CP/M/CPM_CDROM.iso/cpm/gendoc/wirewrap.doc

Internet Message Format | 1985-07-01 | 17.6 KB

Date: Thursday, 27 June 1985
From: Larry J. Huntley
Re:   One-of-a-Kind Systems (LONG!  Ph. Nos., Addresses)

I tried to reach a lot of the people who contacted me by mail, but
without a lot of success, so I will now subject the net to this
volume of verbiage.  I know this is long and some of it is redundant,
but I'm trying to answer a lot of different questions which I got as
a result of my previous postings.  Have patience.


The cut-strip-wrap tools we have been using here are manufactured by
Swiss Precision, Inc in Palo Alto.  The representative goes by the
name of OEM Associates in Sunnyvale.

The one we're currently using is for 30-ga wire, and makes a modified
wrap (the first 1-2 turns of the wire have insulation on them.) It's
called "CSMW", part no. 23430.

I recommend you contact OEM (408/374-0381) so that they can direct
you to the representative or distributor in your area.  These things
are listed in the current catalogs (Contact East for one) but at
outrageous prices ($221.65.)  The last ones I bought came from
Coastal Marketing in Canoga Park; they were around $185.

There is one caveat -- you need to be careful concerning the wire
that you use with these bits.  If the insulation adheres to the wire
too well, you will get wraps where the wire is not completely
stripped, i.e. small strands of insulation will be wrapped around the
post along with the conductor.  Regular Alpha Wire 30-ga. Kynar
insulated wire-wrap wire seems to be okay.  There is a special wire
made for these bits called Ad-Wrap; it's made by (are you ready?)
Advance Wire Co. As Howard Hull noted, you do have to be careful as
to what happens to the ends of the wire that the bit cuts off.  Most
of the time it falls into the forest of pins and wires on the wiring
side of the board.  Sometimes it's just insulation, sometimes it's
bare wire. Turn the board over and tap these guys out every once in
while and be sure to visually inspect the board after wrapping.  Of
course, you do that anyway, right?

Now, on to back-force guns.  I don't know if these can be retro-
fitted onto existing guns, and if it can, if it's a factory
modification or not.  Since I found out about them, I have always
bought tools with the back-force nosepiece fitted.  I would call the
manufacturer of your particular gun and ask.  Once again, if you're
buying new guns, expect to pay about $10 additional for these
widgets.

Here are some phone numbers; I hope they are of use.

Swiss Precision Inc.            Gardner-Denver
415/493-0440                    616/842-0200
Manufacturer of the             Wrapping tools and Equipment
"Cut, strip and wrap" bit.

OEM Associates                  OK Machine & Tool
408/374-0381                    212/994-6600
Rep. for Above                  More Tools

Coastal Marketing               Standard Pneumatic
714/241-7112                    702/329-6311
Distributor for Hand tools      More w/w tools
and production Equipment

Advance Wire & Cable            Alpha Wire & Cable
415/592-4550                    201/925-8000
Makers of "Ad-Wrap" wire        Makers of wire

Contact East
617/272-5051
Seller of Tools and Equipment

(Some basic comments on wiring techniques follow)

Wire-Wrap:

The components are interconnected with (usually) 30 gauge or
(sometimes) 26 gauge silver-plated annealed solid copper wire.  The
wire is insulated with one of several plastics, usually Kynar.  The
insulation is stripped off each end of the wire and the bare
conductor is wrapped around a tin-or gold-plated socket/pin (post.)
The post is 0.025" square and is usually die-cut such that the
corners are VERY sharp and they "bite" into the conductor as it wraps
around the post.  This results in a phenomenon called "cold-flow"
where the wire slowly comes into more intimate contact with the post
with time.  Very reliable.  The average wrapped connection includes
8 - 10 wraps around the post, so you get about 40 gas-tight
connections on each pin.  The Military and computer industry use the
method extensively.

