DF40HC(3.5)-20DS-0.4V(51) from Hirose Electric Co Ltd is a fine-pitch rectangular board-to-board mezzanine receptacle designed for compact electronic assemblies that need reliable interconnect density in limited PCB space. With a 0.40 mm pitch, 20 positions, dual-row layout, and 3.5 mm mated stacking height, it is well suited for portable electronics, industrial control modules, embedded computing platforms, display assemblies, and other space-constrained designs where stable signal routing and low-profile stacking are important. As part of the Hirose DF40 series, this connector is positioned for engineers seeking compact, surface-mount interconnect solutions from a recognized connector manufacturer. The provided specification identifies the product status as Active, which generally supports ongoing design consideration, although lifecycle confirmation should still be verified through the manufacturer or authorized documentation. RoHS compliance information is not explicitly provided in the supplied data, so compliance status remains information not available and should be confirmed with the latest datasheet, declaration, or manufacturer compliance statement before production release.