We’ve all had that treasured pair of headphones fail us. One moment we’re jamming out to our favorite song, then, betrayal. The right ear goes out. No wait. It’s back. No, damn, it’s gone. It works for a while and then no jiggling of the wire will bring it back. So we think to ourselves, we’ve soldered before. This is nothing. We’ll just splice the wire together.
So we open it up only to be faced with the worst imaginable configuration: little strands of copper enamel wire intertwined with nylon for some reason. How does a mortal solder this? First you try to untwine the nylon from the strands. It kind of works, but now the strands are all mangled and weird. Huh. Okay. well, you kind of twist them together and give a go at soldering. No dice. Next comes sandpaper, torches, and all sorts of work-a-rounds. None of them seem to work. The best you manage is sound in one ear. It’s time to give up.
Soldering this stuff is actually pretty easy. It just takes a bit of knowledge about how assembly line workers do it. Let’s take a look.
Every soldering station on an assembly line will have three things. A roll of brand new solder, flux (I like Kester 951, you can buy it in a pen), and a nice soldering iron. That’s all you need.
So what is enamel wire anyway? Enamel wire starts off as, typically, a freshly drawn copper strand so there’s absolutely no oxidization or surface film on it. It’s then immediately run through an enamel mixture (typically polyurethane) and dried. This results in a very thin, practically invisible flexible coating all along the strand. The coating isn’t exactly perfect, when looked at under a microscope there will be obvious thick sections along its profile depending on how it was wound, the speed it was coated, and how the coating was dried. Either way, the name of the game is to selectively remove this coating on all the little strands at once without removing any where you don’t want to.
Since this coating is so thin it doesn’t take much to break through and get to the shiny copper underneath. Going back to the assembly line, all it takes is a bit of heat and flux and you’re good to go. The nylon stranding can be safely ignored, it melts and floats to the surface of the solder bead during soldering. As long as you have flux it will keep the remaining organics from interfering. This is why you may see some black specs on the surface of a typical connection to enamel wire.
As for soldering the wire. The first step is to make sure you have a really clean cut into the strands. For this I recommend first carefully prying away a generous amount of shielding. Then, with a brand new blade on a utility knife, slicing the stranded ends flat against a cutting mat. Even with my nicest end cutters, the strands were just too thin to cut nicely.
Next, simply apply a generous amount of flux to the end of the enamel wire you’d like to solder. It doesn’t hurt to flux the tab or wire you’re trying to connect it to as well. Try to thread or intertwine the wire to its mating part without disturbing any strands. Then, use good solder and bond the usual way. The trick is to apply heat until you see solder just creeping up the enamel wire. It will be pretty hard to see as only the enamel closest to the joint will burn away cleanly enough for wicking to occur, so a magnifying glass is recommended.
For larger gauges of wire this technique will work too, up to a point. It’s only when you get to the serious gauges of enamel wire that a bit of sandpaper is productive. For the small stuff flux and heat is your friend.