Global concerns over the environmental impacts and health
effects of Pb-based solders in consumer electronics has led to the development
of Pb-free solder alternatives. Among the potential alternatives for Pb-Sn
solder, Sn-Ag-Cu alloy is one of the most promising as a result of its
relatively low melting temperature, superior mechanical properties, good
solderability, and relatively low cost. Although these materials are, in
principle, suitable as replacements for Pb-Sn, there remain many issues to
address, in particular, the lower ductility of the alloy. The lower ductility of
the solder has important implications because it relates directly to mechanical
shock and drop resistance, which becomes increasingly important as consumer
products become smaller and more portable. Indeed, Sn-4Ag-0.5Cu and Sn-3Ag-0.5Cu
alloys, the current industry standard, are significantly worse than Pb-Sn alloys
in terms of shock performance (as much as 40% lower) compared to eutectic Pb-Sn.
Researchers at Arizona State University have developed
Sn-Ag-Cu solders with minute additions of the rare earth element Ce, which
substantially improves the ductility of the solder alloy. Meanwhile, the
presence of Ce, in addition to improving the ductility of solder, also refines
the Sn dendrite microstructure and decreases the thickness of the Cu6Sn5
intermetallic layer that forms upon solder reflow to a Cu substrate. Equally
important, while rare earth materials are notorious for being susceptible to
oxidation, these Ce-containing solders have excellent oxidation resistance in
comparison to other rare earth-containing solders (e.g. La, Y).
Potential Applications
- Electronics
- Plumbing
Benefits and Advantages
- Provides Pb-Free Solder without Sacrificing Ductility ?
traditional lower ductility Pb-free solders lack mechanical shock and drop
resistance, which becomes increasingly important as consumer products become
smaller and more portable (existing Pb-free alloys provide as much as 40%
lower shock performance compared to eutectic Pb-Sn solder)
- Possesses Excellent Oxidation Resistance Compared to
Alternative Rare-Earth-Containing Solders (e.g. La, Y)
- Offers the Existing Benefits of Sn-Ag-Cu Alloys
- Relatively Low Melting Point
- Superior Mechanical Properties
- Good Solderability
- Relatively Low Cost
- Relatively Low Melting Point
- Refines the Sn Dendrite Microstructure and Decreases the
Thickness of the Cu6Sn5 Intermetallic Layer that Forms upon Solder Reflow to a
Cu Substrate