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Thread: PCB-production

  1. #1
    Senior Member+ Frank B's Avatar
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    PCB-production

    I need some help !
    I want to create a small circuit board . What software do I need , and which is suitable for beginners ? I have some practice with breadboard PCBs .
    The board is about as large as the Teensy be and place some SOIC8 ICs (SPI-Memory + logic for CS) to it, on both sides, eventually ( For smaller packages my eyes are suboptimal ) .

    How much does something like that cost in the production ? For 10-20 pieces ?
    Anyone for a beginner like me to help ? :-)

  2. #2
    Senior Member PaulStoffregen's Avatar
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    Eagle and Kicad are the two free ones. Both have significant learning curves, but lots of tutorials exist.

    There are a few PCB vendors that have free, relatively simple software, but they create encrypted files that lock you into only than 1 vendor. I'd recommend avoiding those.

    For getting boards made, OSH Park is the best for small size boards. For larger boards, iTead, Seeed and many others in China are pretty good. Often their quality is great, but it sometimes varies.

  3. #3
    Senior Member onehorse's Avatar
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    Frank,

    Take advantage of Sparkfun's tutorials on how to use EAGLE. You can download the EAGLE lite version for free and it has everything you need to design your pcbs. Then submit the EAGLE-generated gerber files to OSH Park where it cost $5 per sq. inch for three pcbs. For the Teensy footprint, this is about $5 for three boards with free shipping anywhere in the world (has anyone actually tried ordering from Antarctica?).

    I encourage you to learn to do this for yourself, but if you would like instead, I will do it for you gratis for the help you have provided me if you sketch out what you want.

  4. #4
    Senior Member+ Frank B's Avatar
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    Wow thank you. I really want to learn it.
    Ok, i'll download eagle and try it.
    I'll upload my first tries here..
    Thank you for the help

  5. #5
    Senior Member+ defragster's Avatar
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    Good pointer THX: https://learn.sparkfun.com/tutorials...nd-setup-eagle

    That links to the rest of their tutorials - or a search will

    •Your PCB design is limited to a maximum size of 100 x 80mm (3.94 x 3.15in). 12.4 in2 of PCB real estate, which is still pretty darn big. Even if you’re designing a big ‘ol Arduino shield, you’ll still be well under the maximum size.
    •Only a two signal layers allowed. If you need more layers check into the Hobbyist or Standard licenses.
    •For non-profit use only. If you’re going to go out and sell your design, maybe check into the “Light” version of the software.
    Last edited by defragster; 05-13-2015 at 04:48 PM.

  6. #6
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    Eagle is very good and there's plenty of help available on the net when you inevitably need a hand with how to do something, however there are limits on the size board you can produce.

    RS Designspark PCB is also an option; it's entirely free with no limits and comes packaged with some great tools and wizards for creating components or pulling them from their repository (modelsource).

    Having said all that, it still occasionally frustrates me by doing stupid things.

    Definitely start with Eagle and sparkfun's tutorials though. Everything you learn there is pretty much universally transferable to any pcb design package.

  7. #7
    Senior Member Epyon's Avatar
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    Since you're from Germany, I can recommend Eurocircuits. I place all my orders there, be they for my own or my professional projects. They have a prototyping service which has very competitive prices and quite fast delivery (standard delivery: 5 days). They now even have a ultra low-cost solution that delivers boards without solder mask or silk print for fast and easy prototyping.

    Best thing (imo) is the data upload proces. You can upload your Eagle .brd files directly to their production system. This automatically checks against their design rules (you can also download their rules to perform the check in Eagle) and presents you with simulated images of the finished PCB. They are also very helpful when you have questions (e.g. I wasn't sure how to indicate slots to be milled on the board file, they showed how).

  8. #8
    Senior Member Constantin's Avatar
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    Another vote for Eagle. While its user interface can only be described as 'quirky' at times, it does get the job done.

    The only thing I would avoid like the pits is the autorouter. Since the autorouter seems to not to care about the signals it is trying to connect, you end up with PCBs that look a lot like early Arduino boards, ie lots of vias and so on. Freerouter was much better but sadly offline now. Eagle is claimed to have a better autorouter in version 7, but I believe in routing my boards by hand, which takes time but which also allows me to generate 2-layer boards with almost unbroken ground planes.

    Good libraries to download include Adafruit, spark fun, and the plethora of stuff at cadsoft itself. However, I warn you to check footprints carefully as I have been repeatedly burned by bad footprints or signal connections.

