[SI-LIST] Re: AW: fiber weave effect

  • From: "Lee " <leeritchey@xxxxxxxxxxxxx>
  • To: <ken@xxxxxxxxxxxxxxxx>, <shlepnev@xxxxxxxxxxxxx>, <jeff.loyer@xxxxxxxxx>, <Gert.Havermann@xxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
  • Date: Fri, 15 Aug 2014 15:31:44 -0700

When diff pairs are tightly coupled, they must be made narrower in order to 
make each one 50 ohms.  As a result, skin effect loss goes up.  Further, 
they may not be separated in order to snake through a pin field because, 
when they are not separate and not tightly coupled, their impedance shoots 
very high.  Not  a good thing.

As to the question of how does one handle many diff pairs from an FPGA 
without tight coupling, I suspect that this person is routing two traces 
between pins on a 1 mm pitch BGA.  If one does a proper tolerance analysis 
of the manufacturing process, it will be discovered that this cannot satisfy 
IPC class 2, let alone class 3 which is what most designs must satisfy.

Where does that leave us?  We must not route more than one trace between 
pins on 1 mm pitch BGAs and by definition, this will result in loosely 
coupled pairs.

-----Original Message----- 
From: Ken Cantrell
Sent: Friday, August 15, 2014 2:21 PM
To: leeritchey@xxxxxxxxxxxxx ; ken@xxxxxxxxxxxxxxxx ; shlepnev@xxxxxxxxxxxxx 
; jeff.loyer@xxxxxxxxx ; Gert.Havermann@xxxxxxxxxxx ; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: AW: fiber weave effect

Lee,
You made an interesting statement on "never" using tightly coupled traces,
and that there are too many down sides.  Can you enumerate a few of those
down sides.  I assume we are not talking about the issues with the
manufacturing process that have been discussed previously in this thread.
So, let's just say that you peaked my interest.

Thanks,
Ken

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Lee
Sent: Friday, August 15, 2014 2:58 PM
To: ken@xxxxxxxxxxxxxxxx; shlepnev@xxxxxxxxxxxxx; jeff.loyer@xxxxxxxxx;
Gert.Havermann@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: AW: fiber weave effect

Ken,

What do you mean by elaborate?

-----Original Message-----
From: Ken Cantrell
Sent: Friday, August 15, 2014 12:44 PM
To: leeritchey@xxxxxxxxxxxxx ; shlepnev@xxxxxxxxxxxxx ; jeff.loyer@xxxxxxxxx
; Gert.Havermann@xxxxxxxxxxx ; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: AW: fiber weave effect

Lee,
Would you like to elaborate on your "for the record" statement?

Thanks,

Ken

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Lee
Sent: Friday, August 15, 2014 11:38 AM
To: shlepnev@xxxxxxxxxxxxx; jeff.loyer@xxxxxxxxx;
Gert.Havermann@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: AW: fiber weave effect

Ah!  Since then we have built several more test PCBs using other glass
styles with great results.  The DesignCon 2013 paper was the stimulus for
building more test PCBs including some using GigaSync with results similar
to yours.  We are about to build several more.

What we learned with the DesignCon paper is that there are two different
versions of 3313 weave, one that is mechanically spread in both directions
and one that is mechanically spread in only one direction- the weave used in
the DesignCon paper.  You can see that skew in on axis is very good and in
the other it is poor.

Out of this has grown a movement to define what mechanically spread means.
We are a long way from getting this one settled.

For the record, I never use tightly coupled traces.  There are too many down
sides and very few up sides.

-----Original Message-----
From: Yuriy Shlepnev
Sent: Friday, August 15, 2014 10:06 AM
To: 'Lee ' ; jeff.loyer@xxxxxxxxx ; Gert.Havermann@xxxxxxxxxxx ;
si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: AW: fiber weave effect

Hi Lee,

For the test boards (there were a few) we used Isola's I-SPEED with 3313
glass on one side. As follows from your DesignCon 2013 paper, you observed
59 ps maximal skew for 14' horizontally oriented lines (table on page 10)
for that specific case - did I miss something?
Isola's GigaSync on 2116 glass was used on the other side of the board.
There were no measurable differences in the skew for the tightly coupled
traces between two materials. The skew was actually too small to make any
conclusions in both cases. However, GigaSync produced smaller far-end mode
transformation, that looks like much better metric for the material
inhomogeneity, comparing to the direct skew comparison (especially for the
tightly coupled traces).

