I've become fairly familiar with the clearance and creepage requirements of UL/IEC/etc 60950, 60730 and derived/related standards. I've just realised, though, that they only refer to distances through air (clearance) or along a surface(creepage). In fact, solid insulation is specifically used as a barrier to increase the distances. Does this mean, then, that the PCB itself is considered solid insulation, and completely removed from the clearance rules? Can I safely have 240VAC on one side of the PCB and user accessible low-voltage circuits on the other, provided there aren't any vias in the vicinity?
Extending the question, what role does the thickness, dielectric strength, etc play? If a thing is considered "solid insulation" is the only requirement that it passes the hipot testing, and if so, at what voltages?