In the illustrated embodiment, the backplane 160 includes attachment layers 660, 662, etc. and routing layers 670, 672, etc. The attachment layers are located in the upper portion of the backplane 160, and the routing layers are located below the attachment layers. The attachment layers 660, 662, etc. and the routing layers 670, 672, etc. are adhered together to form a single structure in the form of a printed circuit board. The number of attachment layers and the number of routing layers in a particular backplane may vary according to application.

As shown in FIG. 6, backplane 160 may include ground planes 640 between the layers of the structure and may include signal traces in or between the routing layers. It will be understood that the ground planes 640 do not contact the signal vias 530 and 532 and may be separated from the signal vias by providing antipad 542 (FIG. 5B). A signal trace 644 is shown as connected to signal via 530, and a signal trace 646 is shown as connected to signal via 532.

The signal vias 530 and 532 include plating in the attachment layers and in one or more of the routing layers. The signal vias 530 and 532 may be backdrilled in the lower region of the backplane 160 to remove the plating.