Moleish SMT Heatsinks
Well, no one ever did give me a reasonable estimation at how deep a mole of moles would cover the earth. But then, I didn't go back and dig up my old chemistry notes and see if I could find my calculations from nigh on eighty years ago either. Nor did I get out my old Handbook of Chemistry and Physics and try to recreate the calculations from scratch. Maybe I didn't give enough information or parameters for the question - like, just what kind of mole are we talking about here?
Anyway... back to something you might actually care about... I ran across some writing about thermal vias and big parts the other day. Not that the material had anything to do with Avogadro - except maybe that sometimes it looks like a board will have a mole of via holes on the thermal pad in an attempt to get heat away from a power part. If done properly (filled and plated over), that can be a viable option.
For some chips there may be other options too though. A couple of companies make SMT placeable heat sinks for D2Pak and similar chips. I haven't personally used any of these, so I can't speak to the performance, but AAVID and Wakefield are two examples.
The basic idea is that you make the thermal pad a little bit wider, put a small strip of solder mask in between the part and the heatsink spot and you won't need an vias. Look at the heatsink data sheet specs to get the exact dimensions of everything. You'll end up with a part footprint that looks something like this one.
The cross hatch area represents bare copper (or whatever board surface you are using) and the rest would have solder mask. The thin layer of mask between the part and the heatsink will help to ensure that you have better control over the amount of solder under the part and the sink. It should also help prevent solder balls as well.
How about gophers?