0.40mm Pitch, 40-Position Mezzanine Receptacle — Hirose DF40C Series
The Hirose DF40C-40DS-0.4V(51) is a 40-position, 2-row receptacle with center strip contacts, part of the DF40 series of board-to-board mezzanine connectors. The mated stacking height of 1.5mm is fixed — no height adjustment options in this variant — so the board-to-board gap is locked at that dimension.
Mated Stacking Height and Board Fit
For a board layout engineer, this is the number that drives the z-height budget: if your enclosure has 2mm of clearance between boards, this connector fits; if you need 2mm stack height, you're looking at a different DF40 variant. The 0.40mm pitch means trace escape from the inner rows requires micro-vias or tight neck-downs — plan for at least two signal layers if routing all 40 lines out.
The DF40C series offers the same 0.40mm pitch and 1.5mm stacking height across position counts from 30 to 50. The DF40C-40DS-0.4V(51) sits at 40 positions, between the 34-position DF40C-34DS-0.4V(51) and the 50-position DF40C-50DS-0.4V(51). The footprint is the same width for all three — the extra positions just extend the connector length along the board edge. If your BOM calls for 40 I/O, this is the one; if you need 34 or 50, the sibling parts are a direct swap on pitch and height.
It is RoHS Compliant, so it clears the EU material restriction without exemptions.