GB2171415A - Grain refining a solder alloy - Google Patents
Grain refining a solder alloy Download PDFInfo
- Publication number
- GB2171415A GB2171415A GB08510039A GB8510039A GB2171415A GB 2171415 A GB2171415 A GB 2171415A GB 08510039 A GB08510039 A GB 08510039A GB 8510039 A GB8510039 A GB 8510039A GB 2171415 A GB2171415 A GB 2171415A
- Authority
- GB
- United Kingdom
- Prior art keywords
- mass
- solder alloy
- tellurium
- alloy
- selenium
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C11/00—Alloys based on lead
- C22C11/06—Alloys based on lead with tin as the next major constituent
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
- B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
- B23K35/24—Selection of soldering or welding materials proper
- B23K35/26—Selection of soldering or welding materials proper with the principal constituent melting at less than 400 degrees C
- B23K35/268—Pb as the principal constituent
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C13/00—Alloys based on tin
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electric Connection Of Electric Components To Printed Circuits (AREA)
Abstract
A solder alloy which comprises lead and tin (e.g. one comprising 8 to 90 mass % tin, 0.5 to 3.3 mass % antimony, balance lead and incidental impurities) may be grain refined by incorporating selenium and/or tellurium into the alloy when in a molten condition prior to solidifying it, the selenium and/or tellurium being incorporated in such a way that it is at least partly chemically combined with lead to form nucleant particles. The selenium and/or tellurium may be added by means of a master alloy, e.g. one comprising antimony and selenium (preferably comprising 2 to 50 mass % selenium, balance antimony and incidental impurities), or one comprising antimony and tellurium (preferably comprising 40 to 70 mass % tellurium, balance antimony and incidental impurities).
Description
SPECIFICATION
Grain refining a solder alloy
This invention relates to grain refining a solder alloy, and in particular to grain refining a solder alloy which comprises tin and lead.
In order to improve the mechanical, electrical and metallurgical properties of soldered joints made using such solder alloys, it would be desirable to find a way of causing the grain structure of the solder used in such joints to be more refined. So far as we are aware, no successful method of grain refining these alloys has ever been found.
According to the present invention, there is provided a method of grain refining a solder alloy which comprises tin and lead, the method comprising incorporating selenium and/or tellurium into the alloy when in a molten condition prior to solidifying it, the said selenium and/or tellurium being incorporated in such a way that it is at least partly chemically combined with lead to form nucleant particles.
The method can be applied to a full range of solder alloys containing tin and lead, and in particular to those having a tin content over the range from 8 to 90 mass %. Of the solder alloys having such a tin content, we prefer those having an antimony content of from 0.5 to 3.3 mass %. Preferred solder alloys are those having a composition 8 to 90 mass % tin, 0.5 to 3.3 mass % antimony, balance lead and incidental impurities.Particularly effective grain refinement has been obtained by the method of the invention with solder alloys having tin contents of from 8 to 35 mass %; more recently similar results have been obtained with tin contents up to about 70 mass
In particular, good results have been obtained with solder alloys of the following compositions:
(a) about 8 mass % tin, about 0.5 mass % antimony, balance lead and incidental impurities;
(b) about 25 mass % tin, 1.7 mass % antimony, balance lead and incidental impurities;
(c) about 30 mass % tin, about 2.0 mass % antimony, balance lead and incidental impurities;
and
(d) about 60 mass % tin, about 3.2 mass % antimony, balance lead and incidental impurities.
We have found the invention to be very effective when the solder alloy is in accordance
with the German industrial standard DIN 1707.
The work of the inventors has shown that the usual impurities found in commercial
solder alloys do not have any noticable adverse effect on the grain refinement which can
be achieved by the method of the invention.
The selenium and/or tellurium (as the case may be) can be incorporated by inoculating
the molten solder alloy with the respective element or a mixture of the elements; the
required nucleant particles form without any special steps being taken. Conveniently, the
element or elements may be enclosed within a non-deleterious wrapping material, such as
lead foil, for example.
However, we prefer to incorporate the selenium and/or tellurium by inoculating the
molten solder alloy with a master alloy comprising the respective element or elements.
This is a particularly convenient method of adding the element(s), and, once again, the
required nucleant particles form without any special steps being taken.
Where the solder alloy is to be inoculated with selenium, the master alloy can be an
antimony-selenium master alloy, preferably one comprising from 2 to 50 mass % sele
nium, balance antimony and incidental impurities: most preferably, the selenium content in
this master alloy is about 5 mass
Where the solder alloy is to be inoculated with tellurium, the master alloy can be an
antimony-tellurium master alloy, preferably one comprising from 40 to 70 mass % tellu
rium, balance antimony and incidental impurities: most preferably, the tellurium content in
this master alloy is about 50 mass %.
