Yuriy,
Thank you for your clarification. I think there were initial misunderstandings
all around.
To answer your question, yes you are correct. Equation (11) in my DesignCon2019
paper follows equation (14), which follows from equation(11)in your paper.
My EDICon 2016 paper is the best example of the cubic-close packing of equal
spheres model (a.k.a "Cannonball" model)derivation and how I got such good
results with the CMP28 platform measurements from data sheets alone.
Our DesignCon 2018 paper, with same measurements, we show that when you also
correct Dk due to roughness and apply a causal metal model, similar to your
Hurray-Bracken model, you get even better results for phase delay using the
same roughness numbers from data sheets.
The default foil used on CMP-28 platform's FR408HR core laminates is MLS, Grade
3, controlled elongation RTF from Oak-matsui. Roughness Rz parameters for drum
and matte sides are 120μin (3.048 μm) and 225μin (5.715μm) respectively for 1
oz. copper foil (see link below for data sheet).
An oxide or micro-etch treatment is usually applied to the copper surfaces
prior to final lamination. This provides enhanced adhesion to the prepreg
material. MultiBond MP is an example of an oxide alternative micro-etch
treatment commonly used in the industry. Typically 50 μin (1.27μm) of copper is
removed when the treatment is completed, depending on the board shop’s process
control (see link below for reference to 50uin).
The etch treatment creates a surface full of micro-voids which follows the
underlying rough profile and allows the resin to squish in and fill the voids
providing a good anchor. Because some of the copper is typically removed during
the micro-etch treatment, the published roughness parameter of the matte side
is reduced by nominal 50 μin (1.27 μm) for a new thickness of 175μin (4.445μm).
In a subsequent paper by J.A. Marshall, your paper [Ref 11], further supports
that roughness smoothens and decreases on RTF foil after OA application.
Here is the link to the foil data sheet used on FR408HR with RT foil. Please
note the numbers are in micro inches and was converted to microns in the EDICon
2016 paper.
http://www.oakmitsui.com/uploads/mls.pdf
And here is the link to MacDermid Oxide Alternative. Need to scroll down to
MultiBond MP near the bottom to find the reference to 50 uin copper removal
after application.
https://electronics.macdermidenthone.com/products-and-applications/printed-circuit-board/surface-treatments/innerlayer-bonding
Of course the biggest gotchya is how well does the board shops control the etch
treatment process. This is an issue for either method.
My counter argument to yours is that the material extraction fitting process is
only as accurate for the sample from which it was extracted and the software
used to do the extraction. There will be variation in the numbers sample-sample
from the same fab shop and more so from different fab shops because they have a
different etch line and oxide alternative process. Lee Richie has shown an
example of this many times in his presentations.
So if I only measure one sample, for example, will it be right if I need to use
it in real design? How do you factor process variation? What if it was from a
crappy board shop process? How would you know?
For example, if you look at the slides from my DesignCon 2019 paper near the
end where I give a practical example of modeling a backplane channel you will
see the simulation results for 4 cases, where all that was changed was the
backplane trace lengths. All measurements were from the same backplane PCB and
plug-in daughter cards. The only thing changed, in addition to the different
backplane lengths, were the layers from which the pairs were routed.
As you can see there are differences, even though exactly the same roughness
and dielectric models were used in each case. There are various degrees of
accuracy, but nothing that is grossly wrong. This is a real world application
we need to design, and often in the architectural phase of a program, you need
to come up with engineering decisions sooner, rather than later. Thus the
motivation for my work.
I am not saying my method is more accurate or better than the material
extraction method. In fact I think they could complement one another. What I am
saying is would I have got any better results in the 4 cases if I extracted the
material properties beforehand? At the very least, my method gives reasonable
starting point, and maybe good enough if you finally go the next step and do
IBIS-ami channel simulation. As you can see from the one example, there was
excellent correlation in PAM-4 eye simulations for case 1.
I also recommend that at some point you include a test coupon on the same panel
as the prototype PCB so that the original model can be validated as was
expected.
In the end, there is no magic. I hope this clears up some of the doubts and
leads to further clarification to your paper.
All my papers and slides referenced above can be found here:
http://lamsimenterprises.com/Awards_and_Publications.html
Regards,
Bert Simonovich
Signal/Power Integrity Practitioner | Backplane Specialist | Founder
Email:Lsimonovich @lamsimenterprises.com
LAMSIM Enterprises Inc.
