Additive printed circuit boards with flat surface and indented primary wiring conductors

In an additive method of printing primary wiring patterns onto insulating substrates, the improvement comprising the steps of:

• establishing a desired printed wiring pattern on an insulating panel by forming a substantially flat surface over the panel by depositing thereon a layer of liquid photopolymer insulating material, defining by photographically forming and developing in said layer patterns of a plurality of conductor lines indented from said flat surface with insulation barriers of hardened photopolymer dispersed between adjacent conductor lines of the patterns, with the conductor lines patterns comprising indented channels in the hardened photopolymer layer presenting substantially perpendicular to the panel adjacent sidewalls of substantially the thickness of the patterned layer,
• forming simultaneously thin film metallic conductors in the channel bottoms, on the flat top surface, and on the opposing channel sidewalls above the metallic conductors in the bottoms thereby extending the conductor with available between adjacent conductors by substantially twice the thickness of the photopolymer layer, and,
• removing any conductive material on the substantially flat top surface of the patterned layer thereby to define by photographic exposure and development of the photopolymer layer an insulation gap of known dimensions between adjacent conductors and to form a primary wiring pattern of conductors indented in the photopolymer layer.

The additive method of processing printed wiring boards to produce primary circuit patterns thereon, comprising the steps of:

• providing a basic substrate panel with a substantially flat surface subject to irregularities from flatness of the order of at least 0.001 inch,
• depositing thereover a layer of liquid photopolymer of pastelike consistency having a thickness of greater than 0.002 inch,
• photoprinting with a flat glass plate image bearing body in contact with the liquid polymer to produce a flat surface thereon and a surface contour having said flat surface and a wiring pattern disposed in the layer of polymer on the substrate panel defined by channels indented downwardly from the flat surface into the polymer layer to have sidewalls substantially perpendicular to the substrate panel,
• simultaneously depositing in the bottoms of the channels and extending upwardly on the sidewalls above the deposits in the bottoms a thin film layer of metallic conductor to form the wiring patterns whereby the width of the conductors is effectively increased by the heights of the two sidewalls, and
• machining off any residue conductor on the top flat surface to assure a predetermined width of insulation barrier between adjacent conductors.