Electronics Assembly Knowledge, Vision & Wisdom
Low Temperature SMT Solder Evaluation
Low Temperature SMT Solder Evaluation
Recent advances in alloy "doping" have opened the door to revisit Sn/Bi alloys as a possible alternative to SAC-305 for many applications.
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Authored By:
Howard "Rusty" Osgood, David Geiger, Robert Pennings, Christian Biederman, Jie Jiang, Jon Bernal
Flextronics International
Milpitas, CA, USA

Summary
The electronics industry could benefit greatly from using a reliable, manufacturable, reduced temperature, SMT solder material (alloy-composition) which is cost competitive with traditional Sn3Ag0.5Cu (SAC305) solder. The many possible advantages and some disadvantages / challenges are discussed.

Until recently, the use of Sn/Bi based materials has been investigated with negative consequences for high strain rate (drop-shock) applications and thus, these alloys have been avoided. Recent advances in alloy "doping" have opened the door to revisit Sn/Bi alloys as a possible alternative to SAC-305 for many applications.

We tested the manufacturability and reliability of three low-temperature and one SAC-305 (used as a control) solder paste materials. Two of these materials are doped Sn/Bi/Ag and one is just Sn/Bi/Ag1%.

We will discuss the tests and related results. And lastly, we will discuss the prospects, applications and possible implications (based on this evaluation) of these materials together with future actions.

Conclusions
Preliminary results investigating the low temperature paste alloys against the Sn3Ag0.5Cu paste alloy look promising. Limited internal testing to date, combined with limited external testing data, indicates that these newer, doped, lower temperature solders perform as well or better than Sn3AgCu(SAC305).

Further testing and evaluation is needed and is underway. We are proceeding with drop/shock and higher strain rate monotonic bend testing which is where we expect to see differentiation between the doped and non-doped solders under investigation.

Initially Published in the SMTA Proceedings

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