Definition

A stencil is a thin stainless steel sheet (typically 100-150 µm thick) with laser-cut apertures that align with PCB pads. During SMT assembly, the stencil is placed over the board and solder paste is squeegeed across, depositing paste only where apertures exist. Stencil thickness and aperture size control paste volume. Thinner stencils (100 µm) suit fine-pitch components; thicker stencils (150 µm) provide more paste for larger components. For mixed designs, step stencils have different thicknesses in different areas. Aperture design follows area ratio rules: aperture area ÷ wall area should exceed 0.66 for reliable paste release.