Xilinx Spartan 7 seen - Page 1
Forum section: electronics / general

author: hamster_nz
author_rank: Super Contributor
timestamp: April 05, 2017, 06:53:40 pm
content: ...on what looks to be a new Digilent Dev boardVideo says parts are "available for order"

author: lukier
author_rank: Unknown
timestamp: April 05, 2017, 07:10:19 pm
content: Looks nice, but bloody PMOD or even worse Arduino connectors that are not even aligned to 0.1" - somebody has to stop this stupid trend. I was considering once to buy STM32F7 Discovery board and it also has only Arduino pins broken out (and on the bottom side!). Fortunately STM32F7 Nucleo has two normal dual pin header footprints (but in addition to something Arduino like)I'd rather see all the pins (except really commited ones, like the DDR memory etc) broken out onto 0.1" or some high speed connector, this is particularly important for the FPGAs.

author: rstofer
author_rank: Super Contributor
timestamp: April 05, 2017, 07:15:00 pm
content: I didn't see that board at Digilent but I did see a more affordable Zynq board:http://store.digilentinc.com/arty-z7-apsoc-zynq-7000-development-board-for-makers-and-hobbyists/Not cheap but it might be worth it for the education.

author: julianhigginson
author_rank: Frequent Contributor
timestamp: April 05, 2017, 08:45:43 pm
content: cool! Spartan 7 has been a while in the works. very keen to see the price performance tradeoff with artix 7...Sent from my A0001 using Tapatalk

author: PDXjason
author_rank: Contributor
timestamp: April 05, 2017, 10:57:20 pm
content: Quote from: lukier on April 05, 2017, 07:10:19 pmSomething like an FMC but cheaper? I might know something in the works like that.

author: lukier
author_rank: Unknown
timestamp: April 05, 2017, 11:29:08 pm
content: Quote from: PDXjason on April 05, 2017, 10:57:20 pmYeah, FMC is a buggerI was just thinking it would be good to have a board with some signals on 0.1" pin headers for simple stuff and quick tests and some routed to a more high speed suited connector. On one of the dev. boards I have (Spartan 3E Starter Kit) uses Hirose FX2 for that, not extremely expensive, but I'm not sure it is high speed enough by today's standards.My rant against Arduino headers is simply related to the fact that one of the points of an FPGA is to have a ton of IO (what sometimes is a problem in the hobbyist context with the crazy BGA packages FPGAs come in), so putting Arduino 20 something pins on a dev board is a joke (the same arguments stands for such feature rich MCU as STM32F7).Often I would prefer something like system on module, in the FPGA or high performance MCU context probably not with 0.1" or 0.05" inch headers because pulling out a module with 100 pins is no funThe downside is that, surprisingly!, such SoMs are (I think) not subsidized like popular dev. boards and often more expensive and available from 3rd party vendors, unrelated to manufacturer's marketing department. It baffles me, full blown dev. board has more connectors, components, features, accessories and is still cheaper than a SoM which is a tiny PCB with FPGA/CPU + SDRAM/FLASH, some power & clocks and 2-3 high density connectors or even cheaper - SODIMM 204 pin edge connector.But it's getting better in that respect, TrenzElectronic makes nice FPGA SoMs, hotmcu.com Allwinner or AM335X based ones or Myirtech Z-turn Board with Zynq.

author: ehughes
author_rank: Frequent Contributor
timestamp: April 06, 2017, 01:15:02 am
content: So much for "low cost"https://www.digikey.com/product-detail/en/xilinx-inc/XC7S6-1CSGA225Q/XC7S6-1CSGA225Q-ND/6823618

author: KE5FX
author_rank: Super Contributor
timestamp: April 06, 2017, 01:33:20 am
content: Those seem to be automotive-rated parts (125C). Hopefully they'll expand the listing soon.

author: Someone
author_rank: Super Contributor
timestamp: April 06, 2017, 03:13:25 am
content: Quote from: lukier on April 05, 2017, 11:29:08 pmThe manufacturer can sell (a limited quantity) of the parts for a very low price into dev boards to induce uptake, or even outright subsidise development boards as an marketing expense.

