Soldering ultrafine wire - Page 1
Forum section: electronics / projects

author: ian.rees
author_rank: Contributor
timestamp: May 11, 2016, 10:17:17 pm
content: Hi Folks,I'm working on a project that involves working with some 54AWG copper magnet wire (0.00019mm^2) with solderable P155 insulation. One of the issues I'm running in to is that I have to be quick with soldering to avoid what looks like the copper dissolving in to the molten solder, not too long after the insulation is stripped off. I'm new to working with this sort of wire, and am wondering what is likely to be the cause, or if this is just to be expected?My iron is a Hakko FX888 (though it could well be a knockoff) - seems to work well for general usage and I've got the temperature set to around 275C (haven't confirmed that temperature but suspect it's reasonably accurate). Solder is an old roll of fine Alpha Metals 60/40 rosin core that I've had around for ages, plus a bit of homebrew isopropyl + rosin flux. Haven't noticed similar issues when working with "normal size" SMT stuff.Have considered trying some solder 2% silver in it, but would prefer to stay away from lead free as this is reworking stuff from well before the lead free era. Thanks! -Ian-

author: Someone
author_rank: Super Contributor
timestamp: May 11, 2016, 11:45:19 pm
content: You can find copper loaded solder in leaded and lead free varieties which will reduce the erosion.

author: Fsck
author_rank: Super Contributor
timestamp: May 11, 2016, 11:45:46 pm
content: it's to be expected. normally (for lead or tin based solder) the part is large enough that the metal that is dissolved is negligible. or the part is tinned, gold plated or otherwise has some other interface (which is "sacrificial" and expected to dissolve a bit).for thin wiring, you would normally use a solder (for lead or tin based) which has a composition which has some notable fraction (at least 1%, preferably more) of the material you're soldering. this will slow down the rate of dissolution.at 54awg, you're already in wire bonding range. the notable fraction of the solder, will probably no longer be notable, and be a significant fraction or even be nearly pure. do you have to solder at that size? I would normally never go below 36awg with hand soldering.what exactly is it connecting to?

author: ian.rees
author_rank: Contributor
timestamp: May 11, 2016, 11:52:59 pm
content: Quote from: Fsck on May 11, 2016, 11:45:46 pmI'm rewinding coils for "tuning fork" electronic watches - currently focusing on the Accutron 214. The originals were soldered, and I'd like to stick to that out of aesthetic considerations. Have had success so far with hand soldering, but it's a bit more finicky than I'd prefer.

author: Vgkid
author_rank: Super Contributor
timestamp: May 11, 2016, 11:59:04 pm
content: At that size, I wonder if welding the wires. Would be easier/ more reliable.

author: IanB
author_rank: Super Contributor
timestamp: May 12, 2016, 12:03:31 am
content: Maybe technique helps? There could be a soldering process that works better than other processes.For instance, trying to guess a good process:1. Tin the end of the wire by adding a drop of flux to the wire, adding a blob of solder to the tip of the iron, and touching the wire to the iron just long enough to melt the insulation2. Place a clean blob of solder on the contact point3. Reflow the tinned wire into the blob of solder by touching it briefly with the iron

author: KL27x
author_rank: Super Contributor
timestamp: May 12, 2016, 07:53:52 am
content: I bet the insulation is the tricky part. Getting it to melt without dissolving the conductor...Anyhoo, you can solder solderwire, even, when you get the knack. I wonder if similar technique would work for the wire. Small tip, small bead. Have a bit of extra length on the wire, so you can feed it in a little as you make the joint. W/e dissolves, no matter, so long as the end of the wire bonds to the bead and doesn't move too much around as it cools.

author: Richard Head
author_rank: Frequent Contributor
timestamp: May 12, 2016, 08:43:11 am
content: I'm rewinding coils for "tuning fork" electronic watches - currently focusing on the Accutron 214. The originals were soldered, and I'd like to stick to that out of aesthetic considerations. Have had success so far with hand soldering, but it's a bit more finicky than I'd prefer.Why don't you rather take up building model ships in bottles. It's probably easier!

author: Pjotr
author_rank: Frequent Contributor
timestamp: May 12, 2016, 09:09:41 am
content: Quote from: ian.rees on May 11, 2016, 10:17:17 pmIt is to be expected. Your options are: Do it as quick as possibleandkeep temperature as low as possible. The rate of dissolving also depends on the temperature of the molten solder. In this regard eutectic Pb/Sn/Ag is the best.

