Is it good/safe to route under resistor/capacitor? As below, it's a 0.5mm wire under a 1206 chip resistor.
\$\begingroup\$
\$\endgroup\$
2
-
\$\begingroup\$ lol everyone answered within 30s of each other. \$\endgroup\$– efox29Commented Dec 30, 2015 at 7:45
-
1\$\begingroup\$ Under a 1206 : no problem. I try to avoid it under an 0603. \$\endgroup\$– user16324Commented Dec 30, 2015 at 10:59
Add a comment
|
4 Answers
\$\begingroup\$
\$\endgroup\$
1
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.
-
\$\begingroup\$ It's a part of a six stage active filter, the bigger chip is OpAmp. \$\endgroup\$– divergerCommented Dec 30, 2015 at 7:53
\$\begingroup\$
\$\endgroup\$
Yes, you can do this as long as it passes the DRC (design rule check). In fact, some designers use a 0-ohm resistor to "jump" over a trace, to avoid having to make have traces on the bottom of a PCB..
\$\begingroup\$
\$\endgroup\$
I do not know about any habits, customs or commandments telling not to do so.
As long as your DRC are correct, there is no problem, I think. I myself used this trick very often in production - exactly with 1206 - to save the vias (as they really wanted bit more space than I can save changing to smaller resistor.
\$\begingroup\$
\$\endgroup\$
As long as there is enough clearance between the trace and the pads, it should be OK. Note that PCB manufacturers have some tolerance in the soldermask layer registration, so there could be maybe plus/minus 0.010 inch offset (depending on PCB fab house). If the trace is too close to the pad, and the PCB soldermask opening exposes the trace, there's a possibility of a solder short between the trace and the pad.
For smaller components, like EIA size 0402, I think our company's CAD team adds a soldermask line to the part outline, to help separate the two pads. This supposedly helps for those cases where the pads are so close together that there's one big soldermask opening instead of two separate openings.
