34 circuits at 0.40mm pitch — the board-stacking connector for tight z-height budgets
The Hirose BM20B(0.8)-34DS-0.4V(53) is a 34-position receptacle with center strip contacts, part of the BM20 series of board-to-board mezzanine connectors. The 0.016" (0.40mm) pitch packs 34 circuits into a narrow footprint, while the 0.031" (0.80mm) height above board sets the mated stack height at 0.8mm — one of the lowest profiles available for this circuit count.
0.80mm stack height — the z-height constraint that decides the enclosure
The mated stack height of 0.8mm is the single most restrictive dimension for this connector. The 0.40mm pitch means the PCB fab must support fine-line routing; typical trace width and spacing for this pitch is in the 0.10mm to 0.15mm range, so confirm your board house can hold those tolerances before committing the layout.
Solder retention — why this connector stays put on the SMT line
The solder retention features are metal tabs or dimples on the connector body that reflow to the board pads, anchoring the part during wave or reflow soldering. On a 0.40mm-pitch connector with 34 surface-mount tails, the lateral force from a cable or a mating header can shift the part if it isn't locked down. The retention features prevent that shift, keeping the contacts aligned with their pads through the solder joint's solidification phase. This is a practical advantage for high-volume SMT assembly where placement accuracy and first-pass yield matter.
34 positions vs 30 and 40 — picking the right circuit count for the BOM
The BM20B(0.8)-34DS-0.4V(53) sits between the 30-position BM20B(0.8)-30DS-0.4V(53) and the 40-position BM20B(0.8)-40DS-0.4V(53) in the same series, all sharing the same 0.016" (0.40mm) pitch, 0.031" (0.80mm) height, and gold contact finish. The 34-circuit count is the BOM match point — if your signal count is 34, this is the exact fit. The 30-position variant leaves four signals unconnected; the 40-position variant requires four extra PCB pads and a larger footprint. No other functional difference exists between the three — the choice is purely the position count.