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I feel silly asking this question but I am mystified. I can't seem to tin the 24 gage stranded wire used in Christmas tree lights. I've tried every kind of solder/ soldering iron combination I have , even tried various paste fluxes, all to no avail. The solder wont wet the copper. Am I looking at an oxidation problem?

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  • \$\begingroup\$ A picture would help. Solder flows well on copper as long as it's clean and there is enough heat to properly liquify the solder. Tony's idea of it being enamel coated would be my guess too if you hadn't said it was stranded. Again, show a picture. Get a good closeup and focus properly. \$\endgroup\$ – Olin Lathrop Jul 17 '12 at 18:42
  • \$\begingroup\$ Thank you Olin, Tony called it, the wire was aluminum with a copper coating, no wonder it wouldn't solder. Duh ! \$\endgroup\$ – Fred Paine Jul 17 '12 at 19:15
  • \$\begingroup\$ No, that doesn't add up. Copper coated would still solder since the solder sees the copper coating, not the aluminum inside. There is still something else going on. Again, show a (good) picture. \$\endgroup\$ – Olin Lathrop Jul 17 '12 at 21:23
  • \$\begingroup\$ I thought the same thing so I did a comparison with real copper(stranded)wire. Using the same soldering iron with RadioShack 62/36/2 Silver Bearing Solder, I had no problem wetting out the real copper wire. The copper coated aluminum wire did not wet-out at all . I don't have a camera so I cant post a picture but I examined the wire with my magnifying glasses and the wire looks like pristeen copper, no sign of any contamination or oxide, it conducts well with just a light touch of my voltmeter probes doing a simple continuity check. What would you like me to try next? \$\endgroup\$ – Fred Paine Jul 17 '12 at 23:47
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I have been running into a lot of that funny wire lately. It looks just like any other wire I have used for years - but it won't wet right. Upon closer inspection, I see some of it was copper coated steel wire ( magnet attracts it ). Some of it was copper plated aluminum ( wonder how they did that ), and other was plain old stranded aluminum wire ( it was a dollar-store USB cable I bought to hack into for a source of five volts ).

It looked great until I tried to solder it. At first it would seem to wet, then solder just rolled off it. Not even GOOT flux worked. What happened is the solder dissolved the thin layer of copper off. Must have been electroplated on. When I took it to the lab and saw what was going on under the microscope, it became obvious what the problem was.

I guess with today's technology where most everything is crimped, aluminum and steel wire is a lot cheaper than copper wire and works good enough to avoid a customer return.

Google sent me here while I was seeing if this situation existed. The evidence left here shows that is indeed what is going on. I leave my experience for others also trying to figure out they were losing their mind because they can't do something they have done for years.

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It may be coated magnet wire or litz wire or plastic coated to prevent oxidation such as purelane. Is the copper surface clean? There are solvent solutions to dip the wire and then there are flame solutions to burn off the insulation. It must look like shiny white copper colour that turns reddish with oxide or orange with coating.. Careful scraping with an razor edge knife may work.

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  • \$\begingroup\$ It looks like normal 24ga stranded copper wire, it is not discolored in any way, looks shiny. As a comparison I took some stranded 24 ga wire from RadioShack and used the same solder and iron , it tinned up nicely. I can't figure it out :-( \$\endgroup\$ – Fred Paine Jul 17 '12 at 18:05
  • \$\begingroup\$ Is it possible that it is an aluminum compound wire? That has poor solderability. What type of solder Pb-free or 50/50 40/60? It is easier with Pb. It must be a wire type that is not solderable. Or it is oxidized.? \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 17 '12 at 18:16
  • \$\begingroup\$ Tony you are right, it is aluminum wire with a copper coating. I scraped off the copper to reveal the beautiful shiny aluminum underneath. I never would have guessed this. Thank you :-) \$\endgroup\$ – Fred Paine Jul 17 '12 at 18:31
  • \$\begingroup\$ welcome.. cut shorter and solder...I remember an experiment from a research who had a gold plated aluminum casting on our BB IV payload onboard. He said it improved ease of soldering coax anywhere anytime. It was a VNA in a box. circa 1977. Looked like a million$ box even if just 10um flash plated. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 17 '12 at 18:34

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