At 02:36 PM 12/2/2010, you wrote: On Thu, 02 Dec 2010 12:21:00 -0500 Rick Collins <gnuarm.2...@arius.com> 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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