23 Oct
1999
23 Oct
'99
12:36 p.m.
-----Original Message-----
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu>
Date: Saturday, October 23, 1999 4:51 PM
Subject: Re: OT: how big would it be? - PCBs at home
I am reliably informed that the persulphate etchants break down if
overheated. You might want to watch this (<50C?)
> ><things like getting track widths right (!), which really messed up some
of
By which point you might as well have done the darn thing yourself...
I rarely do a board JUST for prototype/experimental reasons. Most of my
boards end up in production so it's a lot easier to iron out the bugs in the
prototype stage for production. I take it you do mostly one-off experimental
stuff.
Been there, done that.
after
The idea of prototype to me is have the "ideal" conditions. Boards with
these problems are easy to find BUT many intermittant problems can come from
them. Ie: move the board and it craps out.
> >Most shops cost a
> >fortune to drill and etch a 10x8 card with a quantity of 2. Wire wrap
for
> >this design is out of the question.
> >
>
>
> Sounds like you folks have been quoted a lot higher than I am paying for
> prototype PCBs (if you had them done in a shop). Could be your the lack
of
Well, you seemed to be implying you got them done for $1 or something
(you claimed no set-up charges). I've never heard of pricing like that
for one-offs...
Of course not.. on a small board like that... usually a $100 for 10 or so.
I have never paid a set up fee. Again, most shops will. I got lucky. This
shop and I have done quite a bit of business and I have helped him get some
solder fountain equipment for his tests...
I get an excellent rate... and it makes my prototypes boards bug free. I
like that!
<I've found that the typical 'cheap' hobbyist's setup (disk of FeCl(3),
Ferric Chloride is awful. If I *have* to do a quick small one-off board I
use very hot Ammonium Persulfate. > ><the striplines. We even had boards come
back with the layers in the
wrong
<order. We _very_ quickly learnt to (a) check
everything and (b) do the
<prototype ourselves if at all possible, to ensure the basic design was
<sound...]
I know, on critical strip line work I sit down with the guy and we double
check the widths on the film. I learnt years ago that if you have to check everything
that somebody
else (PCB house, etc) is doing at every stage, then quite simply it's a
lot faster and less hassle to do it yourself..
>
> That's my point exactly. I just don't have the time anymore to screw
around
with bad
etches... even good etches can be bad in one small place causing
A lot of minor faults can be patched over for prototypes...
all kinds of
grief. I've had boards that we did in house that had
*microscopic* traces either shorting two pins or jumping two traces
together. I had one short so fine once that I could not see it by viewing
the board through light... I found it with a meter!
I've had boards come back from a PCB house with a note saying that
they've checked them against my netlist. And I've _still_ had internal
shorts (which _weren't_ in the netlist).
I got to the point of checking for real nasties (power-ground shorts,
etc) with a meter, and then populating them, checking as I go. Quite
simply, if you don't know what effect a short or open will have on your
design then you don't really understand the design in the first place.
But as ever, you check things a little at a time.
>
> And don't even get me started on those pre-sensitized boards... I've had
> many with hair line cracks in the coating which causes LOADS of grief the board is
done and sometimes when the board is bent. :-(
Hmm... Again, _for prototypes_ you should know just what effect such a
crack would have. And then you can easily fix it (the signal reflection
at a small repair like this will cause no problems at all!).
Almost every board I have been involved with has been
an experimental
design/prototype. So cut-n-jumper mods are occasionally necessary anyway.
Fixing PCB problems (which are _NOT_ common in my experience on homebrew
boards) is no great hassle.
Okay that's different. I design products, final stuff. I design a board,
have about 10 prototypes knocked out.. sometimes some minor changes are
made, then it goes to production. My own prior company (outside my current
employer) did lots of this work so after a few prototypes were assembled I
would send the job to Taiwan with a schedule. I try to wirewrap when
possible on experimental type stuff but nothing beats quick PCBs.
Again, depends on your pocket $$, application, turn around time, and if it's
a hobby or serious $$.
-tony