as the porous layer the initial porous layer is coated at its opposite surfaces with the second slurry and the slurry coated porous layer is heated at a temperature in the range as described above since the carbon is burnt out to form the pores it is possible to make fine pores evenly distributed because the carbon evaporates so as not to remain the properties of the crystalline glass are not adversely affected thereafter the thus prepared substrate structure may be metallized through general metallizing treatments for example a thick film wiring method a simultaneous baking method or a thin film wiring method may be used to form conductors on the substrate in the simultaneous baking method a pattern of conductive paste is formed on a green sheet and then the green sheet is subjected to simultaneous heating to form both the substrate and the conductor as the conductive material it is preferable to use a material in the group of au cu and ag pd for thick film formation a material in the group of au pt pd and cu for inner layer conductors in the case of simultaneous heating or ti mo ni or w for thin film formation the low temperature heated substrate according to the present invention may be used for an ic package a multi layer circuit substrate and a transistor package and is suitable as an ic element substrate for a high speed computer 100 portions of zno mgo al 2 o 3 sio 2 10 portions of binder an organic binder 30 portions of solvent 1 portion of dispersant and 50.