Do you have the model of your soldering iron? The lead-free stuff does indeed require a higher melting point. Based on wikipedia it say the Sn-Ag-Cu melts at around 217'C vs. 188'C for the 60/40 solder.
Mine is a Weller WP35. But at the class we had at least eight different irons and I think no two were the same. (This is an entirely volunteer-run class with essentially no budget, so we have to make do with what friends will loan us). Three of the irons had bases with variable power output. Just marked 1 to 5 though, not calibrated to temperature. All of those we turned up to their highest level since we were using lead-free.
All the irons were capable of melting the solder just fine, it just didn't *stick* to them and their tips quickly turned brown/black.
Did you try any solder flux? That stuff really is amazing when you're having a hard time getting stuff to stick - i've used a solder flux based pen and it had great results.
We had a small jar of flux we were dipping the irons into in an attempt to clean them off and get them to tin. It seemed to help a little, especially if i then tried to tin them with lead solder, rather than silver. But only a little. One of the more knowledgeable volunteers commented that it wasn't a particularly aggressive flux and we might try another.
(For clarity, we did have a roll of lead solder available. I was using it in my attempts to get the irons working again, but for safety/toxicity reasons the head instructor didn't want the kids using it themselves.)
I think that it is pretty well covered here. A couple of points however. I avoid lead free solder wherever possible as it is indeed harder to use. Tanners resin (as used in resin core solder and on the hands of Gymnasts can be dissolved in methylated spirits and painted onto a PCB like a layer of varnish. This helps the solder immensely as it acts as a non corrosive flux. I have used 60/40 tin/lead solder on a roll for 50 years, and all I do is wash hands (if I remember) before eating. I recently had a heavy metals blood test done, and I was well within acceptable limits. I would have no hesitation about 60/40 solder with children. The worst injury I ever had from it was when cleaning the soldering iron and splashed it into my sock. Ouch!. I hope this also helps at least with perspective. Remember it is what ultimately happens to the solder in land fill that is important.
I'm a hardware engineer myself and I do quite a lot of soldering that needs to conform to ROHS standards. Flux pens will make your life so much easier. I know they add cost to something where you have no budget, but if you want to stay with lead free solder, it's your best bet.
In my experience, the lead-free stuff is not more difficult to solder if: 1)the iron is hot enough 2)wiped clean with a wet cloth 3)it is solder with a flux core (but desoldering from double sided pcb's is a nighmare)
I suspect point 3 is the problem
however: solder smoke from classic 40/60 with rosin core is actually less toxic than lead free stuff with far more agressive flux. The lead does not vaporize at normal soldering temperatures, the smoke is just from the resin. The kids just need to wash their hands after soldering.
I don't find any difficulty in soldering with Sn-Ag-Cu lead free solder. If tip of soldering iron is getting black and not getting tinned, reason could be. 1) Pit might have formed in the tip. 2) Clean the tip with wet cloth when tip is hot. 3) Soldering iron may be old and may not be giving sufficient heat. Use 40 watt soldering iron for best results. Follow steps given below for better soldering. 1) Check if large pit is formed file it with smooth file to remove pit. 2) If no pit in the tip, rub tip on Zero grade emery paper; when tip is hot and the tin the tip using lead free rosin core solder. If solder is not rosin core type, Rub tip on wet cloth then on paste flux and then on solder wire simultaneously for 3 to 4 times or till tip gets tinned. 3) You may use well known brand solder wire and solder past. solder wire must be 16 gauge or more.
There should not be any problem in soldering with lead free solder wire. Follow tips given below. 1) Use 40 watt soldering iron. 2) Check mains supply voltage it must be as mentioned on soldering iron. if it is a temperature controlled set temperature to 250 degree C. 3) file the tip and make it flat and oval shaped (pit must be removed by filing if present). 4) tin the tip using solder, flux alternately rubbing on wet cloth. if still tip appears black rub on zero grade emery paper. This procedure tins the tip and holds solder.
The metal to be soldered needs to be clean to the point of being shiny where it is to be soldered. Apply flux to every part to be soldered, before soldering.
Some metals, like aluminium and stainless steel, are very resistant to being soldered, unless using special solder and flux. It is also a problem if the metal has even slight surface corrosion. Even copper can be difficult to solder if it has a slight brown corrosion film on the surface.
These are all standard inexpensive electronic components: resistors, LEDs, copper wire, etc. So I'd guess a mix of copper and nickel-plated steel? I realize I don't actually know for sure what most leads are made of.
The components themselves are soldering just fine, when we get the irons to work. It's really just getting the irons to tin that's the problem.
Thanks to everyone for all the helpful replies overnight!
