DF40C-90DP-0.4V(51) from Hirose Electric Co Ltd is a fine-pitch rectangular connector plug designed for compact board-to-board interconnect applications where high contact density and reliable surface-mount assembly are important. As part of the DF40 family, it is well suited for space-constrained embedded hardware, industrial electronics, portable equipment, communication modules, and other designs that need a 90-position interconnect with gold-plated contacts and outer shroud construction. Engineers typically choose this type of connector for signal routing in densely packed assemblies where mechanical alignment and repeatable mating performance matter. Based on the available data, the lifecycle status is unknown, so design teams should confirm current manufacturer status before committing to long-term production. RoHS compliance information is not available in the provided specifications, and compliance should be verified directly through the official Hirose datasheet or manufacturer documentation before use in regulated markets.