I am designing my own board using a similar schematic as an Arduino Mega with a few twists. While designing the layout, I thought of a question. When putting down traces, Do the D- and D+ lines have to be of equal length going from the USB port to the ATmega16u2 and from there to the ATmega2560 or can one be longer than the other. What I'm concerned about is that data will take longer to travel on one line if that line has a greater length than the other. This could produce a phase shift in the signals, resulting in some data becoming corrupted. Is this really an issue or am I over thinking it?