âSkewâ IMHO is not a good metric for 50GHz level signal integrity (32G NRZ,
56G PAM-4). I realize this may be slightly veering from the initial thread,
but it relates to what is going on with IEEE p370 activity and relates keeping
the eye open.
For our Custom Channel Modeling platforms we use the following metrics for
fabrication and material performance:
1. Variation of impedance trace to trace, where the impedance is an average,
this relates to the typical 5% impedance tolerance
2. Variability of trace impedance using a fast TDR, or a measure of
homogeneity of the material for a single trace. Traces need to be rotated
from in line with weave to orthogonal. Poor homogeneity, such as 2-3ohms, for
15-45 degree rotations is really not a good thing. We will probably start
identifying specific laminate systems and fabricators with a 3sigma number and
histogram the variation as well.
3. Group delay variation from DC to Fmax s21, s43 and SDD21. This is a much
better metric than skew, especially for microstrip transmission lines or test
fixtures mixing single and differential.
4. Differential to common mode, SDC21 transformation for carefully balanced
systems (no bends or twists). The device/package can potentially generate
skew based on poor return loss or mode issues as well.
5. Group delay noise, SDD21, or s21 and s34 or forward transmissions.
We find that simulation to measurement correspondence, material identification,
and the commonly used de-embedding schemes (AFR for example) work out much
better using this comprehensive look at materials. Yuriy Shlepnev suggested
some time back looking at both real/imaginary parts of the s-parameter but I
havenât got my head around that yet. We are using cross section for
VIAâs , trace geometries, but not for X-Y yet, thanks for the idea Lee and
Bill. The X-Y cross section will juxtapose nicely against the electrical
verification.
Any positive comments or other ideas?
- Al Neves
Products for the Signal Integrity Practitioner
Alfred P. Neves
Chief Technologist
Office: 503-679-2429
www.wildrivertech.com <http://www.wildrivertech.com/>
2015 Best In Design&Test Finalist
On Dec 30, 2015, at 9:09 AM, Lee Ritchey <leeritchey@xxxxxxxxxxxxx> wrote:
I polish two of the edges, one X and one Y and use a microscope to see what
the glass styles are.
Since I want to know before I accept delivery, I require the fabricator to
include a copy of the traveler with the shipment. This shows what glass
styles were used.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Bill Hargin (Nan Ya, USA)
Sent: Monday, December 28, 2015 12:26 PM
To: bbakshan@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Glass Weave effects and Cross sectioning
Hi Boris:
If the boards have already been built, and you know the relative dimensions
you're looking for with respect to the yarn width and height, you could do
that. If it were me, I'd first work backward from the fabricator to the
laminate manufacturer first - to see what kind of information I could get on
whether spread glass was used. In most cases, you should at least be able to
get a yes/no answer on that. It's less likely, but some fabricators/laminate
manufacturers will even be able to provide specific cross-section dimensions
for various weave constructions.
Armed with whatever information you can get for free, you can certainly do
some cross sectioning and SEM measurements, if you have the means, and you
have an idea regarding the aspect ratios you're looking for.
I have this kind of data for our fabric, which is all spread, as a general
practice. I believe that Isola provides this info for their glass
constructions, as well. Let me know if that data would help, and I'll
provide it offline.
Out of curiosity, have you had (glass weave) skew problems, or is it just a
concern at this point.
Bill Hargin
Director of North American Sales and Marketing Nan Ya Copper-Clad Laminates
billh@xxxxxxxxxxxxx ⪠425-301-4425 ⪠Skype: bill.hargin
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Boris Bakshan
Sent: Sunday, December 27, 2015 10:17 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Glass Weave effects and Cross sectioning
Hi experts,
I've been reading much on glass weave effects and its contribution on skew.
If I encounter a skew problem, can I say anything on weave type ,whether it
is mechanically spread or not by doing a cross section of my traces?
If not, how can I guarantee that the right type of weave was indeed selected
when building my board?
Thank you all!
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