[0057] The high thermal resistance electronic part is joined to the
electronic circuit board by using another solder joint.
[0058] The another solder joint includes another soldering alloy
having a melting point higher than the liquidus temperature of the
soldering alloy included in the solder joint.
[0059] A twentieth invention further has the following features in
the eighteenth invention.
[0060] The electronic circuit board further includes a low thermal
resistance electronic part which has a lower thermal resistance
temperature than the electronic part.
[0061] The low thermal resistance electronic part is joined to the
electronic circuit board by using another solder joint.
[0062] The another solder joint includes another soldering alloy
having a melting point lower than the solidus temperature of the
soldering alloy included in the solder joint.
[0063] A twenty-first invention is a multi-layer electronic circuit
board.
[0064] The multi-layer electronic circuit board includes a first
board and a second board.
[0065] The first board includes an electronic part joined by using
the solder joint of the seventeenth invention.
[0066] The second board is laminated on the first board. The second
board includes a high thermal resistance electronic part which has
a higher thermal resistance temperature than the electronic
part.
[0067] The high thermal resistance electronic part and the second
board are joined by using another solder joint.
[0068] The another solder joint includes another soldering alloy
having a melting point higher than the liquidus temperature of the
soldering alloy included in the solder joint.
[0069] A twenty-second invention is a multi-layer electronic
circuit board.
[0070] The multi-layer electronic circuit board includes a first
board and a second board.
[0071] The first board includes an electronic part joined by using
the solder joint of the seventeenth invention.
[0072] The second board is laminated on the first board. The second
board includes a low thermal resistance electronic part which has a
lower thermal resistance temperature than the electronic part.
[0073] The low thermal resistance electronic part and the second
board are joined by using another solder joint.
[0074] The another solder joint includes another soldering alloy
having a melting point lower than solidus temperature of soldering
alloy included in the solder joint.
BRIEF DESCRIPTION OF DRAWINGS
[0075] FIG. 1 is a diagram showing a relationship between a content
of In in Sn--In based alloy and a melting point thereof;
[0076] FIG. 2 is a diagram showing a relationship between a content
of Ag in Sn-20In-Ag based alloy and the melting point thereof;
[0077] FIG. 3 is a diagram showing a relationship between a content
of Bi in Sn-20In--Bi based alloy and the melting point thereof;
[0078] FIG. 4 is a schematic view showing a first example of an
electronic circuit board;
[0079] FIG. 5 is a schematic view showing a second example of the
electronic circuit board;
[0080] FIG. 6 is a schematic diagram showing a first example of a
multi-layer electronic circuit board;
[0081] FIG. 7 is a schematic diagram showing a first example of a
multi-layer electronic circuit board;
[0082] FIG. 8 is a diagram including cross-sectional SEM
photographs of Example 2 and Referential example 2;
[0083] FIG. 9 is a diagram including cross-sectional SEM
photographs of Example 3 and Referential example 4;
[0084] FIG. 10 is a diagram including cross-sectional SEM
photographs of Example 2 and Referential example 2; and
[0085] FIG. 11 is a diagram including cross-sectional SEM
photographs of Example 3 and Referential example 4.
DESCRIPTION of EMBODIMENTS
[0086] The present invention is described in detail below. In this
specification, "%" of an element contained in a soldering alloy
represents "mass %" unless otherwise specified. In addition, in
this specification, the intermediate to low temperature range
represents a temperature range from 160 to 210.degree. C. An
intermediate temperature range represents a temperature range above
an upper limit of the intermediate to low temperature range (i.e.,
210.degree. C.). A low temperature range represents a temperature
range below a lower limit of the intermediate to low temperature
range (i.e., 160.degree. C.). In addition, in this specification, a
melting point represents a solidus temperature or a liquidus
temperature.
1. Soldering Alloy
[0087] The soldering alloy according to the present invention
includes an alloy composition consisting of 13-22% of In, 0.5-2.8%
of Ag, 0.5-5.0% of Bi, 0.002-0.05% of Ni, and a balance Sn.
Hereinafter, the elements constituting this alloy composition and
their contents will be described.
