Rework (or re-work) is the term for the refinishing operation or repair of an electronic printed circuit board (PCB) assembly, usually involving desoldering and re-soldering of surface-mounted electronic components (SMD). Mass processing techniques are not applicable to single device repair or replacement, and specialized manual techniques by expert personnel using appropriate equipment are required to replace defective components; area array packages such as 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. A rework station is a place to do this work—the tools and supplies for this work, typically on a workbench. Other kinds of rework require other tools. Reasons for rework Rework is practiced in many kinds of manufacturing when defective products are found. For electronics, defects may include: Poor solder joints because of faulty assembly or thermal cycling. Solder bridges—unwanted drops of solder that connect points that should be isolated from each other. Faulty components. Engineering parts changes, upgrades, etc. Components broken due to natural wear, physical stress or excessive current. Components damaged due to liquid ingress, leading to corrosion, weak solder joints or physical damage. Process The rework may involve several components, which must be worked on one by one without damage to surrounding parts or the PCB itself. All parts not being worked on are protected from heat and damage. Thermal stress on the electronic assembly is kept as low as possible to prevent unnecessary contractions of the board which might cause immediate or future damage. In the 21st century, almost all soldering is carried out with lead-free solder, both on manufactured assemblies and in rework, to avoid the health and environmental hazards of lead. Where this precaution is not necessary, tin-lead solder melts at a lower temperature and is easier to work with. Heating a single SMD with a hot-air gun to melt all solder joints between it and the PCB is usually the first step, followed by removing the SMD while the solder is molten. The pad array on the conductor board should then be cleaned of old solder. It is quite easy to remove these residues by heating them to melting temperature. A soldering iron or hot air gun can be used with desoldering braid. The precise placement of the new unit