Thermal Path
Thermal reflow profile geometries describe the temperature journey of a board as it passes through an oven. A ramp-to-spike profile moves the assembly steadily upward in temperature until it reaches the melting point of the solder. This method differs from the traditional soak profile by eliminating the long plateau phase.
It is often used to reduce the total heat exposure for sensitive components.
Wetting Characteristic
Solder paste responds differently to rapid heating than it does to a slow soak. The use of ramp-to-spike heating can improve the wetting of certain alloys by keeping the flux active until the last possible moment. This leads to cleaner joints and fewer oxidation issues.
Such a profile requires precise control of the oven’s heating elements to avoid overshooting the target temperature.
Defect Control
Minimizing the time spent at high temperatures reduces the risk of damaging the board laminate. Manufacturers select ramp-to-spike profiles to prevent the growth of excessive intermetallic layers which can make a joint brittle. This approach also helps in reducing the power consumption of the reflow process.
Careful monitoring with thermocouples ensures that the spike remains within the safe operating window. The profile is a common choice for lead-free soldering where the process window is very narrow.
