Authored By:
Watson Tseng
Shenmao America, Inc.
CA, USA
Chunyu Chang, Tzu-Chi Chia, Coti Chung, Keith Lee, Ken Lin
Shenmao Technology Inc.
Hsinchu County, Taiwan
Summary
Low-temperature soldering (LTS) offers energy savings and improved production yields but introduces compatibility challenges, especially with BGA components using LTS solder balls. Building on previous research [1] demonstrating superior thermal reliability for LTS ball components soldered with SAC paste, this study evaluates their mechanical shock reliability. Test vehicles underwent immediate mechanical shock, or shock after 168/336 hours of 100°C storage. Microsectioning assessed joint evolution, and daisy-chain resistance monitored failure. Results confirm the superior performance of homogeneous LTS-SAC joints, highlighting the impact of bismuth content on mechanical shock reliability.
Conclusions
This study investigated the mechanical shock reliability of various SAC and LTS ball-paste combinations, revealing key insights into LTS compatibility and performance:
- Homogeneous Joint Structures: Homogeneous solder joints (SAC-SAC, LTS-LTS, LTS-SAC) exhibited superior mechanical shock resistance compared to the hybrid SAC-LTS configuration, emphasizing the importance of minimizing material mismatch at the joint interface.
- Bismuth Content Optimization: The LTS-SAC combination, with its moderate bismuth content, demonstrated enhanced thermal and mechanical performance, surpassing the SAC-SAC benchmark. This highlights the potential of tailoring bismuth content for optimal solder joint reliability.
- Microstructure and Failure Mechanisms: The observed variations in crack initiation and propagation patterns across different test groups and storage conditions suggest a strong correlation between microstructure evolution and failure mechanisms under mechanical shock.
- LTS Potential: Despite compatibility challenges, LTS soldering, particularly with optimized ball-paste combinations like LTS-SAC, offers a promising avenue for enhancing solder joint reliability in applications demanding both thermal and mechanical robustness.
These findings contribute valuable insights into solder joint reliability and provide guidance for the effective implementation of LTS soldering in the SMT industry. Future research should further explore the interplay of bismuth content, microstructure, and other factors influencing solder joint performance under diverse stress conditions.
Initially Published in the SMTA Proceedings
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