In an electronic component soldering method of connecting a terminal provided on a flexible substrate to an electrode of a rigid substrate, after solder-mixed resin in which solder particles are mixed in thermosetting resin has been applied onto the rigid substrate so as to cover the electrode, the flexible substrate is put on the rigid substrate and heat-pressed, whereby there are formed a resin part that bonds the both substrates by thermosetting of the thermosetting resin, and a solder part which is surrounded by the resin part and has narrowed parts in which the peripheral surface is narrowed inward in the vicinity of the terminal surface and in the vicinity of the electrode surface. Hereby, the solder parts are soldered to the electrodes and the terminal at acute contact angles so that the production of shape-discontinuities which lowers fatigue strength can be eliminated.