Until now, a semiconductor device mounted with semiconductor elements that generate heat attributable to their operation includes a metal base plate made of metal such as copper that excels in thermal conductivity, in order to enhance heat-dissipation performance. In a conventional semiconductor device, heat generated by semiconductor elements is dissipated through an organic insulation sheet and ceramic substrate to a metal base plate connected to a cooling unit. In recent years, the heat-dissipation characteristics need to be enhanced even more with growing high-density integration of the semiconductor elements.
A semiconductor device is disclosed in Patent document 1, in which a ceramic insulation substrate is disposed on a metal base plate via solder, and in addition on the ceramic insulation substrate are mounted semiconductor elements such as power chips via solder. Heat generated by the semiconductor elements is transmitted to the metal base plate via the ceramic substrate, and then dissipated outside through a cooling unit connected to the metal base plate. The ceramic substrate is made by sintering inorganic materials such as aluminum nitride (AlN), aluminum oxide (Al2O3) and silicon nitride (SiN), and its heat-dissipation performance is thereby enhanced.
When the organic insulation sheet is interposed between the semiconductor elements and metal base, the heat-dissipation performance of the organic insulation sheet needs to be enhanced. Inorganic powder with high thermal conductivity for enhancing the heat-dissipation performance is disclosed in, for example, Patent document 2. This inorganic powder with high thermal conductivity includes inorganic powder whose average particle size is 1 to 20 μm and maximum particle size is 45 μm or less; an inorganic powder X constituted of particles sized ranging from 3 to 40 μm is spherically-shaped with a roundness of 0.80 or more and in addition a thermal conductivity of 10 W/mK or more; an inorganic powder Y constituted of particles sized ranging from 0.1 to 1.5 μm is spherically- or aspherically-shaped with a roundness in a range from 0.30 to 0.80 and in addition a thermal conductivity being the same as or less than that of the powder X; and the mass ratio of X/Y is between 1 and 30. Thereby, a resin composition has been intended to be prepared, which is provided with excellent heat-dissipation performance, as well as the viscosity of which would not easily increase even if resin is densely filled with the powder.