Board-to-Board Mezzanine Connection at 0.40 mm Pitch
The Hirose DF40TC(3.5)-40DS-0.4V(51) is a 40-position receptacle from the DF40T series, designed for board-to-board mezzanine stacking. Its 0.016" (0.40 mm) pitch packs 40 contacts into two rows, making it a dense interconnect for compact handheld or portable equipment where PCB real estate is tight. The connector sits at a 3.5 mm mated stacking height — that's the z-height from the bottom of the header board to the top of the receptacle board when mated, a dimension you need to lock early in the enclosure design.
At 0.40 mm pitch, the trace-and-space on the PCB needs to match — you're looking at micro-via or HDI board capability to route signals out of the inner rows. This is a center-strip contact arrangement, so the footprint is a dense rectangle of SMT pads, not staggered rows.
Surface Mount with Pick-and-Place Features
The receptacle is surface mount (SMT) with a pick-and-place cap and solder retention features — that means it's set up for automated assembly on a standard reflow line. Tape & Reel packaging feeds into the pick-and-place feeder directly.
It's not built for repeated field-service disconnect/reconnect cycles. The gold provides a corrosion-resistant mating surface for signal-level currents in a clean, enclosed environment.
Mating Plug and DF40C Cross-Reference
This receptacle mates with the matching DF40T series header at the same 0.40 mm pitch and 3.5 mm stack height. The DF40TC variant is the current active version of that design.