A fella here at work leaves his via grid at 'none' which allows him to place his vias out to our system extents of .01 MILS. It tried to explain to him that he should keep it on some user defined grid of 5 MILS or maybe down to 1 MIL. He said Why? I tried to explain the drill machine would be more accurate along with the fact that if you use the via as a testpoint it needs to be on a more robust grid. He said that was maybe true years ago but not anymore. DOes anyone have a beeter reason than my 'because that's how I do it!' answer? Thanks!
There is really no reason to stay on a larger grid, unless your manufacturer is REALLY having problems. If your fabrication drawing is calling out a GDT tolerance of .003 true position (pretty standard) it really doesn't matter if you are on a 1 mil grid, or a .1 mil grid, or a .01 mil grid since they are _ALL_ smaller than the actual drilling tolerance. Same with most test fixtures, the main constraint is keeping the probes far enough apart, not their absolute placement. Sorry I can't provide your amunition