Stencil design for mixed technology through‐hole/SMT placement and reflow Available to Purchase

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 as well as surface mount devices and the subsequent reflow of both simultaneously. This in turn eliminates the need to wave solder or hand solder through‐hole components. The effect of component material type, pin type, lead length, and standoff height of the through hole components is reviewed. Board design issues including plated through‐hole size, pad size, board thickness, and solder mask type are also reviewed. Three stencil designs are considered: single thickness stencils with oversized stencil apertures for overprinting solder paste in the through‐hole pad areas; step stencils with oversized 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 recommended stencil designs.