What's the right PCB substrate for USB4?
Some colleagues are working on a project that leverages USB4 and looking to design their own PCB. The insertion loss limits are pretty clear in the USB4 standard (see image), which leaves routing, trace sizing, and the substrate as ways to mitigate insertion loss.
What PCB substrate materials do you recommend to combat insertion loss in USB4 systems? Also, does a 2-layer design have a snowball's chance of passing EMC testing?
I hope some of the PCB and hardware engineers in server - @Petr Dvořák @pallavaggarwal @Joseph Ogbonna - may be able to answer this question. Thanks.
8 Replies
2 layer, no way. 4 layer for high speed signals, please. FR4 should work fine
I dont really think 2layer is a good choice
The return current will be distanced
I have not done a project with USB4 yet but have done with USB3 10Gbps
Yes four layers is ok. Let the plane be very close to the signals @techielew
Thanks. I've heard FR4 can get dicey with high-frequency designs. But I'm assuming 10 GHz is nowhere near that threshold... Or is it and you're just a rebel 🤓
FR4 with shorter lengths works fine
if you need long length routing, we need to got for High freq pcb material like Rogers
@techielew Who will manufacture the PCB? This should be the very first question. When the answer is answered, the PCB manufacturing representative will advice the best substrate for 10 GHz. For FR4 materials, the substrate must be dense with a homogenous polymer resin filling to achieve homogenous transmission line impedance. I always start with the PCB manufacturer representative consultancy.
Thanks for this. We I'll return to this thread when @DougSandy and I determine a manufacturing partner.