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How hot is too hot for magnet wire?

12/26/2005 11:47 AM
Joe Gwinn	How hot is too hot for magnet wire? One issue that comes up from time to time is the reports that a too hot iron will cause subsequent breakage of the #42 or so wire, the fear being that 800 degrees F is too hot, even though it works lickety-split on solderable magnet wire. So, I did a little digging. The bottom line is that material properties don't change below the annealing temperature, typically about one half the absolute melting temperature, which is abouit 405 degrees C (761 degrees F), but annealing takes forever (at least 30 minutes) at that temperature, and intentional annealing is done above 700 degrees C (1,300 degrees F, a nice red heat). http://www.evergreengardenworks.com/copperwi.htm The above is from an artistic community, one with a metallurgical connection. http://www.copper.org/innovations/1997/Dec1997/wiremetallurgy.html And the above is no-holds-barred technical, from the Copper Folk. Look for the chart titled Annealed Grain Size, Microns, about 2/3 the way down. The bottom line is that 800 degrees F is OK, but don't linger. And, temperature control is needed for 800 degrees to be reliable. Those cheap little Radio Shack irons idle at far too high a temperature, and have damaged many things.

12/26/2005 11:47 AM

Joe Gwinn

How hot is too hot for magnet wire?

One issue that comes up from time to time is the reports that a too hot iron will cause subsequent breakage of the #42 or so wire, the fear being that 800 degrees F is too hot, even though it works lickety-split on solderable magnet wire. So, I did a little digging. The bottom line is that material properties don't change below the annealing temperature, typically about one half the absolute melting temperature, which is abouit 405 degrees C (761 degrees F), but annealing takes forever (at least 30 minutes) at that temperature, and intentional annealing is done above 700 degrees C (1,300 degrees F, a nice red heat).

http://www.evergreengardenworks.com/copperwi.htm

The above is from an artistic community, one with a metallurgical connection.

http://www.copper.org/innovations/1997/Dec1997/wiremetallurgy.html

And the above is no-holds-barred technical, from the Copper Folk. Look for the chart titled Annealed Grain Size, Microns, about 2/3 the way down.

The bottom line is that 800 degrees F is OK, but don't linger. And, temperature control is needed for 800 degrees to be reliable. Those cheap little Radio Shack irons idle at far too high a temperature, and have damaged many things.

12/26/2005 7:05 PM
Dave Stephens	One thing you're not considering is that the solder is involved and rosin. Lollar said if I remember right that a 40watt iron used on magnet wire to leads joint, he had failures after about a year later. That wire is so tiny and you are drenching it in other metals at high heat, metals can and do migrate under those circumstances and even just sandwiched together they will migrate, I learned that in my jewelry art career. You can make gold foil attach to sterling silver just by putting the silver on a hotplate and burnishing the gold foil down, it will stay there forever. A cool technique. So the other thing is that magnet wire is really tiny and I would think would anneal at alot lower temperatures, as an example I'm thinking is you can burn steel with a match if you burn steel wool fibers, you can't burn a steel blade with a match. So there is more going on here than published metallurgical knowledge which applies to heavier pieces of material. I'm sticking with my 15 watt iron, stuff I soldered two years ago still works fine.....Dave

12/26/2005 7:05 PM

Dave Stephens

One thing you're not considering is that the solder is involved and rosin. Lollar said if I remember right that a 40watt iron used on magnet wire to leads joint, he had failures after about a year later. That wire is so tiny and you are drenching it in other metals at high heat, metals can and do migrate under those circumstances and even just sandwiched together they will migrate, I learned that in my jewelry art career. You can make gold foil attach to sterling silver just by putting the silver on a hotplate and burnishing the gold foil down, it will stay there forever. A cool technique. So the other thing is that magnet wire is really tiny and I would think would anneal at alot lower temperatures, as an example I'm thinking is you can burn steel with a match if you burn steel wool fibers, you can't burn a steel blade with a match. So there is more going on here than published metallurgical knowledge which applies to heavier pieces of material. I'm sticking with my 15 watt iron, stuff I soldered two years ago still works fine.....Dave

12/27/2005 1:45 PM

Joe Gwinn

On 12/27/2005 2:05 AM, Dave Stephens said:

quote:
"One thing you're not considering is that the solder is involved and rosin. Lollar said if I remember right that a 40watt iron used on magnet wire to leads joint, he had failures after about a year later."