Best regards,
Yuriy

Yuriy Shlepnev, Ph.D.
President, Simberian Inc.
3030 S Torrey Pines Dr. Las Vegas, NV 89146, 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, Fast, Easy and Affordable Electromagnetic Signal
Integrity Software
2010 and 2011 DesignVision Award Winner


-----Original Message-----
From: Lee [mailto:leeritchey@xxxxxxxxxxxxx]
Sent: Friday, August 15, 2014 9:47 AM
To: shlepnev@xxxxxxxxxxxxx; jeff.loyer@xxxxxxxxx;
Gert.Havermann@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] Re: AW: fiber weave effect

We have built many test PCBs with a variety of glass weaves of mechanically
spread glass, done for laser drilling not SI, to see what control can be had
over skew using such materials.  The results have been very good.  Skew of
less than 2-3 pSec over 16".  We have also evaluated two materials from
Isola designed to minimize skew and found similar excellent results.

These are GigaSync and a new material tentatively called ISE-41.  They
provide very low skew, independent of the glass weave style.

-----Original Message-----
From: Yuriy Shlepnev
Sent: Friday, August 15, 2014 9:17 AM
To: jeff.loyer@xxxxxxxxx ; Gert.Havermann@xxxxxxxxxxx ;
si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: AW: fiber weave effect

Hi Jeff,

Thank you for the comments. The numerical experiment actually predicts your
"intuitive" conclusion on the relationship between trace pair dimensions and
observed skew (even for not spread glass type). I just did not find
published confirmation of that observation.  Considering the experimental
data, we will follow your advice and try to make it less "anecdotal" :-)

I totally agree with you on the need for the statistical investigation of
the effect. To make it possible, the first step is to develop a fast
macro-model for transmission line with inhomogeneous and possibly
pseudo-random distribution of the dielectric properties along and across.
Development of such model was the focus of the theoretical part of the paper
- how to make dielectric properties change along and across the line similar
to the behavior of composite and without violation of casualty. The first
application was to evaluate the worst case scenario. The next application
would be statistical analysis. Though, as you mentioned, the actual
distribution of the dielectric properties is the unknown so far.

Are those data below for the single-ended traces?
Did you investigate the tightly-coupled traces?

Best regards,
Yuriy

Yuriy Shlepnev, Ph.D.
President, Simberian Inc.
3030 S Torrey Pines Dr. Las Vegas, NV 89146, 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, Fast, Easy and Affordable Electromagnetic Signal
Integrity Software
2010 and 2011 DesignVision Award Winner


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Loyer, Jeff
Sent: Friday, August 15, 2014 8:23 AM
To: Gert.Havermann@xxxxxxxxxxx; shlepnev@xxxxxxxxxxxxx;
si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: AW: fiber weave effect

I agree with Gert.  I'm also sure there is quite a bit of information about
the effect of spread glass on FWE (Lee Ritchey, Isola, NovaSpeed,
Compunetics?).   And it seems intuitive that trace dimensions, relative to
the weave, would influence the skew predictably.  To my thinking, having
traces very close together, such that their environment is more similar,
should reduce the skew (since the glass is typically a little larger than
the traces).
I would also stress the need for any FWE study to use many boards with many
instances of test structures on each board to accurately evaluate the
effect.  They are very subject to random effects which cannot be controlled:
*       Exact trace alignment to glass
*       Glass alignment to panel edge
o       May be different for warp vs. fill
*       Wandering of glass
o       Will be different for warp vs. fill
Without many samples, you may draw erroneous conclusions from anecdotal
evidence.
For instance, below is a plot of skew between the "p" and "n" of several
samples on our 10 original test boards (the 10" coupons).  Note the
significant difference in skew, depending on the particular sample.  If you
happened to measure "Bd10", you would conclude a maximum of 30ps of skew;
"Bd9" would only have 5ps of skew (these boards were part of the same build,
manufactured identically at the same time).

