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Evaluation of Stencil Technology for Miniaturization
Evaluation of Stencil Technology for Miniaturization
The objective of this study is to assess the impact of various stencil materials and fabrication methods on the repeatability of solder paste deposition.
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Authored By:
Neeta Agarwal
Robert Farrell
Benchmark Electronics Inc., Nashua, NH, USA

Joe Crudele
Benchmark Electronics Inc., Rochester, MN, USA

Chrys Shea
Shea Engineering Services
Burlington, NJ, USA

Ray Whittier
Vicor Corporation, Andover, MA, USA

Chris Tibbetts
Analogic Corporation, Peabody, MA, USA

Summary
Miniature components are ubiquitous and require repeatable solder paste depositions to ensure a reliable interconnect and minimize rework. The objective of this study is to assess the impact of various stencil materials and fabrication methods on the repeatability of solder paste deposition. A test was designed to assess the performance of 18 different stencils, submitted by 6 different suppliers, using a variety of materials, coatings, and fabrication methods. Performance metrics include stencil aperture accuracy and topography, along with print volume repeatability and transfer efficiency for 0.4mm and 0.3 mm pitch BGAs and 0201 components with area ratios in the challenging range of 0.45 to 0.70.

Conclusions
For miniaturized components, many different stencil construction technologies were tested. A wide array of results were observed.

The data indicates that the best performing stencils for the miniature components appear to be B5 and B6, and D14 and D16. Interestingly, B5 and D16 had no nanocoating on them. They were cut from name brand stainless steel on new, state-of-the-art cutters. B6 and D14 were also cut on new, state-of-the-art cutters and nanocoated with thermally cured fluoropolymer nanocoating.

The electroformed stencil demonstrated the poorest size accuracy of the 18 stencils tested, which is in agreement with 3 previous studies since 2011.1-3

Stencils that were laser cut with nickel overplate did not appear to perform as well as laser cut SS without overplate, with or without nanocoating.

New, investigative technologies that were tested show much promise for delivering quality prints at better price points, thereby representing better values to SMT assemblers.

Initially Published in the SMTA Proceedings

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