The Hirose DF12NC(3.5)-20DP-0.5V(51) is a 20-position header from the DF12 series, designed for parallel board stacking with a fixed mated stack height of 3.5mm. It uses outer shroud contacts on a 0.50mm pitch in two rows, with the connector body sitting 2.80mm above the board surface. This is a surface-mount part intended for mezzanine-style interconnects where the top and bottom PCBs run parallel with a precise z-height gap.
Stack Height and Footprint — What the 3.5mm and 0.50mm Pitch Mean
That 3.5mm gap is fixed by the connector design — not adjustable — so the board-to-board clearance in the enclosure must match this exactly. The 2.80mm above-board height on the header side leaves room under the top board for other components, but the receptacle side will add its own height.
Gold plating at 8.00µin on the contacts handles repeated mating cycles typical of mezzanine board stacks that may be separated for rework or testing. The outer shroud contacts provide some alignment guidance during mating — the shroud walls take the initial misalignment before the signal pins engage.
If the BOM calls for more I/O at the same 3.5mm stack height, the DF12 series offers 40-position (DF12NC(3.5)-40DP-0.5V(51)) and 50-position (DF12NC(3.5)-50DP-0.5V(51)) variants with the same 0.50mm pitch, 2.80mm above-board height, and gold plating. The footprint widens to accommodate the extra positions, so the PCB layout must scale accordingly. For the same 20 positions but a taller stack, the DF12NC(4.0)-20DP-0.5V(51) gives a 4.0mm mated height with a 3.30mm above-board profile.