Visible-light curing resin or photoresist - Page 1
Forum section: electronics / projects

author: Whales
author_rank: Super Contributor
timestamp: March 01, 2025, 10:55:10 am
content: I want to cure thin layers of something (anything) using an ordinary computer projector. Overall goals is to use it as an etch resist or mix conductive materials into the resin for fun.EDIT: I specifically want to avoid using UV so that I can stick to cheap, off-the-shelf video projectors as my light source. They have very small image source planes, so they are potentially easier to add external optics onto to miniaturise the image down to tiny sizes, which is a future potential goal. A resin printer's bed is not a small image source.Where can I get visible-light (blue?) curing UV resins or photoresist?Is there an industry term? Can I buy the activator ingredient and mix it in myself? Maybe the resin 3d printing market already has something like this?At the moment I'm trying dry-film resist (commonly used to etch PCBs) and some UV soldermask (spread very thin). Both of these assume you are using a UV light source to cure them, so I'm struggling to get them to do much.Dry film: I can just barely get a little bit of crosslinking (darkening) to occur with anything from 20minutes to 90minutes of exposure in front of my existing projector (arc lamp + LCD + trichroic cube); but it's not enough for it to survive developing in sodium carbonate. My film is good, a few seconds of UV torch exposure cures it extremely well.I am working on modifying my projector to hopefully get some more UV out of it, but I suspect every layer of glass and maybe even the LCDs or their polarisers are blocking it. Also projectors are expensiveso I don't want to accidentally trash it.

author: Whales
author_rank: Super Contributor
timestamp: March 01, 2025, 11:12:33 am
content: Some pictures in case anyone finds this fun or interesting.Overall setup:Example image that I'm projecting. The board (black and white) is much smaller than the projected image (red) because I can't get the projector to focus at a smaller size. Good enough for now (TM)After about 100 minutes of exposure I can get faint bits of the dry resist to develop and stay, but they're so weak even a drop of water lifts them:

author: jpanhalt
author_rank: Super Contributor
timestamp: March 01, 2025, 11:19:49 am
content: Dental resins are said to cure at 450 nm (e.g.,https://scheu-dental.com/en/scheu-dental/products/pressure-moulding-technique/light-curing-resin/durasplintr-lc/3261). I suspect those are quite expensive. Maybe MSLA resins will work?

author: reodor
author_rank: Contributor
timestamp: March 01, 2025, 11:35:39 am
content: It's an interesting idea. If you were able to find a cheap projector where the light bulb has burned out, you could try to replace the old light bulb with your UV torch? You'd probably still see some attenuation due to the glass lenses and LCD, but maybe, with enough time, you could get some results?For me, this technique falls between two chairs, though. If I don't have time to wait for professional manufacturing, I'll use the toner transfer method. This is where laser toner is ironed directly onto the copper, so that the laser toner itself becomes the etch mask. No chemicals involved at all (except the etchant), and fast.

author: Whales
author_rank: Super Contributor
timestamp: March 01, 2025, 11:48:30 am
content: @JpanHalt:Interesting. I will have to dig for a supplier, but I suspect they won't even let me see the price without an account. Time to learn how to pretend to be a dental practice@reodor:The lamp in my existing projector should already be a big UV emitter. I plan to open up its optics again and slot my UV torch in, then see where along the light path the most attenuation is occurring by using a fluorescing target (ordinary white office paper seems to do the trick).It's not all about PCBs, it's just easier place to start because it's macro scale (requires no further optics). I really want to try micrometer resolution exposures on small targets, but I am taking it in babysteps.

author: Whales
author_rank: Super Contributor
timestamp: March 01, 2025, 12:07:52 pm
content: Potential lead: "daylight resin" for SLA printers. Sadly very rare, Photocentric makes the stuff but it looks like my minimum order is most of $1000 (eg reseller Bilby3d)

author: Someone
author_rank: Super Contributor
timestamp: March 01, 2025, 12:20:06 pm
content: Quote from: Whales on March 01, 2025, 11:48:30 amThen all the optics will be changing anyway! DLP + microscope objective will do micron scale structured light down into UV and you can swap out different magnifications relatively easily.

author: jpanhalt
author_rank: Super Contributor
timestamp: March 01, 2025, 12:28:54 pm
content: It's probably not so much the source; it's the optics. Some may actually be coated to block near UV.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: March 01, 2025, 07:48:07 pm
content: This seems like the hard way around. It might be better to create a digital negative and expose the board with UV photoresist in a UV frame. Visible light cure resin sounds like a troublesome substance!

author: wraper
author_rank: Unknown
timestamp: March 01, 2025, 07:52:13 pm
content: Isn't it easier to just get SLA 3D printer or just a display part for it, and use it for exposing normal photoresist?

