[Depends on stackup] meaning the stackup will determine how much of an effect
it will have on loss.
Ryan
------ Original message------
From: Ryan Lott
Date: Tue, Feb 21, 2017 8:53 PM
To: lists@xxxxxxxxxxxxxx;si-list@xxxxxxxxxxxxx;
Subject:[SI-LIST] Re: common PCB material for routing refclk in PCIe4 designs?
Gary,
I'm not very savvy on PCIe4 but here's my opinion:
I would get data sheets from the manufacturers (not the fab shops), grab a 2d
field solver, learn what you need to build, and get to work.
Given your scenario, for laminates and prepregs, pay close attention to the
glass weave styles (spreading and resin content -- 1086MS is a great example
for minimizing glass weave skew), dk and df values at 2Ghz or above (try and
find values obtained using bereskin stripline method), cu roughness of the
bonding side of laminate cu [depends on stackup], cu roughness of the resist
side of laminate cu after oxide treatment (fab shop controls this) [depends on
stackup], and cu roughness of foils from fab shops especially if you are
planning on doing outer layer high speed diff pairs [Again, depends on stackup].
A big piece missing from this is Tg, stack up design, and... Launches!!! Don't
screw up the launches! I recommend Simbeor for coaxial launch design as it is
easy to design launches and is extremely accurate, given that you have the
right material properties...
Another tip, for my fancy. Don't just say FR4. That term is meaningless from an
electrical standpoint. There are over 20 different kinds of FR4 materials out
there in the world. We, as an industry, need to stop being lazy using this
jargon. Just my two cents.
Good luck,
Ryan Lott
------ Original message------
From: Gary Giust
Date: Tue, Feb 21, 2017 7:12 PM
To: si-list@xxxxxxxxxxxxx;
Subject:[SI-LIST] common PCB material for routing refclk in PCIe4 designs?
Hi, I'm designing a test board to evaluate reference clocks for PCIe 4.0
market. The standard calls for a 12" differential 100 Ohm trace, but I
don't think it specifies the PCB material (FR4, Rogers, Tachyon,
Nelco-13, Megtron-6, etc.) to use.
Since I have to pick a material, I'm looking for recommendations which
one would be realistic (although perhaps on the pessimistic side) for
actual PCIe 4 designs. I want to avoid picking a material that is
clearly too high loss, or too low loss, compared to what may actually be
used.
Any recommendations?
Best regards, Gary
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