Library

A library is a shelf of named drawings kept for reuse: inverters, landings, board parts, or scripted devices, stored so a project can stamp them instead of redrawing them.

Three different drawings on a shelf: a crossing, a landing, and a two-gate device.

An inverter, or an 0805 resistor, is not redrawn for every job. The shelf holds cell masters, or footprint masters, sometimes PCell scripts, and a statement of which PDK those masters belong to. Place an instance and the design depends on that shelf staying stable. A library manager may list the shelves as stdcells, pads, or my_passives. A digital library of 400 cells and a board library of 30 footprints are the same kind of shared shelf.

LEF publishes the outsides of the digital library. A stream can carry the library cells into a chip file, or it can reference them and leave the shapes on the shelf. Board tools keep footprint libraries beside the symbol libraries used by the schematic. Copying a cell into the design "to be safe," and then editing that copy, leaves two versions of the truth. Referencing the library and giving it a version keeps a single source.

Treat the shelf as a product. Tag it stdcells_1.4, and do not overwrite a master in silence after a chip has taped out. The mismatch shows up months later: an instance still named INVX1 whose innards no longer match the LEF the router used. A footprint library on a board needs the same care, or a reel of parts meets the wrong lands.

See cells and instances, footprints are almost cells, and what is a layout.