An alternative way to incorporate the selenium and/or tellurium would be to inoculate
the molten solder alloy with a material comprising the respective element or elements at
least partly chemically combined with lead to form nucleant particles. For example, the
molten solder alloy could be inoculated with a master alloy comprising the said nucleant
particles.
We prefer that the amount of selenium and/or tellurium (as the case may be) incorpor
ated into the solder alloy be such that the total amount of any selenium plus the total
amount of any tellurium so incorporated is from 0.005 to 0.5 mass %, most preferably
about 0.1 mass %.
The present invention also comprehends a solder alloy, whenever grain refined by the
method of the invention.
The invention further comprehends a method of soldering using a solder alloy which
comprises tin and lead, characterised in that the solder alloy has been grain refined by a
method in accordance with the invention. Soldering may be carried out by normal solder
ing techniques, starting with a solder alloy which has already been grain refined by the
method of the invention. Indeed, we have found that repeated melting and solidifying of
the solder alloy (up to 10 times, for example) does not have a substantially adverse effect
on the degree of grain refinement in the final soldered joint. Similarly, we have found that
prolonged holding of the molten solder alloy (e.g. in a soldering bath), for up to 20 hours,
has substantially no adverse effect on the grain refining efficiency.
It is possible to make a grain refined soldered joint in accordance with the invention
starting with a solder alloy into which no selenium or tellurium has been incorporated, the
selenium and/or tellurium content being added while the solder alloy is molten, during the
making of the joint, so that grain refinement takes place for the first time when the
molten solder alloy solidifies to form the joint.
We have found, surprisingly, that once the selenium and/or tellurium has been incorpor
ated into the solder alloy, the melt has a noticably improved fluidity. While not wishing to
be bound by this theory, we suggest that this could be due to an absence of dendrite
formation which otherwise would hinder the flow of the metal, and that this gives rise to
an improved filling ability.
We have also found, again surprisingly, that a solder alloy which has been grain refined
in accordance with the invention has the following further advantages for soldering pur
poses, as compared with a solder alloy of the same composition but not grain refined:
(a) it is easier to melt; and
(b) when molten, it spreads faster on the surfaces of substrates which are to be soldered,
and thus has a lower surface tension and a higher wettability.
Easier solder melting means that soldering can be performed with a lower energy requirement and with less risk of damaging the substrates being soldered or components in thermal contact with them.
Better fluidity and lower surface tension substantially improve the soldering process, because they help the solder to enter, by the capillary effect, into the gaps between the substrates being soldered. Improved wettability improves the ability to achieve the required adhesion of the solder to the substrate materials.
Solder alloys which have been grain refined by the method of the invention can have the
following additional advantages:
1. Improved mechanical properties, especially shear strength, which is important for soldered
joints.
2. Better resistance to fluctuation in temperatures; lack of such resistance with known, un
grain refined solder alloys sometimes gives rise to joint cracking, due to microstresses.
3. Better corrosion resistance.
In order that the invention may be more fully understood, an embodiment in accordance therewith will now be described, by way of example only, in the following Examples, with reference to the accompanying drawings, wherein:
Figure 1 is a typical microstructure of a commercially pure Pb. 25 mass % Sn, 1.7 mass % Sb soft soldering alloy, which has not been grain refined, at a magnification of 200:1
Figure 2 is a typical microstructure of the same soldering alloy as in Fig. 1, but grain refined in accordance with the invention by a 0.1 mass % selenium addition, also at a magnification of
200:1
Figure 3a is a photograph, at a magnification of 5::1, of two copper plates which have been
soldered together, using an un-grain refined soft soldering alloy the microstructure of a sample
of which is shown in Fig. 1;
Figure 3b is a photograph, also at a magnification of 5:1, of two copper plates which have
been soldered together under the same conditions as employed to solder the plates shown in
Fig. 3a, except that the solder used had been grain refined in accordance with the invention by a
0.1 mass % selenium addition.
Figure 4a is a photograph, at a magnification of 1.5:1, of three brass plates which have been heated under identical conditions at a relatively low temperature, the plates having on their surfaces cubic sample of: (a) the un-grain refined alloy which is the subject of Fig. 1; (b) an alloy as used in (a), but grain refined in accordance with the invention by a 0.1 mass % selenium addition; and (c) an alloy as used in (a), but grain refined in accordance with the invention by a 0.1 mass % tellurium addition.
Figure 4b is a photograph, also at a magnification of 1.5:1, of three brass plates which have been heated exactly as in Fig. 4a, except at a higher temperature.
Example 1
About 509 of a commercially pure PbSn25Sb1.7 soft soldering alloy in conformity with
German Industrial Standard DIN 1707-LSn 25 was melted in a steel crucible and superheated to 400 C.
