Author Topic: UV silkscreen  (Read 1162 times)

beikeland

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UV silkscreen
« on: October 13, 2016, 07:11:07 AM »
So my biggest hope for my 2.5W laser was to use it to apply soldermask and silkscreens to PCBs. From my research 2.5W was a major overkill, but I figured I could adjust it down.

Well, partly wrong. I have however attached another lower power laser to the machine and made some test exposures. Not sure where the artifacts i'm seeing come from though.

Just for a sample i used the first open source pcb hit in google image search, and made a couple of exposures at different feed rates. Took a while before I noticed that LaserWeb3 had feeds in mm/s instead of mm/min though.. Do take the mW written with a might big pinch of salt, its loosely based on guestimates from PWM driving a non-TTL driver.

Attached is the result, there is probably some parallax issues, and even spreading of the paint seems be an issue on the 2nd row. But my main concern is the S shaped lines along the X axis. And lets ignore that the picture is intended for the copper traces and not the silkscreen, its just a sample with fine-ish details.

Anyone else have experience with what work better for this type of UV paint? Higher feed, lower power, more passes?

ggallant571

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Re: UV silkscreen
« Reply #1 on: October 13, 2016, 07:36:12 AM »
Quite by accident I discovered that the "Neon" blank index cards (10.2 x 15.2 cm) from Walmart make excellent test material. Cheap and the top color layer burns off nicely with relatively low power. That being said, please post the image file you were testing with and I will try to reproduce.

George
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Agastar

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Re: UV silkscreen
« Reply #2 on: October 13, 2016, 08:09:49 AM »
My suggestion would be to do several high speed passes with the laser on at full power.

beikeland

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Re: UV silkscreen
« Reply #3 on: October 13, 2016, 08:11:33 AM »
Source file was this: http://reprap.org/mediawiki/images/thumb/a/ab/Outp0.png/300px-Outp0.png

Rasrer scanned with 300 dpi and 0.1mm dot size in laserweb3.

Agastar

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Re: UV silkscreen
« Reply #4 on: October 13, 2016, 08:12:25 AM »
You said you were using Leserweb3 to etch the PCB silkscreen image?

beikeland

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Re: UV silkscreen
« Reply #5 on: October 13, 2016, 08:16:18 AM »
Still not sure what the max speed for this machine is, the "documentation" varied fro 800-2500mm/min; so it will have to go a lot faster than 2500mm/min to not burn the paint like the "50mW" sample did. Will repeat some speed tests taking acceleration into account over the weekend. I got to about 10000mm/min before I realised there wasn't any change in speed as acceleration and available movement limited the speed way lower.

What acceleration and feeds are you guys using?

beikeland

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Re: UV silkscreen
« Reply #6 on: October 13, 2016, 08:17:28 AM »
You said you were using Leserweb3 to etch the PCB silkscreen image?
Well, i took the sample .png and used LaserWeb3. For custom work I'd have to either use gerber files or print .png from KiCad or something. One step at the time. And I applied a coating of UV curable silkscreen and then "engraved" it to selectively cure the paint and rub off the uncured paint.

Edit: I guess the sample would be more like soldermask-ish. But same process for silk screen, have green and white paint, intend to do both if results are good.
« Last Edit: October 13, 2016, 08:21:27 AM by beikeland »

Agastar

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Re: UV silkscreen
« Reply #7 on: October 13, 2016, 08:54:02 AM »
Kicad can export the board in several different formats. I have done SVG, PDF, DXF, as well as gerber. For silkscreens I would probably export to SVG and use that in LaserWeb3. For traces, I will probably export to DXF and use that in BCL. If you export to an image I would use T2Laser if you have it because detail is important for traces.

beikeland

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Re: UV silkscreen
« Reply #8 on: November 18, 2016, 09:53:25 AM »
Lower power and possibly more passes seems to be the trick. Using a 30mW diode at 50% and two passes at F2000 gave a really good result, think I might be able to get soldermask between pins on a SOP chip.

Software wise I used KiCad, plot as Gerber, import in FlatCam and turn into g-code was a bit finicky but it worked well in the end. Zax has implemented Gerber support and the results are quite good there as well.

Agastar

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Re: UV silkscreen
« Reply #9 on: November 23, 2016, 11:16:03 AM »
Looks really good to me :)

beikeland

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Re: UV silkscreen
« Reply #10 on: November 24, 2016, 11:42:33 PM »
The biggest problem is getting a thin, even coat of UV paint and accurate registration for the board when taking it in and out of the laser.

Can't really cut a pocket either as the machine doesn't run quite square yet. Sigh.

For uniform coating I'll be looking at using an old harddive to spin coat the boards; found some videos of guys having made vacuum chucks on old drives to coat various stuff. Unfortunately newer drives with fluid bearings won't allow the drive shaft to be drilled for a vacuum to pass. Might just try using an RC outrunner motor and replace the shaft with some hollow tubing and see if I can hold the boards and spin them up.

Either that or finding UV dry film in other colours, but wasn't easy in low volume.

Having tried a more powerfull laser now, running it at 3-5% really limits the effect the dynamic laser power feature can have on the exposure so its not as good as using a lower power diode. might look into setting up two drivers or something with a relay to swich between high and low power to keep some granularity in the power levels S0-S255.

Agastar

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Re: UV silkscreen
« Reply #11 on: December 01, 2016, 12:28:02 PM »
I have the makings of a spin coat machine (motor, and driver) but sadly that project has been put on the back burner. Unfortunately I could have used it this morning while messing around with my PCB etch resist paint formula. I do have another option though, a rubber ink roller used for applying fingerprinting ink :) https://www.amazon.com/Speedball-Deluxe-4-Inch-Rubber-Brayer/dp/B000BYVMFC/ref=sr_1_1?ie=UTF8&qid=1480623720&sr=8-1&keywords=ink+roller

If you can set the current limit on your driver, you could lower that and then you would still be able to use S255.

I did a test run the other night of my paint and I noticed it doing the same thing as the UV stuff in that it would melt the surrounding ink as well and the edges were not real crisp. I'll have to run it with lower power and/or faster or I will get the bleeding effect as well.

Thanks for posting your experiences, this is helping me out with my ink project as well so TYVM :)

Lob0426

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Re: UV silkscreen
« Reply #12 on: December 01, 2016, 01:20:46 PM »
Those rollers put down a pretty consistent layer of ink. You cannot really regulate the layer depth accept by varying the viscosity of the ink.

I have done a hundred or so finger prints in my time.
Richard
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Agastar

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Re: UV silkscreen
« Reply #13 on: December 01, 2016, 01:30:56 PM »
Isn't fingerprinting ink pretty thick too?

Another way to get a even coat is to put down two strips of tape, put the paint in between the two strips of tape and spread with a putty knife. The tape will keep the edge of the putty knife slightly above the surface and should give you an even coat.

Lob0426

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Re: UV silkscreen
« Reply #14 on: December 01, 2016, 01:44:30 PM »
It used to be real thick like printing press ink. The newer easy clean stuff is thinner. At the end I used some that was like wax. Most of it is moving to live scan now!
Richard
A5 2.5W w/homing switches on L7
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Experimenting with Mega2560 board upgrade