author: Whales
author_rank: Super Contributor
timestamp: March 01, 2025, 10:19:03 pm
content: Quote from: Someone on March 01, 2025, 12:20:06 pmI hope to keep the projector optics as-is and add optics externally, so that the projector can be swapped out if need be with a minimum of fuss and cost. I expect this will sacrifice resolution, but I'm not doing this for work, I'm doing it for fun.A visible-light curing resin would make this magnitudes easier.Quote from: jpanhalt on March 01, 2025, 12:28:54 pmYes. I'm going to fish through the optics in my projector today and see if it's any one particular optic that's blocking UV (coatings) or several of them (lens bodies).Quote from: Conrad Hoffman on March 01, 2025, 07:48:07 pmHow would exposing a negative be harder or easier than exposing a positive? Either way I need UV.Or are you thinking printed masks? I am hoping to skip the printed masks, I always have troubles with them due to poor toner density and they give me no pathway to miniaturisation.Quote from: wraper on March 01, 2025, 07:52:13 pmBed LCD SLA printerswork for dry film exposuresand I think even for direct resin-mask printing. Pros and cons versus using a projector:+ Someone has done it before so you know it works+ Uses off-the-shelf resin- Require slicing software & making 3d models of your parts (or other workarounds). Versus just displaying a picture on a monitor.- I don't own one, but I do have a projector I found on the side of the street for free + a $50 replacement discharge lamp that revived it.- "Image" is very big (compared to the ~1inch LCD inside a projector), necessitating harder optics if you want to shrink it to eg 1x1cm.There are also videos of usinggorgeous fibre-laser galvo machines to ablate masks and even the copper itself directly. If you are willing to donate me one then I will accept all discussion of this method

author: wraper
author_rank: Unknown
timestamp: March 01, 2025, 10:24:21 pm
content: Quote from: Whales on March 01, 2025, 10:19:03 pmShrink it for what? You can get 9K resolution for like $200, even cheaper for 4k. Also don't forget about dimensional distortion you'll likely get with projector.Quotevs trying to get the dimensions right. I'd rather get proper dimensions right away rather than fiddle with it all the time.

author: Whales
author_rank: Super Contributor
timestamp: March 01, 2025, 10:28:27 pm
content: To do a less hardcore version of maskless photolithography, at perhaps a factor of 10 worse resolution (10~50um if I'm lucky?) with an ordinary 1080p resolution projector:https://youtu.be/watch?v=_w0Z2Y5vaAQhttps://youtu.be/watch?v=XVoldtNpIzIIn particular I'm curious if it's possible to make something interesting with positive exposures only. Ie spincoat on layers of resin mixed with very finely powdered metals and metal oxides, then expose regions you want to keep and wash the rest away. I suspect I will never get something that works, but it will be fun trying, plus I'd get lots of tiny pictures I can force on people as unwanted gifts.

author: Whales
author_rank: Super Contributor
timestamp: March 01, 2025, 10:33:38 pm
content: I will have to dig into the chemistry a bit further, but it looks like I might be able to useruthenium as a photoinitiatorto get resins to set under visible light (edit: possibly not, I think ruthenium might not be compatible with common resin monomers). Specifically 400-450nm blue light, which would let me use red lighting as safe lighting just like in old black and white photo development labs.This red insensitivity might also mean I can set the projected image to red whilst aligning, possibly just with a xgamma/brightness tables script set on a timer, which would make the image editing & exposure workflow super easy.Ruthenium is rather toxic. I might be able to get it aqueous in a dropper bottle (rather than as a powder), which could make handling significantly simpler. I would then in theory just need to mix it into existing resin products (perhaps even UV curing resins, I assume having multiple initiators is not a problem).

author: jpanhalt
author_rank: Super Contributor
timestamp: March 01, 2025, 11:07:44 pm
content: It may be hard to identify which lenses are coated without a spectrophotometer.Google AIQuoteDiamond Coatings:https://diamondcoatings.com/anti-reflective-glass-for-projectors/

author: Simmed
author_rank: Frequent Contributor
timestamp: March 02, 2025, 12:39:22 am
content: found this by chance on YTit appears to be normal 3DP resin applied on bare PCByou could see the bowing of the corners (pic 0001) on some kind of retainer screenmanual hand alignment of the edges to the LCDvery quick exposure like secondslooks like a winner

author: moffy
author_rank: Super Contributor
timestamp: March 02, 2025, 02:18:04 am
content: Quote from: Simmed on March 02, 2025, 12:39:22 amI have seen a similar video where presensitized PCB was used, no need for resin.

author: Whales
author_rank: Super Contributor
timestamp: March 02, 2025, 02:21:00 am
content: I've linked to such a video above. All of these videos are of UV processes, which are not what I want.I am after a visible-light curing resin or photoresist because it makes several other things easier (see my posts above: can use a normal video projector which in turn gives potentially easier and cheaper pathways to miniaturising the projection later on). EDIT: Edited the original post to match, I'm probably a bit scatterbrained with my info in this topic, sorry.

