| Summary: | 碩士 === 南台科技大學 === 奈米科技研究所 === 98 === This study has investigated the effect of electromigration on Sn-3.5Ag solder and electroless nickel plate interface layer. This study investigates the effects of electromigration on the microstructure and interface reaction of solder joints . First of all, TiO2 and Ni power were added to Sn-3.5Ag solder paste and were mechanically stirred so that they were evenly distributed within the solder paste. By so doing, a composite solder was formed, strengthening the substrate of Sn-3.5Ag. Next, in the temperature of 70 ℃, 150 A/cm2 of current density was imposed on various kinds of solder joints which power for 0, 100, 200, and 400 hours. The data obtained were compared with those without electrification. Additionally, the structures of intermetallic compound layers, the compositions of solder joints, and shear strength were examined with optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), the surface composition of Auger electron image (Mapping) and micro-load testing machine.
The results show that electromigration did not affect the compositions of the interface of solder joints, but had divergent influences on the growing rates of the generated phases. In the system of the electroless nickel plate / Sn-3.5Ag / electroless nickel plate, electroless nickel plate / Sn-3.5Ag-1wt% TiO2 / electroless nickel plate,electroless nickel plate / Sn-3.5Ag-3wt% TiO2 / electroless nickel plate, electroless nickel plate / Sn-3.5Ag-0.5wt% Ni / electroless nickel plate, and electroless nickel plate / Sn-3.5Ag-3wt% Ni / electroless nickel plate, while the electronic flow and the diffusion of tin atoms were in the same direction at the interface, electromigration accelerated the growing rate of interface layers and made them thicker than unelectrified. On the other hand, while the electronic flow and the diffusion of tin atoms were in an opposite direction, electromigration slowed the growing rate of interface layers and made them thinner. In conclusion, electric migration changed the interfacial thickness of solder joint on both sides. When adding 3wt% TiO2 and 3wt% Ni powder through the current in 200 hours which can cause the anode of intermetallic compound growth slowly, and the growth thickness would be more thin than the anode of Sn-3.5Ag. It is show that adding TiO2 and Ni can
enhance the base of solder and inhibit the migration of power.
Using the Sn-3.5Ag by adding the composite solder of 1wt%TiO2、3wt%TiO2、0.5wt% Ni and 3wt% Ni powders in the shear test, and then use the reflow soldering to make single-shear specimen. Then use the non-electric experimental specimen to take the shear stress test, and observe the change of shear stress. The shear stress of the Solder joint will be increased by adding the solder 1wt%TiO2、3wt%TiO2、0.5wt% Ni and 3wt% Ni. But after through current and increased the thermal-storage time , the shear stress of the solder joint will be decreased. No matter in any systems, the react process will through Ni3Sn4 generated ; Appropriate reaction can enhance the wettability which raise the mechanical strength between the solder and substrate. It will cause the solder joint damage because of the metal compound over thick, and then decreased the shear stress.
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