Desoldering
In electronics, desoldering is the removal of solder and components from a circuit board for troubleshooting, repair, replacement, and salvage.
Suction pumps are used to suck away molten solder, leaving previously joined terminals disconnected.
The desoldering head must be designed so that the extracted solder does not solidify so as to obstruct it, or enter the pump, and can be removed and discarded easily.
Use of too high a temperature or heating for too long may damage components or destroy the bond between a printed circuit trace and the board substrate.
If a multi-pin component need not be salvaged, it is often possible to cut the pins, then remove the residual ends one by one.
To remove and recover all components, both through-hole and surface-mount, from a board which itself is usually no longer needed, a flame or hot air gun can be used to rapidly heat all parts so they can be pulled off.
If they do not need to be re-used, some surface-mount components can be removed by cutting their leads and desoldering the remnants with a soldering iron.
Hot air (or gas) may be applied with tools ranging from some portable gas soldering irons such as the Weller Portasol Professional which can be fitted with a narrow hot-air nozzle, set to a temperature not controlled but approximately correct, to an industrial rework station with many facilities including hot-gas blowing, vacuum part holding, soldering iron head, and nozzles and fitting specific to particular component packages.
Several vendors offer systems that use heat shields to concentrate hot air where it needs to be, protecting nearby components and avoiding damage to the board or the QFP.
The extractor uses a spring system that gently pulls the IC upward when the liquid stage of solder has been reached.
Another way to remove these devices is to use Field's metal, an alloy which melts at around 140 °F (62 °C), lower than the boiling point of water.
The metal is melted into the solder joints of the device, where it remains liquid even once cooled down to room temperature, and the chip can simply be lifted off the board.