author: Fungus
author_rank: Super Contributor
timestamp: May 12, 2016, 09:27:48 am
content: Quote from: Richard Head on May 12, 2016, 08:43:11 amI once soldered some tiny SMD LEDs on the end of 40AWG magnet wire so I could suspend them 'invisibly' in a little jar with plants in it (little 'fireflies' controlled by an ATtiny85 hidden in the lid - see pic, I outlined a couple of the LEDs with red circles).Edit: I just looked up the size of the LED. It's an OSRAM"firefly"(perfect name!) and they measure 1.8x1.2x0.5 mm.It's fiddly. 40AWG wire justdoesn'tstay where you put it. I killed about 50% of the LEDs because their little metal end caps came off on the soldering iron. I don't know if I'd try it again, certainly not with that size LED.On the upside: It's been running for 3 years on the same CR2032. At least that part of the experiment was a success.Quote from: ian.rees on May 11, 2016, 10:17:17 pmI don't remember that happening to me. Sounds like your flux is really aggressive. Maybe try a different brand.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 12, 2016, 11:18:07 am
content: I worked on some projects using 50 - 60 AWG magnet wire. When we first started, I would scrape the wire under under a microscope pulling it under a razor blade. The insulation was higher temp and the iron would not melt it. Later we purchased an Eraser to strip the wire. This was a lot faster.I had a friend who made a laser welder that did this in high volume.

author: Fungus
author_rank: Super Contributor
timestamp: May 12, 2016, 11:41:52 am
content: Quote from: joeqsmith on May 12, 2016, 11:18:07 amI used very fine sandpaper. Pinch the wire between two pieces of sandpaper and pull it out. Repeat until the wire is shiny all round. It's a real pain to do both ends of a dozen pieces of wire (plus re-do all the wires that snapped because you squeezed the sandpaper too hard).Quote from: joeqsmith on May 12, 2016, 11:18:07 amYep. Apparently there's magnet wire you can just solder without stripping it first but I never found out where they sell that.

author: Pjotr
author_rank: Frequent Contributor
timestamp: May 12, 2016, 12:34:33 pm
content: The old trick to pre tin fine multi stranded litz wire is to use "Purine" as flux. Apply purine carefully to all the spead out wires, then twist it back into shape and dip it shortly in a tin pot. Works like a charm. Tinning 300 x 50AWG is easy that way. But you still need to do it fast and solder the end result also fast, otherwise all the wires will still dissolve. This worked for me with all kinds of enamelled transformer wire. Although I didn't try the very high temperature ones.

author: Neilm
author_rank: Super Contributor
timestamp: May 12, 2016, 06:51:26 pm
content: I do know that very small wires can "dissolve" when soldered due to chemical reactions between the solder and the copper. I seem to recall that you need a special solder to get it to hold without dissolving - don't remember the make up though

author: Ian.M
author_rank: Super Contributor
timestamp: May 12, 2016, 08:22:01 pm
content: Savbit solder Sn:50/Pb:48.5/Cu:1.5 - contains enough copper to slow dissolving of fine wires by two orders of magnitude

author: ian.rees
author_rank: Contributor
timestamp: May 12, 2016, 08:42:23 pm
content: Thanks for the replies everyone! That lead/tin/copper solder sounds like the ticket, I'll order some soon and will report back. -Ian-

author: uncle_bob
author_rank: Unknown
timestamp: May 12, 2016, 11:27:40 pm
content: HiAre you sure it is copper wire? Most of the very fine gauge stuff like you describe was done with something other than copper. The solubility in solder is one issue, the other issues are things like strength while doing the windings. You may need a solder loaded with something other than copper.Bob

author: ian.rees
author_rank: Contributor
timestamp: May 12, 2016, 11:43:20 pm
content: Quote from: uncle_bob on May 12, 2016, 11:27:40 pmYes, it's new wire bought for the purpose. Got the winding sorted; it's a delicate operation to say the least. -Ian-

author: uncle_bob
author_rank: Unknown
timestamp: May 13, 2016, 12:04:19 am
content: Quote from: ian.rees on May 12, 2016, 11:43:20 pmHiI guess the better question:Are you sure that the original wire was copper? Back when I was doing this sort of thing, we didn't use copper wire if it was being soldered.Bob

author: ian.rees
author_rank: Contributor
timestamp: May 14, 2016, 05:53:46 am
content: Yes, old wire is copper too as far as I can tell.Have ordered some 60% tin, 38% lead, 2% copper solder to try. -Ian-

author: SeanB
author_rank: Super Contributor
timestamp: May 14, 2016, 08:14:36 am
content: If it is a solder though insulation simply tin the pad, add flux then hold the still coated wire on the pad then touch the tip to the pad to both melt the solder, activate the flux and strip the insulation in one go. That way there is only one heat cycle to leach the wire. Pull the excess lead on the other side off afterwards, which will tell you that the join has been made by not moving through the solder joint.

author: Ian.M
author_rank: Super Contributor
timestamp: May 14, 2016, 08:43:25 am
content: I'd do some tests on a sample of the wire with the savbit solder to see how long it takes to dissolve enough to weaken the wire - start by carefully stripping it by pulling it through folded 400 grit wet&dry paper, flux it and keep prodding it into a big blob of solder on the tip of your iron until it crumples while timing it. If the time to failure is over ten seconds, you wont have major problems soldering it normally.Also, it *may* be worth trying the clean hot iron pressing the wire into a non-soluble aspirin tablet trick to strip the enamel, to minimise the time the solder has to dissolve the copper - *IF* you've got adequate fume extraction. Wipe with distilled water then IPA, as you don't want traces of acids left to corrode your very thin wire.

