Questions about diy pcb UV solder mask - "mechanic" brand. U - Page 1
Forum section: electronics / projects

author: Fflint
author_rank: Frequent Contributor
timestamp: December 31, 2020, 01:34:10 am
content: :-+I bought some of the "Mechanic" brand uv solder mask that comes in 10cc syringes. I saw all the YouTube vids and I looked at every link Google knows about, but no one really gives a clear complete description how to use it properly (other than by exposing the whole board and milling it away).Specifically I'm having trouble with avoiding air bubbles under the foil. For those that don't know how it works: one is supposed to dispense some from the syringe in the middle of the board. Cover the board with suitable transparent film (pvc, acetate, cellophane etc all work as long as the substance is fully cured before removal). Use a squeegee through the foil to spread the solder mask over the entire board. Put a mask over the pcb covered with foil and expose under uv lamp (365-400nm). Once cured remove the foil, remove uncured solder mask with a napkin, or solvent if necessary.The problem I have with the above process is that the solder mask is very thick and spreading it with a squeegee from a central spot results with too thick coat in the middle and too thin near corners. However, if more than one spot of the substance is used bubbles of air become trapped and mess up the solder mask. I found it is easy to spread the substance on the pcb by using a small brush or a piece of pvc foil, but then it is impossible to put the foil and mask over it without huge amount of air bubbles again.It would be great if the solder mask could be dried somehow without curing so the mask can be pressed without disturbing the coat, then remove the uncured portion with some solvent. I found some info online that says the solder mask can be dried at 100-105degC without curing, but it supposedly cures at 115degC so one has to be very careful.My question is, does anyone have a good method to use it with or without heating. Also, it would be great to have some way to remove partially cured mask from the board to fix boards that were under/over exposed.Another issue I have with it is with finding the correct exposure time. So far in all my tries I had emulsion under develop, or develop fully including under masked areas. In youtube vids people use double masking. My mask is very high contrast so I was hoping one is sufficient. I use the same single mask for photoresists.

author: sleemanj
author_rank: Super Contributor
timestamp: December 31, 2020, 02:04:02 am
content: Oh man, it's horrible to work with this stuff. My advice, when you need soldermask, just get it fabbed, so cheap now from china that it just doesn't make sense to try and DIY it when you get to the level of wanting soldermask (let alone silkscreen!).However if you really reallyreally really reallywant to DIY then I seem to recall I had the"best" (read: not complete trash) results with the red colour, maybe I just got lucky that time.It can be thinned down with "banana oil", Isoamyl Acetate / Amyl Acetate or Ethyl Acetate, that might help a bit (especially if you could spray it on, and dry it). Ultimately, after a lot of trial and error, I... gave up, it's just such a PITA of stuff to use.I did make a few soldermasked pcbs using Vitrea 160 (threads here about it, search) sprayed on with toner masking the pads and later dissolved out, and that frankly got me the best results in the end, the Vitrea is quite tough once it's baked.You can get dry film soldermask, applies like dry-film resist but it's stronger. The only one I've seen sold (outside of industrial quantity) is Dynamask, only green and it's not sold on Aliexpress or other cheap chinese places I've seen, basically only on eBay. I guess it's just not used in China so they don't have it to sell.

author: M4trix
author_rank: Frequent Contributor
timestamp: December 31, 2020, 03:36:23 am
content: Quote from: sleemanj on December 31, 2020, 02:04:02 am+1I've tried everything and I mean everything but that nasty stuff is simply useless. That ink is for silkscreen printing.It's wet and it stays wet no matter how many days you try to dry it. If you dry it in an oven, drying time and the temperatureare critical. Too long, it will cure. Too short, it will go off while wiping with cloth and banana oil. Exposing it to UV is also time critical.Cut the long story short.... ditch it !Btw, if you want to use dry film soldermask, look here ->http://www.fortex.co.uk/product/dry-film-solder-mask-resist/Edit: more stuff regarding that UV ink ->https://www.eevblog.com/forum/beginners/diy-solder-mask/msg1260727/#msg1260727

