Soldered joints, if improperly done, may need to be â€˜desolderedâ€™ or the solder removed in order to resolder them. A poorly soldered joint can result in failure of the electrical circuit over a period of time. This can happen for a number of reasons. Low quality solder or failure to properly clean the surface before soldering or even lack of proper technique and corrosion of the joint due to leftover flux, movement (shake) of the joint before the solder has cooled may all cause a poor soldered joint.
There are other reasons you might need to desolder a joint. Desoldering and resoldering may also be required in order to replace a defective electronic component or if you are troubleshooting an electrical circuit.
One common method of desoldering is to use a desoldering pump which is a vacuum pump similar in operation to a bicycle pump in reverse. The spring loaded plunger breaks the solder and gets sucked away by the pump. Repeated operation of the pump may be required in order to completely desolder a joint, or you can also use the solder pump to take up the bulk of the flowing solder and finish up the job with solder wick. Either way works – the solder wick is more expenisve so you may want to use both if you have a large job. Be careful – the pump should be operated carefully so that no damage the PCB or the electronic components occurs.
A solder wick or braid is an alternative to desoldering pumps. Here the copper wick is placed over the joint and the solder is melted by means of soldering iron. The solder gradually flows into the wick and hence gets removed. The wick must be removed from the PCB before it cools down as otherwise it may damage the board.