Stencil design for mixed technology through-hole/SMT placement and reflow

Reviews stencil design requirements for printing solder paste around and in through-hole pads/openings. There is much interest in this procedure since full implementation allows the placement of both through-hole components a s well as surface mount devices and the subsequent renew ei both simultaneo usly. This in rum eliminates the need to wave solder or hand solder through -hole components. The effect of component material type, pin type, lead len gth, and standoff height of the through hole components is reviewed. Board design issues including plated through-hole size, pad size, board thickness , and solder mash type are also reviewed. Three stencil designs are conside red: single thickness stencils with oversized stencil apertures for overpri nting solder paste in the through-hole pad areas; step stencils with oversi zed stencil apertures for overprinting solder paste in the through-hole pad areas; thick stencils (0.384-0.635 mm thick) for printing solder paste in the through-hole pad areas. The latter thick stencil is the second stencil in the two-print stencil process. Several examples are reviewed with the re commended stencil designs.