bubble vs spray etch pcb - Page 1
Forum section: electronics / general

author: CopperCone
author_rank: Super Contributor
timestamp: July 28, 2018, 04:16:54 pm
content: So i have a acrylic tank about 1.5x10x10 inches that I use for bubble etching. I pipe in air using a nail-station thing I bought, its basically a quiet little compressor, which I connect to some PEX tubing with a buncha holes drilled in i, which sits on the bottom of the tank. I just have some heating strips that are adhesived to the side of the tank and I use a variac for temperature control.I have seen spray-etching machines.I am interested in small geometries, like TDFN parts and such, in designed mixed with large geometries (i.e. to-220, DIP, DDPAK) to make full pcbs that have power and (large) signal stages. I am also interested in home made RF/microwave PCBs.I noticed that getting the etch right with the 0.5mm pin pitch on a big PCB is kind of difficult, on a large PCB I don't have confidence the process will work. Sometimes I need like 3 attempts, careful baby sitting, and sometimes I put masking half way during the etch to prevent excessive erosion. The boards I work with are like 6x9 inches.I do my exposure using sodium silicate, NaOH and water on MGchemicals PCB.I don't have a light box and I was instead putting it under a bench magnifier fluorescent ring light. I plan on building a exposure box with some LED strips (will warm white LED work?), but I also have seen some designs for rotary or spray etch machines.The other upgrade I have planned is to make the bubbles smaller, using something like a 0.3mm drill, right now the holes are probobly made with something like a 1mm drill bit.Do spray etchers offer significantly better performance in this situation? Are they worth the trouble? I have not been able to find side by side comparisons of bubble eched vs spray etched pcb.I don't care how long it takes, just which method has higher quality* I mean so long I don't get undercutting

author: KL27x
author_rank: Super Contributor
timestamp: July 28, 2018, 08:34:39 pm
content: Thickness of the copper matters. It is more difficult to get fine pitch correct when the copper is thicker. This is a lesser known reason why high current stuff and bitty fine pitch stuff are often put on separate pcb, rather than just separated with the appropriately wide gap on the same pcb.It sounds like you have identified two problems with your process.1. The exposure is not even to the edges. Can't help, here. Fix your setup?2. The etching is not occurring evenly, and you are having to manually intervene to prevent over-etching of spots.I have no idea what that etchant is like or what other things you might do to improve it. But you brought up the bubbler being a bit crude. And you mentioned a nail thingy, which I assume you mean a nail gun compressor?Google "fish tank bubble wall." It's an airstone shaped like a porous plastic tube... very roughly 3/8" OD, I suppose. It seems to come in lengths of about 14". If you put enough air/psi it produces lots and lots of super fine bubbles. Not sure if it is ok with your etchant, mind you. It is not particularly useful, IMO, using a fish tank pump. It would not work in my tank for very long before the thing clogged and no air bubbles are made, at all. But with higher psi and air like you would get with a nail gun compressor, it is super impressive how very very small, consistent, and numerous are the bubbles that this makes. I'm not sure of the psi, needed. It's probably less than 20. You would need an air pressure regulator, which a nail gun compressor usually has, built in. Just don't leave it hooked up when it's not running. With cupric, at least, you will corrode the regulator.If you are talking about some little thing to dry nails after your manicure, then buy a nail gun compressor. From your other posts, it sounds like you could use one. Along with an 18 gauge brad nailer and an air blow gun. Air nailer and hammer and nail are like two different things, altogether. The air nailer teleports the nail into place without shifting anything, and the hold is way higher for the gauge of nails. Maybe because they are square and have rough edges? Dunno.As for spray etching? No. That's all.

author: CopperCone
author_rank: Super Contributor
timestamp: July 28, 2018, 09:38:08 pm
content: Ok I am working on making a bubbler out of pex tubing using 0.5mm or smaller drill to make the holes. It is a pain in the ass. I broke like 6 drill bits.. as soon as I moved up to the slightly larger one by like 0.1mm they stopped breaking and I can make holes continuously without any snapping (harbor freight drill bit carbide one with proxxon drill press). The density of holes will be like 2 orders of magnitude more then my old bubbler tube.And the compressor I am using is a small compressor meant for air brushing your make up or nails. It has a pressure regulator screw on it but it is fairly low pressure.I have a real air compressor too in the garage which I may use if the pressure is not low enough. I just drilled like 200 holes, I will test the bubble density soon. I hope I don't have to use the regular air compressor because this one is very quiet, cheap and I can move the whole thing easily and quickly into the middle of my back yard so nothing gets contaminated from the ferric chloride/HCl aerosol that is produced, I wanted to make a piece of wood with cutouts for everything so I can efficiency use it out doors like 40 feet away from any thing. It would be light and easy to carry and I can put all the funnels and containers on one plank of wood to get rid of the 'i can't be fucked making a pcb' feeling that I get oh so often... I am way more likely to do things if I have a dedicated 'station' available. I also have a tiny little variac to pair with it.

author: CopperCone
author_rank: Super Contributor
timestamp: July 28, 2018, 09:47:56 pm
content: Also, I have 2 fairly thin pieces of plexiglass to use for exposure. I want to make a light box, they are left over flex-fire LED's that I was going to use for room lighting but I gave up on the project because of how much work it was to prevent dead insects from accumulating behind the molding, I would need to buy an ass load of plexiglass to seal it, and my home walls are not really too strait so you would need to make little sections that are joined by flexible caulk and I scrapped the project due to all the hangups.They are fairly bright, their second best grade, I was going to power them from a logarithmic brightness controller and DC / DC converter.I intend to use LED strips to expose it.Do you think I should make it as optically clear as possible or should I give it a brushed texture with some kind of grit of sand paper to act as a diffuser? Ideas on what grit I should use if any?And is the blue peak in white LED's good enough? I swear I read some where that someone had good results with it, but I can't find what I read. That stuff should be sensitive up to like 450nm?

