It is a tooled aluminum foil (or stainless steel foil) with opening window cut by laser, to simply transfer the solder paste via this window to the surface of SMD pad on the bare circuit board.

The quality of stencil is most important of high quality PCB assembly, all WELLER’s stencil is tooled by high quality of aluminum material with high precious laser cut process with REDUCE ALL APERTURES BY 10%.

Refer WELLER-SMT-Stencil-Technical-Specification