DF40C-40DS-0.4V(51) from Hirose Electric Co Ltd is a fine-pitch rectangular board-to-board receptacle connector designed for compact electronic assemblies where space, profile, and interconnect reliability matter. As part of the DF40 family, it is well suited for mobile devices, industrial control boards, medical electronics, embedded modules, and other high-density PCB stacking applications that require a 0.40 mm pitch and low mated height. Engineers typically select this connector family for compact multilayer board architectures, stable SMT processing, and proven use in volume manufacturing. The supplied status indicates Active, with sufficient supply and high market popularity, which supports ongoing design and procurement planning; however, the separate lifecycle field is listed as unknown, so design teams should still confirm long-term availability directly with Hirose or current channel data. For compliance, the provided specifications indicate halogen-free compliant status, but RoHS status is not explicitly stated in the input, so engineers should verify formal RoHS and REACH declarations through official manufacturer documentation before release.