As solder paste is printed through the stencil apertures, it forms deposits that hold the components in place and, when reflowed, secures them to the substrate. The stencil design ― its composition and thickness, the size and shape of its apertures - ultimately determines the size, shape and positioning of the deposits, which are critical to ensuring a high-yield process with minimal defects. Today, a wide variety of materials and fabrication techniques enable suppliers to design stencils that meet the assembly challenges of fine-pitch technology, miniaturized components and densely packed boards. In addition, stencil technology now serves a full range of mass imaging materials. As stencil designers have gained in-depth knowledge about how aperture size and shape affects deposition, new technologies extend the capabilities of printing platforms and stencils into applications as varied as adhesive deposition and wafer bumping. The stencil serves two primary functions. The first is to ensure precise placement of a material, such as solder paste, flux or encapsulant, on a substrate. The second is to ensure the formation of properly sized and shaped deposits.
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