PCIe Gen4_PCB Material


We are planning to use a M.2 module with PCIe Gen4 (Only Single TX/RX pair).

We have terminated PCIe Gen4 from ORIN to M.2 with zig-zag routing as mentioned in the design guide.

Can we proceed with the standard FR-4 PCB material for the above config, since it is a single PCIe pair and routed length is only around ~40mm?

Or do we need to change the PCB material similar to the ORIN devkit (spread-glass) mentioned in the FAB note?

Any suggestions on this.

It depends whether the material can fullfil the requests. You can check with PCB vendor for the detail info. The target is to follow the guidelines in Design Guide.

Incidentally, the FR-4 or other material consideration might change impedance due to dielectric changes. I would think that if the required impedance is correct, then it wouldn’t care if it is due to FR-4 or something else.

Thanks both for the reply.

It is mentioned in the design guide to use spread glass material especially to reduce the intra pair skew.

Considering I’m only using a single Tx/Rx pair, we can able to minimize the intra pair skew as per the recommendation in the design guide.

We have also requested the pcb vendor about the speed supported but not sure if they could help correctly on this.
So in my opinion, a zig zag routing with proper length matching would work on FR4.

Any suggestions/comments are welcome.

I couldn’t give you details on how to do it, but if you have the IBIS model and the specs of the material and traces, then the program which uses that IBIS model would be able to predict the impedance. I’m the wrong guy to tell you any details on that though.

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