Web Site: http://lamsimenterprises.com
Blog: http://blog.lamsimenterprises.com/
-----Original Message-----
From: Yuriy Shlepnev [mailto:shlepnev@xxxxxxxxxxxxx] ;
Sent: 20-Mar-19 5:08 PM
To: dmarc-noreply@xxxxxxxxxxxxx; hungdn.hcmut@xxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx; 'Bert Simonovich'
Subject: RE: [SI-LIST] Re: Megtron6 vs. Megtron 7 vs. Isola MT40
Bert,
Yes, I was puzzled with the number of simplified models you suggested in your
papers (it is actually more than 3) - thank you for the clarification.
With your explanation, it is even simpler now - here is definition of the true
"cannonball" model:
The "cannonball" model is the Huray "snowball" model with the roughness factor
(RF) fixed to 8.33 (or Hall-Huray surface ratio fixed to 4.887) and the radius
of the spheres fixed to r=0.06*Rz (follows from formula (11) with Rz and (14)
in http://www.simberian.com/AppNotes/SnowballsToCannonballs.pdf or Equation 11 ;
in your DesignCon2019 paper). Is that correct?
There is nothing wrong with the simplified version of Huray model that you
suggested. Your claim that all you need is Rz from a spreadsheet and
illustrations on how perfectly it works - that part is confusing and
misleading. As it follows from your paper, it may take more than that, to have
reasonable correlation with measurements.
Let' take one example. How do I get Rz for CMP-28 for instance? It is widely
available test platform from Wild River Technology. We use it for demos and
training on the material characterization. Can you share a reference to a
document with the Rz number that gives so excellent correlation as you
demonstrated many times? Or Rz requires some adjustments before the use in the
formula? What is the range? - that will define the error margin. There is
nothing wrong with the adjustment or fitting of the model to measured data -
that is how it should be done, to start with. And such fitting does not require
any spreadsheet data - all it needs is the measured S-parameters. And when it
comes to the fitting, the original Huray model with two parameters is
preferable - it is more flexible and accurate. That is why Hammerstad model was
extended with the second parameter (roughness factor) into the Modified
Hammerstad version in 2011 - to make it more accurate!
Also, you did not claim that the model with one parameter is "more accurate" -
that was my answer to those people who asked me is the "cannonball" model more
accurate and why Simbeor software does not have it.
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 to Design Predictable Interconnects!
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 Bert Simonovich (Redacted sender "bertsimonovich" for DMARC)
Sent: Wednesday, March 20, 2019 8:28 AM
To: shlepnev@xxxxxxxxxxxxx; hungdn.hcmut@xxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx; 'Bert Simonovich'
Subject: [SI-LIST] Re: Megtron6 vs. Megtron 7 vs. Isola MT40
Yuriy,
Unfortunately your summary paper has created more confusion. First of all,
there is only one “Cannonball” model, and it is based on the cubic close
packing of equal spheres, also known as face-centered cubic (FCC) packing.
https://en.wikipedia.org/wiki/Close-packing_of_equal_spheres
Although the hexagonal packing of equal spheres model (HCP), as described in my
DesignCon2015 paper is similar, it is NOT the Cannonball model.
All my model does is take Huray’s methodology, as explained in his book, “The
Foundations of Signal Integrity,” Pg 202, one step further.
https://www.amazon.ca/Foundations-Signal-Integrity-Paul-Huray/dp/0470343605/ref=sr_1_fkmrnull_1?keywords=foundations+of+signal+integrity&qid=1553030893&s=gateway&sr=8-1-fkmrnull
---Start quote
“Loss for a high profile surface: A methodology must be chosen to optimally
represent the surface protrusions with stacked snowballs. A lower limit can be
chosen by calculating the number of snowballs that will completely fit within a
pyramid with a height of 5.8µm and a base width of 9.4µm, which are the RMS
values of the protrusions measured on the high profile copper samples using an
optical profilometer. Using the superposition argument, we have replicated the
structure seen in SEM photographs with an ensemble of various size spheres to
represent the geometry of the pyramid structures for high profile samples”
End quote----
Huray himself chose an HCP sphere ensemble to represent the sphere structure
seen in SEM photographs. He ALSO assumes the height of the model is the RMS
values of the protrusions measured by a prolifometer. Then he fits between the
minimum and maximum number of spheres that will fit in the area and height
defined until he gets a good fit, as I have described in almost all of my
papers!
