DF40HC(3.5)-50DS-0.4V(51) from Hirose Electric Co Ltd is a fine-pitch 50-position board-to-board receptacle designed for compact electronic assemblies that need reliable mezzanine interconnect performance. With a 0.40 mm pitch, 2-row layout, SMT mounting, and 3.5 mm mated stacking height, it fits space-constrained designs such as industrial controls, portable devices, communications hardware, and embedded systems. Engineers typically choose this DF40 series connector when they need dense signal routing, precise board stacking, and gold-finished contacts for stable electrical performance in high-density PCB layouts. Based on the provided data, this part is supplied in tape-and-reel packaging for volume assembly and carries MSL 1 handling characteristics. Lifecycle status is currently listed as unknown, so design teams should verify long-term availability directly with the manufacturer or authorized supply channels before locking it into new programs. RoHS compliance information is not explicitly provided in the supplied specifications, so engineers should confirm compliance status and documentation using the latest datasheet or manufacturer declaration.