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I understand that the best way to make a PCB the photo-resist way is to print a super-dark mask on a transparency put it on a circuit board, expose it and develop. The problem is that is expensive and my printer doesn't print 100% dark.

I currently use vellum (translucent paper) as my paper for PCB masks and even then when I try to do the PCB, some tracks go missing after using the developer yet the rest of the circuit is well intact.

I was researching and noticed from https://smrsoftware.com/vellumtips.php that one could use a spray called "Krylon tm Artist's Matte finish spray #1311" to spray the artwork side of the paper to make the toner appear darker.

I'm wondering, is this a good idea, or are there chemicals in this particular spray that may negatively affect the PCB development process? And if I shouldn't use this spray, then what else can I do to darken the toner on the paper without trying to print on top of the artwork over and over again? Is there a better chemical out there? I'm looking for something that's for sale in canada. Maybe I need a chemical that has a certain ingredient? I don't know.

Please advise.

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    \$\begingroup\$ Have you tried printing on flimsy junkmail and transferring the toner directly to a board with a clothes iron? Takes some practice, folding over the edge of a carrier sheet to get it through the printer, etc, but you can skip right to the etching step. \$\endgroup\$ – Chris Stratton Aug 29 '16 at 6:01
  • \$\begingroup\$ "Toner transfer" is the method that @ChrisStratton is talking about. I have used it to make PCBs where the traces were around .25mm wide. It makes things much easier (also when using the conventional photo-resist method) to have large copper surfaces. Layout your board as usual, then make a large copper pour connected to ground. That leaves the traces "cut out" of the copper surface. The reason for doing this is that it takes a long time to etch large surfaces. The less material you have to remove, the less the chance that your traces will get eaten. \$\endgroup\$ – JRE Aug 29 '16 at 7:17
  • \$\begingroup\$ I use the advertisements from a particular German computer magazine to do toner transfer. They are printed on thick paper, but it has a very heavy coat of some stuff (kaolin?) that makes it easy to remove the paper from the board. \$\endgroup\$ – JRE Aug 29 '16 at 7:19
  • \$\begingroup\$ Use an ink jet printer. I've had excellent results printing onto Mega Electronics (UK) transparency material using a cheap HP printer. \$\endgroup\$ – Leon Heller Aug 29 '16 at 7:59
  • \$\begingroup\$ Not an answer to your question but if you manage to find an old 90s wax printer with flat bed/paper path, you can print right on top of your photoresist, expose and etch them. Can't find the link to where I saw it at the moment. \$\endgroup\$ – winny Sep 28 '16 at 9:33
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I'm not aware of your spray and how it works, but there are special toner density sprays, which you often get from shops selling everything for PCB etching. This sprays contain a solvent which dissolves the toner on the paper a just a little, so it fills the small gaps and pores of the paper. It evaporates completely, and there is no concern about any residues left on the paper. But I guess your spray is not that different.

I had a Brother HL2030 laser printer, and its printouts got really really dark with this spray. Unfortunately, the printer stopped working, and I have a Brother HL2340 now. And the spray has absolutely no effect on its printouts. The toner cartridge is almost empty, and I've already ordered a new, 3rd party one. Maybe, the spray will work with that.

So, if such a spray works depends on the type of toner, too!

To my experience, the darkness of the toner heavily depends on the paper. On transparencies, it's far from being really dark, and even on translucent paper, the result is not so good.
In contrast, the printout is really dark on normal paper, and to my experience, the density spray has the best effect on this paper, too.

Now, there is a second kind of spray, which makes normal paper translucent, as oil does. I only know Transparent 21 from Kontakt Chemie, a german company specialized on sprays for electronics. They sell at least europe wide, not sure if also world wide.

I didn't try, but a few drops of oil should do the job, too. Just clean the PCB thoroughly but gently with some dish liquid or so. But oil could also dissolve the toner. Glycerine should not, and it's easy to rinse it off the PCB, but it might swell the paper. Just try out.

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