UV blockng transparent LCD

[antenna]

I want a transparent LCD that is capable of selectively blocking UV light for the purpose of making a device that allows me to upload a circuit trace and directly expose the photoresist-coated board without having to print on acetate and stack layers.  It doesn't have to be too big, 150mm x 100mm maybe.  I'd like to use an arduino or similar to upload to the LCD via SPI using an SD card or similar for storage.

[inse]

I can hardly imagine the contrast ratio of a LCD is suitable for exposing photoresist.
LCDs with backlight are transparent by definition, you would just have to swap the light source.
It’s questionable whether the are any with specified  UV behaviour.
Nice idea but not realistic in my opinion.
P.S. transparent LCDs to be placed on an overhead projector had been a thing like 20y ago…

[antenna]

I got the idea from UV resin printers (well, a video of one guy using his for PCB exposure).  I cannot remember what it was called.  I figured these screens would be available since they are used in resin printers.

[antenna]

this video

[coppercone2]

I wanted to do that but I got mad at the software and also I never figured out a good way how to make indexing pins to do a double layer board

the best one I had was to make a thing you attach to the 3d printer top bed, with pins, so then you lower it until the PCB fits on it, and when you flip the PCB its aligned. Perhaps very shallow cones on the pcb. Its annoying if you have to cut it super square, and its a problem for irregular shaped boards, unless you can align it some how

[inse]

Cool stuff, didn’t expect this to work.
Now you need to find a SLA printer to salvage 😉

[rteodor]

I want a transparent LCD that is capable of selectively blocking UV light for the purpose of making a device that allows me to upload a circuit trace and directly expose the photoresist-coated board without having to print on acetate and stack layers.  It doesn't have to be too big, 150mm x 100mm maybe.  I'd like to use an arduino or similar to upload to the LCD via SPI using an SD card or similar for storage.

SPI ? That would be nice to have but from what I saw displays for SLA printers tend to have MIPI or other large bandwidth interface. Maybe with some kind of adapter or maybe drive them from a Raspberry Pi via a HDMI to MIPI interface adapter.
Like the exposure table in this project (that was discussed on this forum somewhere sometime ago).

[cunningfellow]

without having to print on acetate and stack layers.

You are using the wrong printer/media for your photo-tool if you need to stack them.  A laser printer on clear film just does not have the contrast.

Good - Laser printer on poly "vellum"
Better - COLOUR laser printer on poly vellum
Best - inkjet printer on multi-layer transparency film

Black and white laser on poly vellum can be improved with [toner density spray] which is mostly acetone mixed with isoprpyl

[jpanhalt]

If speed is not a problem, and that appears to be the case, there are numerous 4-bit and 8-bit parallel interface backpacks to I2C and  SPI available.

[ftg]

If HDMI from some computer instead of arduino is acceptable, these LCD's are meant for exposing 3d printer resin to UV and should also work for PCB.
https://www.aliexpress.com/item/1005003489538804.html
If you shop around, buy the HDMI-MIPI-DSI driver and screen at the same time, do not buy them separately.
The HDMI-MIPI boards are not generic and need to be programmed per LCD.
And make sure you get an LCD without backlight, so that you can shine the UV through it.

[stj]

wont the UV slowly destroy the polarising film on the display?

i wonder if rasterizing a uv laser and drawing directly to the pcb would be better?
maybe use the raster mechanism from a laser printer and a moving bed with geared down steppers driving it.

[antenna]

I don't make too many PCB's so if it gets destroyed after 500 uses, it will have probably served its purpose.  Im just a small time hobbyist.

[jpanhalt]

Also read the datasheet for your photoresist.  Most work well with 395 to 405 nm UV.  Some ordinary fluorescent bulbs provide that.  Germicidal lamps (254 nm) are not only unnecessary but are less effective and can cause unwanted reactions in the resist..

[antenna]

Also read the datasheet for your photoresist.  Most work well with 395 to 405 nm UV.  Some ordinary fluorescent bulbs provide that.  Germicidal lamps (254 nm) are not only unnecessary but are less effective and can cause unwanted reactions in the resist..

