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From: deanr@sco.COM (Dean Reece)
Newsgroups: sci.electronics
Subject: Re: PCB vs. wirewrap
Message-ID: <3767@scolex.sco.COM>
Date: 13 Nov 89 20:47:35 GMT
References: <850@carroll1.UUCP>
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Reply-To: deanr@sco.COM (Dean Reece)
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Organization: The Santa Cruz Operation, Inc.
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In article <850@carroll1.UUCP> dnewton@carroll1.cc.edu (Dave 'Post No Nicknames' Newton) writes:
>
>   I don't like routing PCBs by hand, but I don't like wire-wrapping large 
>boards either.  (Manual tool at this point)
>   Is either one of them better?  I've heard that a lot of critical circuits
>are wire-wrapped for reliability.  Is this true?  Is wire wrap harder to debug?
>
>   Just wondering.
>
>   Oh, can anyone recommend a cheap auto-routing PCB design package?

Well, I've experimented with several techniques and my favorite is still point
to point wiring using 30 guage wire-wrap wire.  Its sloppy looking, but I find
it easier to debug/correct/modify than either wire wrap or PCBs.  The only real
problem I have with PCBs is the ammount of time it takes to lay on out.  I need
several layers, or lots-o-feedthroughs, so I came up wuth an alternative:

Figure out how many layers you really need (usually 1 or 2 for power and 1 or
2 for busses & signals)  Lay out each layer and produce a drill pattern.  Drill
as many SINGLE SIDED PCB Blanks as layers, (do this by drilling all of them at
one time, or you'll never fit them together) then etch each PCB with a layer.
You can then use wire wrap sockets to assemble the thing. (You solder one layer
on at a time.) If you want to get fancy, you can make the TOP layer (component
side) a double sided board, which allows Double sided Edge card connectors,
and/or better shelding.  One nice side effect is that you can leave some of
the Unknowns out of the design and wire-wrap them later, since you'll have
about 1/2" of the WW pins remaining.

This hybrid idea works well (unless you goof on an internal layer) since you
don't have to work so hard to keep the paths on 1 or 2 layers only.  I usually
made the top layer a double sided board with connectors and power busses ONLY.
This way, the decoupling caps need only go as deep as the 1st board.  The next
board or two were the 'simple' paths like data and address busses.  The outer
layer(s) were for the more complex (read: likely to be wrong) connections.
Sometimes this outer layer was omitted and done only in Wire Wrap or point
to point.

Well, thats my 2 cents worth - hope it helps - I would be interested in other
ideas for simple, single unit production.
 ______________________________________________________________________
| Dean Reece     Member Technical Staff |"The flames are all long gone |
| The Santa Cruz Operation 408/458-1422 | but the pain lingers on"     |
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