Chuck,
We're in the architecture stage right now on this project. To define channel
routing requirements, I've already done a "what-if" simulation using
Nelco-13-SI as a baseline.
With its loss tangent and my system constraints, I have come up with
routing guidelines that allow the channel to meet the PCIe-Gen 4 channel
specifications - just barely. I am right at the limits of allowed loss for
the channel. I did a sensitivity analysis to maximize the
routing length I can allow - which is tight right now in this application.
Hence, my position is any material "as good as or better" than the
Nelco should work (where "as good as" generally means a loss tangent
less than or equal to). Clearly, once we have a final material
selection, have
the stackup defined and the routing is complete we will need to
resimulate to
confirm proper channel operation.
Thanks!
Ralph
On 6/7/2021 12:36 PM, Chuck Corley wrote:
Hi Ralph,
There are quite a few good materials now, I would write you a list of
some of the good ones but I’m not at my desk right now And I don’t want
to slight any of the great manufacturers who make these good materials.
But I can say there are now less expensive materials that are lower loss
than the one you mentioned.
Before you start shopping for materials though, as a first step you
should probably calculate the actual loss that you are willing to
tolerate for your communication links. Once you know what amount of
loss you can tolerate over the actual worst-case trace lengths your
design will have then that will enable you to choose the right material
at the best cost. For example, If your longest traces were actually
fairly short lengths, then you might be able to use a more lossy and
less expensive PCB material for your design and still meet your signal
loss targets. Many designs have short trace runs and may not need more
expensive low loss materials.
Chuck
---
Chuck Corley
On 2021-06-07 08:48, Ralph Wilson wrote:
It's been a few years since I've worked with any PCB fab house on------------------------------------------------------------------
stackups and materials for
high speed SERDES routing, so I've lost track of what is in vogue and
at
the knee of the curve
in terms of cost/performance. For the current product I'm looking at
we're "only" dealing with
PCIe-Gen 4 (16Gbps). In "the old days" Nelco-13-SI on a 1080/2116 glass
was a reasonably
priced, low loss, reasonably temperature stable, reasonably flat weave
product applicable
to the 2, 4 and 10G channels of the day. What has the industry moved to
these days?
I fully expect some of yesterdays exotic materials may have become
mainstream and affordable.
What materials and glass weaves are at the knee of the cost/performance
curve today that
provide a good environment for 16-25Gbps channels?
Thanks!
Ralph Wilson
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