author: KL27x
author_rank: Super Contributor
timestamp: July 28, 2018, 10:02:48 pm
content: I have zero experience regarding UV method. A diffuser should certainly be desirable, in my guess. I wouldn't even bother trying to scratch up the plexi, though. I'm thinking tracing paper or something like that. Perhaps folded up like an accordian and then opened up again? I'm full of ideas, so don't be upset if most of them are dumb.Regarding the air compressor thing, here is what i do. I fill a cheap 5 gallon tank and carry just that to the back yard and plug it in with a regulator. It will etch a full sized board and beyond on one fill. It doesn't take very much pressure or air... just a lot more than a fish tank diaphragm pump. I remember the first thing I tried in order to boost the pressure was buy a large and expensive fish tank pump with 4 lines and hook them up together. So I learned that the pressure doesn't add together when you do that.I bet an air brush compressor is more than adequate.

author: CopperCone
author_rank: Super Contributor
timestamp: July 28, 2018, 10:04:07 pm
content: My experience with plastic tanks to store air is1) they deform2) it can explodeI also don't wanna make the station that annoying to use. Having to go to the garage to fill a bucket is irritating but I guess thats a good solution. It's been a while since I made a PCB but IIRC with my old diffuser that little pump was more then enough to make the thing start to bubble over and spill. The wax paper is a interesting idea.Ideally I would like to make it out of glass, have glass heat exchanger coils for the heating, and get a long micropourus glass frit to work as a bubbler. Maybe next decade I can get all that stuff together?

author: KL27x
author_rank: Super Contributor
timestamp: July 28, 2018, 10:11:29 pm
content: No plastic. It's a steel 5 gallon tank that holds up to 125 psi. They are like $20.00 if you shop in the discount aisle, ala Harbor Fright.

author: CopperCone
author_rank: Super Contributor
timestamp: July 28, 2018, 10:18:44 pm
content: I wonder if pure oxygen would work better then atmospheric air

author: 2N3055
author_rank: Super Contributor
timestamp: July 28, 2018, 10:28:11 pm
content: You don't have problem with etching but exposure.. You need to buy /make exposure box.I tried all kinds of lighting, and finally bought an exposure box... It was best spent money in my life.Also, use only presensitized boards. Buy small batch, chop a small piece and calibrate exposure. Then keep timer on that until you spend boards.Also, NaOH is very sensitive to temperature when developing resist. Aquarium heater with thermostat is probably good thing too.

author: nctnico
author_rank: Super Contributor
timestamp: July 28, 2018, 11:10:05 pm
content: Quote from: 2N3055 on July 28, 2018, 10:28:11 pmI agree. I have made my own UV box where the distance between the CFLs and glass plate is about 12cm to give the light enough distance to spread evenly. There is also a lot of quality variation in the presensitized boards so buy the more expensive ones. The CIF brand carried by Farnell sucks really bad. I use readily made developer which I keep & use at room temperature because it is very temperature sensitive.Still the money is probably better spend on having PCBs made. Forget about etching your own RF boards with matched impedance traces to form things like filters. The tolerances on self etching are about +/-0.15mm.

author: CopperCone
author_rank: Super Contributor
timestamp: July 28, 2018, 11:20:11 pm
content: Quote from: nctnico on July 28, 2018, 11:10:05 pmwhat kind of tollerance does a factory made RF pcb provide? I see agilent recommends +-25um for 29GHz. 0.15 is 150um, or 6 times the value.

author: 2N3055
author_rank: Super Contributor
timestamp: July 28, 2018, 11:22:19 pm
content: Quote from: nctnico on July 28, 2018, 11:10:05 pmAnd I agree with you. I make PCB myself maybe once, twice a year for some prototypes that needs to be done right now.. I simply order boards, it is quite quick, even from China and China ones are inexpensive. I just have better things to do than make PCB anymore. I rather spend more time designing the PCB itself... And they are professionally made with silkscreen, solder mask, routing etc..I can actually get pretty fine features on boards. My biggest problems is that drilling is pain in the ass.. Not so much nowadays with SMD, but still..Regards,Sinisa

author: CopperCone
author_rank: Super Contributor
timestamp: July 28, 2018, 11:29:14 pm
content: also what does a pcb fab do that improves tolerance?

author: 2N3055
author_rank: Super Contributor
timestamp: July 28, 2018, 11:37:38 pm
content: Quote from: CopperCone on July 28, 2018, 11:29:14 pmThey use high quality films, collimated professional UV sources, high resolution photo resist, vacuum film adhesion, clean room practice so no dust in photo process..Also, PCB process is a chemical process, so they use etchants with controlled underetching, very controlled temperature, humidity, etc etc... They calibrate process continuously...It is science, engineering and art... Many books written ... I still have my Printed Circuits Handbook,by Clyde F. Coombs Jr. Thick book.

author: CopperCone
author_rank: Super Contributor
timestamp: July 28, 2018, 11:43:00 pm
content: That is too many things to do at home. And I don't really care about cost or time, I find it interesting to make my own stuff.Are there any low hanging fruit to improve home quality without getting too crazy but raising the bar some what?

