Ultrasonic soldering bonds glass, titanium, stainless steel, ceramics, tungsten, nichrome...

today on applied science i'm going to show you this technique of ultrasonic soldering this lets you bond all kinds of unusual metals to non-metals such as copper to silicon or aluminum to nickel or phosphor bronze to glass pretty much any reasonable metal or ceramic or glass can be bonded with this technique so in today's video i'm going to show you how this works the science behind it how you can build your own rig and then also some options for commercial equipment so to make this work you need two things one the ultrasonic soldering iron and this is actually relatively easy to build with parts you can get right away and you can buy it commercially too but we'll take this apart later and see exactly how i built it and then the next thing you need is this special solder this whole process is a chemical reaction between an active solder and the base materials so it completely doesn't work with just normal you know electronic solder or really any other kind of solder that you might encounter these active solders are only made by two or three manufacturers worldwide and as far as i can tell they don't use distributors and so you'll never find these solders on digikey or any other easy to buy place so what you have to do is go to the manufacturer's website and it says you know call us for more details so whenever i see that i always feel like that's a good prompt to kind of come up with an alternative so i use this for most of the experiments today and this is actually an alloy that i made myself by melting down the ingredients in a vacuum induction furnace and then poured it out and cut it into strips so that's we'll uh talk about that in my next video but uh whether it's through money or connections or determination you have to come up with some of this active solder so let's look at the chemistry first and see how this process is so different from regular soldering so in conventional soldering what we're looking for is a metal to metal bond and this is good because all metals as far as i know use this metallic bonding where it's this sea of electrons so basically if you get any metals next to each other and you warm them up a bit they will bond together the problem is that we live in an oxygen atmosphere here so if you have a metal laying out the surface here is not copper it's actually copper oxide because this thing's been sitting out in the air for a while and so that's a problem because this copper oxide gets between the solder and the base metal and that's not a metal so then this metallic bonding can't work so the whole point of flux is that we remove the oxide layer and then we have metal to metal contact and then the flux also creates this little bubble like literally an encapsulation of the joint so that oxygen can't get in there while you're working and this works very well you know the joke goes what's the difference between someone just beginning soldering and a pro flux and it's true you've got to use lots of flux and use the right kind of flux and that's what makes soldering work in atmosphere one thing that i always found paradoxical is that you know if you don't clean certain types of flux off the metal after you're done with it it will actually cause the metal to corrode so how could it be that flux removes corrosion and then also causes it the answer is that the skin of oxide is actually what's preventing this copper from corroding away like iron so if you have iron it basically flakes apart as it rusts and disintegrates but copper doesn't do that because the coating on here is continuous and it actually protects the metal so if we covered this in flux the first thing would happen is we eliminate the oxide coating and now we have nice fresh metal easy to solder but then if we leave the flux on there that coating is no longer available to protect the metal so then as the oxygen diffuses in it will corrode the metal and then the flux removes that oxide and then more oxygen gets in and corrodes it so counter-intuitively it's corrosive and it removes corrosion at the same time okay so that's good for metal to metal bonding but what happens if we want to solder to something that isn't metal or we want to solder to a metal that is so reactive that we can't come up with a chemical flux that works at reasonable temperatures like let's say titanium for example titanium is notoriously difficult to bond because it's so incredibly active then what do we do then we go to this active soldering technique when using an active solder there is no flux and so instead of trying to eliminate the oxides that are present on the materials here we're actually going to use a chemical reaction between the ingredients in the flux and whatever oxides are present and so if we look at the ingredients they're actually very similar so the first three ingredients are the same tin silver and copper is what's very commonly used as a lead-free solder these days sac sac and the active solder has almost the same thing but to it we add titanium at about a couple percent and then just a tiny tiny amount of cerium and gallium and the purpose of these other ingredients is to make the solder bond to things that aren't necessarily metals so for example the titanium as i mentioned is super reactive so if we put a little bit of that in the solder then the solder is able to stick to things that aren't metals because it in part will create these titanium oxide type structures that can bond to non-metals the reason that we need the ultrasonic mechanical energy is because the surface wetting is still a