Hi Sherman,
There is no the relationship between Dk/Df and bulk conductivity of
dielectric - they describe different physical properties of material.
Dielectric constant Dk and dissipation factor (Df or loss tangent)
characterize polarization properties of the material (bound charges) -
mostly atomic polarization in composite PCB dielectrics.
Df or loss tangent is zero at DC - no polarization losses.
On the other hand, bulk conductivity is defined by presence of free charges.
The conductivity is very low for PCB dielectrics and does not change much
from DC up to THz frequency range. It increases with the temperature.
Surface resistivity measurement is just a way to measure the bulk
conductivity on a surface of material. I guess such control was introduced
to control contamination of the surface with free charges (ions?) that
reduce the resistivity.
The polarization and conductivity effects sometime are mixed into "complex"
permittivity - conductivity divided by i*omega is added to imaginary part
(polarization loss) of the permittivity. Because of the loss tangent is just
a ratio of the negative imaginary part of relative permittivity to the real
part, it will increase at lower frequencies (a few Hz for PCB dielectrics)
and will be infinity at DC. This approach is not suitable for building
models with proper DC asymptotes.
See more in our "Material world..." tutorial #2016_01 at
http://www.simberian.com/TechnicalPresentations.php ;
Best regards,
Yuriy
Yuriy Shlepnev, Ph.D.
President, Simberian Inc.
2629 Townsgate Rd., Suite #235, Westlake Village, CA 91361, USA
Office +1-702-876-2882; Fax +1-702-482-7903
Cell +1-206-409-2368; Virtual +1-408-627-7706
Skype: shlepnev
www.simberian.com
Simbeor - Accurate, Productive and Cost-Effective Electromagnetic Signal
Integrity Software
2010 and 2011 DesignVision Award Winner, 2015 Best In Design&Test Finalist
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Sherman Shan Chen (Redacted sender "shan" for DMARC)
Sent: Saturday, September 14, 2019 4:58 PM
To: Scott@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Surface Resistivity-PCB materials for RF design
Scott,
My sim showed that the loss difference between 5.8e7 S/m and 4.3e7 S/m,
which is close to the worst case for the copper used in package based on
my previous experience, is 0.007dB/in (same VLP Roughness model). For
Kandou's CNRZ technology which is mainly aimed for USR/XSR applications,
such delta might not be significant. But for Kandou's ENRZ coding which
also covers LR applications, this is definitely something we should take
into consideration - on customer side, anything could happen. So, thanks
for the caveat.
As Oscar pointed out, the original question from Naveen was asking about
the impact of the surface resistivity (о│s) of the dielectric materials.
That's a very interesting question to me. Based on my limited knowledge
about the properties of dielectric materials, it seems the loss tangent
of the material is in proportion to the conductivity of the material
whilst I didn't see clear connection between Dk and the conductivity.
However, if we look at the datasheet of dielectric materials, we can see
some of them come w/ same о│s but different Df, or vice versa. Anyone can
shed a light on why this is so?
Personally, I would think as long as the material has a о│s larger than
1e5Ohm/sq, there should be no concern about it. Note the о│s must be
measured under standard IPC test method since it is very sensitive to
the test steps/conditions.
Regards,
/Sherman Shan Chen/
SI/PI Group, Kandou Bus
5 Queensbridge, Northampton,UK, NN4 7BF
Office: +44 1604 635826б=Email: shan@xxxxxxxxxx
reinventing the BUS
On 9/13/2019 6:59 PM, Scott McMorrow wrote:
Sherman,
That would be incorrect. Cu used in PCB manufacturing can range from a
conductance of 5.8 e7 S/m down to around 4.5 e7 S/m, with something around
5.6 e7 S/m being a reasonable value for most well-sourced copper. I've
seen off-shore Copper foil that is horrible. Since loss from Surface
roughness is linearly dependent upon the conductance of the metal, you
might want to look a bit closer.
I'm surprised that you do not know this, considering that the Kandou
signaling technology is primarily focused on in-package interconnect,
where the conductance of electrodeposited copper is on the order of 4e7
S/m, and the interconnect is dominated by resistive losses.
Scott McMorrow, CTO Signal Integrity Group
Samtec
Office 401-284-1827 | +1-800-726-8329
www.samtec.com<http://www.samtec.com/>
Scott McMorrow,
Office: 401-284-1827
www.samtec.com
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