Here's the raw data, in case the figure doesn't come out (2 different
formats, raw text and original format):
0 Degree Rotation with soldermask
Bd1     Bd2     Bd3     Bd4     Bd5     Bd7     Bd8     Bd9     Bd10
Layer   Orientation     Length  Sample  Direction       Polarity
Sample ID       "skew (p2-p1)
(+ = m1 on left)"
1       V       10      01      1       1       LYR01OVL10S01D1 1       1
9       6       -1      -3      -3      5       -4
1       V       10      02      1       1       LYR01OVL10S02D1 5       0
-7      -2      3       3       5       -3      12
1       V       10      03      1       1       LYR01OVL10S03D1 0       2
8       5       -2      0       -4      4       -15
1       V       10      04      1       1       LYR01OVL10S04D1 6       1
-9      -3      5       0       5       -3      20
1       V       10      05      1       1       LYR01OVL10S05D1 -2      0
10      9       -3      0       -3      2       -20
1       V       10      06      1       1       LYR01OVL10S06D1 9       0
-9      -4      5       0       4       2       23
1       V       10      07      1       1       LYR01OVL10S07D1 -1      3
9       7       -2      0       -2      0       -22
1       V       10      08      1       1       LYR01OVL10S08D1 8       1
-5      -4      5       -1      3       3       29
1       V       10      09      1       1       LYR01OVL10S09D1 -4      -2
5       7       -4      3       -3      -1      -26
1       V       10      10      1       1       LYR01OVL10S10D1 10      5
-3      -2      4       -3      2       6       26

0 Degree Rotation with soldermask       Bd1     Bd2     Bd3     Bd4     Bd5
Bd7     Bd8     Bd9     Bd10
Layer   Orientation     Length  Sample  Direction       Polarity
Sample ID       skew (p2-p1)
(+ = m1 on left)
1       V       10      01      1       1       LYR01OVL10S01D1 1       1
9       6       -1      -3      -3      5       -4
1       V       10      02      1       1       LYR01OVL10S02D1 5       0
-7      -2      3       3       5       -3      12
1       V       10      03      1       1       LYR01OVL10S03D1 0       2
8       5       -2      0       -4      4       -15
1       V       10      04      1       1       LYR01OVL10S04D1 6       1
-9      -3      5       0       5       -3      20
1       V       10      05      1       1       LYR01OVL10S05D1 -2      0
10      9       -3      0       -3      2       -20
1       V       10      06      1       1       LYR01OVL10S06D1 9       0
-9      -4      5       0       4       2       23
1       V       10      07      1       1       LYR01OVL10S07D1 -1      3
9       7       -2      0       -2      0       -22
1       V       10      08      1       1       LYR01OVL10S08D1 8       1
-5      -4      5       -1      3       3       29
1       V       10      09      1       1       LYR01OVL10S09D1 -4      -2
5       7       -4      3       -3      -1      -26
1       V       10      10      1       1       LYR01OVL10S10D1 10      5
-3      -2      4       -3      2       6       26


In my experience, FWE is a statistical beast which doesn't easily lend
itself to precise analysis.  We're missing some critical information, such
as the statistical distribution of weave wandering.  But, I welcome all
efforts to quantify it better.

Thanks for sharing,
Jeff Loyer

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Havermann, Gert
Sent: Friday, August 15, 2014 7:35 AM
To: shlepnev@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] AW: fiber weave effect

Hello Yuriy,

I'm not surprised that tight coupling is less attracted to weave effect on
3313 glass.
Mechanically spoken, tighter coupling decreases the dielectric differences
in between traces of a differential pair. Look at Figure 5 of your paper and
imagine what the difference of effective dielectric surrounding the traces
would be when the spacing is close to one tracewidth. The difference would
be very small, especially when flat weave or even flattened weave is used.

BR
Gert


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-----UrsprЭngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx<mailto:si-list-bounce@xxxxxxxxxxxxx>
[mailto:si-list-bounce@xxxxxxxxxxxxx] Im Auftrag von Yuriy Shlepnev
Gesendet: Freitag, 15. August 2014 16:08
An: si-list@xxxxxxxxxxxxx<mailto:si-list@xxxxxxxxxxxxx>
Betreff: [SI-LIST] fiber weave effect

Hello Everyone,

Some results of our on-going investigation of fiber-weave effect (FWE) were
recently presented at IEEE EMC 2014 symposium (at SIPI section) and the
paper and presentation are now available at
http://www.simberian.com/AppNotes.php - see #2014_04.
One of the interesting outcomes was practically negligible FEW impact on the
tightly coupled traces on spread fiber fabric (voltage coupling coefficient
about 0.2). We have observed it both on strip and micro-strip (one sheet of
dielectric fabric) configurations.
We did not find any published confirmation of this result. Any comments or
thoughts?

Best regards,
Yuriy

Yuriy Shlepnev, Ph.D.
President, Simberian Inc.
3030 S Torrey Pines Dr. Las Vegas, NV 89146, 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<http://www.simberian.com>
Simbeor - Accurate, Fast, Easy and Affordable Electromagnetic Signal
Integrity Software
2010 and 2011 DesignVision Award Winner

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