High speed Designs - Part 21 (What is the impact of copper thickness on high speed signals?)

We bother about the copper thickness when there is high power involved in the PCB. We alter the copper thickness as per the current carrying capacity required. If we are not bothered much, we generally, see 0.5oz or 1oz of thickness used in the PCB. How is copper thickness going to impact the high speed signals? We should think of the losses associated with the change in thickness. 

The first factor we check is the impedance change due to this. The variation of impedance with copper thickness is not that high but still have some impact.

What dominates here is the surface roughness of the copper. Compared to this, the change with copper thickness is less. Still we need to simulate and see the impact.

Below is the simulation in Hyperlynx using 0.5oz copper and 1oz copper for a 250 MHz signal. A 6-layer board is used with routing in the top and 3rd layer. In this simulation, we are trying to see how much signal parameters are changed versus oz parameter.

The first scenario is covering simulation with 1oz copper thickness and checking the overshoot and peak-to-peak

The second scenario is covering simulation with 0.5oz copper thickness and checking the overshoot and peak-to-peak

Conclusion: As we see from the plots, 0.5oz has better signal performance than the 1oz scenario, even though it seems very negligible.