[info] stm32f4 MPU module LQFP 100

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stm32f4 MPU module LQFP 100

Post by russian » Tue Dec 24, 2013 6:49 pm



Image

Image

SVN repository
brain_board.zip
Schematic.pdf

also https://svn.code.sf.net/p/rusefi/code/t ... SD_Card_1/
https://oshpark.com/shared_projects/KCdXUUDD

BOM @ google

STM32™ microcontroller system memory boot mode
The STM32F40xxx/41xxx bootloader is activated by applying pattern1.

Pattern1 Boot0(Pin) = 1 and Boot1(Pin) = 0
Boot1=PB2=pad#37 is always GND on our board


We need our own KiCad board with some stm32f4 chip in order to a) get the schematics ready 2) test my soldering skills

-1) for the first revision, we are targeting STM32F407VGT6 chip which is LQFP 100
0) dimensions: 57mm by 67mm
1) Should be an exact clone of stm32f4 from the pinout prospective
2) needs the same 4 LEDs
3) needs the reset button (?)
4) I guess 'user' button is not needed
5) should have some means of loading the firmware - could be UART or USB

For larger processor see http://rusefi.com/forum/viewtopic.php?f=4&t=749
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Re: stm32f4 main chip module

Post by Mad Max » Tue Dec 24, 2013 9:36 pm

Do you need schematic of Stm32F4 board in Kicad format (except some unused chips as DAC and G-sensor)?
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Re: stm32f4 main chip module

Post by russian » Tue Dec 24, 2013 10:44 pm

Mad Max wrote:Do you need schematic of Stm32F4 board in Kicad format (except some unused chips as DAC and G-sensor)?
Yes. Not only schematic but also the PCB design. It would need to have one of the stm32f4 family chips and have the exact same physical connectors as discovery so that I can test it with existing modules. And I do not need all the crap we do not use - just the chip and the required capacitors oscillators etc.

Ideally it would have the LEDs and reset button but that's optional. I guess a 144 pin chip would be the balance between the size and number of pins.
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Re: stm32f4 main chip module

Post by kb1gtt » Wed Dec 25, 2013 2:24 am

The Discovery F4 is a 4 layer board design. I seem to recall the gerber files are out there some where. Kicad can import a gerber, this may be helpful. However in the past I've failed to connect the gerber traces to a schematics netlist. Perhaps there are new tools in this most recent version, or perhaps a script can be made to associate net names. When you import the gerber, it would give everything one net name, and I couldn't figure out how to change a net name.
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Re: stm32f4 main chip module

Post by russian » Wed Dec 25, 2013 4:22 am

What is the whole story with 2 layer versus 4 layer? Would it have to be a 4 layer around any stm32 chip?
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Re: stm32f4 main chip module

Post by kb1gtt » Thu Dec 26, 2013 11:08 am

Generally, the 2 internal layers are PWR and GND. Also generally you place the GND vias as close to the GND pin as possible, as well as the PWR via and you avoid any physical barriers on those planes. Then the signal traces are on the top and bottom layers. So I would say yes the STM wants the 4 layers, but we might get away with out it, if we do a respin. However it's better technical design to do 4 layer.
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Re: stm32f4 main chip module

Post by davidbuzz » Thu Jan 02, 2014 7:23 am

STM32F4 Discovery gerbers can be found here.
http://www.st.com/web/catalog/tools/FM1 ... 2/PF252419

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Re: stm32f4 main chip module

Post by puff » Fri Jan 24, 2014 6:03 am

Soldering stm32f4 could become a real pain in the ass. Soldering paste and reflow oven could be quite helpful?
Hope, by the time I get to building the final device, PCB houses will offer a service of populating at least those hard-to-solder parts.

