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Terry,=20
=20
It is not tough to find DK values that allow one to calculate impedance =
correctly. Most laminate manufacturers have very good tables that list =
DK by resin content and frequency. We use them all of the time with =
field solvers to develop stackups.
=20
Good fabricators also use these tables. Those that are stuck in the =
past do as you describe. They don=E2=80=99t qualify to do stackups for =
me and my clients.
=20
Further, I don=E2=80=99t have fabricators do my stackups. There are far =
too many other parameters such as cross talk, interplane capacitance and =
weave style that are important for today=E2=80=99s designs that a =
fabricator is not qualified to determine.
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From: Terry Ho <***@163.com>=20
Sent: Wednesday, October 31, 2018 7:41 PM
To: ***@earthlink.net
Subject: =E7=AD=94=E5=A4=8D: [SI-LIST] =E7=AD=94=E5=A4=8D: TUC-933+ =
Laminate
=20
Hi Lee,
=20
Yes, almost all fab shops used empirical DK to match the target =
impedance. As you said "DK is a fixed value for a particular glass to =
resin ratio and frequency, but the "fixed" DK is an average value of the =
Prepreg/Core.
The glass-resin mixed dielectrics with nonuniform DK distribution and =
impedance E-filed is also nouniform, so the =E2=80=9Cworking DK=E2=80=9D =
will be a variable affected by all the factors: W/H/T/Glass/RC/Cu% .
It=E2=80=99s a tough job to predict the =E2=80=9Cworking DK=E2=80=9D. =
I=E2=80=99m working on it now.
=20
=20
=20
=20
Terry Ho
www.sisolver.com <http://www.sisolver.com>=20
=20
=20
-----=E9=82=AE=E4=BB=B6=E5=8E=9F=E4=BB=B6-----
=E5=8F=91=E4=BB=B6=E4=BA=BA: ***@earthlink.net =
<mailto:***@earthlink.net> [mailto:***@earthlink.net]=20
=E5=8F=91=E9=80=81=E6=97=B6=E9=97=B4: 2018=E5=B9=B411=E6=9C=881=E6=97=A5 =
0:44
=E6=94=B6=E4=BB=B6=E4=BA=BA: ***@163.com =
<mailto:***@163.com>=20
=E4=B8=BB=E9=A2=98: RE: [SI-LIST] =E7=AD=94=E5=A4=8D: TUC-933+ Laminate
=20
Some fab shops have been known to assume a DK to make their equations =
predict the right impedance! I had a fab shop once use a different DK =
for surface microstrip, buried microstrip and stripline, even though all =
the material came from the same box!
=20
I asked him why and he said that was what it took to get the impedances =
to match what was measured! Turns out he waa using equations that would =
never yield good results.
=20
-----Original Message-----
From: si-list-***@freelists.org <mailto:si-list-***@freelists.org> =
<si-list-***@freelists.org <mailto:si-list-***@freelists.org> > =
On Behalf Of PCB_Layup
Sent: Monday, October 29, 2018 9:16 PM
To: ***@gmail.com <mailto:***@gmail.com> ; =
si-***@freelists.org <mailto:si-***@freelists.org>=20
Subject: [SI-LIST] =E7=AD=94=E5=A4=8D: TUC-933+ Laminate
=20
Hi Boris
=20
Sharing some data we measured the DK of TU-933+ @5.15Ghz SPDR: PP1080 =
RC69%=3D2.73( lower than vendor's databank 3.1) and this measured data =
showed good correlation with impedance results of 16L test boards.
Personally I guess your boards shop used DK 2.6 is back-calculated =
empirical value for impedance design.
=20
Terry Ho
www.sisolver.com <http://www.sisolver.com>=20
=20
-----=E9=82=AE=E4=BB=B6=E5=8E=9F=E4=BB=B6-----
=E5=8F=91=E4=BB=B6=E4=BA=BA: si-list-***@freelists.org =
<mailto:si-list-***@freelists.org> =
[mailto:si-list-***@freelists.org]
=E4=BB=A3=E8=A1=A8 Boris Bakshan
=E5=8F=91=E9=80=81=E6=97=B6=E9=97=B4: =
2018=E5=B9=B410=E6=9C=8829=E6=97=A5 15:35
=E6=94=B6=E4=BB=B6=E4=BA=BA: si-***@freelists.org =
<mailto:si-***@freelists.org>=20
=E4=B8=BB=E9=A2=98: [SI-LIST] TUC-933+ Laminate
=20
Dear experts,
I received a stackup from one of the board shops in the east which shows =
a new material named TUC-933+.
Does anyone have an experience with this new "plus" version?
The stackup calls for an extremely low DK values of 2.6 for PP and =
cores.
Does this make any sense to you?
=20
Thank you.
=20
=20
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