Commercially pure (99.6 mass %) selenium enclosed within a lead foil sealing cone was added, and the melt stirred by means of a ceramic rod. After a holding time of 20 minutes, the melt was poured into an unheated steel mould having an internal diameter of 20mm and a height of 30mm.
Fig. 1 shows the microstructure of the alloy without addition, and Fig. 2 shows the effect of adding 0.1 mass % selenium to the alloy in accordance with this Example. As can be seen, substantial refinement of the grain structure resulted.
When the grain refined solder alloy was used to make soldered joints, in a conventional manner, the grain structure of the solder in the resulting joint was similar to that shown in Fig.
2.
It was found that repeating this Example, but replacing the selenium addition by an addition of 0.1 mass % tellurium (again enclosed within a lead foil sealing cone) resulted in a grain refined microstructure similar to that shown in Fig. 2.
Scanning electron microscope studies have shown that, in the selenium- and tellurium-grain refined alloys described in this Example, the nucleant comprises, respectively, lead and selenium, and lead and tellurium. At present we believe that the respective nucleants are PbSe and PbTe.
Additions of, respectively, 0.1 mass % selenium and 0.1 mass % tellurium, by a procedure similar to that described in this Example, to each of the following additional alloys which are in accordance with the German Industrial Standard DIN 1707 have resulted in a degree of grain refinement similar to that obtained as described above with LSn 25:
Composition (mass %)
Alloy designation Sn Sb Pb (and impurities)
LSn 8 8 0.5 balance
LSn 30 30 2.0 balance
As indicated above, the experiments described in the above Example can be repeated with greater convenience by making the Se and Te additions by means of master alloys such as Sb,
Se 5 mass % or Sb, Te 50 mass
Example 2
Two copper plates were soldered together using a sample of the commercial soft soldering alloy employed as a starting material in Example 1.The experiment was repeated under identical conditions, except that in this case the solder alloy had been grain refined by a 0.1 mass % selenium addition as described in Example 1. The resulting soldered joints are shown in Figs. 3a and 3b, respectively. When the experiment was repeated again, except in this case using an alloy which had been grain refined by a 0.1 mass % tellurium addition; the result was very similar to that shown in Fig. 3b.
It will be seen that the fluidity of the melt of the grain refined alloy is substantially better than that of the un-grain refined alloy. This can be attributed to the formation of dendrites in the unrefined alloy substantially hindering the flow of the melt, whereas we believe that in the grain refined alloys the dendrites are substituted by the fine globulitic primary phase in the solidification interval.
Example 3
Three brass plates (a), (b) and (c) were coated with soldering oil and heated on an electrically heated plate, while supporting a cube-shaped sample of soft solder alloy, under identical conditions, except that the samples differed, as follows:
(a) the un-grain refined alloy used as a starting material in Example 1;
(b) the grain refined alloy of Example 1 containing 0.1 mass % selenium; and
(c) the grain refined alloy of Example 1 containing 0.1 mass % tellurium.
In a first experiment, heating was performed at a relatively low temperature: the results are shown in Fig. 4a. The experiment was then repeated, at a somewhat higher temperature: the results are shown in Fig. 4b.
The following observations were made:
(i) The refined alloys melted much faster than the unrefined one. This is thought to be because of the better distribution of the eutectic phase by grain refinement (the eutectic phase has a lower melting point).
(ii) The refined alloys spread faster on the surface of the copper plate, which indicates a lower surface tension and a higher wettability.
Claims (31)
1. A method of grain refining a solder alloy which comprises lead and tin, the method comprising incorporating selenium and/or tellurium into the alloy when in a molten condition prior to solidifying it, the said selenium and/or tellurium being incorporated in such a way that it is at least partly chemically combined with lead to form nucleant particles.
2. A method according to claim 1, wherein the solder alloy comprises from 8 to 90 mass % tin.
3. A method according to claim 2, wherein the solder alloy comprises from 0.5 to 3.3 mass % antimony.
4. A method according to claim 3, wherein the composition of the solder alloy is 8 to 90 mass % tin, 0.5 to 3.3 mass % antimony, balance lead and incidental impurities.
5. A method according to any one of claims 2 to 4, wherein the solder alloy comprises from 8 to 70 mass % tin.
6. A method according to any one of claims 2 to 5, wherein the solder alloy comprises from 8 to 35 mass % tin.
7. A method according to any one of claims 2 to 5, wherein the composition of the solder alloy is about 8 mass % tin, about 0.5 mass % antimony, balance lead and incidental impurities.
8. A method according to any one of claims 2 to 5, wherein the composition of the solder alloy is about 25 mass % tin, about 1.7 mass 0A antimony, balance lead and incidental impurities.
9. A method according to any one of claims 2 to 5, wherein the composition of the solder alloy is about 30 mass % tin, about 2.0 mass % antimony, balance lead and incidental impurities.
