Research On The Soldering And Interfacial Reactions In The Self-propagating Reactive Bonding Process Based On Al/Ni Foils

This thesis presents a research into the solder interconnects made through the reactive bonding process based on the self-propagating reaction.A numerical study of soldering conditions in the heat affected zone(HAZ)during bonding was initially carried out to understand the relating influencing factors.This was subsequently followed by an extensive experimental work to evaluate the feasibility and reliability of the reactive bonding process to enable the optimisation of processing parameters,which had provided a detailed understanding in terms of interfacial characteristics and bonding strengths.In addition,by focusing on the mechanism of the formation of the bonds resulted from the self-propagating reactions,the interfacial reactions and microstructural evolution of the bonded structures and effects of high-temperature aging were studied in details and discussed accordingly.A 3D time-dependent model is established and used to describe the temperature and stress field induced during self-propagating reactions.This thus allows the prediction of the melting status of the intermediate solder and the stress concentration in the bond under certain soldering conditions,e.g.ambient temperature,pressure,dimension and kind of solder materials.Following the numerical predictions subsequently implemented to investigate the effect of influencing factors on the soldering conditions,the experimental characterization of interconnects bonded using various materials under different technical conditions is carried out.This ultimately assists the understanding of the feasibility of reactive bonding technique,as well as the criteria and optimization to form robust joints.Furthermore,the reliability and failure modes of the joints formed through self-propagating reaction are revealed in connection with the interfacial behaviour.The formation of phases such as intermetallic compounds(IMCs)and mechanism of interfacial reactions during reactive bonding and subsequent aging are elaborated through the comparative analysis of microstructural characterization and soldering condition predictions at the specific locations of interest.The composition,dimension,distribution of phases and their crystal structures have been examined through cross-sectional observations.The underlying temperature and stress profile which determine the diffusion,dissolution,saturation of elements and the nucleation,crystallization and growth of phases are defined through numerical predictions.Hence,the formation and unique distribution of grains and IMCs in as-bonded self-propagating interconnects are found to be attributed to the solid-liquid-convective diffusion between the self-propagating multilayer foil and solder alloys,as well as the directional solidification and non-equilibrium crystallization.Finally,the transformation and growth of phases during aging are revealed to be resulted from the solid-state diffusion and equilibration induced by the high-temperature heating.In conclusion,the interfacial reactions and microstructural evolution of interconnect developed through self-propagating reactive bonding are correlated with the relating influencing factors through a number of significant evidence that has been obtained from these predictions and experiments.The results and findings enable the extensive uses of self-propagating reactive bonding technology for new design and assembly capable of various applications in electronic packaging.It also greatly contributes to the fundamentals of the crystallization and soldering mechanism of materials under the non-equilibrium conditions.