author: Whales
author_rank: Super Contributor
timestamp: March 02, 2025, 02:45:11 am
content: @jpanhaltyour suggestion of dental resins is paying off, I'm finding some interesting things. It looks like a lot of the dental industry has traditionally used visible-light curing products.Paper: The Photoinitaitors Used in Resin Based Dental Composite - A Review and Future perspectives- I probably want a "type 2" photoactivator, as these tend to be sensitive to visible blue light.- "Camphorquinone" and "Dibenzoyl germanium (Ivocerin)" seem to be good leads, but I will need to see if they are compatible with monomers I can easily get.Also it looks like I can get small syringes of potentially visible-light-curing resins in the form of unbranded dental productshttps://www.aliexpress.com/item/1005007456421873.html

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: March 02, 2025, 03:24:42 pm
content: I'm always amazed at modern dental products. They seem to be miles ahead of the industrial stuff.

author: jpanhalt
author_rank: Super Contributor
timestamp: March 02, 2025, 04:55:33 pm
content: They also have to be relatively non-toxic, which may present a challenge for visible light photosentizers/photoinitiators.

author: Zero999
author_rank: Super Contributor
timestamp: March 04, 2025, 11:48:38 am
content: Why complicate things?Print the artwork on to old projector film and use a UV light box.

author: Whales
author_rank: Super Contributor
timestamp: March 07, 2025, 06:04:31 am
content: Quote from: jpanhalt on March 01, 2025, 11:07:44 pmNot an issue at allYou're imagining me using a broad spectrum light source and a spectrometer. Instead I used a narrow-spectrum light source (cheap UV torch) and something that fluoresces as a sensor (ordinary white printer paper).I was very quickly able to find and remove the UV blocking lenses. Verifying one afterwards with a UV torch and a sheet of white paper:The evenness of the projector output looks like it may have suffered, but nothing severe.Dry film with modified projectorWith this modification I can now expose dry film in around 20 minutes (numbers at top are exposure time):The grid goes down to 1 pixel (~= 0.1mm in this particular setup) and doubles for each size, so this sample only gets to about 0.4mm resolution. Take this with a grain of salt, my temporary projection setup is not stable and jiggles around I as I walk around, so I am surprised I got even this good. I will worry about a sturdy mount and finer detail laterThe 20 minutes exposure is better than my previous attempt, but still not as impressive as I expected. This same dry film cures strongly within seconds of exposure to my UV torch. Some further testing of the optics pathway reveals that the LCDs in the projector (or something near them like the polariser film) is eating most of the UV. 20 minutes is inconvenient compared to a few seconds, so I'm still eager to test out visible-light curing resins.SLA printer resin with modified projectorElegoo standard resin "405nm" did not react at all, it completely washed away. Also it was too thin and runny (low viscosity) so it dripped and left very little on the plate.I suspect that the resin may be suffering "oxygen inhibition", where the air-exposed surface refuses to cure. Covering it in a layer of plastic might help (the dry film does this), otherwise changing to different monomers also helps (UV soldermask paste does not suffer this issue so I will try it next).

author: Whales
author_rank: Super Contributor
timestamp: March 07, 2025, 06:10:16 am
content: Quote from: Zero999 on March 04, 2025, 11:48:38 amI added extra context to my OP:QuoteYour suggestion is good for making thing at the scale I currently am, but that's not my goal. I already make PCBs at home through other techniques.

author: Whales
author_rank: Super Contributor
timestamp: March 07, 2025, 06:24:00 am
content: Quote from: jpanhalt on March 02, 2025, 04:55:33 pmMy current wishlist of photoinitiators to test:- Ivocerin (and other germanium-based photoinitiators), supposed to be relatively non-toxic but very difficult to get.-HuNu series, nontoxic but looks single source and probably expensive.- Camphorquinone, somewhat toxic but I believe safe once cured (used in dental products)- Riboflavin (+triethanolamine as a co-initator?). Might just try mixing some into commercial SLA resins and see if their other coinitators are compatible or not, cheap and got nothing to lose by trying.Also some off the shelf resins I am contemplating buying and testing:https://acrylictech.com.au/product/acri-bond-uv1035/"should fast cure under the visible light" but I want to confirm with them before buying. Seems to be a mixture of polyurethanes, acrylate and vinyl (so maybe it won't suffer oxygen inhibition? Not sure).https://www.himgsurfacerepair.com/products/lca-clearLiterally looks like a dental syringe. Probably a version with no filler and a big markupVarious dental resins that are transparent so they perhaps might not contain solid filler particles:https://shop.dentaurum.com.au/product/92358-orthocryl-lc-clear?categoryId=3224https://www.adamdental.com.au/crown-and-bridge/pattern-resin/tdv-resinlay-pattern-gel-3g-light-curehttps://www.sterngold.com/dental-varnish-lc-5-ml-light-curedApparently some book "overcoating" varnishes light-cure, but it looks like something you would need to custom order. I think this might be the stuff they use as a selective shiny print layer on the covers of some books.Some evidence exists that these companies may be able to make-to-order with visible light initators and custom viscosity. I will have to email them but I am expecting they will want $1000 minimum for their efforts (outside my budget for this hobby project), not sure yet.https://spotamaterials.com/wp/product-category/standard/https://www.sglinc.com/https://bucktownpolymers.com/products00.htmlMore unobtainium products: Loctite 4305, Threebond TB3177, TB3170B, TB3170F, TB1770