yrdbrd@bmcg.UUCP (Larry J. Huntley) (06/27/85)
Well, finally.
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 insu-
lation 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 sus-
pect. 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
-*- "Dear Friends, It's 'ORGAN LEROY' at his organ again." -*-