DF40C-10DS-0.4V(51) from Hirose Electric Co Ltd is a fine-pitch rectangular board-to-board receptacle designed for compact electronic assemblies where space, profile, and connection reliability are critical. With a 0.40 mm pitch, 10 positions, dual-row layout, and SMT mounting, it fits dense PCB designs used in portable devices, industrial modules, embedded control boards, and other miniaturized interconnect applications. Engineers typically select parts in the DF40 family for low-profile stacking, repeatable mating performance, and suitability for automated assembly in volume production. Based on the provided specifications, this part is listed as Active, which supports its use in current designs, although lifecycle verification with the manufacturer is still recommended because the separate lifecycle field is marked unknown. RoHS compliance information is not explicitly provided in the input, so compliance status should be treated as information not available pending official Hirose documentation or authorized distributor confirmation.