Homebrew PCBs

Wow! That was quite a thing!

73,

Todd
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K7TFC / Medford, Oregon, USA / CN82ni / UTC-8
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QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design


On Sun, Apr 7, 2013 at 2:14 AM, Boman33 <boman33@...> wrote:

> **
>
>
> Todd,
>
> The panda is real. I had an opportunity to play with and feed seven of them
> in China.
>
> Bertho
>
> From: Todd F. Carney / K7TFC Sent: Sunday, April 07, 2013 04:54
>
>
> On Sat, Apr 6, 2013 at 11:53 PM, Boman33 <boman33@...
> <mailto:boman33%40vinland.com> > wrote:
> >
> > As I wrote, I know it works but the question is why.
>
> Mine is not to reason why, mine is but to do or . . . hey, wait a minute!
>
> Actually, I suspect the viscosity and surface tension of the emulsion has
> something to do with how the spin-coating method works. It may also be that
> it does end up thinner the farther it gets from the center, but that it
> doesn't matter given the use and the pretty-course image resolution
> required. Back then, I found myself more concerned about the thickness of
> the copper than of the emulsion.
>
> The engineers I worked for had always used 2oz copper clad, and that's what
> they wanted me to use. I wanted to use 1oz copper because a) I could get
> more yield from the etchant, b) it etched faster, and c) because it etched
> faster I could preserve fine lines much easier than with the thick 2oz
> stuff. If etching takes too long, it begins to undercut the traces and then
> the resist flakes off on the edges of the traces for that reason. Thin
> traces, such as dogbones or "sneak-throughs," would just get torn up. But
> it didn't matter how much data or how many calculations of current vs. temp
> rise of traces of thinner clad, they insisted on 2oz. Neither did it matter
> that industry standard by that time (1984) was 1oz except for special
> applications. Even Coombs the Revered (author of the standard text on pcb
> design) could not move them.
>
> I was able to ramrod the abandonment of the spinner/liquid emulsion hassle
> and we started using laminated dry film. In that small industrial setting,
> spun-and-flung liquid emulsion was a real bother, but for the hobbyist I
> think it's not a bad idea, as long as you can put a spinner together for
> next-to-nothing. At some point, the cost of the apparatus (along with the
> minor hassle) and the emulsion chemistry makes presensitized pcbs a much
> better value (and much easier, too!).
>
> Just curious: is that a real panda in your avatar picture?
>
> 73,
>
> Todd
> ----------------------------------------------------------
> K7TFC / Medford, Oregon, USA / CN82ni / UTC-8
> ----------------------------------------------------------
> QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design
>
> [Non-text portions of this message have been removed]
>
>  
>


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