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,
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 with
value in datasheet.
So I have concerns below:
1/. What is the Dk/Df worst value which I should apply to simulation phase?
2/. Could you help to list some application note or paper which talk about
this issue?
Thank you so much.
