Semiconductor device and method of manufacturing the same

1. A method of manufacturing a semiconductor device having a heat-radiation surface for radiating heat to a cooler, comprising:

preparing a base plate having a mounting surface, said heat-radiation surface opposed to said mounting surface, and a thickness direction extending from said mounting surface to said heat-radiation surface;

mounting a semiconductor element on said mounting surface; and

forming a cover having a portion that seals said semiconductor element on said mounting surface of said base plate, said cover having a projecting portion arranged outside said heat-radiation surface and projecting from a level of said heat-radiation surface in said thickness direction, and

forming an intermediate layer arranged on said heat-radiation surface of said base plate, projecting from a level of said projecting portion in said thickness direction, and made of a thermoplastic material in a solid-phase state,

wherein the forming of said intermediate layer includes applying a thermoplastic material in a liquid-phase state on said heat-radiation surface by moving a squeegee on a mask plate arranged on said heat-radiation surface of said base plate.

2. The method of manufacturing a semiconductor device according to claim 1 , wherein the applying of said thermoplastic material includes adjusting a pressure for pressing said squeegee against said mask plate.

3. The method of manufacturing a semiconductor device according to claim 1 , wherein said squeegee has a contact portion brought into contact with said mask plate, and said contact portion has at least one of a protruding portion and a recessed portion.

4. A semiconductor device having a heat-radiation surface for radiating heat to a cooler, comprising:

a semiconductor element;

a base plate having a mounting surface on which said semiconductor element is mounted, said heat-radiation surface opposed to said mounting surface, and a thickness direction extending from said mounting surface to said heat-radiation surface;

a cover having a portion that seals said semiconductor element on said mounting surface of said base plate, said cover having a projecting portion arranged outside said heat-radiation surface and projecting from a level of said heat-radiation surface in said thickness direction; and

an intermediate layer arranged on said heat-radiation surface of said base plate, projecting from a level of said projecting portion of said cover in said thickness direction, and made of a thermoplastic material in a solid-phase state.

5. The semiconductor device according to claim 4 , wherein said intermediate layer has a plurality of patterns separated from each other on said heat-radiation surface of said base plate.

6. The semiconductor device according to claim 4 , wherein said intermediate layer has different thicknesses on said heat-radiation surface of said base plate.

7. The semiconductor device according to claim 4 , wherein said cover has a housing having said projecting portion and a sealing material arranged in said housing.

8. The semiconductor device according to claim 7 , wherein said base plate has a plurality of portions coupled to each other by said housing.

9. The semiconductor device according to claim 7 , wherein said housing has a facing surface facing said cooler, and said projecting portion projects from said facing surface.

10. The semiconductor device according to claim 7 , wherein a through hole for attaching said cooler is formed in said housing, and said projecting portion is configured by a metal bushing inserted into said through hole.

11. The semiconductor device according to claim 7 , wherein said projecting portion is made of a thermoplastic material.

12. The semiconductor device according to claim 7 , wherein said projecting portion is configured by an adhesive portion that bonds said housing and said sealing material to each other.