Applied Science - 2021-09-26
Thermal stress cracking can be completely avoided by CO2 laser cutting thin alumina sheets underwater. I also show how to formulate and apply silver paste, then sinter in a kiln to produce double-sided ceramic printed circuit boards with conductive vias. 60W CW CO2 laser at 80% power. 10mm/sec. Standard lens focal length (50mm). 2mm water above ceramic. 180 passes to cut through 0.75mm thick alumina. Silver paste: 97% silver powder, 3% glass powder by mass. Particle size 1 micron or less. Add poly vinyl alcohol mold release until desired consistency reached. Paste applied with 4 mil thick vinyl stencil. Dried in air 10 minutes, then rapidly brought up to 900*C, held for 10 minutes, then rapidly brought back down to room temperature. Total cycle about 45 minutes. I measured electrical conductivity of the finished traces from my process with vinyl stencils: 4 milliohms per square at 10 micron final thickness. This is pretty close to the Dupont published spec ( less than 2 milliohm/sq at 16 micron thick) Underwater CO2 laser cutting reference: https://sci-hub.se/10.1016/J.JEURCERAMSOC.2011.06.015 60W laser cutter: https://www.ebay.com/itm/294386493292 Ceramic sheets at McMaster: https://www.mcmaster.com/alumina/nonporous-alumina-ceramic-sheets-and-bars/ Ceramic PCB prototypes: https://ceramic-pcb.com/product/alumina-pcb-al2o3-pcb-prototypes-online/ Quickfire kiln: https://kruegerpottery.com/products/par_quikfire6 Raspberry Pi picoReflow oven controller: https://apollo.open-resource.org/mission:resources:picoreflow Silver powder: https://www.ebay.com/itm/122525930519 Glass glaze: https://www.amazon.com/dp/B0044SCR6O Macor: https://www.mcmaster.com/materials/material~glass-mica-ceramic/ Dupont silver paste: https://www.dupont.com/content/dam/dupont/amer/us/en/transportation-industrial/public/documents/en/LF131.pdf Binders for ceramic powder: https://digitalfire.com/article/binders+for+ceramic+bodies PVA mold release: https://www.tapplastics.com/product/fiberglass/mold_releases/tap_pva_mold_release_liquid/67 Very complete study of laser machining of ceramics: https://www.research.manchester.ac.uk/portal/files/54520291/FULL_TEXT.PDF Applied Science on Patreon: https://www.patreon.com/AppliedScience
"Maybe I should do that more often...."
YES YOU SHOULD.
I have never watched your content and not been fascinated and intrigued- even with subjects that I'm not that interested in.
I think if we hired a crew to follow him around everything in his life would be interesting enough to watch!
I love how the solution to both of the biggest hurdles in this project was... water. Plain water. I for one would really enjoy a video on the equipment you put together, using reflow software for that kiln is genius!
Yeah, well the water is really universal thing in this universe.
Yes. More equipment!
I've seen how one can "cut" glass under water with scissors. It seems like water keeps the fast fractures from occurring.
water? blah, disgusting, fish fuck in that
@Armchair Pilot yes ActionLab did a video on how you can cut glass with scissors without it shattering underwater https://youtu.be/tEAxhMECluM . The reason seems to be that the speed of sound is faster underwater and cracks propagate so much faster that it doesn't shatter.
Loved that you took so much effort to find this method! As for ceramic PCB, the easiest way is to cut it is the "green" state (LTCC). You can then also easily create multi-layer boards and drill vias using a laser. As for your question about the crust on your silver: it is silver oxide. You can avoid this by heating in a vacuum oven. This is not complicated, just use a small surplus dental oven. These generally have a vacuum seal and can be bought very cheaply (and are programmable)
@Huygens Optics Silver nanoparticles have a lower melting point than bulk silver (I don't know why). So I think the sintered silver may absorb the heat just fine, but it won't melt unless the laser is on it for much too long.
@Adrian Henle : Are you sure the nanoparticles are melting at a lower temperature, as opposed to some sort of photonicly-augmented cold welding, or reaching the melting temperature easier due to less thermal mass?
