What this 90-position DF40 receptacle does in a board stack
The Hirose DF40JC-90DS-0.4V(53) is a 90-position, 2-row receptacle with center strip contacts, part of the DF40 series of fine-pitch board-to-board mezzanine connectors. Gold-plated contacts (2.00µin) on both mating surfaces handle the signal duty for this position count; the thin flash is adequate for the limited mating cycles typical of a factory-assembled stack, not a field-service disconnect.
Position count and pitch — the BOM match
At 90 positions, this is the highest-count member of the DF40JC subfamily. Against the 70-position DF40JC-70DS-0.4V(53), the extra 20 circuits give you more I/O in the same footprint length, useful when a design adds differential pairs or spare lines without respinning the PCB. The 60-position DF40JC-60DS-0.4V(53) is a further step down; choose the position count that matches your circuit count exactly — there is no room for unused positions at this pitch.
The RoHS compliance is current. There is no official second-source or cross-reference on record; the DF40C-90DS-0.4V(51) shares the same 90-position count and 0.40mm pitch but is a different base product number (DF40C vs DF40J) — verify mechanical interchangeability with your mating header before substituting.
Mating with DF40 series headers
Surface-mount termination on both sides means the reflow profile must be matched to the 0.40mm pitch to avoid solder bridging between adjacent pads.