problem even if the solder is chemically able to bond to non-metals or oxide layers that are on metals sometimes the surface tension is still so high that the solder can't really get into like molecular contact with the surface and so this ultrasonic energy basically just bashes stuff around and increases the surface contact until the solder can start making chemical bonds there in a lot of the diagrams that i've seen online describing this process they show this kind of reaction layer here so there might be pure metal inside the solder blob and if your base is glass or ceramic or something there's this intermetallic region here where we have compounds that have properties of both the non-metal and the metal and form this bridge between so i mentioned titanium is used because it has such a strong affinity to react with oxygen in fact it turns out it's a little too strong what ends up happening is if we have titanium in our blob of solder and we've got the ultrasonics on so that occasionally it will sort of rip the blob open in such a way that fresh titanium is exposed to the joint unfortunately there's still oxygen everywhere because this is all happening in air and what would happen at low temperatures is the titanium would just oxidize so it would rip the solder block open the titanium would oxidize just with atmospheric oxygen and then we wouldn't really have a chance to bond with the surface what we really need is unreacted titanium in contact with the surface so that it can bond with whatever oxides are going on with the surface here and give us a decent bond so a couple of these other ingredients help with that problem the cerium is also quite active and it somehow forms a protective bubble around these titanium rich grains in the solder it's fairly advanced metallurgy and i'll link to some of the interesting papers here the concentration of cerium and titanium is not constant throughout the blob of solder the titanium forms these grains like titanium enriched areas of the solder which is why when you rip one of these things open you get fresh titanium exposed but apparently the cerium also interacts with these blobs and acts like a protective layer to keep the oxygen from getting in pretty advanced stuff as far as i can tell this chemistry was only invented maybe 10 or 20 or 30 years ago or something so it's a relatively new technology when it comes to soldering and then finally the gallium is a surface wetting agent again just to help everything get in contact with each other one last thing i'll point out with the chemistry gallium pure gallium and pure indium can wet non-metals just fine in fact if you put them on glass and warm it up they will absolutely wet the glass just fine so they can be considered active solders in their pure form and even used that way just fine the only problem is the melting point of gallium is way too low if you hold this in your hand even it turns to a liquid and the melting point of indium is also kind of low and so you need to add something to it to raise the melting point to get a practical solder like lead or tin or something and when you do that it's not as active anymore so the reason you go through the trouble of having all this chemistry is to get the melting point you want the strength of the solder you want the aggressiveness in sort of bonding to the surface and the ability to bond to metals as well as non-metals let's take apart this soldering gun so you can see how to build one of these the basic idea is that we want it hot here of course and we want there to be ultrasonic energy directed in there but we can't heat up the transducer because that might you know hurt the transducer if we get up to the curie point or whatever so what we want is basically a long metal rod that connects that goes all the way through the iron and dissipates enough heat by the time it gets to the transducer up here and i basically came up with this design after just looking at a picture of one of the commercial models it could stand to have quite a bit of improvement so as we take it apart i'll explain what i've learned from this thing okay so i wanted a metal here that wasn't a good thermal conductor so i used a piece of stainless steel and then silver soldered it into a threaded rod that threaded in and bolted into the transducer and then also silver soldered it to the existing tip of the of the iron so i actually made this thing by taking apart a a cheapo a soldering iron and i used the heating element and the tip from this this exact iron and so this is actually what it looked like when it was new as you can see there's actually a tremendous amount of erosion on the tip here i've only used this thing for an afternoon of horsing around and the tip is completely gone so i'm not really sure what's going on there uh it might be a little too much or a lot too much ultrasonic energy or perhaps the solder is very corrosive in a way that i didn't anticipate or maybe the tip is just really that bad or something but that's one unknown two it's absolutely true that this transducer is way too large so this is a in theory a 60 watt transducer and driver and the only reason i picked this is because it was easily available i just went on ebay and got the transducer and the driver for you know 40 or 50 or something like that but the commercial ultrasonic soldering irons are generally more in like the 10 to 15 watt range and like you say this is 60. so what i tried to do is use a variac to turn it down but unfortunately the circuit doesn't oscillate if you get it below about 80 or 90 percent of line voltage so it's it is running at close to the full 60 watts