Electronics > Projects, Designs, and Technical Stuff
Toner Transfer
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xavier60:
I have just successfully etched my first board using toner transfer after some experimenting.
I used Celcast Premium Coated Color Inkjet Paper IJ84 94GSM, for the transfer medium.
I used an iron to fuse it to the pre-etched board.
It mostly peeled of with little resistance after wetting. fibers did stick to the toner in some areas.
There is a problem that I have when I use the laser printout directly as a transparency for photo etching.
With my HP6L printer, the toner deposition decreases within larger areas of black causing porosity.
Heating the printout with a hot air gun set to 250°C greatly reduces the porosity.
I didn't expect this step to be necessary for the toner transfer method, but it seemed to contribute to the good result.
Also with my printer, heating the blank paper just before printing to it  increases toner deposition.
Domagoj T:
KL27x, I believe I stumble upon one of your posts about a year or two ago, also home etching thread and you were advocating pre-etching. Your enthusiasm for the method convinced me to try it. Well, I apparently did something wrong because the result was just horrible. Not even close to what my normal procedure is capable of. You mention that HCl + peroxide (which I use, and used in that situation) is a hack etchant, what do you use and recomend instead?

Anyway, I'm getting consistent and good results (6 mil / 0,15 mm with care) with my method. In a test to see what I can get, I managed to route two traces under a 1206 LED. I usually don't need that, but I feel completely comfortable running 12 mil / 0,3 mm traces in tight spaces.
I am using vinyl foil (search Oracal 640, or 641 or similar from other brands). They provide 100% transfer rate to the copper (none left on the foil), require no soaking and rubbing, just let it cool before you peel it off.
The trick to get the porosity out of the picture is to use something called toner reactive foils. It's a foil with a special layer that chemically bonds with toner, fills up the porosity and provides much better etch resistant than toner alone. The procedure to apply it is simple: after the standard toner transfer, just layer the foil on the pcb and pass it through the laminator again. I'm not sure how well it would work with various paper transfer methods if there are paper fibers left on the toner, but with vinyl foil there are no paper fibers and I get perfect coverage.

This toner reactive  foil is not useful for just toner transfer. It's excellent for UV photo procedures as well (positive or negative, doesn't matter). Laser printing on an overhead transparency results in porosity that affects photo procedure, but this thing fills up everything and acts as good UV block.

I use regular cheap laminator. The only modification I did to it was to expand the infeed and outfeed slots. It had some fins to guide the paper, but they were a little too closely spaced for a 1,5mm pcb to pass through easily. I do plan on replacing the thermo-switch with a little hotter one (current one is 140 C, the plan is to put a 160 C one), but never got around doing that.

The printers I use are Lexmark MX310dn and Samsung ML-1640. I haven't noticed any difference in the results between the two.
james_s:
I started out using photo paper, then magazine paper, then I eventually went to some of that blue toner transfer film. It looks expensive at first but it ends up being cheap since you only need to use a piece as big as the PCB you're making. I print out the layout first, then cut a piece of film and tape it at the leading edge right over the printed layout. Then I feed the same sheet back through the printer and it gets printed right onto the piece of film.
KL27x:

--- Quote ---KL27x, I believe I stumble upon one of your posts about a year or two ago, also home etching thread and you were advocating pre-etching. Your enthusiasm for the method convinced me to try it. Well, I apparently did something wrong because the result was just horrible. Not even close to what my normal procedure is capable of. You mention that HCl + peroxide (which I use, and used in that situation) is a hack etchant, what do you use and recomend instead?
--- End quote ---
Interesting! I might be not be understanding your post. This Orocal vinyl, you are laser printing onto this stuff, and then transferring the toner to the board with heat and pressure?

Then this reactive foil, stuff. You apply it over the toner? I'm confused, because you say it is useful for UV, too. How do you get the foil to stick to UV resist? You transfer with heat and pressure, like toner transfer method?  (edit: Ohhh.. you mean you use it on the clear plastic overlay before doing the UV exposure. )

Anyways, I have some guesses. Yeah, the etchant is a good guess. I use only cupric chloride. That might make a difference. Also, you need really high temp and a fiberless transfer medium to reap the benefits of the pre-etch. The orocal is apparently fiberless. But vinyl will melt before you hit the temps I am using. The only paper I know that makes this process possible is Pulsar. (To be clear, I have never found the "good" photo paper, and I have never tried laser printer backing; those might work, too). If you are using vinyl, you are definitely not playing in the same temp range as I am. If you do not know the experience of bubbling and delaminating copper clad, then you have not fully explored the limits that this process will tolerate. You don't know how big your strike zone is, so you might still be throwing it over the plate, because you're used to the umpire calling balls. It's not that you need this high of a temp to get a perfect transfer. It's that getting it this hot ensures there is not that one small spot on the board near the edge that fails and ruins the board.

