Differential Pair Skew at CAN/RS-485 Termination Resistor Junction

[shyammarimuthu123]

Hi everyone,

I’m designing a PCB that includes both CAN and RS-485 interfaces. I’ve routed the differential pairs and matched the trace lengths carefully.

During the differential pair skew check, I observed that the skew is 0 throughout the entire routing except at the termination resistor connection/junction. The D+ and D− (or CANH and CANL) traces have equal overall lengths, but the skew report is still showing a mismatch only around the resistor connection area.

Is this expected behavior because the differential pair is temporarily split at the resistor pads, or is there a recommended routing technique to eliminate this skew?

[abhishek]

That should not be the case if the lengths of CANH and CANL traces are same then skew should also be zero or within tolerance. How are you settings the rule to check for skew? I guess you have set some custom rule for it. On the R12 pad where the traces are connecting check if any other small trace is overlapping on the trace. Make sure it is only one trace connecting the pad and delete all other small pieces of traces on the pad. That is normal issue in Kicad.