Pitch, pin count, and board routing density
The 1MM-HU-D25-VS-00-H-TBP: At 0.039" pitch and 50 positions across two rows, the header occupies about 0.98" (25 mm) of board edge length — routing breakout traces between the 1.00 mm pads requires at least a 4-layer board for fan-out, or a very tight 0.15 mm trace/space on a 2-layer design. The 0.059" insulation height leaves a low profile above the board, which helps with airflow in dense card cages but limits the keep-out zone for nearby components.