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66 SMT007 MAGAZINE I JUNE 2018 Summary and Conclusions The previous work and the work presented in this study, demonstrates the advancement of QFN and other BTC assembly using low void- ing micro-flux solder preform and optimized process parameters such as stencil design, pad design and reflow parameters. Design of the preform, selecting specific flux amount, and optimizing soldering condi- tions resulted in significant reduction in void- ing. For various component sizes, consistent sub-10% voiding was achieved. The use of preforms in conjunction with micro-flux coat- ing technology ensures low voiding in both air and nitrogen reflow environments. Reduction in solder paste volume and controlled amount of the flux on the micro-flux preform generates low residue and ensures high electrochemical reliability of the BTC. Low voiding micro-flux technology is compatible with finishes such as immersion Sn and immersion Ag commonly used in industry. Via design is an important factor in BTC assembly. Via type and diameter could be a critical factor to achieve low voiding and reliable solder assembly. SMT007 Acknowledgement The authors would like to thank Alan Plant, Frank Andres, Karen Tellefsen and Westin Bent for valuable input into the DOE design and for process development; Daniele Perico for support during DOE design; Steven Prokopiak and Bogdan Bankiewicz for material develop- ment and manufacturing. References 1. IPC—Association Connecting Electronics Industries. "IPC-7093 – Design and Assembly process implementation for Bottom Termina- tion Components." 2011. 2. Reza Ghaffarian, NASA. "Body of Knowl- edge (BOK) for Leadless Quad Flat No-Lead/ Bottom Termination Components (QFN/BTC) Package Trends and Reliability." Jet Propulsion Lab – California Institute of Technology (Oct., 2014): 14–15. Print. 3. E. Tormey, J. Sidone, W. Bent, K. Tellefsen, P. Koep, and R. Raut, "The Effects of Preforms in Paste on Voiding Under Bottom Terminate Components," SMTAI, Orlando, FL, October 16–17, 2012. 4. A. Lifton, P. Salerno, J. Sidone, O. Khaselev, M. Marczi, "Void Reduction strat- egy for bottom termination components (BTC) using flux coated preforms," SMTAI, Chicago, Illinois September 19–21, 2017. Editor's Note: This article was originally presented at the technical proceedings of IPC APEX EXPO. Jerry Sidone is a commercial development manager for the Americas at Alpha Assembly Solutions. Anna Lifton is R&D manager at Alpha Assembly Solutions. Paul Salerno is the global portfolio manager for SMT assembly solutions at Alpha Assembly Solutions. Oscar Khaselev is the R&D director at Alpha Assembly Solutions (no image available). Design of the preform, selecting specific flux amount, and optimizing soldering conditions resulted in significant reduction in voiding.

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