Process for fabricating multilayer printed circuits

In a method for manufacturing a multilayer printed circuit having metallized through-holes, wherein (a) a multilayer structure is assembled as an alternating array of one or more copper circuitry innerlayers and one or more layers of partially-cured dielectric substrate material;

• (b) the multilayer structure is thereafter subjected to heat and pressure to cure the structure into an integral multilayer composite in which copper surfaces of said copper circuitry innerlayer are bonded to the now-cured dielectric substrate material in contact therewith;
• and (c) the multilayer composite is thereafter provided with one or more through-holes which are thereafter metallized;
• the improvement comprising the steps of (i) treating the copper surfaces of said copper circuitry innerlayer, prior to its use in assembly of said multilayer structure, to form thereon a conversion coating of copper oxide;
• (ii) thereafter subjecting said copper surfaces having said conversion coating of copper oxide thereon to the action of a dissolution agent effective to controllably dissolve and remove at least a portion of said copper oxide form said copper surfaces;
• and (iii) thereafter utilizing said copper circuitry innerlayer in assembly of said multilayer structure, and wherein said subjecting of said copper surfaces having said conversion coating of copper oxide thereon to the action of a dissolution agent according to step (ii) comprises providing a vessel containing said dissolution agent;
• immersing in said dissolution agent in said vessel the circuitry innerlayer having said conversion coating of copper oxide on its copper surfaces, for a time effective to controllably dissolve and remove said conversion coating of copper oxide from said copper surfaces according to step (ii);
• and substantially continuously recirculating said dissolution agent from said vessel to and through an ion exchange resin effective to substantially remove copper ions from said dissolution agent, and returning the so-treated dissolution agent to said vessel.