author: sleemanj
author_rank: Super Contributor
timestamp: July 28, 2018, 11:43:35 pm
content: I made a small bubble tank a while back, for the tank I got a suitably tall and wide food storage container, like the one of the left herehttps://www.kmart.co.nz/wcsstore/Kmart/images/ncatalog/f/3/41797983-1-f.jpgI actually have two of them one filled with water for rinsing.For the bubble mechanism I used an aliexpress tube type air stone (bubble wall tube), these are an interesting material actually a hollow tube made out of what I would describe as a sort of permeable plasticised paper or something like that, it doesn't so much have holes as the air just escapes, easily cut to length the caps just pull off cut it, put the cap back on.I retain the airstone and the PCB in a standy jiggy sort of thing I 3d Printed, I can't be bothered going out into the shed to take a photo, but this will ghibe you the idea...imagine two facing each other, the bubble wand thing goes through the big hole (just a loose fit) some other rods (I used some 4mm lollypop sticks I had in my one-day-might-be useful drawer) got through the other holes fitting closely to hold everything more or less in alignment, the pcb fits into the groove, and a couple of rubber bands are put around the whole thing using the notches on the sides.For the air supply, I use two 3v mini air pumps in parallel (feeding into a T and then down to the air stone), these are run off an 18650 cell so I can just pick up the tank take it outside along with the pump and flip the switch.If I was just doing single sided, I don't think it would be worth the effort, but on rare occasion a double sided is called for, it is easier this way than trying in the usual rocking tray type of arrangement.I do have a slight issue with shadowing of the bubbles against the etch resist which I don't know how to solve, other than to rotate the PCB a couple times.

author: CopperCone
author_rank: Super Contributor
timestamp: July 28, 2018, 11:45:30 pm
content: uhh I don't understand what your last diagram means.Do you mean that the protrusion of the copper layer leads to greater etching on the bottom of an etched area?I wonder if you can vibrate the PCB or something?My problem was more that I had more etching at the bottom where the bubble density was high. I think its because of hole size. When I think back to it, my methods were seriously primitive.

author: CopperCone
author_rank: Super Contributor
timestamp: July 28, 2018, 11:48:03 pm
content: like this?

author: sleemanj
author_rank: Super Contributor
timestamp: July 28, 2018, 11:52:55 pm
content: Quote from: CopperCone on July 28, 2018, 11:48:03 pmYes viewed from the side. Vibrating the PCB seems like a pain. I've considered adding some top-down flow by pumping etchant from the bottom and returning it to the top, but arranging a pump which would stand up to the etchant and still move enough to be useful might be tricky, a peristaltic pump is the obvious choice but not exactly a high flow rate and I do want to keep it compact.Note that I use Dry Film resist, which has a fairly substantial (in the scheme of things) thickness.

author: CopperCone
author_rank: Super Contributor
timestamp: July 29, 2018, 12:49:13 am
content: Hmm. The other thing I wonder about is the size of your bubbles. It sounds like the method you have of making bubbles makes them incredibly fine, since the device you use was meant for oxygenating water for fish to breath.. I believe that producing large bubbles would actually give the fish grief since they might get an oxygen film forming on their gills, so they have to avoid a larger area of the tank, whereas the fine bubbles dissolve very quickly so the fish can maybe tolerate being above it and stuff?I always imagined the process where the larger bubble kind of has a significant wake behind it as it travels through the fluid, maybe there is a minimum bubble size requirement that you are violating, like there is a lack of some kind of turbulance which I almost imagine like 'peening' metal with very small bubbles intended for oxygenation. Like as the bubble travels upwards there is a kind of suction effect behind it, which encourages the reaction occuring on the PCB surface between the copper and the etchant to get pulled towards the bubbles, so fresh etchant is pulled in? I don't know the dynamics though, its just a guess, I never noticed that effect even with my bootleg setups. Or maybe you need a ratio of large and small bubbles for different effects for the process to occur properly. Maybe they 'orbit' each other and make a little vortex between a group of bubbles? Like a propeller formed out of bubbles that for some reason interact with eachother.A sintered stone or other bulk process will make very uniform bubbles. With this shitty pex tubing I get all sorts of parasitic 'nozzles' that form because of its elasticity and memory and because its squeezed in a vice, so I expect I will have some diversity in size. Some holes I need to puncture with a needle held in a collet thing because they self seal, so its all over the place.but I don't know about dry film, I only ever used the photoexposure kind.

author: Ian.M
author_rank: Super Contributor
timestamp: July 29, 2018, 01:09:48 am
content: If you want etchant flow, this topic from a few months back is worth a look:https://www.eevblog.com/forum/manufacture/p-c-b-foam-etching-machine-without-nozzles-or-air-stones/It gets a reasonably high flow rate over the PCB surface without needing a mechanical pump that can handle etchant or a fine oriface bubbler.The air lift pump could be built as a vertical length of plastic waste pipe with the bottom end capped off and a smaller diameter pipe inside as the actual lift tube, and clamped to the side of your bench then plumbed to the actual etching tank via short flexible hoses.

author: sleemanj
author_rank: Super Contributor
timestamp: July 29, 2018, 01:16:38 am
content: Quote from: CopperCone on July 29, 2018, 12:49:13 amDry film is a uv sensitive film. In one paragraph summary, you apply it to bare copper clad FR4 (with a spray bottle of water, something to squeegee it, and a cool clothes iron), expose it (traces transparent, stuff to remove opaque), develop it (weak washing soda (sodium carbonate) solution), etch it, and strip it (acetone).Easily purchasable online. Same stuff they use in pcb factory. Better than pre-sensitised boards in that it's cheaper, and if you screw up an exposure or artwork and notice before you etch, just strip and re-apply. For more detail:https://sparks.gogo.co.nz/dry-film-tips.pdfand also Big Clive has done a few videos showing the process.

