GB2300197A - A low melting point solder - Google Patents
A low melting point solder Download PDFInfo
- Publication number
- GB2300197A GB2300197A GB9608501A GB9608501A GB2300197A GB 2300197 A GB2300197 A GB 2300197A GB 9608501 A GB9608501 A GB 9608501A GB 9608501 A GB9608501 A GB 9608501A GB 2300197 A GB2300197 A GB 2300197A
- Authority
- GB
- United Kingdom
- Prior art keywords
- gold
- solder
- tin
- bismuth
- percent
- 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.)
- Withdrawn
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C12/00—Alloys based on antimony or bismuth
-
- 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
- B23K35/264—Bi as the principal constituent
Landscapes
- 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)
Description
Bismuth-Tin Solder 2300197 This invention relates to an alloy composition
useful as a solder. More particularly, it is a low melting temperature lead ftee alloy comprising effective amounts of bismuth, tin and gold.
Solders are extensively used in electronic assembly. Lead ftee solders have been pursued to overcome the toxic effect of lead (Pb) by eliminating lead from electronic devices as well as from the manufacturing environment. Solders have been developed that are lead free and have a low melting temperature, making them suitable for many electrical interconnect functions. However as the pitch on IC devices gets ever finer, the mechanical properties of some lead free low temperature solders are problematic, although their electrical properties are adequate.
The mechanical properties essential for commercially viable consumer good interconnects include adequate ductility, strength, and fatigue life. Lead free solders such as eutectic Bismuth-tin (58Bi-42Sn) may have the appropriate melting point for low temperature soldering but lack the requisite mechanical characteristics. Bi-Sn has poor ductility and fatigue resistance, and, thus limited usefulness in electronic assembly. Poor ductility and susceptibility to fatigue translate into device failure as a result of physically ruptured connections either due to the mechanical stress during shipping and handling or after prolonged operation (due to the temperature cycling that corresponds to periods of use and disuse creating "t hermo- mechanical stress").
Electronic assembly will benefit from a lead free low temperature solder demonstrating good ductility, strength and fatigue resistance.
2 The invention taught herein provides an alloy composition that is essentiaUy lead free. The invention further provides an alloy composition that has a low melting temperature, having a melting point of approximately 138 degrees Centigrade. The invention further provides an alloy composition suitable for electrical interconnections and, as compared with eutectic bismuth-tin, demonstrating a greater than one hundred percent improvement in ductility, and a greater than 10% increase in strength and an expected comparable increase in fatigue lifetime.
The present invention relates to compositions comprising effective amounts of bismuth, tin and one of gold, silver or platinum. The preferred alloys are those that improve grain size refinement under a given set of solidification conditions.
Grain size refinement and the related mechanical properties can be improved by adding small amounts of gold, silver or platinum to bismuthtin. The preferred embodiment is an afloy comprising from about 5 7. 1 to 5 7.9 percent by weight bismuth; from about 41.0 to 41.9 percent by weight tin, and at least one of gold, silver or platinum in the amount of from about 0. 1 to 0.99 percent by weight.
In one embodiment of the invention, the composition comprises 57.9 percent by weight bismuth, 41.9 percent by weight tin, and 0.2 percent by weight gold. The addition of gold into Bi-Sn solder connections can be achieved by either using the soldering alloys with gold addition, or by plating gold on the soldering surface and dissolving the plated gold into molten Bi-Sn during soldering process, as shown in the following example.
Copper plates with gold plating of 5 micro inches (10-6 inches) and 50 micro inches thickness were prepared. Solder joints of 10 MilS (10-3 inches) thickness were made by reflowing 58Bi-42Sn solder paste between two gold-plated copper plates. After reflow, gold distributed unifom-dy in the solder joints. forming approximate compositions of 57.9Bi-41.9Sn-0. 2Au (with 5 micro inch plating), and 56Bi-4 1 Sn-2Au (with 50 micro inch plating), respectively.
3 The solder joints of these two compositions were shear tested at room temperature and at two strain rates (0.01 second and 0.001 second'), respectively. Figure I shows the shear test results at 0.0 1 second of four types of solder joint samples. The sample labeled 58Bi-42Sn/5 micro in which is 57.9Bi-4l.9Sn-0.2Au has both greater ductility (strain sustained before the solderjoint separation) and strength (maximum stress) than either the sample labeled 58Bi-42Sn/Cu which is 58Bi42Sn or the sample labeled 58Bi42Sn/40 micro inches which is 56Bi4 I Sn-2Au.
Figure 2 shows the shear test results at 0. 00 1 second". The results are similar to the 0.0 1 second-' test results, except that the ductility of 57.9Bi4l.9Sn-0.2Au now approaches that 63Sn-37Pb, the solder most extensively used in electronic packaging and assembly, Figures 3 and 4 are the optical micrographs of 57.9Bi-4l.9Sn-0.2Au and 58Bi42Sn at the same magnification. It is apparent that the grain (or phase) size of 57.9Bi41.9Sn-0.2Au is significantly smaller than that of 58Bi-42Sn.
