0.80 mm pitch, 5 mm stack — the mezzanine fit
The 0.031" (0.80 mm) pitch and 5 mm mated stacking height are the two numbers that decide the board layout — the pitch sets the footprint density, and the stack height sets the z-height clearance between the two PCBs.
30.0 µin gold — built for reconnect cycles
In a mezzanine application the connector may be separated during board-level test, rework, or field upgrade, so the gold thickness directly governs the usable cycle life. Tin or flash-gold contacts would fret and oxidise under the same duty; this one is specced for it.
40 positions — mid-density in the FH family
The same series includes a 60-position variant (5084618-2) and a 120-position variant (5353999-5), all sharing the same 0.80 mm pitch and 30.0 µin gold plating. The choice between them is purely a circuit-count decision — the footprint pitch and stack height are identical, so a board laid out for 40 positions can scale to 60 or 120 only if the connector footprint length is adjusted for the extra positions.
SMT mounting, Tape & Reel — built for the pick-and-place line
Surface-mount termination and Tape & Reel packaging mean this connector is set for automated assembly. The board guide feature helps the pick-and-place nozzle centre the part on the footprint pads, and the shroud protects the contacts during reflow.