Heat Absorption
Phase transition in which a liquid compound absorbs thermal energy from the environment to transform into a gas during reflow soldering. This process of endothermic evaporation occurs when volatile solvents in the solder paste vaporize as the printed circuit board travels through the preheat zone. The local temperature rise slows down during this phase because the transition consumes energy that would otherwise heat the board assemblies.
Thermal Profile
Profiling instruments measure this energy absorption as a slight plateau in the heating curve of the assembly. If the solder paste contains an excessive concentration of low-boiling solvents, the resulting vapor barrier can displace nitrogen in the reflow chamber and lead to oxidation. Engineers must adjust the zone temperature settings to compensate for this energy loss to ensure that the solder alloy reaches its liquidus temperature.
This careful calibration ensures the reflow process avoids insufficient wetting on dense circuit boards.
Solder Defect
Uncontrolled volatilization during the early stages of heating leads to void formation within the completed joint. When the gas cannot escape before the solder solidifies, it remains trapped as a spherical pocket of empty space. This structural defect reduces the mechanical strength and thermal conductivity of the electrical connection.
