DF40HC(3.0)-50DS-0.4V(51) from Hirose Electric Co Ltd is a fine-pitch board-to-board rectangular connector designed for compact electronic assemblies that need reliable mezzanine interconnection in space-constrained layouts. As part of the DF40 series, it is suited to portable devices, industrial control boards, embedded modules, display interfaces, communication equipment, and other high-density PCB designs where a 0.40 mm pitch and 3 mm stacking height are important design constraints. Engineers typically choose this style of connector for dense signal routing, low-profile packaging, and consistent assembly in surface-mount production. The provided product data indicates an Active product status, which is favorable for ongoing designs, although the broader lifecycle field is listed as unknown and should be verified against current manufacturer documentation before long-term commitment. RoHS compliance information is not explicitly provided in the supplied specifications, so compliance status should be treated as information not available until confirmed through the official datasheet, manufacturer declaration, or authorized distributor documentation.