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Gerber files and Pick and place file

jboavida

Hello,

 

I generate the top layer gerber file (using the standard Job gerb274x with offset zero) and the pick and place file using the mountsmd.ulp. No problems here.

But when I load them in my pick and place machine, there is a offset.

The pick and place coordinates are correct, but the gerber is off center (around 0.4mm in x and y)

 

 

image

What i'm doing wrong?

The problem is not the machine, because files generated with other software (tested with  some Protel files) display ok.

 

Thanks in advance

 

Joaquim

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  • On 03/26/2013 08:23 AM, Joaquim Boavida wrote:

    Hello,

     

    I generate the top layer gerber file (using the standard Job gerb274x

    with offset zero) and the pick and place file using the mountsmd.ulp. No

    problems here.

    But when I load them in my pick and place machine, there is a offset.

    The pick and place coordinates are correct, but the gerber is off center

    (around 0.4mm in x and y)

     

    In each of your CAM job sections, make sure the "pos. Coord" checkbox is

    clear.  Here's why...

     

    With "pos. Coord" checked, the CAM Processor will add an offset such

    that all features included in that gerber file are in Quadrant 1, i.e.

    all features have positive coordinates.

     

    My guess is that you have copper trace around the perimeter of your

    board that's about 0.8 mm wide.  Thus half of the vertical trace is to

    the left of X=0, and half of the horizontal trace is below Y=0.  It

    doesn't have to be a trace - it could be any object or part thereof.

    After the CAM Processor adds offsets, the edge of the trace will be on

    an axis.

     

    This can cascade into an alignment problem between layers.  For

    instance, if you had such a perimeter trace on the bottom layer, but not

    the top, then the bottom would be offset to make sure the entire trace

    is in Quadrant 1, but the top layer would not have such an offset.  This

    potential pitfall can surface in any layer - mask, inner layers, silk

    screen, etc.

     

    You can explore this a bit by placing an arbitrary trace on one layer

    that's well to the left of the vertical axis, run the CAM Processor,

    then look at the gerber file.  Try this with "pos. Coord" turn on, then

    again with it turned off.

     

    As you noted, the pick-and-place coordinates are correct because they

    were obtained through a means other than the CAM Processor.

     

    HTH,

        - Chuck

     

     

  • in reply to dukepro

    Chuck,

     

    Bullseye !!  Thank you very much!

     

    image

    Joaquim

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