Re: gEDA-user: PCB: coordinates and angles of the components

[Rick Collins <gnuarm.2006@xxxxxxxxx>]

   At 02:36 PM 12/2/2010, you wrote:

     On Thu, 02 Dec 2010 12:21:00 -0500
     Rick Collins <gnuarm.2006@xxxxxxxxx> wrote:
     > If the XYRS file output does not output proper centroids, I see
     this
     > as a major issue.  If they are not outputting the correct value
     for
     > asymmetric parts, how do you see the centroid being defined
     exactly?
     Most of my footprints are generated, and the zero point is the
     center of the
     package. I think they are OK for pick point.
     There are other footprints, which I made manually. In that case, I
     imagine the
     best pick point and I put the zero point there.

   I'm not asking about the pick point.  I'm asking about the centroid.
   They are completely different things.  As I think I said, the centroid
   is to tell the assembly house where to put the part.  The pick point is
   a point on the part where the machine will attach the nozzle and has
   nothing to do with the position where the part is to be placed.
   Further, regardless of how you set your files, the pick point is
   selected by the assembly house to optimize how they pick the part.  You
   have no way of knowing where this will be.
   The centroid needs to be a spot on the part that everyone knows without
   requiring it to be explained.  Unfortunately for oddly shaped parts, it
   does not seem to be well understood how to select the centroid.  One
   document I have from "Screaming Circuits" says it is the center of the
   part including the pins and the body.  I have yet to be able to find
   this info in an IPC document.  The IPC document seems to leave out some
   other important info about rotations.  You would think they would
   figure out this is a problem and fix it...
   I can't say if your centroids will give you trouble, but from what you
   are telling me, you are not defining them correctly.  From what I have
   read, I'm not sure PCB does it correctly either.  I found some
   references on the web that says they use the geometric center of the
   pins not including the package.  I don't think that is right.
   Screaming circuits is not the ultimate reference for defining how this
   is to be done, but they have a document that covers all the bases and
   is easy to understand.  In fact, when I pointed out that they had a
   discrpancy with the IPC docs, they immediately fixed it and put the
   updated doc on their web site.  [1]www.screamingcircuits.com
   Rick

References

   1. http://www.screamingcircuits.com/


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