| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 91 === This research is to discuss the effects of the microstructure by adding 0-10wt% Sb into Sn3.5Ag lead-free solder as well as the interfacial microstructure variations of Sn-Ag-xSb solder combining with Au/Ni-P/Cu UBM. The Single Lap specimens and high temperature storage evaluate the influences of different Sb addition for the shear strength of solder joint and thermal resistance.
Sn-Ag-xSb solders that melted by us are fabricated solder ball whose diameter is 1.7mm. Au layer and Ni-P layer are coating on copper substrate individually using ion sputter and electroless plating. Solder balls and Au/Ni-P/Cu UBM are fabricated to Single Lap shear specimens and then carry out high temperature storage at 150°C. The experimental results show that Sb solved into b-Sn matrix when Sb addition into Sn3.5Ag solder is lower 3.85%. The microstructures are composed of Ag3Sn and b-Sn to form circular structure. When Sb addition is more than 3.85%, the laminal SbSn compounds are discovered. However, the cubic SbSn compounds can be found when the Sb addition exceeds 10.05%. After Sn-Ag-xSb solder are combined with Au/Ni-P/Cu UBM, Au layer would solve into solder and Sn atoms react with Ni atoms to form Ni3Sn4 intermatllic compound. Thus remainder P atoms are exhausted toward Ni-P layer to produce dark P-rich layer. The thickness of interfacial Ni3Sn4 and P-rich layer raised with thermal storage time increasing. The morphology of Ni3Sn4 compound at as-soldered appear needle-like or boomerang-shape by deep etching and the morphology transform to polygonal after high temperature storage. The coarse (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 ternary compounds are detected in the interfacial surface after high temperature storage and Kirkendall Voids are discovered apparently in the P-rich layer. Although Ag3Sn compounds coarsen after high temperature storage the Sb addition can reduce coarseness of the Ag3Sn compounds. But Sb addition reach 10.05%, Sb atoms can substitute for Sn atoms in Ag3Sn compound to form coarse Ag3(Sn,Sb) compound. Therefore, the levels of 10.05%Sb addition are harmful to reducing the coarseness of the Ag3Sn compounds.
The shear strength results show that the average shear strength of as-soldering Sn3.5Ag solder joint is 34.7MPa. The shear strength can be raised with the Sb addition increasing. The strength of 1.73, 3.85, 5.12, 10.05wt%Sb are 40.7, 55.6, 58.5, 72.5MPa respectively. The shear strength of the whole solder joint decrease distinctly after 150℃ thermal storage. After 625 hours storage the Strength of Sn3.5Ag solder is 24.1MPa. The strength of adding 1.73, 3.85, 5.12, 10.05wt%Sb are 29.0, 42.4, 42.9, 51.0MPa. The fracture position of solder joints at as-soldered occurred at the inside of solder. However, the fracture position tended to occur at the interfacial surface with storage time increasing. Furthermore, the fracture position tended to occur at the interfacial surface with the Sb addition increasing. According to the shear strength and thermal resistance and ductility, the solder adding 3.85% Sb has better behaviors.
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