there and then of course i didn't want to hang on to the metal myself due to both shock potential and it's too hot to hang on to so i made this fiberglass cover here so i could put my hand hand here without getting beaten up and the heating element is just it's just a metal tube with the wires coming off now i actually did have a problem with this in the first rev i used in the in the original soldering iron it had these flexible fiberglass protectors but unfortunately the ultrasonic energy is so powerful that the wire inside the fiberglass rubs against the shaft here and eventually burns through instead i found another brand of soldering iron that has hard ceramic tube insulators in there and so i just broke this into pieces and used this as the insulator to keep the wires away from the center rod later in my adventures i was able to get a couple samples of commercially made active solder so these are soda soles or 186 and 297 and these are actually leaded alloys and i put these under the xrf gun to determine what was inside there and the results were surprisingly inconclusive i did not find any titanium in either of these alloys which is not too surprising right off the bat because they had zirconium instead and based on my research the zirconium could be as active as titanium and essentially substituted but it's a very small amount just about point one or two percent on the xrf gun analysis and so i have a feeling that the leaded chemistries might be slightly different and despite all the searching i couldn't find much information about making leaded active solder alloys and normally you know electronics folks sometimes prefer leaded solder because it flows more easily but in this active soldering there is no such thing as flowing like you can't reflow these active solders you have to have the mechanical energy and everything it's kind of a rough process it's almost the opposite of very smooth clean electronic soldering so you know without the need to have the solder flowing you don't really need lead as much and i think that's why the focus has been on lead-free alloys especially for this active soldering so anyway so i thought we'd close by taking a look at some especially relevant examples of how you might use this in current technology one especially relevant use of this is to bond to ito coated glass so in this case i've got the circuit powered through the coating through the ito coating that's on the glass there and you can see how nicely the solder has wetted the surface and you know the benefit there is the only other way you could do this is pretty much with a conductive epoxy or maybe a physical clamp but if you're if your application doesn't allow physical clamping then i think your only other applicator or your only other choice is conductive epoxy so this is kind of nice because it's instant and it does give you a pretty high temperature bond and a stronger bond than epoxy might another application is to bond nichrome or nitinol wires to circuit boards so if you want to do a tiny little micro heater in your project or a shape memory alloy actuator in your project often connecting that unusual alloy wire to the circuit board is a problem you have to use clamping typically so the with the active solder you can get it on there and i've had some pretty good bonds with nichrome i don't think the heat would be a problem because the solder alloy is going to melt around 200 but you can get these alloys that melt all the way up to 300 so depending on your application it'd be totally fine similarly soldering tungsten wires is of course very difficult without this process and so if your application needs a really high strength very thin wire tungsten is a good choice but usually again you have to clamp it but this soldering process takes care of that and finally you know i as i was playing around with this i could have sworn i had this work on graphite and if you read in the literature you will find some claims that you can do this ultrasound or ultrasonic soldering process on graphite to bond say copper to it for an electrical connection and i like you say i had this thing work unfortunately i didn't get it on camera and since i've been trying it over and over it hasn't worked so i think i might have just had like a mechanical like it probably froze and just locked into the surface features here or something as far as i can tell i can't get it to work on graphite with my own alloy or the commercial ones similarly i tried this just for kicks on polymers i tried it on polyimide and peak plastic and of course it doesn't stick so basically it works on as near as i can tell all metals and all metal oxides is basically what this thing is best for bonding i also tried it on this titanium nitride coated drill bit and it seems to stick just fine so i guess metal oxides nitrides and all the other stuff too i should also point out this is just soft solder and so you know you're not going to make a trailer hitch out of this you're going to break the solder if you pull hard enough it's meant more for electrical contact and light mechanical connections but it is still pretty impressive in what it can do okay so before i make the next video let me know if you want me to try something specific to see if this ultrasonic technique will work and then next time we'll talk about the induction furnace and how to make metal alloys alright well i hope you found that interesting and i will see you next time bye

Channel: Applied Science

Views: 677,990

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Id: WuYdsStS1MQ

Length: 16min 45sec (1005 seconds)

Published: Tue Sep 08 2020