Composite substrate for printed circuits and printed circuit-substrate

Abstract

To permit firing a composite carrier for a printed circuit in which the carrier has a base of metal, typically steel, and thus is highly vibration and bending resistant, the coating or cover layer is a glass ceramic of BaO-Al.sub.2 O.sub.3 -SiO.sub.2, typically 25 to 40%, preferably 35% of BaO, 5 to 20%, preferably 10% Al.sub.2 O.sub.3 and 40 to 65%, preferably about 55% SiO.sub.2. Rather than using 40 to 65% SiO.sub.2, a lesser quantity of SiO.sub.2, e.g., 30 to 65% may be used and then 0 to 15% MgO, 0 to 15% CaO, 0 to 5% SrO, 0 to 2% B.sub.2 O.sub.3, 0 to 4% PbO, 0 to 3% ZnO and 0 to 4% TiO.sub.2 may be applied. The glass ceramic may be dyed, for example by an inorganic dye, such as cobalt silicate, and standard resistor and conductor pastes, such as Cermalloy or Heraprint may be applied and fired at temperatures below 980.degree. C., and entirely suitable for firing temperatures above 850.degree. C. The coating or cover layer has a thickness of above 20 micrometers, preferably of between about 0.03 to 0.06 mm.