Re: gEDA-user: Has anyone used SSOP28.fp?

[Dave N6NZ <n6nz@xxxxxxxx>]

DJ Delorie wrote:
>> a) pcb paste layer gerber is directly from the pad layer, and I
>> think in many cases that lays down too much solder.  I haven't
>> experimented enough to be able to say for sure.  I'd like to see
>> some paste layer control added to the footprint definition.
> 
> I have a post-processor that sets the paste based on the footprint
> (name and pad; some footprints get paste pushed out, some are
> centered, etc).

That would be useful.  Care to share it?

> 
> But yeah, at some point we need to modify the footprint data structure
> to have independent paste/mask control.

What are the barriers to that happening? I presume that a file format 
change for footprints is a Big Deal.

> 
>> b) My current method for prepping a file for the laser cutter is a bit 
>> of a kludge.  Ideally, I'd like to see the gerber previewer have the 
>> option of exporting .dxf of the pad outlines from the paste layer.
> 
> If you can provide a format that's ideal for your tooling, plus the
> rules for tweaking, we can write a custom exporter for it.

All my tools are DXF based. I used QCAD for viewing/tweaking, and I 
wrote a DXF to Epilog converter that uses QCAD's I/O library. 
Unfortunately, while it is easy to write a .dxf reader (because you can 
ignore lots of the file) it is much harder to write correctly, since you 
have to include all the boiler plate and set-up in the correct order 
with correct semantics.  The QCAD library does simplify that somewhat, 
however.

In the end, All I look for are lines and arcs.  So just about any 
sensible format for pad outlines expressed as lines and arcs with X,Y 
coordinates should be usable.  I looked briefly at trying to interpret 
the Gerber, but decided I had better things to do.

> I was thinking of this number.  Pololu uses 3mil mylar, and specify a
> 10mil minimum hole size.
> 
Interesting.

I'll have to do more experiments to understand my tool limits.

-dave


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