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Reflow soldering

Reflow soldering is a process in which generally a solder paste is used to temporarily attach one or several electrical components to their contact pads, after which the entire assembly is subjected to controlled heat, which melts the solder, permanently connecting the joint. Reflow soldering is the most common method of attaching surface mount components to a circuit board, although it can also be used for through-hole components by filling the holes with solder paste and inserting the component leads through the paste. In the conventional reflow soldering process, there are usually four stages, called “zones”, each having a distinct thermal profile: preheat, thermal soak (often shortened to just soak), reflow, and cooling.