Hi Martin Turns out that 400nm is still within the tolerance range of the DMD display, and is a wave length short enough for commonly used resists to react with. I guess I'll use a 400 nm UV LED (visible part of UV).
Cheers -lev
On Thursday, April 8, 2021 2:08:35 PM WEST Martin Geisse wrote:
Hi David,
I have to admit that using visible light was probably a stupid idea. There seem to be some more photoresists that are somewhat sensitive to visible blue/violet [1], but they seem hard to get.
So back to the idea of using a chip socket so the DMD can be replaced when UV breaks it: This will allow to learn not only about how well the DMD takes UV, but also about the failure modes. For example, blurring the image a bit is probably not as bad, and even faulty pixels are covered by typical design rules (taking MOSIS SCMOS as an example). OTOH if the electronics of the DMD get faulty, it's probably game over. Those are things the datasheet probably won't tell you, so trying it the only way to find out.
Another idea would be test patterns using visible light. If the DMD degrades gradually, a test pattern would allow to find out if it is still usable or not. By that, a degraded DMD is no longer a catastrophic event, but rather is part of the expected lifetime of the DIY kit and allows to factor the price of the DMD into the price of the service, mapped over the number of dies produced with it. For example, if the DMD can shoot 100 images before it breaks, and costs 50€, it's 0,50€ per image or 2€ per die if you need 4 photolitho'd layers.
(BTW, the datasheet only says that bright UV and simultaneous temperatures
70°C are harmful, so that might mean that nothing bad will happen if you
just don't stress the DMD too much)
[1] https://www.lithoprotect.com/en/worth-knowing/
Greetings, Martin
On Thu, Apr 8, 2021 at 2:04 PM David Lanzendörfer <
leviathan@libresilicon.com> wrote:
Hi Martin There's a patent for a very easy to use resist which can be used with visible light, but I've got to do some digging on what suppliers produce it: https://patents.google.com/patent/US7354692B2/en Visible light resist would clearly be preferable, because then the DMD would need to be operated outside of the intended specs.
Cheers -lev
On Thursday, April 8, 2021 12:58:08 PM WEST Martin Geisse wrote:
Hi David,
is there a need to use UV light, e.g. does the photoresist need UV to react? Blue or white light would not only be more friendly to the DMD
chip
but also require less precautions, be directly visible with a microscope for alignment and checking (or at 50u, maybe even a good magnifying
glass),
etc.
At least at 50u the wavelength will be much smaller so sharpness or diffraction isn't a concern.
If you really need UV, I'd suggest using a socket so you can at least replace the DMD chip when it breaks. 30-50€ is okay-ish to try if it survives "long enough" on average.
Greetings, Martin
On Thu, Apr 8, 2021 at 1:32 PM David Lanzendörfer <
leviathan@libresilicon.com> wrote:
Hi So in the data sheet of the DLP2000 they say that UV light will reduce
the
life span of the DMD chip. However. Sam Zeloof is using a DMD display from an overhead projector and it seems to be working ok. Should I take the chance and take this 30 Euro chips from Mouser,
although
the data sheet says, UV wouldn't be advised? I mean, I still can replace the chip afterwards through a more
expensive
UV chip, when the rest of the machine works...
Cheers -lev
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