Definition

Reflow soldering is the standard process for attaching surface-mount components. Solder paste (flux plus solder powder) is stencil-printed onto pads, components are placed by pick-and-place machine, then the assembly passes through a reflow oven with controlled temperature profile. The profile includes preheat (activate flux, equalize temperature), soak (remove volatiles), reflow (solder melts and wets), and cooling zones. Lead-free reflow requires higher peak temperatures (~260°C vs ~230°C for leaded), stressing components and PCBs.