Board-to-Board Stacking at 0.40mm Pitch
The Hirose DF40TC(4.0)-40DS-0.4V(58) is a 40-position receptacle from the DF40T series, built for fine-pitch board-to-board stacking. The mated stacking height is 4mm, set by the (4.0) in the order code, which means the matching header must carry the same stack-height suffix to land at the correct z-height.
SMT Assembly and Retention
The 0.40mm pitch means the solder paste stencil aperture and reflow profile need to be dialed in for fine-pitch parts; tombstoning or bridging is a risk if the pad design doesn't match the Hirose recommended footprint.
RoHS compliant per the listing. The DF40T series is Hirose-proprietary in footprint and stack height.