Copper planar microcoils were processed by U.V. lithography on SiO2/Si and Kapton®. The coils were packaged on different supports in order to create varying thermal exchange conditions. The electric current was increased step by step until the electric connection breaks, the microcoils remaining free on a thermal point of view. The copper temperature was estimated from its resistivity. It allowed to show that the thermal exchange mode of the wire-bonded microcoils is conductive. The current density was calculated taking into account the deterioration of the coils by oxidation. Its maximum value is linearly decreasing with the thermal exchange ability of the support. The failure modes of the microcoils are related to track melting and oxidation, the current density remaining one order too weak to induce electromigration
