The present invention relates to a reflow film containing a thermoplastic resin which is dissolvable in a solvent, and solder particles, wherein the solder particles are dispersed in the film, and also relates to a solder bump formation method which comprises: (A) a step of mounting the reflow film on the electrode surface side of a substrate, (B) a step of mounting and fixing a flat plate, (C) a step of heating, and (D) a step of dissolving and removing the reflow film, and herewith, a reflow film is provided which, by causing localization of the solder component on the electrodes of the substrate by self-assembly, exhibits excellent storage properties, transportability and handling properties during use, and can form solder bumps or solder joints selectively on only the electrodes.