Datasheet would be hard to find.  I bought my photoresist on amazon about 4 or 5 years ago. I doubt I could even find the original ad.

It works quite well with the UV from a fingernail curing station.  I was thinking about repurposing those LEDs.  I will try the fluorescent bulb before I tear that apart though.  I didn't know that was possible, figured I'd need to order a special bulb.  Thanks!

[jpanhalt]

Are you holding the transparency in place with single-pane window glass?

[antenna]

Yes, I do use a sheet of glass.  I have no problems getting good detail, its just the hassle of printing, layering and aligning the prints that I want to eliminate.  For most prototyping, I usually end up drawing it by hand with acrylic nail paint simply because its faster.

I wanted to try the pantograph and etch pen method, but the etch pens I have do not hold up to the warm copper chloride etchant I use.  it starts to eat through near the end of the etch.

[jpanhalt]

Soda lime glass(like window glass) blocks 254 nm UV light.

Source: Research Gate via Google

[antenna]

I think my UV light is 365nm.  It works good through the glass that I have.

[jpanhalt]

365 nm is not a problem and works, but if you are worried about your LCD stability, shifting to 395-405nm should help .  Every positive resist I have seen should still be OK.  The active component for UV absorption is not the resin per se, but what's called a photosensitizer that absorbs at a longer wavelength than the resin.  You may need to lengthen your exposure time a bit.

[fchk]

I want a transparent LCD that is capable of selectively blocking UV light for the purpose of making a device that allows me to upload a circuit trace and directly expose the photoresist-coated board without having to print on acetate and stack layers.  It doesn't have to be too big, 150mm x 100mm maybe.  I'd like to use an arduino or similar to upload to the LCD via SPI using an SD card or similar for storage.

I've seen people using DLP devices for this in commercial projects. The micromirror array reflects any wavelength from IR to UV with no problem. They used HDMI/DVI to output the image to the DLP module.

https://www.ti.com/product-category/dlp-products/overview.html

[ebastler]

In my understanding, cheap SLA printers use LCDs as a mask, and they do damage them over time. Better SLA printers use DMDs. But as mentioned earlier in the thread, the limited lifetime of an LCD is probably not an issue with sporadic use in making PCBs. And the optics are much simpler with an LCD of course, which you can just use as a 1:1 mask sitting directly on the PCB.

To be honest, I struggle with the whole project a bit. It seems to aim at improving the one step in home-making PCBs which I think is in least need of improvement. What's wrong with laser-printing layouts on a transparent film? On the other hand, what about the messy etching, drilling/milling, aligning layers on double-sided boards, and obtaining some kind of connection between them?

For my projects, I don't consider home-making PCBs at all. I'd rather adjust to a one-week wait and get PCBs with much higher trace density, multiple layers, vias, silkscreen, soldermask... It would take major improvements in all steps of the home-made PCB process to get anywhere near the capabilities of the professional PCB houses, which I don't think will realistically happen.

[Haenk]

I've seen people using DLP devices for this in commercial projects. The micromirror array reflects any wavelength from IR to UV with no problem. They used HDMI/DVI to output the image to the DLP module.

https://www.ti.com/product-category/dlp-products/overview.html

Shouldn't a cheap used DLP projector be good enough for some initial testing? Replace the light source by a UV diode. Those used ones should be available for less than 100 bucks. Since performance is not a issue for PCB creation, even more-or-less UV blocking glass lenses should be good enough for some longer exposition timing.

[lgbeno]

If you pay the shipping, I have an Anycubic Photon printer that I would send you.

[abeyer]

You can also just buy the LCDs for SLA printers as they do have a limited lifetime and are (at least somewhat) replaceable... pricing varies but even moderately high dpi monochrome ones (which seems to be the preferred option for printing, at least) can be had in the neighborhood of $30-$40. Salvaging from old printers seems like it might end up costing more in shipping. I've had one sitting in my amazon wishlist for a while, waiting to have time to start a new project, as I am interested to try out that approach.

[antenna]

After thinking about this for a while, I think I will just get a printer and have a dual purpose device.  By the time I get a screen and mess around putting it together, I may as well have spent the $300 on a printer.