Electrical isolating structure for conductors in a substrate

A method for manufacturing a substrate, comprising the steps of:

• providing a first planar dielectric layer;
• forming a first conductive reference plane on the first planar dielectric layer;
• providing a second planar dielectric layer on the first conductive reference plane;
• forming an elongated signal conductor on the second planar dielectric layer;
• providing a third planar dielectric layer on the signal conductor and the second planar dielectric layer;
• defining on each side of said elongated signal conductor a groove extending continuously the entire length of said elongated signal conductor through said third planar dielectric layer, said second planar dielectric layer and said first conductive reference plane, said grooves having inner walls joining to one another beyond opposing ends of said elongated signal conductor;
• applying a conductive layer on said grooves, including said inner walls, and on an upper surface of said third planar dielectric layer;
• and
• defining an insulating signal access area through the conductive layer in alignment with said signal conductor.

A structure for isolating a signal conductor in a substrate having a first planar dielectric layer, a first conductive reference plane on the first planar dielectric layer, a second planar dielectric layer on the first conductive reference plane, an elongated signal conductor on a side of the second planar dielectric layer opposing the first conductive reference plane, a third planar dielectric layer on the signal conductor and the second planar dielectric layer, comprising:

• two grooves, each on one side of said elongated signal conductor through said third planar dielectric layer, said second planar dielectric layer and said first conductive reference plane, said grooves having inner walls joining to one another beyond opposing ends of said elongated signal conductor, said grooves having a conductive layer on their inner walls and in electrical contact with said first conductive reference plane;
• and
• an upper conductive layer on an upper surface of said third planar dielectric layer in electrical contact with said conductive layer on said walls of said grooves;
• and,
• an insulating signal access area in alignment with said signal conductor, defined through said upper conductive layer to the upper surface of said third planar dielectric layer.