Vertical trench routing in a substrate

An electrical interconnect comprising:

• a substrate having a plurality of layers including a first ground plane layer, a first dielectric layer and a second dielectric layer, a surface of the second dielectric layer abutting a surface of the first dielectric layer;
• a pair of signal conductors in the first dielectric layer and that form a differential signal pair, each conductor of the pair of signal conductors having a first portion for inner signal routing and a second portion for trench routing, a first side of the first portion of each of the plurality of signal conductors abutting the second dielectric layer, the second portion extending into at least one of the plurality of layers from a second side of the first portion, the second side being opposite the first side on the first portion, wherein second portion is below the first portion and the width of the second portion is less than width of the first portion;
• and
• wherein the first ground plane layer is only a first partial layer and has a first void region that is closer to the pair of signal conductors than the first partial layer.