Failure Analysis of Diode (Thyristor) Dice from Power Semiconductor Modules after Operation above the Maximum Specified Temperature

Reliability of power modules based on rectifier diode and thyristor devices, above the maximum junction temperature of 125 degC or 150 degC specified in the data sheets has been investigated. Excessive high level of the reverse (blocking current) causing electrical characteristic instability above 150 degC is still a limiting factor for module reliability. Diode and thyristor dice with glass passivation or silicone rubber passivation have been found after module package de-capsulation. Both junction passivation methods indicated excessive high leakage current at the junction edge in power modules. In some modules the level of reverse (blocking) current has been found significantly lower, due to better control of the leakage at the junction edge. Nonetheless continuous current increase may take place with the time above the maximum temperature due to mechanical stress in the package. For rectifier bridge modules with maximum junction temperature of 150 degC, significant increase of the reverse current level has been found after simple storage at 200 degC. Such change was observed especially for silicone rubber passivated junction devices incorporated in the module package. Reliable operation above 150 degC is possible with further advance in the junction passivation techniques and module packaging