1. In a method of fabricating a microminiature electrical interconnection structure, the steps of: providing a conductive sheet having a thickness of the order of 5 to 100 mils, chemically etching a plurality of recesses in at least one surface of said sheet having a pattern corresponding to a microminiature electrical circuit to be formed therein, placing at least one sheet of a curable and flowable elastomeric dielectric material adjacent said one surface, said dielectric material being adherable to said conductive sheet and having a thermal conductivity and coefficient of expansion approximately matching said conductive sheet, said dielectric material comprising a mixture of a polyamide thermoplastic resin and an epoxy thermosetting resin in which the polyamide thermoplastic resin comprises below 20 percent by weight of the mixture, applying heat and pressure so as to cause the dielectric material to flow into the recesses and adhere to the surfaces thereof and completely fill the recesses without voids and to cure the dielectric material, said applying being accomplished by initially applying a relatively light pressure between the conductive and dielectric sheets to evacuate excess air therefrom and then applying a relatively greater pressure while heating the assembly above the curing temperature of the dielectric material, the relative pressure being maintained between the conductive and dielectric sheets until after the cooling of the assembly following curing of the dielectric material, and removing excess dielectric material from said one surface.

3. In a method of fabricating a microminiature electrical interconnection structure, the steps of: providing a conductive sheet having a thickness of the order of 5 to 100 mils, forming a plurality of recesses in at least one surface of said conductive sheet having a pattern corresponding to a microminiature electrical circuit to be formed therein, placing at least one sheet of curable and flowable dielectric material adjacent said one surface, said dielectric material being adherable to said conductive sheet and having a thermal conductivity and coefficient of expansion approximately matching said conductive sheet, said dielectric material comprising a mixture of a polyamide thermoplastic resin and an epoxy thermosetting resin in which the polyamide thermoplastic resin comprises below 20 percent by weight of the mixture, placing the resulting assembly of conductive and dielectric sheets between the heatable platens of a laminating press in a manner so as to be releasable therefrom, moving the platens into engagement with the conductive and dielectric sheets to apply relative pressure therebetween while heating the platens above the curing temperature of the dielectric material, the pressure and heating of the platens being such that the dielectric is caused to flow into the recesses and adhere to the surfaces thereof and completely fill the recesses without voids and to cure the dielectric material, cooling the assembly while maintaining relative pressure between the conductive and dielectric sheets, releasing the resulting cured assembly from between the platens, and removing excess dielectric material from said one surface so as to form a single flush surface containing conductive and dielectric portions, the dielectric portions corresponding to the filled recesses.