4.2 Desoldering of DIL-type packages
It can be desoldered in any one of the following ways:
1. Destructive method: Here the connecting leads on the component side of the board are cut with sharp pliers; the wire is removed from the hole by means of a temperature controlled soldering iron and tweezers; the solder is removed from the hole either by solder sucker or by suction soldering iron or solder wick and the holes are checked for clearance.
2. Here the solder is sucked from the component leads either by solder sucker or by suction soldering iron. The component is removed after checking that all leads are loose and free of solder.
4.3 Removal of SMCs from PCBs:
If the board has been wave soldered, the components will usually have been glued before soldering to the board. The adhesive will be softened by heating, so that the components can be removed easily. For odd components such as potentiometers, trimmers, etc. special tools are recommended, depending on the size and shape of the component.
All removal methods are based on the understanding that the removed components will be discarded (component could be mechanically or electrically damaged).
4.3.1 Soldering iron plus a pair of tweezers:
a) Small components such as resistors, capacitors and small electrolytic capacitors are removed by heating one of the electrodes with a small soldering iron for 2 or 3 sec to melt the solder. At the same time, the component body is held with a pair of tweezers. Then, the other electrode is heated quickly with the same soldering iron. Now, the component can be removed with a pair of tweezers while solder on both electrodes is molten.
b) Small semiconductors such as SOT-23 are removed by heating the two leads on one side together for 2 to 3 sec. At the same time, the component is held with a pair of tweezers. The other lead is then heated quickly and the component is removed with a pair of tweezers.
In both the cases above, the surface of the printed circuit board is easily damaged by the soldering iron tip if the soldering iron is not held horizontally when the solder is removed by braid or when the iron is used to heat the soldered joints before removing the component.
Another way of removing the component is by cutting of leads. The component leads are cut with a very small cutter and the component body is removed. Here the cut lead is held with a pair of tweezers and heated with a soldering iron, until the lead can be removed easily. The solder is removed by means of braid and a soldering iron, or by a suction iron.
4.3.2 Hot-air plus a pair of tweezers or vacuum pipette:
IC packages are removed by heating both sides of the leads with a hot air gun. Care should be taken that other components are not damaged by the hot air flow. The component can be removed easily with a pair of tweezers. This method can also be used when removing a large number of components (resistors, capacitors and semiconductors). An adapted nozzle is required for large components.
4.3.3 Heating block plus a pair of tweezers or special soldering iron:
A heating block plus a pair of tweezers or a soldering iron with a bit adapted to the configuration of the component can be used to heat the component leads and to remove the component.
4.3.4 SMC removal by resistance (de)soldering:
The leads of large IC packages can be heated by means of resistance soldering or reflow soldered with the help of a heated block. The predetermined soldering time is 4 sec. At the moment when the solder on all leads is molten, the component can be removed with the aid of a vacuum pipette. This way it is possible to minimize the damage to the component so that it can be reused.