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 31, 2020, 03:53:45 am
content: Quote from: sleemanj on December 31, 2020, 02:04:02 am

author: lucatz
author_rank: Contributor
timestamp: December 31, 2020, 03:54:31 pm
content: 5:50 mark...seems to work

author: Fflint
author_rank: Frequent Contributor
timestamp: January 01, 2021, 01:38:20 am
content: Yes, it is nasty stuff... The key issue I identified is that the UV exposure time is proportional to thickness of the cover, but not linearly. For example a very thin cover (10-30um) cures in 10s exposure of my led (dual wavelength 365-400um 12w estimated) lamp at "floor level" . A medium thickness (around 50-70um) requires 240s raised by 20mm. And if it exceeds 100um roughly it hasn't cured after 10 minutes raised same as before... The thickness of the cover is very critical.SleemanjI think you (and some others on YouTube) had best results with red is because it doesn't block as much uv as green. Green one cures in layers. The most common failure is when the layer of "ink" is ever slightly too thick and final um fails to cure the whole thing lifts when the film is removed. The problem is that even with my really good contrast mask I get either fully cured cover, or partial lift during failures.Regarding having the board fabbed, yes that's a very valid advice if one simply needs solder mask :-) but what if one wants the satisfaction of having it made by oneself too ;-) It is a hobby for me after all, if I was doing this commercially it wouldn't make a slightest bit of sense. The only use for that paste/ink commercially I think is to restore bits of original solder mask or conformal coating on expensive boards during repair.Anyway, coming back to DIY use. So this got me thinking. To succeed I need to lower the adhesion of the cover foil/film so it is less than the force of surface tension holding slightly under cured mask to the board as fully cured paste doesn't mask well, it has to be under cured for the mask to do it's job of selective curing.To get this I tried giving it a quick "shot" of uv (1 to 5s tested) before applying the cover film so there is a very thin layer of dry mask on top. That gave me encouraging results initially, but I never managed to get complete masking without at least partial lifting.So I thought rather than trying to lower adhesion force by pre-drying/curing I can lower it by making the area of the "pulling force" smaller by using more flexible cover foil. Cellophane is an obvious choice, but for the wrinkles and bubbles.So what I did in the end and what finally worked was to:-put half of the paste I thought I need in a middle of the board-use a tiny brush to spread the paste over entire test board, but leave final outside 3mm with no paste. Use normal white light to observe and spread it evenly.-make a "sandwich" of flexible PCV (binding cover "o-clear" brand), cellophane bigger than PCV and wrapped around spread on the PCV and smoothed ideally with no bubbles/wrinkles etc. Press the sandwich against thick glass to flatten. Remove the sandwich without disturbing the cellophane.-Hold the cellophane/PCV sandwich above the pcb from previous step and squeeze your hand through so the sandwich (cellophane down) has a shape of a cylinder.-press it to the pcb lightly so the contact area forms a horizontal line.-spread the contact area from the middle line towards the edges without pressing too much - this is key to get rid of 99% of air bubbles.-Once uniform contact is made over the most of the board illuminate with white light again and use the color visible and a guitar pick held by a corner flat against the PCV to even out the paste on the pcb.-Once done flatten with a piece of glass, cover with artwork and press with 3mm glass panel.-expose for 120s twice with 10s rest between ecposures(probably not essential) while lifted 20mm above the "floor level" (on a roll of kapton foil in my case).-wait few minutes after exposure just in case-remove glass, unwrap the cellophane from flexible PCV, remove PCV, start removing the cellophane if the corner lifts the paste from the board reassemble the sandwich and give it another 10s (assuming you can align the mask exactly the same). I didn't have to give it any more however. When the cellophane was removed I could see the paste looks cured where it should and uncured where masked.-put in acetone and go over uncured areas with a small delicate brush while submerged. Do not use a napkin, it is easy to remove semi-cured paste as well by pressing too hard.-Once masked areas are clear let acetone dry. Then expose for longer to fully cure the remaining mask.-repeat whole process for the other side of the board...Soo, I managed to succeed with the above process once. I didn't have time to try more times yet, but I will and we'll see if this can be reliable.

author: coppercone2
author_rank: Super Contributor
timestamp: January 01, 2021, 04:15:41 am
content: you are supposed to spin it high speedviscosity is supposed to be right for material, temperature and rpm to get a good coatingnothing is squeegeed for precision work, that is what you do at a gas station

author: Fflint
author_rank: Frequent Contributor
timestamp: January 01, 2021, 11:26:39 am
content: Quote from: coppercone2 on January 01, 2021, 04:15:41 am;-) hmm probably you're correct.I have a large (200mm) speed controlled fan I can use with double side sticky tape as a DIY centrifuge. However, the paste is pretty thick at my current "room temperature". Perhaps heating it a bit with hot air would help.I have access to a lab grade centrifuge that does 8k rpm, but no way I'm sticking anything other than liquids into it... I think it would self destruct pretty quickly.I'll try the diy spinning method if the above process doesn't prove reliable.

