DESOLDERING is the process of removing soldered components from a circuit made on PCB. Desoldering pump along with the soldering iron is used for this purpose. A desoldering pump also known as solder sucker is a small mechanical device which sucks the liquid/molten solder from the joint where the components are mounted. In order to desolder a component from the PCB, we first heat up the solder joint with the soldering iron till the solder liquefies/melts. At the same moment we actuate the soldering pump by pressing the trigger lever and bring the tip over the molten metal and pull the trigger back by pressing a button shown in the below image. At this instant the lever is pulled back and the tip of the pump sucks the molten solder. This process is repeated until all the residue solder is sucked by the pump and the hole on the PCB is clear to solder a fresh component. 

Soldering – a must skill for all electrical and electronic works. ‘Soldering’ is defined as the process of joining two pieces of metals using a filler metal, known as solder, having a low melting point below the melting point of the work piece. It is often confused with welding but the difference in between them is, in soldering the work piece is not melted, they are joined using a filler metal, but in welding work piece is joined by melting.  Soldering was practiced as far back as 5000 years ago in Egypt. Soldering was widely performed around 4000 years ago when tin was discovered as soldering metal. Soldering process was introduced in Mediterranean region, and was followed in the Roman Empire, Swiss and Hungaria.