DF40C-40DP-0.4V(51) from Hirose Electric Co Ltd is a fine-pitch rectangular board-to-board plug connector designed for compact, high-density electronic assemblies. With a 0.40 mm pitch, 40 positions, dual-row layout, SMT mounting, and support for multiple mated stacking heights, it fits space-constrained products where reliable interconnect performance and low profile are important. Engineers commonly consider this series for mobile devices, handheld equipment, industrial control modules, embedded systems, and other compact PCB designs that need stable mezzanine connections. Features such as gold contact finish and solder retention support assembly reliability in volume production. Based on the provided data, the manufacturer status is Active, which is favorable for ongoing procurement and design continuity, although the lifecycle field supplied for this task remains unknown and should be verified against current manufacturer documentation. RoHS compliance information is not available in the provided specifications, so engineers should confirm environmental compliance directly with Hirose or the latest official datasheet before release to regulated markets.