Definition

Solder paste is powdered solder suspended in flux vehicle, printed through stencils onto SMT pads. Composition: SAC305 (96.5Sn/3Ag/0.5Cu) is standard lead-free; Sn63Pb37 for leaded. Powder size (Type 3, 4, 5) affects print resolution - finer powder for smaller apertures. Paste requires refrigerated storage, limited stencil life (abandon after 8-24 hours). Print quality depends on stencil design, squeegee parameters, and paste condition. Post-print inspection (SPI) catches defects before component placement. Paste volume determines joint reliability.