author: pieman103021
author_rank: Contributor
timestamp: April 06, 2017, 12:43:42 pm
content: Quote from: rstofer on April 05, 2017, 07:15:00 pmIt is worth noting that Digilent also offers thePynq-Z1for only $65 with the academic discount.It is a hardware equivalent, except it additionally has a PDM microphone.This is good because while there isn't any support for non-pynq software on the pynq, all of the support made available for the Arty will be directly applicable.

author: rstofer
author_rank: Super Contributor
timestamp: April 06, 2017, 02:33:28 pm
content: Quote from: pieman103021 on April 06, 2017, 12:43:42 pmAlas, I am not eligible for an educational discount and nobody seems to offer an 'old geezer' discount. Bummer!

author: pieman103021
author_rank: Contributor
timestamp: April 06, 2017, 03:00:30 pm
content: Quote from: rstofer on April 06, 2017, 02:33:28 pmIn that case, for learning on a budget there are always lattice dev boards. I think Mike of mikeselectricstuff is a big fan of these:https://www.digikey.com/product-detail/en/Lattice-Semiconductor-Corporation/LCMXO3L-6900C-S-EVN/220-1935-ND/5039065but I have no personal experience with them.Of course, with the Spartan 7 costing $300+ alone, it is safe to say everything mentioned is going to be cheaper than what we see in the OP.Sent from my Nexus 5X using Tapatalk

author: Sal Ammoniac
author_rank: Super Contributor
timestamp: April 06, 2017, 04:59:23 pm
content: Quote from: pieman103021 on April 06, 2017, 03:00:30 pmWhat are you talking about? That part on Digikey that someone posted is $18, not $300+.

author: jnz
author_rank: Frequent Contributor
timestamp: April 06, 2017, 06:32:40 pm
content: Quote from: Sal Ammoniac on April 06, 2017, 04:59:23 pm.... But.... not if you buy 19 of them!

author: rstofer
author_rank: Super Contributor
timestamp: April 06, 2017, 08:22:40 pm
content: Quote from: pieman103021 on April 06, 2017, 03:00:30 pmI just like to whine about not qualifying for the educational discount. I don't really have a budget problem but I do try to keep things rational.The linked Lattice board is a little small for my CPU project, it's about 1/3 the size of my Spartan 3 1200k board and I use just over 1/3 of the chip capability and most of the BlockRAM. OTOH, that board has a lot of IO brought out and for embedding in a larger project, that kind of thing is very helpful.I don't quite see the point of the Spartan 7 and I'll concede that I haven't look at all the details but according to the Overview, the Artix-7 is a bigger chip and the Artix-7 'Arty' boards are fairly cheap. They use a rather modest Artix-7...https://www.xilinx.com/support/documentation/data_sheets/ds180_7Series_Overview.pdfI think the Zynq board will be up next. I could see running Linux in the ARM cores and having an FPGA fabric for my CPU project. My IO subsystem would be much more elegant.

author: KE5FX
author_rank: Super Contributor
timestamp: April 07, 2017, 12:04:11 am
content: Quote from: rstofer on April 06, 2017, 08:22:40 pmI'm starting to wonder about that myself. It doesn't look like they're going to be (much) cheaper than Artix.I thought they were just going to be Artix parts without the high-rate transceiver hardware. But Xilinx is advertising that one of the advantages of S7 is that the commercial parts are good to 125C. That makes me think they're not just binned Artix parts, but something based on a different process altogether.

author: pieman103021
author_rank: Contributor
timestamp: April 07, 2017, 12:11:50 am
content: Quote from: Sal Ammoniac on April 06, 2017, 04:59:23 pmYou make a good argument. That number did seem weird to me, but I guess it should have put a little more thought into it.In that case, I look forward to seeing what comes of this board.Sent from my Nexus 5X using Tapatalk

author: james_s
author_rank: Super Contributor
timestamp: April 18, 2017, 08:22:10 pm
content: Quote from: rstofer on April 06, 2017, 02:33:28 pmWell you can get a senior discount at many restaurants but that probably isn't what you're looking for

author: NorthGuy
author_rank: Super Contributor
timestamp: April 18, 2017, 09:58:56 pm
content: $18 looks substantially cheaper than Artix-7 to me. I'm not sure how real these prices are.

author: Someone
author_rank: Super Contributor
timestamp: April 19, 2017, 12:22:02 am
content: Quote from: NorthGuy on April 18, 2017, 09:58:56 pmCheaper than the other 7 series parts, but still competitive with the older spartan 6 series. Given their substantial differences it would really depend on the design specifics as to which part you would pick.

