Method of manufacturing electronic component device

A method of manufacturing an electronic component device which includes an electronic component mounted on a wiring board, and a heat-spreading component having a plate-shaped principal part and being coupled via a thermal interface material to the electronic component, the method comprising:

• forming a recessed portion, in the plate-shaped part of the heat-spreading component, only at a position on a periphery of a portion thereof corresponding to an area for the electronic component, and storing a thermoplastic resin serving as the thermal interface material in the recessed portion;
• arranging a large number of filamentous thermo-conductive elements serving as the thermal interface material, so as to stand side by side on a surface of the heat-spreading component in which the recessed portion is formed, or on an exposed surface of the electronic component;
• fixing the heat-spreading component to the wiring board in such a manner that a surface of the wiring board on which the electronic component is mounted is faced to the surface of the heat-spreading component in which the recessed portion is formed, and that a clearance is adjusted between the electronic component and the heat-spreading component;
• and
• after said fixing, heating the thermoplastic resin to a softening point thereof into a fluidized state, and causing the resin to flow into the clearance between the electronic component and the heat-spreading component to thereby fill the clearance.