Board-to-Board Mezzanine Fit — 0.40 mm Pitch, 1.5 mm Stack
The Molex 559090274-TR625 is a 20-circuit plug from the SlimStack 55909 series, designed for board-to-board mezzanine stacking at a mated height of 1.5 mm. The 0.016" (0.40 mm) pitch is the tightest dimension on the footprint — it forces a fine-line trace escape and limits via diameter to around 0.20 mm under the part. The 1.5 mm stack height suits low-profile enclosures where the board gap is under 2 mm.
Mating Half and Series Position
The 20-position count is the key BOM match; the 2-row layout keeps the connector body narrow, which helps with routing density on the board edge. Within the SlimStack 55909 family, the 20-position variant is a mid-range density option — higher position counts exist for wider buses, but the 0.40 mm pitch and 1.5 mm stack height are consistent across the series.