pcb design - Is it a good habit to route wire under chip resistor/capacitor?

Is it good/safe to route under resistor/capacitor? As below, it's a 0.5mm wire under a 1206 chip resistor.

Answer

It depends.

If you have a high density board, you might have too, otherwise it means you need a via, or have to take some irregular path on your board.

The problem might come from crosstalk. If you have a sensitive analog signal, and you pass it between a 1206, and the 1206 is part of a digital circuit, well you may get some coupling. However, this is true regardless if placing a trace between a component. Anytime you have any traces < 2-3 trace widths apart, will have cross talk. How much so, depends on frequency, plane distance, geometry etc..

Fortunately, from what in your picture, its a very short distance, and the coupled length is only the width of the pad. This should not be a problem if its a digital signal. If its analog, then it would depend on what your requirements are for that signal. How much noise can you handle before the going out of spec.

So it safe to do so, from a manufacturers perspective, but will it affect your circuit would depend. If you stick with the, keep analog and digital away rule, then you wouldn't have much of a problem.