Wire-wrapping wire can be bought in bulk (on spools) or in pre-cut,
pre-stripped lengths ranging from 1" to 2 feet or so.  There are
completely manual tools (you cut, you strip, you spin the tool to
make the wrap), battery/A.C./pnuematic hand-held wrapping guns (you
cut, you strip, you pull the trigger ), semi-automatic wrapping
machines and fully automatic numerically-controlled (NC) wrapping
machines.  There is also a wire-wrapping bit made to fit into the
hand-held tools called "Cut Strip and Wrap" which you insert the end
of the wire into and as you make the wrapped connection it cuts the
wire to length, strips off the insulation and makes the wrap. Neat
and quick.  The people we have here who do this for a living like
them a lot.

Advantages:  Quick, relatively inexpensive, easy to repair or make
changes to the boards (unwrap tools are available), well accepted by
industry.

Problems:  Not really suitable for full-scale production because
unless each board is fully automatically wrapped, you have to
consider each board as a new entity; errors may have occurred in the
wrapping of the individual board and finding the errors on one board
won't help you find them on the next - they may not be there or they
may be different.  If a wire goes around a pin along its length
somewhere and is streched too tightly, the corner of the pin may cut
through the insulation, causing a short.  You won't be able to see
it, and even if you do a continuity ckeck of the board, just moving
it around may cause it vanish (temporarily.)  Best advice: use
wrapping vendors of good reputation and be wary of any board that
acts "funny."

Recommendations:  Go for the highest quality everything you can
swing.  The best sockets are made with machined pin/terminals with
spring inserts.  There are a few manufacturers that make boards with
pins permanently swaged into the boards; components plug into one
side of the board, wrapped interconnect is done on the other side.
Real neat.  If you intend to wrap things yourself, you're going to
have to practice.  It looks and sounds easy, but it's not. My hat is
off to the people who can do it 8 hours a day and go home and NOT
beat the kids and kick the dog.

Vendors:      Augat              Boards, sockets, pins.
              Mupac              Boards
              Garry              Sockets and pins


Slit-n-wrap:

Forget it.  A cheap version of wire-wrap where the extremely thin
insulation is slit by the tool as the wire is (always) hand-wrapped
around the pin.  Unfortunately, the insulation is also slit by every
other blasted thing on the board.  "The hobbyist's wire-wrap."  I
don't know of anyone, hobbyist or not, who has used it more than
once.  Once was more than enough.


Solder Wrap:

More of the same.  Extremely fine wire (32-36 gauge) covered with yet
thinner insulation and a coating of solder.  Wrap the wire around the
pin, cut it off, touch it with a soldering iron, and VIOLA!...a mess.
Basically non-reworkable, produces shorts if you look at it cross-
eyed. Save your money for beer and pizza or something better.


Scotch-somethingoranother:

This travesty was foisted on us by 3M, makers of cellophane tape,
Velcro, and numerous inhalable adhesives.  The sockets were a two-
piece arrangement where you install the body on the top of the board
and a tulip contact on the bottom.  The interconnect was made by
forcing solid insulated wire into the appropriate contacts, just like
telephone patch boards. 2 or 3 insertions was about the limit; after
that the wire just fell out, or worse, became intermittant.  Quick,
easy, fun, and junk.  Requires special boards, special sockets,
special contacts, special wire, and special tools.  Guess who you buy
this stuff from.


Multi-Wire:

A very nice system.  An epoxy-glass board is drilled to accept the
required component leads, plated thru-holes are made, and connections
are made to power and ground planes made of copper (0.001" or 0.002"
thick.)  A layer of adhesive is screened on and very fine wire (36
gauge) is routed to the appropriate holes to form the signal
interconnect.  Routing can be done on either or both sides.  After
the wire is routed, a solder mask is screened on and then the whole
assembly is cured to harden the adhesive and the mask. Now you have
the wiring sandwiched between the board and the solder-mask and held
in place by the adhesive.  Sockets can be used or contacts can be
installed in the holes or the components can be inserted directly
into the holes, and the board can be wave soldered.  Neat and clean.
The board is re-workable and the wiring can be impedance-controlled
for high-speed work. (I know of a 100K ECL system running at 100MHz
that uses Multi-Wire boards.) Twisted-pair conductors can be used.

Problems:  Not cost effective at small or very large volumes.  Enjoys
a middle position.  Probably best at the 500-piece range.  If you're
going to build 100 - 10,000 of something, talk to Multi-Wire.