Love your videos and especially love seeing you two interact in your comment sections lol
@Adrian Henle It's also only the particles that needs to be heated to the melting point. The individual particles has to pass excess heat off to air, whereas when it's part of a larger mass, the heat is effeciently conducted away from the heat source, so once the particles are hot enough to fuse with the silver path, it's not necessary to heat that particle anymore, so as long as the particles gets hot enough, I assume that it would be fine
@Martin Fyhn Yes, I've noticed this effect with basalt: the powder fuses almost immediately into glass, but a large chunk of glass has much higher thermal conductivity and takes much more heat input to get it to melt again.
Used to work at a company that manufactured thick film substrate circuits, including screening resistors (this was in the seventies). DuPont was the place where we got our inks from. The silver conductive inks that we worked with actually included 7% or more of palladium or platinum. I recall the binder being a petroleum base. Over time the ink would dry out/get thicker in the large cold cream size jars they would come in, so we would have to add a relatively thick thinning agent to bring them back to a screenable consistency. We used 400 stainless steel mesh stretched across relatively small steel frames that fit into a semi automated screen machine. The largest ceramic we would screen would be a little more than 3 square inches. Most were the area of a 14 or 16 pin dip package. The kiln was a multi zone chain linked belt that took 35 to 100 mins for a substrate to be fired, depending on what particular inks were being fired.
On a separate question, what about cutting gorilla glass?
You know how if you actually break the glass it shatters? I bet that would happen.
Another incredible technique that my professors told me was way out of the scope of DIY. Your videos never disappoint. I'm thinking this + thin film sputtering + metal to glass/ceramic soldering = DIY ultra stable resistors??? A certain German volt nut might be interested...
Another instance of the old (but false) adage about the bumblebee: It doesn't know it isn't supposed to be able to fly, so it does it anyway.
@SeanBZA Does it expand or rather bend?
I'm in his discord server, and trust me, he is Very interested 😉
The PPMs require a sacrifice!
Don't give him ideas...
This makes me appreciate the science behind making the ceramic dielectric barrier ozone generator plates with their metal electrodes.
How about glass microballoons, perhaps run through one of those high RPM coffee grinders? Definitely wear a full-face N95 dust mask.
@Winston Smith Now I'm no "One" to argue with a guy named "Winston" , With or without a preceding "Sir", But reflecting back on to my years as a Pharmaceutical Test Engineer, THIS hypothesis seems a bit similar to previously patented concept I recall regarding grinding ice cubes to get a glass of water...no?
This makes one appreciate the science of putting things together as opposed as taking them to bits. That said, I love BigClive's channel, hope, that didn't sound to harsh.
@Winston Smith I thought of microballoons, but realised even the finest are in the tens to hundreds or microns; the suggestion to smash them may well work, although the resulting powder would need to be sieved with an analytic sieve to remove the larger particles.
What's with you and ozone generators
I’ve no experience of laser cutting, so that was truly interesting. Thank you. Silver paste sintering I’ve done quite a bit of though and I’d love to hear if you’ve tried sintering to fused silica. It’s a little different…
Incidentally, after scrubbing your traces to remove the oxide, lift the residue off the alumina by a quick rince in nitric acid. Another approach is to use a vacuum furnace to avoid forming the oxide layer. Used small dental furnaces can be found for very little money.
It might not be silver oxide. That oxide is still conductive.
I’d love to see videos going in depth about your tools and setups
I wish I could upvote this more than once
It's hard to think of anyone who wouldn't...
A video on your kiln would be extremely interesting.
And you'll probably get a lot of interest from the metalworking community in that as well, heat treat ovens aren't cheap so a good DIY version would probably be of significant interest to many.
Spitballing here, but couldn't you cut grooves into the surface like you mentioned was possible with the water+CO2 laser combo then use the groves for the traces? Then you could control the thickness of the traces and not need a mask, just put the paste on, and wipe it off allowing the paste to get stuck in the grooves.
Kinda what I thought was going to happen at the start.
I would imagine you probably could, but it would probably take a lot more time cutting the grooves with the laser than it would using a mask. If you Needed a completely flat board with inlaid conductive traces, I bet you could do it though.
