Definition

Reflow soldering melts solder paste to attach surface-mount components. The process: print paste through stencil, place components, run through reflow oven with controlled temperature profile (preheat, soak, reflow peak, cooling). Lead-free (SAC305) requires peak temperatures of 245-260°C; leaded solder peaks at 210-225°C. Profile matters - too fast causes tombstoning and solder balls; too slow damages components. Double-sided boards need two reflow passes. The thermal mass of the assembly affects profile requirements. Most PCB assemblies use reflow as the primary soldering method.