Method for producing a multilayer ceramic circuit board

A method for producing a multilayer ceramic circuit board for use with copper conductors comprising the steps of:

• forming a multilayer structure comprising patterns of copper-based paste and glass-ceramic layers laminated alternately, at least the glass-ceramic layers located between the patterns of copper-based paste consisting essentially of a mixture of 10 percent to 75 percent by weight of .alpha.-alumina, 20 percent to 60 percent by weight of crystallizable or noncrystallizable glass which is sinterable at a temperature lower than the melting point of copper and not coalescent at temperatures up to 900.degree. C., and 5 percent to 70 percent by weight of quartz glass, based on the total weight of the glass-ceramic, blended with a binder comprising a thermally depolymerizable resin;
• prefiring the multilayer structure in an inert atmosphere containing water vapor, the partial pressure of which is 0.005 to 0.3 atmosphere, in a first prefiring step at a temperature in the range of 350.degree. C. to 450.degree. C. and for a time sufficient to depolymerize substantially all of the resin and in second prefiring step at a temperature in the range of 650.degree. C. to 900.degree. C. and for a time sufficient to assure completion of depolymerization of the resin and to reduce any residual carbon to a desired minimal level, while producing no substantial change in the state of the glass components and the copper;
• and
• firing the multilayer structure in an inert atmosphere containing no water vapor at a temperature in the range of from above 900.degree. C. to below the melting point of copper so as to coalesce the crystallizable or noncrystallizable glass and thereby sinter the glass-ceramic without affecting the metallic state of the copper or coalescing the .alpha.-alumina and quartz glass components.