The Hirose DF12NB-40DS-0.5V(51) is a 40-position receptacle with center strip contacts from the DF12 series, designed for board-to-board mezzanine stacking. The 2.70mm board height accommodates mated stack heights of 3.5mm, 4mm, or 5mm depending on the mating header selected — a useful range for Z-axis constrained enclosures.
The 0.50mm pitch sets the routing density — expect two traces per channel between pads on standard PCB fabrication.
Comparing the 40-Position to the 36-Position Sibling
The DF12NB-40DS-0.5V(51) carries 40 positions against the 36 positions of the DF12NB-36DS-0.5V(51) at the same 0.50mm pitch, same 2.70mm board height, same gold plating thickness. The decision between them is purely a circuit-count match — the footprint length scales with position count, so check that the board real estate and the number of signal lines align. No difference in current capability or mechanical envelope otherwise.