FWIW, I bought 3 packs Pulsars reactive foil overlay. I only used it once or twice. By then I had got my method down, and the foil overlay doesn't make any difference. I get essentially no porosity.

PnP Blue reduces the problem of fattened traces and reduced clearances and shorts by making the paper textured. And it has a solid plastic film to reduce/eliminate problems of porosity. But PnP melts at a fairly low temp. So the failure mode I couldn't completely eliminate (with my highly tuned  >:D process of shooting a board with a heat gun as it goes thru the laminator) were the cold spots that failed to transfer. This was particularly trickly on a double-sided board. PnP works perfectly if you get the temp right across the board. I'm sure you could build some transfer system that is adjustable for board size to get into the correct temp band with any paper. With some experimentation and taking notes. PnP is good stuff; if that's as good as it gets, it's good enough for me to have used 150 sheets of it in my day. But now, I have a can't-miss process.

And considering my methodology with PnP was to make at least 2 to 4 copies of a board, depending on the size, so as nearly eliminate the risk of a re-do, Pulsar isn't necessarily costing me anything significant. Although, most of the time I make small boards and just make one copy, wasting a bunch of my precut Pulsar. I'm usually too lazy to even copy and paste the board into a multi-panel, because I know it is going to come out perfect.
Domagoj T:
Yes, I'm printing onto the vinyl. For the sake of clarity I'll describe each step in detail.
1. This is adhesive foil I stick to the regular printer paper roughly where the artwork will be and run in through the printer.
1a. If it's a double sided board I use tracing paper instead of regular printer paper and translucent vinyl. It makes a world of difference in step 3, but is otherwise irrelevant for the process.
2. I scrub the copper clad with either steel wool or scotch brite. They both work fine. If I was smart enough to turn on my air compressor, I blow the dust off, otherwise use a clean cloth or paper towel to remove tiny steel wool particles.
3. If it's a double sided board I align the layers using a glass table with light underneath it (its actually just a piece of glass and an array of LED strips turned down low so as not to be too bright but still provide even lighting). Transparent foil and tracing paper make it easy to see both layers and align them. I use small pieces of vinyl to stick the top and bottom layer in position, making a pouch. I put the copper clad in the pouch.
If it's a single sided board, I just leave a bit of paper overhanging and bend it over to keep it from moving until I stick in the laminator for the first time.
4. This is the toner transfer step. I pass the board 5 to 6 times through the laminator. If its big board I help keeping it warm with a heat gun (pain stripping type) on low and from medium distance.
5. I let it cool and peel off the vinyl. Usually there is no toner left on it, but if I don't get perfect transfer it is immediately obvious without checking the pcb. Toner is black and vinyl is light gray, white or transparent, so it's easy to see. If there was a screwup and a lot of toner is still on vinyl, I clean the pcb with toner and start over, but when errors happen they are usually just a spot or two which are easily fixed with a touch of a permanent marker.
6. I place the toner reactive foil on the pcb and run it two or three times through the laminator again. It sticks only to the toner and not the bare copper. Excess is easily peeled off.
7. Etch
8. Acetone gets rid of both toner reactive stuff and toner itself.
9. Drill. I have a small purpose built high speed drill press with a ring light around the ER11 collet to give some light from above and another light below the table (shining through the hole in the bed where the drill bit drills). It also has an air pump to blow away the debris.
10. I tin entire board and it's ready for components (vias first).

Yes, I say this toner reactive foil is good for UV, but I don't apply it to the UV resist. I print the artwork on a transparency (is that what it's called? the transparent plastic sheets you use for overhead projectors) and laminate reactive foil on that. This is then placed over UV resist, pressed down with a sheet of glass and exposed. In this case, the transparency with artwork and reactive foil is not consumed in the process and can be used to expose more boards.

How do you achieve such high temperatures? I assume you are using FR4 (the glass-reinforced epoxy laminate) which can withstand such temperatures and not FR2 (pertinax) that falls apart if you are careless with the soldering iron for just a second too long.
How does the laminator withstand such temps? I have a small contactless thermometer and if I remember correctly, and please don't hold me to it, as it's leaving the laminator the board is about 80°C / 175°F. Much too hot to touch and hold by anything other than the paper.
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