Board-to-Board Stacking with the DF40B-12DS-0.4V(58)
The Hirose DF40B-12DS-0.4V(58) is a 12-position receptacle from the DF40 series, designed for parallel board-to-board stacking. The connector sits 0.057" (1.45mm) above the board and mates to a stack height of 1.5mm — a tight z-budget for compact handheld or portable devices where every tenth of a millimeter counts.
At 0.40mm pitch, the DF40B-12DS-0.4V(58) demands tight trace routing between pads — expect to run single traces between vias on the inner layers. The 1.5mm mated stack height is the key dimension for mezzanine spacing; if your board-to-board gap needs to be taller, the DF40B(2.0)-12DS-0.4V(58) sibling uses the same 12-position layout but with a 0.077" (1.95mm) height above board, giving a taller stack. For fewer circuits, the DF40B-10DS-0.4V(58) drops to 10 positions at the same 0.40mm pitch and 1.45mm height — a straight position-count swap if your BOM line needs fewer connections.
No official second-source or direct cross-reference exists; the DF40 series is Hirose-specific, so stick with the listed order code for the BOM.