A Powerful Tool for Special Applications Step StencilS

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 that have both relief etch pockets and reservoirstep pockets are very useful for glue and paste reservoir printing. Electroform 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. Special 3-D electroform stencils are an excellent solution for odd PCBs having some raised areas on the board (up to 0.090” high). The two-print stencil printing process is useful in dealing with the problem of small and large components coexisting on the same PCB. These applications and the stencil design to achieve a solution are discussed in detail in this paper.