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E
eternalSumit
Visitor
July 16, 2026
Question

STM32H7S78-DK — actual PCB stackup & Octo-SPI/Hexa-SPI impedance?

  • July 16, 2026
  • 1 reply
  • 20 views

Hi all,

I'm reusing the STM32H7S78-DK's Octo-SPI flash (MX66UW1G45G) and Hexadeca-SPI PSRAM (APS256) sub-circuits on a custom board and want to match the DK's signal integrity. I can't find the fabrication stackup or impedance spec in the docs. Could ST share, for the DK (please confirm board rev):

  1. Full layer stackup — copper weights and each dielectric thickness/material.
  2. Target impedance (single-ended + any diff) and tolerance for the Octo-SPI / Hexa-SPI nets.
  3. Trace width/spacing for those buses, and their routing layer + reference plane.
  4. Any length-matching constraints on those groups.

For reference, the published Altium reference-design project ships with an unconfigured stackup (single 1.5 mm dielectric, all layers typed Signal), so it doesn't reflect the real fabricated stack — which is why I'm asking for the actual values.

Thanks!

1 reply

CYANG.1
CYANG.1
ST Employee
July 21, 2026

Hi,

You can find suggested stack-up in gerber file. The file named “MB1736D_Gerber.PDF” is in MB1736 Manufacturing files on ST website:https://www.st.com/resource/en/board_manufacturing_specification/mb1736-manufacturing.zip

The stack-up and impedance table are in “Drill Drawing” page in this document. (As shown in below)

 

 

Length-matching constraints are in the sheets of Octo-SPI & Hexa-SPI in schematic :https://www.st.com/resource/en/schematic_pack/mb1736-h7s7l8-d01-schematic.pdf

(Below is Length-matching constraints in Octo-SPI sheet) 

 

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