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?
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
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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.