Hi Dave,
Great to see how you route your boards. By watching an experienced engineer do these things I learn a lot more than just by reading my textbooks. (EE bachelor-student speaking here)
Now I do have a question. You say you keep in mind all sorts of rules, the schematic, etc: lots of stuff that’s become intuitive to you. Now during introduction classes on PCB design last year one of the main rules was to avoid your traces curve so much that between start and end you’ve got a large area. If I recall correctly it had to do mostly with inductive coupling, and becomes more important for higher frequencies. What surprised me a in your design were a couple of long traces doing exactly that. A small example is a short trace from ISP connector to AVR chip that comes in from the bottom right, goes around a few AVR pins, and then connects to its pin from the top left. But I also saw it in larger scale. I just had to ask: why? I know there’s a lot (!) more to PCB layout than the basic (EMC) rules so please enlighten me.
Also I’ve been taught to always try to minimize distance between those that are a differential pair, just like you do. Does that only apply to positive/negative supply traces and signal send/return traces? If not, in what (common) situations do you have to take extra care?
And lastly, at a first glance your layout seems quite a maze here and there: traces going between pins curving a lot until reaching destination. It seemes you just put them where there’s space. Now I know about your intuitive knowledge and experience, but I wondered if that doesn’t give you problems in terms of capacitive or inductive coupling. Could you explain why/when that is, or is not, a problem? And maybe give some insight in your thoughts in the process?
Thanks for sharing your knowledge, and thanks in advance for replying!
Kind regards,
Christean