Vendors:       Multi-Wire (A Division of Kollmorgen Corporation)
               Hitachi  (A licensee of Multi-Wire, apparently)
               Augat  (they call theirs Unilayer-II)


Printed Circuits:

The old standby.  With good reason.  Nothing can beat the performance
and reliability of printed wiring.  Unfortunately, it is not without
its problems.  Be prepared to pay a few thousand dollars to have
artwork made to have 10 prototypes built, at another few thousand
bucks, to find what is wrong with the artwork so you can start over.
If you have to build more than 1000 of almost anything and you aren't
using PC's (NOT Personal Computers -- Printed Circuits!), you need to
re-evaluate what you're doing.  I have had printed circuits built
that were double-sided, with plated thru-holes, gold-plated edge
connectors, with solder plating, about 6" X 8" that were less than
$20 in small ( q < 10 ) quantities.  If you can create your own
artwork and supply the fabrication shop with all the required photo-
tooling and NC tapes, the cost of a PWB can be disgustingly
reasonable.  In a university environment, a small PC shop could be
quite easily set up and support the needs of the CS, EE, Physics,
Industrial Engineering, and Physical Chemistry departments. Costs
increase with several factors.  If you need more density, you may
need more layers.  More layers calls for more dollars.  If you need
controlled impedance wiring, or fine-line lithography, or heavy power
planes, or strip-line structures, etc. etc., you get to pay more. All
in all, PWBs are the best solution when you can afford them and your
volume requires them.  The more you buy, the more you can afford, of
course.


Stitch-Wiring:

This works almost like wire-wrap, except that the wiring is not
wrapped around a square pin but is spot-welded to the flat end of a
cylindrical pin.  The wiring is run continuously from an inverted
cone-shaped "capillary" tool which allows you to locate the wire with
respect to the top of the pin.  A foot pedal then brings the tool
into contact with the pin and an electric discharge is triggered.
The pressure cuts through the insulation and the discharge welds the
now-exposed conductor to the pin. The tool can then be raised and
moved to the next pin in sequence, or the wire can be severed and a
new "trace" begun.

Advantages:  The method is fast, reliable,  and results in a board
with a very low profile.  The wiring is reworkable, but not very
often on the same pin.  Used a lot by the military.

Problems:  The equipment is pretty scarce, the pins are costly (gold
plating), and each time you have to pull a wire from a pin, you tear
off some of the plating.  This limits the number of times a wire can
be welded to the pin. If you have access to such a machine and the
required sockets and such, it's hard to beat for building one or two
of something.  Otherwise, it's out of reach for us humans.


Genuine Point-to-Point Wiring:

If you have to build one (1, unity, 1 each, only 1) of something,
it's really hard to beat point-to-point.  This is especially true if
it's the type of thing that is relatively simple and the design is
stable.  Put some sockets on a piece of Vector board, get a handful
of parts, some red, blue, green, yellow, black, and white wire (22
gauge, solid), some solder, wire cutters and strippers, band-aids,
can of Pepsi, beer, or spring water, bag of M&Ms, bag of Fritos,
trash can, aspirin, and a soldering iron and go build yourself a
circuit.  Keep a continuity tester around to see how you're doing as
you go along.  If you can get the so-called "Pad-per-hole" type of
board (has a copper pad surrounding every hole on the board, but
isolated from all other pads) you can solder the sockets right into
the board and then wire the leads to each other as required.  It may
not be neat, but it is the ultimate in reworkability and flexibility.
I have seen hand-built audio gear that sold for fabulous prices and
18GHz millimeter wave communications gear built this way. If you're
careful, it can rival PWBs in performance and reliability. Highly
labor-intensive, hardware hackers love it.  Most industry types
wouldn't think of it.  Radio amateurs have been using it for as long
as there have been radio amateurs.


