# R8 three-port interposer PCB study — 29 September 2026

**This is a partial native KiCad PCB, not a fabrication package.** The site copy of the [complete editable project](R8_Three_Port_Interposer_Public_Study.zip) includes the `.kicad_pro`, seven schematic sheets, PCB, and local symbol/footprint libraries together. Extract the entire ZIP and open the project file. The [PCB copper view](R8_routed_copper_review.png), [layer SVG](R8_top_bottom_copper.svg), and [R8 schematic PDF](R8_three_port_schematic.pdf) are quick review aids.

R8 places three Molex Type-D receptacles, the six upper/lower stack connector footprints and four holes. Its copper connects **160 MC1/MC2 pass-through contacts plus one MC3-to-Type-D differential pair**. KiCad reports **119 unconnected items**. A conservative 0.20 mm rule reports **61 physical DRC violations** (51 stock Type-D pad clearances and 10 0.15 mm sample-trace width findings), plus 19 schematic-parity warnings. A conditional 0.15 mm study rule reports zero physical spacing/width violations, but the 119 opens and 19 parity warnings remain. Neither rule result establishes fabrication suitability. The 12 V protection branches and separate JTAG probe headers are schematic placeholders and are not placed circuits.

The published ZIP is a portable **project-only derivative** of the dated local R8 study. It omits the Opal Kelly Altium reference archive and generated STEP, while retaining local KiCad libraries and validation reports. The BRK8310 source design is [available from Opal Kelly](https://pins.opalkelly.com/downloads/442/download?category_id=3); XEM/BRK mechanical models are [available from Opal Kelly](https://www.opalkelly.com/products/models/). Footprint and model fit, actual connector stack height, cable overmold clearance, and board revisions still need comparison against the purchased hardware.