No matter how accurate measurements you do, how detailed information you get
from your PCB Fab house, or how good you simulation tool is, there will always
be manufacturing process and temperature/humidity variations. If you are
looking to a single point data type of simulation, chances are that your
product won't work in HVM. Your simulation strategy must include sensitivity
analysis, so you can figure out what are the design parameters that are
affecting the most the performance of your product. Based on the knowledge you
gain from this step you can focus on the tradeoffs that really matter and
optimize for cost. Finally units per million (UPM) analysis is a scientific
tool that you can use to decide how much margins you need to build in your
design such as to make sure that you don't overdesign, but you accurately
predict the failing rate of your product in HVM.
If you want to learn more about that, you can read our DesignCon 2017 paper
from the link below:
https://www.mentor.com/pcb/resources/overview/optimization-methods-for-high-speed-serdes-channels-using-com-metric-424d4b8b-8b1d-415e-855d-15aa82322aed
Thank you,
Cristian
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Hung Dang
Sent: Thursday, May 17, 2018 12:17 AM
To: Alexander Ippich
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,
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, Df 0.0181).
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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