What this DF40 receptacle does in the stack
The Hirose DF40HC(2.5)-30DS-0.4V(70) is a 30-position receptacle with center strip contacts, part of the DF40 series of board-to-board mezzanine connectors. It mates with the matching DF40 header to create a 2.5 mm mated stack height — the (2.5) in the order code is that height, not a guess.
At 30 positions, this receptacle sits between the 20-position DF40HC(2.5)-20DS-0.4V(51) and the 40-position DF40HC(2.5)-40DS-0.4V(58) in the same 2.5 mm stack height family. All three share the 0.40 mm pitch, gold-plated contacts, and SMT mounting — the only decision variable is the circuit count your BOM needs. The 50-position DF40HC(2.5)-50DS-0.4V(51) is also available if the layout has room for the longer footprint.
Surface-mount termination with gold-plated contacts on both rows. The 0.40 mm pitch means the PCB footprint needs controlled trace/space — standard 0.5 mm pitch routing rules won't fit. The 2.5 mm mated height is measured from the top of the PCB to the top of the mated header; the receptacle itself sits 2.40 mm above the board before mating. Alignment posts on the header take the shear load during assembly, so the signal contacts don't take the brunt of board misalignment.