Hi Dan and all, For the DXF exporter I'm currently coding, I use the centroid X,Y-value (as in the BOM exporter) as the insertion point for the 3D model of the package involved, in a mechanical CAD package (for example AutoCAD).
For symmetrical and double symmetrical packages (> 99% of all packages) this should be no issue as it coincides with the center of gravity. The problem lies in assymetrical [PGA, BGA, SIL, TO, connectors, ...] packages where the centroid (a calculated average X,Y-values of the actual existing pins/pads on the package) does not coincide with the center of gravity of the package (basically for X and Y values, since pcb has no notion of Z values). This asymmetricallity arises from pins/pads missing in the pattern, or shape of the connector (pin/pad pattern). IMO it would be a good practice to use the center of gravity as a mark/insertion point for pcb footprints/3D models. Now, there are a lot of footprints out there, and we do not want to break _everything_. So, this [should, could] be solved by using the mark X,Y-values in the DXF exporter and _not_ use the calculated centroid X,Y-value. However, a question that comes to mind is whether anyone is actually using the XY file for "pick and place" of components ? Positive feedback ? (from list members who actually use this feature). If not, it's not lean to _allways_ provide a centroid file, that is, there probably should be a checkbox to be ticked in the BOM exporter if someone _really_ needs this file (default set to unticked). I think I can send a patch if needed. Kind regards, Bert Timmerman. -----Oorspronkelijk bericht----- Van: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Namens Dan McMahill Verzonden: donderdag 8 maart 2007 5:05 Aan: gEDA user mailing list Onderwerp: Re: gEDA-user: PCB Element for a Molex 71661-2068? Ben Jackson wrote: > On Sat, Feb 24, 2007 at 08:31:42PM -0500, John Luciani wrote: > >>On 2/23/07, Ben Jackson <[EMAIL PROTECTED]> wrote: >> >>>I need a PCB element for a Molex 71661-2068: >>> >>>http://www.molex.com/product/micro/71661r.html >> >>I've placed the Molex 71661 series connectors on my website at >> >>http://www.luciani.org/geda/pcb/pcb-footprint-list.html#Connector > > > I was playing with strategies for escaping the pin grid on this part > (the board I'm connecting to uses a different brand of this style > connector which has the odd/even alternation inside out, so all the > signal pins are "inside" on the Molex version). I noticed that the > Mark for this part does not fall on a nice offset from the pins, so it > is impossible to move the part so that the pins fall on the grid > without going off-grid with the Mark. > > Is this to meet a pick & place requirement that was in the datasheet, > or is the Mark arbitrary? The mark is not used by pcb when generating the pick and place file. The center of the part that goes in the XY file is the common centroid of all the pins/pads. -Dan _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user _______________________________________________ geda-dev mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-dev
