Generally, a power electronic module for the electric and hybrid vehicles (EV/HEV) is an assembly of several silicon components (transistors and diodes) on a copper substrate by soldering. The solder, which is often lead rich, ensures the heat transfer to the heat sink via the substrate, and electrical conduction between the components and the substrate. Under the effect of heat losses in service, the power module assembly is subjected to large thermomechanical stresses which may damage the soldered connexion. The thermomechanical stresses increase and the assembly lifetime decreases with increasing difference in thermal expansion between substrate, solder and chip. The elimination of lead in the list of materials for the power electronic industry also encourages the development of composite solders which could show some of the merits of lead rich solders, i.e. relative refractoriness in the soldering process and in service. The lead-free alloys used to date in addition to a low solidus temperature suffer from a low resistance to the thermal ageing. Under the effect of heat, the initial solder microstructure can evolve with the development of intermetallics in the form of plates (needles). These plates are stress concentration zones and reduce the lifetime of the module. This work's main objective is to study composite solders containing a SnAgCu alloy reinforced by refractory particles.
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