To get a good idea of what using a 3V device entails, read Cygnal's application note AN011. Basically, 3V logic can interface with anything that accepts true TTL levels, so in a mixed voltage system you should use HCT, VHCT, ACT, etc.

The one thing you should be aware of is that the I/O pins on the Cygnal device have very short rise- and fall times of around 1 ns. when used in push-pull mode. So for lenghts greater than 7.5 cm. (3"), PCB traces should be treated as transmission lines.

As for soldering a 0.5 mm TQFP: It's easier than it might seem! A steady hand and some form of magnification are essential, though.


Regards,
Rob.