Just did this not an hour ago with the toner transfer method. It was my third attempt, but this is only my first time doing toner transfer! Dual layer board, smallest traces are 12 mil for the MSOP packages. There's a TQFP-44 (16 mils) and several SOPs (20 mils). 20 mils pullback on the copper fill.
The 16 mil traces on the TQFP were a little sketchy, and the 12 mil traces on the MSOPs got through on a wing and a prayer. God bless SO packs and their fat 20 mil wide pads! I had to doctor the board just a little with some masking tape in a few places, but I have continuity everywhere I've checked so far. The big question is getting all the "through holes" soldered and aligned! Thank goodness I have access to a CNC mill and some resharpened carbide bits for this one!
A few things I do to make life easier... make your via's wide, and make the drill hole about 10 mils wide. This gives you a big fat copper pad to solder to, which comes in handy when your layers turn out misaligned. I'm also using the top layer as a power plane. Perhaps inadvisable, but it was nearly impossible to route the board otherwise. (There's actually two power planes in this pic... 5V all around, and +3V3 under the main IC.) Everything goes to ground through a via... There's about 97 of them. Bleh. Maybe I should have made the bottom layer my power plane.
Was using the backing for a sheet of envelope labels as my transfer paper. The waxy surface worked like a charm! I didn't even need to wet it down to remove it, just carefully peeled it off after ironing it for a while. If I saw any breaks, I'd just fold it back down and iron a little more. Usually worked! I originally was pre-heating my boards, but that didn't seem to positively affect the process. On a whim, I tried using an overhead transparency. I started to get a little transfer, but ended up melting the sheet all over the bottom of my mom's iron. Whoop!
Having done toner transfer, the UV sensitized board method, and having a PCB shipped, this is definitely the least reliable for what I'm doing... but it was the cheapest! It was also really nice to be able to scratch off toner with a pick where I didn't want it. If I had access to UV materials though, I'd definitely do that for this board. This was a stretch, and added a few too many gray hairs!
PSL mentioned 0R resistors... Maybe I'd try that with 1206's. 0805 seems too small for that... but it seems feasible. What are you all using for your transfer paper? Everyone seems to be using photo paper, but I can't fathom it! Seems far too thick! Then again, the backing sheet *was* a little flimsy...
(Edited a bajillion times for content and formatting.)