PCBs with SMT on both sides and those with mixed TH and SMTs may start to flex and bow when in the reflow oven or selective soldering machine. For this reason, the maximum size for this type of board is usually smaller than the single-sided. Breaking out the boards manually can stress the board and components near the edges, the solder joints, or leave out rough stubs on the edges
Note that U4, a 10 MHz MEMS oscillator, is also very close to the microcontroller’s clock input pin. It’s always a good idea to minimize the length of traces carrying high-frequency digital signals. First of all, there are noise benefits: a shorter, more direct trace reduces the amount of noise that would otherwise be coupled into adjacent traces, and a shorter trace also reduces electromagnetic interference (EMI) because it is less effective as an antenna. The second issue is related to transmission-line effects. Minimizing trace length is a simple way to avoid problems related to signal reflections. However, reflection is not a significant concern at frequencies in the 10 MHz range, unless you are dealing with long interconnections or a very large PCB.
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