In an alternate embodiment, the invention comprises bismuth, tin and silver in similar proportions by weight, with silver not exceeding 0.99 percent by weight. The resulting composition produces a refined microstructure and improved mechanical properties. Both Au and Ag form acicular intermetaflic phases that will solidify before the remainder of the solder. These may act as heterogeneous nucleation sites. Platinum (Pt) is expected to have a similar effect in bismuth-tin-platinum compositions where platinum does not exceed 0.99 percent by weight.
The invented alloys here may have many applications in electronic packaging and assembly, because the alloys are Pb-free, low-melting, and have superior mechanical properties.
While the invention has been explained in relation to its preferred embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the art. The foregoing disclosure is not intended nor is to be construed as limiting the present invention, or to otherwise exclude other embodiments, adaptations, or equivalent arrangements. The present invention is limited only by the appended claims and the equivalents thereof
4
Claims (7)
1. A lead-free solder composition comprising bismuth, tin and one of gold, silver and platinum.
2. A solder composition as claimed in claim 1, comprising up to 57.9 percent by weight of bismuth.
3. A solder composition as claimed in claim 1 or 2, comprising up to 41.9 percent by weight of tin.
4. A solder composition as claimed in claim 1, 2 or 3, comprising one of gold, silver or platinum in an amount of from 0. 1 to 0.99 percent by weight.
5. A method of producing a solder connection having a solder composition as defined in one of claims I to 4, comprising providing a plating of gold, silver or platinum on a surface to receive said connection, and conducting a soldering process thereon using a bismuth, tin composition.
6. A lead-free solder composition substantially as herein described.
7. A method of producing. a solder composition substantially as herein described.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US43120195A | 1995-04-28 | 1995-04-28 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9608501D0 GB9608501D0 (en) | 1996-07-03 |
| GB2300197A true GB2300197A (en) | 1996-10-30 |
Family
ID=23710910
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9608501A Withdrawn GB2300197A (en) | 1995-04-28 | 1996-04-25 | A low melting point solder |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPH08300182A (en) |
| DE (1) | DE19538992A1 (en) |
| GB (1) | GB2300197A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2013163207A (en) * | 2012-02-10 | 2013-08-22 | Nihon Superior Co Ltd | Sn-Bi-BASED SOLDER ALLOY |
| CN110004323B (en) * | 2019-03-29 | 2020-08-14 | 北京理工大学 | Low-melting-point high-strength thermosensitive material and preparation method thereof |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB388979A (en) * | 1932-06-27 | 1933-03-09 | Friedrich Strasser | Solder for aluminium |
| GB1565618A (en) * | 1977-03-22 | 1980-04-23 | Dentaire Ivoclar Ets | Dental alloys |
| GB2159330A (en) * | 1984-05-19 | 1985-11-27 | Chugai Electric Ind Co Ltd | Electrical contacts |
| EP0336575A1 (en) * | 1988-03-31 | 1989-10-11 | COOKSON GROUP plc | Low toxicity alloy compositions for joining and sealing |
| US5368814A (en) * | 1993-06-16 | 1994-11-29 | International Business Machines, Inc. | Lead free, tin-bismuth solder alloys |
| EP0629466A1 (en) * | 1993-06-16 | 1994-12-21 | International Business Machines Corporation | High temperature, lead-free, tin based solder composition |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5389160A (en) * | 1993-06-01 | 1995-02-14 | Motorola, Inc. | Tin bismuth solder paste, and method using paste to form connection having improved high temperature properties |
-
1995
- 1995-10-19 DE DE1995138992 patent/DE19538992A1/en not_active Ceased
-
1996
- 1996-04-25 GB GB9608501A patent/GB2300197A/en not_active Withdrawn
- 1996-04-26 JP JP13071396A patent/JPH08300182A/en active Pending
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB388979A (en) * | 1932-06-27 | 1933-03-09 | Friedrich Strasser | Solder for aluminium |
| GB1565618A (en) * | 1977-03-22 | 1980-04-23 | Dentaire Ivoclar Ets | Dental alloys |
| GB2159330A (en) * | 1984-05-19 | 1985-11-27 | Chugai Electric Ind Co Ltd | Electrical contacts |
| EP0336575A1 (en) * | 1988-03-31 | 1989-10-11 | COOKSON GROUP plc | Low toxicity alloy compositions for joining and sealing |
| US5368814A (en) * | 1993-06-16 | 1994-11-29 | International Business Machines, Inc. | Lead free, tin-bismuth solder alloys |
| EP0629466A1 (en) * | 1993-06-16 | 1994-12-21 | International Business Machines Corporation | High temperature, lead-free, tin based solder composition |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9608501D0 (en) | 1996-07-03 |
| DE19538992A1 (en) | 1996-10-31 |
| JPH08300182A (en) | 1996-11-19 |
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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) |