The effect of a trace Al addition (0, 0.01, 0.05 and 0.1 wt. %) in the Sn-2Ag-5Bi solder alloy on wettability and intermetallic compound (IMC) formation of the alloy was investigated. The interface between the solder and a Cu(17 µm)/Ni(4 µm)/Au (0.02 µm) under bump metallized (UBM) substrate was studied. The microstructure of the bulk solder and the interface of the soldered joints was observed in a scanning electron microscope (SEM), and the thickness of the interface reaction layers was estimated. Various IMC phases were identified by energy dispersive spectroscopy (EDS) and by the electron probe micro analyzer (EPMA). The experimental results indicated that the addition of 0.01 wt. % Al in the Sn-2Ag-5Bi solder alloy significantly improved the wettability of the solder more than the other Al additions did. The IMC layer between the bulk Sn-2Ag5Bi-0.01Al solder and the Cu/Ni/Au UBM substrate was almost uniform and thinner than those between the solders containing 0, 0.05, and 0.1 wt. % Al and their respective Cu/Ni/Au UBM substrates. Furthermore, the growth rate of the IMC layer between the Sn-2Ag-5Bi-0.01Al solder and Cu/Ni/Au UBM after 1 to 10 reflow times was lower than that of the IMC layer between the Sn-2Ag-5Bi solder and Cu/Ni/Au UBM. The IMCs in the solder joint interface (e.g., Ni3Sn4) of the Sn-2Ag-5Bi-0.01Al solder were well distributed near the Bi and fine Ag3Sn. The addition of 0.01 wt. % Al in the Sn-2Ag-5Bi solder yielded the best wetting properties for the solder and the minimum growth rate of the IMCs because it increased the nucleation rate of Ag3Sn and uniformly segregated the Bi phase.

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Cold drawn gold wires are widely applied in electronic packaging process to interconnect micro-electronic components. They basically provides a conducting path for electronic signal transfer, and experience thermo-mechanical loads in use. The mechanical stability of drawn gold wires is a matter of practical concern in the reliable functioning of electronic devices. It is known that mechanical properties of materials are deeply related to the microstructure. With appropriate control of deformation and heat processes, the mechanical properties of final products, such as tensile strength and elongation can be improved. Severe plastic deformation by torsion usually contributes to grain refinement and increment of strength. In this study, microstructure variations with torsion strain followed by drawing and heat treatment were investigated. Analyses by focused ion beam (FIB) and electron backscattered diffraction (EBSD) were carried out to characterize the effect of deformation and heat treatment on the drawn gold wires. Pattern quality of EBSD measurements was used as a quantitative measure for plastic deformation.