[SI-LIST] Re: surface roughness
- From: "Oluwafemi, Olufemi B" <olufemi.b.oluwafemi@xxxxxxxxx>
- To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 28 Nov 2011 18:34:12 +0000
All,
Maybe it's going to take adding the alphabets A thru z as coefficients behind
Hammerstad equation, before the SI community realizes that the equation is
fundamentally flawed.
Here are some reasons why the equation is flawed:
1) It is an empirical fit to Morgan's data that was published in 1948. There is
no physics to it. "Effect of surface roughness on eddy current sources at
microwave frequencies" Journal of Applied Physics V.20 pp 352-362, 1948
2) The ratio you get from the equation is going to saturate at 2; no matter how
rough the copper is.
3) The only input to Hammerstad equation is rms value. As you all know, it is
possible to have a rough and relatively smooth copper have the same rms value.
Thus Hammerstad equation will give you the same ratio for both.
Apart from providing an equation to use, what Huray et all presented at
DesignCon 2010, was to explain the physics of surface roughness from an EM
perspective.
The presentation also debunked the myth that says, current flows in and out of
the rough structures.
As a community, I think we need to start going back to the physics of the
problem, rather than, rules of thumb or equations that have been passed down
that might not work. We can't keep patching...
I'm not trying to convince anyone to use the Huray Model, but to look at the
physics of the problem.
By the way the Huray model correlates in phase as well. Please check pg 83-84
'Surface Roughness and Its Impact on System Power Losses' Olufemi Oluwafemi,
ProQuest, Ann Arbor , MI.
My two cents,
Thanks,
Femi Oluwafemi
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Scott McMorrow
Sent: Tuesday, November 22, 2011 4:32 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: surface roughness
All
I'd like to be clear. Any simulation model for dielectric and copper
surface roughness modeling must be a good match to measured data in
amplitude and PHASE to be an accurate model. It is clear to me that the
papers presented on the Huray method have thus far not shown any phase
correlation data.
regards,
Scott
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed(r) is the registered service mark of
Teraspeed Consulting Group LLC
On 11/20/2011 1:59 PM, Yuriy Shlepnev wrote:
> 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
>
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