Thanks for the hints.
Alignment hasn't really been that big of an issue - I use more/less the same method you describe. The biggest issues I continue to have are in getting consistent & solid transfer off of the paper onto the board. More often than not its just some small part of a board that doesn't seem to transfer well - I use the same pressure and temperature on the iron and so haven't been able to come up with good answer as to why one area doesn't transfer as well as another. When doing a double sided its just that much more area for something to go wrong. I've also had challenges in drilling the vias where the drill bit will lift and then destroy the trace as it comes through on the bottom side even if I drill into a sacrificial piece - what seems to happen is that the fiberglass will chip and then come lose on the back taking the trace with it. I think the major issue is that the motor on my mill (which I use for drilling) tops out at 1800 rpm when run manually which I think is too slow. So calling these boards failures may be bit unfair as most of them have been usable with some generally minor touch up & repair. I guess I just had delusions that I'd be able to quickly and easily produce usable high(er?) quality boards than I've so far been able to. I bought bits off of ebay and they may be too worn out too may be the cause of some of the issues. I would be interesting in knowing what sizes/speeds are most folks using for drilling vias?
I haven't done as many boards with toner transfer since I have CNC and the PCB-GCode method seems at least as reliable and I can have it do both the trace routing and the drilling. The software is great but the approach has Its own set of challenges mostly around trying to hold the board down flat enough to get consistent depth routing into the board - this is especially critical as the depth defines the width of each trace since I'm using a pointed 45degree V shaped engraving bit for routing. My slow mill spindle is an issue for that also as it leaves a jagged edge on the traces and occasionally rips out a small hunk of the fiberglass board. I'm in the process of making a small vacuum hold down table and also attaching a high speed spindle to my mill which will hopefully address the main issues with this approach. As for paper, I've had more/less same result with glossy photo paper, magazine paper and inkjet transparency film (all with samsung ML-2240 laser printer).
lw
> Hmm, that seems to be a very high failure rate - I've had a 100%
> success rate with getting the registration right with double sided
> boards, done using toner transfer. My second ever board was double
> sided.
>
> Getting the two sides to line up doesn't need to be hard. The best
> method I've found is print on glossy paper (rather than bits of
> magazine), and hold the two sides face in up to the light. The sun
> through a window makes an excellent light source, but otherwise a
> table lamp works adequately. Get the two sides to line up, then tape
> one end of the paper as a "hinge". Double check the line up after
> making the tape hinge, then place the copper board between the sheets
> and get busy with the iron. I've never had a registration failure -
> the worst board I made still had enough overlap that it was usable.
> The worst I've had is an occasional broken trace - but most the boards
> I make at home these days are sufficiently small that it's not a big
> job to find them.
>
> The good thing about home making a board is you can go from PCB layout
> to a functional circuit in hours - there's no two or three week
> turnaround time that there is when you send a design away.
>
> I'd agree if you're making a large complex board with hundreds of
> traces, you'll save a lot of aggravation by using a PCB manufacturer.
> Or if you want to make several boards of the same design (many PCB
> makers have a fairly stiff price for the first board, but successive
> boards get quite a bit cheaper because there's no more setup to do. I
> needed ten of a recent design, and it was obvious that the correct
> thing to do was just get them made by PCB Cart. Especially as it was 4
> layer :-)
>