Fabrication of bi-level circuits

Claim 1

A method of fabricating bi-level circuits including metallizing holes (14 and 15) through an insulating substrate (10) comprising the steps of: depositing a thick film paste (13) onto one major surface (12) of said substrate and filling said holes, said paste including a material selected from the group consisting of a metal and metal oxide, and an organic vehicle comprising a binder and at least one solvent; heating the resulting structure to evaporate the solvent; and firing the remaining paste material to establish a desired conductivity CHARACTERIZED IN THAT the structure is heated with the deposited surface down to create a solvent concentration gradient in the paste filling the holes during heating so that the bulk of the paste accumulates in the holes near the surface (11) opposite the deposited surface to form contact pads (16) at the opposite surface and the remaining paste coats the walls of the holes near the deposited surface.

Claim 2

A method of fabricating bi-level circuits including metallizing holes (14 and 15) through an insulating substrate (10) comprising the steps of: depositing a thick film paste (13) onto one major surface (12) of said substrate and filling said holes, said paste including a material selected from the group consisting of a metal and metal oxide, and an organic vehicle comprising a binder and at least one solvent; heating the resulting structure to evaporate the solvent; and firing the remaining paste material to establish a desired conductivity CHARACTERIZED IN THAT the structure is heated with the deposited surface down to create a solvent concentration gradient in the paste filling the holes during heating so that the bulk of the paste accumulates in the holes near the surface (11) opposite the deposited surface to form contact pads (16) at the opposite surface and the remaining paste coats the walls of the holes near the deposited surface.

Claim 14

A method of fabricating bi-level circuits including metallizing holes (14 and 15) through an insulating substrate comprising the steps of: screen printing a thick film paste (13) onto one major surface (12) of said substrate and filling said holes, said paste including copper, glass frit, and an organic vehicle comprising a binder of ethyl cellulose and at least one solvent; heating the resulting structure to evaporate the solvent; and firing the remaining paste material to establish a desired conductivity; CHARACTERIZED IN THAT the structure is heated with the deposited surface down to create a solvent concentration gradient in the paste filling the holes during heating so that the bulk of the paste in the holes accumulates near the surface (11) opposite the printed surface to form contact pads (16) at the opposite surface and the remaining paste coats the walls of the holes near the printed surface, and firing is done first in an oxidizing atmosphere and then in a reducing atmosphere.

Claim 15

A method of fabricating bi-level circuits including metallizing holes (14 and 15) through an insulating substrate comprising the steps of: screen printing a thick film paste (13) onto one major surface (12) of said substrate and filling said holes, said paste including copper, glass frit, and an organic vehicle comprising a binder of ethyl cellulose and at least one solvent; heating the resulting structure to evaporate the solvent; and firing the remaining paste material to establish a desired conductivity; CHARACTERIZED IN THAT the structure is heated with the deposited surface down to create a solvent concentration gradient in the paste filling the holes during heating so that the bulk of the paste in the holes accumulates near the surface (11) opposite the printed surface to form contact pads (16) at the opposite surface and the remaining paste coats the walls of the holes near the printed surface, and firing is done first in an oxidizing atmosphere and then in a reducing atmosphere.

Claim 16

A method of fabricating bi-level circuits including metallizing holes (14 and 15) formed through an insulating substrate (10) with diameters in the range 3-50 mils and thicknesses in the range 10-75 mils, comprising the steps of: screen printing a thick film paste (13) onto one major surface (12) of said substrate and filling said holes, said paste comprising copper, glass frit, and an organic vehicle comprising a binder of ethyl cellulose and solvents of butyl carbitol acetate and alpha terpineol; heating the resulting structure to evaporate the solvents, and firing the remaining paste material to establish a desired conductivity; CHARACTERIZED IN THAT the molecular weight of the ethyl cellulose is less than or equal to 40,000, the glass frit does not contain lead and the copper and glass frit comprise approximately 40-90 percent by weight of the paste; the structure is heated at a maximum temperature in the range 80-180 degrees C. for 5 min.-2 hrs. with the printed surface down and placed approximately 20-120 mils from a setter plate (25) to control evaporation of the solvents at said surface thereby establishing a solvent concentration gradient in the paste filling the holes during heating so that the bulk of the paste in the holes accumulates near the surface (11) opposite the printed surface to form contact pads (16) at the opposite surface and the remaining paste coats the walls of the holes near the printed surface; the heating can be repeated with the printed surface up to remove any solvent which might have condensed during the first heating; and the paste is first fired at a temperature within the range 700-1100 degrees C. for 1 min.-1 hr. in an oxidizing atmosphere and then at a temperature within the range 250-1000 degrees C. for 1 min.-1 hr. in a reducing atmosphere.

Claim 17

A method of fabricating bi-level circuits including metallizing holes (14 and 15) formed through an insulating substrate (10) with diameters in the range 3-50 mils and thicknesses in the range 10-75 mils, comprising the steps of: screen printing a thick film paste (13) onto one major surface (12) of said substrate and filling said holes, said paste comprising copper, glass frit, and an organic vehicle comprising a binder of ethyl cellulose and solvents of butyl carbitol acetate and alpha terpineol; heating the resulting structure to evaporate the solvents, and firing the remaining paste material to establish a desired conductivity; CHARACTERIZED IN THAT the molecular weight of the ethyl cellulose is less than or equal to 40,000, the glass frit does not contain lead and the copper and glass frit comprise approximately 40-90 percent by weight of the paste; the structure is heated at a maximum temperature in the range 80-180 degrees C. for 5 min.-2 hrs. with the printed surface down and placed approximately 20-120 mils from a setter plate (25) to control evaporation of the solvents at said surface thereby establishing a solvent concentration gradient in the paste filling the holes during heating so that the bulk of the paste in the holes accumulates near the surface (11) opposite the printed surface to form contact pads (16) at the opposite surface and the remaining paste coats the walls of the holes near the printed surface; the heating can be repeated with the printed surface up to remove any solvent which might have condensed during the first heating; and the paste is first fired at a temperature within the range 700-1100 degrees C. for 1 min.-1 hr. in an oxidizing atmosphere and then at a temperature within the range 250-1000 degrees C. for 1 min.-1 hr. in a reducing atmosphere.