In the early days of SMT assembly, step stencils were used to reduce the stencil thickness for 25 mil pitch leaded device apertures. However, as SMT requirements became more complex and, consequently, more demanding, so did the requirements for complex step stencils. Mixed technology applications of solder paste printing for through hole/SMT as well as solder paste/flux printing for flip-chip/SMT require special step stencil designs. Thick metal stencils, having both relief etch pockets and reservoir step pockets, are very useful for glue and paste reservoir printing. E-FAB®* and laser-cut step-up stencils for ceramic BGAs and RF shields are a good solution to achieve additional solder paste height on the pads of these components to cope with non-coplanarity issues. Special 3-D E-FAB stencils are an excellent solution for unique PCBs having some raised areas on the board (up to .120” high). These applications and the stencil design to achieve solutions will be described in detail in this paper.

This article originally appeared in Global SMT & Packaging magazine 6.9 - October 2006.

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Keywords : Step stencils, Photo Stencil, reservoir printing, E-FAB, laser-cut set-up, laser cut setup

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