DF40C-20DS-0.4V(51) from Hirose Electric Co Ltd is a compact DF40 series rectangular board-to-board receptacle designed for space-constrained electronic assemblies that require fine-pitch, high-density interconnection. With a 0.40 mm pitch, 20 positions, dual-row layout, and SMT mounting, it is well suited for portable electronics, embedded modules, industrial control boards, medical devices, and other compact PCB stacking designs where mechanical reliability and low-profile mating are important. Engineers typically choose this connector family for dense interconnect routing, stable sourcing, and broad use in common electronic designs. The supplied status indicates Active, with sufficient supply and high popularity, which supports ongoing procurement planning, although the lifecycle field itself is listed as unknown and an estimated EOL date of 2027 suggests teams should monitor future manufacturer notices. RoHS compliance information is not explicitly provided in the supplied data, so compliance should be treated as information not available pending confirmation from the official Hirose datasheet or manufacturer declaration.