1.1 In: 13-22%
[0088] In has a property of lowering the melting point of the
soldering alloy. FIG. 1 is a graph showing a relationship between
content of In in a Sn--In based alloy and the melting point
thereof. As shown in FIG. 1, the melting point of the Sn--In based
alloy tends to decrease as the content of In increases. However,
when the content of In is more than 20%, the solidus temperature
starts to decrease rapidly. When the content of In is greater than
25%, the solidus temperature drops to about 117.degree. C.
Therefore, the soldering alloy based on an alloy of which the
content of In is more than 25% is not suitable as the soldering
alloy for the soldering performed in the intermediate temperature
range. In this respect, if an upper limit of the content of In is
about 22%, the solidus temperature condition is satisfied.
Therefore, this upper limit is 22%. From a viewpoint to satisfy the
condition on the solidus temperature, a preferable upper limit is
21%, and a more preferable upper limit is 20%.
[0089] In the intermediate to low temperature range, the alloy of
which the content of In is less than 5% forms a Sn-rich phase
called a .beta.-Sn phase. When the content of In is greater than
5%, the alloy forms a phase of InSn.sub.4 compound called a .gamma.
phase. This .gamma. phase is stably formed when the content of In
is 5-25%. However, when the content of In decreases, there is a
risk that a phase transformation occurs between the .gamma. phase
and the .beta.-Sn phase in accompany with temperature change. When
the phase transformation occurs, there is a risk that a mechanical
reliability of the alloy will decrease because a deformation of the
alloy will occur due to changes in volume. In this respect, when
the lower limit of the content of In is 13%, this transformation
can be suppressed. Therefore, this lower limit is 13%. From the
viewpoint of the mechanical reliability, a preferable lower limit
is 15%.
[0090] In addition, the .gamma. phase has a brittle property as
compared with SAC305. Therefore, if the content of In in the
.gamma. phase is increased, there is a risk that ductility of the
soldering alloy may be lowered and the mechanical reliability of
the soldering alloy may be lowered. Therefore, from the viewpoint
to ensure the ductility, it is preferable that the upper limit of
the content of In is not too large. A specific preferred upper
limit is 17%.
1.2 Ag: 0.5-2.8%
[0091] Ag has a property of changing the melting point of the
soldering alloy. FIG. 2 is a graph showing a relationship between
the content of Ag in a Sn-20In-Ag based alloy and the melting point
thereof. As shown in FIG. 2, the liquidus temperature is located in
the intermediate to low temperature range. When the content of Ag
is 2.8% or less, this liquidus temperature tends to decrease as the
content increases. When the content of Ag is greater than 2.8%, the
liquidus temperature will start to rise. Therefore, when the
content of Ag is more than 2.8%, it may prevent the melting point
from decreasing due to the addition of In. Therefore, the upper
limit of the content of Ag is 2.8%. From the viewpoint to suppress
the increase in the liquidus temperature, the preferable upper
limit is 2.5%.
[0092] Ag and In form a Ag.sub.2In compound. When the phase of this
intermetallic compound is precipitated, the modification of the
soldering alloy can be suppressed. From the viewpoint to exert this
effect, the lower limit of the content of Ag is 0.5%. From the
viewpoint to coarsen the precipitate and to enhance this effect,
the preferable lower limit is 1.0%.
1.3 Bi: 0.5-5.0%
[0093] Bi has a property of lowering the melting point of the
soldering alloy. FIG. 3 is a graph showing a relationship between
content of Bi in a Sn-20In--Bi based alloy and the melting point
thereof. As shown in FIG. 3, the liquidus temperature is located in
the intermediate to low temperature range. This liquidus
temperature tends to decrease as the content of Bi increases.
However, it is not desirable that the melting point of the
soldering alloy is too low due to the increase in the content of
Bi. Therefore, the upper limit of the content of Bi is 5.0%. From
the viewpoint to suppress the decrease in the liquidus temperature,
the preferable upper limit is 2.5%.
[0094] Bi is dissolved in Sn in a certain amount. The solid
solution of Bi makes it possible to suppress modification of
soldering alloy. From the viewpoint to exert this effect, the lower
limit of the content of Bi has been set to 0.5%. The preferable
lower limit is 1.0% In addition, an excessive solid solution of Bi
may reduce the ductility of the soldering alloy. From this
viewpoint, it is preferable that the upper limit of the content of
Bi is not too large. The specific preferred upper limit is
2.5%.