Rosin and solder are always involved; all that differs is the tenperature. And, "40 watts" is a power, not a temperature, and mention of power not temperature implies that the iron in question is not temperature controlled. The problem is that a heavy non-controlled iron idles at a much higher temperature than normal soldering range, the theory being that the temperature will be pulled down to the correct range by the thermal load of the item being soldered. A 40-watt iron will not even notice the load from soldering a eyelet to a piece of #43 wire, so this will be soldered at the idling temperature, not the correct temperature, and overheating is almost certain.

quote:
"That wire is so tiny and you are drenching it in other metals at high heat, metals can and do migrate under those circumstances and even just sandwiched together they will migrate."
Yes, this is always true. The question is if 3 seconds at 800 degrees F does anything to the copper that 30 seconds at 700 degrees does not.

quote:
"I learned that in my jewelry art career. You can make gold foil attach to sterling silver just by putting the silver on a hotplate and burnishing the gold foil down, it will stay there forever. A cool technique."
Yes. So that's where the idea came from. It's universally used in semiconductor manufacture, under the rubric "thermocompression bonding". Gold works particularly well, but so does aluminium (maybe with some ultrasonic energy to scrub the oxide film off).

quote:
"So the other thing is that magnet wire is really tiny and I would think would anneal at alot lower temperatures, as an example I'm thinking is you can burn steel with a match if you burn steel wool fibers, you can't burn a steel blade with a match."
Annealing is a function of temeprature and time only, not size. Semiconductors with copper conductors on the silicon surface are annealed to stress-relieve the copper, even though the layers are very thin, far thinner than the diameter of #43 wire.

quote:
"So there is more going on here than published metallurgical knowledge which applies to heavier pieces of material. "
Well, this is precisely what I'm trying to sort out, so so far what I'm seeing is that the problem is use of overly powerful unregulated irons, which reach an unknown but high temperature while idling. In fact, we don't really know what temperature the unregulated irons are achieving, so it isn't clear how we would know that 800 degrees is a problem.

Avoiding this overtemperature problem is one of the standard advantages of temp controlled irons, given as a reason to spend the added money. The other reason given is that with temperature control, the iron can have far higher power without burning the work (or itself), so the iron is able to heat the work up that much faster, avoiding the damage due to heat soaking the work.

quote:
"I'm sticking with my 15 watt iron, stuff I soldered two years ago still works fine.....Dave"
I've been soldering with my trusty 48-watt thermostat-controlled iron for 38 years, and never had a joint fail. The current top of the Weller line is 80 watts (with very good electronic temperature control), in a somewhat smaller tip. All of which is why I wonder about the fear of 800-degree soldering.

Actually, it's relevant how I came to buy that temperature-controlled iron: I was a summer employee at RCA in 1967 and 1968, where I worked as a technician in the Plastics Lab, gluing the pieces of the Apollo Moon Lander together. The next Lab over was the Wireroom, where all the component assembly and soldering was performed. What they used for all soldering were hundreds of Weller W-TCP irons. Hmm. If it's good enough for NASA, it's good enough for me, so I bought one as soon as I could. If I recall, it cost something like US $80, which was real money back in 1968.

These circuit boards were soldered at 600 degrees F, using very good cleaning and flux to allow soldering at that slightly cool temperature. (Commercial work used 700 degree tips.) This low 600 F temperature was used mainly to avoid damage to the epoxy in the glass-epoxy circuit boards if something had to be re-soldered. The problem is that the solder pads would lift off the circuit boards under launch vibration if the bond between copper foil pad and circuit board were unduly cooked, and the unbonded pad would flex, fatigue, and break under that relentless vibration.

Weller still makes the WTCP; this is pretty good for a design patented in 1966 (3,267,254, to Carl Weller et al).

12/27/2005 3:07 PM
Spence	I've used a temperature controlled iron ever since I found one for sale in our rather backward UK shops. I set the temperature relevant to the job in hand. I really can't imagine using anything else now. I don't have failiures with solder joints. That would be a nightmare where warranties are concerned. I can't quite grasp how Lollar pickups solder joints took a year to fail. What happened to cause that?