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Re: stm32f4 main chip module

Post by abecedarian » Fri Jan 24, 2014 7:02 am

Some fab shops provide pick-and-place or assembly options.
"Do not populate" can often be specified in the drawings, and they won't install those components.
Costs more though... around $1 - $2 average per component, from what I've heard.
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Re: stm32f4 main chip module

Post by russian » Fri Jan 24, 2014 12:28 pm

seeedstudio.com offers some assembly - but they have a small (say 80) library of components they solder

If anyone knows a place which would solder stm32 for you it would be cool. I hope that by the time we get to that one of the forum members would simply be soldering stm32 chips for everyone, and I hope it would not be me :)
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Re: stm32f4 main chip module

Post by kb1gtt » Fri Jan 24, 2014 10:33 pm

For a min order of something like $100, Seeed will populate parts provided by someone else. They ask that the parts get purchased, and put in one box, then shipped to them. They will populate based on what's in that box. Don't forget you'll be waiting for a slow boat in both directions.
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Re: stm32f4 main chip module

Post by hasse.69 » Tue Jan 28, 2014 9:05 pm

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Re: stm32f4 main chip module

Post by russian » Sat Feb 01, 2014 12:35 pm

ST has mailed me 8 sample chips. While STM32F407VGT6 would be the default chip, we need to check if the same board would work for 84MHz STM32F401VCT6 and for 180MHz STM32F427VIT6
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Re: stm32f4 main chip module

Post by russian » Mon Feb 03, 2014 5:07 pm

@art_electro rocks.

Silkscreen is not ready yet.
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Re: stm32f4 main chip module

Post by russian » Mon Feb 10, 2014 2:21 pm

New version checked in.

Silkscreen is good enough (I am planning to improve it a hair before ordering), the only pending issue - I want to use another EMI Filter chip, USBUF02W6 is just too small so soldering would be painful.
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Re: stm32f4 main chip module

Post by russian » Wed Feb 19, 2014 1:55 pm

BOM order placed - with all the components I will have a chance to print the board for final validation
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Re: stm32f4 main chip module

Post by Sudo » Thu Apr 03, 2014 1:15 am

So what exactly is the purpose and difference of this board?

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Re: stm32f4 main chip module

Post by russian » Thu Apr 03, 2014 1:18 am

We need our own KiCad board with some stm32f4 chip in order to get the schematics ready
because eventually we better make a board with an stm32f4 chip right on it. Less kinks caused by the discovery components we are not using (they make some pins inoperable), less vibration issues, better licensing situation.

The board design is supposed to be ready and I have even purchased the BOM so that I can validate the packages against a paper version of the PCB. That's where I got distracted and that's where it is for the last month or two.
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Re: stm32f4 main chip module

Post by Sudo » Thu Apr 03, 2014 2:58 am

Ah, I see. At first I thought we are reinventing the wheel, but I get it now.

Anyways a 4 layer design is easier to get clean return paths for high speed signals. Otherwise, you can introduce crosstalking if the returns paths are interrupted. General rule of thumb is that at high speed, return paths are not ground, it is the closest piece of copper. Therefore you can return through another signal causing crosstalk.

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Re: stm32f4 main chip module

Post by kb1gtt » Thu Apr 03, 2014 9:59 am

According to this article http://www.maximintegrated.com/app-note ... vp/id/5450 high speed signals are anything above about 1kHz, and any square wave will have frequency components above 1kHz.
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Re: stm32f4 main chip module

Post by russian » Fri May 02, 2014 2:08 pm

Ordered on May 2nd 2014
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Re: stm32f4 main chip module

Post by UnaClocker » Thu May 15, 2014 1:17 am

I can help soldering these. I have a hot air rework station, a (toaster) reflow oven, and have soldered 100ish pin LQFP packages by hand before (successfully, even). I'd definitely want to order a stencil from OSHStencils and do them in the reflow oven, at least the STM32 chip itself, because doing more than one or two of these would be maddening quickly. ;)
Go for a 4 layer, it's really simple to step up to 4 layers in the cad software, and the increase in signal integrity is worth the extra board cost.
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Re: stm32f4 main chip module

Post by russian » Thu May 15, 2014 1:27 am

http://www.oshstencils.com/pricing.php wow that's pretty cool! Looks like I will try them soon.

