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

Author： Coleman William E. Jean Denis Bradbury-Bennett Julie R.

ISSN： 0954-0911

Source： Soldering & Surface Mount Technology, Vol.12, Iss.3, 2000-12, pp. : 8-12

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Abstract

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.