DF40B-30DS-0.4V(51) from Hirose Electric Co Ltd is a fine-pitch rectangular mezzanine receptacle designed for compact board-to-board interconnection in space-constrained electronic assemblies. As part of the DF40 series, it offers a 0.40 mm pitch, 30 positions, dual-row layout, surface-mount termination, and solder retention, making it well suited for portable devices, embedded modules, industrial control boards, medical electronics, and other dense PCB architectures where reliable stacking height and signal routing matter. The gold-finished contacts support dependable mating performance in high-density designs, while tape-and-reel packaging fits automated assembly workflows. Based on the provided data, this part is commonly positioned for engineers needing low-profile, precision board stacking in volume production. Lifecycle status is currently listed as unknown, so designers should confirm long-term availability directly with Hirose or an authorized source before committing to new programs. RoHS compliance information is not available in the supplied specifications and should be verified through official manufacturer documentation.