1.4 Ni
[0095] Ni has a property of fining an alloy organization. When the
alloy organization is fined, the mechanical property of the
soldering alloy is improved. From the viewpoint to exert this
effect, the lower limit of the content of Ni has been set to
0.002%. The preferable lower limit is 0.003% and the more
preferable lower limit is 0.004% On the other hand, an excessive
miniaturization by Ni has a risk to lower the ductility of the
soldering alloy. In addition, an excessive addition of Ni raise the
liquidus temperature of the soldering alloy. From this viewpoint,
it is desirable that the content of Ni is not too high. Therefore,
the upper limit of the content of Ni is 0.05%. The preferable upper
limit is 0.04% and the more preferable upper limit is 0.03%.
1.5 Sn: Balance
[0096] A balance of the soldering alloy of the present invention is
composed of S n. Further, in addition to the essential elements
described above, an unavoidable impurity may be contained in the
soldering alloy Even if the unavoidable impurity is contained, it
does not affect the effects due to the soldering alloy Examples of
the unavoidable impurity include Pb and As.
1.6 Relationship in Content
[0097] In the soldering alloy according to the present invention,
each content of In, Ag, Bi and Ni is as described above. However,
from results of Examples described later, it is preferable that a
relationship of these contents satisfies the following relationship
(1).
0.9.ltoreq.(In.times.Ni).times.(Ag+Bi).ltoreq.3.4 (1)
[0098] In the relationship (1), In, Ni, Ag, and Bi represent each
content of the respective elements (mass %).
[0099] The soldering alloy of which the content of In, Ag, Bi and
Ni is within the above described range and also satisfies the
relationship (1) is preferred from the viewpoint of the melting
point and the mechanical property. From the viewpoint of an
intended melting point and mechanical property, an upper limit
value of the relationship (1) is more preferably 2.55.
2. Other Additive Elements
[0100] In addition to the essential elements described above, the
following element may be optionally contained in the soldering
alloy according to the present invention. In this instance, Sn
constitutes the balance of the soldering alloy to which the
optional element has been added.
2.1 at Least One Selected from P, Ge and Ga: 0.09% or Less
[0101] P, Ge or Ga have properties of suppressing an oxidation of
Sn and improving a wettability of the soldering alloy. Therefore,
these elements are optionally added to the soldering alloy
according to the present invention. In particular, when the
soldering alloy according to the present invention is used as a
preform solder, at least one selected from these elements is
preferably added because it is possible to suppress a discoloration
of a surface of the soldering alloy.
[0102] When the at least one selected from these elements is added,
the upper limit of the content is 0.09% in total. When the total
content exceeds 0.09%, a fluidity of the soldering alloy on the
solder surface may be inhibited. Each content of the respective
elements is not particularly limited. However, a preferable content
of P is 0.005-0.06% and a more preferable content is 0.005-0.01%.
The preferable content of Ge is 0.003-0.06% and the more preferable
content is 0.003-0.01%. The preferable content of Ga is 0.005-0.06%
and the more preferable content is 0.005-0.01%.
2.2 Sb: 0.005-0.1%
[0103] Likewise Ni, Sb has a property of fining the alloy
organization. Therefore, Sb is optionally added to the soldering
alloy according to the present invention When Sb is added, its
content is 0.005-0.1%. When the content of Sb is less than 0.005%,
the miniaturization effect is not exerted. When the content of Sb
is more than 0.1%, the liquidus temperature of the soldering alloy
is increased.
3. Melting Point of the Soldering Alloy
[0104] The melting point of the soldering alloy according to the
present invention is not particularly limited as long as it is
within the intermediate to low temperature range. However, the
solidus temperature of the soldering alloy according to the present
invention is preferably 160.degree. C. or more. When the solidus
temperature is above 160.degree. C., the following effect is
expected in the step-soldering including the soldering performed in
the intermediate to low temperature range. That is, it is possible
to prevent the soldering alloy according to the present invention
which has been subjected to the soldering and has been soldered
from being re-melted during the soldering performed for a low
temperature soldering alloy. Examples of the low temperature
soldering alloy include Sn-58Bi and Sn-521n. The preferable solidus
temperature is 165.degree. C. or more.
