Evaluation Of Stencil Foil Materials, Suppliers And Coatings
Authors: Chrys Shea and Ray Whittier Company: Shea Engineering Services and Vicor Corporation – VI Chip Division Date Published: 10/16/2011
Abstract: The past few years have brought PCB assemblers a multitude of choices for SMT stencil materials and coatings. In addition to the traditional laser-cut stainless steel (SS) or electroformed nickel, choices now include SS that has been optimized for laser cutting, SS with smaller grain structures, and laser cut nickel. Available post-cutting processes include electrpolishing and nano-coating. Each option touts advantages over the others. To identify the best options for the real-world application of a highly miniaturized, very densely populated SMT product, an experiment was devised. It included different materials, manufacturing methods and suppliers. Stencils were tested in pairs in order to capture the effects of a new hydrophobic coating. The surface treatment was applied to one stencil of each pair, allowing for direct comparison of print performance with and without the coating. Output variables included print yields, transfer efficiencies on 0.5mm BGAs and 0201s, volume repeatabilities on BGAs and 0201s, and dimensional accuracy of the stencils.