| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 93 === Sn-Ag-Cu solder balls are extensively applied in the electronic packaging technique. Because the solder balls are used to transmit current, high current density may induce the failure of solder joints. In addition, the surfaces of Sn-Ag-Cu solder balls discolor at injected or reflowed processes, so the fusion current and the solidification scale of solders need to be investigated.
Sn-3.5Ag-xCu (x = 0、0.5、1.2、1.9、2.2) solders are specimens of the study. The subject of the study divides into two parts. The first part is the effect of Cu content and solidification rate on the microstructure and electric properties. The second part is analyses of the scales with different components (pure Sn, Sn-3.5Ag, and Sn-3.5Ag-2.2Cu) and different solidification rate.
Experimental results show that the Cu6Sn5 content increases with the increasing of Cu content. By adding more than 1.2wt% Cu, the β-Sn dendrites become refined apparently, and the eutectic area increases. It also causes the decrease of fusion current and conductivity. When solders solidify at the slower cooling rate, the features of Ag3Sn in Sn-3.5Ag solders become rod-like. It also causes the increase of fusion current and conductivity. Cu6Sn5 compounds in Sn-3.5Ag-2.2Cu solders expand, but fusion current and conductivity have no obvious change at the slower solidification rate.
The analysis show that oxidization occurs on the surface of discolored specimens and the scales are composed of SnO and SnO2. According to TEM analysis, the depth of scale is ~ 0.5μm. At the same solidification rate, the extent of oxidization on pure Sn is similar to that on Sn-3.5Ag solders. However, the extent of oxidization on Sn-3.5Ag-2.2Cu solders is slightly less. The surface color of solders becomes darker at slower solidification rate, while the chemical state of Sn does not change obviously.
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