[0105] Further, the liquidus temperature of the soldering alloy
according to the present invention is preferably 210.degree. C. or
less. When the liquidus temperature is not exceed 210.degree. C.,
the following effect is expected in the step-soldering including
the soldering performed in the intermediate to low temperature
range. That is, it is possible to prevent an intermediate or high
temperature soldering alloy which has been soldered from being
re-melted during the soldering performed for the soldering alloy
according to the present invention. Examples of the medium
temperature soldering alloy include SAC305. Examples of the high
temperature soldering alloy include a soldering alloy of Sn-90Pb.
The preferable liquidus temperature is 200.degree. C. or less.
4. End-Usage of Soldering Alloy
4.1 Soldering Paste
[0106] The soldering alloy according to present invention is
suitably used as a soldering paste. The soldering paste is produced
by mixing a powdery soldering alloy with a flux containing a
Rosin-based resin, an activator, a solvent, or the like. The flux
is not particularly limited as long as it is commonly used in the
art, and materials used therefor and blending ratio thereof are not
particularly limited. The blending ratio (mass ratio) of the
powdery soldering alloy and the flux is generally 90:10. However,
this blending ratio is appropriately adjusted according to an
end-usage of the soldering paste.
4.2 Preform Solder
[0107] The soldering alloy according to the present invention is
also suitably used as a preform solder molded into a ribbon-shape,
a disk-shape, a washer-shape, a tip-shape, or a ring-shape. The
preform solder is produced by methods commonly known in the art.
The shape of the preform solder is not limited to the above
described shapes, and may be appropriately changed according to its
end-usage. The preform solder may include the flux therein. The
preform solder may be coated with the flux on its surface.
4.3 Soldering Ball
[0108] The soldering alloy according to the present invention is
also suitably used as a soldering ball. The soldering ball is used
to form a hemispherical bump in a semiconductor package such as
ball-grid arrays (BGAs). The soldering ball is produced by methods
commonly known in the art. When the soldering alloy according to
the present invention is used as the soldering ball, its diameter
is preferably in a range of 1-1000 .mu.m. Further, a sphericity is
preferably 0.90 or more, more preferably 0.95 or more, and most
preferably 0.99 or more.
4.4 Wire Solder and Resin Flux Cored Solder
[0109] The soldering alloy according to the present invention is
also suitably used as a wire solder processed into a wire. Further,
the wire solder is also suitably used as a resin flux cored solder
having the flux therein. The wire solder and resin flux cored
solder are suitable for the soldering with a solder iron. The wire
solder and resin flux cored solder are produced in a manner
generally known in the art.
4.5 Solder Joint
[0110] The soldering alloy according to the present invention is
also suitably used as a solder joint. The solder joint connects an
electronic part such as an integrated circuit (IC) chip and a
printed board (e.g., an interposer) in a semiconductor package.
Alternatively, the solder joint joints to connect the semiconductor
package and the printed circuit board. The solder joint is a
connecting portion formed at a bonding portion. The solder joint is
formed under common soldering conditions.
5. Electronic Circuit Board
[0111] When the soldering alloy according to the present invention
functions as the solder joint, an electronic circuit board where an
electronic part is joined via this solder joint corresponds to an
electronic circuit board according to the present invention.
5.1 Single-Layer Electronic Circuit Board
[0112] FIG. 4 is a schematic diagram illustrating a first example
of the electronic circuit board according to the present invention.
A board 10 shown in FIG. 4 includes electronic parts 11 and 12. The
board 10 is, for example, a printed-circuit board. The electronic
parts 11 and 12 are, for example, IC chips. A maximum use
temperature of the electronic part 11 is within the intermediate to
low temperature range. The maximum use temperature of the
electronic part 12 is above the lower limit of the intermediate
temperature range (i.e., 210.degree. C.). That is, a thermal
resistance of the electronic part 12 is higher than that of the
electronic part 11.
