analog signal routing

[at89atbits]

I have a doubt as to which is a better way to route for analog signals
I have two options.
Either I'll have to route it on the bottom layer in which case it'll be under another analog signal in the same plane.
Or I can route it from in between two legs of an electrolytic capacitor.

What is the better option?
Or both will cause problems?
What would be the pros and cons for either of them?

 

[Harald Kapp]

This question cannot be answered in a general way. It depends on the signal levels, the speed of the signals, the impedances involved etc. Generally a shorter trace is better. The small overlap of the signals here should be no issue, since the two traces are perpendicular to each other and the overlap is very small (it is bad practice to run the atop each other parallel for any length of copper).

In this layout you could swap the positions of the lower 0.05µF capacitor and the two components above (100Ω, 15µF) to reduce the length of the analog trace while eliminating the small overlap as well as the need to tunnel to the other side using vias (similar to your 1st image).

 

[at89atbits]

Thank you so much
It didn't occur to me before.

 

[Arouse1973]

I prefer the second version and it's the right way to do it. I know it's difficult but I always prefer not to route tracks under components but it's difficult for densely populated PCBs.

The only time it's recommended to run two tracks on top of each other but on opposite sides of the PCB is for managing signal return current and reducing loop inductance if you don't have a power plane. Side by side traces are purposely used for managing differential impedances when required. You can't easily avoid running traces close together sometimes but you just need to make sure you keep the noisy tracks and quiet track apart as much as you can.
Adam