DF40HC(3.0)-40DS-0.4V(51) from Hirose Electric Co Ltd is a 40-position rectangular board-to-board receptacle designed for compact, high-density interconnect applications. As part of the DF40 series, it supports a fine 0.40 mm pitch, dual-row layout, surface-mount assembly, and a 3 mm mated stacking height, making it well suited for slim embedded products, portable electronics, industrial modules, communication equipment, and other space-constrained PCB designs. Engineers typically select this connector family when they need reliable mezzanine interconnection, reduced board footprint, and established Hirose manufacturing quality. The provided product status indicates Active, which is a positive signal for ongoing design use, although buyers should still confirm current lifecycle details directly with Hirose or an authorized source. RoHS compliance information is not explicitly provided in the supplied specifications, so compliance status should be treated as information not available until verified through the official datasheet, manufacturer declaration, or distributor documentation.