author: tautech
author_rank: Super Contributor
timestamp: July 29, 2018, 01:59:01 am
content: For the bubbling tube I just used a stiff semi flexible but soft clear PVC tube of some sort. ~3/8" OD.Plastic bulkhead adapter through the etch tank wall and perforated the tube with a stout needle. Probably no more than a dozen or so holes over its ~8" length. A single aquarium pump handles it well, in fact this one has an inline air flow control thumbscrew that I've got wound down so not to create a fizzing bubbling mess. You don't need much flow as the primary need for air bubbles is to pick the etching reaction bubbles off the PCB so to get an even etch.You only need a gentle constant stream of fine bubbles so don't overdo it.Too much airwillcool the etchant and then extend etch times longer than they need be.I use folded plastic mesh to carry/hold the PCB, the type used for keeping leaves out of a house rainwater gutter.Easy to pull frequently to check the etch and/or plunge into a bucket for a wash off for detailed inspection.Spray etching on the other hand invites further complexities of how to effectively manage etchant mist let alone how to pump the stuffandapply it evenly to the whole PCB.Tank and bubbler is easy.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 29, 2018, 12:54:10 pm
content: Didn't read the whole thread, but a few hints for good resolution.1) Consider using a point source light. This increased resolution and especially repeatability on our process. Everybody says: build a light box. Nope, do the opposite - make the light source as small as possible, and take it as far as possible! Yes, you lose more lighting power, since the distance must be long enough so you get even enough light, and then most of the lights goes outside of your PCB... But UV LEDs are cheap and the energy consumption is still irrelevant.The point source means if there is any distance between the mask image and the board, it doesn't fail immediately because of that - you get a well-defined shadow, not a blurry image.We were using light box that had its vacuum starting to leak, causing random exposure failures on fine-pitched boards. Also, when our toner was running low and we didn't have a good inkjet, we sometimes needed to sandwich two masks to get good black. This limited the resolution when combined with the diffuse lightbox.Also, every now and them, someone printed the mask image with wrong mirroring settings; when the mask was turned around so that the ink is on the opposite side to the PCB, this effectively limits the resolution to around 12/12 mils on a diffuse lightbox - where with our point source, you still get the same 8/8 mils reliably, limited by all the other factors!So, using a point source gives you one thing less to worry about, and increases the margin for success.Sure, they use diffuse sources in the industry. But they also use professional printing materials, and professional exposure units.We use 20W 405nm UV LEDs (with active area of about 1 x 3 cm), about 40cm away from the PCB, which gives uniform exposure to PCBs up to about 20x20cm. The exposure time is around 5 minutes, with negative-working dry film photoresist.2) Even though you use DIY equipment, use professionalmaterials. (hint: professional material doesn't say "professional"; instead, it's the stuff they use in PCB fabs.) Dry film photoresist (e.g., Dupont Riston) is such a product and typically specified down to 3mil/3mil or even 2mil/2mil work. Professional materials tend to be:- Much better- 10x cheaper- More robust against process variationsDry film photoresist is especially robust compared to any "for hobbyist" materials we ever tested. 5x overexposure - no problem. 5x overdevelopment - no problem.3)Development of the resist is also important - it should optimally be a spray equipment, as well!Dry film photoresist is strong enough so you can physically scrub it. Use hot air gun to bend a toothbrush to make yourself a tool you can brush with in a simple container! Carefully brush all the tight spaces between the traces.4)Now to on-topic:A good spray equipment is always the right thing to do. However, we get great results with a bubbler. The bubbling just needs to be very strong, so that it gets "chaotic" by nature, the bubbles should go everywhere. With too little pressure and airflow, you have a nice-looking upwards motion, which isn't as good. It slides near the board, giving the dragging effects described above. Similarly, with too little pressure, the bubbles run straight upward from the bubbler holes - which are most likely too far from each other, giving streaking. Go for chaotic bubbling with a lot of pressure and airflow!In our vertical tank, etching is a bit uneven between top and bottom, but this has fairly little effect on resolution. In most demanding boards, we flipped the board halfway during etching. Flip both upside-down and swap the sides as well.5) Get some 0.5oz copper clad!With the standard 1oz clad, I have found 8/8 mils is the practical lower limit for reliable work, and I prefer 10/10 mils for some margin.With 0.5oz clad, these limits are 6/6 and 8/8, respectively.We have successfully tested 4/4 mils (with 0.4mm QFPs, and two traces between the pads of 0603s) with 0.5oz clad, but I would go that far for yield, repeatability and robustness reasons. This was achieved with:- An expensive ($1000) Epson photo-quality inkjet printer; printed at 1200 dpi.- Point source UV light, as explained earlier- Dry film photoresist- Strongly bubbled cupric chloride etchant, in a vertical tank.6) Printing the masks.This is a can of worms. Most of our headache relates to printing the original artwork. It seems inkjets are generally better than lasers, but not all inkjets are good enough. Don't only look at the resolution; also look at how deep the black is. With properly deep blacks, you can expose the photoresist properly without risking exposing through the black. If you need to compensate for the black leakage by reducing exposure, you don't fully harden the dry film, leading to jagged edges and uneven widths of the traces.A good black density gives you more robustness against process variations, as you can just increase the exposure time by some 50% or even more from the "smallest acceptable" exposure time, to guarantee properly hardened photoresist material, making development step easier - you can scrub more without damaging it!

