| abstract |
An insulating substrate is used for fabrication of a thick film circuit provided with a conductive pattern made from a paste containing glass frits, and comprises a foundation (1) containing an aluminum nitride and incidental impurities, and a multi-level surface film structure (2) provided between the foundation and the conductive pattern and having a lower surface film (3) of an aluminum oxide provided on a surface of the foundation, an intermediate surface film (4) provided on the lower surface film and formed of a substance having a relatively small acidity and an upper surface film (5) provided on the intermediate surface film and formed of a substance having a relatively large acidity, in which the substance with the large acidity rapidly reacts with the frits in a firing stage for enhancing the adhesion of the conductive pattern but the substance with the relatively small acidity restricts the consumption thereof, so that the total thickness of the multi-level film structure is decreased and, accordingly, the heat radiation capability is improved. |