author: KE5FX
author_rank: Super Contributor
timestamp: April 19, 2017, 12:33:23 am
content: Quote from: NorthGuy on April 18, 2017, 09:58:56 pmThose are less than half the size of the smallest Artix part, though, and cost more than half as much.

author: JoeN
author_rank: Frequent Contributor
timestamp: April 20, 2017, 06:13:30 am
content: The guy in the video says a Microblaze soft processor costs as little as 19 cents to implement in a Spartan 7 FPGA. Does he mean the cost for IP or the cost for both IP and the logic fabric that it will take up? 19 cents seems pretty low. The only device I can get a price on is $18 for 6,000 LEs (link above, the only part listed at Digikey, though not in stock yet). A minimal Microblaze is said to be around 600 LEs, right? So that is $1.80 in fabric for a small device. Do larger devices really lower the price by a factor of 10?

author: Kilrah
author_rank: Unknown
timestamp: April 20, 2017, 08:39:56 am
content: Quote from: rstofer on April 05, 2017, 07:15:00 pmNice! Note that it selects the version with the larger 7Z020 by default, the 7Z010 version is only $149. You can already do quite some stuff with that.I might actually get one since I had something I wanted to try with both HDMI in and out at the same time, which my Zybo doesn't have... and the Snickerdoodle+accessories I backed eons ago is still nowhere close to getting there it seems

author: james_s
author_rank: Super Contributor
timestamp: April 20, 2017, 06:03:17 pm
content: Quote from: JoeN on April 20, 2017, 06:13:30 amThey're probably talking about whatever device is the sweet spot for lowest cost per LE, and also probably in quantities of 1,000+. You're always going to pay more in single quantities and quotes like above are aimed toward mass production.

author: tszaboo
author_rank: Super Contributor
timestamp: April 21, 2017, 02:19:26 pm
content: Quote from: james_s on April 20, 2017, 06:03:17 pmAnd this screw only costs 3 cents. But you need to buy the car, it comes in.

author: james_s
author_rank: Super Contributor
timestamp: April 21, 2017, 07:18:01 pm
content: Well these cost comparisons are always going to be like that. Historically FPGAs have been expensive so they were mostly used for prototyping and low volume/high margin products. The cost just didn't scale well into mass production and pretty soon a microcontroller or custom silicon becomes cheaper. When they say adding the processor only costs 19 cents they are probably suggesting that it is economical vs using a separate processor in a production device. It's pretty common for companies to quote component prices in the thousands or tens of thousands quantity.

author: NorthGuy
author_rank: Super Contributor
timestamp: April 21, 2017, 09:27:35 pm
content: They're certainly want to convey an idea that it is economical, but why 19 cents, not 50, and not 7. What's the math behind this number?Is Virtex-7 2000 economical because you can run multiple Microblazes on it. I don't think so.BTW: Look at the suggested uses - single axis motor control, adaptive LED lighting, automotive data conversion. Who the hell is going to use FPGA for that when it can be done with a simple PIC for a fraction of the cost.Looks like they're a little bit disconnected from reality. Hence the out-of-the blue 19 cents figure.Still, Spartan-7 is faster and better than Spartan-6. If you want to use it for high speed, $18 might be considered economical, because there's nothing else at that price. I wish they had something for $10 or $5.

author: james_s
author_rank: Super Contributor
timestamp: April 21, 2017, 10:28:05 pm
content: Beats me, I'm not a marketing guy, you'd have to talk to a one of them.

author: kony
author_rank: Regular Contributor
timestamp: April 21, 2017, 11:39:46 pm
content: One thing that anyone had not mentioned yet - it is basically Xilinx effort to cover all market segments served under the new (acrively supported and developed) toolchain, anything over this is just nice bonus thrown in.

author: hamster_nz
author_rank: Super Contributor
timestamp: August 19, 2017, 05:54:30 am
content: After a long wait, Spartan 7 devboards are now shipping - XC7S25-CSGA324 or XC7S50-CSGA324, $89 or $109.The fall either side of the XC7A35T-1CPG236C used on most Artix-7 boards, (e.g 80 or 120 DSP slices vs 90 on the Artix 7).https://blog.digilentinc.com/new-product-the-arty-s7/&http://store.digilentinc.com/arty-s7-spartan-7-fpga-for-makers-and-hobbyists/

author: Sal Ammoniac
author_rank: Super Contributor
timestamp: August 19, 2017, 07:07:19 am
content: The Digilent Spartan 7 board is $10 more expensive than the Artix version, but the Spartan 7 they use has about 50% more logic cells/slices.