author: CopperCone
author_rank: Super Contributor
timestamp: July 29, 2018, 02:07:54 pm
content: thats interesting.Do you have recommendations on dry film? I always used MG Chemicals products but maybe I can do better. I don't know if they are considered good or consumer or what. Dupont Riston.. like this stuff?https://www.ebay.com/itm/12x300in-Dry-Film-Photoresist-for-PCB-Dupont-Riston-Photo-Resist-/292420653004It's not something you need to spread out on the PCB with a squeege? I guess thats why its called dry filmThat does seem pretty cool because I guess you can make your own ceramic PCB with it if you get the copper clad substrate?Who makes affordable but good power UV led?Have you ever done cladding yourself? Like to make a multilayer board DIY? I thought maybe you can print all your photomasks out and staple/clamp them together in 2 places so its like a book that you aligned under a light table. And make some larger holes so you can stack it up on machine pins ? I noticed my printer seemed to distort the acrylic or whatever sheets I was using due to heat (or maybe due to ink soaking into it?). A inkjet would probobly be excellent?

author: Siwastaja
author_rank: Super Contributor
timestamp: July 29, 2018, 02:26:26 pm
content: Yeah, we have used Dupont Riston off Ebay successfully. But we happened to have two big rolls from the industry from the early 90's, which should be badly out of date, but it still worked perfectly so we have been using that free stuff without any issues.You can wet laminate it with a squeegee (spray a little bit of water - stick it to the clad - squeegee all the water out - oven at 80 degC for a few minutes IIRC), and we started with that, but then we rearranged our process so that we CNC drill first, and wet lamination stopped working due to the holes. (Drilling first makes alignment easy, and allows you to compensate printing the mask to actually fit holes, instead of destroying the complete board you have worked with for an hour by accidentally drilling it with an offset.)In the industry, the dry film is laminated using heat and pressure - it's basically a big-ass heavy-duty office laminator!Which got us thinking, maybe a standard super-cheapo office laminator (meant for laminating paper in plastic pouches) would work.And yes, it worked perfectly! This is easier than wet lamination, as well.Biggest PCBs we do are A4 size (around 210x290 mm).We built the point source UV unit just using random Ebay UV LEDs... No issue there. Sometimes the Ebay LEDs are crap, though, so we were lucky.IIRC, 380nm would be the optimal wavelength for dry film materials, but 405 nm works well enough (requires maybe 3-4 times more power), but 405nm is at least ten times cheaper per watt so that you obviously want to use that.

author: CopperCone
author_rank: Super Contributor
timestamp: July 29, 2018, 02:46:36 pm
content: Do you think its feasible to make multiple layers at home using this dry film method?For some reason I always had alignment problems with my projector sheet print outs on double layer boards, if I used the default trace thicknesses and stuff from altium, I ended up having to really tape the bottom sheet down and then kinda stretch the top sheet over it under light, then staple it, so it had some tension in it, to get good alignment where I can correctly line up a DIP package or VIA. I thought it was because the ground plane had alot of block on it, so it got thermally warped from the laser printer during printing? I notice this more on big PCB, biggest I made was about 10x6 inches. Like I think I would tape the top side to a sheet of glass then stretch the bottom on it.. it was tricky business that I was frustrated with. Took forever to make it look good when I held it up to a light source to check for alignment.Does it work better with inkjet? I don't expect to make multilayer RF boards, but things that operate in the ultrasonic range at low noise levels with top and bottom ground plane/shields, analog signal layer, power plane, digital plane, etc.Also what glue do you recommend for bonding PCB's together?

author: David Hess
author_rank: Super Contributor
timestamp: July 29, 2018, 02:58:41 pm
content: The good bubblers I have seen used an array of tubes covering the entire bottom of the tank with a spacing of about an inch or less between the holes and the tubes. The holes were large enough and the air volume high enough to roil the surface of the enchant so a cover was a good idea.

author: CopperCone
author_rank: Super Contributor
timestamp: July 29, 2018, 04:06:22 pm
content: so you are supposed to use big ass bubbles?

author: David Hess
author_rank: Super Contributor
timestamp: July 29, 2018, 04:46:54 pm
content: Quote from: CopperCone on July 29, 2018, 04:06:22 pmIf the idea is to agitate the tank, then yes. I am just reporting what we used but I doubt bubble fizz is going to work nearly as well.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 29, 2018, 06:22:01 pm
content: CNC drill the holes first, then expose one side at a time, so you can align them separately, which will be much more accurate and less risky than trying to join the two masks together and get them register reliably.Each printer will require you to find compensation (resize) parameters so that the masks align with the CNC'd holes. I output hi-res images, then resize in GIMP or similar before printing. For example, the resize factors may look like this: X=99.95%, Y=99.80%This takes a bit of trial and error.Getting good masks printed is always the most difficult part.I wouldn't try multilayer.

author: tautech
author_rank: Super Contributor
timestamp: July 29, 2018, 08:36:47 pm
content: Quote from: David Hess on July 29, 2018, 04:46:54 pmWell yes a byproduct of bubbling is agitation but it'snotits primary function which is to remove etching reaction bubbles from the PCB. Too much air cools the the etchant and that's undesirable for any of the heated etchants.

author: CopperCone
author_rank: Super Contributor
timestamp: July 29, 2018, 09:38:37 pm
content: uh so what bubble size should I go for?

author: tautech
author_rank: Super Contributor
timestamp: July 29, 2018, 09:46:25 pm
content: Quote from: CopperCone on July 29, 2018, 09:38:37 pmStudy:https://www.eevblog.com/forum/manufacture/bubble-vs-spray-etch-pcb/msg1708010/#msg1708010

author: CopperCone
author_rank: Super Contributor
timestamp: July 29, 2018, 10:13:59 pm
content: Quote from: tautech on July 29, 2018, 09:46:25 pmbut someone else is using a diffuser and I don't know if their results are bad because of it.

