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 ---------------------------------------- Absender ist HARTING Electronics GmbH, Marienwerderstraъe 3, D-32339 Espelkamp; Registergericht: Amtsgericht Bad Oeynhausen; Register-Nr.: HRB 8808; Vertretungsberechtigte GeschДftsfЭhrer: Dipl.-Kfm. Edgar-Peter DЭning, Dipl.-Ing. Torsten Ratzmann, Dipl.-Wirtschaftsing. Ralf Martin Klein -----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 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx<mailto: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<mailto:si-list-request@xxxxxxxxxxxxx> with 'help' in the Subject field List forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable 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