Jim,

    You mentioned minimum trace width.

    Playing around making a smt board for an oscilator I made this board with 0.016" (16mil) traces, and fortunately the even narrower spaces between (near the chips) did etch out ok.

The worst thing was dealing with solder bridges, so use of solder wick was required from time to time.

 

I've tried out Chucks's suggested paper, and a couple of other re-purposed alternatives. they certainly work, but it took a while to soak off, and I always had trouble cleaning off the paper residue that remains stuck. For a while even I tried working with the "Press'N Peel Blue" plastic transfer film (more costly, but at the time it was on the boss's nickel). But I was convinced on the spot the first time I used the Pulsar paper stuff and saw it just float off the board in about a minute, leaving nothing but toner and clean copper behind - ready to pop directly into the etch bath.

The raw deposited  toner has some porosity and pitting can be seen under magnification. Not nearly enough to be damaging unless traces are really thin. Recently I've started using the"Toner Reactive Foil" product as well and find a much cleaner surface to the un-etched copper and ability to get consistent traces down under 10 mils.  The foil pretty much eliminates the pitting.

Now, for DIY, I just about never use traces smaller than 15 mils, but some of the text legends and such that I'll etch for ID will have lines of 6 or 8 mils, and they usually come out clean.

If you were going to do a "mini mass production" of maybe a few dozen boards (I did that once for a club kit - never again, the drilling was a drudge - hi), a more economical alternative paper is not a bad idea.  But nowadays my DIY boards are just about always one-off, Then if it turns out to be a useful project that others might have interest in, off it goes to a fab house. Nick and I will talk about the "gotchas" for that process. There aren't many, but they are important..... ask me how I know   :^))

If you like Pittsburg style, or SMT, where drilling can be mostly avoided, the DIY route is really attractive, even for modest quantities.

Jim, N5IB