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96 SMT007 MAGAZINE I NOVEMBER 2019 Conclusions A test board was designed to test an isolated set of conditions for void reduction on the ther- mal pad of QFN. The hypothesis that a small enough via diameter would prevent molten solder from wicking in the via while allowing volatiles to escape and facilitate void reduc- tion was limited to three finished TH via diam- eters: 0.00787", 0.0090" and 0.0098". Only a narrow set of parameters displayed a reduced void% and limited the wicking of solder inside the via. Acknowledgments The authors gratefully acknowledge the management support of Marco Gonzalez from Sanmina and the Sanmina Guadalajara process and management teams—especially NPI team from Plant 1—and the support of the regional engineering team; specials thanks for the sup- port of Sanmina NPI team-PCB Division in San Jose, California, and the support of the San- mina Guadalajara Regional Reliability and FA Laboratory. SMT007 References 1. Derrick Herron, Yan Liu, and Ning-Cheng Lee, "Voiding Control At QFN Assembly," Pan Pacific Symposium, 2011. 2. Richard Coyle and Heather McCormick, et al., "Ther- mal Fatigue Performance of a Quad Flat No lead (QFN) Package assembled with Sn-Ag-Cu (SAC) and SnPb Sol- ders," SMTAI 2009. 3. Ning-Cheng Lee, "How to Control Voiding in Reflow Soldering," Chip Scale Review, August/September 2005. 4. Matt Kelly, Mark Jeanson, and Mitch Ferrill, "Via-in- Pad Design Considerations for Bottom-Terminated Compo- nents on Printed Circuit Board Assemblies," SMTAI, 2014. 5. Viktoria Rawinski, "Void Reduction in Reflow Soldering Processes by Sweep Stimulation of PCB Substrate—Process Inte- gration in Industrial Production," SMTAI, 2016. 6. Jennifer Nguyen, David Gei- ger, and Anwar Mohammed, "The Impact of Via and Pad Design on QFN Assembly," SMTAI, 2015. 7. Alfredo Garcia, Cristina Ama- dor, Jose Esquivel, Domingo Vaz- quez, Shane Lewis, Iulia Muntele, and Mulugeta Abtew, "Effect of Termination Finish, Reflow Conditions, and Void Formation on the Reliability of QFN Solder Joints," IPC Tech Summit, 2014. 8. Timothy O'Neill, "Aperture Design to Minimize QFN Voiding," www.aimsolder.com. This paper was first presented at SMTAI 2018 and pub- lished in the technical proceedings. Alfredo Garcia, Engineering Mgr., Sanmina P1 GDL. Domingo Vazquez, Regional Process Mgr., Sanmina SCI GDL. Ricardo Macias, Process Engineer, Sanmina P1 GDL. Rodrigo Ibarra, Foreman, Sanmina SCI GDL. Joe Smetana, Principal Engineer, Advanced Technology, Nokia. Mulugeta Abtew, Ph.D., VP Technology Dev., Sanmina Corp. Iulia Muntele, Process Dev. Engineer, Sanmina Corp. Table 6: PCA#18, A7 via diameter measured at three locations along the via. Iulia Muntele Ricardo Macias Joe Smetana Domingo Vazquez Rodrigo Ibarra Alfredo Garcia Mulugeta Abtew