You can also see that I’ve made it very easy for heat to move away from the regulator (U1) and into the ambient environment or into other portions of the PCB. U1’s thermal tab is connected to a large copper pour, and this copper pour is shot through with vias that conduct heat down to the internal ground plane. If I were really worried about thermal issues I could also connect these vias to a copper pour on the bottom side of the board, but in this case, it would have been total overkill.
It’s always good to be cognizant of trace lengths when you’re laying out a parallel bus, though at moderate frequencies it is nothing to stress about. The propagation time for a signal traveling through a trace is maybe 150 picoseconds/inch. So if you have two traces with a length mismatch of one inch, one signal will arrive 150 ps after the other signal. If your signals are transitioning at a frequency whose corresponding period is much greater than 150 ps, this one-inch mismatch won’t cause problems. Even at 100 MHz (which is pretty fast for a parallel bus), the period is 10 ns, i.e., ~67 times larger than the time-of-arrival discrepancy for a one-inch mismatch.
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