1. Field of the Invention
The present invention relates to a semiconductor device using a thermal-conductive sheet for radiating heat from a semiconductor chip.
2. Description of the Related Art
A conventional semiconductor device, for example, as disclosed in Japanese Laid-Open Patent Publication No. 2005-64168 (Patent Document 1), includes a metal-base circuit substrate in which a circuit including a highly heat-generating electrical part (semiconductor chip) is formed on a metal-base board through a highly thermal-conductive insulating layer (thermal-conductive sheet); here, in the substrate, ceramic particles are filled as highly thermal-conductive fillers into resin. In this semiconductor device, the metal-base board and the circuit are united with each other; thus, the device is configured to conduct heat from the highly heat-generating electrical part into the metal-base board.
Moreover, a conventional semiconductor device, for example, as disclosed in Japanese Laid-Open Patent Publication No. 1997-314747 (Patent Document 2), includes a composite ceramic sheet (thermal-conductive sheet) that is produced by disposing ceramic pieces (ceramic laminae) inside a polymer film, and that is made to utilize the thermal and electrical functions of the ceramic, and also to have flexibility; thus, heat from a heat source is conducted to a heat radiator through the ceramic pieces.
However, in the highly thermal-conductive insulating layer disclosed in patent Document 1, because resin whose thermal conductivity is relatively low intervenes between the thermal-conductive ceramic particles, thermally conductive paths are omni-directionally broken, and improvement of the thermal conductivity is limited by the condition. Accordingly, in order to improve the thermal conductivity, when the ceramic particles have been highly filled, a problem has occurred that the adhesion characteristics decrease.
Moreover, when the composite ceramic sheet disclosed in Patent Document 2 is placed between a metal heat sink provided with a semiconductor chip and a metal base board, caused by the difference in linear-expansion coefficients between the ceramic piece and the heat sink or base board, a warpage generates in the semiconductor device, and peeling of the heat sink or breaking of the ceramic piece generates; consequently, a problem has occurred that the reliability of the semiconductor device decreases.