Differential transmission board set and assembly

A differential transmission board set being a combination of two differential transmission boards electrically connected to each other through a compression connector including four compression contacts arranged in a row, each compression contact including a soldering part and a spring part, and a housing holding the four compression contacts, wherein

• the two differential transmission boards include a mounting board on which the compression connector is mounted and a contact board configured to come into contact with the compression connector,
• each of the mounting board and the contact board is a multilayer board having a plurality of conductor layers and a plurality of insulator layers laminated alternately,
• in each of the mounting board and the contact board, the plurality of conductor layers include a first conductor layer and a second conductor layer sequentially in this recited order from the compression connector side,
• in each of the mounting board and the contact board, the first conductor layer includes four electrode pads corresponding to the four compression contacts,
• the four electrode pads include a first signal pad, a second signal pad, a first ground pad, and a second ground pad,
• the first ground pad, the first signal pad, the second signal pad, and the second ground pad are arranged in this recited order along a first direction,
• in the mounting board, the soldering parts of the four compression contacts are able to be soldered to the first ground pad, the first signal pad, the second signal pad, and the second ground pad, respectively,
• in the contact board, the spring parts of the four compression contacts are able to come into contact with the first ground pad, the first signal pad, the second signal pad, and the second ground pad, respectively,
• in each of the mounting board and the contact board, the second conductor layer is a ground layer and has a penetrating hole,
• in each of the mounting board and the contact board, the penetrating hole is formed in such a way that the first signal pad and the second signal pad are both located inside an inner edge of the penetrating hole when viewed in a laminating direction,
• in each of the mounting board and the contact board, the first ground pad includes an inner region closer to the first signal pad relative to a dividing line that divides a pad area of the first ground pad in half in the first direction, and an outer region farther from the first signal pad relative to the dividing line,
• in each of the mounting board and the contact board, the second ground pad includes an inner region closer to the second signal pad relative to a dividing line that divides a pad area of the second ground pad in half in the first direction, and an outer region farther from the second signal pad relative to the dividing line,
• in the contact board, the penetrating hole is formed to overlap the outer region of the first ground pad and the outer region of the second ground pad when viewed along the laminating direction, and
• in the mounting board, the penetrating hole is formed to be away from the first ground pad and the second ground pad when viewed in the laminating direction.