About Wire Wrap

(Vintage December 1994. A compilation of multiple postings)
(references at end of article updated 8/18/2004)

John Hodgdon (or maybe gregh) asked:

Can someone explain the basic premise behind wire-wrapping? I've built things on breadboards and even made a few simple PCB's with etch-resistant transfers, but every time I see wire wrap tools and such, I look at them and go... now what the heck would I do with that?? Are you just wrapping the wire around pins on the bottom of a board, and then connecting the necessary pins that way? That would sound like a nightmare to debug if anything went wrong...

Philip Freidin responded:

As a veteran designer and builder of home computers, I believe there is no better way for a hobbyist to build anything with more than a few chips in it. Basically, wire-wrap is the wrapping of silver plated wire around square pins. For typical hobbyist use, the wire can be pre-cut and strip wire, that is 30 AWG, and the pins will be .025 inch pins. You can buy wire-wrappable sockets for almost any digital chip, or conversion sockets for weird stuff like surface mount chips. The board you put the sockets in is usually just a grid of holes with maybe ground and VCC bussing. Some boards have ground and VCC planes. I use a rather expensive power wrap gun, and have done over 300000 connections with it, and all connections are perfect. (If the wrap was not good, I took it off and did it again with new wire). (the 300000 is an estimate :-)

Big rules are: Use a tool that does 'modified' wraps (1 wrap of insulated wire, followed by about 10 wraps of uninsulated wire. Never re-wrap a wire you have unwrapped. Put in all your level 1 to level 1 wires first, then the level 2 to level 2. The only level 2 to level 1 wire should be at the end of a chain. If you follow this rule, you never have to take off more than 3 wires to make a change. Check everything twice. Put in all the decoupling caps first, before you wrap, and solder them directly to the power and ground pins of the sockets.

Keep good documentation

I will write about some of the computers I have built in another article.

(I also give wire-wrapping classes for friends :-)

Adam Eberbach responded:

Yes, wire wrap is pretty evil, but we owe those mad scientists a lot. For anyone who hasn't tried it, you should go out and get a reel of wire wrap wire - there is nothing better for hookup in any prototyping system. The OK' stuff I have now strips easily, seems to tin itself happily and if you trouble to bend it into place it stays there. I think they call it 'kynar' or some proprietary name? Anyway, the strippers you can get for this stuff make everything easy. Right now I'm working on a 68302 project which uses a 132 pin QFP CPU - wires take every pin out to larger stripboard tracks, where I can solder without squinting.

Dexter McNeil responded:

One quick note about wire wrap wire being used for other purposes: the Kynar insulation used on 99% of all wire wrap wire is piezo electric! Digital gear that sits in situations were it's not exposed to much in the way of vibrations is ok, and so is simple analog. However if it is a moderately high vibration application, or (for the audio nuts among us, me included) audio applications, it will generate small to medium voltages in response to the vibration. I found this out last spring trying to build some touch sensors for a project for my girl friend. I had taken about 8 feet and zigzagged it across the surface of a piece of copper clad board. After blowing the FET opamp input that was supposed to sense the additional hum when the wire was contacted, I put the scope on it. And found that I could get 15-20 volt spikes between the board as ground and the wire as signal! 1 to 3 volts was to be had with gentle taps on the board. Yeesh! In the end I used a totally different scheme, but I now have a couple of ideas for the wire wrap sensor. I have a musician friend who wants to hear what it sounds like.........

John West responded (to JR Spidell):

>I have seen 40MHz boards wirewrapped! It just takes patience and being careful.

Wire-wrap is good for that sort of thing. I wouldn't try 40MHz myself (I refuse to touch anything above 20), but you can have nice solid power and ground planes (without paying for a 4 or 5 layer board), and little crosstalk between the signals (why should they all be parallel?).

I also prefer fixing bugs on wire-wrap to cutting tracks on a PCB and adding wires. It looks ugly to start with, so you don't have the problem of destroying your beautiful board, and you never have trouble with melting the insulation on a nearby wire when you put a new one in. And it is much easier to add new chips - the holes are already there.

Leon Heller wrote:

I've used wire-wrap a lot in the past, culminating in the prototyping of a couple of transputer modules. The chap who did the CAD for my PCBs (4-layer) had a good suggestion for simulating 4-layer boards. Have them made as 2-sided with PTH, and simulate the +5 V and GND planes with thick stranded wire connecting the appropriate supply and ground pins on the various chips. I haven't tried this, but it should work, and will be very much cheaper for prototypes. I think my transputer boards were on the limit for wire-wrap. I looked at some of the signals and there was lots of ringing and noise. One board I made I could never get to work properly.

