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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.
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