I am doing a 2 layer PCB. Based on my resaerch I have solid ground plane on the bottom and try to route as much as possible on top with unavoidable crossings on the bottom. (see here and here). But you can have at least 2 ways implement such crossing (horizontal and vertical) and the question is about the best way to roganize them.
I have digital connector on top (designed to be plugged directly to a part of I/O of Raspberry Pi). Therefore I preferred vertical crossings, because they present smaller obstacle for the DC currents flowing toward ground pin on the top connector (yellow line).But then I remembered that AC currents (light blue) try to follow the corresponding trace on top, and got doubts if got it right. The question in other words, should I keep current implemention or scrap it and try to minimize the paths of AC return currents?
The AC in this case is represented by SPI interface, which despite being nominally relatively low frequency, would still produce high frequencies on level transitions (edges)
EDIT: while giving it a thought I decided to move the IC on the top right to the left and here is the result: I beleive, this improved the layout (i. e. eliminated the cluster of crossings) to the point making the question irrelevant for this example. But since this sis perhaps not my last engineereing task, I still would like to get the anwser.