DF40HC(4.0)-60DS-0.4V(51) from Hirose Electric Co Ltd is a fine-pitch rectangular board-to-board receptacle designed for compact electronic assemblies that need reliable mezzanine interconnection in a low-profile format. As part of the DF40 series, it is well suited for portable devices, industrial control boards, communication modules, embedded systems, and space-constrained PCB stacking designs where signal density and consistent mating performance matter. This 60-position, 0.40 mm pitch surface-mount connector is typically selected by engineers building compact multilayer architectures with a 4 mm stacking height target. The provided product data lists the part as Active, which is favorable for ongoing procurement planning, although lifecycle confirmation should still be checked against current manufacturer documentation. RoHS compliance information is not explicitly provided in the supplied specifications, so compliance status should be treated as information not available pending official datasheet or manufacturer confirmation. For regulated designs, engineers should also verify REACH status, plating details, and latest compliance documents before release.