author: MattSR
author_rank: Regular Contributor
timestamp: August 19, 2017, 07:17:34 am
content: How does the largest Artix-7 compare to the largest Spartan-7?

author: hamster_nz
author_rank: Super Contributor
timestamp: August 19, 2017, 08:37:48 am
content: Quote from: MattSR on August 19, 2017, 07:17:34 amNot saying anything, but for the currently available parts (7S25 and 7S50)....If you compare the numbers in table 5 (Typical Quiescent Supply Current) ofhttps://www.xilinx.com/support/documentation/data_sheets/ds189-spartan-7-data-sheet.pdfwith table 5 inhttps://www.xilinx.com/support/documentation/data_sheets/ds181_Artix_7_Data_Sheet.pdf,they look identical.Humm.... don't the same size dice have the same static power>And if you compare the size of artix-7 and spartan-7 bitstream fileshttps://www.xilinx.com/support/documentation/user_guides/ug470_7Series_Config.pdf,they look identicalHumm.... they is an equal number of configuration bits as their Artix-7 equivalents?And then if pick a random timing spec, like table 31 (DSP48E timing), they look identical for the matching speed grades.Humm... looks like they are using the same process?Looks like they are doppelgangers - but at least they have different JTAG IDCODEsI also recently saw this on Hack-a-day:http://hackaday.com/2016/05/11/dirt-cheap-dirty-decapping/

author: Someone
author_rank: Super Contributor
timestamp: August 19, 2017, 10:07:09 am
content: Quote from: hamster_nz on August 19, 2017, 08:37:48 amSpartan 6 came in parts with and without transceivers, so it looks like the thats now the only differentiator between 7 series Spartan and Artix. The common dies for the XC7A12T/XC7A25T and XC7A15T/XC7A35T/XC7A50T could make for some interesting hacking (and has been mentioned before on here) but the config sizes suggests that the XC7S6/XC7S15 parts are a different cut so I don't see any possibility to take a cheap spartan and unlock lots of resources.

author: NorthGuy
author_rank: Super Contributor
timestamp: August 19, 2017, 02:48:01 pm
content: Quote from: Someone on August 19, 2017, 10:07:09 amSpartans are supposed to be more power efficient and also they're slower. The Spartan prices on DigiKey are not that great

author: JoeN
author_rank: Frequent Contributor
timestamp: August 19, 2017, 08:06:13 pm
content: Quote from: hamster_nz on August 19, 2017, 08:37:48 amInteresting."Unless pre-arranged, all decapping images are added to an open source die database under a Creative Commons 0 license. Decapped chips cannot be returned. "Anyone know where this database is? I can't locate it.

author: hamster_nz
author_rank: Super Contributor
timestamp: August 19, 2017, 08:32:41 pm
content: Quote from: JoeN on August 19, 2017, 08:06:13 pmHave Tweeted them... will let you know what they say!

author: JoeN
author_rank: Frequent Contributor
timestamp: August 19, 2017, 08:37:33 pm
content: Quote from: hamster_nz on August 19, 2017, 08:32:41 pmThanks. I could have done that I guess but I have never had business with them and I thought someone might know. Maybe this service never took off and they don't have enough to make a serious showing yet. It's cheaper than a professional job, but more than most hobbyists are willing to pay I think. I'd like to acquire some acid and try it myself the more professional way.

author: Someone
author_rank: Super Contributor
timestamp: August 19, 2017, 10:07:50 pm
content: Quote from: NorthGuy on August 19, 2017, 02:48:01 pmExcept as shown above, within the 7 series they have the same quiescent power requirements as the same sized Artix parts and the same switching speeds, so they're neither more efficient or slower than the Artix product line. It looks like the only difference is the availability of the high speed transceivers, which used to be available in the Spartan branding of the previous product 6 series line.Spartan and Artix together are a grouping of the low speed parts, and are indeed slower and lower power than the Kintex range for comparable sized parts.

