0.40mm Pitch, 40-Position Mezzanine Receptacle — the Z-Height is the Constraint
The Hirose DF37NB-40DS-0.4V(53) is a 40-position receptacle from the DF37 series, designed for board-to-board mezzanine stacking. The 0.016" (0.40mm) pitch packs 40 circuits into a dual-row layout, and the 0.038" (0.97mm) height above board sets a tight z-height budget — the mated stacking height is 0.98mm. This is the dimension that drives the PCB gap: if your board stack-up calls for a 1.0mm or 1.2mm separation, this part lands right at the lower end of the range. The center strip contact arrangement mates only with the matching DF37 header — it is not a generic 0.40mm pitch socket.
Gold Flash Plating — Low Mating Cycle Duty
The contacts carry 2.00µin (0.051µm) of gold over the base metal — a flash plating. The gold ensures low contact resistance at first mate; the thin layer will wear through under repeated cycling, exposing the nickel underplate. For a one-time board-stacking application inside an enclosure, this is fine. If the connector sees regular disconnect, step up to a thicker gold variant in the DF37 family.
The housing includes solder retention features — small metal tabs or dimples that hold the connector flat against the PCB pads during SMT reflow. On a 0.40mm pitch part, even a few degrees of skew or a lifted corner can short adjacent pads. The retention anchors prevent tombstoning and keep the contact-to-pad alignment through the solder solidification phase. This is a practical feature for high-volume pick-and-place lines where the part must survive the oven without shifting.
40 Positions vs 34 and 50 — Match the Circuit Count
The DF37NB-40DS-0.4V(53) sits between the 34-position DF37NB-34DS-0.4V(51) and the 50-position DF37NB-50DS-0.4V(53) in the same series. All three share the 0.40mm pitch, 0.97mm height, gold flash plating, and solder retention. The 40-position version gives a 7.9mm-wide footprint (40 × 0.40mm ÷ 2 rows), which is 6 positions more than the 34-position variant and 10 fewer than the 50-position option. There is no official cross-reference or second-source; the DF37NB-40DS-0.4V(51) suffix variant is the same connector with a different packaging code (Digi-Reel vs Cut Tape).