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Mise en oeuvre de nouveaux matériaux d’assemblage dans les modules multipuces de puissance (MCM)

Abstract : Use of wide band gap chip in the power electronic industry requires an optimization of the close environment (packaging). Indeed, the can often sustain lower temperature than the die, especially the solder that are used to bond the parts of the module. Consequently, new bonding methods are investigated to enhance the performance of the packages. Silver sintering bonding technique is one the most promising. This method allow to bond parts at moderate temperature and the formed joint to operate at very high temperature (until the melting point of silver). This work is focused on the development of this bonding technique in the case of bonding a dies on a substrate. A study of the influence of the different parameters on the strength of the formed bond has been done. It revealed a major influence of the finishes of the bonded parts. Bonding on silver finished substrate results in good mechanical strength of the bond even after ageing. Furthermore, no interface issues are observed. However, the most used finish for power electronic is not silver but nickel-gold. Regarding this type of finish, the bond quality depends on the gold thickness, sintering profile and also sintering atmosphere. A solid solution of silver and gold seems to develop on the surface of the substrate, decreasing the section of the silver grains in contact with the substrate. Thus the mechanical strength of the assembly is decreased. This effect should be limited by the gold available for the Au-Ag solid solution growth. When sintering under nitrogen, the diffusion of silver on the gold surface is much lower than under air. Good results have been obtained with these configurations and even after ageing. Adding pressure during the thermal treatment seems also to minimize the phenomenon, probably by increasing the number of silver grains in contact with the substrate surface and so reducing the free surface for Au-Ag layer formation. Those results have been used to build prototypes, one of whom has been electrically tested with success at temperatures up to 300°C.
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  • HAL Id : tel-02003509, version 1

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Stanislas Hascoët. Mise en oeuvre de nouveaux matériaux d’assemblage dans les modules multipuces de puissance (MCM). Electronique. INSA de Lyon, 2013. Français. ⟨NNT : 2013ISAL0123⟩. ⟨tel-02003509⟩

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