  9. #9
    Senior Member+ Frank B's Avatar
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    Thanks.
    Yesterday, i draw my schematic (Eagle). I have some trouble with the board now, but i think somehow i get it done. Needs time.
    I tried the autorouter too. Indeed it produces a lot of vias. I have no experience reg. routing by hand, and it looked not too bad (max freq. will be 30MHZ SPI, so i think it's ok - a circuit like this works perfect with long "flying" wires.. so i assume it's ok, even with more vias than needed)
    I'll upload my work here.. (hehe...or better not ?) But before that i need to learn more..

    Regarding manufacturers: Any experiences with "Bilex" ( bilex-lp.com) ?
    Last edited by Frank B; 05-14-2015 at 12:44 AM.

  10. #10
    Senior Member Constantin's Avatar
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    My manufacturing experience is in the U.S. (osh park) and the Far East (IteadStudio) both are great resources but both have advantages and disadvantages. So I use both, depending on the project. Little boards go to osh, big ones go to IteadStudio. IteadStudio also makes my stencils.

  11. #11
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    Suggest ignoring the autorouter. Route by hand, then use the electrical rules check to be sure schematic and board correspond. Then use a design rules check (for example the one from OSH Park) to check things like overlap, minimal distances, etc. Lastly, print out the board and physically place the components on top to check for fit. If using through-hole components, put a polystyrene tile under the printout so you can push the leads through.

  12. #12
    Senior Member Constantin's Avatar
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    Yup. The better packages out there allegedly allow you to designate signals with attributes so that the router is more intelligent. For example, analog and high-speed signals will not pass near each other unless there is a ground plane in between, etc. Similarly, differential signals are routed together with a trace diameter and keep-out area around them to help (i.e. USB signals should be around 10 mil with a 6.25 separation and a 30 mil t- or b-restrict around them)

    The free push-pull type freerouter was excellent at creating designs with minimal vias. But it's primary purpose for me was to establish whether I had a 'efficient' design on my hand, i.e. had I done a good job with my component placements to allow a eventual design with few, if any vias.

    These days, I think I do a better job in general with hand-routing traces. This is especially relevant in the context of mixed signals applications where keeping high-speed signals away from sensitive analog areas. It's amazing how much information re: high speed design is out there and to what extent it can be contradictory. I've ended up in the camp where I use a single GND plane but segment the components in a way that no digital signals ever cross into the sensitive areas of the analog divide. Paul uses a different approach (which he likely researched at length!) where the AGND is separate but connected to the GND via a ferrite to keep out interference.

  13. #13
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    high speed design is out there and to what extent it can be contradictory
    I agree, it can seem contradictionary, but for different frequencies different effects play a role, so you should always be aware of what background someone has and with what application.
    For example all these generic EMC guidelines are helpfull only for the 10s of MHz to the low 100s of MHz, above that several measures become even detrimental. (Being an microwave engineer myself, I see EMC more as a belief. A rule of thumb of some EMC guru is considered more valid than actually using Maxwells laws).
    Also for 100s of MHz lines in digital circuits people like to use differential lines (with somewhat valid arguments), but when designing analog circuits at a couple of GHz, no sane microwave engineer would ever use differential lines. And when I design around 100 GHz, even other effects come into play. It is all dependant on the application.

    An obvious example of where to be aware of the context is the line widths for the USB signals you mention. Here you should also be aware about the context. These values are most likely taken from a multi-layer board. USB signals should have an odd mode impedance of 45 ohms (ie 90 ohm differential) given your dimensions this is only applicable when having the ground layer 5 mil below the lines. Your clearance is also dependant on the board height, for a standard 1.6 mm double sided FR4 board, the fringing fields of a line are about 30 mil. So a minimum clearance that will prevent fringing fields from overlapping would be 60 mil.

  14. #14
    Senior Member Constantin's Avatar
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    Apologies for the mistake (I took this as gospel from another forum member) and I had a look at the microstrip calculator over at eeweb.

    Click image for larger version. 

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    I fail to get to the right impedance no matter what I try for a 'normal' setting (i.e. FR4 @ 4.8 dielectric with 0.8mm-1.6mm thickness, and 1 oz/ft^2 trace thickness). It makes me wonder how 2-layer boards can be made with USB striplines that are in spec. Any suggestions re: conductor width vs. separation? FWIW, the traces on the board are about 3 inches long.

  15. #15
    Senior Member+ Frank B's Avatar
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    Ok, here is my SPI-Memoryboard, it has space for three "jedec" SPI-Memories, uses two Teensy-pins for Chipselect.
    Perhaps i want to use the space on the Backside for optional additional SPI-Chips. Can this cause any problems ?

    Click image for larger version. 

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    Click image for larger version. 

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    The EAGLE-Project including Board (+ a "DRU" File from Eurocircuits):
    (I must admit, the routing made the autorouter)
    Memoryboard.zip

    Tips and critique are welcome !
    I tried to add Polygons for GND, but this did not work. How can i connect a polygone to GND ?
    Last edited by Frank B; 05-14-2015 at 07:48 PM.

