: It's a known limitation of the R-C extraction in magic that it uses the ".sim" file format, which has no concept of a substrate. Fixing this is high up on my list of things to do between shuttle runs. I know more or less how to fix it, which is to rip out the part that reads the .sim file and replace it with reading the .ext file, which has all the information needed for R-C extraction (it's a pity they didn't do this originally, but at the time magic would only generate a flattened SPICE netlist output). Meanwhile, the lack of any substrate definition in the .sim format means that the substrate cannot be parsed, and ends up showing up as "error" in the output. If you do a search and replace of "error" with the substrate net name, it should be correct.