@Keith Yinger Long yes, but that will also make it "set it and forget"-setup.
100% I'd like to see videos of your raspberry pi kiln controller and any other hacked together tools you use. Your ingenuity is the reason I'm here.
So if you could etch pockets very accurately can you use the laser to directly etch the circuit board and then fill the "pockets" with the silver paste? Yeah it would take longer but you eliminate the step of cutting out and peeling vinyl and it would probably be better for more accurate work.
As usual, this is awesome!
I was thinking the same, plus you could control the thickness of the trace dependant on current requirements.
All of this is true, but it takes a lot longer!
that would make sunken pads though which are no fun on smt boards since the silver shrinks like 10:1 from paste to trace when fired
This is always the most incredible channel - every video has multiple points where I'm amazed you managed to get something to work, followed by enough science that I understand how you made it work. Great job as always!
Hi Ben, I wonder if the glass coating after the sintering step could be removed by a quick etch in HF? Depending on how thin it is. Silver is somewhat attacked by HF, but much more slowly than glass. If there's only a few-micron thick layer due to surface tension of the molten glass, it should be removed quite quickly. Alumina is also attacked by HF so you might have undercut issues if the etch time is too long.
P.S. I think it would be neat to look at the traces before/after sintering with your SEM!
Feasible to sinter in vacuum or inert atmosphere?
@Gordon Chin I was thinking there's an oxide layer too. Argon is fairly cheap.
We definitely need a follow up from Ben!
@Gordon Chin I think even if you do the sintering in vacuum, the molten glass will flow and coat the silver particles due to surface tension. Maybe better temp control so the glass only softens and doesn't actually melt? That's what's supposed to happen during a sintering process, but the shiny/smooth appearance of the traces coming out of the kiln suggest that the temp is too high and the glass does fully melt.
As always, something complicated that requires high technologies is implemented in home laboratory conditions. Great, awesome work!
That spirit is why I love this channel!
not to mention unravelling analogues to secret formulas.
Your videos have entertained me for years. Though I always have appreciated how thorough and well documented your processes are, I have often wished for more frequent postings at the potential sacrifice of a polished final product.
That aside, I would enjoy learning about the tools and equipment you employ. Some of my most utilized tools were discovered from people that I have worked with or followed on Youtube. Always anxious for an opportunity to learn something.
Thanks!
What a SUPER useful video! You’ve opened up an entire new class of material for makers and scientists!
I’m actually not at all surprised that the technique didn’t work for glass: Alumina has a relatively high thermal conductivity (anywhere from 0.5 - 1x that of steel, depending on the alloy and heat treatment). Thanks to that, the thermal energy can be quickly conducted away to the surrounding areas and transferred to the water, so it’s acting as it’s own heat sink. Glass is about a factor of 30 less thermally conductive, so the energy can’t dissipate. Fused silica has very(!) low thermal expansion, almost a factor of 10 lower than alumina, so there’s way less thermally induced strain to begin with. (I suspect you might even be able to cut it without the water, have you tried that?)
Anyway, a fantastically useful video, thanks!!
The self-heating reflow was hilarious. :)
Your videos are always a treat, and I think a lot of people would appreciate some how-to videos on techniques and tools you've discovered that made projects more convenient.
Hey Ben, I really like your videos and you’ve inspired me to try some of this stuff out at home. One thing I haven’t really nailed is the vinyl stencils as a replacement for screen printing. I find there’s a good amount of variability between vinyls in terms of thickness and adherence. I was hoping you could point me towards the vinyl you use.
Thanks!
I really appreciate you giving me all this advice as if I was ever able to reproduce anything of what you’re showing here. But it makes me feel like I could :) Fantastic video.
Ben, for the oxide build up, you can use argon, or an even more reducing gas (e.g. "forming" gas). There's something called an Ellingham diagram that can be used to determine the oxide stability in different atmospheres.