author: Fflint
author_rank: Frequent Contributor
timestamp: January 01, 2021, 03:58:34 pm
content: One more thing, I tried multiple solvents trying to remove the cured solder mask and nothing works. I tried:- hot lye solutionCold solvents below:- dichloromethane- acetone- IPA- petrol- ethyl acetate- toluene- xylene- ethylobenzeneAll of the above only for short time each. Perhaps leaving it for longer (overnight) would work. Also acetone and ethyl acetate seem best in removing uncured paste.

author: coppercone2
author_rank: Super Contributor
timestamp: January 01, 2021, 08:11:00 pm
content: well now that I think about it the big things they make in a factory they probobly made a squeegee formula too, its not going to be nice like semiconductors anymore at those low low pricesare you sure they don't use a rubber roller ? in china its probably like working as a wall painter. high technology lol

author: sleemanj
author_rank: Super Contributor
timestamp: January 01, 2021, 09:58:03 pm
content: As above, can be thinned with Banana Oil for spraying (or spin?). It's screened on industrially I think.As for removing cured soldermask, one of the reasons of mask is it's a protective coating, so it's supposed to be as impervious as can be. I imagine anything that removes the cured mask would likely remove the copper, and possibly the pcb's epoxy too.

author: coppercone2
author_rank: Super Contributor
timestamp: January 01, 2021, 11:45:24 pm
content: well if you do it yourself it comes off pretty easy with alcohol

author: sleemanj
author_rank: Super Contributor
timestamp: January 02, 2021, 12:20:14 am
content: Quote from: coppercone2 on January 01, 2021, 11:45:24 pmNot after curing

author: coppercone2
author_rank: Super Contributor
timestamp: January 02, 2021, 04:17:05 am
content: I mean do you just leave it on the PCB afterwards? I generally scoured it off with alcohol

author: sleemanj
author_rank: Super Contributor
timestamp: January 02, 2021, 04:23:58 am
content: Sounds like you are confusing soldermask and etch resist. This thread is about soldermask.Soldermask is the permanant impervious coating on pcbs, clasically green.Etch resist is the temporary coating used to protect the copper you want to keep from the etchant that is removing the copper you don't.

author: coppercone2
author_rank: Super Contributor
timestamp: January 02, 2021, 04:36:22 am
content: maybe brillo pad ball brush?that is a 1 part UV sensitive : acrylic, epoxy, polyurethane? (depends on which one)

author: sleemanj
author_rank: Super Contributor
timestamp: January 02, 2021, 05:21:00 am
content: Yes it's a 1 part uv cured epoxy "ink" similar consistency to screen printing ink, thick paint.https://www.allpcb.com/soldermask/lpi_soldermask.html

author: coppercone2
author_rank: Super Contributor
timestamp: January 02, 2021, 05:42:40 am
content: if its cationic (uv generated super acid) cured epoxy then you will need a epoxy dissolver to remove it, problem is the substrate is also a epoxy resin. uv acrylic relies on free radicals and polyurethane type I don't know.So I think abrasion is the safest option (coarse brillo) i.e. walter coarse or extra coarse abrasive. in the metal working world its supposed to take over after 120 grit sand paper. goes extra coarse, coarse, medium, fine, superfine.. then typical polishes (i.e. the kind you use with a foam pad).very light pressure on a rotary tool should be good, the dremel brillo buffs might be good (but keep in mind they don't last long). I think you need to work in small sections so you 'stay with the grain' on the copper traces like with wood or beef. The dremel will work as a mini linear polisher and they have 3 grades of abrasives available. Rotary polishing might not be the best option because it might lift traces. Working wet will decrease heat and increase the strength of the glue under the traces during work, so you are less likely to cause trace lifting.