author: uncle_bob
author_rank: Unknown
timestamp: May 15, 2016, 01:11:00 pm
content: Quote from: ian.rees on May 14, 2016, 05:53:46 amHiAfter a bit of research....The original wire was chemically stripped. The soldering process was "tricky" and the operators that did it were trained in the process. My guess is that you will need to spend some quality time experimenting ...Bob

author: ian.rees
author_rank: Contributor
timestamp: May 15, 2016, 08:26:19 pm
content: Quote from: uncle_bob on May 15, 2016, 01:11:00 pmCould you share your source for this? Might be other useful answers to questions I haven't thought of asking yet! -Ian-

author: uncle_bob
author_rank: Unknown
timestamp: May 16, 2016, 08:15:00 pm
content: Quote from: ian.rees on May 15, 2016, 08:26:19 pmHiA conversation with a ex-Bulova engineer. This was in about 1982. He has been gone now for a couple of decades.Bob

author: Richard Head
author_rank: Frequent Contributor
timestamp: May 17, 2016, 08:13:55 am
content: What's "Purine"?

author: Pjotr
author_rank: Frequent Contributor
timestamp: May 17, 2016, 08:44:09 am
content: Purine by itself is a basic raw material used for many purposes. One of them is a classic non aggressive solder grease.

author: Ian.M
author_rank: Super Contributor
timestamp: May 17, 2016, 09:03:14 am
content: The MSDS for CFS/Griffon's Purene paste flux tells me it contains Zinc Chloride, so its fairly aggressive.I wouldn't use it for fine wires because of the risk of corrosion problems in high humidity environments if its residue isn't totally removed. A good liquid R or RMA flux would be a better choice compared to any paste flux as the hard rosin residue is close to inert at room temperature and as long as you avoid RA fluxes with metal salts or chlorides, the risk of chemical corrosion is low.

author: Pjotr
author_rank: Frequent Contributor
timestamp: May 17, 2016, 09:36:40 am
content: I wouldn't use ultrafine copper in a high humidity environment anyway. Have used this method without problem and joints made 20 years ago are still alive and kickingBut maybe there are more modern solutions? I don't know, and didn't come up in this thread. A very experienced technician at the machine lab of the Delft University pointed me to this method long time ago, when I had to do about 100 2KW/400Khz transformers with ultra fine multi stranded litz wire.Did try many modern fluxes, they do not work if you do not carefully remove the enamel mechanically on forehand. And most "solder-able" enamels are in fact not so solder able in reality.

author: ian.rees
author_rank: Contributor
timestamp: May 24, 2016, 08:35:43 am
content: Received a new roll of Edsyn "Sn60PbCu2 FSW32" solder from Element14 today - works great! I kept a molten bead of solder over some of the wire for a minute or so and didn't have any problems with the wire dissolving away. Thank very much! -Ian-

author: hr8799
author_rank: Newbie
timestamp: September 08, 2016, 02:04:58 pm
content: Hello ian.rees,I just stumbled upon this thread and am very interested to learn how things turned out. I've been toying with the idea of repairing 214 (and 218) coils and would benefit greatly from hearing about your experiences. Were you able to successfully rewind a coil and end up with a working circuit with the appropriate resistance?I would like to give this a try (I have 6 or 7 coils that need work)!

author: N2IXK
author_rank: Frequent Contributor
timestamp: September 08, 2016, 05:50:29 pm
content: I work with similar fine magnet wire when wiring up strain gages for force measurement. I use the thermally strippable wire, dip the end in a liquid rosin flux, and tin the end in a solder pot. Then trim back the tinned end as needed for the specific connection to be made.

author: ian.rees
author_rank: Contributor
timestamp: September 08, 2016, 09:06:02 pm
content: Hi hr8799,It is still a work in progress (has been probably 9 months worth of occasional evenings and weekends), but I can currently re-wind 214 coils and don't expect 218 ones to be too much additional work. The re-winding is a bit more nuanced than I anticipated at the outset, beyond getting the wire tension right.Soon I hope to start selling re-wound coils (through Accutron repair people like Rob Berkavicius, who has been immensely helpful in this) on an exchange basis, and once I've recouped the cost of the project my plan is to do a series of blog posts about the project. Thanks for your interest! -Ian-

author: hr8799
author_rank: Newbie
timestamp: September 09, 2016, 03:03:38 am
content: Very cool! I am looking forward to reading your blog posts, as I'm sure many others are.My biggest roadblock at the moment is obtaining the wire. It looks like everyone wants you to buy $1000 worth the stuff. I just want a small amount to experiment with. I may use something "close" to setup the winding apparatus. I never imagined it would be so expensive.Bets of luck!

author: ez24
author_rank: Super Contributor
timestamp: September 09, 2016, 08:33:01 am
content: Quote from: Fungus on May 12, 2016, 11:41:52 amI also used very fine sandpaper. I put the wire on the paper and pressed down on it lightly with my finger and pulled lightly on the wire.The wire made a great security perimeter wire because it would break so easy. But I did not solder it. I made connection with a small spring