| Summary: | 碩士 === 國立中興大學 === 化學工程學系所 === 99 === For the tendency of lead-free solder, the traditional SnPb solder has been replaced. Sn3Ag0.5Cu is similar with the traditional SnPb solder for many property tests. It has been the most popular Pb-free solder for consumer electronics packaging. But its melting point(217℃) is higher than the conventional Sn37Pb solder(183℃), which makes direct application of this solder in the traditional reflow process more inconvenient and difficult. Addition of a fourth element to SnAgCu solder is a method commonly used to improve the solder’s physical or chemical properties. It was reported that a small amount addition of Bi to SnAgCu solder can reduce the melting point. The electromigration behavior of a Sn3Ag0.5Cu3Bi solder stripe between two Cu electrodes under current stressing at various current densities has been investigated at temperature of 120℃. After current stressing at a density of 1.0×104A/cm2, the solder matrix exhibited slight microstructural change as well as the formation of a distributed Cu6Sn5 phase near the anode-side solder/Cu interface. Upon increasing the current density to 3.9×104A/cm2 and 5.0×104A/cm2, high density of distributed Cu6Sn5 phase was formed across the entire solder stripe, resulting in pronounced microstructural change of the solder. Hillocks were also formed near the anode-side interface due to accumulation of Sn-rich phase, Bi-rich phase, and distributed Cu6Sn5 phase, while voids were formed in the solder matrix and at the opposite cathode side. For knowing the effect of solder microstructure with adding Bi more clearly, we will increase the addition of Bi to 5～10wt.%. Then, we found the Bi precipitate align regularly, and most of the extrusion is replaced by Bi instead of Sn at the anode side. We also found the formation of voids there, which would cause the bottom intermetallic compound exposed. The mechanisms of formation of the distributed Cu6Sn5 phase and migration of Bi and Sn are discussed. Beside, we made a 3D structure different from thin film sample, and adjusted the height of Cu in under bump metallization to observe electromigration behavior.
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