This was the initial inspiration to developing my model. All I am doing is
determining the base area of the spheres based on the sphere radius which is
derived from the total RMS height as measured by prolifometer.
As far as your confusion on using Ra for one side and Rz for another. Simply
put, data sheets generally specify Ra for the smooth, or drum side of the foil,
while Rz generally specifies the roughness of the nodule-treated side that gets
bonded to core. In my DesignCon 2015 paper case study, I clearly said that Ra
was the drum side roughness WITH oxide alternative (OA) etch treatment applied.
I used what was specified as average roughness by the OA vendor. My latest
DesignCon 2019 paper and slides explains the process in more detail.
I never claimed Cannonball model was more accurate than Huray’s. I can get
good enough results from manufacturer’s data sheets alone. I am not a magician
and I do not pull rabbits out of a hat, as was implied by my excellent
correlation to measurements. I have the actual data sheet roughness parameters
to back everything up.
I stand by my methodology and my numbers. For anyone who wants to try it I
suggest following my last DesignCon 2019 paper. It is the culmination of the
last 4 yrs of my research into one document. I also invite anyone to share with
me their experience, good or bad if you try it.
Regards,
Bert Simonovich
Signal/Power Integrity Practitioner | Backplane Specialist | Founder
Email:Lsimonovich @lamsimenterprises.com
LAMSIM Enterprises Inc.
Web Site: http://lamsimenterprises.com
Blog: http://blog.lamsimenterprises.com/
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Yuriy Shlepnev
Sent: 18-Mar-19 6:14 PM
To: dmarc-noreply@xxxxxxxxxxxxx; hungdn.hcmut@xxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx; 'Bert Simonovich'
Subject: [SI-LIST] Re: Megtron6 vs. Megtron 7 vs. Isola MT40
Bert,
I tried to follow what you are doing by reading your papers - here are some of
my observations http://www.simberian.com/AppNotes/SnowballsToCannonballs.pdf
This is also done for those who wants to convert 2-parameter Huray "snowball"
model into the "cannonball" model and use just Rz as the single parameter. Very
easy to do - just try it and see if it works in your case (just make sure that
you have measurements to validate it).
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 to Design Predictable Interconnects!
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 Bert Simonovich (Redacted sender "bertsimonovich" for DMARC)
Sent: Friday, March 15, 2019 11:27 AM
To: hungdn.hcmut@xxxxxxxxx; shlepnev@xxxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx; 'Bert Simonovich'
Subject: [SI-LIST] Re: Megtron6 vs. Megtron 7 vs. Isola MT40
To add to Yuriy's Comments, and try to explain why Cannonball model works.
Actually the roughness parameters Ra, Rq and Rz are derived from the roughness
profile, as measured with a mechanical prolifometer. A mechanical prolifometer
records the roughness peaks and valleys as it is dragged across the surface of
the sample being measured. It is essentially a 2-D measurement. Think of a
record player needle being dragged across a vinyl record.
Ra is defined as the average roughness of the measured profile over the sample
length. Rq is the RMS value of the profile shape over the sample length. And
finally Rz is the 10-point mean value, which is the sum of the average of the 5
highest peaks and 5 lowest valleys, of the profile over the sample length.
As part of the electrodeposited process, the matte side of the foil is the side
facing the CU sulfate solution, as it gets electro-deposited onto the large
rotating drum. The drum side is the side in contact with the drum. The drum
side takes on the profile of the stainless steel drum and is fairly smooth
compared to the matte side. Afterwards the foil goes through a nodule treatment
process where it deposits tiny nodules, usually on the matte side of the foil
or the drum side. The standard nodule treatment is done on the matte side but
when applied to the drum side it is known as reverse treated foil, or RTF.
Almost all foil suppliers will give Rz numbers for their treated side of the
foil, and Ra for the untreated or drum side.
Yuriy is correct, in that there is no exact conversion between Rz and Rq. But,
in the words of E.P.Box, "All models are wrong, but some are useful", if we
assume Rz represents the average peak-valley profile over the sample length,
and if we model the peak-valley profile as a triangular waveform profile, with
the peak-peak height equal to Rz, then the RMS value of that triangular profile
over the sample length is simply Rz/2/sqrt(3). I use this as a rough
approximation for Rq from Rz and vice versa when needed.
