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Not sure if this is the right stack to ask this question on, but it relates to an engineering project that I and a student electrical engineer are starting.

Can an LCD screen be used as a masking layer between a UV light and a photosensitive material?

I have looked at a lot of other options and this seems the simplest and cheapest. Because LCD screens are inexpensive, have a high resolution, and are easy to control (no spinning mirrors or mechanical parts). This only works if the LCD screen is capable of controlling where the UV back light is admitted on its surface.

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    \$\begingroup\$ I don't think this will work. However DLP projection techniques can be used to project UV light, for example for stereolithography. DLP uses electronically controlled micromirrors. \$\endgroup\$ – Spehro Pefhany Sep 12 '18 at 23:08
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    \$\begingroup\$ It would depend on wavelength, among other things. UV-A, perhaps. UV-B or C, doubtful. @SpehroPefhany has a good suggestion, since mirrors are broad-band and don't absorb as much light as polarizers in LCD screens do. \$\endgroup\$ – DrMoishe Pippik Sep 12 '18 at 23:15
  • \$\begingroup\$ You could also try a video projector, possibly with an extra lens placed above the PCB to produce a very small, comparably high-res image. Exposure times will be longer than with 'pure' UV light though. \$\endgroup\$ – JimmyB Sep 13 '18 at 12:38
  • \$\begingroup\$ This has been done. Here's a YouTube video of one in operation. Most YouTubers aren't very secretive about the design of that sort of thing. I haven't found a place where his build info is posted but searching for his name yielded a forum that discusses how to build what you want \$\endgroup\$ – K H Sep 15 '18 at 4:33
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I have thought about this, there are problems. The resolution will go way down because the light will difract around the pixels (I think)

The main problem is the transmission and adsorption of the LCD material itself, which starts to fall off after ~300nm, which may or may not work for your source. This is also dependent on the display and type of glass and LCD chemical, however it is most likely that displays are designed with a UV cutoff because UV is harmful to the eye and not desirable in a screen.

enter image description here
Source: Cholesteric Liquid Crystal Display With Flexible Glass Substrates

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Source: https://pubs.rsc.org/en/content/articlelanding/2012/jm/c2jm14918d/unauth#pnlRelatedContent

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Assuming that the aim is to make PCBs, the major issue with making PCBs is to achieve high contrast in the photomask which in turn makes the boards less sensitive to overexposure.

This is a problem with using laser printers etc to create artwork - the toner is so thin that some light will get through.

I developed a prototype process for PCBs that was reliable every time, and capable of fine pitch work. The key is good contrast (timed exposure), a controlled etching bath - I used pump to flow FeCl over the board.

Sounds like what you are proposing would be possible, but some things I'd advise:

  • Get high quality material precoated with etch resist. I used these
  • Use a darkroom
  • Don't underestimate the brightness of UV light you'll need - UV leds could work but would need to be high power varieties
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