It's been a while now, but I've had quite some success cutting and engraving Keraflex unsintered porcelain sheets with a CO2 laser in my lab. If I remember correctly the sheets are the same thickness, if not thinner, than what you are using there. They are fairly flexible in their "raw" state. You'll obviously need to sinter them, but the cool thing is you could shape them before firing. When laser cutting it in its unsintered state the cut line seems to sinter which makes the unsintered parts easy to separate. Be aware that the powder created in the cut line will wreak havoc on your linear guides and bearing surfaces, but I assume you're pretty familiar with that by now 😁
If the powder is a problem couldn't you combine the water technique to capture the dust?
@Daniel Parker the Keraflex porcelain sheets are not fired/sintered, and would probably dissolve in water. They might have some wax or thermoplastic binder, but I doubt they would last long in water.
The ceramic powder isn't a problem if the machine is thoroughly cleaned after use.
Seeing one of your videos in my subscriptions instantly makes my day. There is so much interesting information packed into a single video and it always feels like being part of some bleeding-edge research. It makes me want to experiment with these kind of things as well, but honestly, I would probably not have the patience that you have to try all those variations you test at each step.
I'd love to see more details on the kiln, with an eye towards application to a diy metal foundry.
MACOR shrinks A LOT when you fire it afterword.
In order for the glass to fuse in properly, its coefficient of expansion must match that of the alumina, or it will form micro-cracks.
There is a process using manganese & molybdenum to form metal-to alumina bonds. This is used in the manufacture of argon laser tubes (mentioned in some Coherent patents), & is very robust against stress & CTE mismatch. There is also a "silver palladium" process used by RCA in the 1990's to manufacture thick-film hybrids.
For the cleaning prep: use the original cut file to make a "cleaning stencil" to lay on top of the board during cleaning... it will ~mask the non-trace portions of the board
couldnt you try some photolithograph material? you would need some that survives the sintering temps but can be burned away with the laser cutter during cutting adding some more passes while its already in there wouldnt be a huge deal and there would be no alignment problems after the sintering you could clean as normal and when you smear trace material into the sourounding well you remove that masking material and all the dirt that is in there would be removed as well job done. maybe a higher melting metal that does not create bonds to your silver would work one that is chemically removable with a solvent that is not preferring the silver over the masking-metal
alternatively burn in pouches in the ceramic at the traces and use the photolithography mask idea in combination. add more trace so you can etch away mask and part of the trace later to ensure still having enough left over trace after wards. assumes that the material inside the trace is more usable (which the video suggests)
Amazing stuff as always, thank you. I particularly liked how you fathomed out the silver paste. As feedback on a point you raised in the video, I for one would certainly like to see you do videos on some of the shop tools e.g. the kiln. So let's see what others think.
Hey, the colour of the plain glass is probably due to sodium vapour emission. The fused silica won't have that, it also won't have inherent lattice defects, maybe that's why it cuts better.
Absolutely stunning amount of work you put into this. Thanks for sharing! I am super interested in laser etching pcb:s. Have you ever looked into this? If one could alter the power, it would be of huge interest trying to set the speed/power perfectly correct to etch the copper but also spray soldermask onto it and then etch this and in the end cut the pcb outline. Cnc micro milling is just not accurate enough for the work i need.
Hi Ben, thanks for the exceptional content over the years, been a long time watcher. I would love to see specific tools covered, such as the raspberry pi kiln controller. In line with that, maybe the vacuum induction furnace from the soldering video? https://youtu.be/WuYdsStS1MQ?t=85
I would love to see more short (or long) videos about tools and process controls you use. Its great stuff.
Thanks - very interesting process. I love how you describe the thinking behind developing something. You present it so simply that suddenly something that is totally out of reach becomes possible for the DIY - without the megabucks laboratory. So to answer the question about creating a video of the RPi development of software - same applies. If you explain, like you normally do, your thinking, I get a hell of a lot from that. The project you are working on really isn't as important as your presentation for me. Just a big thank you regardless of how you decide!
I love that you walk us through the discovery process. I learn so much from that alone!
Hey Ben, thanks for taking the time to give us another great video!
It would be great to see some of the behind the scenes stuff, like your raspberry pi build would be great to see. Maybe or them on a second channel if you don't feel it fits in here.
