DF40B-10DS-0.4V(51) from Hirose Electric Co Ltd is a compact board-to-board rectangular connector receptacle designed for dense electronic assemblies where space, profile, and interconnect reliability matter. As part of the DF40 series, it supports fine-pitch mezzanine stacking in applications such as portable devices, industrial control boards, communication modules, embedded systems, and compact medical or instrumentation designs. Engineers typically choose this type of connector for high-density PCB mating, low-profile mechanical integration, and surface-mount assembly efficiency. Based on the provided specifications, this part is listed as Active, which supports use in ongoing production and maintenance planning. Its tape-and-reel packaging and standard 5,000-piece pack size also align with volume manufacturing workflows. RoHS compliance information is not explicitly provided in the supplied data, so compliance status should be treated as information not available pending verification through the official datasheet, manufacturer declaration, or authorized distributor documentation. For regulated builds, engineers should also confirm current REACH status and any material-content declarations before release to production.