DF40C-120DS-0.4V(51) from Hirose Electric Co Ltd is a fine-pitch board-to-board mezzanine receptacle designed for compact electronic assemblies that need high contact density in a low-profile format. With 120 positions, 0.40 mm pitch, dual-row construction, and surface-mount termination, it is well suited for space-constrained products such as portable devices, industrial control modules, embedded computing boards, medical electronics, and communication equipment. Engineers typically select this DF40 series connector when they need reliable interconnect performance, tight stacking geometry, and efficient board-to-board signal routing in dense layouts. Based on the provided specifications, the part status is Active, which is favorable for ongoing design use, although broader lifecycle confirmation should still be verified through Hirose or authorized documentation because the input lifecycle field is listed as unknown. RoHS compliance information is not explicitly provided in the supplied data, so compliance status should be treated as information not available until confirmed through the official datasheet, manufacturer declaration, or distributor compliance records.