The Hirose BM20B(0.8)-40DP-0.4V(53) is a 40-position header from the BM20 series, designed for board-to-board mezzanine stacking at a mated height of 0.8mm.
That dimension is set by the connector design — it is not adjustable. The 0.40mm pitch drives tight routing: trace widths and spaces in the breakout region will need to match the fine pitch, typically requiring controlled impedance design if the signal speed is high.
The connector includes solder retention features that anchor the part to the PCB during reflow. On a 40-position, 0.40mm-pitch SMT header, those retention pads prevent the connector from shifting as the solder paste reflows — a common failure point on fine-pitch connectors without them.
No obsolescence notice or last-time-buy window is on record. There is no official cross-reference or second-source on file; the BM20B(0.8)-40DP-0.4V(51) shares the same pitch, position count, and stack height but carries a different plating thickness spec (2.00µin (0.051µm) gold), which may matter for high-cycle-count applications.