Definition

Surface Mount Device (SMD) is any component mounted on PCB surface pads rather than through holes. SMD packages include passives (0201, 0402, 0603), ICs (SOIC, QFP, QFN, BGA), and connectors. For PCB design, SMD requires precise pad geometry per IPC-7351 footprints, copper-defined or solder-mask-defined pad styles, and thermal relief connections to planes. Choose SMD over through-hole when: board space is limited, automated assembly is planned, or high-frequency performance matters (shorter leads = less inductance). Through-hole remains better for high-current connectors and mechanically stressed components.