Author Topic: UV silkscreen  (Read 928 times)

Agastar

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Re: UV silkscreen
« Reply #15 on: December 01, 2016, 01:50:25 PM »
Yeah, for my CW permit in Memphis they used ink but here in Florida it was all electronic.

Another way might be to airbrush the paint onto the PCB :) I'll have to thin out the paint a bit but it might work :)

beikeland

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Re: UV silkscreen
« Reply #16 on: December 01, 2016, 02:05:18 PM »
The soldermask paint i got is super thick, nearly thixotropic, and the limited listings said not to use a thinner.

I've also bough a cup of "blue ink" that was described as mainly a photoresist and was intented to be used with a thinner, as well as a bottle of "blue ink thinner", I suspect these are all the same type of stuff but we'll see when the blue stuff arrives.

The tape as a spacer was a good idea, but I buy super cheap tiny 50x70mm or 70x100mm scrap boards so I'd be doing a lot of taping, and I think even then the layer would be too thick.

So far using a stainless steel pin/tube as a roller gets me a thin and sort of uniform layer, but with a texture - then applying the plastic film removed before etching sort of smooths it out, but the end result is still quite thick.

I'm hoping the paint isn't too thick to spin coat (i guess its mainly a matter of RPM). Stubmled across an instructable suggesting to use old hard drives and drill out the centre of the motor shaft to create a vacuum chuck which sounded brilliant. Until I realised all my "old" hard drives have fluid bearing and drilling through the seal breaks the bearing.

Have a DC brush less motor and a stainless tube that is the same diameter as the shaft - plan is try to put outside or inside threads on the tube, and replace the motor shaft with the tube. Put a shaft seal on one end and a surface to form a vacuum chuck on the other, and cross my fingers. If that works I might try to use a hard drive motor with a pulley just to get something low profile and roughly the right speed range.

Or maybe see if I can find a place to go dumpster diving and recover a pre 1990's drive without fluid bearings.

Agastar

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Re: UV silkscreen
« Reply #17 on: December 01, 2016, 03:13:52 PM »
The etch resist paint I made is about normal paint consistency but I can see needing something a little thicker for solder mask paint. When I'm done, I want to have etch resist paint, solder mask paint and silkscreen layer paint :)

Whatever you come up with for the spin coating machine, I'd love to see some pictures :D

beikeland

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Re: UV silkscreen
« Reply #18 on: December 01, 2016, 03:19:01 PM »
I'm hoping to be using the same cheapo UV curable ink in different colours for "everything", one layer for photo resist, one for soldermask and one for silkscreen if needed.

One downside to the thick UV stuff I have now is that it doesn't really clean easily. The dry film I just put in lye and it either develops or strips. The UV ink can be rubbed off before it dries or needs nasty smelling solvents to clean, was hoping to avoid solvents as much as possible.

But yeah, spin coating may take a while, projects hit funding problems, but I guess I will be tinkering with super gluing boards to hard drive spindles some time during the next few weeks just to see if its even doable at up to 5.4 or 7.2k RPM. Will post pictures if progress is made ofc.

beikeland

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Re: UV silkscreen
« Reply #19 on: December 01, 2016, 10:34:27 PM »
I guess the rectangular shape of the 50x70mm scrap boards combined with using paint that been left in a syringe for maybe two weeks out in the open (but not in direct sunlight) makes a sub optimal result.

Think I'll wait for the "blue ink" and accociated thinner before trying again. Looks like it will work, but its not super uniform, center dot and outwards streaks, but it does appear to be both thinner and more uniform than I could do by hand, despite having used 4-6 times as much paint.

I believe this was a 5.4k rpm drive; maybe rolling the paint on and then spin coating it could help a combine the best of both worlds, but that quickly becomes a lot of extra cleanup for a one-off board.




« Last Edit: December 01, 2016, 10:37:15 PM by beikeland »

beikeland

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Re: UV silkscreen
« Reply #20 on: December 02, 2016, 03:57:10 AM »
Decided to give higher RPMs a go, not having a hollow shaft I cut up a PCB chuck of sorts and have 10k+ RPM a go.

Much better uniformity, and less streaking, some signs of pitting of what you'd want to call it a after a while, but I'm guessing that can be attributed to poor surface preparation.

Chuck:

Result:


Used a 980kV outrunner and screwed the "chuck" on top of the bell, lets just say it was not perfectly ballanced and it rattled like he** but seems to have gotten the job done. Gonna try some more with the diluted "blue ink" and green solder mask with better surface preparation over the weekend.

Agastar

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Re: UV silkscreen
« Reply #21 on: December 02, 2016, 08:54:08 AM »
Looking good! You're making more progress than me lol.

My goal is to have paints that cure with heat and clean up with water. I don't mind working with solvents like acetone and what not but I know a lot of people don't and its just easier if you can clean it up with water :)

So how much does the cheap UV paint cost you and for how much?

beikeland

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Re: UV silkscreen
« Reply #22 on: December 02, 2016, 02:11:13 PM »
Paint seems to be $6-7 for a 100g jar for the stuff that needs solvents to clean up.

I haven't found the emulsion screen printers use, in small quantities for a low price, but it's water soluble and I would have preferred to use it over the paint, however I fear it would dissolve in the etchant too.

