Authored By:
Sinan Su, Francy Akkara, John Evans, Gregory Harris
Department of Industrial and Systems Engineering
Thomas Sanders
NASA Jet Propulsion Lab
Jiawei Zhang
Broadcom Limited
AL, USA
Summary
In this paper, a direct comparison was conducted between SnPb and lead-free solder joints focused on long-term thermal cycling reliability after being exposed to high-temperature aging for a long period of time using two test vehicle designs. Ball Grid Array (BGA) packages with SAC305 (Sn-3%Ag-0.5%Cu) and eutectic SnPb (63%Sn-37%Pb) were compared in this research. After the test, IMC thickness and failure modes of BGA components on the different test vehicles were investigated. The results from the post-test examination were analyzed to explain certain unexpected outcomes of the two test vehicle designs when comparing the reliability results among the two programs of tests.
The results showed that for the TC1 test vehicle, SAC305 solder joints show better reliability than the SnPb solder joints; while the reliability of the SnPb solder joints outperformed the SAC305 solder joints after 6 months of high-temperature aging for the TV7 test vehicle. Meanwhile, even on the same test vehicle, the failure modes varied between components with SAC305 and SnPb solder joints.
Conclusions
Two solder materials (SAC305 vs. SnPb) were compared from two different test vehicle designs in thermal cycling test. Different results were observed for each test vehicle, where SnPb demonstrated better thermal cycling reliability for different aging durations with the TV7 test vehicle, while SAC305 demonstrated better thermal cycling reliability with the CT1 test vehicle. Failure modes were analyzed after the test for TV7 test vehicle, and SnPb solder joint showed thinner IMC thickness and relatively lower creep rate after thermal cycling, which contributed to a larger fatigue life. More investigations are needed before a definitive conclusion can be drawn for the cause of the reverse trend observed in the CT1 test vehicle.
Initially Published in the SMTA Proceedings
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