| Summary: | 博士 === 國立清華大學 === 化學工程學系 === 96 === Soldering is the most important joining technology in the electronic packaging industry. During the soldering processes, the molten solders wet and react with the substrates. Even though the soldering time is short, the substrates' interfacial reactions with the molten solders are much more intensive than those with the solid phases. The performance of the electronic products is close related to the interface reliability of solder joints. The diffusion of atoms and the formation of the reaction layers arise from the difference of the chemical potential existing at the interface between the different materials. The evolution of the reaction layer is crucial for the joint properties, and their information is fundamentally important for the proper reliability assessment of the electronic products.
Pb-Sn alloys are the most common solders. However, owing to the environmental and health hazardous concerns of Pb, various Pb-free solders have been developed to eliminate the usage of Pb. The Sn-0.7wt%Cu alloy and eutectic and near eutectic Sn-Ag-Cu alloys are highly recommended. Ni has relatively low reaction rates with most solders, and is usually used as the barrier layer material in the metallization substrate. With the emerging Sn-0.7wt%Cu solder, the Sn-Cu/Ni contact will be frequently encountered. This study investigates Sn-Cu/Ni interfacial reactions at 250oC with different Cu contents and reaction times. The morphologies and microstructures of the reaction phases are determined, the effects of Cu on the interfacial reactions are analyzed, and the reaction progressions of the interfacial reactions are proposed.
The passage of electric currents is the most important characteristic of the electronic products and it causes Joule heating and electromigration effects. Interfacial reactions are accelerated with elevated temperatures. Electromigration has polarity effects, and it might retard or enhance interfacial reactions. This study aims to examine the effects of electromigration on interfacial reactions of Sn/Cu, Sn/Ni, Sn-0.7wt%Cu/Ni and Sn-3wt%Cu/Ni joints, and the samples are prepared using a casting method. At the interfaces where electrons flow from the solder side to the substrate side, the results are similar to those without passage of electric currents. At the interfaces where electrons flow the substrate side to the solder side, large and non-planar reaction phase regions are formed.
Co and Co-alloys have been examined for their applicabilities as Pb-free solders and as under bump metallization materials. This study investigates the kinetics of Sn/Co solid/solid interfacial reaction. The reaction phase shows linear growth and the unique cruciform pattern which is observed for the first time in the solid/solid reaction. As electric currents pass through the Sn/Co interface, the difference of temperature due to significant Peltier effect affects the CoSn3 growth.
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