[0113] In the first example, the electronic part 11 is joined to
the board 10 via a solder joint 13. The solder joint 13 is composed
of the soldering alloy according to the present invention. On the
other hand, the electronic part 12 is joined to the board 10 via a
solder joint 14. The solder joint 14 is composed of the
intermediate temperature soldering alloy or the high-temperature
soldering alloy. That is, the solder joint 14 is composed of
another soldering alloy having the melting point (more precisely,
the solidus temperature) higher than the liquidus temperature of
the soldering alloy according to the present invention.
[0114] FIG. 5 is a schematic diagram illustrating a second example
of the electronic circuit board according to the present invention.
Note that the electronic part 11 and the solder joint 13 shown in
FIG. 5 are common to those shown in FIG. 4. Therefore, the
descriptions for these elements are omitted. A board 20 shown in
FIG. 5 includes an electronic part 21. The board 20 is, for
example, a printed-circuit board. The electronic part 21 is, for
example, an IC-chip. The maximum use temperature of the electronic
part 21 is below the lower limit of the low temperature range
(i.e., 160.degree. C.). That is, the thermal resistance of the
electronic part 21 is lower than that of the electronic part
11.
[0115] In the second example, the electronic part 21 is joined to
the board 20 via a solder joint 22. The solder joint 22 is composed
of a low temperature soldering alloy. That is, the solder joint 22
is composed of another soldering alloy having the melting point
(more precisely, the liquidus temperature) lower than the solidus
temperature of the soldering alloy according to the present
invention.
5.2 Multi-Layer Electronic Circuit Board
[0116] FIG. 6 is a schematic diagram illustrating a first example
of a multi-layer electronic circuit board according to the present
invention. A board 30 shown in FIG. 6 is a multi-layer board in
which aboard 32 and an interposer 33 are laminated on aboard 31.
The board 31 is, for example, a printed-circuit board. The board 32
is, for example, a packaging board. The board 32 includes an
interposer 33 and an electronic part 34. In the present invention,
the board 32 and the interposer 33 corresponds to a first board or
a second board. The interposer 33 includes an electronic part
35.
[0117] The electronic parts 34 and 35 are, for example, integrated
circuit chips. The maximum use temperature of the electronic part
34 is above the lower limit of the intermediate temperature range.
The maximum use temperature of the electronic part 35 is within the
intermediate to low temperature range. That is, the thermal
resistance of the electronic part 34 is higher than that of the
electronic part 35.
[0118] In the first example, the electronic part 35 is joined to
the interposer 33 via a solder joint 36. The solder joint 36 is
composed of the soldering alloy according to the present invention.
On the other hand, the electronic part 34 is joined to the board 32
via a solder joint 37. The solder joint 37 is also used for a
junction between the boards 31 and 32 and the junction between the
board 32 and the interposer 33. The solder joint 37 is composed of
the intermediate and high soldering alloy. That is, the solder
joint 37 is composed of another soldering alloy having the melting
point (more precisely, the solidus temperature) higher than
liquidus temperature of the soldering alloy according to the
present invention.
[0119] FIG. 7 is a schematic diagram illustrating a second example
of the multi-layer electronic circuit board according to the
present invention. Note that the boards 31 and 32 and the
interposer 33 shown in FIG. 7 are common to those shown in FIG. 6.
Therefore, the descriptions for these elements are omitted. A board
40 shown in FIG. 7 includes an electronic part 41. The interposer
33 includes an electronic part 42.
[0120] The electronic parts 41 and 42 are, for example, integrated
circuit chips. The maximum use temperature of the electronic part
41 is within the intermediate to low temperature range. The maximum
use temperature of the electronic part 42 is below the lower limit
of the low temperature range. That is, the thermal resistance of
the electronic part 42 is lower than that of the electronic part
41.
[0121] In the second example, the electronic part 41 is joined to
the board 32 via a solder joint 43. The solder joint 43 is composed
of the soldering alloy according to the present invention. The
solder joint 43 is also used for the junction between the boards 31
and 32 and the junction between the board 32 and the interposer 33.
