Rework is the term for the refinishing operation or repair of a PCB assembly, usually involving desoldering and re-soldering of surface-mounted electronic components.   

Mass processing techniques are not applicable to single device repair or replacement, and specialised manual techniques by expert personnel using appropriate equipment are required to replace defective components; ball grid array (BGA) devices particularly require expertise and appropriate tools.  

A hot air gun or hot air station is used to heat devices and melt solder, and specialised tools are used to pick up and position often tiny components.