| Summary: | 博士 === 國立清華大學 === 化學工程學系 === 98 === Very different sizes of solder joints are produced in different packaging levels. The phase formation and phase transformation in the solder joints are crucial to the reliabilities of electronic products. This study examines the phase formation and phase transformation from the solidification and interfacial reactions in the solder joints of different sizes. Phase diagrams are also proposed in this study based on phase equilibria, and the results in solidification and interfacial reactions are well illustrated by the phase diagrams.
The degrees of undercooling of various solder alloys are examined. The primary factors controlling undercooling are the primary solidification phase and the substrates. When the primary solidification phase and the substrates are the same, the degrees of undercooling could be different if the compositions of the melts are different. However, this compositional effect is not very significant. The degrees of undercooling and their variations are more significant for smaller-sized solders, but the relative orders of undercooling of various solders remain the same. The liquidus projection of Sn-Zn-Cu ternary system is experimentally determined, and the thermodynamic modeling is developed. Ten primary solidification phases, six class II and one class III invariant reactions are found.
Interfacial reactions between solders and substrates are investigated. The reaction rates and substrate dissolution in the Sn-0.7wt%Cu/Fe couples are higher than those in the Sn-37wt%Pb/Fe couples. The reactive phase transitions at higher temperatures in the Sn-37wt%Pb/Fe and Sn-57wt%Bi/Fe couples are caused by the ternary phase equilibria tie-line shift. With increasing Co additions, the reaction phase thicknesses in the Sn-8.8wt%Zn/Cu and Sn-57wt%Bi/Cu couples are decreased and increased, respectively. The transition of different reaction stages in the Sn-8.8wt%Zn/Cu couples and the morphology of reaction phase in the Sn-57wt%Bi/Cu couples are influenced by both the minor Co additions and the sizes of solder joints.
Phase diagrams including Sn-Zn-Cu liquidus projection and isothermal section, Sn-Zn-Co liquidus projection, Sn-Fe phase diagram, Sn-Pb-Fe isothermal sections, and Sn-Bi-Fe isothermal sections are established. The solidification phases and solidification paths of solder alloys and the reaction phases and reaction paths in the interfacial reactions are well illustrated by the phase diagrams.
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