Author Topic: UV silkscreen  (Read 1163 times)

Agastar

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Re: UV silkscreen
« Reply #30 on: December 06, 2016, 01:48:11 PM »
Yeah all the paint I'm making is cured with heat. So, if I go with the laser for curing the solder mask paint then the laser would need to basically pass over the entire board. Spraying the board with a can of enamel spray paint would just need the laser to pass over the pads to burn off the paint. I guess a test would help here lol.

I wanted to go with the laser curing the paint because when the paint dries it will stick to the board but not set until you hit it with the laser. This makes the cleanup easily done with water. The process using a can of spray paint requires you to use acetone after you laser it because the laser doesn't completely remove all of the chemicals from the spray paint. So I guess it's a trade off between easy cleanup and time.

I did look into UV cure resin as an option for my binder in my paints but I'd like to see if I can get this heat cured paint recipe to work first.

If I can get it to work I'll start a post in the projects section with some pics. :)

beikeland

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Re: UV silkscreen
« Reply #31 on: December 07, 2016, 09:50:55 AM »
Received the last jar of paint, the mysterious "blue ink", it does smell a little different - but it doesn't appear to behave any different with respect to using the thinner or the laser curing.

Water soluble would be pretty cool, looking forward to see how you progress. For now I've got 3x100g of this UV paint in green, white and blue so it'll probably take me a while to literally burn through it, and if I'm quick about it its possible to just rub the excess uncrured paint of with a dry paper towel, so its not too bad.

Stuggling to get an thicker and even layer of paint for the slik screen; the super thin layer for etching and solder mask is okay, but silk screen seems to need a thicker layer to become readable. But the laser seems to be on the fritz so gonna have to take a break while waiting for new stepper drivers. The drv8825 drivers I had lying seems to be way too jerky compared to the regular a4988

PD0RUZ

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Re: UV silkscreen
« Reply #32 on: December 07, 2016, 10:02:13 AM »
@ Beikeland,
Looked at you spinner. I worked at philips here in holland, Semiconductor industry.
Repared lots of coaters. The way to get a homogenic layer, is to let it turn like 200rpm, dispense with a 3mm nozzle the coating 2mm from the center, till you dispense about 1.5ml
and ramp your speed too 3000 rpm.
And let it spin till the color on you object doesn't change anymore.
This gives you a very nice topcoat.
Try it. learned a lot from our process engineer overthere.
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Agastar

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Re: UV silkscreen
« Reply #33 on: December 07, 2016, 10:44:31 AM »
@NicoNijenhof, nice tip!

@Beikeland, yeah you definitely have enough paint to last you for a while :)

One idea I had that might help you out is to use a piece of transparency film with thick paint and some rollers. It would probably leave a glossy finish but it might work nice.

So the steps would be...

1. Apply thick paint to PCB.
2. place a piece of clear transparency film over the pcb and smooth out the paint.
3. place some spacers along side the board for the rubber roller to ride on. use some shims to adjust the height and then run the roller back and fourth.
4. With the transparency film left on, run the board through the laser to cure.
5. Once cured, peel the film off of the PCB and clean up the un-cured areas of the board.

If you need it thicker, just add more shims.

beikeland

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Re: UV silkscreen
« Reply #34 on: December 08, 2016, 12:25:50 AM »
@ Beikeland,
Looked at you spinner. I worked at philips here in holland, Semiconductor industry.
Repared lots of coaters. The way to get a homogenic layer, is to let it turn like 200rpm, dispense with a 3mm nozzle the coating 2mm from the center, till you dispense about 1.5ml
and ramp your speed too 3000 rpm.
And let it spin till the color on you object doesn't change anymore.
This gives you a very nice topcoat.
Try it. learned a lot from our process engineer overthere.
Is the 2mm off center meant to be the center? As in leave 0.5mm distance from the outer diameter of the nozzle? I've come to the conclusion that different speeds is the way to go indeed. And that the streaks I've been seeing are actually "chunks" or debris in the paint; have ordered some filters and will see if filtering the paint will help with uniformity.

Although for etching and solder mask, the results are already quite acceptable, apart from one sample i stirred with something that left debris in the paint and the streaks were much worse.

The challenge will be in getting viscosity right for a somewhat thicker layer.

1. Apply thick paint to PCB.
2. place a piece of clear transparency film over the pcb and smooth out the paint.
3. place some spacers along side the board for the rubber roller to ride on. use some shims to adjust the height and then run the roller back and fourth.
I've tried something to this effect, but was not quite pleased with the results, used a steel roller and tape for shims and some of the thin plastic films removed form the dry film I've used earlier. Buying thicker plastic films would be more expensive than buying the dry film so thats not happening. And the blue dry film on white solder mask gives pretty good contrast if that is what it comes down to.

beikeland

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Re: UV silkscreen
« Reply #35 on: December 08, 2016, 07:28:05 AM »
The following is just randomness, but shows acceptable results. The white traces that pretend to be silkscreen are about 0.4mm, Still UV paint that is spin coated, but slightly thicker, and less RPMs and shorter spin cycle. Think I've got this sorted now. The issue becomes repeatability now..

Agastar

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Re: UV silkscreen
« Reply #36 on: December 08, 2016, 09:49:41 AM »
That looks pretty good to me

PD0RUZ

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Re: UV silkscreen
« Reply #37 on: December 08, 2016, 10:28:29 AM »
yes indeed, looks really nice allready!!
The 2mm meassured from center spinner to center nozzle.
Whe used spinner aggitation too. They let it spind at 300 rpm, dispense and the resolvermotor is shaking a little for a few seconds, then  ramps up the speed to 3000rpm.
Spinspeed is rule of resist thickness. So higher spinspeeds result in lower thickness of resist. Cause it all spins off.
Whe used 1210nm thicknes. But thats on silicon wafers, not on copper.
So try to ramp up to 3000rpm en let it spin at this speed till color does not fade anymore.

For resist whe used 0.1 micron filtering and dispencing was done with a milipore pump, but you can also use a syringe to dose the amount of resist.
*A3 Laser 2500mW
*T2Laser Licensed software*
*Modified 2.5Watt laser module*
*Running Agastar Linear Pwm laser board*
*Co2 Laser 40W*