[SI-LIST] Re: surface roughness
- From: "Yuriy Shlepnev" <shlepnev@xxxxxxxxxxxxx>
- To: <nagachander.sing@xxxxxxxxxxxxxxxxxxxx>, "'si-list'" <si-list@xxxxxxxxxxxxx>
- Date: Sun, 20 Nov 2011 10:59:47 -0800
Hi Naga,
As Jeff mentioned the theory of conductor roughness is still evolving
research area and there is a lot to do here. However, this may be important
only for the completeness of the theories. For practical purpose we can use
heuristic models that capture the macroscopic observable effect of the
roughness (similar to how we characterize dielectrics). Practically any
roughness theory produces a roughness correction coefficient, that can be
used to adjust surface impedance of a conductor surface locally for accurate
electromagnetic analysis or to adjust skin-effect matrix extracted with a
static field solver (in case if less accurate static field solver is used
for the analysis). In both cases the parameters of a roughness model can be
identified by fitting the parameters of the correction coefficients to
measured data (reflection-less generalized modal S-parameters are best
suitable for such fitting). See a brief overview of roughness correction
coefficients in Y. Shlepnev, C. Nwachukwu, "Roughness characterization for
interconnect analysis". - Proc. of the 2011 IEEE International Symposium on
Electromagnetic Compatibility, Long Beach, CA, USA, August, 2011, p. 518-523
- paper is available at
http://ieeexplore.ieee.org/search/freesrchabstract.jsp?tp=&arnumber=6038367&;
openedRefinements%3D*%26filter%3DAND%28NOT%284283010803%29%29%26searchField%
3DSearch+All%26queryText%3Dshlepnev
Sorry for the long link - you can just search for authors names at
ieeeexplore.org, and paper and presentation are also available at
www.kb.simberian.com (in publications and presentations sections,
registration is required).
This paper proposes a simple 2-parameter Modified Hammerstad Correction
Coefficient (MHCC) as an extension of 1-parameter Hammerstad model used in
microwave IC applications for decades. The paper shows how to identify 2
parameters of MHCC by fitting GMS-parameters, assuming that the parameters
of a broadband dielectric model are identified separately. The model shows
excellent correlation with measurements up to 50 GHz. Parameters in Huray's
snowball model can be also identified with GMS-parameters with minimal
knowledge about the surface structure - no expensive conductor surface
investigation is required for such identification. Note, that the identified
Huray's model produces practically the same results as MHCC - we will show
that in our oncoming paper at DesignCon 2013. Both models are capturing well
the effect of additional absorption by surface due to increase of the
surface area.
Considering the roughness effect on PCB or packaging interconnects, I can
draw a parallel here with the wideband Debye dielectric model (also known as
Djordjevic-Sarkar or as Swenson-Dermer) that produces very good correlation
in analysis of interconnects in PCB and packaging applications over
ultra-wide frequency band. The model describes a dielectric with a
continuous spectrum over a wide frequency band. It correlates well with the
measured data and is used in practically all SI software nowadays. Though,
as engineers we do not care much about the internal structure of the
composite dielectrics that produces behavior captured by the model - all we
need is 2 or 3 model parameters that characterize a particular dielectric. A
multi-pole Debye model has more parameters can be used to describe almost
any dielectric used in PCB/Packaging and we do not care what structure
produces those poles - all we need are just values of the poles and residues
that produce good correlation within the spectrum bandwidth of our signal.
Considering the effect of roughness on degradation of signal in
PCB/packaging interconnects, rough surface leads to increase of attenuation
(insertion loss) and increase of inductance at high frequencies due to
simple increase of the total surface of the conductor. Both MHCC or Huray's
snowball models capture this increase in loss and inductance if applied
appropriately in the electromagnetic analysis. Conductor surface impedance
adjustment for instance produces causal models that take into account
current distribution within a conductor due to roughness on just one side of
plane or strip or due to additional plating layers for instance. Note that
both low and high profile copper roughness lead to a substantial increase in
attenuation above 10 GHz. In addition roughness also increases the
capacitance of conductor - that is clearly visible in cases with large
roughness and thin dielectric layers - see the paper and presentation cited
above. The capacitive effect of roughness due to surface singularity is
practically frequency-independent and was reported in IC applications a few
yeas ago - see for instance this paper and references there: A. Albina at
al., Impact of the surface roughness on the electrical capacitance,
Microelectron. J. 37 (2006) 752-758.
Finally, if you need a software that correlates with the measured data up to
50 GHz, it has to have at least wideband and multi-pole Debye models for
dielectrics in addition a selection of advanced models for roughness (MHCC
or Huray's snowball models for instance) that can be easily identified
without expensive investigation of the surface structure. Classical
Hammerstad model has low accuracy and not usable above 3-5 GHz in general.
The software has to be validated with measurement over the bandwidth of your
signal. Though, the software is only a part of the story here. In addition
you have to establish a procedure to identify the parameters of both
dielectric and conductor models. Without the rigorous material parameters
identification it is "garbage in - garbage out" no matter how advanced is
the analysis. Models that describe dielectrics and roughness over a wide
frequency band from MHz to 50 GHz are typically not available from
manufacturers at this time and have to be identified. Companies like
Teraspeed Consulting Group for instance can help you to establish such
material identification procedure.
Best regards,
Yuriy Shlepnev
www.simberian.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of nagachander.sing@xxxxxxxxxxxxxxxxxxxx
Sent: Friday, November 18, 2011 11:35 PM
To: si-list
Subject: [SI-LIST] surface roughness
Hi all,
What is the best tool to simulate surface roughness when simulating for the
differential S-parameters for striplines and microstripline in IC packages?
I am interested in simulating till 50GHz.
What kind of effects are you seeing with surface roughness? i mean things
like does your insertion loss increase? what abt diff return loss?
Any good papers to understand the problems in detail...
Any feedback will be appreciated
Thanks,
Naga
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
