The Hirose FX10A-120S/12-SV(71) is a 120-position receptacle from the FunctionMax™ FX10 series, built as a center strip contact mezzanine connector. It mates with the matching FX10 header at a 0.020" (0.50mm) pitch — tight enough to route dense differential pairs through a single board layer, but the via fanout needs careful planning. The 120 circuits line up with the BOM count directly; no spare positions to waste or missing channels to jumper. This is a surface-mount part with a board guide, ground plate, and solder retention features built into the body. The ground plate provides a low-inductance return path for high-speed signals and helps contain crosstalk between rows. The board guide takes the alignment load during assembly — without it, the fine-pitch contacts can skid off their pads. Solder retention tabs hold the part flat during reflow, preventing tombstoning on a 120-position footprint. Typical use is board-to-board stacking in compact telecom, networking, or server gear where the mated height budget is tight — the FX10A-120S/12-SV(71) supports stacking heights of 4mm and 5mm, so the same receptacle can serve two different board-spacing builds without requalifying the connector.
Stacking Height and Board Fit
The mated stacking heights are 4mm and 5mm — both are listed directly on the spec, meaning the receptacle is designed to work with both header heights in the FX10 family. If your board stack-up calls for a 5mm gap between boards, this part covers it; if the next revision shrinks to 4mm, the same receptacle stays on the BOM. The 0.126" (3.20mm) height above board is the receptacle's own profile before mating. At this pitch, trace escape from inner rows typically requires micro-vias or blind vias on high-layer-count boards. The ground plate and board guide are not optional extras — they are part of the connector's alignment scheme, and omitting the corresponding PCB cutouts or keep-outs will cause assembly issues.
If your build requires frequent board swaps, step up to a thicker gold option in the FX10 family or plan for a limited number of mates.
Comparing to Siblings in the FX10 Family
The FX10A-120S/12-SV(71) sits between the 80-position FX10A-80S/8-SV(71) and the 140-position FX10A-140S/14-SV(71) in the same 0.020" pitch, 2-row, gold-plated, SMT receptacle line. The 120-position count is the one to pick when your signal count lands exactly at 120 — the 140-position sibling adds 20 unused contacts that still need to be accounted for in the footprint and the BOM cost. The 80-position version is the choice for a narrower bus. The FX10A-144S-SV is also a 2-row, 0.50mm pitch receptacle but lacks the ground plate and the (71) suffix, which typically indicates a different packaging or plating variant. If your design relies on the ground plate for return current management, the FX10A-120S/12-SV(71) with that feature is the correct call — the 144-position sibling without it may introduce a ground discontinuity in the signal path.