In soldering an electronic component, for the purpose of leading molten solder during re-flow, metallic powder 8 is mixed into flux employed so as to intervene between a bump and an electrode. The metallic powder 8 has a flake or dendrite shape including a core segment 8a of the metal molten at a higher temperature than the liquid phase temperature of solder constituting a solder bump and a surface segment 8b of the metal with good-wettability for the molten solder and to be solid-solved in the core segment 8a molten. In the heating by the re-flow, the metallic powder remaining in the flux without being taken in a solder portion is molten and solidified to become substantially spherical metallic particles 18. Thus, after the re-flow, the metallic powder does not remain in a flux residue in a state where migration is likely to occur, thereby combining both solder connectivity and insurance of insulation.