  We present a novel mechanism of s-wave pairing in Fe-based superconductors.
The mechanism involves holes near dxz/dyz pockets only and is applicable
primarily to strongly hole doped materials. We argue that as long as the
renormalized Hund's coupling J exceeds the renormalized inter-orbital Hubbard
repulsion U', any finite spin-orbit coupling gives rise to s-wave
superconductivity. This holds even at weak coupling and regardless of the
strength of the intra-orbital Hubbard repulsion U. The transition temperature
grows as the hole density decreases. The pairing gaps are four-fold symmetric,
but anisotropic, with the possibility of eight accidental nodes along the
larger pocket. The resulting state is consistent with the experiments on
KFe2As2.
