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12 SMT Magazine • February 2014 by Chrys Shea ShEA ENgINEErINg SErVICES and ray Whittier VICor CorP. abstract Previous experimentation on a highly min- iaturized and densely populated SMT assembly revealed the optimum stencil alloy and flux-re- pellent coating for its stencil printing process. Production implementation of the materials that were identified in the study resulted in ap- proximately 5% print yield improvement across all assemblies throughout the operation, vali- dating the results of the initial tests. A new set of studies was launched to focus on the materials themselves, with the purpose of optimizing their performance on the assem- bly line. Using a similar test vehicle as the prior experiments, DOEs characterized key aspects of the stencil manufacturing process by varying the laser cutting parameters and coating materi- als. As the scope of the DOE grew, it also includ- ed evaluation of new materials and a compari- son of microBGA aperture designs. Eventually, additional runs were added to investigate the effects of nanocoating on wipe frequency and compare two different stencil cutting processes. Results of the prior tests are reviewed, and the new test vehicle, experimental setup and re- sults are presented and discussed. Introduction This study builds upon the results of a previ- ous investigation that identified the best stencil FEATUrE 12 SMT Magazine • February 2014 Stencil Image Courtesy of Photo Stencil.