12/27/2005 3:07 PM

Spence

I've used a temperature controlled iron ever since I found one for sale in our rather backward UK shops. I set the temperature relevant to the job in hand. I really can't imagine using anything else now. I don't have failiures with solder joints. That would be a nightmare where warranties are concerned. I can't quite grasp how Lollar pickups solder joints took a year to fail. What happened to cause that?

12/27/2005 7:16 PM
Dave Stephens	JOe and Spence, the fact that a 40 watt iron caused some of Lollar's magnet wire solder joints to fail a year later is the UNKNOWN factor that we are talking about. Seymour Duncan talks on his site about not cooking the solder joint, so obviously he has run into the same problem. Part of the unknown is due directly to soldering to something finer than a human hair, and made of copper. I don't know what causes the failures but I think its enough to know that using too much heat or soldering for too long causes the joint to disentegrate over time. My 15 watt iron seems to have just enough heat to do the job. I would think you would want to use just enough power to make soldering melt into the eylet and no more if using a controllable iron. I wanted one of those soldering stations but they always seem to be out of my budget.

12/27/2005 7:16 PM

Dave Stephens

JOe and Spence, the fact that a 40 watt iron caused some of Lollar's magnet wire solder joints to fail a year later is the UNKNOWN factor that we are talking about. Seymour Duncan talks on his site about not cooking the solder joint, so obviously he has run into the same problem. Part of the unknown is due directly to soldering to something finer than a human hair, and made of copper. I don't know what causes the failures but I think its enough to know that using too much heat or soldering for too long causes the joint to disentegrate over time. My 15 watt iron seems to have just enough heat to do the job. I would think you would want to use just enough power to make soldering melt into the eylet and no more if using a controllable iron. I wanted one of those soldering stations but they always seem to be out of my budget.

12/27/2005 9:55 PM
Jabs	Temperature control is a great thing. It would be interesting to know the wattage being pulled at idle by one of these Weller dealies, versus trying to desolder a covered pickup--my least favorite project. I have an iron that cost me $3.95. I picked it up in an emergency when my longstanding iron kicked. I'll tell you--this thing just about 'runs away' at idle, it gets so hot. For delicate work, I have to 'duty cycle' it or the wire literally goes up in smoke. And it STILL doesn't have the guts to melt the solder on a covered pup! I imagine it was designed mainly for extracting information from enemy agents...

12/27/2005 9:55 PM

Jabs

Temperature control is a great thing. It would be interesting to know the wattage being pulled at idle by one of these Weller dealies, versus trying to desolder a covered pickup--my least favorite project.

I have an iron that cost me $3.95. I picked it up in an emergency when my longstanding iron kicked. I'll tell you--this thing just about 'runs away' at idle, it gets so hot. For delicate work, I have to 'duty cycle' it or the wire literally goes up in smoke. And it STILL doesn't have the guts to melt the solder on a covered pup!

I imagine it was designed mainly for extracting information from enemy agents...

12/28/2005 1:45 AM
Greg Simon	If you're using a cheaper Weller without temperature control, then going with a 15w to 25w would be just about right. Anything more and you're likely to mess up the wire and heat something up inside the coil. You COULD use a heat sink if you're stuck with using a larger soldering iron. If you have the money though, a temperature controlled station is the way to go. Once you figure out what temp range gives you enough heat to do the joint without melting stuff, then you're set. They are spendy but they're worth it. It makes soldering a lot easier because they work faster. Also, the amount of heat that gets transferred to the wire depends on what type of tip you use and how you hold the tip on the wire. So you would want to choose the right tip for the job. Greg

12/28/2005 1:45 AM

Greg Simon

If you're using a cheaper Weller without temperature control, then going with a 15w to 25w would be just about right. Anything more and you're likely to mess up the wire and heat something up inside the coil. You COULD use a heat sink if you're stuck with using a larger soldering iron.

If you have the money though, a temperature controlled station is the way to go. Once you figure out what temp range gives you enough heat to do the joint without melting stuff, then you're set. They are spendy but they're worth it. It makes soldering a lot easier because they work faster. Also, the amount of heat that gets transferred to the wire depends on what type of tip you use and how you hold the tip on the wire. So you would want to choose the right tip for the job.

Greg

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