Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site geowhiz.UUCP
Path: utzoo!linus!philabs!cmcl2!seismo!uwvax!geowhiz!karsh
From: karsh@geowhiz.UUCP (Bruce Karsh)
Newsgroups: net.arch,net.micro
Subject: Re: How to fab One-Of-A-Kind systems?
Message-ID: <183@geowhiz.UUCP>
Date: Tue, 7-May-85 19:57:20 EDT
Article-I.D.: geowhiz.183
Posted: Tue May  7 19:57:20 1985
Date-Received: Fri, 10-May-85 20:33:23 EDT
References: <202@ganehd.UUCP>
Organization: UW Madison, Geology Dept.
Lines: 56
Xref: linus net.arch:968 net.micro:8980

> 
> I want to build some one-of-a-kind stuff to try out ideas on
> parallel systems.  My first question is how should I
> fabricate the equipment.  While this may be an easy question
> to answer for production design, it is not so easy for a
> OOAK system.
> 
> My choices are:
> 
> 1)        wire wrap
> 
> 2)        make a pc board
> 
> I don't like (1) because of reliability.  I understand that
> as wire wrap ages it develops the flakies.

  I disagree.  Wirewrap is more reliable than hand soldered pc
boards.  We have instruments which we use in our field operations
that have both pc and wirewrap boards in them.  These boards
are subject to a lot of vibration and temperature cycling.  The
wirewrap boards are much better than the pc boards.

  The wirewrap boards are also more dense than the pc boards.

  The reason that wirewrap is so reliable is that:

    1) The wire is held under tension against the post.  That
       keeps it from falling off due to thermal expansion/
       contraction.

    2) The corners of the posts are sharp and form an airtight
       connection with the wire.

    3) Since there are 4 corners on each wirewrap post, and about
       8 wraps, there are 32 connections per post.  Thats a awful
       lot of redundancy.  It is very unlikely to fail.

  For one of a kind projects and small production runs, wirewrap
is hard to beat.

  A good reference is a publication called Wire-Wrap from The 
Cooper Groop, PO Box 728 APex NC 27502.  (919)362-7510.
Catalog No. 55548.  This goes into the materials science aspects
of wire wrap.

  Of course, if you don't do the wraps properly, it won't work.  But
it's pretty easy to do right, and a proper wrap has about 100,000 
lbs/sq in of contact force.

  Wire wrap is covered under mil-spec MIL-STD 1130.
-- 
Bruce Karsh                           |
U. Wisc. Dept. Geology and Geophysics |
1215 W Dayton, Madison, WI 53706      | This space for rent.
(608) 262-1697                        |
{ihnp4,seismo}!uwvax!geowhiz!karsh    |