Even when you do everything mentioned by seveal people here and use the
phase as a basis to measure phase delay, and ultimately effective Dk, you
will find that the effective Dk will be higher in proportion to the
roughness of the foil.
You must apply the correction factor described in the paper for core and
prepeg separately using 10-point mean roughness (Rz) of the Matte and Drum
side of the foil, then use these numbers instead of data sheet numbers in
your field solver simulator.
But this is only one part. The simulator must also use a causal metal model,
like that found in Simbeor or HFSS to get best correlation.
In our subsequent DesignCon 2018 paper, I coauthored with Vladimir
Dmitriev-Zdorov and Igor Kochikov, found on my web site
(http://lamsimenterprises.com/), describes a causal metal model and showed
that when we applied effective Dk due to roughness and use a causal metal
model to measured data we got excellent correlation with insertion loss,
phase delay and impedance. This continues to hold true with other stackups
and measurements I have done since then.
Bert Simonovich
Signal/Power Integrity Practitioner | Backplane Specialist | Founder
Email:Lsimonovich @lamsimenterprises.com
LAMSIM Enterprises Inc.
Web Site: http://lamsimenterprises.com
Blog: http://blog.lamsimenterprises.com/
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Havermann, Gert
Sent: 17-May-18 3:00 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Dk/Df value is increased very much after fabric
progress
In addition to the other comments you have to check if your process of
measuring dk is correct. Do you measure it based on impedance or phase? The
impedance based measurement isn't precise because surface roughness and
geometrical shape of the impedance cell take a big part of it. Phase
measurement (two different length traces and measure the phase difference)
will give more accurate results.
Alexanders point is very important too because some prepregs are available
with different Resin content but same glass style, so if you only specify
the glass style, you might be surprised in the end.
And maybe the supplier simply used a different material (happened to me some
times).
BR
Gert
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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx> On Behalf
Of Hung Dang
Sent: Thursday, May 17, 2018 8:17 AM
To: Alexander Ippich <Alexander.Ippich@xxxxxxxxxxxxxxx>
Cc: istvan.novak@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Dk/Df value is increased very much after fabric
progress
Thank you so much, Experts.
As Mr Alexander said that, I often get stack-up from Fab house. And I see
that Dk/Df value is often higher than Dk/Df in datasheet.
But in this time, Dk/Df from Fab house is very smaller than datasheet and
actual measurement value.[Dk = 3.5 (Fab house) --> Dk = 4.2(Datasheet) -->
Dk = 4.7 (measurement) at 4Ghz].
The big different Dk will make the gap between design and actual board such
as trace match length in DDR, estimated SerDes loss channel...
By the way, Thanks much Bert, I have read your paper and understand more
Roughness, Fabric process...It helps me configure more accurate stack-up in
3D simulation.
Thanks.
2018-05-17 12:11 GMT+07:00 Alexander Ippich <
Alexander.Ippich@xxxxxxxxxxxxxxx>:
Folks,Df 0.0181).
I would guess, that the reason is much simpler:
Hung mentioned, that he has picked the Dk/Df values from the data sheet.
Typical datasheets list values that are applicable to a certain
laminate thickness / construction. Very often, this is for a 0.060"
laminate (as lot of IPC-TM650 tests are based on that thickness) and
also a heavy glass weave (like 7628).
If he is now measuring on an actual board that is using a different
construction, Dk/Df values can differ significantly. This is why a lot
of laminate suppliers (including the company that I work for) offer
tables that show Dk/Df values for different constructions.
Let me just pick values from our 370HR material: we show resin
contents as low as 41% (Dk 4.44, Df 0.0134) and as high as 71% (Dk 3.89,
Bottom line, talk to your PCB supplier or a technical contact from the
laminate supplier that provided the material. Lot of things can be
explained, when understanding which materials / construction /
processes were used.
Best regards,
alex
------------------------------------------------------------
------------------------------------------------------------
----------------
Alexander Ippich
Technical Director, Signal Integrity & Advanced Technology Product
Manager RF/Microwave OEM Marketing Europe
e-mail: alexander.ippich@xxxxxxxxxxxxxxx
web: www.isola-group.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Istvan Novak
Sent: Thursday, May 17, 2018 4:19 AM
To: hungdn.hcmut@xxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Dk/Df value is increased very much after fabric
progress
If you search the SI-list archives you will find several threads on
related topics.
Because of unavoidable tolerances and second-order effects, you can
never expect very good agreement unless you extract the Dk/Df values
very carefully yourself. However, a 28.7% difference seems to be too
big, which begs the question what is the basis of your measured Dk and
Df values?
Regards,
Istvan Novak
On 5/16/2018 9:21 PM, Hung Dang wrote:
Dear Expert,with
When I run SI simulation, I apply Dk/Df of PCB material from datasheet.
After fabric progress, I measured on the actual board, Dk is
increased 28.7% (3.65 --> 4.7) and 41.6%(0.012 --> 0.017) for Df
when comparing
value in datasheet.phase?
So I have concerns below:
1/. What is the Dk/Df worst value which I should apply to simulation
2/. Could you help to list some application note or paper which talkabout
this issue?
Thank you so much.
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