As for this particular brain board, since that's just a proof of design in a perfect scenario it would be enough to solder exactly one, make sure it works and call the design confirmed. Next step would be integrating this brain module into a larger PCB with all I/O, at least that's the way I see it.
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Re: stm32f4 main chip module

Post by kb1gtt » Thu May 15, 2014 11:16 am

Plastic stencils have pros and cons. The plastic gets a bit thicker at the cut edge. So a 3 mil thick sheet will deposit about 4 mil of paste also some residue stays near the cut edge. So you really should clean the mask after use or you can get some small gobs of old paste. Also this lip make it a bit harder to get a good paste scape with slight dry paste or subpar paste the bump kind of prevents the paste from getting around edge. All in all plastic stencils are reasonably good they just need some extra work to make them work well.

I understand the etched aluminium stencils are significantly nicer to work with. Those often come with the boarder which holds the pub while you scape the paste and stainless is the MFG preferred.
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Re: stm32f4 main chip module

Post by UnaClocker » Thu May 15, 2014 7:12 pm

Yeah, in the end, plastic at that price is great for the DIYer, and WAY better than no stencil at all.
Use good paste.
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Re: stm32f4 main chip module

Post by kb1gtt » Thu May 15, 2014 11:47 pm

kester 256 is good stuff. Getting good paste in small quantity is kind of a blah. I like this fellow he puts it in a syringe. I got a tub of the stuff years ago. They demanded to overnight it in a cooled container and the tub cost $99. So it was a bit pricy. Is there a source for diy stencil paste? If I'm making multiple's of million dollar boards I can see the cooled shipping but that not required for diy. As well I didn't need a life time supply. A better source would be nice. Also mine seems to have dried up quite a bit so I could use some new stuff. I'm well past the shelf life of my paste.

http://kd5ssj.com/solderpaste
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Re: stm32f4 main chip module

Post by russian » Fri May 16, 2014 9:38 pm

I'm afraid of this PCB :(

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Re: stm32f4 main chip module

Post by kb1gtt » Fri May 16, 2014 10:14 pm

The hardest part to solder is the main chip. If you put on to much solder you can remove excass with solder wick. The key is to place the chip accurately. With an iron you can tack one pin down then adjust the far side until it aligns correctly. Then you heat up the original pin to relieve stress. After that your hot air will do the bulk of work.
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Re: stm32f4 main chip module

Post by russian » Sat May 17, 2014 12:10 am

Set #1. I've applied soldering paste on the board, put the chip above and tried my best to align. Two rows seemed fine, but two I could not see anything because of the paste. Kind of tacked it with soldering iron, seemed ok, applied hot air. Nope, it was off, and funny thing - there just was no connectivity into too many pins. I think this set is pretty much ruined.

Took set #2 and here is the deal: the lacquer layer shapes a perfect bed for the chip! So, it goes right into where it should go - and it would not move anywhere, the edge of the lacquer layer is holding it in place. Fine, I've applied some solder paste above the pins while the chip is sitting on the board. Good news: everything is aligned perfectly, Bad news: since I am applying the paste on top of the paste, I had to re-apply it because nothing gets between the pins and the PCB pads - it all stays above. And once I really, I have too many pins soldered together. And while I was trying to use the wick, I've bend some of the pins :( They are too fragile.
This second would maybe be fine for a test - even with some pins soldered together it would be good enough for a test, but only for a test.

F@$@ it. Time for some red wine, I am definitely not enjoying soldering TQFP 100. If anyone wants to save set #1 or try soldering set #3, please PM me and I will mail you this stuff.
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Re: stm32f4 main chip module

Post by kb1gtt » Sat May 17, 2014 12:51 am

Another possible tactic might be to apply paste, then heat such that the paste flows, then install the chip. This will ensure you have solder under the leads. Also alignment can often be done off the silk markings. So if you can't see the pads or pins you can often reference the chip edge to the silk.
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