a pad

A pad is one of the small exposed copper islands on a PCB where a component's leg actually gets soldered down. If a trace is a road, a pad is a parking spot: the specific patch of bare copper where one pin of a part lands and is bonded with solder. Every component leg, every connector pin, every wire that joins the board does so at a pad. They are the points where the flat copper world of the board meets the three-dimensional world of the parts.

Pads come in two main styles matching the two ways parts mount. A through-hole pad is a ring of copper around a drilled hole; the component's wire lead pokes through and solder fills the ring on both faces. A surface-mount pad is a flat rectangle of copper sitting on the surface, with no hole; the part's metal terminal simply sits on top and solder bonds the two. In both cases the solder mask is deliberately left open over the pad (that opening is the solder mask aperture), so solder can wet the bare copper and form a strong, shiny joint.

Why it matters: pad size and shape are not cosmetic — they decide whether a joint is strong and whether the part solders reliably. Too small and there is not enough copper for a robust joint or for heat to flow during soldering; too large and on fine-pitch parts adjacent pads risk bridging. Manufacturers publish recommended land patterns for exactly this reason. A row of correctly sized pads in the right positions is what a footprint is built from, and a single misplaced or wrong-sized pad can make a part impossible to solder.