Help with designing a controlled impedance flex ribbon

[nergal]

Hello all,

Anyone willing to help out a fellow EE. I am designing a dual layer straight flex ribbon cable to pass 4x PCIe signals between two boards and I am having issues with the GND cross hatching pattern.

Can anyone with access to Simbeor make a small calculation for me and post the dimensions of the hatch pattern? Software like this is expensive and was not able to find a free version.

Target impedance is 100ohm for differential traces. And the stackup is the default jlcpcb dual layer flex. The ribbon is straight 15cm, no bends or anything. I can give you the Kicad brd file if that helps.

Any help is higly appreciated.

[nctnico]

You might be able to simulate with a free version of Sonnet (Sonnet Lite) but I don't know if they still have free version available.

[nergal]

Thank you for the reply. I tried Sonnet Lite but unfortunately I cannot upload the Gerber files as that feature is not available on the Lite version. Either I am not using it correctly or the Lite version is not meant to do this.

[nctnico]

You don't upload the gerber files. Simulation would take too long anyway. Instead you draw a portion of the flex pcb and simulate that to check whether you get the widths and height correct.