The Hirose DF40TC(3.5)-30DS-0.4V(51) is a 30-position receptacle with center strip contacts from the DF40T series, built for board-to-board mezzanine stacking at a fixed 3.5mm mated height.
0.40mm Pitch and the Board Footprint
At 0.40mm pitch, this is a fine-pitch connector — the board layout needs matched trace widths and controlled impedance if the signals run at any speed. The 30 positions in two rows mean the PCB footprint is narrow but long; the pad pattern must align with the Hirose recommended land pattern to avoid solder bridging. The surface-mount termination and solder retention features (Pick and Place pad) let it run through a standard reflow oven without shifting.
Stacking Height and Mating Partner
The 3.5mm mated stacking height is baked into the part number — the DF40TC(3.5) designation means the receptacle is designed to mate with a DF40 series header of the same height code to achieve that exact board-to-board gap. The mating half is a DF40C header (the male pin side) with the corresponding 3.5mm stack height. The 30-position count must match on both sides; the header is available in the same DF40T series with the same 0.40mm pitch.
Comparing the 3.5mm and 3.0mm Stack Options
The DF40TC(3.0)-30DS-0.4V(58) is the same 30-position, 0.40mm-pitch receptacle but mates at 2.9mm instead of 3.5mm — a 0.6mm difference in board-to-board gap. If your mezzanine height budget is 2.9mm, the 3.0 version fits; if you need 3.5mm, this is the one. The contact plating and dual-row layout are identical, so the only decision driver is the z-height clearance under the top board.