Gideon Analytical Labs received a failed IR FR22ON MOSFET within DC-DC converter. All the MOSFETs were shorted on all terminals. The MOSFETs were tested by lifting the gate and source wires from the circuitry. The Idss leakage for a good IR MOSFET is typically around less than 1 nano-amp. All the good MOSFETs tested were around .8 nano-amps, BVdss 220V, Vgsth 3.6, Igss <100nA. This IR FR220N has thermal damage. This typically overwhelms the junctions with current (heat) and the weakest hex cells are destroyed first. The black areas are produced by the anaerobic carbonization of the epoxy packaging.
The MOSFET is in a circuit with a transformer which gave an inductive kickback causing the MOSFET to be overwhelmed with the current. The transformer was changed and the MOSFET failures disappeared. Actually, Gideon suggested it was the wire being used on the transformer that was causing the problem. This was the case and it was changed.
Gideon Analytical Labs can save you frustration and money by solving the problems that lead to failures. Let Gideon Analytical Labs do your failure analysis. 845-255-5356