Low-temperature fired ceramic circuit substrate with improved Ag-Au connection reliability

A low temperature fired ceramic circuit substrate comprising:

• a plurality of laminated insulating layers each formed of a low-temperature fired ceramic fired at a temperature ranging between 800.degree. and 1,000.degree. C., the insulating layers including at least one inside insulating layer and at least one surface insulating layer;
• an inside layer wiring conductor formed of a conductive material of Ag system which is mainly composed of Ag, the inside layer wiring conductor being disposed in the inside insulating layer;
• a surface layer wiring conductor formed of a conductive material of Au system which is mainly composed of Au, the surface layer wiring conductor being disposed on the surface insulating layer;
• and
• an intermediate metal layer formed of a thick film paste of a conductive material of Au/Ag system which is mainly composed of Au/Ag, wherein said Au/Ag system is an allow powder of Au and Ag or a mixed powder of Au powder and Ag powder, the intermediate metal layer being interposed between the inside layer wiring conductor and the surface layer wiring conductor said intermediate metal layer contacting said inside and surface layer wiring conductors.