author: tautech
author_rank: Super Contributor
timestamp: July 29, 2018, 10:21:38 pm
content: Quote from: CopperCone on July 29, 2018, 10:13:59 pmTank design will be the decider and the reason why I built mine skinny so a single bubble tube is all that's needed.If you've got a wide tank and can do multiple PCBs of course you'll need either multiple bubble tubes or some sort of bubble diffuser/spreader.

author: David Hess
author_rank: Super Contributor
timestamp: July 29, 2018, 10:43:00 pm
content: Quote from: tautech on July 29, 2018, 08:36:47 pmMore heat!We were using ammonium persulfate purchased in drums so the tanks were heated.

author: james_s
author_rank: Super Contributor
timestamp: July 29, 2018, 11:03:15 pm
content: The biggest challenge I had building a bubble tank is getting the bubbles to be evenly distributed. I suppose that could be a challenge with spray etch too but it seems it would be simpler to get an even flow. I went with bubbles because I wanted a compact vertical tank and didn't like the idea of HCl spraying around.

author: jmelson
author_rank: Super Contributor
timestamp: July 30, 2018, 09:28:40 pm
content: Quote from: CopperCone on July 29, 2018, 02:46:36 pmYes, but...Laser printers are not accurate enough to do two-sided boards of any significant size. I built a laser photoplotter that is accurate to a few thousandths of an inch over the whole film size. So, I print out the two artworks and have alignment marks on them. I take a piece of scrap PC board material and glue it to one edge of one artwork. I then slip a piece of Plexiglas the same thickness as the board between the two films and align. Then, I glue the 2nd film to the PC board scrap, making a kind-of 2-page book. To print the board, I just slip it between the "pages" and expose both sides without releasing the vacuum in the double-sided exposing frame.But, for double-sided boards over 100 mm, I just don't know what others can do, without an accurate source of artwork. To check yours, make a grid of lines on 1" / 25 mm spacing, and print one normal, and one mirror-imaged on your printer. Then, put them on a light table and see if the lines align. You will likely be very unpleasantly surprised at how far off the two sheets are.Jon

author: KL27x
author_rank: Super Contributor
timestamp: July 30, 2018, 10:37:57 pm
content: QuoteThose of us who have discovered the "bubble wall" wand are very happy with it. The main drawback is you need higher pressure than what you can get with a fish tank diaphragm pump.I am no stranger to doing detailed work, but getting the bubbles to work evenly by drilling holes in a tube was a fruitless task. The bubbles are huge, and half the air wanted to go through a few of the holes.The bubbles you get from a bubble wall tube are almost microscopic. I once tried to take a picture, but they didn't show up. I can't see them until I almost have my nose against the tank. They're so small, they don't even perceptibly rise to the surface... so the etchant level in my tank will rise the better part of an inch when the bubbler is on and there's a huge volume of air in there, and a ginormous surface area of contact between etchant and air which works great for cupric. It is super impressive. It feels like the bubbles should coalesce, more. I have speculated that by shooting enough air in there and adding a tiny dash of soap, you could etch with 100% foamed etchant. I doubt it would be a benefit, but as long as you are intent to overcomplicate things (like anyone who wants to make a spray etcher), this might be of interest to you.Poked holes in a tube just make big bubbles that rise to the surface in 1 second and splash more etchant, which is fine if your etchant just needs the bubbles for agitation.QuoteMaybe this is more important for ammonium based etchants. IME, ferric and cupric doesn't produce significant bubbles on the pcb , unless you have added peroxide. With pure ferric with a low/zero free acid, I think the agitation is important to displace the solid sediment?

author: CopperCone
author_rank: Super Contributor
timestamp: July 30, 2018, 10:43:01 pm
content: I realized why I never had serious alignment problems: I always use a solid ground plane.When I get more transparancies I will test the alignment method by the way you describe.

author: CopperCone
author_rank: Super Contributor
timestamp: July 30, 2018, 11:29:36 pm
content: Ugh, testing my tube carefully, I noticed its difficult to do this right.What I see is that when you increase the pressure to get significant agitation, the bubbles form a mushroom cloud type thing in the tank, where they are pulled in towards the middle. It seems to work ok with very small pressure with the bubbles going strait up but I found that over the last 2 days the pex tubing self sealed alot of the drill holes.I think the proper way is to make a square bubbler out of acrylic and put it on the bottom of the tank and drill holes uniformly at the base, then to carefully adjust the gas flow to prevent the convection like effect with the bubbles being pulled in towards the middle to make a trunk. Buncha small holes drilled for nothing. Maybe you even need to stuff it with some kind of wool material to make a pressure drop across it so the bubble emission is uniform.I see basically no bubbles on within a few inches of the sidewall of the tank. If I get enough flow to make a few centimeters of agitation on the top you get the trunking effect with significant deadzones on the edges. I don't know how uniform the trunk is, if its fairly uniform you can make a wider tank I suppose, but the tank needs to be like 40% wider then the PCB in my case. I did not see this with the shitty bubbler I had before for some reason.

author: tautech
author_rank: Super Contributor
timestamp: July 30, 2018, 11:42:18 pm
content: Yeah and that's why I decided to use the PVC gutter guard mesh as a PCB carrier because it helps disperse the bubbles rather than have them just rise vertically to the surface. The mesh rests on the bubble tube so the PCB is right near the bubble path.Quote from: KL27x on July 30, 2018, 10:37:57 pmYes but there's the agitation benefit of the bubble path too that keeps solution from stagnating in one place and that can of course speed the etch.

author: CopperCone
author_rank: Super Contributor
timestamp: July 31, 2018, 12:02:05 am
content: do you notice the convection/mushroom cloud effect in your setup ?How much wider is your tank then the PCB? I can only use like 60% or less of my tank.

