Laser Etched DIY Soldermask?

[TheAdmiralty]

Evening, everyone!   

Was wondering about something, and how you guys would recommend going about doing it.  I'll be churning out a few more PCBs using an LPKF Protomat C60 mill in the near future for a sponsored project, and was wondering about opinions on soldermask.  Little board mill works great for low-volume prototyping.

We'll be needing a handful of TSSOP packages and maybe a QFN if it absolutely can't be helped, and there are a few other places where a solder mask would be awfully helpful.  I've got a Universal Laser Systems desktop laser engraver on hand, and was thinking that it would work pretty well to just dip a board in some sort of solder resist and selective burn it off; laser's only 30W or so.  What's nice is that DipTrace (my preferred software by a long shot) will print any layer of the PCB straight to a printer, which is perfect since the VLS interfaces like a regular printer and so we'd just have to get the alignment perfect and let it fly.

Any recommendations for a good coating to try this out with that I can get in something less then a five gallon bucket?  Am interested to see how well this works out.

[sleemanj]

DIY soldermask is a real PITA, aside from actual soldermask ink/paint or dry film soldermask (as opposed to dry film resist), both of which you can buy on eBay etc, the best substance I'm aware of is Pebeo Vitrea 160 Glass Paint, specifically that brand other brands of glass paint I have tried didn't work.  It is readily available in artist supply stores in many colours.

It is typically applied over the top of a board with the pads masked by toner transfer, dried, baked, and then acetone to remove the toner.  But maybe you could burn it off with laser too.

As I say though, it's a total PITA to do any of the soldermask methods, except maybe dry film but that's more expensive and harder to get.  My opinion is if you need soldermask, you should get the boards manufactured.

https://www.eevblog.com/forum/beginners/diy-solder-mask/
https://www.eevblog.com/forum/eda/tool-for-gerber-to-homebrew-artwork-(toner-transfer-uv)/

[TheAdmiralty]

I'll see if any of the local craft stores have that specific paint and give it a try.  I'll probably have to try a few different things, as I can imagine a lot of these will end up just charring to the surface instead of cleanly vaporizing off.  I don't have access to any sort of UV curing lamp, which is going to be a pain in terms of finding a liquid mask on eBay for obvious reasons.

Some of these dry films sound promising; I've never had reason to investigate them before, but I'll probably order a small sheet here just to sample and see how it goes.  Shouldn't be hard to laminate at all.

[IconicPCB]

I do mechanically etched PCB prototypes.

I use a LPISM and epoxy inks to print the solder mask and component overlay.
Printing done with a UV laser.
Shown a finished prototype PCB with soldermask and overlay, copper silver plated.

[sleemanj]

Printing done with a UV laser.

Do you just raster-scan the laser across to image it?  What speed?  I'd kinda assumed that given the LPISM takes quite a bit of UV exposure to cure that laser scanning would take forever, I guess unless you have a really powerful laser.

[IconicPCB]

Scanning is time consuming.

Main issue is inertia and dynamics of the scanning mechanism not so much the laser energy.