STM32H735G_DK STACKUP

[davidlil]

Hello,

I am starting a project using this eval board.

I need to route octo-spi flash and ram (like on the eval board).

Do you have information about the stackup used ? 

Altium files give me a stackup but I find it a bit weird :

Cu1 is 42µm / D1 is core 100µm 

Cu2 is 35µm / D2 is prepeg 100µm

Cu3 is 35µm / D3 946µm core

Cu4 is 35µm / D4 is 100µm prepeg

Cu6 42µm

Flash and Ram tracks impedance are not 50ohms using those parameters. 

W (tracks width is 120µm).

Regards,

Dli

[LCE]

At least some ST evaluation boards are good examples that things are working even with sub-optimal layout. :D

If you have some PCB layout experience, forget about their specific board stack.

If not:
- check your PCB supplier's standard multi-layer stacks and use these (I really like 6-layer boards, with 2 GND-planes, 1 underneath top and bottom each)
- make sure to have an unbroken GND plane underneath all high speed tracks
- keep trace lengths roughly equal (with +-2 mm you should be good at 100 MHz)
- impedance... keep the lines as short as possible, and "somewhere around 50R", more important keep it equal between the signals
- use serial resistors on all lines (as ST does on the DK)