On the other hand, the electronic part 42 is joined to the
interposer 33 via a solder joint 44. The solder joint 44 is
composed of the low-temperature soldering alloy. That is, the
solder joint 44 is composed of another soldering alloy having the
melting point (more precisely, the solidus temperature) lower than
the liquidus temperature of the soldering alloy according to the
present invention.
6. Others
[0122] In the step soldering, the soldering by using a soldering
alloy having a relatively higher melting point is performed
earlier. The soldering by using a soldering alloy having a
relatively lower melting point is performed later. The step
soldering is performed using, for example, a reflow method. In the
reflow soldering, it is preferable to raise an ambient temperature
to a temperature about 5 to 20.degree. C. higher than the liquidus
temperature of the soldering alloy to be subjected to the
soldering. Then, it is preferred to cool the ambient temperature at
2-3.degree. C./sec. By performing such the reflow soldering, the
miniaturization of the alloy organization is enhanced. Other
bonding conditions are appropriately adjusted according to the
soldering alloy and properties of bonding objects.
7. Examples
[0123] A soldering alloy consisting of alloy composition shown in
Table 1 was prepared and the melting point of soldering alloy was
measured. The reliability of these soldering alloy was evaluated by
a shear test with cryogenic cycles.
7.1 Melting Point
[0124] Solidus temperature and liquidus temperature were carried
out by the same DSC (Differential scanning calorimetry) method as
JISZ 3198-1 measuring method. Samples of which the solidus
temperature are above 160.degree. C. were evaluated as "GD",
whereas those of which the solidus temperature are lower than
160.degree. C. were evaluated as "PR". Samples with solidus
temperature above 165.degree. C. were evaluated as "EC". Samples
with liquidus temperature below 210.degree. C. were evaluated as
"GD". Samples higher than 210.degree. C. were evaluated as "PR".
Samples with liquidus temperature below 200.degree. C. were
evaluated as "EC".
7.2 Shear Test with Cryogenic Cycles
[0125] Solder alloy was atomized to give a solder powder. Solder
powder was mixed with fluxes to produce a soldering paste. This
soldering paste was printed on a 0.8-mm-thick printed board
(material: FR-4) using a 100-.mu.m-thick metal mask. The BGA
component was mounted on the print board using a mounter. Then,
reflow soldering was performed at a maximum temperature of
200.degree. C. for a holding time of 60 seconds to obtain board
samples.
[0126] Board samples were placed in a heat cycle tester set at low
temperature -40.degree. C., high temperature+100.degree. C., and
holding time of 10 minutes and removed at 1000 cycles. Thereafter,
this test board was measured for shear strength (N) by a shear
strength measuring device (STR-1000 manufactured by RHESCA Co.,
Ltd.) under a condition of 6 mm/sec. Samples having a shear
strength of 30.00N or more were evaluated as "GD" by determining
that they are at a level which can be used without problems in
practical use. Samples with a shear strength of less than 30.00N
were evaluated as "PR". Samples for which the melting point was
evaluated as "PR" were excluded from shear test.
[0127] The evaluation results are shown in Table 1 and Table 2.
TABLE-US-00001 TABLE 1 Sn In Ag Bi Ni Other elements (In*Ni)*(Ag +
Bi) Solidus Liquidus Shear test Ex. 1 Balance 13 2.5 3 0.02 1.43 EC
EC GD Ex. 2 Balance 15 2.5 2 0.02 1.35 EC EC GD Ex. 3 Balance 17
2.5 1.5 0.02 1.36 EC EC GD Ex. 4 Balance 20 1 1 0.05 2 GD EC GD Ex.
