kicad-developers team mailing list archive

[Lorenzo Marcantonio <l.marcantonio@xxxxxxxxxxxx>]

On Mon, 30 Aug 2010, Alex G wrote:

> But, we may take the size of the courtyard and draw a circle on the
> silkscreen. This would help with positioning footprints such as mounting
> holes. Not exactly standard-ish, but should help kicad users understand
> not to put anything else there.

Of course, that's a good idea. I use the comment layer for "keep out"
zones (like the antenna clearance for radio modules).1

> So if you have a 700V line, you will most likely put it in a net class
> with huge clearance, and kicad will take care of you (at least it _should_).

Last time I did it worked correctly. A sick board with 240VAC switching,
about 30A of pulsed load on the incoming 24VAC rail *and* thermocouple
conditioning. Incredibly I successfully decoupled the thermocouple
signals from the switching transients from the really big(tm) SCRs...

> Personally, it's 0.25mm clearance, and the smallest track I ever did was
> 0.4mm. This with a 1200dpi printer, UV LED's for exposure, and Bungard
> pre-sensitized boards. I don't know what process Oyvind had in mind when
> designing the footprints, but this is definitely an interesting point to
> consider. So for an 8mil, it should be a 7.4mm pad with 0.2mm clearance,
> right?

Correct. Bungard user too:D I like their blue resist...

> Jurgen Bungard (the big boss of Bungard) told me in an email that their
> pre-sensitized boards can go down to 1 mil. I don't know if any
> manufacturer actually supports this. For me the problem is the artwork.
> I daren't go below 0.25mm tracks of fear that imperfections will eat
> away the track.

Probably you could do it with direct laser imaging or really goods
phototools (they go up to 4000dpi IIRC). But the etching would be really
critical, and probably only with spray etchers to keep the etchant
circulating. And of course optical inspection on the bare board:D

> Anyway, back to the point, for a component such as a DSUB connector, it
> makes sense to consider an 8mil process, while for other finer-pitch
> components, we have no choice but to go lower than that.

I use 8mil process up to 0,50mm pitch. For finer things (or a lot of
tracks under BGAs) 6mil is mandatory.

> Time to try my skills at cut'n'pastin' components into libraries.

Or just load connect-1.brd from my modules if you checked them out...

--
Lorenzo Marcantonio
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