0.6mm Stack Height, 0.35mm Pitch — Mezzanine Fit
The Hirose BM28B0.6-20DS/2-0.35V(51) is a 20-position receptacle with center strip contacts from the BM28 series, designed for board-to-board mezzanine stacking at a mated height of 0.6mm. The 0.014" (0.35mm) pitch is the tightest constraint — it drives the board footprint and limits routing density between pads.
What the 0.6mm Stack Height Means for the Layout
The mated stacking height of 0.6mm is the dimension that drives the board-to-board spacing — not the connector body height alone. With the receptacle sitting 0.024" (0.61mm) above the board, the total stack after mating with the matching BM28 header lands at exactly 0.6mm. That leaves almost no clearance for components on the inner faces; this is a connector for ultra-thin mezzanine pairs where the two PCBs sit nearly flush. If your board stack-up budget is tighter than 0.6mm, this series won't fit — you'd need a different mezzanine family.
Gold Flash Plating — Limited Mating Cycles
It protects the mating surface during initial assembly and a few reconnections, but it won't survive hundreds of mating cycles. For a one-time board stack in a consumer device or a low-service-life assembly, it's adequate. If the design requires frequent field reconnections or repeated board separation, the flash will wear through to the base metal and contact resistance will drift. The gold is cosmetic for corrosion resistance during storage; the real cycle life is limited.