How does burnt substrate affect the return loss of a CPW line?

[microgod]

Hi everyone,

I am trying to fabricate a board that includes a CPW line with a 2 mil width and 2 mil spacing with an LPKF laser. My current power settings are able to blow off the copper for the spacing, but the substrate gets badly burnt. If I dial down the power, the substrate is slightly less burnt, but at the cost of not blowing off all the copper. There could be a happy medium, but it would take some more trial and error to figure that out.

The actual results show a 10 dB difference in return loss compared to the simulated results, which we could attribute to the burnt substrate. However, I'm curious—how exactly does burnt substrate affect the return loss of the CPW? The substrate I'm using is Duroid 6010 (Dk = 10.2).

Thanks,
Micro

 

[aliarifat794]

The substrate material, Duroid 6010, has a specific dielectric constant (Dk) of 10.2. Burning or thermally damaging the substrate can alter the material's composition.