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Re: ground layer polygon spacing

autodeskguest

Redcutlass wrote on Thu, 10 September 2009 18:23

Hello eagle users,

I am a newcomer to this forum, so here goes "me" on my first post.

First off, I'd like to say that I didn't like Eagle at first, but in a week's time I've grown to like it more and more. Or maybe it's because I know how to use it now. Anyway, I am having a strange problem on my ground layer that even a coworker has never seen. We both think it's some kind of clearance issue, but not sure where to change it, if even it is that.

 

So, I made a polygon on the bottom layer of my double sided board (pretty high-tech eh?) and named it, appropriately, GND. As soon as I do that, I get an area that is filled in to 0.050" of the contour (edge) of my board. Here is a picture:

image

 

Bear in mind that the Isolation and Spacing attributes are set to 0 and 0.01, respectively. I have a large 40 thou gap on each side of the ground plane, so, what's going on?

 

 

Hello Owen,

 

I think what you are seeing is a classic gotcha.  If you read the help about the polygon command it does mention it.  Basically, there is nothing for your polygon to connect to so it behaves not as expected.

 

Plop a via somewhere in your polygon, name it gnd, and then run the ratsnest command to redraw.  I bet it will look more like you imagined.

 

Cheers,

 

James.

 

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  • Why thank you for the quick reply James, I will be sure t try that as soon as I am back at work Friday!

     

    I will also reread the section on polygons...

     

    Owen

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  • you are complaining that you don't get poly coverage to the edge of the

    board? as it is drawn in the dimension layer? how thick is that line in

    the dimension layer? check your DRC design rules under the distance tab

    and see what setting for copper/dimension spacing you have.

     

    nb. normally you don't want copper anywhere near that saw or routed

    cut, the possibility of unintended short to another layer or nearby wire

    or metal is my understanding of why....

     

  • in reply to autodeskguest

    Hi Gary,

    thank you! Yes, I discovered that it was in fact that. But I had no

    choice. I guess the default parameters are just, well, strange! I changed

    it for 6 thou, which gives a reasonable clearance from the absolute edge of

    the board, so as to prevent any shorts, as you said. Now I remember dealing

    with the side effects of a board designed with no clearance, in another

    job... It caused occasional shorts that restarted the  microprocessor every

    time the side of the housing was pressed too much!

     

    Anyway, thank you, your help is appreciated, I didn't have to wait too

    long!

     

    Owen

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  • in reply to autodeskguest

    i think .006 is too close if that's the distance to the actual edge.

    maybe you are also getting some clearance for saw or router kerf.

     

    but I would go with the advice of your boardhouse and depends on how

    they cut the boards. as you mentioned, this can be a very expensive and

    annoying problem. consider the possibility that layers get shorted

    together as well during the cutting process.