DF37NB-20DS-0.4V(51) from Hirose Electric Co Ltd is a fine-pitch rectangular board-to-board receptacle designed for compact electronic assemblies where low profile, precise alignment, and reliable SMT mounting are important. With 20 positions, 0.40 mm pitch, dual-row construction, gold contact finish, and solder retention features, it fits space-constrained designs such as portable devices, display modules, industrial controls, embedded systems, and other high-density interconnect applications. Engineers typically choose this series when stack height control and compact PCB layout are key design priorities. The provided status indicates Active, which supports use in ongoing production, although the overall lifecycle field is listed as unknown and should still be confirmed through the manufacturer or latest datasheet before committing to long-term programs. RoHS compliance information is not explicitly provided in the supplied specifications, so compliance cannot be confirmed from this dataset alone. For regulated builds, engineers and buyers should request current RoHS and material declaration documentation from Hirose or an authorized source.