Having trouble with soldering irons in a class for kids. Help!
I've been volunteering with a program called Kids Building Things recently; last weekend we ran a class in soldering. The kids made a little LED bracelet (powered by coin cells) we'd designed for them.
We had more trouble with the soldering irons than I'd ever witnessed. We were using an Sn-Ag-Cu leadfree solder, which I've never used before (my own personal roll of classic 60/40 has never run out in the 20 years I've had it, since I'm just an occasional hobbyist).
Anyway, we had about 8 different irons loaned by different people, and for the most part couldn't get them clean enough to tin. Solder would just bead up and roll off the iron. Often there was a visible black or brown layer of oxide on them.
This included my own iron, which I've used for a decade without any trouble. I even put a brand new tip in it halfway through the class. Five minutes later it had a black layer covering the tip and was difficult to make a joint with. I was watching the kid the whole time - he wasn't doing anything wrong (like burning plastic with it or anything). Every couple of minutes I'd have to scrub the tip vigorously on a sponge to expose a shiny spot just barely large enough for him to work with.
Is the lead-free stuff really just that much harder to work with? That was the only thing different from the way I've always used my iron, and I've never had any trouble like this.
Any suggestions greatly valued, thanks!
EDIT: Thanks to everyone for all the helpful replies!
Thanks to you for bringing this problem up. As an electronic technician and hobbyist for many years, I have for a long time been suspicious of "the new stuff" ! Lead free solder has already been shown to have problems in industrial use.
Here is a good recommendation for you for Soldering Irons
Very good company to deal with inclusive magnifying glasses and have excellent inter personnel customer relations
“I don’t say this lightly either If they are not good I say so too” , but they are excellent and very well priced again I don’t ever lie I say exactly what I want to say regardless
Also for fluxes and solder including leaded solder which I still use I can’t stand this lead free stuff either
So I’m in agreement with you I think its junk ,waste of time ,and solves nothing except creates more problems than its worth
If we are at such a throw away age what the bloody point anyway you cant dispose of pcb’s or silicon or multilayer boards You only have to go to the rubbish dump to work this out so as for the unleaded solder story I cant quite see what they have achieved , still …….
Breached to the brim cant get anymore in their if they tried I said this would happen some 7 ,8 years ago when they brought this idea out said it would never work , Low and behold what have we here the first of many to say they are finding this extremely difficult ,non clean joints, bad solder joints, equipment failing left right and center, just as
I said would happen and it has “No point in arguing with them is their after all they know best, ho hum “
Anyway here is the next decent company you can deal with Good fluxes expensive but good ao do high quality leaded solder
I think we had a few trouble makers who were hell bent in trying to put everyone out of business who were any good , never works does it you see word of mouth is what counts and experiance !!
Thank god for the few friends I still do have but the they always were Shows you doesent it
✨ The discussion addresses challenges encountered when using lead-free solder (Sn-Ag-Cu alloy melting at ~217°C) in a kids' electronics class, particularly rapid oxidation and poor tinning of soldering iron tips. Multiple soldering irons, including a Weller WP35, were used, often with variable power settings but lacking precise temperature control. The lead-free solder requires higher temperatures and more aggressive flux to ensure proper wetting and tip maintenance. Flux application, including flux pens and dipping, was recommended to improve solder adhesion and tip tinning. Cleaning methods such as wiping hot tips with wet cloths, filing or sanding pits on tips, and using zero-grade emery paper were suggested to restore tip condition. A 40-watt iron with temperature control set around 250°C is advised for lead-free soldering. The components soldered are typical electronic parts (resistors, LEDs, copper wire), primarily copper and nickel-plated steel. Some participants expressed preference for traditional 60/40 tin/lead solder due to ease of use and lower toxicity concerns with proper hygiene. The discussion also touched on the environmental and practical trade-offs of lead-free solder. Recommendations included sourcing quality flux pens (e.g., from Farnell) and considering reputable suppliers like pcb-soldering.co.uk for equipment and materials. Generated by the language model.
TL;DR: For lead‑free Sn‑Ag‑Cu, run ~250°C/40 W and keep tips freshly tinned; “There should not be any problem in soldering with lead free solder wire.” [Elektroda, Shrikant Kamble, post #21667052]
Why it matters: This FAQ helps instructors and hobbyists fix rapid tip oxidation and poor wetting when teaching kids to solder lead‑free.
Lead‑free needs more heat and active flux. If the tip runs cool or oxidizes, solder beads and rolls off. Set the station near 250°C or use a solid 40 W iron, apply flux, and re‑tin often. Persistent black oxide blocks wetting and mandates reconditioning. [Elektroda, Shrikant Kamble, post #21667052]
What temperature or power should I use for lead‑free soldering in class?
