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Thermal Cycle Fatigue Life of Low-Temperature Solders
Thermal cycling fatigue is one of the main reliability concerns for solder. For the introduction of low temperature solders with reflow peak temperatures below 200℃, their thermal cycle fatigue life must be characterized. This paper presents a multiple component type test and time to failure data for solder interconnects formed with low temperature solders for BGAs, QFNs, and SMR component types.
Technical Paper
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Authored By:
Michael Osterman, Ph.D., Aaron Mendelsohn
CALCE/University of Maryland
MD, USA
Summary
Solder interconnects are required to provide low resistance connections between terminals of packaged devices and printed boards over the expected life. Thermal cycling fatigue is one of the main reliability concerns for solder. For the introduction of low temperature solders with reflow peak temperatures below 200℃, their thermal cycle fatigue life must be characterized. This paper presents a multiple component type test and time to failure data for solder interconnects formed with low temperature solders for BGAs, QFNs, and SMR component types.
Conclusions
The results of this experiment reflect an increased lifetime under thermal cycling conditions for LTS 1-3, as compared to SAC305. This outcome highlights the advantages which hybrid SnBi interconnects have over SAC305 solder in particular. This increase in average lifetime indicates characteristics in enhanced SnBi solder which are more desirable to manufacturers than the current characteristics of SAC305. These characteristic differences may be used as rationale for prioritization of SnBi use over that of SAC305. More study should be performed into the other mechanical characteristics of enhanced SnBi solder to come to any definitive conclusions, including greater focus on the impact of dwell times on thermal stresses due to CTE. However, these results are still strong reason to consider usage of these solders in most applications.
The results of this experiment reflect an increased lifetime under thermal cycling conditions for the low temperature solders as compared to SAC305. This outcome highlights the advantages of low temperature solder for applications with thermal cycle challenges. Hybrid interconnects present a mixed result with some hybrid SAC305 and low temperature solder be nearly equivalent to SAC305 while other being superior. Enhancements with the addition of antimony and silver present appear to provide an improvement over simple tin-bismuth solder. This increase in average lifetime indicates characteristics in enhanced SnBi solder which are more desirable to manufacturers than the current characteristics of SAC305.
These characteristic differences may be used as rationale for prioritization of enhanced SnBi use over that of SAC305. However, more study should be performed into the other mechanical characteristics of enhanced SnBi solder to come to any definitive conclusions, including greater focus on the impact of dwell times on thermal stresses due to CTE. However, these results are still strong reason to consider usage of these solders in most applications.
Initially Published in the SMTA Proceedings
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