Effects of Aspect Ratio on Microstructural Evolution of Ni/Sn/Ni Microjoints
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Under the simultaneous influence of volume shrinkage and surface solder diffusion, the microstructural evolution in Ni/Sn/Ni microjoints exhibits a conformable tendency among different joint sizes. This conformable tendency is the necking of the Sn layer and the initiation of voids which occur only near the periphery of the Sn layer. The reasons for this joint-size dependency have been theoretically evaluated and proposed in this study. This dependency remains applicable until the Ni3Sn4 layers growing in opposite directions impinge on each other. Afterward, microvoids are able to form everywhere along the centerline of the joints. It is hypothesized that the electrical and mechanical performance of microjoints is significantly related to the microstructures in these joints. With the help of the joint-size dependency proposed in this study, it is expected that the dimensional design of microjoints is capable of being optimized to assure high reliability.
KeywordsMicrojoints volume shrinkage surface diffusion interfacial reactions NiSn4
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The authors are grateful to the financial support of the Ministry of Science and Technology of Taiwan through Grants 104-2221-E-002-040-MY3 and 104-2221-E-002-052-MY3.
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