Reflow Soldering
What Is Reflow Soldering?
Reflow soldering is the dominant assembly process for surface mount PCBs, where solder paste applied to component pads is heated through a carefully controlled temperature profile to melt the solder and form permanent electrical and mechanical connections. The reflow process occurs in a convection oven with multiple temperature zones: preheat (gradual temperature ramp to activate flux), soak (temperature equalization across the board), reflow (peak temperature above solder melting point), and cooling (controlled temperature descent to solidify joints).
The reflow temperature profile must be optimized for the specific board design, considering factors such as board thermal mass, component heat sensitivity, solder paste chemistry, and the thermal uniformity across all solder joints. PCB layout directly affects reflow quality: large copper areas act as heat sinks that slow local heating, small components near large thermal masses may not reach reflow temperature, and unequal pad connections create the thermal asymmetry that causes tombstoning. Engineers must consider these thermal reflow dynamics during layout to ensure that all solder joints reach and maintain the correct temperature for the required duration.
Reflow-Aware Component Placement
Physics-driven AI layout tools that incorporate thermal awareness during component placement can optimize part locations and orientations to improve reflow soldering quality. By evaluating the thermal environment around each component — considering nearby copper areas, adjacent component heat loads, and the relative thermal mass of each solder joint — these tools can minimize the thermal gradients that cause assembly defects. This reflow-aware placement approach is particularly valuable for complex boards with mixed component sizes, where maintaining uniform thermal conditions across all solder joints is most challenging.






