Abstract: In a method and a system in which while carrying objects to be treated to a preheating chamber and a reflow chamber adjacent thereto, hot gases are blown against the objects to be treated by cross flow blowers provided in the preheating chamber and the reflow chamber to melt solder so as to solder electronic parts on a circuit substrate; a free air introducing port is controllably provided in the vicinity of an intake port of the cross flow blower in the preheating chamber, and an exhaust port and an exhaust fan for exhausting gases having an amount corresponding to the free air taken from the free air introducing port, out of the preheating chamber are provided.

Abstract: A reflow soldering apparatus having a pre-heating chamber and a reflow chamber, wherein a hot gas recirculation system including a cross-flow blower, a diverging nozzle and a heater is provided in the reflow chamber or both in the pre-heating chamber and the reflow chamber, so that a hot gas such as heated air is uniformly applied to the object such as a combination of a substrate and an electronic parts carried by the substrate, whereby uniform distributions of temperature and flow velocity of the hot gas are attained. The hot gas recirculation means may be arranged so as to vary the angle at which the hot gas impinges upon the substrate and the breadth over which the hot gas is applied.