Re: gEDA-user: How to make a foot print

[Colin D Bennett <colin@xxxxxxxxxxx>]

On Wed, 29 Dec 2010 12:45:14 +0100
Levente Kovacs <leventelist@xxxxxxxxx> wrote:

> On Wed, 22 Dec 2010 17:29:24 -0800
> Colin D Bennett <colin@xxxxxxxxxxx> wrote:
> 
> > You are not alone.  Making footprints in pcb takes a lot of
> > practice, for me a least.  I have made many footprints in pcb over
> > the past couple of years and still I have to refer to guidelines,
> > if I haven't made a footprint for some time and have gotten rusty.
> 
> I recommend using footprint generators for the majority of the
> footprits. I use the footgen.py python script.

Actually, I am impressed with the flexibility of your footgen.py
script.  It looks like you've created many different types of
footprints using it.

However, unfortunately for me at least, I cannot use it for "the
majority" of my footprints.  Most of my custom footprints require
individualized design.  For instance:

- SMT LED footprints with special oversized pads as specified by
  manufacturer for thermal dissipation.

- FFC/FPC connector, proprietary 1.25 mm SMT header, etc. with special
  extra pads for mechanical support, and silk screen indication of
  reference pin (e.g., arrow for pin 1).

- SMT aluminum electrolytic capacitors, two-pin polarized devices that
  should have special silk screen including a beveled corner and "+"
  symbol by one pad.

- Illuminated push-button, 5 pin through hole with non-standard pin
  arrangement.

My point is not to take away from the usefulness of your script, but to
show that many footprints (I would even say "most") require manual
design for the best results.  The tool, pcb, should make this easier
and faster for users.

For me, the most difficult part of drawing a footprint in pcb is getting
various dimensions from part specifications into the pcb drawing as I
create a footprint. If pcb had a dimensioning tool that could place
dimension measurements on the drawing as one is working on it, then
that would make my job much faster.  As it is, I always sketch the
footprint by pencil on graph paper and figure out dimensions from there
based on part specifications, then transfer these into pcb as I draw,
making heavy use of the Ctrl-M measurement tool.

I will say that I am getting much more confident and much faster at
creating footprints in pcb as I gain experience with it, and I'm no
longer scared when I face a new part with an odd footprint. :-)

Regards,
Colin


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