Two forces affect ionized atoms in a conductor: 1) The direct electrostatic force F, as a result of the electric field , which has the same direction as the electric field, and 2) The force from the exchange of momentum with other charge carriers F, toward the flow of charge carriers, is in the opposite direction of the electric field. In metallic conductors F is caused by a so-called "electron wind" or "ion wind".
The resulting force F on an activated ion in the electrical field can be written as
where  is the electric charge of the ions, and  the valences corresponding to the electrostatic and wind force respectively,  the so-called effective valence of the material,  the current density, and  the resistivity of the material
Electromigration occurs when some of the momentum of a moving electron is transferred to a nearby activated ion. This causes the ion to move from its original position. Over time this force knocks a significant number of atoms far from their original positions. A break or gap can develop in the conducting material, preventing the flow of electricity. In narrow interconnect conductors, such as those linking transistors and other components in integrated circuits, this is known as a void or internal failure (open circuit). Electromigration can also cause the atoms of a conductor to pile up and drift toward other nearby conductors, creating an unintended electrical connection known as a hillock failure or whisker failure (short circuit).  Both of these situations can lead to a malfunction of the circuit.