Need help making a PCB layout

Discussion in 'The Projects Forum' started by christophee, Nov 8, 2012.

  1. christophee

    Thread Starter New Member

    Jan 15, 2012
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    I am really having a hard time doing the design for our project since we have about 30 ICs. Please help me with my dilemma. With autoroute, it ends up like this, please help me. thank you!

    [​IMG]
     
  2. John P

    AAC Fanatic!

    Oct 14, 2008
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    Christophee, you're hijacking someone else's thread. And your design is, ah, in need of some serious help.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    I am afraid John P has the right of it.

    A thread belongs to the OP (original poster). Trying to take over someone elses thread is called hijacking, which is not allowed at All About Circuits. I have therefore given you a thread of your very own.

    This was removed from Project: How to make PCBs .

    The first things that jump out is you have not named the package you are using. You are not showing the schematic drawn with that unnamed package, which is used to generate a netlist, and generally the chips are laid out in a geometric pattern before laying out the traces.

    Basically you are trying to let the software do all the work, it does not work that way. Computers are dumb, humans are smart. With Express PCB you lay out the parts, and the software shows you what pins need connecting to what. I am not sure it works that way with every package, but I suspect it mostly does.
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    I run into this all the time with auto routers.. You either need to move parts round till the routing is possible or increase via costing (let it use more vias) or increase layer counts or manually run the remainder of the traces.

    Or send me the schematic, board dims and.hhmmmm.. $2500 :)
     
  5. Sparky49

    Active Member

    Jul 16, 2011
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    That looks like PCB wizard to me.

    I'd recommend something a bit more powerful for boards with that number of ICs, like Eagle.

    The guys are right, you cannot let the computer do it very well.

    I'll beat mcgyvr's offer and do it for $2000.;)
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Well you cannot expect a free/low cost auto router to do it well.
    The more money you spend on it and the more rules you tell your auto router the better it will do.

    I do 90% of the traces using the autorouter functionality in Diptrace. The rest is manual routing for what it can't do.. Diptraces auto router is pretty "stupid" too.. I usually spend a good 20/30 minutes going back and fixing the stupid stuff it does.. And I move components around as much as possible until the auto router gets as close as I think it should.. (2-5 nets left unrouted) I HATE manual routing. (not to mention its very time consuming/inefficient.)
     
  7. John P

    AAC Fanatic!

    Oct 14, 2008
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    Actually I'm sure the autorouter that FreePCB uses would do a fine job--it always has for me. As far as the size of the board and the number of components are concerned, it doesn't look too challenging. Now cue my usual denunciation of Eagle. You won't get a board that size with the free version.

    But Christophee, please put the chips all the same way around, and add filter capacitors. You are just guaranteeing an unreliable board which you'll never be able to debug. Making a PCB is fairly expensive, far more than the chips will cost; surely you don't want to waste your money?

    Speaking of which, 2000 bucks is robbery! I'll do it for 1500!
     
  8. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Like others said, something more powerful like Eagle might do a better job, but unless you help the autorouter by placing the chips right, the job it does will suck anyway.

    First you need to say a few basic things, like are you etching the board by yourself, or are you going to a fab house? If you can use doublesided board with vias, things will get a lot easier. Is your manufacturer able to place a trace between the two legs of an IC?

    Second, look at your schematic diagram and try placing the chips all vertically and in the order they are used in the schematic. Swap the gates and chips until you get some more reasonable ratsnest, then try routing it. Of course you can make some horizontal, but it is esaier to start with all chips facing the same way. Also try making the board like two times larger, keep changing placement until you get optimal reults with the autorouter, and then start shrinking the board.
     
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