The dry film I've been using for a photoresist is about $7 for 1m2 - so the paint is a lot cheaper. However needing solvents quickly adds to the cost as even the cheapest options start in excess of $10/litre locally. The "blue ink thinner" was $7 for 100ml, or more like $7 for 30ml as it had leaked in transit and the post office gave me a stern look collecting that package :P

But the paint is easily cheaper than the dry film, and quite possibly a more forgiving method when using sub standard scrap boards, but if I were to find the dry film in at least two contrasting colours I wonder if I would have used that for all three steps.

beikeland

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Re: UV silkscreen
« Reply #23 on: December 03, 2016, 01:03:18 AM »
Received the thinner yesterday, not sure I could identify it from smell. Probably ester based at least, Ethyl acetate is the closet I've smelled I think. (I'm hardly a chemist though!)

Mixed up roughly 1:2 paint to thinner just to start in the more fuild part and adding more paint as needed, hindsight being 20/20 should have gone the other way as it would be quicker to stir in more thinner than more paint I guess. Left the thinned paint sit over night to see if it would stay suspended in the thinner, seems good this morning.


YES, there is a layer of soldermask paint on that board, slight dot in the center and a brim along the edge, but the surface looks fabulous, except for the scratch in the board. Curious to try if the such a thin layer is sufficient for etching and soldering. This was spun on the old hard drive, superglued to the hub, probably at 1-2k RPM. Should really get a tachometer or something going, but I can do comparative testing based on input to the speed controller at least.

Unfortunately something went wrong with GoPro so the 120 FPS footage was lost, but I did a second take nn my phone. Roughly distributed the  paint first and gave it a quick spin:
https://www.dropbox.com/s/51kkxt8std1ibui/2016-12-03%2008.29.28.mp4?dl=0

Next step, more paint for a thicker solution and try to find a way to use a optical sensor or something to detect a uniform layer at the edge.  Would have been easier with circular boards i guess.

beikeland

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Re: UV silkscreen
« Reply #24 on: December 03, 2016, 02:39:32 AM »
Just a sample, ESP8266 footpint and some 0805, SOT-23 and SOT-223 size parts. 10x10mm grid below.

One advantage of the extremely thin layer was that it needed a lot more laser power to cure, I think. Ran the etch at full power twice and just lightly rubbed off the excess paint with a paper towel, no additional solvent needed. So dialing in the thinner to ink ratio for a slightly thicker layer and perfecting spin coating and I think I'll be happy with this.

The streaks are artifacts of the g-code and the laser being too thinly focused for the code generated, I hope. Using dry film and the same code the streaks were not there, but the dry film also seems to exhibit more bleed around the laser.  Gonna have to try etching a board and see soon!

Gonna try to coat a board and leave it to dry and see if I can pre-coat boards in batches before the etching and just do the solder mask and possibly silk screen when I need a board made. Should make it easier to get consistent results if working in slightly bigger batches I think.


beikeland

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Re: UV silkscreen
« Reply #25 on: December 03, 2016, 10:23:06 AM »
So I just realized I'm trying to add paint and cure it to essentially mark a board. Surely it would be quicker to just use a light coloured solder mask, crank up the laser power and burn the solder mask where marking is needed? I think I saw a picture on one of the listings for a laser that marking pcbs directly should work. Would save time and consumables.

I tried coating the above board with white paint and to add the silk screen, but no success. My puny laser module was not able to burn the thinned UV paint but I think I'll leave well enouhg alone for now and wait for my replacement laser which apparently the manufacturer has agreed to send. Unless they start asking for videos again like last time..

beikeland

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Re: UV silkscreen
« Reply #26 on: December 05, 2016, 01:03:52 AM »
Btw - the easiest way to spin up a hard drive is with a RC ESC, if you get one with a BEC it can power an arduino to generate the control pulses, or you could use a servo tester as well.

ESCs are dirt cheap now, not sure I trust the 30A rating, but I also think its sufficient for a hard drive
https://www.aliexpress.com/item/30AMP-30A-SimonK-Firmware-Brushless-ESC-w-3A-5V-BEC-for-RC-Quad-Multi-Copter-Quality/32700290599.html

Agastar

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Re: UV silkscreen
« Reply #27 on: December 06, 2016, 11:01:40 AM »
Yeah ESC and cheap servo tester is what I use too :)

I had some success with my paint over the weekend but it needs some more tweaking lol.

Most videos and articles online show spray painting the board and then using the laser to burn off the paint from the pads. I wanted to be able to cure the paint with the laser but I'm with you, that may take longer than just burning the paint away from the pads.


beikeland

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Re: UV silkscreen
« Reply #28 on: December 06, 2016, 11:49:48 AM »
So I tried to coat a couple of boards 3-4 days ago and let them sit in a relatively dark container, and tried to run an exposure on them last night as the L7 board crapped out.

Seems to yield alright results even if the paint was almost dry, slight tackyness. Have more coated boards and will repeat the test in a few more days when I fix the laser up with a new control board.

But should be possible to batch coat a bunch of boards for pre-etching and just have the solder mask and silk screen to be spinning up when a board is needed. Should save some time for one offs, especially if a solder mask is not neccecary.

beikeland

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Re: UV silkscreen
« Reply #29 on: December 06, 2016, 11:54:08 AM »
may take longer than just burning the paint away from the pads.

Given the UV paint needs less power to cure than to burn away paint I would have thought burning paint was slower.

BUT if one were to run a isolation routing burn, etch, and then run another burn exposing the pads I guess you'd kinda have a solder mask as well - depending on how well the paint can handle solder temps.

The uv paint did not seem to want to burn off nor be marked with the laser I had available. Hopefully Banggood will ship replacement soon, manufacturer has agreed to replace it, but not to allow a TTL upgrade. But nothing has been shipped yet afaik.