Tensile and Fatigue Behavior of Al-1Si Wire Used in Wire Bonding

In this work, the mechanical properties of Al-1Si microelectronic wire were studied. The microstructure of the wire was examined to characterize the distribution of Al-Si inclusions and grain size. The wires had a diameter of 63.3 +/- A 0.1 mu m and an elongated grain structure due to the hot extrusion process used to fabricate them. The transverse grain size was measured to be 1.1 +/- A 0.3 mu m. The anisotropy in grain structure was characterized by dual-beam focused ion beam (FIB). The Young's modulus was measured by conducting experiments at various gage lengths. The measured modulus was 71.7 +/- A 6.1 GPa, similar to that of bulk Al-Si. Strength data were measured for many wires, and the variability evaluated by Weibull statistics. The wires had a strength slightly less than 200 MPa and strain to failure of over 2%. A Weibull modulus of 110 was obtained, indicating very low variability in the data. Stress versus fatigue cycles was also conducted. Specimens that survived 10(6) cycles exhibited a significant decrease in strength over the as-processed material. Fractographic analysis showed a significant amount of plastic flow and fracture by necking to a single point.