Etching with Photoemulsion

JJGross said:

I've also found that you can do a clean (and very cheap) toner transfer using the backing paper from stickers. I used the backing sheets from CD labels since they're full letter sized and don't jam up my old HP laser printer I got @ Goodwill for $10.

I was using old band advertising slicks (8x10 glossy thin paper) and got really good results, but the slightly waxy but thick sticker backing is the schnitz.

Cheers!

Click to expand...

There are two things you need in a paper. It needs to hold the toner well enough to keep it from moving or falling off during the process. It also need to release the toner after fusing to the copper.

Cooking parchment and ALU foil do not hold the toner well enough.
The mailing label backing paper I tried was too loose but usable if one was careful.
Most other papers allow the toner to soak into the paper fibers. No problem holding the image but a bear to remove the paper.

The starch is a very good idea because it holds the toner well when dry and releases it 100% when wet.

I haven't tried it but I imagine that would could toner transfer the silk screen to the board using the usual process and protecting it with a conformal coating or even varnish.

You could probably also make a proper solder resist (not just the fake one you get with P&P) by painting the areas you wish to solder with grease and spraying over the top with a solder-proof conformal coating. In theory the coating won't stick to the grease so it can be easily picked off. Also it should make this easier if you use a thick grease like Vaseline or pump grease .

Toner PCB Process Notes

3v0 said:

The starch is a very good idea because it holds the toner well when dry and releases it 100% when wet.

Click to expand...

I think the big problem with trying to use starch is that it would have to go onto the paper wet and that creates wrinkling problems unless you pretty much have a way to calendar the paper to smooth it out.

I also tried gelatin with the same idea as the starch for release and, because it went on wet, did have the wrinkling problems.

Cooking parchment releases well but, the surface texture can be a problem.

I've had some success with vellum but, not great.

I've also tried the backing paper for adhesive stickers and also had problems with getting the toner to stick well enough to it. In fact, in one instance it ended up on my fusing rollers (fortunately, in a copier that was easier to access than a laser printer).

I've also had some success, with small boards, by just laying down a strip of 2" wide plastic packing tape on a sheet of bond paper and printing the pattern onto the tape (the cheap tape is better since it tends to be thinner than the name-brand tape). While it strips off clean, for the most part, it always seems to leave a few tiny bits on some edges. If anyone comes up with a good sequence for improving this method, please post it.

Connecting the Dots

Hero999 said:

You could probably also make a proper solder resist (not just the fake one you get with P&P) by painting the areas you wish to solder with grease and spraying over the top with a solder-proof conformal coating. In theory...

Click to expand...

In practice I think you'd find the grease everywhere but where you want it. Conformal coating tends to be pretty tough and could be difficult to cleanly separate away from just about any masking material under it.

If paint or varnish were used, maybe adhesive dots (you could tediously punch out of adhesive lables with a paper or leather punch). It would be a laborious process to stick down the dots but, for a one-of or small-lot boards, could be feasible.

On single sided boards I paint the top white with crylon fusion. I transfer a toner image of the silk screen artwork and coat it with conformal or other spray acrylic. Works great but many flux cleaners will mess it up.

For hand soldering I have not seen the need for solder masks.

The transfer paper from pulsar is thick and rigid. More like a thin smooth cardboard. I guess now we know why. I think the starch they use is the same as used to make tapioca pudding.

I would much rather give pulsar $15 a year for their paper then mess with anything else. If you live where you can not get their paper then that is another matter. It can be had in the US and Canada. Not sure where else.

EDIT:
The pulsar stuff works for more the PCBs. It can also produce some very nice decals and such to add a professional touch to your projects.

One thing I haven't seen mentioned that I think is extremely important regards the edge preparation of the circuit board blank. There can be NO "ridge" of copper (from the cutting or shearing). Even the slightest raised copper will prevent intimate contact when fusing the toner to the board and WILL result in an imperfect transfer.

I will usually lightly file the edges (in a downward direction only) with a file (usually a flat needle file) and then burnish down the edge of the copper, too.

Even so, I've noticed that (for reasons I can't really explain), most fusing problems tend to occur near the edges and especially near the corners of the boards (even though I pay special attention to those areas with my iron).