Kicad and 2-layer PCBs

Discussion in 'General Electronics Chat' started by kgstewar, Nov 22, 2013.

  1. kgstewar

    Thread Starter Member

    Apr 5, 2012
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    Hi all,

    I'm a brand new Kicad user and have some basic questions after designing my first board:

    1. My PCB is two layer yet all of my components are through-hole. How do you solder an IC socket, for instance, if some of the tracks leading to the pins are on the top and some are on the bottom?

    2. I have put all the power flags in correctly on my schematic and get no errors when I run the checker but the finished PCB has no obvious place to connect Vcc and GND. Is Kicad expecting me to make a "ground plane" and a "Vcc plane"? If so, is one plane covering one side of the board, the other plane covering the opposite side?

    3. There are a number of places where the track must go from the front of the board to the back of the board. I believe these are called "vias"? How do I actually connect a via? Or does this get done by the board manufacturer?

    Many thanks in advance!

    Kevin
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Never used Kicad BUT..
    #1-There should be "pads" on both sides of the board and those pads are plated through holes. So even if there is no trace on the solder side when you solder that through hole pin its connected to the trace via the plated through hole/pad.

    #2-Not sure why you used "power flags".. But you will need to add a connector or whatever you want to connect Vcc/GND to.

    #3-Yes "vias" allow traces to go from one side of the board to the other.. When you do a via, again like #1, it will be a plated though hole.
     
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  3. MrChips

    Moderator

    Oct 2, 2009
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    Pads and vias (in fact all holes) will be plated through by the board manufacturer.

    If you are etching your own PCB then you don't have the luxury of plating your holes.

    Here is what you can do.

    Make the vias as large as a regular pad. Make the holes large enough to take a resistor lead (0.028") and use the discarded resistor leads to fill the via holes.

    Make sure you can solder resistor and capacitor pads on both sides of the board (assuming traces are connected to the pad on both sides of the board). This will serve as your plated-thru hole.

    If you are using DIP ICs make sure you can solder IC pins to the pads on the top (component) side, especially if the trace runs underneath the IC.

    This means that you cannot use IC sockets.
     
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  4. Gibson486

    Member

    Jul 20, 2012
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    1. Through holes go through all layers of the board. If you have a plane that can't touch the through hole, KiCAD (or any PCB suite) will take care of that. If you have a trace on the other side of the board, just attach eh trace to the through hole.

    2. All you have to do is call the power flags somewhere. KiCad does not know that connector XX is a power connector. All it cares about is that you have a positive and negative. The only reason those flags are there are to ensure you do not hook your supply to an i/o pin or such. That said, if you do not call out the pins on your device correctly, then you will always get errors. Furthermore, if you do call it correctly, but you put something like a fuse in front of a power pin, KiCAD will complain.

    3. See number 1. Same concept, just smaller hole.
     
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  5. kgstewar

    Thread Starter Member

    Apr 5, 2012
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    Thanks Mr. Chips, macgyvr and Gibson. I am now clear on how vias and 2-sided boards work! I'm still unclear, however, about where exactly I am supposed to connect power and ground on the finished PCB (my question #2 above).

    I have used the power flags in Kicad correctly (I think), and I get no errors when I run the checker.

    The finished PCB, however, does not have pads labeled "Vcc" or "GND". Do I simply add these pads by hand? Easy enough to do but I'm a bit surprised that Kicad doesn't take care of this. Or am I missing something (likely!).

    Thanks again!

    Kevin
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    I can't speak for KiCad since I have never used it. I use Eagle.

    When you lay a trace and then switch to another layer Eagle automatically places a via that is isolated from any surrounding plane.

    If the signal happens to be the same as the flood plane, Eagle takes care of it and draws thermal reliefs at the pad if so desired.
     
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  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    I suspect Kicad works like others.. "flags" are meant to be used when you split your schematic into separate parts or pages..and the flags will take care of making sure the connections are there on the physical board BUT you still must connect those traces to a connector or a pad if you intend to just solder wires to the board for VCC/GND..
    So if you aren't splitting your schematic up into chunks then you don't need to use flags at all.
    Flags are really just for following the schematic when you print it out and its on multiple pages..
     
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  8. kgstewar

    Thread Starter Member

    Apr 5, 2012
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    Ok, then I THINK I"m using flags correctly..

