PCB Design/layout

Discussion in 'General Electronics Chat' started by Veracohr, Jan 24, 2014.

  1. Veracohr

    Thread Starter Well-Known Member

    Jan 3, 2011
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    I'm working on the PCB layout for my senior capstone project. It's quite complicated (for my level of experience anyway), and has both surface mount and through-hole components (will be hand-soldered). At the moment it looks like a plate of spaghetti and I'm nowhere near done.

    I'm wondering about "best practices" for PCB layout. I know a few, but I'm sure there are others I don't know about. For instance, I'm finding that to get all the signals and power where they need to go, I have to do a fair amount of passing traces through the board, switching layers, in order to cross them over each other. Is that OK?
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Well, call it "undesirable." Placement and routing is a skill or a knack that develops over time.

    "Undesirable" means your board may work just fine with a rats nest stuck in the middle, though it also may not work. The neater the work the easier it is to check.

    A very good PCB design tutorial.
     
  3. t06afre

    AAC Fanatic!

    May 11, 2009
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    I guess it is allowed to post you design for some pointers.
     
  4. John P

    AAC Fanatic!

    Oct 14, 2008
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    Depending on the type of circuit you have, layout may or may not be an issue. If you have high frequencies or sensitive instrumentation, you definitely have to worry about how the traces go, which signals are near each other and whether you're using grounding properly. For a typical microcontroller setup though, you probably don't need to do anything except make sure the right points are connected. But using good practice will certainly make the system easier to work with and if it's an academic project, your instructor will be more impressed by a good job than a bad one.

    Note that there are free PC layout programs available, some of them with auto-routing facilities which can do a tolerably efficient layout, i.e. minimizing trace lengths and vias. If you want to use an autorouter and need to be fussy about some signals, you should do the sensitive parts by hand and let the program take care of the rest.

    Before anyone else says it, we've had arguments here about whether autorouters (or at least the cheap or free ones) produce acceptable output. I think they do for most purposes, but not everyone agrees with that.
     
  5. Veracohr

    Thread Starter Well-Known Member

    Jan 3, 2011
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    The circuit is for audio, so not terribly high frequencies, but anything that could affect the signal even slightly would be undesirable. There is a microcontroller (Arduino board) connected to some muxes and a DAC and a couple other things. I have a bunch of external controls (pots and encoders) that have to be placed at certain spots, so I also have to work around that, while also trying to keep traces as short as possible.

    I'm actually making it a bit hard on myself doing the PCB in the first place. It wasn't strictly necessary, but I wanted to do it for my own satisfaction.

    I'm using ExpressPCB because I used ExpressSCH for the schematic, and I plan to use them to make the board. I don't believe it has autorouting.

    Thanks for the tutorial file, I'll take a look at that.
     
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Last time I used it ExpressPCB didn't have any autorouting, but it does ID nets from the ExpressSCH schematic,meaning when you click on a pad it changes color, and all other features common to that pad also change color.
     
  7. Veracohr

    Thread Starter Well-Known Member

    Jan 3, 2011
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    Yeah I knew that, good feature.
     
  8. brucefu

    New Member

    Sep 1, 2014
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    Last edited: Sep 1, 2014
  9. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Awesome self promotion inside a necropost for your very first post !!!
     
  10. Lestraveled

    Well-Known Member

    May 19, 2014
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    I love ExpressPCB. It is the perfect software for you to develop layout skills. Spend 80 percent of your time working out placement. If your placement is good then routing is a snap.
     
  11. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    I too use ExpressPCB. One suggestion I can make is to question your layout. Sometimes moving a device/device block will result in a cleaner routing. In my game show circuit project, I routed between the ICs laid out relative to each other as in the schematic. This resulted in a rats nest. Then, I questioned the layout and positioned the ICs in a more functional way. Ithe PCB made much more sense and was easier to is. Check out the two versions of the PCB at http://forum.allaboutcircuits.com/threads/game-circuit.82641/#post-725650
     
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