74 SMT007 MAGAZINE I JULY 2019
sumption is significantly reduced during the
reflow process (Figure 34). These low-temper-
ature solders are estimated to save 20–25% in
(reflow) energy cost over SAC-305.
It is also estimated that using these low-tem-
perature solders would also reduce the CO
2
emissions by 1.1 metric tons per week
[1]
. This
is roughly equivalent to 10 average gasoline
vehicles (driven in the U.S.) per year.
Conclusions
Preliminary results investigating the low-tem-
perature 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 a dif-
ferentiation between the doped and non-doped
solders under investigation.
Future Work
If the materials continue to make it past the
tests previously mentioned, additional qualifi-
cation testing will include SIR, cleanliness, and
application-specific scenarios, such as large
BGA assembly, high-mix assembly, paste-in-
hole assembly, and rework.
Finally, to fully understand the manufactur-
ing process window for reflow, a DOE will be
conducted to define the range of peak tem-
peratures and their effect on mixed alloy reli-
ability across a multitude of alloys (i.e., when
used to attach SAC-305 or low silver containing
SAC125 BGAs.
SMT007
References
1. S. Sahasrabudhe, S. Mokler, M. Renavikar, S. Sane, K.
Byrd, E. Brigham, O. Jin, Pubudu, Goonetilleke, N. Badwe,
S. Parupalli, "Low-Temperature Solder: A Breakthrough
Technology for Surface-Mounted Devices," IEEE 68
th
Elec-
tronic Components and Technology Conference, 2018.
2. R. Aspandiar, "Characterization of Mixed Alloy SAC-
BiSn BGA Solder Joints: Part II of Report on iNEMI Project
on Process Development of Bi-Sn-Based Low-Temperature
Solder Pastes," Pan Pacific SMTA.
This paper was first presented at the IPC APEX EXPO
2019 Technical Conference and published in the 2019
Technical Conference Proceedings.
Howard "Rusty" Osgood is manager,
assembly and test technology, in the
Advanced Manufacturing Engineering
Group at Flex Inc.
David Geiger is the senior director
of AME assembly and test technology.
Christian Biederman is an engineering
technologist in the Advanced
Manufacturing Engineering Group.
Jon Bernal is an engineering
technologist in the Advanced
Manufacturing Engineering Group.
Robert Pennings and Jie Jiang are no longer with the
company.
Figure 34: Comparison of the typical reflow profiles for
both SAC-305 (red) and the low-temperature solder
(green)
[1]
.
