Now what is LEF? LEF (short for Library Exchange Format) is used by CAD tools in the EDA industry. It contains physical information on an IC technology such as metal layers, vias, and sites. It also contains descriptions of a number of macros. Since the macros are used during the placement and routing of an IC they have information on the physical layout such as pin and blockage locations. More information on LEF and other collaborative efforts in the EDA industry can be found on Si2.