The medium, through which heat is being transferred in convection reflow systems, is either air or nitrogen. Circulating with fans hot air or nitrogen through the tunnel transfers the heat to the assembly. An arrangement of multiple convection modules in series, each module programmable to a different temperature setting, allows setting up the correct profile for a specific assembly. When the board moves on the conveyor through the process zone, it is exposed to these different temperatures. After the last heated zone (the peak zone), in which the solder paste is brought to a melt, cooling zones are provided which cool down the boards prior to leaving the oven.