Microstructural evolution and micromechanical properties of gamma-irradiated Au ball bonds

The effect of gamma radiation on the mechanical and structural properties of gold ball bonds was investigated. Gold wires from thermosonic wire bonding were exposed to gamma rays from a Cobalt-60 source at a low dose (5Gy). The load–depth curve of nanoindentation for the irradiated gold wire bond has an apparent staircase shape during loading compared to the as-received sample. The hardness of the specimens calculated from the nanoindentation shows an increase in value from 0.91 to 1.09GPa for specimens after exposure. The reduced elastic modulus for irradiated specimens significantly increased as well, with values from 75.18 to 98.55GPa. The change in intrinsic properties due to gamma radiation was investigated using dual-focused ion beam and high-resolution transmission electron microscope analysis. The dual-focused ion beam and high-resolution transmission electron microscope images confirmed the changes in grain structure and the presence of dislocations. The scanning electron microscope micrographs of focused ion beam cross sections showed that the grain structure of the gold became elongated and smaller after exposure to gamma rays. Meanwhile, high-resolution transmission electron microscopy provided evidence that gamma radiation induced dislocation of the atomic arrangement. •Nanoindentation technique provides a detailed characterisation of Au ball bond.•P–h curve of irradiated Au ball bond shows an apparent pop-in event.•Hardness and reduced modulus increased after exposure.•Elongated and smaller grain structure in irradiated specimens•Prevalent presence of dislocations in the atomic arrangement