The laminate of green sheets is heated to a burnout temperature of 720??? to 785??? C. Then the laminate is later heated to a crystallization temperature of about 920??? to 970??? C. Here the composition of the glass particles is quite different from those employed here in view of the presence of P2 O5, B2 O3 and in some cases SnO2 and the absence of a stabilizing compound such as yttria plus the