  16. #16
    Senior Member+ defragster's Avatar
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    How/Why did you pick your SPI pins? #12 is primary DIN, and #7 is 2nd (grey) DOUT? And #14 2nd SCK.

    You will manually set CS through the MUX with #2 and #3? Have you hooked this up to work - that is - do the LIBS accommodate these pins?

    Which pin [SCK or CS] is cycled during SPI commands?

    Are you using other SPI device like the ILI9341 as well on this system?

  17. #17
    Don't forget GEDA http://www.gpleda.org/ !

  18. #18
    Senior Member Constantin's Avatar
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    I am flummoxed re: the use of a multiplexer. Why bother? All you save is one pin. I think I can get this board done with only two vias but so far I cannot move the components around. Also, are the multiplexer lines a requirement or could they be adjusted to other pins?

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    I can imagine my remarks can be considered like critique and that I seem to be a know-it-all. This is probably partly cultural. However, my intentions are to help people.

    @Constantin, it is not my intention to hijack this thread, but you need to increase trace width. Just from memory, the width should be in the order of 40 - 50 mil. For USB 1.x you do not really have to care, since as you mention the line lenght is short. For USB 2.0/high speed (480 Mbit/s) I would use the proper line impedances. For microcontrollers you do not see a lot of high-speed USB (if at all).

    @Frank B.
    Just some remarks about the layout.
    - The vias look a bit small, in general you would want to aim for a 4:1 or 5:1 ratio between board (or layer) height and hole diameter. Anything higher and the liquids used in the hole plating process cannot easily pass through the hole
    - Even with autorouted boards, you have to clean up afterwards. It is good practice to exit pads at the ends and not in between neighbouring pads. Also when connecting neighbouring pads, it is preferable to place the connection just outside of the pads, (ie not in between the pads), to prevent the connection to be confused with an accidental soldering bridge.
    - Talking about soldering bridges, you want to spread out the lines where possible. If the soldermask is a little bit misaligned, you can now have exposed copper of both the pad and a trace around it in the same solder mask hole, thereby risking solder bridges.
    - If you are not using the 3+1 pins on the inside, just remove them, it will give you just a little bit more space.
    Finally, you might want to check connectivity. In the image, the board does not look fully routed. I see dangling wires, and also the capacitor is not connected to the 3v3

  20. #20
    Senior Member+ Frank B's Avatar
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    Wow, thank you for all the tips. I did not notice that not all pins are routed :-)

    Ok, a little more Info :

    The used pins are compatible to Pauls Audioboard and the ILI3941, both can still be used, simultaneously.
    Nearly all pins are used in this setup, so I want to use the decoder. Additionasl It gives the option to add more RAM/FLASH/WHATEVER on the backside - perhaps i extend the circuit a bit, i'm a bit undecided at the moment.
    My current (working) setup is: Audioboard + Windbond Flash + RAM (glued on top of the Flash and some wires :-( ), SD Card, another RAM on a little breadboard ontop of the teensy, the ILI9341 Display. A lot of SPI :-). Plus, last, but not least, a switching regulator 5v->3.3V and an Espressif, ESP-01. [Edit] Ups.. no, since yesterday the Olimex ESP8266 Dev Board[/Edit][Edit]I forgot the IR receiver[/Edit]
    The intention of this board is to be compatible to the Audioboard + ILI9341 and give much RAM/FLASH, whatever. Both sound and graphics can be very hungry for memory.

    The decoder is a unknown variable for me. Will it work this way ?
    Last edited by Frank B; 05-14-2015 at 10:05 PM.

  21. #21
    Senior Member+ Frank B's Avatar
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    Click image for larger version. 

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    Current setup... this needs to be better :-)

    I'm a software guy...
    Last edited by Frank B; 05-14-2015 at 10:15 PM.

  22. #22
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    At first sight it looks OK. I appreciate especially the two resistors, that keep a well defined CS state during start-up.
    Maybe it is me, but when clicking your link, I see
    Invalid Attachment specified. If you followed a valid link, please notify the administrator

  23. #23
    Senior Member+ Frank B's Avatar
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    I re-uploaded the picture,I hope it is ok now. But you did'nt miss anything important :-)

  24. #24
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    For good performance of the antenna, you do not want it to be near any other metal. Either lift it up a few centimeters (ie more space between the two pcb's), Or shift it so that the antenna overhangs the display, in such a way that the overlap starts at least at the crystal.
    For the rest, this is what you expect from a prototype.

  25. #25
    Senior Member+ Frank B's Avatar
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    It's not good to see on the picture, but there is some space between the antenna and the display. I can lift it more, it's only connected with cables.
    The whole thing is a mp3/aac-streaming-audio (webradio) player.

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