Definition

A thermal profile defines the temperature that a PCB assembly experiences through a reflow oven over time. Key zones: preheat (ramp rate <3°C/s to avoid thermal shock), soak (flux activation, typically 150-200°C for 60-120s), reflow (above liquidus, 30-60s above 217°C for SAC305), and cooling (controlled rate to avoid brittle joints). Profile depends on solder paste, component thermal mass, and board size. Too hot damages components; too cool causes poor wetting. Thermocouples on the actual assembly verify the profile. Lead-free requires higher peak temperatures than leaded.