Method for manufacturing multilayer ceramic substrate
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According to this method for manufacturing a multilayer glass-ceramic circuit board, a green sheet laminate is fired in a non-oxidizing atmosphere in a first firing step so that a void content of at least 10% is maintained and strength of the ceramic laminate is increased. Then the laminate is fired in an oxidizing atmosphere in a second firing step so that the organic binder contained in the laminate is removed and the residual carbon content is at most 200 ppm. Thereafter the laminate is fired in a reducing atmosphere in a third firing step to reduce the oxidized conductor circuit. Finally, the laminate is fired in a non-oxidizing atmosphere in a fourth firing step to densify the ceramic laminate. The firing temperature in the first, second and third steps is 100.degree.-200.degree. C. lower than the softening point of the glass and the firing temperature in the fourth step is higher than the softening point of the glass and lower than the melting point of the conductor.