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Electronic power devices used for transportation applications
(automotive and avionics) experience severe temperature variations which
promote their thermal fatigue and failure. For example, for power modules
mounted on the engine of an aircraft, temperature variations range from –55°C (in
the worst case of storage before takeoff) to +200°C (flight). The studied modules
are composed of direct bonded copper (DBC) substrates which allow isolating the
active parts of the module (silicon dies) from their base plates. The failure occurs
in DBC substrates, which are copper/ceramic/copper sandwiches. The Weibull
approach was used to model the brittle fracture of the ceramic layer from a natural
defect. Using the finite element method, it was possible to analyse how a thermal
loading history may modify the risk of failure of the DBC substrate. It was shown,
in particular, that three overcooling cycles should produce an “overload
retardation effect”.