Why does crosstalk occur in high speed design only?
The reason why crosstalk problems mostly appear at high frequencies is because the parasitics are more important at high frequencies.
Consider a situation where you have 10 pF between two signal lines, each of which have a ~50 Ohm impedance. For a 1 GHz interference, the coupling between the lines is ~15 Ohms. Therefore, the interference will remain to a large fraction on the victim line. In the same situation, if the interference is at 1 MHz, the interference has to &quot;penetrate&quot; a 15 kOhm impedance to reach the victim at then gets flushed away with a low 50 Ohm node impedance, so it will be stronly attenuated.
Similar arguments can be derived for inductive coupling. The tiny stray inductances become more influential at high frequencies.
Common impedance coupling can rise at high frequencies because the e.g. Ground plane impedance rises. This would be the situation if chips are grouped badly. In practise with good layout, common impedance coupling can become less of a problem at high frequencies, because currents through the plane are more confined to the signal traces and therefore interfere less with neighboring signals using the same plane for return.