author: Fflint
author_rank: Frequent Contributor
timestamp: January 02, 2021, 10:31:59 am
content: Quote from: coppercone2 on January 02, 2021, 05:42:40 amAbrasion it is then...However, for fully cured mask no tiny rotary tool will do. I had to use a 2kw buffer with buffing wheels replaced with steel wire wheel on one side and brass wire on the other. Steel is definitely too harsh, brass is fine as long as one doesn't press too much.However, this "buffer" is the only machine I own I don't like using. It is a monster. Wire wheels have to be ideally balanced (by inserting screws into their central disks) and have to be periodically rebalanced as they loose wires. The wires fly away with great force so you need a face shield, a leather apron and non-woven gloves(because if it grabs your hand it is better the glove rips rather than entangles you)... Definitely not a good "hobby" machine. After few minutes it did the job.First pic are two of solder mask failures. Second shows the wheel and pcbs with mask removed.

author: Fflint
author_rank: Frequent Contributor
timestamp: January 02, 2021, 02:27:59 pm
content: I'm starting to get more encouraging results with 4 layers of mask (laser printed on transparency then improved by dry erase marker). I'll post more details if it works consistently.

author: Fflint
author_rank: Frequent Contributor
timestamp: January 02, 2021, 05:19:01 pm
content: Ok, I'm finally quite happy with how it works.The key to good results is:-heat the pcb before applying paste to 40 degC- apply a small amount, spread it with a small brush, then put acetate foil on top (laser printer transparency type) and tape it to the board in corners.-chase all air bubbles out with a guitar pick-put 4 layers of artwork on it taping it to the board-press everything down (I use 3mm glass weighted down with 4:lead fishing weights)-expose (540s in my case)-take foils off-remove uncured paste with a napkin carefully-clean to remove trace of uncured paste (I use acetone)-give it few more minutes under the lampSome results below (two sides of the same pcb). The actual pcb will be cut from the middle of this so it will look better). There are some small air bubbles present, but they are not very deep.For my hobby use this is "good enough".

author: coppercone2
author_rank: Super Contributor
timestamp: January 02, 2021, 05:29:29 pm
content: I would say brass is too aggressive, but I am not sure. They have brillo-like pads for both belt sanders and circular systems. And brillo pad wheels for bench grinders but the RPM is not quite right I think. Big wire wheels make me nervous.*keep in mind grit availability of these products depends on dimensions, they don't seem to have every grade of everything for every wheel size, if you are interested look in the catalogFrom experience:might work if you are really gentle with the pressure but I think it might mangle the PCBhttps://www.walter.com/products/abrasives/twist-finishing/fx-surface-cleaning-discsthat is the best paint and rust stripper there is if you have the settings dialed in right. It will restore more crappy metal then your back can take... I will try one out in a die grinder later when I find a bad PCB. But if your settings not right it will disappear infront of your eyes and you will think its a rip off.. key is RPM limiting.have interest in but not evaluated, might buy it in the summerhttps://www.walter.com/products/abrasives/twist-finishing/twist-blendex-u-discshave some hope in and might test tonight on PCB (but I only have medium, fine and super fine, I am waiting on a shipment of coarse and I would need to buy extra-coarse).https://www.walter.com/products/abrasives/twist-finishing/twist-blendex-conditioning-discsThen form for those products can be stuff like thishttps://www.walter.com/products/-/producttradename/abrasives/finishing/blendex-drumsThat is just one manufacturer. I am often surprised by the performance of these things in situations that don't quite work out. They seem superior to wire wheels in many cases. I use the twist ones though (circular finishing). But those drums would be the best bet for wide flat things, I think.Walter and many others sell that in different forms including drums, round twist on flat disks, belt-sander type, like big matted padsI have seen 'buffs' made of the same stuff sold for bench grinder wheels and also for use with a hand drillBTW if you got the money I highly recommend them for whatever you were trying to do with that giant brass brush. That thing is ultra janky.

