A soldering flux is disclosed which exhibits improved shape retention properties during printing, can inhibit sagging upon heating, and exhibits high electrical reliability between conductors. The soldering flux contains an epoxy resin, an organic carboxylic acid and, as a heat-resistant shape-retaining agent, and a plastic having a linear structure, wherein the epoxy resin and the organic carboxylic acid are blended so that the quantity of carboxyl groups in the organic carboxylic acid is 0.8 to 2.0 equivalents relative to 1.0 equivalent of epoxy groups in the epoxy resin, and the total quantity of the epoxy resin, the organic carboxylic acid and the plastic having a linear structure is 70 mass % or more relative to the total mass of the flux.