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Ageing tests

In the power systems involved, the IGBT modules are subjected to different types of stress which can be combined partially or totally of variable types.  Nevertheless, the thermic fatigue represents one of the important causes for the failure of IGBT modules.  Its impact varies according to the type of requests endured by the module and depends on the type of the case used. For these reasons, the works realized in the laboratories are mainly linked with the thermic fatigue of these devices.

Hence, the tests consist of put through the test vehicles under cyclic thermic constraints with the objective of revealing failure modes representing the ageing and to analyze the structural degradations.

Two types of thermic cycles are implemented: the passive cycles which are due to the environment and active cycles which are due to self-heating of the chip. The first ones might be of very high amplitudes (sometimes up to 250°C) but of very low frequencies, and the second ones are of low amplitudes ( a few dozens of °Celsius) but highly frequent. The first ones are reproduced with the help of environmental tests methods (climatic chambers), the second ones utilize the power cycle benchs developed in the laboratories. Moreover, the thermic modeling and thermo mechanics are driven to evaluate the constraints suffered by the components in the applications.

The combination Ageing tests/ failure and degradation analyze and the estimation of thermo mechanical and electro thermic constraints suffered by the components allows us to enlighten and to model the degradation mechanisms.

 These works allows us to reveal, for ex, to understand the degradation mechanisms which affects the metal coated insulating ceramics substrates  (DCB) and the brazing joints and to demonstrate the input of new technologies or new materials. These modeling by completed elements are also allowed to reveal the behavior and the hardening effect of copper films in the electronic modules and to explain the fractures noticed in the insulating substrates. The degradations of newly brazed  (?)  specific ‘high temperatures’ are also subjected to experimental tests like cavitation formed by thermo migration due to elevated  working temperatures.