There are mixed views on this issue. The truest answer is that they tested the SoC in literal ovens so no, it doesn't need a heat sink.
That said, if you just want to be overly cautious then you won't hurt anything by adding a heat sink.
There are several threads open discussing various aspects of this issue so I'm going to close this duplicate thread, but please feel free to comment on one of the other ones. Try using the search feature of the forum for the phrase "heat sink" or "heat sinks" and you should find the threads pretty quick