A circuit device having superior mechanical strength at the interface
between a circuit board and heat sink and superior efficiency for
radiating heat from a circuit element to the heat sink through the
circuit board. The circuit device includes the metal-based insulation
board for installing the circuit element, and the heat sink, over which
the insulation board is installed with a paste arranged therebetween. The
insulation board has a projection arranged on the surface facing the heat
sink along a peripheral portion. At least part of the projection contacts
the heat sink through the paste layer.