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