On Mon, 2011-02-21 at 15:23 -0700, Russell Dill wrote: > I'm starting a new design and all my components are metric based, > including a few 1mm pitch BGA components. I'd really like to do the > layout in metric, but I'm worried about two factors. The first of > which is that PCB does not yet have the option to store things > internally in metric (at least from what I understand) so rounding may > occur on that end. In addition, my board house rounds everything to > 2.4 format (0.1 mil). I can envision several scenarios where my design > meets DRC in PCB, but fails when I send it to the board house. > > What is my best option? > > Just use imperial units and cope with weird grids? > > Use metric spacing, but recalculate DRC based on worst case rounding? > > Some other option? >
Use metric grid/unit, I guess most of us use that. Internal resolution is 0.01 mil, which is good. Of course nm would be better. One problem for me was, that a few 0.01 mil garbage lines were generated for the layout. Not a big problem. Some not really smart people have tried to use a very very fine grid, 0.01 mm or so. That is like using no grid at all, I call that silly. Try to use a useful basic grid like 0.25mm grid if most of your parts have 0.5mm pitch -- I think that was what I did, I am not sure. Important: Enable snap to pads/pins, so you can make good connections to imperial parts which are not on the metric grid. >my board house rounds everything to > 2.4 format (0.1 mil). Strange -- so pitch of metric parts may vary from pad to pad a bit. That was a problem in very old days of PCB, when 1mil internal units was used. _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
