The Hirose BM20B(0.6)-34DP-0.4V(53) is a 34-position, dual-row header from the BM20 series, designed for board-to-board stacking with a mated stack height of 0.6mm. The 0.016" (0.40mm) pitch packs 34 circuits into a compact footprint, making it a fit for dense PCB layouts in portable electronics, wearables, and handheld devices where z-height is tight.
The 0.40mm pitch drives the board footprint — expect tight routing between pads, and the mating receptacle must match this pitch exactly. The 0.6mm mated stack height sets the gap between the two PCBs; the 0.020" (0.50mm) height above board on this header leaves little clearance for components on the underside of the top board. Gold contact finish at 2.00µin (0.051µm) provides corrosion resistance for the fine-pitch contacts, though the thin plating limits mating cycles compared to heavier gold deposits — treat this as a low-cycle-count interconnect, not a frequent disconnect point.
The BM20B(0.8)-34DP-0.4V(51) shares the same 34 positions and 0.40mm pitch but increases the mated stack height to 0.026" (0.65mm) and adds solder retention features; choose that variant when the board gap needs 0.05mm more clearance or when the header needs extra SMT hold-down during reflow.