5 Balance 21 0.5 0.5 0.05 1.05 GD EC GD Ex. 6 Balance 17 0.5 1.5
0.02 0.68 EC EC GD Ex. 7 Balance 17 1 1.5 0.02 0.85 EC EC GD Ex. 8
Balance 17 2 1.5 0.02 1.19 EC EC GD Ex. 9 Balance 17 2.8 1.5 0.02
1.462 EC EC GD Ex. 10 Balance 18 1.5 0.5 0.04 1.44 EC EC GD Ex. 11
Balance 17 2.5 2 0.02 1.53 EC EC GD Ex. 12 Balance 14 1 5 0.03 2.52
EC EC GD Ex. 13 Balance 17 2.5 1.5 0.002 0.136 EC EC GD Ex. 14
Balance 17 2.5 1.5 0.005 0.34 EC EC GD Ex. 15 Balance 17 2.5 1.5
0.05 3.4 EC EC GD Ex. 16 Balance 17 2.5 1.5 0.02 P: 0.005 1.36 EC
EC GD Ex. 17 Balance 17 2.5 1.5 0.02 Ge: 0.003 1.36 EC EC GD Ex. 18
Balance 17 2.5 1.5 0.02 Ga: 0.005 1.36 EC EC GD Ex. 19 Balance 17
2.5 1.5 0.02 P: 0.01 1.36 EC EC GD Ex. 20 Balance 17 2.5 1.5 0.02
Ge: 0.01 1.36 EC EC GD Ex. 21 Balance 17 2.5 1.5 0.02 Ga: 0.01 1.36
EC EC GD Ex. 22 Balance 17 2.5 1.5 0.02 P: 0.005 1.36 EC EC GD Ge:
0.005 Ex. 23 Balance 17 2.5 1.5 0.02 Sb: 0.005 1.36 EC EC GD Ex. 24
Balance 17 2.5 1.5 0.02 Sb: 0.1 1.36 EC EC GD Ex. 25 Balance 15 2.5
1 5 0.015 0.9 EC EC GD Ex. 26 Balance 17 2.5 1.5 0.02 P: 0.03 1.36
EC EC GD Ex. 27 Balance 17 2.5 1.5 0.02 Ge: 0.03 1.36 EC EC GD Ex.
28 Balance 17 2.5 1.5 0.02 Ga: 0.03 1.36 EC EC GD Ex. 29 Balance 17
2.5 1.5 0.02 P: 0.06 1.36 EC EC GD Ex. 30 Balance 17 2.5 1.5 0.02
Ge: 0.06 1.36 EC EC GD Ex. 31 Balance 17 2.5 1.5 0.02 Ga: 0.06 1.36
EC EC GD Ex. 32 Balance 17 2.5 1.5 0.02 P: 0.09 1.36 EC EC GD Ex.
33 Balance 17 2.5 1.5 0.02 Ge: 0.09 1.36 EC EC GD Ex. 34 Balance 17
2.5 1.5 0.02 Ga: 0.09 1.36 EC EC GD Ex. 35 Balance 17 2.5 1.5 0.02
P: 0.04 1.36 EC EC GD Ge: 0.05 Ex. 36 Balance 17 2.5 1.5 0.02 Ge:
0.02 1.36 EC EC GD Ga: 0.03 Ex. 37 Balance 17 2.5 1.5 0.02 P: 0.01
1.36 EC EC GD Ga: 0.01
TABLE-US-00002 TABLE 2 Other Sn In Ag Bi Ni elements (In*Ni)*(Ag +
Bi) Solidus Liquidus Shear Test Ref. 1 Balance 20 2.8 -- PR EC --
Ref. 2 Balance 15 2.5 2 -- EC EC PR Ref. 3 Balance 16 2.5 2 -- EC
EC PR Ref. 4 Balance 17 2.5 1.5 -- EC EC PR Ref. 5 Balance 8 2 1.5
0.01 0.28 GD PR -- Ref. 6 Balance 25 2 1.5 0.01 0.875 PR GD -- Ref.
7 Balance 15 2 1.5 0.3 15.75 GD PR -- Ref. 8 Balance 8 3.5 0.5 0.5
16 GD PR -- Ref. 9 Balance 12 3.5 0.5 1.5 72 GD PR -- Ref. 10
Balance 12 2 2 1 46 GD PR -- Ref. 11 Balance 12 2.8 2 1 57.6 GD PR
-- Ref. 12 Balance 12 2 1 2 72 GD PR -- Ref. 13 Balance 12 2.8 1 2
91.2 GD PR -- Ref. 14 Balance 18 2 2 1 72 GD PR -- Ref. 15 Balance
18 2.8 2 1 86.4 GD PR -- Ref. 16 Balance 18 2 1 2 108 GD PR -- Ref.
