-----Original Message-----
From: Allison J Parent <allisonp_at_world.std.com>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Saturday, October 23, 1999 12:19 PM
Subject: Re: OT: how big would it be? - PCBs at home
><> Making PCBs at home is a ridiculous waste of time. I have a vacuum
lightb
>
>No it's not. Right now I'm doing a design that requires two sided and
>design rules down to 10mils.
Most of my designs are 10mil clearance. My PCB maker *likes* 10mil
clearance.
> There are three flat packs <64 pins and
>and daughter cards for more. The worst part was drilling the 2000 holes
>and a 3axis NC machine (home grown is not that hard).
Yuck.
>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
volume production in the past...I guess it depends what your time is worth
and the type of project. I'll still knock out quick single boards for
patches or small circuits. I do a lot of RF and high speed (50Mhz) design.
><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.
><modelmaker's drill, rub-down transfers or a pen as the resist) is a total
><waste of time and energy. But the above stuff, which is easily possible
><to consider for serious home use (remember the sort of tools and test
><gear that I tend to own...) is certainly useable.
>
>I've done boards that way too. Even hand drawn simple RF layouts on the
>board with a SHARPIE pen (solvent based marker pens) for one ups.
>
I haven't tried that. I use Protel for everything.
><After a bit of practice, we could easily make striplines for ECL and/or
><RF stuff, SMD boards (no problem at all with SOICs, PQFPs, PLCCs, etc),
><and of course conventional pin-through hole. The ECL stuff clocked at
><200-300 MHz as well.
>
>The real trick is fine line stuff.
>
><[As an aside, we found some PCB companies were remarkable _bad_ about
><things like getting track widths right (!), which really messed up some of
><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.
>
>There are plenty of things that can really mess up an otherwise good design
>and bad etchs are hell to trace in when bring up for the first time.
>
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
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!
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 after
the board is done and sometimes when the board is bent. :-(
john
>Allison
>
Received on Sat Oct 23 1999 - 12:10:33 BST