    What I ended up doing was creating two filled copper "squares", one on each side of the board that encompass the entire circuit. One is assigned Vcc, the other is GND. These seem to connect to all the proper pins. So I guess I just need to put a solder pad on each plane and these will be my power and ground connections.

    Thanks for the help again, and please let me know if anything I've said so far sounds like a problem.

    Kevin
     
  9. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    It does not sound like you are using flags correctly to me..

    You still should have a connector or a "dummy" component in your schematic that is just a pad that you tie Vcc/GND to. If.. for example you are going to just solder a wire to your board for both Vcc/gnd then you should have a component in your library that is just a pad and properly sized through hole.

    I have a whole subsection of my component library that is just different wire solder pads..
    The schematic symbols for those are the typical single position connector (or jack or plug) symbol.

    flags are (or should be) just a visual "tag" indicating that this wire is tied to that net. Flags are not intended to be a replacement for a physical connector or pad. It just allows you to read the schematic easier.. Let me see if I can find a good example of a flag. give me a second.
     
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  10. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Here.. this shows a small section of one of my schematics..
    The flags are just used so its easy to follow one wire from one section of the schematic to another. It also joins those 2 wires in the same net.. BUT its not a replacement for a proper connector or wire pad. (or in my opinion anyways.. and I do PCB layout professionally)

    Of course, I've also learned that it really doesn't matter what steps you take to get there as long as your PCB comes out correctly..
     
    Last edited: Nov 22, 2013
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  11. kgstewar

    Thread Starter Member

    Apr 5, 2012
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    mcgyvr, you are absolutely correct, I am NOT doing it right.

    I see now. Per your suggestion, I'm going to go back to my schematic and add a 2-pin power connector and then flag those pins to my schematic. Many thanks!

    Kevin
     
  12. BobTPH

    Active Member

    Jun 5, 2013
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    If I am wiring power and ground to a board, I put a 2 pin connector in my schematic, then use a .1 in spacing two pin header on the board, which gives me 2 pads to connect the leads to. I also place a larger hole near these pads, and run the wire first up through the hole (including the insulation) and then down through the pad, for strain relief.

    Bob
     
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  13. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    @kgstewar: sounds like you're on the right track.

    Each connection (two or more pads in a common connection) is called a "net."

    A flag is one way to get a net a name. It is not a physical part, it is just a convienence when designing the board. I'll sometimes turn them on, which puts a nice name on every track on my board.

    By adding a two pin connector to your schematic, and connecting it to other elements you get the ability to put that connector on.

    If you're even decent at creating your own symbols and footprints you can do tricks like define a pin symbol and a pad footprint. Then you are free to put your power connections anywhere you want; that's sometimes easier then editing a two (or more) pad footprint.
     
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  14. kgstewar

    Thread Starter Member

    Apr 5, 2012
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    Thanks to all for the help. As suggested, the key was to include a 2-pin power connector. I did that and labeled the pins (Vdd and GND) so that Kicad knew to connect all of these on the finished schematic. For some reason I did have to attach a "power flag" to each of these pins. Once I did that it all worked like a charm.

    Now to make sure I didn't screw up something else before sending it off. Thanks again!

    Kevin
     
  15. ErnieM

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    Apr 24, 2011
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    It's surprising how many surprises may be lurking in even a very simple board.

    I average between 2 and 3 board spins before it is ready for prime time.
     
  16. MrChips

    Moderator

    Oct 2, 2009
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    I just received my PCBs. Works great but I've made a list of 7 things to change on the next run.
     
  17. kgstewar

    Thread Starter Member

    Apr 5, 2012
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    Mr.Chips, where do you send your boards? I'm sure it will take me at least a few tries to get my board right, and this one is definitely simple (4 ICs and a handful of caps and resistors). More than anything it was an excuse to learn Kicad and get away from stripboards. Or maybe it's just that I am addicted to the steep part of every learning curve!

    Kevin
     
  18. MrChips

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    Oct 2, 2009
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    I use APCircuits. I choose basic prototype service, two layer, no solder mask, no silkscreen. Boards received in 3 days.

    http://www.apcircuits.com/
     
  19. mcgyvr

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    Oct 15, 2009
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  20. MrChips

    Moderator

    Oct 2, 2009
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    I placed the same order with imall.iteadstudio at the same time with APCircuits just to compare.
    The price is 1:5 difference. Got the APCircuits back in 3 days over the weekend. The board is up a running beautifully. Will show and tell sometime.
    Still waiting for the boards from China.
     
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