A substrate for an electrical circuit system and a circuit system using that substrate

An electrical circuit system having a semiconductor device (14) electrically and thermally connected to an electrically conductive circuit layer (16) of a substrate (12) and having a heat-dissipating base layer (18) of an aluminum metal material in the substrate has an electrically insulating hard coating dielectric layer (20) of aluminum oxide directly adherent to the base layer mounting the electrically conductive circuit layer thereon in selected electrically insulated relation to the base layer while providing improved heat-transfer to the base layer, the aluminum metal material of the base layer being substantially free of iron and copper constituents and the electrically insulating hard coating of aluminum oxide being substantially free of iron and copper inclusions for achieving the selected electrically insulated relationship with a very thin dielectric layer to provide improved heat-transfer between the electrically conductive circuit layer and the base layer. Preferably the electrically insulating hard coating layer of aluminum oxide comprises a multiplicity of sections of the aluminum oxide hard coating material which are individually adherent to the base layer and are separated by an electrically insulating adhesive material which is disposed on and between the sections of the hard coating layer for cooperating with the sections of the hard coating layer in securely bonding and mounting the electrically conductive circuit layer in the desired electrically insulated relation to the base layer with improved heat-transfer to the base layer.