Let's say an alien race drops a microscopic 72135 metric ton black hole into the center of the earth. It's Schwarzchild radius is too small (only 0.0001071103 femtometers) so it won't actually be able to interact with any particles inside the earth and it won't accrete any mass.
Instead it should falls straight through the earth, ping-ponging back and forth before reaching a critical mass and exploding in a burst of hawking radiation exactly 1 year later. However this wouldn't be enough to blow up the Earth because the binding energy of the earth is $2.24 \times 10^{32}$ J and during the final second of the black holes life it will produce only $2 \times 10^{22}$ J.
Edit: From my own calculation it seems impossible to actually blow up the Earth with a black hole, so I'm changing this question to "liquefy."
How big of a microscopic black hole would you have to drop inside the Earth for it to have enough energy to liquefy the surface from energy dumped into the interior. Let's assume it reaches the critical last second while it's deep inside the Earth (not passing back and forth at the crust level) It dumps so much energy into the interior that the surface of the planet erupts in magma and the crust is liquefied.
Edit: This is the calculator I'm using: http://xaonon.dyndns.org/hawking/