Why does the C-C bond break earlier than the C-F bond in the pyrolysis of perfluroethane?
I got this explanation from one of my seniors.

It is true that $\ce{C-F}$ bond is highly polar as fluorine is more electronegative than carbon. In fact it is this very difference in electronegativity that makes C-F bond very strong. This is because, in addition to the covalent bond strength between carbon and fluorine, there is an additional electrostatic attraction between positive carbon and negative fluorine.

We can think of it has the $\ce{C-F}$ bond has both covalent  and ionic character. This makes C-F bond extremely stable and hard to break.

In fact in organic chemistry we usually say that the $\ce{C-F}$ bond is not broken in reactions. 



We can also verify this from their bond energies:

$\ce{C-F}$: $\pu{544 kJ mol-1}$
$\ce{C-C}$: $\pu{346 kJ mol-1}$