17 Balance 18 2.8 1 2 136.8 GD PR --
[0128] From the results in the melting point of Examples 1-37, it
was found that each of these examples satisfied the condition with
respect to the melting point. Example 1 had the solidus temperature
of 180.degree. C. and the liquidus temperature of 196.degree. C.
Example 2 had the solidus temperature of 173.degree. C. and the
liquidus temperature of 195.degree. C. Example 3 had the solidus
temperature of 167.degree. C. and the liquidus temperature of
191.degree. C. These results prove that the intended melting point
was realized by adding an appropriate amount of In, Ag and Bi
having the property of lowering the melting point of Sn as a main
component. From the shear test results, it was also found that
these examples were excellent in the cold-heat cycling resistance.
These results prove that the intended mechanical property was
realized by adding an appropriate amount of Ag, Bi and Ni that
improves the mechanical property.
[0129] The result in the melting point of Referential example 1
showed that the solidus temperature of Referential example 1 was
154.degree. C., being lower than 160.degree. C. This result
indicates that the solidus temperature continues to decrease as the
content of Ag increases.
[0130] The results in the melting point and the shear strength of
Referential examples 2-4 indicate that these referential examples
are inferior in the cold-cycle resistance, although their melting
points are well evaluated. The results in the shear strength
indicate that absence of Ni may have an effect.
[0131] The results in the melting point of Referential examples 5,
8-13 indicate that these referential examples had the liquidus
temperature above 210.degree. C. These results indicate that the
liquidus temperature is not sufficiently lowered when In was added
in a small amount. The results in the melting point of Referential
example 8-13 indicate that the liquidus temperature may be
increased when In was adding in a large amount. This possibility is
supported by the fact that the results in the liquidus temperature
of Referential examples 7, 14-17 and those of Referential examples
8-13 were the same.
[0132] The result in the melting point of Referential example 6
showed that the solidus temperature of Referential example 6 was
135.degree. C. and it was found that the solidus temperature was
lower than 160.degree. C. This result indicates that the solidus
temperature drops sharply when the added amount of In is higher
than 25%.
7.3 Observation of Alloy Organization
[0133] To confirm the discussion in Referential examples 2-4, the
soldering alloy of Examples 2 and 3 and the soldering alloys of
Referential examples 2 and 4 were prepared. The soldering alloy of
Referential example 2 has a composition obtained by removing Ni
from that of Example 2. The soldering alloy of Referential example
4 has a composition obtained by removing Ni from that of Example
3.
[0134] A resin mold was used to form these soldering alloys to
obtain samples. Each of the samples was polished by about half, and
the polished portion was photographed with a FE-SEM at a
magnification of 1000 times. FIG. 8 is a cross-sectional SEM
photography of Example 2 and Referential example 2. FIG. 9 is a
cross-sectional SEM photography of Example 3 and Referential
example 4. It was found from FIGS. 8 and 9 that the alloy
organization of Example 2 or 3 in which Ni is included was fined as
compared to that of the corresponding referential examples. This
results indicate that the considerations discussed in Referential
examples 2-4 may be reasonable. Note that the black portions shown
in FIGS. 8 and 9 represent intermetallic compounds lost by the
polishing.
[0135] In addition, the solder powders prepared from these
soldering alloys was used to obtain board samples. The method for
preparing the board samples was performed according to that in the
shear test. Then, a bonding interface of the BGA terminal and the
printed board was photographed with the FE-SEM at a magnification
of 1000 times. FIG. 10 is a cross-sectional SEM photography of
Example 2 and Referential example 2. FIG. 11 is a cross-sectional
SEM photography of Example 3 and Referential example 4. It was
found from FIGS. 11 and 12 that the miniaturization of the alloy
organization in Example 2 or 3 were maintained even in a state of
the BGA terminal. The results indicate that soldering alloy
according to present invention may be useful as the BGA terminal
and the solder joint.
REFERENCE SIGNS LIST
[0136] 10, 20, 30, 31, 40 Board [0137] 11, 12, 21, 34, 35, 41, 42
Electronic part [0138] 13, 14, 22, 36, 37, 43, 44 Solder joint
[0139] 33 Interposer
* * * * *