I'm working on a PCB which has to be very small. There is a QFN IC which has a big thermal pad, although it doesn't really need to dissipate that much heat. So to save some space, I came up with the idea of reducing the footprint of the thermal pad so that I can place some vias and traces in there. It would be covered by solder resist so it doesn't sound unreasonable to believe that this might be okay.
However, if it were such a good idea, everyone would be doing it, and I'm wondering how bad it is. I've seen this similar question but it's not exactly the same thing.
The traces are 0.2 mm (7.87 mil) wide, the via diameter is 0.7 mm and the drill is 0.3 mm.