My Cannonball model relies on a stack of 14 equal sized spheres stacked in a
close-packing of equal spheres arrangement over a square tile base with an area
of 36(r^2) - where r is the radius of the sphere. The unique thing about the
Cannonball model is that it simplifies the Huray equation to just 1 parameter
equal to the radius of a sphere, for an N-equal size sphere model.
Because the area of the square tile base is determined directly from the radius
of the sphere, they cancel out in that part of equation, thereby reducing the
Hall-Huray surface ratio, or roughness factor to a constant = 1.56(pi) or ~
4.6. This is the "SR" parameter for Ansysis and Cadence tools. In Simbeor, RF1,
as defined in the tool, will be ~ 8.33. By the very nature of the Huray
equation, these numbers are constant - regardless of the size of the sphere.
So even if you want to use the material identification method, as Yuriy
described to try and come up with material properties, all you have to do is
use the appropriate constant for SR or RF1 (depending on the tool) and adjust
the radius parameter until you get a fit to measurements. Personally I have
found that when I adjust Dk due to roughness from engineering data sheets, as
described in my DesignCon 21017 paper, then tune the respective radius
parameter, you can get excellent results from essentially laminate supplier's
data sheets. Thet's it. Rz is not in the picture yet!
But, in my opinion, the material extraction process is really only good for the
samples from which they were extracted, the quality of the measurement and for
the software used for the fitting. They do not represent the intrinsic values
of the material, especially the roughness of the copper foil used. All results
really show is how well the software fits measurements.
The reason I say this is laminate suppliers usually have 2 or more copper foil
suppliers from which they buy from and each of them will have slightly
different roughness based on their nodule treatment process. And furthermore,
there will be oxide alternative (OA) treatment variations, depending on where
the final design board will be fabricated. Each board shop has their own OA
process, and there is no guarantee the product board you carefully
characterized will be built from the same fab shop forever.
Over the last few years, I have also shown that you can indeed get excellent
results using Rz parameters from foil manufacturer’s data sheets in conjunction
with my Cannonball model to describe the roughness profile. In my method, Rz is
only used for the 10-point mean peak-valley height then my algorithm converts
that into a sphere radius to complete the Cannonball-Huray simplified model, as
described above. If the Rz is known, then the radius of a sphere can be
approximated as 0.06(Rz).
But you have to get the foil roughness numbers from laminate supplier, NOT
board shops. In the example of my DesignCon2019 paper, (
http://lamsimenterprises.com/Awards_and_Publications.html ;), I knew the actual
supplier of copper foil used on the core laminates of the test board. When I
used exact numbers from the foil mfr data sheet, and the effect of OA on RTF
foil, I got excellent results for both insertion loss and phase delay, just by
using data sheet values!
Mentor Hyperlynx and Polar Instruments field solvers have adopted the
Cannonball-Huray model within the tool so all that is needed is Rz. In this
case all you need to tune for material identification is Rz parameter in the
tool, if that is your end goal.
In the end, even though the Cannonball model may be “technically wrong” from
reality, it is still just a model and useful, depending on what you are trying
to accomplish. The Hammerstad model, which has been used for many years, by the
way, is also "technically wrong" but was useful in its time. It relied on RMS
profile of the peak-valley triangular profile of the model, but because of
model limitations it loses accuracy after 3-15 GHz, depending on the roughness
of the foil.
The bottom line is my Cannonball-Hurray model gives you the simplicity of use
as the Hammerstad model, but with better accuracy of Huray model, regardless
what method you like to follow.
Bert Simonovich
Signal/Power Integrity Practitioner | Backplane Specialist | Founder
Email:Lsimonovich @lamsimenterprises.com
LAMSIM Enterprises Inc.
Web Site: http://lamsimenterprises.com
Blog: http://blog.lamsimenterprises.com/
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On ;
Behalf Of Hung Dang
Sent: 15-Mar-19 12:31 AM
To: shlepnev@xxxxxxxxxxxxx
Cc: dmarc-noreply@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Megtron6 vs. Megtron 7 vs. Isola MT40
Thank you so much, Bert, Yuriy, Bill.
I will try to config on my simulation.
Và o Th 6, 15 thg 3, 2019 vaÌ€o luÌc 04:34 Yuriy Shlepnev <
shlepnev@xxxxxxxxxxxxx> đã viết:
Hi Hung,
You need measurements for at least 2 line segments to identify 2
parameters in the Huray model with either GMS-parameters, SPP Light,
Gamma-T or eigenvalue techniques - just pick your method. There are no
other scientific ways to come up with the model parameters, even for
the worse-case scenario.
