Desoldering - how to remove a component
By Michael S. Fisher  WT9W

If you have gotten into the act of building kits, you are inevitably going to face the situation where you need to remove a component that you have soldered on to a pc board.   This may be due to an error or a modification to the circuit that will really make it "hum".  Or you have finally located a faulty component and need to replace it.  Whatever the case, your desoldering technique can make the difference between a successful effort and a damaged pc board.  This guide is for conventional components although some of the steps may be applied to the removal of surface mount components.  Also, I strongly recommend that you read The Basic Soldering Guide by Alan Winstanley.  This is an excellent guide for the process of soldering and desoldering .

First, you will need some special tools to perform this task as painlessly as possible.   They include:
Soldering Iron
Solder
Desoldering Pump
Desoldering Braid
Long Nose Pliers
Wire Cutters (preferred thin blades for getting in to tight places)
PanaVice (Optional)

The first rule for desoldering components is: THE BOARD IS MORE IMPORTANT THEN THE COMPONENT THAT YOU ARE REPLACING.  Always, sacrifice a component before risking damage to the pc board.  It is much easier and less costly to replace a component then to try to repair or replace a damaged pc board.  Some boards you may work with are doublesided with plated through holes.  These are more difficult to desolder.

The second rule is:  DO NOT OVERHEAT THE SOLDER JOINTS.   Overheating a solder joint can damage the pc board by causing a pad or trace to detach.

The first step is to locate the solder joints for the component that you want to desolder.  This can be a difficult task on a densely populated board.  You want to be certain that you locate the correct joints so that you don't needlessly damage other components. 

Once you locate the correct solder joints, you will remove as much of the solder as possible using a desoldering pump.  To do this, place the tip of your soldering iron on the solder joint so that when the solder melts, it heats the lead and the pad at the same time.   At the same time you will need to hold the desoldering pump so that the tip is positioned to suck up the molten solder.  Trigger the pump when the solder has melted.  The trick is to heat the solder joint sufficiently to melt all of the solder on the pad and in the hole.  Since this takes some judgment, you will become more proficient with practice.  PC boards that have plated through holes will need to be heated a little longer then normal solder pads.  DO NOT OVERHEAT THE SOLDER PADS.  The goal is to remove as much of the solder as possible.   Perform this procedure on all of the solder joints for the component to be removed.  In some cases, on components with only one or two leads, you may find that you have removed enough of the solder so that the component  is loose and can be removed easily.  This rarely occurs and you should not try to force the component off of the board! 

In most cases you must proceed to the next step which is to carefully snip the component leads on the component side of the board using the wire cutters.  This is where you sacrifice the component to guarantee you won't damage the board.  The goal is to be able to remove the component leads from the board, one at a time.  Once you have removed the component, you can heat each solder joint and remove the lead from the hole using the long nose pliers.  To do this, find which side of the board has the most lead exposed.  Hold the lead with the long nose pliers.  Place the tip of the soldering iron against the pad and the lead. This must be done on the bottom side of the board unless the board is double sided (pads on both sides) or has plated through holes.    Remove the lead when the solder has melted.

If it is necessary to remove any remaining solder from the solder pads, you can use the desoldering braid.  To do this, place the desoldering braid flat against the solder pad.  Place the tip of the soldering iron on the desoldering braid.  When the braid becomes sufficiently hot, you will see it "wick up" the excess solder.  Remove the iron from the braid and the braid from the solder pad at the same time.  The pad will appear tinned but should be free of excess solder.
 
The next step is to remove any remaining solder from the holes using the desoldering pump.  Place the soldering iron against the pad while holding the desoldering pump against the hole.  This usually works better if you can hold the desoldering pump on the opposite side of the board from the soldering iron.  If you have a board holder, such as a PanaVice, it will leave both of  your hands free to perform this step.   Trigger the pump when the solder has melted.  All of the solder should have been removed and the hole should now be open.

You can now install the new component, unless you are doing a modification that calls for leaving this part out.

You may be wondering why I remove the solder from the solder joints before cutting the component off of the board.  When you snip the component leads, you are applying some stress to the board that could wind up damaging it by lifting a pad or trace.   By removing the excess solder, you minimize the components mechanical connection to the board   and reduce the chances of damage when you snip the leads.

Well, that's all there is to the process.  It can be somewhat time consuming when removing components with multiple leads like IC's.  However, you definitely want to take your time.  Your patience will be rewarded with a successful job and an undamaged pc board.  If you are a hombrewer and like to tinker with your projects, you will need to master this process.  Experimenting with your projects and enhancing them will require you to perform this task many times.