Yeah, the through-hole version was one of my early tests; photoresist, 50
mil large traces, etc. Imagine a caveman drawing with a wax crayon.
The SMD was done solely with toner transfer. You can't see the traces but I
can tell you it's pretty compact. I might have been able to save a 1/2" of
surface area, but I couldn't make that board 1/4" shorter. I have to
contend with the size of the piggy-back circuit and making sure it does not
stick out the PCB area. I used 10 - 20 mil traces with equal spacing;
trying to squeeze out more space would have been an exercise in wasted time
(for my application).
That engine block paint is really good. I used the top brand which can take
a LOT of heat (more cure = more heat resistance), but I'm sure the cheaper
brands would have been adequate for our purposes. The only curing I did was
when I passed it through the laminator during the toner transfer. I can't
wait for something to dry and I smudged my fingerprints on a few places.
With proper drying and curing, I'm sure this paint would yield perfect
results.
Yeah, the masking is a pain. That's why you'll notice I took shortcuts, I'd
cut strips of tape whenever possible. I totally covered the SOIC
components, I didn't want paint under the belly to lift the IC in the air.
Look at the bottom row on both sides, I just masked everything in one
streak. Basically I wanted to have paint wherever I was going to have
silkscreen. The board is tinned so some exposed areas is not a problem.
Masking is dangerous 'cause I used an exacto to cut the tape; too much
pressure and you can cut/damage a trace. Ideally, I'm still looking for a
'gel' that I could plop on the lands, spray paint the PCB, let dry and then
wipe with a towel leaving the lands exposed (the gel preventing the paint
from adhering to the lands).
Robert
:)
-----Message d'origine-----
De :
Homebrew_PCBs@yahoogroups.com [mailto:
Homebrew_PCBs@yahoogroups.com] De
la part de Stefan Trethan
Envoyé : avril 13 2006 15:58
À :
Homebrew_PCBs@yahoogroups.comObjet : Re: [Homebrew_PCBs] Surface mount VS Through-hole comparison
On Thu, 13 Apr 2006 21:46:02 +0200, Robert Hedan
<
robert.hedan@...> wrote:
> Files:
>
> --------
>
> PCB size SMD.JPG
>
> PCB size non-SMD.JPG
>
>
> These pics are to scale
Well, these pictures more or less show that you can waste space with
either technology ;-)
I'm sure you could make the THP pcb the same sice as this smd one if you
really had to...
But i really like the engine paint idea for the legend, i must try that
one of these days.
If only one wouldn't need to mask the pads....
ST
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