An Affordable Ultrasonic Soldering Iron

One of the most interesting facets of our community of hackers and makers comes from its never-ending capacity to experiment and to deliver new technologies and techniques. Ample demonstration of this came this morning, in the form of [Hunter Scott]’s Hackaday.io project to create an ultrasonic soldering iron. This is a soldering technique in which the iron is subjected to ultrasonic vibrations which cavitate the surface of the materials to be soldered and remove any oxides which would impede the adhesion of the solder. In this way normally unsolderable materials such as stainless steel, aluminium, ceramic, or glass can be soldered without the need for flux or other specialist chemicals. Ultrasonic soldering has been an expensive business, and [Hunter]’s project aims to change that.

This iron takes the element and tip from a conventional mains-powered soldering iron and mounts it on the transducer from an ultrasonic cleaner. The transducer must be given an appropriate load which in the case of the cleaner is furnished by a water bath, or it will overheat and burn out. [Hunter]’s load is just a soldering iron element, so to prevent transducer meltdown he keeps the element powered continuously but the transducer on a momentary-action switch to ensure it only runs for the short time he’s soldering. The project is not quite finished so he’s yet to prove whether this approach will save his transducer, but we feel it’s an interesting enough idea to make it definitely worth following.

This is the first ultrasonic soldering project we’ve featured here at Hackaday. We have however had an ultrasonic plastic welder before, and an ultrasonic vapour polisher for 3D prints. It would be good to think this project could spark a raft of others that improve and refine DIY ultrasonic soldering designs.

57 thoughts on “An Affordable Ultrasonic Soldering Iron

    1. Now, with a straight face, is sonic screwdriver (not a whovian multi-potent artefact) a sound idea: would a screwdriver with a transducer on it allow loosening of rusted bolts, or to the contrary, weld good ones locked?

    1. I dont mean to sound sarcastic, but did you read the article ?

      1. used for soldering..
      2. “the iron is subjected to ultrasonic vibrations which cavitate the surface of the materials to be soldered”
      3. this will “remove any oxides which would impede the adhesion of the solder”

      1. After having a thought … with this, why would we need solder anyway? Just use the ultrasound to weld the device contacts to the pads! As a bonus, we can do away with expensive and scarce copper and tin, and use good-enough cheap aluminium clad boards instead.

      2. Sorry i missed it in there. I only brossed threw it. There was a artical that I read last week and it did not explained this in it, and this artical started off the same way as the other one. So I thought there was no new info. Thank you for letting me know what it did..

          1. Come on Yarr, he probably has a new phone and disabled auto correct. That’s what I did. Spell-check on Android is very strange.
            He admitted that he skimmed and missed one point. I think he is from another country so misspellings are expected.

    2. Read.

      “This is a soldering technique in which the iron is subjected to ultrasonic vibrations which cavitate the surface of the materials to be soldered and remove any oxides which would impede the adhesion of the solder. In this way normally unsolderable materials such as stainless steel, aluminium, ceramic, or glass can be soldered without the need for flux or other specialist chemicals. Ultrasonic soldering has been an expensive business, and [Hunter]’s project aims to change that.”

  1. Can you elaborate on “in this way normally unsolderable materials such as stainless steel, aluminium or ceramics or glass can be soldered”.

    Ultrasonics are going to have a hard time removing ceramic aluminum oxides or, glass oxides? Glass is kind of already bulk oxidized though. Unless I am completely missing something here (which is indeed possible). What material solders ceramics or glass at room temperatures anyway?

      1. I think he’s imagining the room would be at room temperature. Rather than inside a furnace or kiln or whatever. Obviously the solder would be hot! If you could solder to glass, that would be very impressive. I suppose it has lots of bumps and crevices on a micro-scale, for the solder to stick to. Is that how normal solder works, or is there some inter-metallic bond thing going on?

        1. Traditional glass artwork, like stained glass and Tiffany lamps, are soldered at high temperatures, hot enough to vaporize the lead. I don’t know much else about soldering glass other than that.

          1. My mom used to make tiffany lampshades and decorations. You do not directly “solder” the glass shards together! The trick was to first cover the edges of the glass shards with a strip of copper foil all around, basically making a C-shaped wrap around the edges. Then you would just solder the copper together with tin, and the added tin would make the copper foil stable enough so it could hold the glass pieces in place.

        2. Correct, though one could certainly heat the bulk up.to traditional soldering temperatures as well and I don’t think it would improve adhesion. Either way, I still am struggling to determine how you can achieve adhesion of solder to ceramics or glass, irregardless of the temperature or “surface scale” that isn’t really even present on glass to begin with. I am certainly not an expert in this particular field though I do have some experience with parts of this, mostly involving adhesives though.

          1. Soldering glass is not done with tin, tin-lead or in general metals. Solder for glass is a low melting glass with high content of boron and/or lead-oxide.

  2. I have read that indium s0lders to glass.

    Long ago I read a toss-off mention of a “vibroblade” daggar in a Heinlein story and I often wondered if a knife somehow attached to an ultrasonic source might make a good weapon or even a superior chef’s kitchen instrument. I know nothing of the mechanics that might be applicable.

        1. Can’t get the video working right now (prob at my end), but does soldering mean with actual solder? The tin stuff? Or is he actually welding them together by making the glass molecules mix together?

    1. Vibroblades, knives and swords, are also standard human melee weapons in the Mechwarrior universe. They get very hot, apparently. Not sure if that means they cauterise the wounds they cause, and if that diminishes their killing power.

