On Mon, Dec 03, 2007 at 02:28:13PM -0600, John Griessen wrote: > Stefan Salewski wrote: > > Hello, > > > > til now I only did hand soldering of prototypes. > > > > But I am curious, can gEDA (pcb) data be used for automatic placement > > and soldering of boards? (This may be a stupid question, but currently I > > do not know which data board manufactures use for placement of devices.) > > The footprint origin is available and can be gotten somehow -- I have not > done it yet. > You will need to make your footprints compatible with the process; probably > all > with origin at pads centroid, or if you know there is an optimum grab > point on top of the package that is not at footprint centroid, make sure that > package > has its origin there.
I have only gotten as far as getting quotes, and for that the gerbers, BOM, and xy file were adequate. I think that because of the lack of any standard for defining the centroid and rotation precisely, assemblers are used to using the provided information as a starting point with manual review. I envision a simple CAD tool that includes a database of package dimensions and takes gerbers, BOM, and an xy file as inputs. A little manual intervention lets the tool find the correct package for each part number in the BOM, and then uses the xy file to draw a shadow/outline of the package over the gerber. The operator adjusts position and rotation manually. If the tool is smart, it will rember the postion/rotation offsets for that particular footprint and use them as defaults for any other parts of the same footprint. I don't think this would take long, and the assembly quotes I got all included NRE (non-recurring engineering) charges which would more than pay for the half an hour of labor to do all that. (NREs also included stencils and "frames" that hold the boards in place through the process.) If the industry has its act together enough to make that fully automated, I'd be surprised and pleased. I think that small-quantity prototype assembly doesn't even bother with all that and uses manually-guided pick and place machines. Those would presumably zoom to the coordinates provided in the xy file but then the operator finishes the job with a joystick. I will know early next year what it takes to actually go beyond the quoting step. I should also note that many of the shops I got quotes for wanted to handle getting the boards fabbed as well. They outsource this -- usually to Advanced Circuits/4pcb.com for low volume -- but I think they like to get their hands on the gerbers to adjust things like soldermask aperatures to fit their own particular process -- including the properties of the solder paste they intend to use. They also have to manufacture stencils appropriate for their process -- I doubt they just use the paste layer unmodified, since the ideal aperature depends entirely on the type of paste, stencil thickness, etc. The shops specializing in low-volume prototype assembly (which I think is largely manual) were happy to allow me to provide the boards. They still made the stencils from the gerbers. -- Randall _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