author: NorthGuy
author_rank: Super Contributor
timestamp: August 20, 2017, 02:27:54 am
content: Quote from: Someone on August 19, 2017, 10:07:50 pmYou're right. There's no grade -3 for Spartans, but grades -2 and -1 are identical to Artix.Given the same speed, they're priced a little bit less, which is not bad if you don't use PCIe and GTH transceivers anyway:$73.29 for XC7S50-2FGGA484I$101. 99 for XC7A50T-2FGG484IHowever, if XC7A50T is the same as XC7A15T, then$52.36 for XC7A15T-2FGG484Ilooks even better.

author: asmi
author_rank: Super Contributor
timestamp: August 22, 2017, 07:19:40 pm
content: I also remember hearing that smaller devices will be available in BGA-196 1.0 mm pitch package which was specifically designed to be fully routed out on a 4 layer board.Initially Xilinx announced even QFP-144 package, but it was quietly cancelled somewhere down the road.Still can't wait to get my hands on these chips to play around with them! Manufacturing 6-layer PCBs is significantly more expensive at the moment, so I limit myself to 4-layer boards, and that package sounds like a great deal for me.

author: jmelson
author_rank: Super Contributor
timestamp: August 22, 2017, 09:08:24 pm
content: Quote from: asmi on August 22, 2017, 07:19:40 pmIf you don't need the performance of the Spartan 7, Xilinx's Spartan 3A is still quite affordable at about $11 each for the smallest device, in QFP-144 package. You can also get the 3AN with internal configuration PROM for about $13.I'll keep using these until they stop making them. I've got a project I did in the XC3S50AN with 32-bit counters running at 150 MHz, and I don't think that was anywhere near the limit.Jon

author: asmi
author_rank: Super Contributor
timestamp: August 22, 2017, 09:15:47 pm
content: Quote from: jmelson on August 22, 2017, 09:08:24 pmNo, I don't want to use such old ICs. I like new and shiny stuffBesides, I really like Vivado, and the fact that Microblaze softcore is free for all 7 series devices.

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 22, 2017, 10:02:25 pm
content: Quote from: hamster_nz on April 05, 2017, 06:53:40 pmDid anyone notice the job title? "Cost-Optimized Portfolio Product Line Manager" With a title that long, you'd think the job must really stink

author: NorthGuy
author_rank: Super Contributor
timestamp: August 22, 2017, 10:24:10 pm
content: Quote from: asmi on August 22, 2017, 07:19:40 pmIf you don't mind leaving some close-to-center pins unconnected, you can get more usable pins from bigger packages (such as 484-pin BGA) on the 4-layer board than you would get from the 196-pin BGA.

author: asmi
author_rank: Super Contributor
timestamp: August 22, 2017, 10:54:43 pm
content: Quote from: NorthGuy on August 22, 2017, 10:24:10 pmWhat's the point in spending money on a more expensive 484 package if you can only break out about half of those pins using cheap 0.15/0.15/0.3 process? Even with 256 package you can't break it out completely (I tried when I was designingthis board).

author: NorthGuy
author_rank: Super Contributor
timestamp: August 22, 2017, 11:25:38 pm
content: Quote from: asmi on August 22, 2017, 10:54:43 pmThe point is to save money by using 4-layer design instead of 6-layers. Of course, this only makes sense if you save on board production more than you have to pay for a bigger package.For example, partial fanout of 484-BGA on 4-layer board may give you more pins and cost less than full fanout of 256-BGA on 6-layer board. Or 676-BGA on 4-layer board may give you more pins and cost less than 484-BGA on 6-layer board.

author: asmi
author_rank: Super Contributor
timestamp: August 22, 2017, 11:59:53 pm
content: Quote from: NorthGuy on August 22, 2017, 11:25:38 pmI see what you mean but I'm not sure I approve such waste of resources. Not only 484 packages are significantly more expensive, but there are also cases where you need to route out specific pin groups (for example if you want to have DDR2/3 memory device, you are quite limited in selection of pins).

