PCB design glossary
Footprint
The land pattern (pads, courtyard, silkscreen) on a PCB that physically holds a component.
A footprint is the physical mounting pattern for a component on the PCB: the metal pads the leads solder to, the courtyard that reserves space around the part, the silkscreen outline that helps an assembler orient it, and any mechanical holes or fiducials.
Footprints are typically drawn from the manufacturer's datasheet using IPC-7351 land-pattern guidelines. Getting the footprint wrong is one of the more common reasons a board fab succeeds but assembly fails.
What a footprint contains
- Copper pads, numbered to match the pins of the schematic symbol.
- A courtyard: the area the part reserves so neighbours cannot collide with it.
- A silkscreen outline and a pin-1 mark, so an assembler places it the right way round.
- A fabrication-layer outline of the real body, and often a 3D model for checking fit.
- Holes, slots or fiducials for through-hole parts and connectors.
How footprints are sized
Pad sizes come from the manufacturer's recommended land pattern in the datasheet, or from IPC-7351, which calculates pads from the part's lead dimensions and tolerances. IPC-7351 defines three density levels: most (larger pads, easy hand soldering), nominal (the usual default) and least (tight, for dense boards). Footprint names like SOIC-8_3.9x4.9mm_P1.27mm encode the package, body size and pin pitch.
Common footprint mistakes
- Pin numbering that does not match the symbol, so every connection lands on the wrong pad.
- The right package with the wrong variant: SOT-23 transistors and regulators come with different pin orders.
- Mixing millimetres and mils when drawing from a datasheet.
- Pin 1 marked on the wrong corner, or hidden under the part's body.
- Thermal pads left off QFN footprints, or drawn without the paste pattern the datasheet asks for.
Work it out with a free tool
Part missing from your library?
Type the package dimensions from the datasheet and the footprint generator draws an IPC-7351 land pattern you can save as a KiCad footprint.
Generate a footprint