We're using standard .03" boards (I think that's the thickness) with an ABS printed carrier. The printer is good to 0.3mm (0.01"), but abs is pretty easy to sand down, if we need to.
The main problem is the thin boards want to flex and crack the solder joints. Anything with not enough solder tends to pop apart (especially the data lines, being in the middle of the connector). And of course, you can't tell that until you have the board mounted - with the chip facing down - and by then it's too late
Still looking for a way to get better joints than a R/S 30 Watt soldering iron....
But I've got time. Arkhan has to optimize atlantean yet
Good luck with sanding the boards down. I'd hate to ruin a bunch by sanding off the traces accidentally
My best suggestion would be to bevel the outside long edges. But you have a trace running pretty close to the side, so....might work, might not.
BTW, if you're interested in helping with building the ABCard, version 3, let us know. We need someone who understands programmable circuits for that version