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Re: Potential issues with oaa_ lib


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On 08/30/2010 09:59 PM, Lorenzo Marcantonio wrote:
> 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
That's an even better idea, but is there a way in kicad to store lines
on the comments layer within the footprint library? I can see why we
wouldn't want to contaminate the silkscreen with backyards (oh, I meant

>> 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...
You're doing good. I can't afford really big SCR's, and even if I could,
no one is going to give me 30A of AC power. I'd probably blow the fuses
in the entire building (Yes, we still use fuses, not circuit breakers
:-p ). The most I'm planning to tackle is 200A at 7V switched from the
AC line.

>> 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...
I like the resiliency of the copper traces. It takes some effort to burn
one off.

>> 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
Bungard offers a photoplotter that spposedly does the job, but I don't
like the need to scotch-tape the transparency to the roller.
Etching a 1-mil track... I honestly have no idea how they pull that one
off. And of course, by optical inspection, I'm assuming you mean
something else than an eyemetric inspection.

>> 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.
What do you use for generating the artwork? I need to stick two
transparencies on top of each other to avoid pinholes. And if I'm lucky,
I get horizontal lines of toner going straight through the board, just
asking for a nice cutter-job after the board is etched.

>> 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...
Nopo, I've never been told before that I take the path of most
resistance. :-)
You have some interesting footprints. Perhaps after Oyvind releases his
generator script, you may make some 3d packades for them.

To Oyvind:
The pins of the LEDs are on optical.brd are labeled incorrectly. The
anode (square pad) should be pin #1, but it's pin #2.
Also, it would be nice to have two versions of each LED. One that stays
a distance above the board, like the ones already there, and one with a
larger hole, where the base of the LED would touch the board (the
stopper on the leads would fit through the hole). The latter is the
configuration I use for making LED exposure boards. :-)
(sorry if I already said this; today is email-writing day for me, and I
lost track of what I said, to whom, why, and generally my purpose for being)


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