Solderability of Enamelled Copper Wire

Kevin asked about the solderability of the wire I had used in the wiring pencil. I picked the wire I had in stock that was subjectively the was the right gauge and the easiest to solder based on past experience. I hadn't however made detailed tests, so this quick experiment was undertaken to detail the performance of the particular brands I had in stock.

The Wire Range Available For Testing

I just happen to have a wide variety of gauges and brands of wire in stock, collected over the years from various suppliers. The supplies may no longer carry the particular wire I tested, or carry something different identified by the same catalogue number, so this data is only really for my benefit, but the experiment is easy to perform for yourself.

I generally find enamelled copper wire is much easier to tin from a cut end. Submerging the cut end in a puddle of solder on the tip of the iron will rapidly burn back the varnish except for especially refractory varnishes, of which I only have a few samples, mostly on quite heavy gauge wire. Tinning in the middle of an unbroken length is generally quite difficult, at normal soldering temperature, except for very fine gauge wires.

I have a cheap DSE sourced temperature controlled soldering station (catalogue number T-1976) which I purchased last year after my previous unit (also DSE sourced, the more expensive T-2200) was no longer supported by DSE for spares and I was in need of a new element. The unit is adjustable from 250 - 450 °C. I normally run at 340 °C, so I picked four test temperatures, starting with 340 °C and going right up the the units limit of 450 °C. Temperatures below 340 °C were not investigated.

Samples of wire were taped to a cardboard frame and tinning attempted at each of the four temperatures. The heat effected zones may have overlapped, especially for the thicker more conductive gauges, but lower temperatures were attempted first, progressing to higher ones. The tinning was attempted to a maximum of 20 seconds per test. Wires up to 500 um only were tested.

Supplier Catalogue Number Gauge Colour Solderability Comments
340 °C 380 °C 410 °C 450 °C
DSE W-3136 125 um Red Easy Easy Easy Easy By far the easiest wire to tin
DSE W-3132 200 um Red Easy Easy Easy Easy Quite similar to the 125 um wire, takes slightly longer to tin, but otherwise very easy to use and mechanically more robust.
DSE W-3126 400 um Amber No Hard OK Poor Quite hard to tin at low temperatures. Lots of burnt material at higher ones.
Jaycar WW4012 250 um Amber Easy Easy Easy Easy In most ways identical to the 200 um DSE wire, just a different colour and slightly thicker gauge.
Jaycar WW4013 300 um Red No Poor OK OK Takes a long time to burn through and tin. Lots of heat works eventually, fair amount of burnt junk results.
Jaycar WW4014 400 um Amber No Poor OK Poor Around 410 °C seemed optimal for this wire, producing less burnt material than higher temperatures, but being hard to tin much below this. I found this result a little surprising.
Jaycar WW4016 500 um Amber No Hard Poor OK Needs lots of heat, not too bad otherwise.
Hendricks QRP Kits NA 321 um (#28) Red Fair OK Easy OK "Thermaleze" wire. Tins with rubbing to get it started at the lowest temperature. Higher temperatures tin easier, but very high temperatures start to produce more burnt material.
Hendricks QRP Kits NA 321 um (#28) Green Fair OK Easy OK Same as the Red except or the colour.
W8DIZ "The Toroid King" NA 255 um (#30) Red/Green No Fair OK OK This is a twisted pair of red and green wires, intended for easy construction of bifilar RF transformers. Both colours behave the same. Tins with rubbing eventually, but not at the lowest temperature. Higher temperatures tin easier. Somewhat difficult to tin from a cut end at the lowest temperature. No burnt material at high temperatures, but the enamel colour fades in the heat effected region, appears to thin out and melt away from the heat.
Unknown NA 400 um Dark Amber No No OK OK Sourced from Wyong Field Day 2009. Needs lots of neat to tin. Was the only material that didn't tin eventually at 380 °C.
Unknown NA 250 um Light Amber No OK OK Poor Sourced from Wyong Field Day 2009. Fairly typical of the harder to tin wires. Burnt material at high temperatures.

In general the results indicate thinner gauges are easier to tin. All wires tested tin from a cut end at the lowest temperature, but may take quite some time and effort/rubbing. All wires will tin mid-wire eventually at 380 °C, but some can take quite a long time and require rubbing back and forth with the iron to start penetration of the enamel. At 410 °C and above all wires tin pretty easily. Higher temperatures are more robust and quicker to tin, but also tend to produce more blackening and slaggy solder.

Dick Smith vrs Jaycar ECW Test Card

Wires that tin only with difficulty tend to produce a blackened region near the edge of the enamel layer which appears to be a mixture of burnt enamel and rosin flux. The blackening also seems correlated with decreasing quality of the solder. Wire that really needed a lot of cooking produces very slaggy solder that ideally would be removed and replaced with fresh material to make a nice joint.

The smell of the hardier enamel burning is quite different to that of the easily tinned material. There is a fair variety of enamel chemistries available, but I am unsure which correspond to the easiest tinning wires as the wire is uncharacterised as to its particular enamel chemistry. At least here in Australia, unless you order directly from a wire supplier, you seem to get almost random material. In particular the same type of spools are used for different kinds of wire, probably because of rebranding and splitting of bulk lots by the retailers. Some material purchased years apart, but of the same gauge, colour and brand has different enamel. This will no doubt frustrate attempts to use the data above.

One thing I didn't test which might be of more practical value is tinning when twisted around an IC socket pin in contact with PCB pads. This is the ultimate fate of the wire used in the wiring pencil, so good performance there is highly desirable. The two easiest to tin materials also happen to be those I chose for the wiring pencil, and I know that in practice they work quite well in that application. Unfortunately they are also the oldest sourced and perhaps are no longer consistent with what is currently offered by Dick Smith.


Parent article: Wiring Pencil.