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Analog Angle Blog

Learning from a wire-wrapping misassumption

Many years ago, before PCBs and high pin count, non-dual-inline package (DIP) ICs took over the world, I encountered “wire wrap” as a technique for doing interconnects on both prototypes and even low-volume production runs. While I won’t go into full details here — don’t worry, there are numerous historical and tutorial resources with full details online such as the references at the end — it involved using a manual or small power tool to wrap a few inches of stripped, thin wire seven times in a spiral around a skinny, square post, and then connecting the other end of the wire to another post.

Everything about wire wrap was special: the thin wire (usually #30 AWG), the extremely thin yet strippable Kynar or similar insulation, and the two acceptable wire-wrap techniques (called “regular” and “modified”). The posts to be wrapped were extended rectangular pins of special sockets for ICs and passives, all mounted on a board. Wire wrapping could be used for a few connections or for complicated boards (Figure 1 and Figure 2, respectively). The technique was so indispensable at the time that there were even huge programmable machines that could wrap thousands of posts on production computer circuit boards.

photo of a wire wrapped Arduino smart controller boardFigure 1 Hobbyists have used wire wrapping to build Arduino-based smart-controller boards such as this one for an automated chicken coop. Source: Chicken-Pi

 

photo of hand wrapped Z80 computer boardFigure 2 This Z80-based computer was hand wrapped by a serious hobbyist in around 1977. Source: Wikipedia

The result of a properly done wrap was seven wire turns grabbing the four post corners, yielding 28 “gas-tight” non-oxidizing connections. It was a labor-intensive but effective way to wire a board, as long as you paid attention to what you were doing: it was easy to get mentally numb and connect the wrong posts, or get sloppy and have little cut shards of wire and end-pieces short out adjacent pins.

Wire wrap has pretty much gone the way of the dinosaur in our industry (there are a few exceptions and outliers), and I am not going to praise it or lament its passing here. It had its time but that time has passed, as the copper-clad and etched PCBs, high-density circuits, and higher frequencies became the norm. Wire wrap simply cannot compete in that arena. But dealing with wire wrap taught me, once again, that it is so easy to be naïve, to assume, and to be very wrong.

What was my misassumption about wire wrap? It’s simple: based on my personal experience with breadboarding circuits, I was sure that wrapping a wire around a post simply could not be a reliable technique. In my world, you soldered wires, you crimped them with a proper crimping tool, or you attached them around and under a screw terminal (even better, with a spade lug or ring terminal) if you wanted a solid connection. Anything less was asking for short- and long-term reliability trouble, the likelihood of which increased at least linearly if not exponentially, with the number of connections.

Of course, my curiosity about wire wrap’s supposed virtue and my presumption about its unreliability led me to do some research. It turned out that extensive testing by the experts at Western Electric (the manufacturing arm of AT&T, back in the day when AT&T was the one-and-only “phone system”) showed that if done correctly it was an extremely reliable method; it was even used for the Apollo guidance computer. Admittedly, that was a big “if” for a novice wrapper like me and many novices around me, but I figured if the guys who designed and tested standard phone handsets for a 40-year operating life said it was OK, then it must be OK. No need for me to worry, as it was like soldering: if done properly, you would get a good, reliable connection; if done poorly, it was intermittent and failures would appear sooner or later. And please, don’t follow the very wrong “how to solder” column from a recent Popular Mechanics, which is guaranteed to produce a cold sold joint (Figure 3).

magazine scan of Popular Mechanics article "How to use a soldering iron"Figure 3 This “tutorial” column from Popular Mechanics is mistitled; it should be “How NOT to Solder”: Step 4 is 100% contrary to proper soldering technique and will undoubtedly result in a cold-solder joint, while Step 3 will likely lead to excess use of flux when a flux-core solder would be a much-better choice. Source: Hearst Corp/Popular Mechanics

Once again, my initial assumption, based solely on personal experience, led me prematurely to a wrong conclusion. Each time that happens, I say it won’t happen again. But it’s human nature to jump to conclusions even before the evidence is in, or perhaps there is no time to do any checking.

Have you ever held opinions based primarily on your own experience and supposition that turned out to be wrong? If so, how did you find out? What happened when you did?

References

  1. Wire Wrap,” Wikipedia
  2. Wire Wrapping vs. Soldering: How and When to Use Wire Wrapping,” Jameco Electronics
  3. Wire Wrap Is Alive And Well!,” Nuts and Volts
  4. Ask Hackaday: Whatever Happened To Wire Wrapping?,” Hackaday

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1 comment on “Learning from a wire-wrapping misassumption

  1. anon9303122
    October 7, 2020

    And I would never sand a soldering iron tip with sandpaper as most soldering iron tips are plated with a special iron alloy over copper. Once you wear through the iron, the remaining copper tip will essentially erode away in no time. Popular Mechanics should be ashamed they didn’t even consult Wikipedia before publishing that drivel.

    Wikipedia quote, “Soldering” downloaded 06 Oct 2020: “To simplify soldering, beginners are usually advised to apply the soldering iron and the solder separately to the joint, rather than the solder being applied directly to the iron. When sufficient solder is applied, the solder wire is removed. When the surfaces are adequately heated, the solder will flow around the workpieces. The iron is then removed from the joint. ”

    Bill, thank you for continuing to write. I appreciate your ‘old school’ approaches to writing as too many journalists today, especially in the mass media are way too sloppy and fixated on getting a story out fast rather than right.

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