author: tautech
author_rank: Super Contributor
timestamp: July 31, 2018, 12:17:28 am
content: Quote from: CopperCone on July 31, 2018, 12:02:05 amNo, I'm careful to control the air flow so to not create a mist of etchant however there is a tiny bit of splatter.QuoteFrom an old thread:Here's mine, knocked up from stuff I had lying around.Base: plastic road markerTank: custom thermoformed 150mm waste pipe(using large propane torch and timber and wedges to get to flat form)PVC solvent adhesive for plastic gutters.Bubbler tube (not visible): extruded (straight) semi soft plastic tube, multi pierced with a stiff needle (fine ground file tang)PCB holder: folded gutter guardFits 220 x 150 mm PCB. 750 ml etchant capacity.

author: KL27x
author_rank: Super Contributor
timestamp: July 31, 2018, 12:24:19 am
content: Another 2 cents:I try to leave at least 4" empty at the top in my vertical tank. But I can go all the way up when I need to. When I etch larger boards, I lay a bit of paper towel over the edges that are uncovered to soak up the overspray.There is zero splashing with the microbubbler I use for my tank. The bubbles form a head where they coalesce into larger bubbles. The popping of the bubbles is what shoots tiny bits of etchant up about 4".This is one reason why virtually all commercial vertical etch tanks are much taller than they are wide. Mine is square because of the logistics of buying small amounts of plexiglass and not wanting to spend more than I had to.

author: CopperCone
author_rank: Super Contributor
timestamp: July 31, 2018, 12:24:53 am
content: Quote from: tautech on July 31, 2018, 12:17:28 amNo, you misunderstood me. I meant a bubble mushroom cloud under water, where the bubbles seem to be pulled towards the middle of the container in a column, rather then flowing laminarly upwards. I basically get no contact with the PCB within like 2 inches of my container walls. If I drastically decrease the effect the problem goes away.It seems there is water recirculating near the walls of the tank in some kind of eddies or some shit, so the bubbles are pushed away from the sides.It seems like its going to be a pain in the balls to make this right.

author: CopperCone
author_rank: Super Contributor
timestamp: July 31, 2018, 12:28:36 am
content: like thisThey are literarly pushed away into a lower pressure region or some shit, I can see sharp deflection angles.

author: tautech
author_rank: Super Contributor
timestamp: July 31, 2018, 12:32:11 am
content: Quote from: CopperCone on July 31, 2018, 12:24:53 amYou can see as mine is so narrow and the PCB is central and in the mesh carrier I have none of those issues.If you have a strong enough bubble flow the agitation will cause central column movement upwards while the edges of the tank will have a downward flow.Naturally the bubbles will want to remain central in the tank.

author: KL27x
author_rank: Super Contributor
timestamp: July 31, 2018, 12:37:42 am
content: I've tried 1.5" tank. Went to 3/4". Copper, do you hang multiple boards in your tank with some sort of spacer? I'm curious to see a solution for this.

author: CopperCone
author_rank: Super Contributor
timestamp: July 31, 2018, 12:42:40 am
content: No I only did single boards and I did not do too many of them either, and my solution was so dirty I never saw what was actually going on in there, I kind of just did some fly by night stuff with making my PCBs. All my time went into the design and equipment.

author: CopperCone
author_rank: Super Contributor
timestamp: July 31, 2018, 12:45:25 am
content: My most successful PCB were actually when I made a etchant tank by soldering garbage bags together using a soldering iron, sticking a tube in there I poked a bunch with a needle with a clip on one end, and putting that inside of another garbage bag that had a immersion heater in there.. then sandwiching it between some crap and letting it run off a big air compessor, but this kind of shit resulted in cleanup with a garden hose... however the PCB were really nice and I never had multiple attempts, I thought this tank would be a step up.I mean cut garbage bags, and I soldered it by putting a sheet of paper ontop of my bags and dragging the iron across it at some determined temperature. It did leak some though, a heat sealer would work nice.I made a PCB that was 6x10 inches with like 200 components on it from TDFN to TO220 on it with those garbage bags first try. Exposed that shit with a bench magnifier too, and it was double sided.I hate how freaking messy and trashy it is though.. but considering the # of boards I wasted in this fucking acrylic tank, it must be like 100$ worth of PCB.

author: KL27x
author_rank: Super Contributor
timestamp: July 31, 2018, 12:53:21 am
content: Ahh. Copper, you seem to have a bit too much time on your hands. And if you're gonna curse, how hard is it to mix it up, a little? Watch some AVE videos if'n you need some pointers.

author: CopperCone
author_rank: Super Contributor
timestamp: July 31, 2018, 12:55:18 am
content: i am not in a mood to entertain when I am bleeding cash like that, he is a showman, if you are all eloquent and funny like the joker when your upset that means your not upsetperhaps if I got a load of free stuff and patreon funding I would write my posts like a comedy script.

author: james_s
author_rank: Super Contributor
timestamp: July 31, 2018, 01:05:11 am
content: You're.

author: helius
author_rank: Super Contributor
timestamp: July 31, 2018, 01:18:06 am
content: Quote from: CopperCone on July 30, 2018, 11:29:36 pmMaybe the answer is to drill the holes all on thebottomside of the tube and then they will by necessity rise along the sides?

author: KL27x
author_rank: Super Contributor
timestamp: July 31, 2018, 01:26:48 am
content: QuoteWell, damn. Who knew you were actually upset? And why are you upset? It sounds like it's because you are very painfully reinventing the wheel? No matter what people post, you already have a reason to do it another way. You already have a better method that you've invented (but are just working out some minor details).And in the process you are doing a great disservice to a host of quality swear words. Mix in the occasional f bomb for cunt's sake!QuoteWell, I trump you one. Since he is etching single board at a time, why not put the board in the center of the tank?

