Method for forming electrical connection to the inner layers of a multilayer circuit board

A method for forming electrical connection to the inner layers of a multilayer circuit board having a copper foil surface layer and copper containing inner layers comprising the steps of:

• (a) forming at least one through hole or blind hole in the multilayer circuit board;
• (b) cleaning said through hole or blind hole;
• (c) selectively etching the surface of the copper foil layer by a method comprising the steps of:
• (1) immersing the multilayer circuit board in an etching solution selected from the group consisting of a sulfuric acid solution and a nitric acid solution;
• (2) immersing a cathode in said etching solution, said cathode comprising at least one electrode;
• (3) applying an etching potential to the copper foil surface to etch said copper foil;
• and
• (4) maintaining a passivation potential at the copper containing inner layers, wherein said passivation potential does not equal said etching potential;
• (d) electrolessly depositing a conductive metal onto the surface where the copper foil was etched and onto the surface of said through hole or blind hole to form an electrical connection to the copper containing inner layers.