Composition and process for filling vias

Claim 1

A method for forming electrically conductive vias between electrically functional layers separated by a dielectric layer comprising the sequential steps: A. Forming via holes in a copper-clad substrate which separates electrically functional layers; B. Filling the via holes with a via fill composition comprising 85-93 wt % of a trimodal conductive mixture wherein the trimodal conductive mixture consists of particles of spherical silver, flake silver and silver-coated copper dispersed in an organic medium; C. Drying the composition; D. Removing residue from the surface of the substrate; E. Subjecting the filled substrate to heat; F. Preparing the surface of the filled substrate for plating; G. Plating the filled substrate by electrolytic flash; H. Preparing the surface of the plated substrate; I. Applying a photoresist to the prepared substrate; J. Exposing the photoresist to generate a pattern; K. Developing and removing the exposed photoresist; L. Etching the exposed copper; M. Stripping the remaining photoresist from the copper.

Claim 2

A method for forming electrically conductive vias between electrically functional layers separated by a dielectric layer comprising the sequential steps: A. Forming via holes in a copper-clad substrate which separates electrically functional layers; B. Filling the via holes with a via fill composition comprising 85-93 wt % of a trimodal conductive mixture wherein the trimodal conductive mixture consists of particles of spherical silver, flake silver and silver-coated copper dispersed in an organic medium; C. Drying the composition; D. Removing residue from the surface of the substrate; E. Subjecting the filled substrate to heat; F. Preparing the surface of the filled substrate for plating; G. Plating the filled substrate by electrolytic flash; H. Preparing the surface of the plated substrate; I. Applying a photoresist to the prepared substrate; J. Exposing the photoresist to generate a pattern; K. Developing and removing the exposed photoresist; L. Etching the exposed copper; M. Stripping the remaining photoresist from the copper.

Claim 3

A method for forming electrically conductive vias between electrically functional layers separated by a dielectric layer comprising the sequential steps: A. Forming via holes in a copper-clad substrate which separates electrically functional layers; B. Filling the via holes with a via fill composition comprising 85-93 wt % of a trimodal conductive mixture wherein the trimodal conductive mixture consists of particles of spherical silver, flake silver and silver-coated copper dispersed in an organic medium; C. Drying the composition; D. Removing residue from the surface of the filled substrate; E. Subjecting the filled substrate to heat; F. Preparing the surface of the plated substrate; G. Applying a photoresist to the prepared substrate; H. Exposing the photoresist to generate a pattern; I. Developing and removing the exposed photoresist; J. Etching the exposed copper; K. Stripping the remaining photoresist to bare the remaining copper; L. Plating the: surface of the bared copper by electroless plating.

Claim 4

A method for forming electrically conductive vias between electrically functional layers separated by a dielectric layer comprising the sequential steps: A. Forming via holes in a copper-clad substrate which separates electrically functional layers; B. Filling the via holes with a via fill composition comprising 85-93 wt % of a trimodal conductive mixture wherein the trimodal conductive mixture consists of particles of spherical silver, flake silver and silver-coated copper dispersed in an organic medium; C. Drying the composition; D. Removing residue from the surface of the filled substrate; E. Subjecting the filled substrate to heat; F. Preparing the surface of the plated substrate; G. Applying a photoresist to the prepared substrate; H. Exposing the photoresist to generate a pattern; I. Developing and removing the exposed photoresist; J. Etching the exposed copper; K. Stripping the remaining photoresist to bare the remaining copper; L. Plating the: surface of the bared copper by electroless plating.

Claim 5

The method of claims 1 or 2 wherein the method employed for filling via holes is selected from the group consisting of screen printing, stenciling, doctor blading, syringe or bladder printing.