Use a 40 W iron or set a temperature‑controlled base near 250°C. This compensates for the higher melting point of Sn‑Ag‑Cu alloys and maintains wetting margin during repetitive joints by learners. Wipe and re‑tin frequently to protect the plating. [Elektroda, Shrikant Kamble, post #21667052]
How do I rescue a blackened, non‑tinning tip? (3‑step)
While hot, wipe on a wet sponge, then apply paste flux.
Lightly polish with zero‑grade emery paper if oxide persists.
Yes. Lead‑free alloys wet slower, so a flux pen speeds wetting and reduces dwell time. As one engineer put it, “Flux pens will make your life so much easier.” Budget one pen; a single pen can service many stations in a class. [Elektroda, Mike P OKeeffe, post #21667049]
Is the Weller WP35 powerful enough for lead‑free?
It can melt lead‑free, but wetting fails if the tip oxidizes or lacks flux. In class tests, multiple irons—including a WP35—melted solder but wouldn’t hold it when oxidized. Keep tips clean and fluxed, and re‑tin frequently during sessions. [Elektroda, Evan Dorn, post #21667045]
Why did our tips oxidize so fast during the kids’ workshop?
Long on‑time at higher heat, minimal flux, and repeated exposure to air cause rapid oxidation. In the class, tips browned or blackened within minutes and stopped tinning until scrubbed. Add flux, reduce idle time, and re‑tin after every few joints. [Elektroda, Evan Dorn, post #21667043]
What’s the best quick routine between joints to prevent oxidation?
Use a wet wipe and re‑tin cycle. Wipe on a damp sponge to remove residue, touch the solder to flood the tip, and return to work. This maintains a protective solder film that blocks oxygen. Keep the interval short in teaching settings. [Elektroda, Shrikant Kamble, post #21667051]
What is flux, and which type should I use?
Flux cleans oxides so solder can wet metal surfaces. For lead‑free, use rosin or no‑clean flux pens for targeted application. If a mild jarred flux struggles, step up to a more active flux to re‑establish wetting on tips and pads. [Elektroda, Joe Wolin, post #21667046]
Which solder wire size is suitable for beginners?
Use thicker solder for easier feeding and heat transfer. Guidance from the thread recommends 16‑gauge or larger wire when training, combined with rosin‑core flux. This reduces hesitation and shortens dwell time on pads and leads. [Elektroda, Shrikant Kamble, post #21667051]
Are kids ok to use leaded solder, or should we keep lead‑free only?
One contributor notes rosin smoke drives most fumes and says lead doesn’t vaporize at normal temps. Emphasize handwashing and fume management. Policy choices vary, but good hygiene and ventilation are essential regardless of alloy. Include a safety briefing. [Elektroda, Ruben Proost, post #21667050]
Does brand or supplier matter for flux and solder?
Quality helps consistency. The thread recommends established suppliers for fluxes and leaded or lead‑free solder, noting better results and support. This reduces joint failures and tip issues over time in classroom programs. [Elektroda, Mark Harrington, post #21667056]
Is lead‑free inherently worse for reliability?
Some practitioners express long‑term concerns with lead‑free in industry settings. The thread’s perspective highlights skepticism and field issues. For classes, focus on process control—heat, cleanliness, and flux—regardless of alloy choice. [Elektroda, Frank Bushnell, post #21667055]
What does Sn‑Ag‑Cu (SAC) mean in solder specs?
SAC denotes a tin‑silver‑copper alloy used for lead‑free soldering. It melts hotter than 60/40 tin‑lead, so you raise tip temperature and rely more on fresh flux to secure wetting and reduce oxidation. [Elektroda, Joe Wolin, post #21667044]
Could our mixed pile of irons be the problem?
Mixed gear complicates consistency. In the class, at least eight different irons behaved differently, and variable bases were run at maximum. Standardize temperature or power and enforce the same tip‑care routine across stations. [Elektroda, Evan Dorn, post #21667045]
Any tricky edge cases we should expect?
Desoldering on double‑sided PCBs with lead‑free can be painful. Expect longer dwell times and tougher through‑hole clearing. Train on single‑sided kits first, and keep braid and flux handy to avoid pad lifting. [Elektroda, Ruben Proost, post #21667050]
Our components solder fine, but tips won’t tin—are the metals to blame?
No. Standard parts like resistors, LEDs, and copper wire soldered fine once tips worked. The root cause was tip condition and flux activity, not lead composition on component leads. Prioritize tip care and flux selection. [Elektroda, Evan Dorn, post #21667054]
