Issue link: https://iconnect007.uberflip.com/i/1546933
OCTOBER 2026 I SMT007 MAGAZINE 41 the overall voiding level but also the shape and distribution of the voids. Since void morphology can impact both thermal performance and mechanical reliability, future studies should investigate how void distribution correlates with long-term reliability. This includes further testing under thermal cycling and mechan- ical stress conditions. Conclusion This study demonstrates that solder joint voiding in QFN assemblies is primarily influenced by mate- rial-related factors. Among these, stencil thickness emerged as the dominant variable, with the 5-mil stencil consistently producing lower voiding levels compared to the 4-mil stencil. Adjustments to the reflow profile had a measurable but secondary effect on voiding, while the choice of solder paste contributed to a lesser effect. These findings highlight that selecting favorable material combinations is critical to achieving voiding performance targets and ensuring process compli- ance. It should be noted that ImSn surface finish data could not be included in this analysis due to limited data availability, as Trial 3 focused primarily on OSP finishes. These results underscore the importance of optimizing material selection early in the process development phase, as this provides a more robust foundation for subsequent fine-tuning of process parameters such as reflow profiles. For BTCs, voiding acceptance criteria beyond IPC-A-610 are often defined as "as agreed between user and supplier" (AABUS). Overall, compliance to IPC-A-610 Class 3 require- ments was reliably achieved only under favorable material combinations, most notably OSP with 5 mil stencils and the mixed-alloy solder paste. These findings highlight that stencil thickness, profile, and solder paste choice are the critical levers for voiding reduction. It is especially relevant to auto- motive and aerospace electronics, where voiding control is essential. In the previous study, reflow profile modifica- tion was identified as a major factor in reducing voiding. 1 In that work, profiles were evaluated within a single and mixed alloy solder paste/stencil thick- ness system. In the present broader DOE, profile changes continued to show a measurable effect, but the impact was secondary compared to stencil thickness. This indicates that while profile optimiza- tion can reduce voiding within a given material set, material-driven factors ultimately dominate voiding behavior across assemblies. SMT007 References 1. "Enhancing PCB Reliability: Voiding Reduction Design with a Mixed-Alloy Solder Paste," by T. Nguyen, H. Zhang, R. Lasky, and A. Murling, Proceedings of IPC APEX EXPO 2025. 2. "Low-Voiding High-Reliability Lead-Free Solder Paste for Automotive Applications," by J. Geng, H. Jilani, and H. W. Zhang, Proceedings of SMTA International 2023. 3. "Effects of Solder Voiding on the Reliability and Thermal Characteristics of Quad Flatpack No-lead (QFN) Components," by R. Wilcoxon, D. Hillman, and T. Pearson, Proceedings of the 37th Semiconductor Thermal Measurement, Modeling & Management Symposium, 2021. 4. "Reliability Study of Bottom Terminated Components," by J. Nguyen, H. Marin, D. Geiger, A. Mohammed, and M. Jurwa, Proceedings of IPC APEX EXPO 2014. 5. "The Attempt of Lower Temperature Soldering Process for Large Plastic Ball-Grid Array Board-Level Assembly," by H. W. Zhang, T. Richmond, F. Mutuku, and H. Wang, Proceedings of IPC APEX EXPO 2024. 6. "A Lower Temperature Lead-Free Solder Paste for Wafer-Level Package Application that Outperforms SAC305," by H. W. Zhang, T. Richmond, H. Wang, J. Geng, C. Nash, J. S. Sjoberg and C. Hotvedt, Proceedings of IPC APEX EXPO 2023. 7. "A Bismuth-free In-containing Lower-Temperature Lead-Free Solder Paste for Wafer-Level Package Application that Outperforms SAC305," by H. W. Zhang, T. Richmond, K. Aserian, H. Wang, J. Geng, C. Nash, J. S. Sjoberg, and C. Hotvedt, Proceedings of the 2023 IEEE 73rd Electronic Components and Technology Conference. At Indium Corporation, Thuy Nguyen is a technical support engineer, Hongwen Zhang is R&D director and principal research metallurgist, Ron Lasky is senior technologist, and Adam Murline is a tech- nical manager.