author: KL27x
author_rank: Super Contributor
timestamp: July 31, 2018, 01:42:48 am
content: The amount of setup and clean up you are talking up is straight up messed up!Spend a little more time and effort and money up front. And you will have a lot less work, forever. People already done the hard work of trial and error. Just go out and pick your poison. Well, be careful. I bet a lot of the tanks setups you can find on the web last 1 year, tops. Spoiler: you can't glue plexiglass with just silicone.

author: tautech
author_rank: Super Contributor
timestamp: July 31, 2018, 01:52:40 am
content: Quote from: KL27x on July 31, 2018, 01:42:48 amYou can but thermal cycling will raise its head and bite you.Originally I used clear PVC solvent like plumbers use for socketed pipe joints but it wouldn't stand up to the thermal cycling so I went to a white gutter solvent one thick enough to form a decent bead with and that solved joint cracking problems. I didn't go totally anal and use a PVC solvent primer but did take the gloss off all parts of the joint in some attempt to ensure good solvent penetration and adhesion.

author: KL27x
author_rank: Super Contributor
timestamp: August 03, 2018, 02:03:19 am
content: Re:Sleemanj's shadow effect, it might be due to the thickness of his resist layer. Also, I am not sure what etchant he is using. I've never seen it. If it is specifically related to the bubble wand/finer bubble, it maybe requires some other factor which is different between our setups.I leave my board in there with no problems with the evenness of etching. Haven't once turned repositioned a board since using Pulsar, pre etch, vertical etch tank, cupric chloride, and super fine bubbler. I can leave it in there twice as long as necessary and the board is still fine. I have to forget the board overnight to totally mess it up. I don't use a timer/alarm. The window of a good result is really, really wide.If anyone actually wants to get 8/8 PCB with no problems and no hassle, I can provide all the details. If you follow the algorithm, you simply can't go wrong, and there's no fine tuning/timing/mixing/tweaking/prayer involved.

author: KL27x
author_rank: Super Contributor
timestamp: August 03, 2018, 02:57:01 am
content: Toner transfer 8/8 every time.1. Print your circuit onto Pulsar dextrin coated toner transfer paper and turn on your laminator to let it heat up.2. Take your copper board and put it on a cutting board.3. Wet the board and add a drop of dish soap4. Scrub the board with stainless steel wool.5. Pre etch*: Dunk the board in your tank for about 3 seconds. Flip it and dunk the other side for another 3 seconds.6. Let it drip back into the tank for a few seconds, then dunk it in a bucket of water.7. Take the board out and shoot it with a 1200w heat gun until it is dry. It will have streaks all over, but that doesn't matter.8. Inspect the board for any grease spots that prevented the pre-etch. If you find any in an important spot, go back to step #2.9. Take the still hot board and put the transfer paper on it.10. Run it through the laminator. Turn on your 1200w heat gun and set it to full power to warm up while the board is making its first pass.11. Take the board and put it through again, but this time shoot it with the hot air gun from about an inch away. Back and forth right were it goes into the laminator. For this reason, you should have removed the plastic cover of your laminator and screwed the laminator to a board. Wear shoes while you are doing this and don't do it while your hands are wet, unless you like getting shocked.12. If your board delaminated, then you just found out how much heat to not give it. Start over from step 1, and don't do this again, lol.12b. If you have another side to do, then repeat the same procedure for the second side. You should have already taken steps to ensure alignment; I print alignment pads in the corners and pre-drill them in the paper. So at this point, I would take the board with one side transferred, locate those pin holes, and I would drill those holes through the board in order to align the second side.13. Etch in real etchant. Not acid peroxide.* The reason for the pre-etch is not what you may think. I've read about this idea for at least 10 years. Today, most people say it like "I read about it, but this step is optional; I have DISCOVERED that it's not really needed." This seems to be part and parcel of the internet age where things happen fast. People are expert on something in a day. Then they don't actually have any more boards to make, or they progress to ordering their stuff from China. And they move on to become one day experts in something else. The reason to do it is so that the transfer doesn't run and smoosh and fatten when you heat and press it against the copper. There is a super smart guy who has discovered the secret method to perfect transfers. It's by controlling the time/temp perfectly to partially melt the toner in order to avoid this smudging. Super smart, except trying to get toner to partially melt but not totally melt on the board is like trying to get the morning 1mm layer of snowflakes on your driveway to partially melt but not totally melt. It's stupid; because you don't need to do that. And trying to post your results so that someone else can copy them with different boards and oven is even more stupid. If you pre etch the board, you can completely liquify the toner and the transfer will come out fine.** That said, this step is one of the reasons you cannot use acid peroxide. The peroxide is in there to oxidize the copper. The acid can only etch oxidized copper. If you pre-etched and dried the copper, it is oxidized. The acid will undercut the resist. And the copper ions produced will catalyze the breakdown of peroxide, making bubbles. And the bubbles will further compromise the resist. And acid peroxide is a bad etchant when it comes to undercutting to begin with.**This is also the reason you do not want to use magazine paper or photo paper. Maybe you have found other things which work. But if you want the ability to get consistent results without microcalibrating your transfer time and temp and pressure for every size board you will ever make, you need the ability to liquify the toner. And if you liquify it, magazine paper or the like will get stuck, and you will have fibers stuck to the board which limit your effective resolution. With mag paper you might get down to 8/8 when it goes right, but for high consistency you will be stuck around 12/12.