Re: gEDA-user: gEDA for mass production?

[Randall Nortman <geda-lists@xxxxxxxxxxxxxxx>]

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


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