Stan Eker responded:

The best stuff I'd seen (commercially) was the Pads 'N Planes boards from Vector. It's a perf grid with plated holes, and all the area between pads is flooded with copper, making an isolated plane on each side. Using a .036" ID, .047" OD eyelet allows you to make connections under WW sockets and connectors to the plane(s). Works great, but they screwed up the idea by adding wasted space for surface-mount bypass caps. Since at least ONE end has to go to a via (to hit the other plane), there's no point to the SMD caps, and it makes it annoying or useless for bigger projects. I did roughly the same *without* the SMD crud and the boards work excellently. No power bus noise or ringing with normal bypass methods. It's quick to do the power busses compared to the method you described (I've done that, too).

I've also seen it done horribly wrong, before. We had one board with ~ 60 74LS and 74S chips that had the power wiring daisy-chained. At the end of the chain, there was less than 3V of power, and the board was neurotic. The daisy-chain was with 30 gauge wire, of course. What a mess! It all had to be ripped off and replaced. To add insult to injury, the board had BOTH power and ground bus bars in a horizontal stripe pattern that weren't used.

Stan Eker also wrote:

Wow! Am I doing it wrong? Using the correct wire-wrap sockets (.025" square posts of hard copper), I've *never* broken a pin. Ever. 'Course, the proper sockets (preferably with the machined pins, not the cheezy dual- wipe jobs) cost a bundle, roughly 10X what a soldertail socket does. Wire wrap is great if you're only going to do ONE prototype. If you might want two or more, it's quicker to do a homebrew PCB as Mark suggests.

And Eric Edwards responded:

What kind of wire wrap tools do you use? I've seen essentially 4 kinds in Digikey:

1) Manual tools: ~$20 (more for better quality, of course)

2) Electric wire wrap tool: ~$80

3) Manual cut-strip-wrap tool: ~$100

4) Electric cut-strip-wrap tool: ~$400

I'm in a position of being willing to pay for pricey tools if there is real advantage.

Most of what I intend to do will be one-offs. Prove the design works and then on to bigger stuff.

Stan Eker responded:

My favorite is the top-of-the-line OK electric wrap tool. I also have one of the nice OK cut&strip handtools to make *that* end easier. I've tried others, and the OK guns seem to last longer, and do a nicer job. There's no reason to save a few bucks on the tools and spend it in time.

BTW - other guns work well for other people; it's all in what you're used to. I never had much luck with the cut-strip-wrap or JustWrap tools, so stuck with the best of the older technologies.

Eric Edwards : I'm in a position of being willing to pay for pricey tools if there is real advantage.

As I'd said, it's always worthwhile. Check out the Erem handtools, too. They're about $30 each, but last a lifetime without much care. After you've chucked your fourth pair of $5 needle-nose, you might consider them. Nothing p!sses me off more than wasting time with cheap tools, where ever they're made.

Eric Edwards : Most of what I intend to do will be one-offs. Prove the design works and then on to bigger stuff.

Amazingly, we do most of our prototypes in real PCBs. If the first ones are close enough to work, we save the proto stage and go direct to production, sometimes with a few wires. If you're only doing one-offs, it'd be foolish.

Update April 2002:

Well I just got some email from a company that is very proud of their wire wrapping products, and they noticed that this page did not mention them.
(read the 8/18/2004 update (below) before you spend too much time on these links :-)
So here is a link:  Standard Pneumatic & Electric Tool Company  and the following pages also seem to be worth looking at:

• Tools
• If I was buying a new gun, I would look at this 120V gun
• For their tutorial page, with some good pictures, look here.

Update August 18 2004:

Well I just got some email telling me that all of these links are broken, so I guess the company is probably out of business.
So I did some searching, and found the following, which is a PDF catalog section that includes so pictures of what wirewrap joints should look like. Look at pages 2, 3 and 4.
    The Catalog from Cooper Tools
I have also been asked where to buy pre-cut and stripped wire. I live in Silicon Valley, and the following stores still carry these items:
    HSC Electronic Supply, wirewrap wire is from Page Digital
    Anchor Electronics, wirewrap wire is from Page Digital
    JDR Microdevices (wire on spools too)
    And, so does MarVac Electronics (looks like quite a selection!)

The following have 30 gage wirewrap wire on spools, cut and strip it your self

    Digikey
    Jameco

Other Links:

    OK Industries
             My favorite cut and strip tool is the ST-100-30