In a simplified view, engineers often tend to assume that PCB conductors behave perfect with zero resistance and no energy loss or dispersion, but in reality this is not the case. Instead, PCB designers working on high-speed or RF designs have to deal with impedance from an early stage — trace impedance in particular — and more recently also power-plane impedance, but seldom thought on resistance quantities in particular This particular emphasis on impedance has created the situation that the layout engineers as a consequence often struggle with the relation between trace copper resistance, impedance, and reactance. Read more
