Stencil deformation during stencil printing

Abstract

Uneven solder mask thickness or other artifacts on PCBs can keep the stencil away from the PCB during stencil printing, which cause large deposited solder paste volume, and can result in solder bridges after reflow soldering. In our experiment we have investigated the deformation properties of stencils. The load-strain curve of a 125 µm thick stainless steel stencil was measured on nine locations. By the deformation experiments, the FEM (Finite Element Method) model of the stencil was created. With FEM simulations, the minimum technological distances (distance between artifacts and solder pads) for a range of step heights (difference between artifact height and pad height) and for different stencil thicknesses were determined. With the adherence to this technological distance, the stencil can bend down to the pad, and the proper amount of solder paste can be deposited onto the pad.