10. A method according to any one of claims 2 to 5, wherein the composition of the solder alloy is about 60 mass % tin, about 3.2 mass % antimony, balance lead and incidental impurities.
11. A method according to any one of claims 2 to 10, wherein the solder alloy is in accordance with the German industrial standard DIN 1707
12. A method according to any one of claims 1 to 11, wherein the selenium and/or tellurium is incorporated by inoculating the molten solder alloy with the respective element or a mixture of the elements.
13. A method according to claim 12, wherein the said element or elements is or are enclosed within a non-deleterious wrapping material.
14. A method according to claim 13, wherein the wrapping material is lead foil.
15. A method according to any one of claims 1 to 11, wherein the selenium and/or tellurium is incorporated by inoculating the molten solder alloy with a master alloy comprising the respective element or elements.
16. A method according to claim 15, wherein the master alloy comprises antimony and tellurium.
17. A method according to claim 16, wherein the master alloy comprises from 2 to 50 mass % selenium, balance antimony and incidental impurities.
18. A method according to claim 17, wherein the master alloy comprises about 5 mass % selenium.
19. A method according to claim 15, wherein the master alloy comprises antimony and tellurium
20. A method according to claim 19, wherein the master alloy comprises from 40 to 70 mass % tellurium, balance antimony and incidental impurities.
21. A method according to claim 20, wherein the master alloy comprises about 50 mass % tellurium.
22. A method according to any one of claims 1 to 11, wherein the selenium and/or tellurium is incorporated by inoculating the molten solder alloy with a material comprising the respective element or elements at least partly chemically combined with lead to form nucleant particles.
23. A method according to claim 22, wherein the molten solder alloy is inoculated with a master alloy comprising the said nucleant particles.
24. A method according to any one of claims 1 to 23, wherein the total amount of any selenium incorporated into the solder alloy plus the total amount of any tellurium incorporated into the solder alloy is form 0.005 to 0.5 mass %.
25. A method according to claim 23, wherein the said total amount is about 0.1 mass %.
26. A method of grain refining a solder alloy, substantially as hereinbefore described in the foregoing Example 1.
27. A solder alloy, whenever grain refined by a method in accordance with any one of claims 1 to 26.
28. A method of soldering using a solder alloy which comprises lead and tin, characterised in that the solder alloy has been grain refined by a method in accordance with any one of Claims 1 to 26.
29. A method according to claim 28, wherein the solder alloy, after being grain refined, and prior to being used as a solder, has been at least once remelted and resolidified.
30. A method according to claim 29, wherein the solder alloy has at least 10 times been remelted and resolidified as aforesaid.
31. A method according to any one of claims 28 to 30, wherein the total amount of time for which the solder alloy has been in a molten condition since the incorporation into it of the selenium and/or tellurium prior to its use for soldering is up to 20 hours.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08604331A GB2171720A (en) | 1985-02-21 | 1986-02-21 | Grain refining a solder alloy |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB858504415A GB8504415D0 (en) | 1985-02-21 | 1985-02-21 | Grain refining solder alloy |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8510039D0 GB8510039D0 (en) | 1985-05-30 |
| GB2171415A true GB2171415A (en) | 1986-08-28 |
Family
ID=10574827
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB858504415A Pending GB8504415D0 (en) | 1985-02-21 | 1985-02-21 | Grain refining solder alloy |
| GB08510039A Withdrawn GB2171415A (en) | 1985-02-21 | 1985-04-19 | Grain refining a solder alloy |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB858504415A Pending GB8504415D0 (en) | 1985-02-21 | 1985-02-21 | Grain refining solder alloy |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB8504415D0 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102248331A (en) * | 2011-06-29 | 2011-11-23 | 绍兴市天龙锡材有限公司 | Preparation method of tin-selenium interalloy |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB487305A (en) * | 1937-11-30 | 1938-06-17 | Cleveland Graphite Bronze Co | An improved bearing metal alloy |
| GB1074861A (en) * | 1965-02-02 | 1967-07-05 | Peter Siegfried Muetzel | Improvements in tin-lead base solders |
-
1985
- 1985-02-21 GB GB858504415A patent/GB8504415D0/en active Pending
- 1985-04-19 GB GB08510039A patent/GB2171415A/en not_active Withdrawn
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB487305A (en) * | 1937-11-30 | 1938-06-17 | Cleveland Graphite Bronze Co | An improved bearing metal alloy |
| GB1074861A (en) * | 1965-02-02 | 1967-07-05 | Peter Siegfried Muetzel | Improvements in tin-lead base solders |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102248331A (en) * | 2011-06-29 | 2011-11-23 | 绍兴市天龙锡材有限公司 | Preparation method of tin-selenium interalloy |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8510039D0 (en) | 1985-05-30 |
| GB8504415D0 (en) | 1985-03-27 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |