Authored By:
Michael Osterman, Ph.D., Aaron Mendelsohn
Center for Advanced Life Cycle Engineering, University of Maryland
MD, USA
Summary
Low temperature solders are currently being used in the portable computer industry and will continue to expand into other industries. As a critical component for electronic products, it is important to understand their reliability. With regards to reliability, thermal cycling and drop performance are important metrics in establishing reliability. This paper presents an examination of three low temperature solders and provides a comparison with tin-silver-copper solder. The test vehicle includes SAC305 BGAs, QFNs, and SMR packages. Current test plan and test results are presented.
Conclusions
Printed board assembly test vehicles with three BGA types and two leadless package types have been fabricated and characterized. For the BGA package types, the paste to solder sphere ratios ranged from 50 to 62 percent with the lowest occurring for the package with the largest solder spheres. Thermal cycling and drop tests are planned. At the time of this presentation, the QFN package types were the first to fail for all solders under the -50 to 100 ℃ thermal cycle test condition.
This failure is due to the large distance to neutral point of these packages, resulting from the center pad not being soldered. Current failure trend indicates that solder interconnects formed with low temperature solder exhibit greater thermal fatigue life than those formed with SAC305 solder. Similar results have been observed by others. However, broader conclusions cannot be made until testing is completed and failure analysis is conducted.
Initially Published in the SMTA Proceedings
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