author: coppercone2
author_rank: Super Contributor
timestamp: January 02, 2021, 05:48:07 pm
content: *all this seems not recommended on their website though for materials choice, I think I musta been mistaken. it might be because it leaves remains of abrasive inside of plastic at high speeds. if I find a bare PCB i might test the normal blendex though*I remembered? this, but I can't seem to find the video.. the only thing similar is the one on conformal coating removalI want to say theu-disk blendex is the industry choice for abrasives used for mask and conformal coating removal. That is a mixture of leather and diamonds or something like that. It is sold as points and disks (linked above) but I don't own em.It is supposed to be a system that goes into a weld bead after it is die grinded with a burr to make it smooth and polished looking, in 3 steps.Pacesold? small versions of these points for their PCB-repair system on 1/8th inch collets. I might buy some in the summer for 3/8 shaft size from walter. For a bare PCB a 2 inch u-disk might be what the doctor ordered. I believe its slightly more aggressive and much more longer lasting then the scotch-brite/brillo pad type finishing pads.This u-material I believe is recommended by pace to1) removal conformal coating that is applied in thin layers prior to chip removal2) remove solder mask on the top layer of PCBthen to do repairs the system has a special dremel that is connected to the conductor being worked on, which haults the motor when it makes electrical contact with the conductor (digs deep enough into the PCB/fiberglass). Then you are supposed to go back to the U-point again and carefully expose the trace and patch it up with epoxy when you are done. I guess the u-point is not aggressive enough to really get into copper and fr4, but is good on it if its been weakened with a metal cutter.https://www.walter.com/products/-/producttradename/abrasives/finishing/blendex-u-pointand then the u-disc. Pace must have a contract to get 1/8th versions made. Probably also available from jewelry places.maybe have a look here for microchine accessorieshttp://www.gsaservice.com/PACE_Consumables_Spare_Parts_Catalog.pdfalso for your mask, do the paint test. finish a PCB and score a tiny tiny grid with a razor blade some where on the PCB, wipe it with isopropyl alcohol and stick the best tape you can over the region and yank it off like a week later.

author: coppercone2
author_rank: Super Contributor
timestamp: January 02, 2021, 08:52:10 pm
content: ok it looks like the normal blendex scotch brite circular rotary pads are not appropriate for this. They tend to smear and they are too hard and attack the traces a little. I think you need something linear.The dremel brillo buffs are loose and linear (and I have seen gigantic versions at harbor freight). Maybe that would work better. i attempted the blendx on a green perf board and it attacks the plating and traces because those blend-x metal pads are not soft enough. You need to go with the grain along the traces carefully it looks like.. no good bulk way to do this. This stuff is tough. I would say that brass brush gave you good results. And I only tried the medium one, I think the coarse and extra coarse will tear up the pads. I think chemicals are too risky to use because it will cause pad seperation.

author: Fflint
author_rank: Frequent Contributor
timestamp: January 03, 2021, 02:31:33 pm
content: Thanks,the Walter stuff looks neat. My brass brush looks janky because of the m8 bolt sticking out of it :-/ unfortunately that was the right way to balance it for the buffer rpm. When I bought it I made sure it is rated for much higher rpm, but still it had a horrible imbalance.It worked pretty well for this. Based on the difficulty /ease of removal of this solder mask I have to say anything gentler wouldn't work. It is possible to mess up traces with it if one presses a lot on a clean part of pcb, but it doesn't happen instantly so it is doable... Definitely not what I would want to be doing a ot of. One, two boards mac."Typical" use for this wheel is cleaning corrosion out of steel etc. It is good if you just need to clean a small spot and there is a wrong abrasive loaded in the blasting cabinet.This actually gave me an idea for really neat (abrasive) way to remove solder mask. If the pcb is flat enough it should be possible to use a surface grinder to remove it. There is this surface grinding "trick" that is some times done as a demonstration of one's skill etc. It involves surface grinding a part, marking it with a sharpie and then attempting to remove the sharpie mark from the part without touching the metal. It is doable on a good machine :-) workholding might be a challenge without a vacuum chuck.Coming back to the original subject. I've managed to use that product semi-consistently and I'm quite happy with it. However, I had one failure that was interesting. I did everything as before, with exception of using a pcb I was testing tin plating for possibly too long of a time with. When I was removing the cover film, the solder mask ripped tin plating clean off the board revealing clean copper underneath. So the conclusion is not to tin plate the entire pcb before solder mask.

author: coppercone2
author_rank: Super Contributor
timestamp: January 03, 2021, 02:48:00 pm
content: yea I think you will in general experience a pain in the ass removing epoxy from anythingi think it will foul your surface grinder stone

author: Brentd27
author_rank: Newbie
timestamp: January 14, 2022, 08:27:19 pm
content: I know this is an old thread, but I was wondering if using FEP film, as used in 3D resin printers, for the solder mask film might work. Don't know if toner will stick to it though.

author: coppercone2
author_rank: Super Contributor
timestamp: January 14, 2022, 11:22:34 pm
content: freezing it before working might help, this might be application of cryogrinding, in reference to grinding epoxy