What is the difference between soldering and desoldering? How do we desolder components and wires from a circuit board? Well, there are several different methods we can employ depending on what you want to remove.
Some of the ways for desoldering are, hot air, wicking, and solder suction with and without applied heat tips. You can also use a low temperature method using an alloy called "Chip Quik", that is an excellent tool for removing stubborn components without damaging them.
In order to select the correct method you first must decide how much heat you want to use in order to remove the component from its bonds without damage to the board. A poorly soldered joint will be unreliable and is likely to cause problems in the future. It may not have a good electrical connection or could work fine at first and then fail at a later date.
It can be hard to judge the quality of a soldered connection just by looking at it. For one thing, you may not know if the joint is bonded to the surrounding surfaces correctly.
A joint which is poorly formed is often called a "cold solder joint". Usually it results from some sort of contamination that prevents the parts from being soldered together. Possibly from not cleaning the surface properly. You will most likely notice this as the solder may exhibit globs, pock marks, or what is commonly known as "Measeling". This is where the solder looks like it has bumps all over it caused by the solder cooling too quickly.
There will come a time when you will need to remove solder from a bad joint. A few different methods can be used to accomplish this. No "one way" is always the best way. Some people prefer to use handheld desolder pumps. These employ a spring loaded body with a plunger inside that when you release the plunger the unit sucks up the molten solder. This method is not recommended by most professionals because it can create static charges capable of damaging the components or circuit board you are working on.
Another way, (I use this the most), is by utilizing a desoldering station with a vacuum pump. It is a handheld unit much like a soldering iron with a heated tip that is hollow in order to allow the vacuum to suck up the melted solder and store it in a holding chamber.
Here is a demonstration on how a desoldering unit works.
You can also use desoldering braid. This is a copper braid that will soak up the old solder from the joint when heat is applied with a soldering iron. Or, you can use hot air to heat up the joint and then remove the component. Just apply some flux to the joint to aid in heat transfer, slowly heat the joint with the hot air and then ramp up to a temperature level that is sufficient to melt the solder but leaving the surrounding area unharmed.