Selective soldering is an automated process. It gives you the precision of hand soldering with none of its delays and inconsistencies.
 

• Preparation: The first step is to program the solder pot with the positions on the PCB that have to be soldered.
• Fluxing: In the fluxing stage, flux is applied to the components that must be soldered. This is a major difference to wave soldering, where flux covers the entire PCB.
• Preheating: Then the temperature of the assembly is raised until there is sufficient heat for activating the flux. This ensures the effective filling of spaces with solder.
• Soldering: Finally, there is the soldering process itself. A soldering pen distributes solder material on the board in a pattern programmed to only cover the points that need to be soldered. Then the soldering of the leads to the PCB can commence. The solder pot lowers and moves to the next spot. 

Different soldering methods are available for PCB production. The most common are wave, selective soldering and reflow soldering. In the choice between these options, selective soldering offers distinct benefits:
 

• Selective soldering results in better wetting, which refers to the ability of the molten solder to create a bond between component and PCB.
• It also reduces the amount of flux required, which lowers operating costs and reduces the leftover residue.
• Selective soldering eliminates the need for PCB cleaning or brushing because it results in clean, shiny joints.
• The process reduces defect formation and other problems.

Because of its inert properties, nitrogen is applied in soldering to ensure the process is free from oxygen. That is because oxygen would react with the solder. This would create an oxide layer that can lead to quality problems or short circuits in the selective soldering units.