  3. Nice!
    Until the ultrasonic welder will be ready, aluminum can be soldered with a normal soldering iron if you solder under a big drop of oil. The initial thin layer of oxides is removed mechanically by the soldering tip, then the oil prevent the oxygen to come in contact with the welding surface and form new oxides. Also, there is some special flux you can buy for soldering on aluminum.

        1. He didn’t ask WHY you would use oil, he asked WHAT oil you would use, because any oil that either he or I can think of would catch fire well before solder would melt.

          Seriously, does everyone in this comments thread have a learning disability or something? You’re at least the third person so far who is clearly incapable of doing something as simple as reading.

  4. Am I missing something? He’s attaching a heating element (presumably 250+ degC) to an ultrasonic transducer using a 3D printed plastic part – something which sounds ill-suited to high temperatures and indeed as a medium for efficiently coupling the ultrasonic energy.

    I’d even be a little sceptical about using aluminium as he says he’d have preferred, it can be quite soft and wouldn’t be my 1st choice for this application.

  5. From what little I’ve read about using these transducers, the geometry and materials of anything you connect to them must be carefully chosen to transfer the sonic energy to the load. The exact details of which seem to be a black art.

    But I think the following is safe to assume:

    1) Adapter covers only ~50% of the surface of the transducer’s horn. Where the horn surface is exposed to air, almost all the energy will be reflected back to the transducer, so that’s 50% loss.
    2) The same issue exists on the front (iron) surface of the square adapter. Energy will reflect off the ~30% of that surface not covered by the iron.
    3) Adapter is made of plastic. Much lower density than the aluminum of the transducer horn. So it will present an impedance mismatch, where additional energy will be reflected at the interface rather than transmitted. And again at the interface of the adapter and iron.

    “The project is not quite finished so he’s yet to prove whether this approach will save his transducer…”

    That’s a good question, and so is whether he’ll get a useful amount of energy at the iron tip. A test is needed, and it looks finished enough to perform such a test immediately. Even if it’s only to see if the unheated iron tip can perform some lesser feat, like atomizing a small amount of water.

    “One of the most interesting facets of our community of hackers and makers comes from its never-ending capacity to experiment and to deliver new technologies and techniques.”

    Agreed, but no experiment has yet been performed here. So it’s not as interesting as it could have been. Considering a test seems possible in the near future, HAD jumped the gun featuring this in my opinion.

  6. Nice idea. It will be interesting to see whether the mass loading of the solder element and the coupling to the ultrasonic transducer will allow sufficient energy to reach the piece to be effective. BTW how do you hold the device without dampening the effect? Also, cavitation takes place in liquids so I assume that it is cavitation of the solder that is expected to clean the material. I suspect that it will have a hard time removing oxides on, say, aluminum but it might make regular soldering work without flux. I look forward to a follow up artice.

  7. BTW I was also wondering whether ultrasonics could help speed PCB etching. I use heat and air bubbles to help etch but maybe ultrasonics would work better. I know most people send out PCB designs for manufacture, but I still have a need to be able to make one-off simple single sided PCBs quickly.

    1. That’s an interesting idea, although I think you would need a very tough resist to hold up under ultrasonic agitation. But be aware that single-frequency ultrasonic cleaners, such as used for jewelry, create powerful standing waves which can damage crystals, IC bond wires, and other delicate electronic features. Ultrasonic cleaners for electronics use are designed to sweep the transducer frequency to avoid standing waves.

      https://www.youtube.com/watch?v=2wetLSvoQwQ

      Most cheap ultrasonic cleaners use a self-resonant circuit tuned to drive the transducer at its optimal frequency. I’m interested in dynamically detuning the driver to avoid the standing wave issue, but I haven’t performed any experiments.

    2. you might end up cleaning the etch resist right off the board. sounds interesting though. personally I use a pump and just let the acid rinse over the board for a while.

  8. I spent a long time repairing domestic electronics and that mean resoldering a lot of dry joints.

    At that time domestic electronics had a lot of specialized components and in many cases the dry joint was a delayed result of component lead oxidization prior to the original assembly.

    Normal soldering wouldn’t *wet* these joints properly so there was two solutions.

    One solution was to completely remove the part and clean the component lead by scraping it with a sharp surface.

    The other solution was to move the iron back and forth while hard against the component lead while soldering and the screeching sound that would make helped for a then unknown reason.

    Now I know why.

    This would be so good for the service industry and even in manufacture where there is always some degree of component oxidization.

    +100, love it!

    1. As long as the ultrasonic energy does not destroy the component (or a nearby component), delaminates your copper traces/pads from the epoxy-board or has any other harmful effect, maybe that could be useful. I just have a feeling that the energy you need to remove oxyde layers exceeds what most small components tolerate. Multilayer ceramic capacitors, wire-bonding in ICs and LEDs, everything MEMS or any crystal seem very likely to have a bad tolerance for high energy ultrasonic vibrations.
      If you need very well cleaned boards to apply conformal coatings or for some medical applications, you have to be very careful when trying to speed up the cleaning time by using an ultrasonic cleaning bath too.
      It’s probably okay to use on connectors and large components, but with todays miniaturization and board density, my guess would be that using any chemical agent to remove oxydation is better than applying ultrasonic energy.

  9. Much like kickstarter campaigns, it would be good to know how many of these featured projects every actually work. I don’t mind featuring work in progress but at this stage there’s a vast chasm of thorny potential issues between “nearly finished” and “actually works as intended”.

  10. Matching (accoustically) your transducer to the tip will be very difficult. You will be better off to use half or quarter Inch ceramic disc stack. it will fit inside the handle of Weller and most probably would not need heating element as vibration alone will heat the solder and melt it, Send me a slug mail address and I will send you a box of them to try. I may be able to find some completed stacks for you if I could remember where I stored them (Some 20 years ago !)

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