Proto-Boards:

These aren't really a wiring methodology, but they fall into the
realm of hacking and cut-and-try design.  They are plastic blocks
with holes arranged in a 0.100" X 0.100" matrix that you push
component leads down into.  The holes are usually grouped into sets
of 5, so you get 4 common tie-points for every component lead.  You
then wire your circuit elements together with 20 or 22 gauge solid
wire.  You can change anything and everything.  Once you get the
circuit behaving like you want it, you go to one of the above
methods.  Or, if it's REALLY one of a kind, or a one-shot lab
experiment, you tear it down and build something else on the board.
Obviously, it's not a production, or pre-production, or prototype
method; it's sort of pre-prototype.  It's very useful, however, and
makes experimentation quite simple.  Proto-Boards are to hardware as
Forth is to software.  Look for them in hardware hobbyist catalogs.


Basic Recommendations:

For Experimenting:  Proto-Boards, point-to-point.

Building 1: Point-to-point, wire-wrap

Building 2: Point-to-point, wrap-wrap

Building 10: Wire-wrap

Building 100: Wire-wrap (as long as someone else is doing the wrapping),
              begin investigating Multi-wire or printed wiring

Building 500: Multi-Wire or PWB

More than 1000: PWBs


General Comments:

Regardless of the method used, the most common error made is lack of
attention to power and ground supplies to the board.  The rules of
thumb are simple: 1) Heavy gauge conductors, as many as practical  2)
Plenty of decoupling capacitance to keep the power supply lines quiet
3) Low inductance power supply leads 4) Well distributed power and
ground wiring.

Make a wiring list and spend some time doing the physical design of
your circuit.  I know this sounds trivial but it's easy to turn the
whole project into so much spaghetti without a little planning.  It's
also easy to turn the board into a near work of art with planning.
Use up a few sheets of a quadrille pad, and do it right.

Failure to observe any or all of these rules will only cause grief.
I saw a memory board where the write enable pulse vanished too soon
to ever write data into the memories due to ignoring 2 & 3.  On the
other hand, I've built wire-wrapped memory boards (BIG memory boards
- 22" X 16") that accessed in less than 35 nsecs and the pulses were
as clean as mountain water.  But I followed the rules.


Some Addresses:

Multiwire Division
Kollmorgen Corporation
3901 East La Palma Ave.
Anaheim CA 92807
714 632-7770

Hitachi Chemical Company America Ltd.
1333 Lawrence Expressway  Ste. 265
Santa Clara  CA  95051
408 244-2570

Augat Interconnection Systems Group
40 Perry Avenue
P.O. Box 1037
Attleboro  MA  02703
617 222-2202

OK Machine and Tool Corporation
3455 Conner St.
Bronx  NY 10475
212  994-6600

Vector Electronic Co. Inc.
12460 Gladstone Ave.
Sylmar  CA  91342-0336
818 365-9661

3M/Electronics Products Division
225-1 3M Center
N Saint Paul  MN  55144
612 733-7408


Books:  Bell Labs once published a 3-Volume set called "The Physical
Design of Electronic Systems".  It's great.  (I don't know anyone who
can understand it, but it must be great.  It's from Bell Labs.)  It's
also not the book for stuff like this.

Most of this stuff is half magic and half instinct.  I would
recommend trying to get subscriptions to trade journals.  Some of the
reasonable ones are "Electronic Packaging and Production", "Circuits
Manufacturing", "Insulation Circuits", "Connection Technology",
"Electri-Onics", "Micro-electronic Manufacturing and Testing", and
"Hybrid Circuit Technolgy".

There *is* a book called "Microelectronic Interconnection Methods" or
something like that around.  I think it was written for your basic
hobbyist ($9.95 paperback with slick front cover art having nothing
much to do with microelectronics or interconnections...)  I'll try to
track it down and determine real title and source.  That's the only
potentially reasonable book I can think of.  Unfortunately, not a lot
gets written concerning this topic.  Not very glamorous, I suspect.
More money to be made writing "Yet Another, Still Easier, Faster
Better, Effective, Upwardly-Mobile Guide to Using Lotus 1-2-3 (tm)
for The Management-Type with The Intellect of Your Average Crowbar."
Sigh.

'brd
--
Larry J. Huntley         Burroughs -(B)- Corporation
                       Advanced Systems Group   MS-703
                  10850 Via Frontera   San Diego, CA  92128
                              (619)  485-4544