author: NorthGuy
author_rank: Super Contributor
timestamp: August 23, 2017, 12:47:53 am
content: Quote from: asmi on August 22, 2017, 11:59:53 pmIt depends on what are resources for you. If you save money by ordering a cheaper PCB, or if you save time by simplifying your routing job, this seems like resources are being saved, not wasted.Pins? I don't think you really save them. When you buy a Xilinx part in a smaller package, it has all the same pins as the same part in a bigger package (e.g. XC7A15T-2FGG484C is exactly the same as XC7A15T-2FTG256C), only some of the pins are not bonded out.Quote from: asmi on August 22, 2017, 11:59:53 pm$20-30 isn't a big deal compared to $200 saved on PCB fabrication. Of course, if you go to production, the economy changes. But this is no brainer for prototyping.Quote from: asmi on August 22, 2017, 11:59:53 pmDDR pins are abundant in 7-series. There are some pins that are in the middle, such as JTAG or config pins. But these are always the same regarding of the package, and always in the middle.May be if Xilinx thought about people who's going to fan out their FPGAs, it would be easier with smaller parts. But it certainly looks like they locate their pins specifically to make fanouts as difficult as they can - all the big customers will have gazillion-layer boards anyway.

author: asmi
author_rank: Super Contributor
timestamp: August 23, 2017, 01:06:42 am
content: Quote from: NorthGuy on August 23, 2017, 12:47:53 amIt still offends my feelings as engineer, so I will stick to 256 unless I will actually need more pinsQuote from: NorthGuy on August 23, 2017, 12:47:53 amIt's not that simple. For memory interfaces there are quite strict rules as to which pins can be used. I haven't actually tried making a MIG design with 484 pin part to see if I can get away with only using pins from 3 outer "layers" of pins, but my gut feeling suggests it won't be possible because most DQ groups contain pins that are "deeper" than outer 3 rows, and you can only user pins from the single bank column for controller.Quote from: NorthGuy on August 23, 2017, 12:47:53 amThey did actually think of it, and even issued a document which outlines what's the best way to break out their ICs, and how many layers do they recommend depending on what PCB process you're going to use. When I was routing the board mentioned above, I had very little issues with routing. I especially like how they placed power/gnd pins next to each other in such a way that it's easier to place 0402 caps next to them under the package.

author: NorthGuy
author_rank: Super Contributor
timestamp: August 23, 2017, 02:38:37 pm
content: Quote from: asmi on August 23, 2017, 01:06:42 amOn a stock 4-layer boards, the pre-peg is usually quite thick, so laying 50-Ohm traces on the top layer is impractical - they would have to be too wide. So, you would have to go to layer 2 or 3, which means you only have dog-bones on the top layer. If you select pins which are 3-5 rows deep into FPGA, it should work quite well. It is not that difficult to fan out a group of adjacent pins (2*DQS + 8*DQ and may be 1*DM) in one layer. I guess, even if you had 10-layer board you would do it in one layer anyway.

author: asmi
author_rank: Super Contributor
timestamp: August 23, 2017, 02:56:43 pm
content: Quote from: NorthGuy on August 23, 2017, 02:38:37 pmThis is not necessarily the case. Infact, if you order 1.2 mm thick 4 layer boards from PCBWay, they will use 0.13 mm prepreg (full stackup is 0.035 Cu/0.13 PP/0.035 Cu/0.73 Core/0.035 Cu/0.13 PP/0.035 Cu), which means 50 Ohm traces are quite narrow at ~0.225 mm. That is what I've done for my board with HyperRAM chips as they operate at 166 MHz DDR (so DQ lines switch at 333 MHz), and it works with no problems on a real board. Of course in breakout areas I had to use minimal-width 0.15 mm traces, but this is universally recommended practice as there is simply no other way to do it.Currently I'm trying to see if I can route FPGA + DDR3 on a 4-layer board with 0.125/0.125/0.25 process, already attempted a couple times, but failedBut now I'm much better quipped to do that tools-wise, so I'm hopeful I would be able to get it done and the board will actually work

author: Scrts
author_rank: Frequent Contributor
timestamp: August 25, 2017, 07:20:09 pm
content: Quote from: asmi on August 23, 2017, 02:56:43 pmYou will most likely have power/gnd integrity issues with a 4 layer board and FPGA+DDR3. If the power will float, then the signal condition doesn't even matter...

author: asmi
author_rank: Super Contributor
timestamp: August 25, 2017, 07:33:23 pm
content: Quote from: Scrts on August 25, 2017, 07:20:09 pmWhy would you think it would float on 4 layer board, but not on 6 layer one? What does it have to do with amount of layers? I'm just learning the ropes, so I'd appreciate more details on this.