I don't know the full depth of the trade space of stackup parameters. I go with what the fabs provide. While trying to do some 200 V routing recently I found

I don't know the full depth of the trade space of stackup parameters. I go with what the fabs provide. While trying to do some 200 V routing recently I found out something interesting. Higher weight copper layers have thicker prepreg. This is interesting to me because the rule of thumb for 200 V clearance is "0.4 mm in outer layers and 0.2 mm in inner layers". Most prepreg is 0.1 mm, but going to 2 oz copper means 0.22 mm prepreg. This lets me route 200 V without having to worry about arcing through prepreg, specifying a more expensive board material, or going to more layers.