One or more customization layers can be added to a wiring substrate. The customization layers can provide customized electrical connections from electrical contacts of the base wiring substrate to electrical contacts at an outer surface of the customization layers, which can allow the contacts at the outer surface of the customization layers can be in a different pattern than the contacts at the surface of the base wiring substrate. The customization layers can comprise electrically insulating material, electrically conductive via structures through the insulating material, electrically conductive traces, electrically conductive jumpers electrically connecting two traces without contacting a trace disposed between the two traces, and/or other such elements. A jumper can be formed by making a relatively small deposit of electrically insulating material between the two traces to be connected and then making a relatively small deposit of electrically conductive material on parts of the two traces and the insulating material. Via structures can be coupled to traces and an insulating material can be cast around the via structures. Alternatively, via structures can be formed in openings with sloped side walls in an insulating layer.