This is an old technique. It predates printed circuit boards. Until 1980, this technique was not only a method for making prototypes. Many factories used big and fast wirewrap machines for producing high quality circuit boards, especially in the television branch.

But these times have gone. Presently, wirewrap is a prototyping technique and one that is on the border of extinction. It's hard to find the wire, sockets and tools. If you look good, you can still find all of it, but you need the internet to do a global search.

I started with wirewrap in the early 80's. I tried to make some PCB's at home but that always ended in a big mess. Even though I had a darkroom and a chemical background, things would not go as expected. So after some tests with copper etching I gave up and decided to buy me a dry prototyping method: wirewrap.

Even in those days, the materials were hard to find. Lucky for me I read some US magazines and had obtained copies of JDR and Jameco catalogs. No internet in those days. So ordering parts was a matter of months, not weeks. And the dollar was at an all time high. But I'm still using the supply of wires I bought 25 years ago. So I guess it was a good investment.
Until a decade ago, also reichelt sold wirewrap sockets. But that's not the case anymore. So if you want to start with this clean technique, first make sure you can get all of this:

Wire wrap wire with Kynar insulation (Page Digital, OK industries)
Wire wrap sockets and posts
Wire wrap tool

Wirewrapping is done on Vero board, just like most of the other prototyping methods.

As with 2D wiring, a ready made PCB is used as an example.

On the right we see a circuit built with wirewrapping technique. At first you won't notice it. But take a closer look at how the resistors are mounted: they seem to lie in a kind of cradle. And the transistors were mounted on something resembling IC sockets. For the record: this is a circuit from 1993.

For wirewrap you wrap wire around square pins. On a round pin, the contact is very poor, so resistors and capacitors need to be squared up. So you use special 'cradles' with a fork on top and a square pin on the underside.
From 1995 or so, I started to use another method for resistors: solder the wirewrap wire directly to the round posts. That saved on hard to get cradles. And it was cheaper and faster.

Now let's see how it looks from down below.

You asked for it. Now you get it. The underside of a wirewrapped circuitboard. It looks like a mess. It looks like you got lots of noise coupled into other signals. And let me assure you: it's neither a mess nor noisy. Wires cross eachother, they don't run alongside for inches. So there is only very little interaction.

If wirewrap was a noisy construction method in the first place, it would and could not have been used in televison production for so many years.

As will be clear, any pin can be connected to any other pin. And it can be unwrapped as well, so errors are easily fixed, even when there are many connections running on the board (unlike this one). Only when you connection is on the bottom of a stack it's hard to get it out. But then you take a scissors and just cut out the wire as close to the posts as possible.

Here is closer look of a wrapped board. Here you see some of the strong points of wirewrapping technology:

wires in many colours
wraps can be stacked on a post (4 - 6 levels are normal)
the pins have a square cross section
the pointy heads makes it easy to insert it in the wrapping tool
used on plain old cheap Vero board
any two points can be connected
the method is cold and clean
the silver plated wires still look fresh after 15 years

This board was wired in about to hours. Drawing the circuit took longer. I must say that I am a lazy wrapper: I use prestripped precut wires. It's very painful to buy wirewrap wire on the meter and then strip it in a stripping tool. Your fingers really hurt and sometime you make deep cuts in your flesh. Not a good idea. Also: prestripped wire is cheaper and available in many more colours.

One condition however: your eyesight needs to be good at short distances. Myopia is an advantage here. When over 50, the method looses most of it's charm since you most probably cannot do without a magnifier.

Here you see an example of the precut prestripped wire and the wrapping tool. I forgot the price of the tool but I think it was something around USD 40. This is no typo: FOURTY US dollars. These wrapping tools have always been pricy and it's not likely it will change for the better over night. Forgot about the price of the wire, but an assorted package of 5000 wires cost something like USD 50.
The composition of a precut prestripped wirewrap wire is as follows:

one inch of bare metal
n/2 inches of insulation (n = 1, 2 ... 10)
one inch of bare metal

The metal is silver plated copper. The insulation is Kynar; a tough kind of Kevlar, which in its turn is a tough kind of Teflon. It will not melt or burn when touched with a hot soldering iron. The wire is AWG 28.

The tool in the picture is from OK Industries. Not sure if it is still in business. Still, Mouser and RS-Online sell their products. Even the wrapping tool, for something like €30.

The wire used to be made by Page Digital or OK industries. See if you can find it with Yahoo.

Here you see my collection of seldomly used wirewrap sockets, connectors and related parts. In the old days, just about anything was available in 'soldertail' and 'wirewrap' formfactor.

Mouser seems to still sell a lot of wirewrap equipment and parts. At a price, but this technique has never been cheap. Fast, flexible, clean, cold, fixable, reusable, but never cheap.

This is a typical wirewrap socket in low profile form factor. Always go for this low profile kind. It has better contacts tthan the high profile version. Prices differ only little so why not choose the much better then?

These Wirewrap sockets have

turned contacts (not visible here)
square pins, level 5
low profile body

For the rest it's just a socket with slightly longer pins.

The wrapping tool is on the left. The black tube on the right of it has two openings in the bottom:

a big one for accepting the wirewrap post (yellow)
a small one for accepting the wirewrap wire (green)

The graph in the bottom of the picture shows how the tool looks like, head on.

In the tube is a slot and the wire is sticking out through that slot in the picture. This way you can see how far the wrapping has proceeded.

This is a loaded wrapping tool that has slipped over the Wirewrap post. Push it in as far as it goes. Then start turning clockwise until there is no wire inside the tool anymore. All of it has been turned (wrapped) onto the square post. The corners of the posts are very sharp so they force the wire into the metal of the post, thereby guaranteeing a very tight fit that comes close to a soldered joint.

Mechanically and electrically this is a very good connection.

The picture is not ultra sharp. Still, you can see that the connection was made. This time at level 0 (closest to the Vero board) but if required, 4 to 7 extra levels can be added. Now wrap the other end of the wire.

This is a 16 KB SRAM extension board for the ZX-81

The original Sinclair RAM extension pack was rather wobbly. One wobble and it reset itself, thereby loosing all data and programs. So I designed and made this RAM card based on 6116 SRAM chips: a whopping 2048 bytes in each black box.

And this is a detail of the wire routing

The board has always worked flawlessly. This board was made from spools of wire. I still feel the wires cutting through my skin while stripping the insulation. But it was worth the effort. Even after 25 years.

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