Reliability assessment of low-voltage MOSFETs driving inductive loads

Reliability and compactness are two aspects often fighting among themselves when speaking about power electronics, but, indeed, they are the keys for the success of any new circuit or device. Reliability, in particular, is the word of the moment, powering the development of advanced device design techniques having the reliability as a major goal. Endurance tests is the traditional way to evaluate the reliability of power devices. However, they are very time expensive, requiring even months of uninterrupted testing. An interesting alternative is the estimation of the reliability of a device through a suitable model, but, no standard techniques have been developed up to now to accomplish this task. A possible approach is followed in this paper to assess the reliability of Power MOSFETs driving inductive loads, by exploitation of a dynamic analysis of the temperature distribution over the source metal. Coupling such an analysis with a reliability model, carried out from the Coffin-Manson law, the device life time is estimated. Such a procedure is then used to assess the reliability of Power MOS devices tasked to control the brake pump in a modern vehicle. The consistence of the reliability estimation is confirmed by comparison with results of endurance tests. The described approach can be usefully applied to a large set of applications of MOSFETs in the automotive field.