Why is reflow soldering called reflow

Why is reflow soldering called "reflow"? Reflow soldering refers to a process in which the solder paste reaches the melting point of the solder paste, under the action of liquid tin surface tension and flux, the liquid tin reflows to the component pins to form solder joints, so that the circuit board pad and the component are welded as a whole, which is also called "reflow" process. Jeenoce electronic through reflow soldering process, so that we can more intuitive understanding.

1. When the PCB circuit board enters the reflow soldering heating zone, the solvent and gas in the solder paste evaporate. At the same time, the flux in the solder paste moistens the pads, component ends and pins. The solder paste softens, collapses and covers the pads, isolating the pads and component pins from oxygen.

2. When the PCB circuit board enters the reflow soldering insulation area, the PCB and components shall be fully preheated to prevent the PCB from suddenly entering the soldering high temperature area and damaging the PCB and components.

3. When the PCB enters the reflow soldering area, the temperature rises rapidly to make the solder paste reach the melting state. The liquid solder wetts and diffuses the PCB pad, component ends and pins, and the liquid tin reflow mixes to form the solder contact.

4. The PCB enters the reflow soldering cooling area, and the liquid tin reflows to solidify the solder joint under the action of reflow soldering cold air; The reflow is now complete.

The whole working process of reflow welding is inseparable from the hot air in the reflow furnace. Reflow welding depends on the action of hot air flow on the solder joint, and the colloidal flux reacts physically under a fixed high-temperature air flow to achieve SMD welding; The "reflow" of reflow welding is because the gas circulates back and forth in the welding machine to produce high temperature to achieve the purpose of welding, so it is called reflow welding.