Attach this attribute just like the device= (3.1) attribute. This is a free standing or floating attribute.
package_name is the pcb footprint or package type like DIP14 or DIP40. Although this attribute in principle is pcb package dependent, gEDA/gaf conventions exist to make this attribute as portable as possible, allowing for easy collaboration and sharing between users. See the Footprint naming conventions in the gEDA/gaf Symbol Creation Document.