Gregg Eshelman wrote: > 'Course the easiest fix would be to get the boards made to a higher > standard and use a mechanical alignment jig so the system doesn't have > to compensate for errors. > You can't trust the outer dimensions of the board to match the traces. They are done on different machines, so there is an unavoidable alignment shift. It is common practice to put alignment fiducial marks on the boards. Even my old Philips pick and place machine has a sensor to pick up these fiducials and align the placement to that. But, I'm surprised at the large dimensional variations. I make solder paste stencils myself, and trust that the boards will match quite closely. I have done boards up to 9 x 11 inches (230 x 280 mm) and if there was more than a few thousandths of an inch error over the whole size of the board, the paste would be visibly off. I think that comes out to about one part in 2500 or so.
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