Electronic unit and method of making the same

1. An electronic unit comprising:

a substrate;

a heat-generating electronic component mounted on a heat-generating electronic component mounted area of the substrate;

other electronic components mounted on an outside of the heat-generating electronic component mounted area of the substrate;

a heat sink disposed on the heat-generating electronic component; and

a hot-melt resin layer disposed on at least one of the other electronic components,

wherein the heat sink includes an upper part that serves as a radiating portion and a lower part that has a recess facing downward and that includes a peripheral wall surrounding the recess and having an end face and a side face, the recess of the heat sink covering the heat-generating electronic component, and the end face of the peripheral wall of the heat sink placed on a surface of the substrate,

wherein the hot-melt resin layer continuously covers at least part of the surface of the outside of the heat-generating electronic component mounted area of the substrate and at least part of the side face of the peripheral wall of the heat sink, and

wherein the peripheral wall separates the heat-generating electronic component from the hot-melt resin layer.

2. The unit according to claim 1 , wherein the heat sink is fixed to the surface of the substrate by adhesion of the hot-melt resin layer.

3. The unit according to claim 2 ,

wherein the end face of the peripheral wall is placed on the surface of the substrate with an adhesive layer in between, and

wherein the hot-melt resin layer retains the heat sink on the substrate with a force greater than a force with which the adhesive layer retains the heat sink on the substrate.

4. The unit according to claim 1 , wherein the substrate has a communication path through which a space inside the recess of the heat sink communicates with a side of the substrate remote from the surface of the substrate.

5. A method of making an electronic unit, the method comprising the steps of:

(a) preparing a substrate on which a heat-generating electronic component is mounted on a heat-generating electronic component mounted area and other electronic components are mounted on an outside of the heat-generating electronic component mounted area and a heat sink including an upper part that serves as a radiating portion and a lower part that has a recess facing downward and including a peripheral wall surrounding the recess and having an end face and a side face;

(b) setting the heat sink and the substrate into a mold such that the recess covers the heat-generating electronic component and the end face of the peripheral wall of the heat sink is placed on a surface of the substrate; and

(c) injecting melted hot-melt resin into a cavity in the mold to form a hot-melt resin layer that continuously covers at least part of the surface of the outside of the heat-generating electronic component mounted area of the substrate and at least part of the side face of the peripheral wall of the heat sink.

6. The method according to claim 5 , wherein the peripheral wall separates the heat-generating electronic component from the hot-melt resin layer.

7. The method according to claim 5 , wherein the heat sink is fixed to the surface of the substrate by adhesion of the hot-melt resin layer.

8. The method according to claim 5 ,

wherein in the step (b), the radiating portion of the heat sink is positioned outside the cavity in the mold, and

wherein in the step (c), the hot-melt resin injected into the cavity is in contact with the side face of the peripheral wall without being in contact with the radiating portion.

9. The method according to claim 5 ,

wherein in the step (b), the end face of the peripheral wall is placed on the surface of the substrate with an adhesive layer in between, and

wherein the hot-melt resin layer retains the heat sink on the substrate with a force greater than a force with which the adhesive layer retains the heat sink on the substrate.