Definition

A screen printer (or stencil printer) deposits solder paste onto PCB pads by forcing paste through stencil apertures using a squeegee blade. The machine aligns the stencil to the PCB using fiducials, lowers the stencil onto the board, sweeps paste across with controlled pressure and speed, then separates cleanly. Print quality depends on stencil design, paste rheology, squeegee parameters, and separation speed. For PCB designers, screen printing affects: fiducial placement and design (required for alignment), pad design (affects paste release), and solder mask design (mask near pads can interfere with stencil gasketing). Consistent pad sizes within a design improve print quality across the board.