Great work! It's been fun to watch all the variations of making circuits you've done Ben. I'd be very interested in tools you use.
About the glass, I can provide some information: you can cut quartz due to its very low expansion coefficient, while the stress in other glasses will propagate cracks during the process. The machine we use for laser cutting glass (including borofloat and soda-lime) employes a short-pulsed Nd:YAG to induce filamentation inside the glass: this create a series of tunnels inside the glass, 2um wide and about 8mm long. Then you propagate a crack between the channels after you finished to separate the piece. Using tightly focused beams and very short pulses prevent the creation of cracks during the cutting process.
About the yellow light, it is due to the sodium inside the glass, which is absent in fused silica
I would be happy to see videos on your tools and setup. I also love the way you do videos now too, as a viewer I can tell you out a lot of work and thought into your finished products. You are the type of engineer I strive to be.
Great work! Always something new to see!
It would be awesome to also see the software you run on the Kiln and tools, etc. If you feel this is a departure from your normal work it would help someone like me who is starting out and more information would be great help! Of course this is more work, but might be fun to make if you always enjoy it.
Out of curiosity, I went looking for 3D printable material with low dielectric loss. I finally found
“high impact polystyrene” (HIPS). Apparently it’s a copolymer of polystyrene and rubber, with a dielectric loss in between the two. It has better dimensional stability than other polymers. This is important for preventing print “warping” and delamination.
I'm always amazed how far you take this stuff. Thanks!
Very interesting about the fused silica! Might have to try that with my fiber laser and see if it's similar. Is it also pretty slow (e.g. might be possible to etch pockets)? Regarding the "silver smear" after buffing, might be able to laser it back off with a few passes of the CO2? Hopefully without taking too much of the actual trace off 😅 Very cool stuff! Definitely adding a few of these tricks to my toolbox!
Yes, please more videos on the tools you use in your shop! A couple of my favorite videos were the ones on solvents and adhesives.
I would definitely enjoy seeing a video on your RPI kiln setup, plenty to talk about with the control algorithm (PID or otherwise) and the materials used to withstand the heat. Keep up the good work, always enjoy your videos!
Jaw droppingly awesome science, engineering and innovation. The work that goes into one of your videos is staggering. Thank you for putting this content out there.
I love your channel. I've learned so much. I really enjoy the way you research and try different things based on your observations and then modifying you attack. Man I wish I had a science teacher like you when I was in school. You really cultivate the curiosity in me.
I'm glad that Youtube suggested this channel and video. You're doing very impressive work and an excellent documentation of it.
Documenting your programming and alteration of the Raspberry 'Pico Reflow' code would be very interesting to see, as would it's interface to (and identification of) the solid state relay
Hi Ben, you should look into ultrafast-high temperature sintering! Could be pretty cool for rapid sintering approaches as an alternative to your little kiln. The paper came out mid last year in science I believe, and it's already been replicated a few times. I've built a setup for my lab, and it's not that hard to do!
This is such a cool video. Thank you! Personally, I would love to see a video or two about the tools and equipment in your lab.
Consider cutting troughs and valleys for "in-board", components, resistors, caps, battery, antenna, etc. using graphite, electrolytes, etc.
I highly second this. Kinda like a 2,5D sandwich (maybe even more layers) structure with loads of integrated circuit-stuff as a neat compact block.
Malachi Landis - 2021-09-26
I would enjoy seeing videos about your tools, especially the custom electronics / custom programmed devices. I feel like those are the ones that I would be the least likely to go out and make (mechanical engineer here), so seeing your methods would be useful.
S Lantern - 2021-09-26
I'd be fascinated to see a video on your kiln controller, as well as your other tools.
andrew hunter - 2021-09-27
Agreed! Short videos on the tools would be really interesting, and a great resource for anyone who would want to make something similar in the future.
Emily Davidson - 2021-10-01
I would also like to see this, with no qualiifications.
transient aardvark - 2022-08-04
+1
FJ S - 2022-10-24
@zyeborm Yes, you said it the right way. Not, I feel like those are the ones that I would be the least likely to go out and make