0.40 mm pitch mezzanine receptacle, 20 positions, 1.45 mm stack height
The Hirose DF40C-20DS-0.4V(51) is a 20-position receptacle from the DF40 series of board-to-board mezzanine connectors. The mated stack height is 1.5 mm, with the connector body sitting 0.057" (1.45 mm) above the board. This is a signal-density interconnect for parallel PCB stacking where the z-height budget is tight — the 0.40 mm pitch keeps the board footprint small, but the trade-off is that routing between pads requires finer trace and space rules than a 0.50 mm or 0.80 mm part.