EMC issue on 6 layer PCB design
Lots of CAD tools exist to check your design for EMC issues. Hyperlynx is one I've used my self, I know that OrCAD has some built in, as did PADS last time I looked at it. There was talk of Altium having something, but I think that was more signal integrity rather than EMC emission related.

You seem fixed on it being a schematic issue. Most EMC design methods are to do with layout, not schematic entry. Without seeing your layout we can't judge, but the usual suspects are:


Crossing of power planes
Inadequate reference planes
Unbalanced signal lines
No proper termination on signal lines
Improper decoupling capacitor values or placement


If you have checked all these, then check your PCB for antenna. There are lots of ways to accidentally create one, though 64MHz is quite a low frequency for one.

Don't forget that a square wave produces a lot a frequencies. It is not one frequency, as a square wave can't exist in the real world on it's own, it's actually made up of lots of sin-waves to give the required frequency.

If it is a signal line which is causing this emission, it is due to high currents down a trace. To fix this, you can usually reduce your source current driver from whatever source you are using, or, if that is not an option, a series termination resistor at the required end will do the job. Simulate the signal for signal integrity and it will highlight what is required.