To start with, you can use the numbers from the publications I cited below.
The actual losses may be higher or lower - it will depend on the
copper foil and PCB manufacturer. Fair comparison of dielectric
performance can be done only with the same type of copper foil for the
same PCB manufacturing process.
There are two mechanical parameters that approximately define the
frequency of the skin effect onset on the rough surface - those are
peak-to-valley parameters Ra and Rq (or Sa, Sq if measured optically).
It follows from the physics of the skin-effect. When skin layer depth
is becoming comparable with the Ra or Rq, the losses due to the
roughness start growing (rough surface absorbs more energy). The
growth rate and maximal value are defined by the surface shape - there
are no mechanical parameters from manufacturers that can be used to
characterize that. One-ball or one-level Huray model has
2 parameters - ball radius defines the skin-effect onset and
Hall-Huray surface ratio or roughness factor defines the maximal
possible increase in losses due to absorption by the surface. There
are no ways to identify both parameter from the mechanical or optical
measurements (though there are some attempts). The reason is very
simple - the model describes absorption by a small sphere (or multiple
separate spheres) - it is a solution for a "spherical cow in vacuum"
(Paul Huray actually used this analogy at our presentation at
DesignCon 2015). Though, the formula captures the physics of the
skin-effect onset process. The stacks of balls in the original paper
was purely for illustrative purpose - no connections with the loss
increase formula. Though, unfortunately, some people took the
illustration too literally and it went as far as the model parameters
derivation from just Rz.
Considering availability and use of Rz - this parameter is simply not
relevant to the electrical roughness characterization. Ra or Rq cannot
be derived from Rz - as simple as that. See mathematical definitions
at https://en.wikipedia.org/wiki/Surface_roughness. It is easy to ;
proof or illustrate. Two surfaces with same Ra may have very
different Rz. Or, the other way around, two surfaces with identical Rz
may have very different Ra values - it follows from the definition.
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 to Design Predictable Interconnects!
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 Hung Dang
Sent: Wednesday, March 13, 2019 7:25 PM
To: shlepnev@xxxxxxxxxxxxx
Cc: dmarc-noreply@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Megtron6 vs. Megtron 7 vs. Isola MT40
Dear Yuriy,
As you said: "The foil manufacturers may provide some mechanical data
that are not relevant to the electrical behavior of copper"
I'm extracting 25Gbps differential traces by ANSYS HFSS, I'm confused
how to choose the suitable roughness model of traces.
What are the parameters or specification which we can base on that? I
need to cover the worst case of losses due to surface roughness.
Thanks.
Vц=o Th 5, 14 thg 3, 2019 vaл-o luл│c 06:49 Yuriy Shlepnev <
shlepnev@xxxxxxxxxxxxx> д-цё viÐ│©t:
Hi Dan,the
Meg6 was used in the analysis to measurement validation project
EvR-1 -
results were reported last year at DesignCon 2018 - see #2018_01 andThe
#2018_07 at http://www.simberian.com/AppNotes.php Complete solutions ;
for the material model identification and automation scripts for
that project are available on request.
Meg7 was extensively studied in another project with the results
reported at DesignCon 2019 - see #2019_01 at
http://www.simberian.com/AppNotes.php
goal in this project was to build statistical models for dielectricitself
and for the conductor roughness.larger
Note, that in both cases the identified Dk and Df were close to the
data provided by manufacturer. However, the actual traces exhibited
much
losses due to the conductor surface roughness. The boardwere
manufacturers in both studies did not have any numbers for the
electrical characterization of the copper roughness. The foil
manufacturers may provide some mechanical data that are not relevant
to the electrical behavior of copper. In addition, the copper is
also treated by the board manufacturer - there
no data on this process either. Any guess in such case would bethan
better
nothing, but if you want accurate characterization and comparison,have
you
to do the model identification with the measurements.Finalist
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 to Design Predictable Interconnects!
2010 and 2011 DesignVision Award Winner, 2015 Best In Design&Test
designs
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
On
Behalf Of Dan Bostan (Redacted sender "dbostan" for DMARC)
Sent: Wednesday, March 13, 2019 11:27 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Megtron6 vs. Megtron 7 vs. Isola MT40
Does anyone have direct experience with all of those materials, for
above 32Gbaud?I used successfully Megtron6 in the past, but I am
looking for alternatives.Any pricing information would be
appreciated, as well.Cheers,Dan Bostan
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